@article {2627, title = {Noninnocent Behavior of Ancillary Ligands: Apparent Trans Coupling of a Saturated N-Heterocyclic Carbene Unit with an Ethyl Ligand Mediated by Nickel}, journal = {Journal of the American Chemical Society}, volume = {131}, number = {30}, year = {2009}, note = {ISI Document Delivery No.: 479FFTimes Cited: 6Cited Reference Count: 26Steinke, Tobias Shaw, Bryan K. Jong, Howard Patrick, Brian O. Fryzuk, Michael D. Green, Jennifer C.}, month = {Aug}, pages = {10461-10466}, type = {Article}, abstract = {Oxidative addition of the tridentate N-heterocyclic carbene (NHC) diphosphine ligand precursor ([PCP]H)PF6 (1) {[PCP] = o-(Pr2PC6H4)-Pr-i(NC3H4N)o-(C6H4PPr2)-Pr-i} to Ni(COD)(2) results in the formation of the nickel(II) hydride complex ([PCP]NiH)PF6 (2). This hydride undergoes a rapid reaction with ethylene to generate a nickel(O) complex in which an ethyl group has been transferred to the carbene carbon of the original NHC-diphosphine ligand. If the first intermediate is the anticipated square-planar nickel(II) ethyl species, then the formation of the product would require a process that involves a trans C-C coupling of the NHC carbon and a presumed Ni-ethyl intermediate. Deuterium-labeling studies provide evidence for migratory insertion of the added ethylene into the Ni-H bond rather than into the Ni-catene linkage; this is based on the observed deuterium scrambling, which requires reversible P-elimination, alkene rotation, and hydride readdition. However, density functional theory studies suggest that a key intermediate is an agostic ethyl species that has the Ni-C bond cis to the NHC unit. A possible transition state containing two cis-disposed carbon moieties was also identified. Such a process represents a new pathway for catalyst deactivation involving NHC-based metal complexes.}, keywords = {ACTIVATION, CHEMISTRY, COMPLEXES, MECHANISM, MIGRATORY INSERTION, NHC, ORGANOMETALLIC CATALYSIS, palladium, REDUCTIVE ELIMINATION, ruthenium}, isbn = {0002-7863}, url = {://000268644400040}, author = {Steinke, T. and Shaw, B. K. and Jong, H. and Patrick, B. O. and Fryzuk,Michael D. and Green, J. C.} } @article {2376, title = {Plectosphaeroic Acids A, B, and C, Indoleamine 2,3-Dioxygenase Inhibitors Produced in Culture by a Marine Isolate of the Fungus Plectosphaerella cucumerina}, journal = {Organic Letters}, volume = {11}, number = {14}, year = {2009}, note = {ISI Document Delivery No.: 472NMTimes Cited: 1Cited Reference Count: 29Carr, Gavin Tay, Wendy Bottriell, Helen Andersen, Sarah K. Mauk, A. Grant Andersen, Raymond J.}, month = {Jul}, pages = {2996-2999}, type = {Article}, abstract = {Laboratory cultures of the fungus Plectosphaerella cucumerina obtained from marine sediments collected in Barkley Sound, British Columbia, yielded the novel alkaloids plectosphaeroic acids A (1) to C (3). The alkaloids 1-3 are inhibitors of indoleamine 2,3-dioxygenase (IDO).}, keywords = {CANCER, CELLS, chemotherapy, EXIGUAMINE-A, EXPRESSION, IDO, MECHANISM, METABOLITES, SUPPRESSION, TRYPTOPHAN DEGRADATION}, isbn = {1523-7060}, url = {://000268138800011}, author = {Carr, G. and Tay, W. and Bottriell, H. and Andersen, S. K. and Mauk, A. G. and Andersen, R. J.} } @article {2553, title = {Pseudospectral method of solution of the Fitzhugh-Nagumo equation}, journal = {Mathematics and Computers in Simulation}, volume = {79}, number = {7}, year = {2009}, note = {ISI Document Delivery No.: 429KBTimes Cited: 3Cited Reference Count: 41Olmos, Daniel Shizgal, Bernie D.}, month = {Mar}, pages = {2258-2278}, type = {Article}, abstract = {We present a study of the convergence of different numerical schemes in the solution of the Fitzhugh-Nagumo equations in the form of two coupled reaction diffusion equations for activator and inhibitor variables. The diffusion coefficient for the inhibitor is taken to be zero. The Fitzhugh-Nagumo equations, have spatial and temporal dynamics in two different scales and the solutions exhibit shock-like waves. The numerical schemes employed are a Chebyshev multidomain method, a finite difference method and the method developed by Barkley [D. Barkley, A model for fast computer simulation of excitable media, Physica D, 49 (1991) 61-70]. We consider two different models for the local dynamics. We present results for plane wave propagation in one dimension and spiral waves for two dimensions. We use an operator splitting method with the Chebyshev multidomain approach in order to reduce the computational time. Zero flux boundary conditions are imposed on the solutions. (C) 2009 IMACS. Published by Elsevier B.V. All rights reserved.}, keywords = {3-DIMENSIONAL EXCITABLE MEDIA, Chebyshev multidomain, Convergence, DYNAMICS, Fitzhugh-Nagumo equations, MECHANISM, MODEL, REACTION-DIFFUSION-SYSTEMS, SELECTION, Spiral waves, SPIRAL-WAVE, TRANSITION}, isbn = {0378-4754}, url = {://000264918200021}, author = {Olmos, D. and Shizgal, B. D.} } @article {2690, title = {A triple-stranded helicate and mesocate from the same metal and ligand}, journal = {Chemical Communications}, number = {45}, year = {2009}, note = {ISI Document Delivery No.: 517VNTimes Cited: 4Cited Reference Count: 37Zhang, Zhan Dolphin, David}, pages = {6931-6933}, type = {Article}, abstract = {A pair of triple-stranded helicates and mesocates were, for the first time, isolated from the same reaction of a novel alpha-free bis(dipyrromethene)ligand with either Co3+ or Fe3+.}, keywords = {CHEMISTRY, cobalt(II), COMPLEXES, dipyrrins, DIPYRROMETHENE LIGANDS, INVERSION, iron, MECHANISM, STRUCTURAL-CHARACTERIZATION, TWIST}, isbn = {1359-7345}, url = {://000271647200007}, author = {Zhang, Z. and Dolphin, D.} } @article {2303, title = {The crystal structure of MexR from Pseudomonas aeruginosa in complex with its antirepressor ArmR}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {105}, number = {39}, year = {2008}, note = {ISI Document Delivery No.: 386WWTimes Cited: 15Cited Reference Count: 41Wilke, Mark S. Heller, Markus Creagh, A. Louise Haynes, Charles A. McIntosh, Lawrence P. Poole, Keith Strynadka, Natalie C. J.}, month = {Sep}, pages = {14832-14837}, type = {Article}, abstract = {The intrinsic antimicrobial resistance of the opportunistic human pathogen Pseudomonas aeruginosa is compounded in mutant strains that overexpress multidrug efflux pumps such as the prominent drug-proton antiporter, MexAB-OprM. The primary regulator of the mexAB-oprM operon is the MarR family repressor, MexR. An additional repressor, NalC, also regulates mexAB-oprM by controlling expression of ArmR, an antirepressor peptide that is hypothesized to prevent the binding of MexR to its cognate DNA operator via an allosteric protein-peptide interaction. To better understand how ArmR modulates MexR, we determined the MexR-binding region of ArmR as its C-terminal 25 residues and solved the crystal structure of MexR in a 2: 1 complex with this ArmR fragment at 1.8 angstrom resolution. This structure reveals that the C-terminal residues of ArmR form a kinked alpha-helix, which occupies a pseudo-symmetrical and largely hydrophobic binding cavity located at the centre of the MexR dimer. Although the ArmR-binding cavity partially overlaps with the small molecule effector-binding sites of other MarR family members, it possesses a larger and more complex binding surface to accommodate the greater size and specific physicochemical properties of a peptide effector. Comparison with the structure of apo-MexR reveals that ArmR stabilizes a dramatic conformational change that is incompatible with DNA-binding. Thus, this work defines the structural mechanism by which ArmR allosterically derepresses MexR-controlled gene expression in P. aeruginosa and reveals important insights into the regulation of multidrug resistance.}, keywords = {DEINOCOCCUS-RADIODURANS, DNA-BINDING, EXPRESSION, GENE, gene regulation, MarR, MARR FAMILY, MECHANISM, mexAB-oprM, MULTIDRUG EFFLUX OPERON, OPRM, PA3719, protein peptide, REPRESSOR, TRANSCRIPTIONAL REGULATOR HUCR}, isbn = {0027-8424}, url = {://000261914300004}, author = {Wilke, M. S. and Heller, M. and Creagh, A. L. and Haynes, C. A. and McIntosh, L. P. and Poole, K. and Strynadka, N. C. J.} } @article {2232, title = {Investigation of substituted-benzene dopants for charge exchange ionization of nonpolar compounds by atmospheric pressure photoionization}, journal = {Journal of the American Society for Mass Spectrometry}, volume = {19}, number = {7}, year = {2008}, note = {ISI Document Delivery No.: 329LWTimes Cited: 7Cited Reference Count: 24Robb, Damon B. Smith, Derek R. Blades, Michael W.}, month = {Jul}, pages = {955-963}, type = {Article}, abstract = {Atmospheric pressure photoionization (APPI) using a dopant enables both polar and nonpolar compounds to be analyzed by LC/MS. To date, the charge exchange ionization pathway utilized for nonpolar compounds has only been efficient under restrictive conditions, mainly because the usual charge exchange reagent ions-the dopant photoions themselves-tend to be consumed in proton transfer reactions with solvent and/or dopant neutrals. This research aims to elucidate the factors affecting the reactivities of substituted-benzene dopant ions; another, overriding, objective is to discover new dopants for better implementing charge exchange ionization in reversed-phase LC/MS applications. The desirable properties for a charge exchange dopant include low reactivity of its photoions with solvent and dopant neutrals and high ionization energy (IE). Reactivity tests were performed for diverse substituted-benzene compounds, with substituents ranging from strongly electron withdrawing (EW) to strongly electron donating (ED). The results indicate that both the tendency of a dopant{\textquoteright}s photoions to be lost through proton transfer reactions and its IE depend on the electron donating /withdrawing properties of its substituent(s): ED groups decrease reactivity and IE, while EW groups increase reactivity and IE. Exceptions to the reactivity trend for dopants with ED groups occur when the substituent is itself acidic. All told, the desirable properties for a charge exchange dopant tend towards mutual exclusivity. Of the singlysubstituted benzenes tested, chloro- and brornobenzene provide the best compromise between low reactivity and high IE. Several fluoroanisoles, with counteracting EW and ED groups, may also provide improved performance relative to the established dopants.}, keywords = {APPI, MASS-SPECTROMETRY, MECHANISM, MS, POTENTIALS, PROTON AFFINITY, SOLVENT}, isbn = {1044-0305}, url = {://000257870100007}, author = {Robb, D. B. and Smith, D. R. and Blades, M. W.} } @article {2285, title = {Probing General Base Catalysis in the Hammerhead Ribozyme}, journal = {Journal of the American Chemical Society}, volume = {130}, number = {46}, year = {2008}, note = {ISI Document Delivery No.: 406QZTimes Cited: 8Cited Reference Count: 53Thomas, Jason M. Perrin, David M.}, month = {Nov}, pages = {15467-15475}, type = {Article}, abstract = {Recent structural and computational studies have shed new light on the catalytic mechanism and active site structure of the RNA cleaving hammerhead ribozyme. Consequently, specific ribozyme functional groups have been hypothesized to be directly involved in general/acid base catalysis. In order to test this hypothesis, we have developed an affinity label to identify the functional general base in the S. mansoni hammerhead ribozyme. The ribozyme was reacted with a substrate analogue bearing a 2{\textquoteright}-bromoacetamide group in place of the nucleophilic 2{\textquoteright}-hydroxyl group which would normally be deprotonated by a general base. The electrophilic 2{\textquoteright}-bromoacetamide group is poised to alkylate the general base, which is subsequently identified by footprinting analysis. Herein, we demonstrate alkylation of N1 of G12 in the hammerhead ribozyme in a pH and [Mg2+] dependent manner that is consistent with the native cleavage reaction. These results provide substantial evidence that deprotonated N1 of G12 functions directly as a general base in the hammerhead ribozyme; moreover, our experiments provide evidence that the pK(a) of G12 is perturbed downward in the context of the active site structure. We also observed other pH-independent alkylations, which do not appear to reflect the catalytic mechanism, but offer further insight into ribozyme conformation and structure.}, keywords = {ACTIVE-SITE, CLEAVAGE, CRYSTAL-STRUCTURE, DELTA VIRUS RIBOZYME, HAIRPIN RIBOZYME, MECHANISM, METAL-ION, MONOVALENT CATIONS, NUCLEOBASE CATALYSIS, RNA}, isbn = {0002-7863}, url = {://000263311300051}, author = {Thomas, J. M. and Perrin,David M.} } @article {2037, title = {Synthesis of indoleamine 2,3-dioxygenase inhibitory analogues of the sponge alkaloid exiguamine A}, journal = {Journal of Medicinal Chemistry}, volume = {51}, number = {9}, year = {2008}, note = {ISI Document Delivery No.: 295USTimes Cited: 17Cited Reference Count: 20Carr, Gavin Chung, Marco K. W. Mauk, A. Grant Andersen, Raymond J.}, month = {May}, pages = {2634-2637}, type = {Article}, abstract = {Synthetic analogues of the sponge natural product exiguamine A (3) have been prepared and evaluated for their ability to inhibit indoleamine 2,3-dioxygenase in vitro.}, keywords = {CANCER, CATABOLISM, CELLS, chemotherapy, EXPRESSION, IDO, IMMUNE TOLERANCE, MECHANISM, SMALL-MOLECULE INHIBITORS, TRYPTOPHAN DEGRADATION}, isbn = {0022-2623}, url = {://000255500000008}, author = {Carr, G. and Chung, M. K. W. and Mauk, A. G. and Andersen, R. J.} } @article {ISI:000251974000023, title = {An electronic rationale for observed initiation rates in ruthenium-mediated olefin metathesis: charge donation in phosphine and N-heterocyclic carbene ligands.}, journal = {J. Am. Chem. Soc.}, volume = {129}, number = {51}, year = {2007}, month = {dec}, pages = {15774{\textendash}6}, chapter = {15774}, abstract = {Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.}, keywords = {ALKENES, Alkenes: chemistry, BOND, carbenes, CATALYSTS, CL, DFT, ELECTRONS, Heterocyclic Compounds, Heterocyclic Compounds: chemistry, HYDROCARBONS, Hydrocarbons: chemistry, KINETICS, LIGANDS, MECHANISM, METHANE, Methane: analogs \& derivatives, Methane: chemistry, MOIETY, NHC LIGANDS, OLEFIN METATHESIS, phosphines, Phosphines: chemistry, RAY-ABSORPTION SPECTROSCOPY, ruthenium, Ruthenium: chemistry, TRANSITION-METAL-COMPLEXES, XAS}, isbn = {0002-7863}, issn = {1520-5126}, doi = {10.1021/ja0747674}, url = {://000251974000023 http://www.ncbi.nlm.nih.gov/pubmed/18047332}, author = {Getty, Kendra and Delgado-Jaime, Mario Ulises and Kennepohl, Pierre} } @article {1522, title = {Indoleamine 2,3-dioxygenase inhibitors from the Northeastern Pacific marine hydroid Garveia annulata}, journal = {Journal of Natural Products}, volume = {69}, number = {10}, year = {2006}, note = {ISI Document Delivery No.: 098ZQTimes Cited: 17Cited Reference Count: 20Pereira, Alban Vottero, Eduardo Roberge, Michel Mauk, A. Grant Andersen, Raymond J.}, month = {Oct}, pages = {1496-1499}, type = {Article}, abstract = {Crude extracts of the marine hydroid Garveia annulata show potent inhibition of indoleamine 2,3-dioxygenase (IDO). Fractionation of the extract led to the identification of the new polyketides annulin C (1), 2-hydroxygarveatin E (4), garveatin E (5), and garvin C (9). Annulins A (2), B (3), and C (1) were found to be submicromolar inhibitors of IDO.}, keywords = {CANCER, chemotherapy, ENZYME, HUMAN LENS, MECHANISM, METABOLITES, NUCLEAR CATARACT, REJECTION, TOLERANCE, TRYPTOPHAN DEGRADATION}, isbn = {0163-3864}, url = {://000241562700025}, author = {Pereira, A. and Vottero, E. and Roberge, M. and Mauk, A. G. and Andersen, R. J.} } @article {1605, title = {Ortho-selective C-Hactivation of substituted benzenes effected by a tungsten alkylidene complex without substituent coordination}, journal = {Organometallics}, volume = {25}, number = {17}, year = {2006}, note = {ISI Document Delivery No.: 070PZTimes Cited: 13Cited Reference Count: 36Tsang, Jenkins Y. K. Buschhaus, Miriam S. A. Legzdins, Peter Patrick, Brian O.}, month = {Aug}, pages = {4215-4225}, type = {Article}, abstract = {{Gentle thermolysis of the bis(neopentyl) complex Cp*W(NO)(CH2CMe3)(2) (1) at 70 degrees C in various substituted benzenes results in the loss of neopentane and the generation of the transient alkylidene complex Cp*W(NO)(=CHCMe3) (A), which subsequently effects single C-H bond activations of the benzenes. These activations exhibit a pronounced selectivity for the C-H linkages ortho to the benzene substituents. Thus, thermal reactions of 1 with C6H5X lead to the preferential formation of the corresponding Cp*W( NO)(CH2CMe3)(o-C6H4X) complexes, the ortho-selectivity, i. e.}, keywords = {CLEAVAGE, CRYSTAL-STRUCTURE, ELIMINATION, H BONDS, IRIDIUM, MECHANISM, METAL-COMPLEXES, {ARYL}, isbn = {0276-7333}, url = {://000239536800028}, author = {Tsang, J. Y. K. and Buschhaus, M. S. A. and Legzdins,Peter and Patrick, B. O.} } @article {1464, title = {PseG of pseudaminic acid biosynthesis - A UDP-sugar hydrolase as a masked glycosyltransferase}, journal = {Journal of Biological Chemistry}, volume = {281}, number = {30}, year = {2006}, note = {ISI Document Delivery No.: 065VFTimes Cited: 12Cited Reference Count: 40Liu, Feng Tanner, Martin E.}, month = {Jul}, pages = {20902-20909}, type = {Article}, abstract = {The flagellin proteins in pathogenic bacteria such as Campylobacter jejuni and Helicobacter pylori are heavily glycosylated with the nine-carbon alpha-keto acid, pseudaminic acid. The presence of this posttranslational modification is absolutely required for assembly of functional flagella. Since motility is required for colonization, pseudaminic acid biosynthesis represents a virulence factor in these bacteria. Pseudaminic acid is generated from UDP-N-acetylglucosamine in five biosynthetic steps. The final step has been shown to involve the condensation of 2,4-diacetamido- 2,4,6-trideoxy-L-altrose ( 6-deoxy-AltdiNAc) with phosphoenolpyruvate as catalyzed by the enzyme pseudaminic acid synthase, NeuB3. The 6-deoxy-AltdiNAc used in this process is generated from its nucleotide-linked form, UDP-6-deoxy-AltdiNAc, by the action of a hydrolase that cleaves the glycosidic bond and releases UDP. This manuscript describes the first characterization of a UDP-6-deoxy-AltdiNAc hydrolase, namely PseG ( Cj1312) from C. jejuni. The activity of this enzyme is independent of the presence of divalent metal ions, and the values of the catalytic constants were found to be k(cat) = 27 s(-1) and K-m = 174 mu M. The enzyme was shown to hydrolyze the substrate with an overall inversion of stereochemistry at C-1 and to utilize a C-O bond cleavage mechanism during catalysis. These results, coupled with homology comparisons, suggest that the closest ancestors to the hydrolase are members of the metal-independent GT-B family of glycosyltransferases that include the enzyme MurG.}, keywords = {CAMPYLOBACTER-JEJUNI, FLAGELLIN, FUNCTIONAL-CHARACTERIZATION, GLYCOPROTEINS, glycosylation, HELICOBACTER-PYLORI, IDENTIFICATION, MECHANISM, N-ACETYLGLUCOSAMINE 2-EPIMERASE, NUDIX HYDROLASES, SYNTHASE}, isbn = {0021-9258}, url = {://000239187300027}, author = {Liu, F. and Tanner, M. E.} } @article {1279, title = {The enzymes of sialic acid biosynthesis}, journal = {Bioorganic Chemistry}, volume = {33}, number = {3}, year = {2005}, note = {ISI Document Delivery No.: 931CJTimes Cited: 36Cited Reference Count: 59}, month = {Jun}, pages = {216-228}, type = {Review}, abstract = {The sialic acids are a family of nine carbon a-keto acids that play a wide variety of biological roles in nature. In mammals, they are found at the distal ends of cell surface glycoconjugates, and thus are major determinants of cellular recognition and adhesion events. In certain strains of pathogenic bacteria, they are found in capsular polysaccharides that mask the organism from the immune system by mimicking the exterior of a mammalian cell. This review outlines recent developments in the understanding of the two main enzymes responsible for the biosynthesis of the sialic acid, N-acetylneuraminic acid. The first, a hydrolyzing UDP-N-acetyl-glucosamine 2-epimerase, generates N-acetylmannosamine and UDP from UDP-N-acetylglucosamine. The second, sialic acid synthase, generates either N-acetylneuraminic acid (bacteria) or N-acetylneuraminic acid 9-phosphate (mammals) in a condensation reaction with phosphoenolpyruvate. An emphasis is placed on an understanding of the mechanistic and structural features of these enzymes. (c) 2005 Elsevier Inc. All rights reserved.}, keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, BIFUNCTIONAL KEY ENZYME, biosynthesis, ESCHERICHIA-COLI K1, FIRST 2, KDO8P SYNTHASE, MECHANISM, N-ACETYLGLUCOSAMINE 2-EPIMERASE, N-acetylmannosamine, N-ACETYLNEURAMINIC ACID, NEISSERIA-MENINGITIDIS, PHOSPHATE, phosphoenolpyruvate, RAT-LIVER, sialic acid synthase, STEPS, SYNTHASE GENE, UDP-GlcNAc 2-epimerase}, isbn = {0045-2068}, url = {://000229463100007}, author = {Tanner, M. E.} } @article {1132, title = {Expeditious, high-yielding construction of the food aroma compounds 6-acetyl-1,2,3,4-tetrahydropyridine and 2-acetyl-1-pyrroline}, journal = {Journal of Organic Chemistry}, volume = {70}, number = {26}, year = {2005}, note = {ISI Document Delivery No.: 995HBTimes Cited: 10Cited Reference Count: 38}, month = {Dec}, pages = {10872-10874}, type = {Article}, abstract = {The key compound responsible for the aroma of bread, 6-acetyl-1,2,3,4-tetrahydropyridine (1), has been constructed in an efficient three-step procedure from 2-piperidone in an overall yield of 56\%. Compound I was liberated in the final step under basic conditions. A related synthetic route produced 2-acetyl-1-pyrroline (2), the principal component of cooked rice, in 10\% overall yield.}, keywords = {BICYCLIC ENAMINES, BREAD FLAVOR COMPONENT, COOKED RICE, HYDROLYSIS, MECHANISM, MODEL SYSTEMS, POPCORN, QUANTITATIVE-ANALYSIS, ROAST-SMELLING ODORANTS, TERTIARY ENAMINES}, isbn = {0022-3263}, url = {://000234090300034}, author = {Harrison, T. J. and Dake, G. R.} } @article {1219, title = {Synthesis and insulin-mimetic activities of metal complexes with 3-hydroxypyridine-2-carboxylic acid}, journal = {Journal of Inorganic Biochemistry}, volume = {99}, number = {6}, year = {2005}, note = {ISI Document Delivery No.: 934IJTimes Cited: 16Cited Reference Count: 28}, month = {Jun}, pages = {1275-1282}, type = {Article}, abstract = {Metal complexes of 3-hydroxypyridine-2-carboxylic acid (H(2)hpic), [Co(Hhpic)(2)(H2O)(2)] (1), [Fe(Hhpic)(2)(H2O)(2)] (2), [Zn(Hhpic)(2)(H2O)(2)] (3), [Mn(Hhpic)(2)(H2O)(2)] (4), and [Cu(Hhpic)(2)] (5) have been synthesized and characterized by mass spectrometry, elemental analysis, magnetic susceptibility, infrared, electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. The solid-state structure of 1 has been established by X-ray crystallography. The EPR spectra of 4 and 5 displayed six and four-line hyperfine splitting patterns, respectively, due to coupling of the unpaired electron with the Mn-55 (I=5/2) nucleus and the Cu-63 (I=3/2) nucleus. In the EPR spectrum of 5, an additional five-line super-hyperfine splitting pattern was observed at 77 K, caused by additional interaction of the unpaired electron with ligand nitrogen atoms (I=1), indicating that the structure of 5 was retained in dimethyl sulfoxide solution. The insulin-mimetic activity of these complexes was evaluated by means of in vitro measurements of the inhibition of free fatty acid (FFA) release from epinephrine-treated, isolated rat adipocytes. Complex 5 was found to exhibit the most potent insulin-mimetic activity among the complexes examined in this study. (C) 2005 Elsevier Inc. All rights reserved.}, keywords = {3-hydroxypyridine-2-carboxylic acid (H(2)hpic), CHEMISTRY, DIABETIC-RATS, GLUCOSE, insulin-mimetic drug, MECHANISM, MONONUCLEAR, RAT ADIPOCYTES, VANADIUM}, isbn = {0162-0134}, url = {://000229702200002}, author = {Nakai, M. and Sekiguchi, F. and Obata, M. and Ohtsuki, C. and Adachi, Y. and Sakurai, H. and Orvig, Chris and Rehder, D. and Yano, S.} } @article {972, title = {Active site mutants of the "non-hydrolyzing" UDP-N-acetylglucosamine 2-epimerase from Escherichia coli}, journal = {Biochimica Et Biophysica Acta-Proteins and Proteomics}, volume = {1700}, number = {1}, year = {2004}, note = {ISI Document Delivery No.: 833VCTimes Cited: 4Cited Reference Count: 26}, month = {Jul}, pages = {85-91}, type = {Article}, abstract = {The "non-hydrolyzing" bacterial UDP-N-acetylglucosamine 2-epimerase catalyzes the reversible interconversion of UDP-N-acetylglucosarnine (UDP-GlcNAc) and UDP-N-acetylmannosamine (UDP-ManNAc). This homodimeric enzyme is allosterically activated by its substrate, UDP-GlcNAc, and it is thought that one subunit plays a regulatory role, while that of the other plays a catalytic role. In this work, five active site mutants were prepared (D95N, E117Q, E131Q, K15A, and H213N) and analyzed in terms of their effects on binding, catalysis, and allosteric regulation. His213 appears to play a role in UDP binding and may also assist in catalysis and/or regulation, but is not a key catalytic residue. Lys15 appears to be quite important for binding. All three of the carboxylate mutants showed dramatic decreases in the value of k(cat) but relatively unaffected values of Km. Thus, these residues are playing key roles in catalysis and/or regulation. In the case of E117Q, the reaction intermediates are released into solution at a rate comparable to that of the overall catalysis. This may indicate that Glu117 plays the role as an acid/base catalyst in the second step of the UDP-GlcNAc epimerization reaction. All three carboxylate mutants were found to exhibit impaired allosteric control. (C) 2004 Elsevier B.V. All rights reserved.}, keywords = {2-acetamidoglucal, 2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, ACID BIOSYNTHESIS, allosteric regulation, enterobacterial common antigen, EPIMERIZATION, HOMOLOGY, MECHANISM, MUTAGENESIS, RAT-LIVER, SEQUENCE, sialic acid, STREPTOCOCCUS-PNEUMONIAE, TRANSFERASES, UDP-N-acetylmannosamine}, isbn = {1570-9639}, url = {://000222367400011}, author = {Samuel, J. and Tanner, M. E.} } @article {619, title = {Diamidophosphine complexes of niobium(III) and (IV): imide formation via ancillary ligand decomposition}, journal = {Inorganica Chimica Acta}, volume = {350}, year = {2003}, note = {ISI Document Delivery No.: 700BTTimes Cited: 10Cited Reference Count: 32}, month = {Jul}, pages = {293-298}, type = {Article}, abstract = {The diamidophosphine complexes of niobium (CyPh)[NPN]NbCl(DME) (2), (CyPh)[NPN]NbCl2 (6), and (PhPh)[NPN]NbCl2 (9), where (RR{\textquoteright})[NPN]=RP(CH2SiMe2NR{\textquoteright})(2) have been prepared, isolated and characterized. Generation of (RR{\textquoteright})[NPN]NbCl(DME) species competes with the production of ((RR{\textquoteright})[NPN]NbCl)(2)(mu-N-2) and can be controlled with N-2 pressure. (CyPh)[NPN]NbCl2 spontaneously decomposes into (CyPh)[NPN]NbCl(=NPh) (7), CyP(CH2SiMe2)(2)NPh (8), and a paramagnetic impurity. Compound 7 was characterized by an X-ray diffraction study and its structural features are discussed. The Nb-N-imido bond length is 1.789(2) Angstrom with a Nb-N-imido-C bond angle of 167.9(2)degrees in a distorted square pyramidal structure. Reduction of (PhPh)[NPN]NbCl2 (9), with KC8 produced (PhPh)[NPN]NbCl(=NPh), PhP(CH2SiMe2)(2)NPh, and a paramagnetic impurity. (C) 2002 Elsevier Science B.V. All rights reserved.}, keywords = {ALKYNES, COORDINATION, diamidophosphine ligands, imido, MECHANISM, MEDIATED IMINE METATHESIS, NIOBIUM, ORGANOIMIDO COMPLEXES, REDUCTION, ROUTE, Si-N bond cleavage, tantalum}, isbn = {0020-1693}, url = {://000184093300036}, author = {Fryzuk,Michael D. and Shaver, M. P. and Patrick, B. O.} } @article {727, title = {The photochemistry of trans-1,4,4,4-tetraphenylbut-2-en-1-one: A highly efficient aryl migration (type B) enone photorearrangement}, journal = {Canadian Journal of Chemistry-Revue Canadienne De Chimie}, volume = {81}, number = {6}, year = {2003}, note = {ISI Document Delivery No.: 706UATimes Cited: 0Cited Reference Count: 18}, month = {Jun}, pages = {705-708}, type = {Article}, abstract = {Photolysis of trans-1,4,4,4-tetraphenylbut-2-en-1-one (3) in acetonitrile or benzene leads to trans-cis isomerization (7) along with rearrangement to trans-1 -benzoyl-2,2,3-triphenylcyclopropane(8). Formation of the latter product represents a new example of the aryl migration (type B) enone photorearrangement reaction first reported by Zimmerman and co-workers for 4,4-diphenylcyclohex-2-en-1-one (1). The quantum yield in the case of enone 3 (0.4) is approximately 10 times greater than that for 4,4,-diphenylcyclohex-2-en-1-one, a result that is ascribed to steric acceleration of phenyl migration from the triphenylmethyl group plus greater resonance stabilization of the intermediate biradical.}, keywords = {aryl migration, ASYMMETRIC INDUCTION, di-pi-methane, enone, EXPLORATORY ORGANIC PHOTOCHEMISTRY, MECHANISM, MIGRATION, PHENYL, PHOTOCHEMISTRY, PHOTOCYCLIZATION, REARRANGEMENT, STATE}, isbn = {0008-4042}, url = {://000184472400035}, author = {Scheffer, J. R. and Vishnumurthy, K.} } @article {498, title = {An atmospheric pressure ion lens that improves nebulizer assisted electrospray ion sources}, journal = {Journal of the American Society for Mass Spectrometry}, volume = {13}, number = {8}, year = {2002}, note = {ISI Document Delivery No.: 588METimes Cited: 7Cited Reference Count: 27}, month = {Aug}, pages = {906-913}, type = {Article}, abstract = {An atmospheric pressure ion lens improves the performance and ease of use of a nebulizer assisted electrospray (ion spray) ion source. The lens is comprised of an oblong-shaped stainless steel ring attached to an external high voltage power supply. The lens is located near the tip of the conductive sprayer, and is maintained at a potential less than that of the sprayer. The ion lens improves the shape of the equipotential lines in the vicinity of the sprayer tip. This lens gives approximately a 2-fold reduction in the signal RSD, a 2-fold increase in the ion signal, an increase in the number of multiply charged ions, and a much broader range of usable sprayer positions. (C) 2002 American Society for Mass Spectrometry.}, keywords = {CAPILLARY-ZONE-ELECTROPHORESIS, DISSOCIATION, EVAPORATION, IDENTIFICATION, INDUCED, INTERFACE, IONIZATION MASS-SPECTROMETRY, JUNCTION, MECHANISM, PROTEIN-ANALYSIS, SHEATHLESS}, isbn = {1044-0305}, url = {://000177704600002}, author = {Schneider, B. B. and Douglas, D. J. and Chen, D. D. Y.} } @article {348, title = {The calcium activation of gelsolin: Insights from the 3 angstrom structure of the G4-G6/actin complex}, journal = {Journal of Molecular Biology}, volume = {324}, number = {4}, year = {2002}, note = {ISI Document Delivery No.: 625PRTimes Cited: 48Cited Reference Count: 32}, month = {Dec}, pages = {691-702}, type = {Article}, abstract = {Gelsolin participates in the reorganization of the actin cytoskeleton that is required during such phenomena as cell movement, cytokinesis, and apoptosis. It consists of six structurally similar domains, G1-G6, which are arranged at resting intracellular levels of calcium ion so as to obscure the three actin-binding surfaces. Elevation of Ca2+ concentrations releases latches within the constrained structure and produces large shifts in the relative positioning of the domains, permitting gelsolin to bind to and sever actin filaments. How Ca2+ is able to activate gelsolin has been a major question concerning the function of this protein. We present the improved structure of the C-terminal half of gelsolin bound to monomeric actin at 3.0 Angstrom resolution. Two classes of Ca2+-binding site are evident on gelsolin: type 1 sites share coordination of Ca2+ with actin, while type 2 sites are wholly contained within gelsolin. This structure of the complex reveals the locations of two novel metal ion-binding sites in domains G5 and G6, respectively. We identify both as type 2 sites. The absolute conservation of the type 2 calcium-ligating residues across the six,domains of gelsolin suggests that this site exists in each of the domains. In total, gelsolin has the potential to bind eight calcium ions, two type 1 and six type 2. The function of the type 2 sites is to facilitate structural rearrangements within gelsolin as part of the activation and actin-binding and severing processes. We propose the novel type 2 site in G6 to be the critical site that initiates overall activation of gelsolin by releasing the tail latch that locks calcium-free gelsolin in a conformation unable to bind actin. (C) 2002 Elsevier Science Ltd. All rights reserved.}, keywords = {actin, ACTIVATION, ACTOPHORIN, BINDING DOMAIN, CA2+, calcium, CAPPING PROTEIN, F-ACTIN, FAMILIAL AMYLOIDOSIS, FINNISH TYPE, gelsolin, IDENTIFICATION, MECHANISM, PLASMA GELSOLIN, REGULATION, severing}, isbn = {0022-2836}, url = {://000179825300011}, author = {Choe, H. and Burtnick, L. D. and Mejillano, M. and Yin, H. L. and Robinson, R. C. and Choe, S.} } @article {529, title = {Definitive evidence for monoanionic binding of 2,3-dihydroxybiphenyl to 2,3-dihydroxybiphenyl 1,2-dioxygenase from UV resonance Raman spectroscopy, UV/Vis absorption spectroscopy, and crystallography}, journal = {Journal of the American Chemical Society}, volume = {124}, number = {11}, year = {2002}, note = {ISI Document Delivery No.: 531UMTimes Cited: 53Cited Reference Count: 79}, month = {Mar}, pages = {2485-2496}, type = {Article}, abstract = {Ultraviolet resonance Raman spectroscopy (UVRRS), electronic absorption spectroscopy, and X-ray crystallography were used to probe the nature of the binding of 2,3-dihydroxybiphenyl (DHB) to the extradiol ring-cleavage enzyme, 2,3-dihydroxybiphenyl 1,2-dioxygenase (DHBD; EC 1.13.11.39). The lowest lying transitions in the electronic absorption spectrum of DHBD-bound DHB occurred at 299 nm, compared to 305 nm for the monoanionic DHB species in buffer. In contrast, the corresponding transitions in neutral and dianionic DHB occurred at 283 and 348 nm, respectively, indicating that DHBD-bound DHB is monoanionic. These binding-induced spectral changes, and the use of custom-designed optical fiber probes, facilitated UVRR experiments. The strongest feature of the UVRR spectrum of DHB was a Y8a-like mode around 1600 cm(-1), whose position depended strongly on the protonation state of the DHB. In the spectrum of the DHBD-bound species, this feature occurred at 1603 cm-1, as observed in the spectrum of monoanionic DHB. Raman band shifts were observed in deuterated solvent, ruling out dianionic binding of the substrate. Thus, the electronic absorption and UVRRS data demonstrate that DHBD binds its catecholic substrate as a monoanion, definitively establishing this feature of the proposed mechanism of extradiol dioxygenases. This conclusion is supported by a crystal structure of the DHBD:DHB complex at 2.0 Angstrom resolution, which suggests that the substrate{\textquoteright}s 2-hydroxyl substituent, and not the 3-hydroxyl group, deprotonates upon binding. The structural data also show that the aromatic rings of the enzyme-bound DHB are essentially orthogonal to each other. Thus, the 6 nm blue shift of the transition for bound DHB relative to the monoanion in solution could indicate a conformational change upon binding. Catalytic roles of active site residues are proposed based on the structural data and previously proposed mechanistic schemes.}, keywords = {3, 4-DIOXYGENASE, BIPHENYL, CRYSTAL-STRUCTURE, EXTRADIOL CATECHOL DIOXYGENASES, FE(II) ACTIVE-SITE, FE3+ LIGAND, LIGAND-BINDING, MECHANISM, MOLECULAR-STRUCTURE, PROTOCATECHUATE, SUBSTRATE-BINDING}, isbn = {0002-7863}, url = {://000174435700037}, author = {Vaillancourt, F. H. and Barbosa, C. J. and Spiro, T. G. and Bolin, J. T. and Blades, M. W. and Turner, R. F. B. and Eltis, L. D.} } @article {529, title = {Definitive evidence for monoanionic binding of 2,3-dihydroxybiphenyl to 2,3-dihydroxybiphenyl 1,2-dioxygenase from UV resonance Raman spectroscopy, UV/Vis absorption spectroscopy, and crystallography}, journal = {Journal of the American Chemical Society}, volume = {124}, number = {11}, year = {2002}, note = {ISI Document Delivery No.: 531UMTimes Cited: 53Cited Reference Count: 79}, month = {Mar}, pages = {2485-2496}, type = {Article}, abstract = {Ultraviolet resonance Raman spectroscopy (UVRRS), electronic absorption spectroscopy, and X-ray crystallography were used to probe the nature of the binding of 2,3-dihydroxybiphenyl (DHB) to the extradiol ring-cleavage enzyme, 2,3-dihydroxybiphenyl 1,2-dioxygenase (DHBD; EC 1.13.11.39). The lowest lying transitions in the electronic absorption spectrum of DHBD-bound DHB occurred at 299 nm, compared to 305 nm for the monoanionic DHB species in buffer. In contrast, the corresponding transitions in neutral and dianionic DHB occurred at 283 and 348 nm, respectively, indicating that DHBD-bound DHB is monoanionic. These binding-induced spectral changes, and the use of custom-designed optical fiber probes, facilitated UVRR experiments. The strongest feature of the UVRR spectrum of DHB was a Y8a-like mode around 1600 cm(-1), whose position depended strongly on the protonation state of the DHB. In the spectrum of the DHBD-bound species, this feature occurred at 1603 cm-1, as observed in the spectrum of monoanionic DHB. Raman band shifts were observed in deuterated solvent, ruling out dianionic binding of the substrate. Thus, the electronic absorption and UVRRS data demonstrate that DHBD binds its catecholic substrate as a monoanion, definitively establishing this feature of the proposed mechanism of extradiol dioxygenases. This conclusion is supported by a crystal structure of the DHBD:DHB complex at 2.0 Angstrom resolution, which suggests that the substrate{\textquoteright}s 2-hydroxyl substituent, and not the 3-hydroxyl group, deprotonates upon binding. The structural data also show that the aromatic rings of the enzyme-bound DHB are essentially orthogonal to each other. Thus, the 6 nm blue shift of the transition for bound DHB relative to the monoanion in solution could indicate a conformational change upon binding. Catalytic roles of active site residues are proposed based on the structural data and previously proposed mechanistic schemes.}, keywords = {3, 4-DIOXYGENASE, BIPHENYL, CRYSTAL-STRUCTURE, EXTRADIOL CATECHOL DIOXYGENASES, FE(II) ACTIVE-SITE, FE3+ LIGAND, LIGAND-BINDING, MECHANISM, MOLECULAR-STRUCTURE, PROTOCATECHUATE, SUBSTRATE-BINDING}, isbn = {0002-7863}, url = {://000174435700037}, author = {Vaillancourt, F. H. and Barbosa, C. J. and Spiro, T. G. and Bolin, J. T. and Blades, M. W. and Turner, R. F. B. and Eltis, L. D.} } @article {454, title = {Dehydroalanine-based inhibition of a peptide epimerase from spider venom}, journal = {Journal of Organic Chemistry}, volume = {67}, number = {24}, year = {2002}, note = {ISI Document Delivery No.: 620AATimes Cited: 17Cited Reference Count: 42}, month = {Nov}, pages = {8389-8394}, type = {Article}, abstract = {Ribosomally produced peptides that contain D-amino acids have been isolated from a number of vertebrate and invertebrate sources. In each case, the D-amino acids are introduced by a posttranslational modification of a parent peptide containing only amino acids of the L-configuration. The only known enzyme to catalyze such a reaction is the peptide epimerase (also known as peptide isomerase) from the venom of the funnel web spider, Agelenopsis aperta. This enzyme interconverts two 48-amino-acid-long peptide toxins that differ only by the stereochemistry at a single serine residue. In this paper we report the synthesis and testing of two pentapeptide analogues that contain modified amino acids at the site normally occupied by the substrate serine residue. When the L-chloroalanine-containing peptide 3 was incubated with the epimerase it was converted into the dehydroalanine-containing peptide 4 via an elimination of HCl. The dehydroalanine peptide 4 was independently synthesized and found to act as a potent inhibitor of the epimerase (IC50 = 0.5 muM). These results support a direct deprotonation/reprotonation mechanism in which a carbanionic intermediate is formed. The observed inhibition by 4 can be attributed to the sp(2)-hybridization of the a-carbon in the dehydroalanine unit that mimics the planar geometry of the anionic intermediate.}, keywords = {ACID, ACTIVE-SITE, ENZYME, GLUTAMATE RACEMASE, GRAMICIDIN-S SYNTHETASE, INFLUENZAE DIAMINOPIMELATE EPIMERASE, INITIATION MODULE PHEATE, MECHANISM, PROLINE RACEMASE, RESIDUES}, isbn = {0022-3263}, url = {://000179509400011}, author = {Murkin, A. S. and Tanner, M. E.} } @inbook {423, title = {Pre-steady-state kinetics of enzymatic reactions studied by electrospray mass spectrometry with on-line rapid-mixing techniques}, booktitle = {Enzyme Kinetics and Mechanism, Pt F: Detection and Characterization of Enzyme Reaction Intermediates}, series = {Methods in Enzymology}, volume = {354}, year = {2002}, note = {ISI Document Delivery No.: BV53FTimes Cited: 8Cited Reference Count: 42Review525 B STREET, SUITE 1900, SAN DIEGO, CA 92101-4495 USA}, pages = {50-64}, publisher = {Academic Press Inc}, organization = {Academic Press Inc}, address = {San Diego}, keywords = {ACID, BETA-LACTAMASE, CATALYSIS, COMPLEXES, INTERMEDIATE, ION, IONIZATION, MECHANISM, REAL-TIME}, isbn = {0076-6879}, url = {://000179267700003}, author = {Konermann, L. and Douglas, D. J.} } @article {520, title = {Understanding nature{\textquoteright}s strategies for enzyme-catalyzed racemization and epimerization}, journal = {Accounts of Chemical Research}, volume = {35}, number = {4}, year = {2002}, note = {ISI Document Delivery No.: 544TBTimes Cited: 65Cited Reference Count: 36}, month = {Apr}, pages = {237-246}, type = {Review}, abstract = {Epimerases and racemases are enzymes that catalyze the inversion of stereochemistry in biological molecules. In this article, three distinct examples are used to illustrate the wide range of chemical strategies employed during catalysis, and the diverse set of ancestors from which these enzymes have evolved. Glutamate racemase is an example of an enzyme that operates at an "activated" stereocenter (bearing a relatively acidic proton) and employs a nonstereospecific deprotonation/reprotonation mechanism. UDP-N-Acetylglucosamine 2-epimerase acts at an "unactivated" stereocenter and uses a mechanism involving a nonstereospecific elimination/addition of UDP. L-Ribulose phosphate 4-epimerase also acts at an unactivated stereocenter and uses a nonstereospecific retroaldol/aldol mechanism.}, keywords = {ALDOLASE, CLASS-II, ESCHERICHIA-COLI, GLUTAMATE RACEMASE, IDENTIFICATION, L-FUCULOSE-1-PHOSPHATE, L-RIBULOSE-5-PHOSPHATE 4-EPIMERASE, MECHANISM, N-ACETYLGLUCOSAMINE 2-EPIMERASE, PHOSPHATE, RESIDUES}, isbn = {0001-4842}, url = {://000175175800005}, author = {Tanner, M. E.} } @article {5183, title = {Catalysis and binding in L-ribulose-5-phosphate 4-epimerase: A comparison with L-fuculose-1-phosphate aldolase}, journal = {Biochemistry}, volume = {40}, number = {49}, year = {2001}, note = {ISI Document Delivery No.: 500CJTimes Cited: 15Cited Reference Count: 15}, month = {Dec}, pages = {14772-14780}, type = {Article}, abstract = {L-Ribulose-5-phosphate (L-Ru5P) 4-epimerase and L-fuculose-1-phosphate (L-Fuc1P) aldolase are evolutionarily related enzymes that display 26\% sequence identity and a very high degree of structural similarity. They both employ a divalent cation in the formation and stabilization of an enolate during catalysis, and both are able to deprotonate the C-4 hydroxyl group of a phosphoketose substrate. Despite these many similarities, subtle distinctions must be present which allow the enzymes to catalyze two seemingly different reactions and to accommodate substrates differing greatly in the position of the phosphate (C-5 vs C-1). Asp76 of the epimerase corresponds to the key catalytic acid/base residue Glu73 of the aldolase. The D76N mutant of the epimerase retained considerable activity, indicating it is not a key catalytic residue in this enzyme. In addition, the D76E mutant did not show enhanced levels of background aldolase activity. Mutations of residues in the putative phosphate-binding pocket of the epimerase (N28A and K42M) showed dramatically higher values of K-M for L-Ru5P. This indicates that both enzymes utilize the same phosphate recognition pocket, and since the phosphates are positioned at opposite ends of the respective substrates, the two enzymes must bind their substrates in a reversed or "flipped" orientation. The epimerase mutant D120N displays a 3000-fold decrease in the value of k(cat), suggesting that Asp 120{\textquoteright} provides a key catalytic acid/base residue in this enzyme. Analysis of the D120N mutant by X-ray crystallography shows that its structure is indistinguishable from that of the wild-type enzyme and that the decrease in activity was not simply due to a structural perturbation of the active site. Previous work [Lee, L.V., Poyner, R.R., Vu, M.V., and Cleland, W.W. (2000) Biochemistry 39, 4821-4830] has indicated that Tyr229{\textquoteright} likely provides the other catalytic acid/base residue. Both of these residues are supplied by an adjacent subunit. Modeling Of L-Ru5P into the active site of the epimerase structure suggests that Tyr229{\textquoteright} is responsible for deprotonating L-Ru5P and Asp 120{\textquoteright} is responsible for deprotonating its epimer, D-Xu5P.}, keywords = {CLASS-II, CLEAVAGE, ESCHERICHIA-COLI, MECHANISM, MUTAGENESIS, PHOSPHATE}, isbn = {0006-2960}, url = {://000172608100006}, author = {Samuel, J. and Luo, Y. and Morgan, P. M. and Strynadka, N. C. J. and Tanner, M. E.} } @article {5175, title = {The disintegration of a molecule: The role of gelsolin in FAF, familial amyloidosis (Finnish type)}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {98}, number = {5}, year = {2001}, note = {ISI Document Delivery No.: 407EHTimes Cited: 8Cited Reference Count: 13}, month = {Feb}, pages = {2117-2118}, type = {Editorial Material}, keywords = {actin filament, MECHANISM, MODEL, PROTEIN}, isbn = {0027-8424}, url = {://000167258900003}, author = {Robinson, R. C. and Choe, S. Y. and Burtnick, L. D.} } @article {5138, title = {The structure of L-ribulose-5-phosphate 4-epimerase: An aldolase-like platform for epimerization}, journal = {Biochemistry}, volume = {40}, number = {49}, year = {2001}, note = {ISI Document Delivery No.: 500CJTimes Cited: 18Cited Reference Count: 45}, month = {Dec}, pages = {14763-14771}, type = {Article}, abstract = {The structure of L-ribulose-5 -phosphate 4-epimerase from E. coli has been solved to 2.4 Angstrom resolution using X-ray diffraction data. The structure is homo-tetrameric and displays C-4 symmetry. Each subunit has a single domain comprised of a central beta -sheet flanked on either side by layers of alpha -helices. The active site is identified by the position of the catalytic zinc residue and is located at the interface between two adjacent subunits. A remarkable feature of the structure is that it shows a very close resemblance to that of L-fuculose-1-phosphate aldolase. This is consistent with the notion that both enzymes belong to a superfamily of epimerases/aldolases that catalyze carbon-carbon bond cleavage reactions via a metal-stabilized enolate intermediate. Detailed inspection of the epimerase structure, however, indicates that despite the close overall structural similarity to class II aldolases, the enzyme has evolved distinct active site features that promote its particular chemistry.}, keywords = {CHEMISTRY, CLASS-II, CLEAVAGE, ENZYME, ESCHERICHIA-COLI, EVOLUTION, GALACTOSE, L-FUCULOSE-1-PHOSPHATE ALDOLASE, MECHANISM, SEQUENCE, SUPERFAMILIES}, isbn = {0006-2960}, url = {://000172608100005}, author = {Luo, Y. and Samuel, J. and Mosimann, S. C. and Lee, J. E. and Tanner, M. E. and Strynadka, N. C. J.} } @article {5205, title = {Surface effects in chromate conversion coatings on 2024-T3 aluminum alloy}, journal = {Journal of Materials Science}, volume = {36}, number = {13}, year = {2001}, note = {ISI Document Delivery No.: 443DLTimes Cited: 17Cited Reference Count: 28}, month = {Jul}, pages = {3215-3220}, type = {Article}, abstract = {Chromate conversion coatings formed on samples of 2024-T3 aluminum alloy, which had been given different pre-treatments, were examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and corrosion tests. Two pre-treatments were considered, namely a simple mechanical polish, and polishing followed by an etch in a HF-H2SO4 solution. The latter treatment leads to significant Cu enrichment at the oxide-alloy interface, and this in turn can lead to a deleterious effect on the corrosion protection afforded by a subsequently applied chromate coating. Discussions are given of the behaviour of Cu in the coating formed on the sample that received an acid etch in the pre-treatment. This involves both migration through the coating and a non-uniform redeposition of Cu on to the coating surface. By contrast, the sample that initially was given just the mechanical polish in the pre-treatment does not show a Cu enrichment in the surface region, and the subsequently applied coating appeared stable after a 24 h immersion in a NaCl test solution. (C) 2001 Kluwer Academic Publishers.}, keywords = {COPPER IONS, CU ALLOY, FILMS, GROWTH, MECHANISM, mobility}, isbn = {0022-2461}, url = {://000169325100017}, author = {Sun, X. and Li, R. and Wong, K. C. and Mitchell, K. A. R. and Foster, T.} } @article {4856, title = {Binding site analysis of cellulose binding domain CBDN1 from endoglucanse C of Cellulomonas fimi by site-directed mutagenesis}, journal = {Biochemistry}, volume = {39}, number = {30}, year = {2000}, note = {ISI Document Delivery No.: 339RJTimes Cited: 17Cited Reference Count: 59}, month = {Aug}, pages = {8844-8852}, type = {Article}, abstract = {Endoglucanase C (CenC), a beta 1,4 glucanase from the soil bacterium Cellulomonas fimi, binds to amorphous cellulose via two homologous cellulose binding domains, termed CBDN1 and CBDN2. in this work, the contributions of 10 amino acids within the binding cleft of CBDN1 were evaluated by single site-directed mutations to alanine residues. Each isolated domain containing a single mutation was analyzed for binding to an insoluble amorphous preparation of cellulose, phosphoric acid swollen Avicel (PASA), and to a soluble glucopyranoside polymer, barley beta-glucan. The effect of any given mutation on CBD binding was similar for both substrates, suggesting that the mechanism of binding to soluble and insoluble substrates is the same. Tyrosines 19 and 85 were essential for tight binding by CBDN1 as their replacement by alanine results in affinity decrements of approximately 100-fold on PASA, barley beta-glucan, and soluble cellooligosaccharides. The tertiary structures of unbound Y19A and Y85A were assessed by heteronuclear single quantum coherence (HSQC) spectroscopy. These studies indicated that the structures of both mutants were perturbed but that all perturbations are very near to the site of mutation.}, keywords = {4-GLUCANASE CENC, BETA-1, ESCHERICHIA-COLI, LIGAND-BINDING, LIMITED PROTEOLYSIS, MECHANISM, N-ACETYLGLUCOSAMINE, NUCLEAR-MAGNETIC-RESONANCE, REESEI CELLOBIOHYDROLASE-I, TRICHODERMA-REESEI, TRYPTOPHAN RESIDUES}, isbn = {0006-2960}, url = {://000088491500018}, author = {Kormos, J. and Johnson, P. E. and Brun, E. and Tomme, P. and McIntosh, L. P. and Haynes, C. A. and Kilburn, D. G.} } @article {4751, title = {The first structure of UDP-glucose dehydrogenase reveals the catalytic residues necessary for the two-fold oxidation}, journal = {Biochemistry}, volume = {39}, number = {23}, year = {2000}, note = {ISI Document Delivery No.: 324PRTimes Cited: 62Cited Reference Count: 49}, month = {Jun}, pages = {7012-7023}, type = {Article}, abstract = {Bacterial UDP-glucose dehydrogenase (UDPGlcDH) is essential for formation of the antiphagocytic capsule that protects many virulent bacteria such as Streptococcus pyrogenes and Streptococcus pneumoniae type 3 from the host{\textquoteright}s immune system. We have determined the X-ray structures of both native and Cys260Ser UDPGlcDH from S. pyogenes (74\% similarity to S. pneumoniae) in ternary complexes with UDP-xylose/NAD(+) and UDP-glucuronic acid/NAD(H), respectively. The 402 residue homodimeric UDPGlcDH is composed of an N-terminal NAD(+) dinucleotide binding domain and a C-terminal UDP-sugar binding domain connected by a long (48 Angstrom) central alpha-helix. The first 290 residues of UDPGlcDH share structural homology with 6-phosphogluconate dehydrogenase, including conservation of an active site lysine and asparagine that are implicated in the enzyme mechanism. Also proposed to participate in the catalytic mechanism are a threonine and a glutamate that hydrogen bond to a conserved active site water molecule suitably positioned for general acid/base catalysis.}, keywords = {alanine, ALIGNMENT, CRYSTAL-STRUCTURE, ESCHERICHIA-COLI, GROUP-A STREPTOCOCCI, INSIGHTS, MECHANISM, MOLECULAR CHARACTERIZATION, REDUCTASE, SUBSTRATE-BINDING}, isbn = {0006-2960}, url = {://000087631000031}, author = {Campbell, R. E. and Mosimann, S. C. and van de Rijn, I. and Tanner, M. E. and Strynadka, N. C. J.} } @article {4557, title = {Catalytic acid/base residues of glutamate racemase}, journal = {Biochemistry}, volume = {38}, number = {13}, year = {1999}, note = {ISI Document Delivery No.: 182QZTimes Cited: 43Cited Reference Count: 37}, month = {Mar}, pages = {4106-4113}, type = {Article}, abstract = {Glutamate racemase is a cofactor-independent enzyme that employs two active-site cysteine residues as acid/base catalysts during the interconversion of glutamate enantiomers, In a given reaction direction, a thiolate from one of the cysteines abstracts the alpha-proton, and the other cysteine thiol delivers a proton to the opposite face of the resulting carbanionic intermediate. This paper reports that the C73S and C184S mutants are still capable of racemizing glutamate with specificity constants about 10(3)-fold lower than those of the wild-type enzyme, A "one-base requiring" reaction, the elimination of water from N-hydroxyglutamate, has been used to deduce which thiol acts as the base for a given enantiomer. With D-N-hydroxyglutamate the C73S mutant is a much poorer catalyst than wild-type enzyme, whereas the C184S mutant is a somewhat better catalyst. This trend was reversed with L-N-hydroxyglutamate, suggesting that Cys73 is responsible for the deprotonation of D-glutamate and Cys184 is responsible for the deprotonation of L-glutamate. In addition, with C73S the V-max/K-M isotope effect on D-glutamate racemization was greater than that seen with wild-type enzyme, whereas the isotope effect with L-glutamate had decreased. The results were reversed with the C184S mutant. This is interpreted as being due to an asymmetry in the free energy profiles that is induced upon mutation, with the deprotonation step involving a serine becoming the more cleanly rate-determining of the two. These results support the above assignment and the notion that a carbanionic intermediate is formed during catalysis.}, keywords = {BACILLUS-STEAROTHERMOPHILUS, DIAMINOPIMELATE EPIMERASE, ENERGETICS, ESCHERICHIA-COLI, INHIBITOR, IRREVERSIBLE, L-ALANINE, MANDELATE RACEMASE, MECHANISM, PROLINE RACEMASE, PURIFICATION}, isbn = {0006-2960}, url = {://000079510800031}, author = {Glavas, S. and Tanner, M. E.} } @article {4667, title = {Sugar ring distortion in the glycosyl-enzyme intermediate of a family G/11 xylanase}, journal = {Biochemistry}, volume = {38}, number = {17}, year = {1999}, note = {ISI Document Delivery No.: 193YMTimes Cited: 122Cited Reference Count: 50}, month = {Apr}, pages = {5346-5354}, type = {Article}, abstract = {The 1.8 Angstrom resolution structure of the glycosyl-enzyme intermediate formed on the retaining beta-1,4-xylanase from Bacillus circulans has been determined using X-ray crystallographic techniques. The 2-fluoro-xylose residue bound in the -1 subsite adopts a B-2,B-5 (boat) conformation, allowing atoms C5, O5, C1, and C2 of the sugar to achieve coplanarity as required at the oxocarbenium ion-like transition states of the double-displacement catalytic mechanism. Comparison of this structure to that of a mutant of this same enzyme noncovalently complexed with xylotetraose [Wakarchuk et al. (1994) Protein Sci. 3, 467-475] reveals a number of differences beyond the distortion of the sugar moiety. Most notably, a bifurcated hydrogen bond interaction is formed in the glycosyl-enzyme intermediate involving H-eta of Tyr69, the endocyclic oxygen (O5) of the xylose residue in the -1 subsite, and O-epsilon 2 of the catalytic nucleophile, Glu78. To gain additional understanding of the role of Tyr69 at the active site of this enzyme, we also determined the 1.5 Angstrom resolution structure of the catalytically inactive Tyr69Phe mutant. Interestingly, no significant structural perturbation due to the loss of the phenolic group is observed. These results suggest that the interactions involving the phenolic group of Tyr69, O5 of the proximal saccharide, and Glu78 O-epsilon 2 important for the catalytic mechanism of this enzyme, and it is proposed that, through charge redistribution, these interactions serve to stabilize the oxocarbenium-like ion of the transition state. Studies of the covalent glycosyl-enzyme intermediate of this xylanase also provide insight into specificity, as contacts with C5 of the xylose moiety exclude sugars with hydroxymethyl substituents, and the mechanism of catalysis, including aspects of stereoelectronic theory as applied to glycoside hydrolysis.}, keywords = {ACTIVE-SITE RESIDUES, BACILLUS-CIRCULANS XYLANASE, beta-glucosidase, CELLULOMONAS-FIMI, glycosidase, IDENTIFICATION, LEAVING GROUP, MECHANISM, REACTION COORDINATE, TRICHODERMA-REESEI}, isbn = {0006-2960}, url = {://000080165400009}, author = {Sidhu, G. and Withers, S. G. and Nguyen, N. T. and McIntosh, L. P. and Ziser, L. and Brayer, G. D.} } @article {4706, title = {Vanadyl-biguanide complexes as potential synergistic insulin mimics}, journal = {Journal of Inorganic Biochemistry}, volume = {76}, number = {3-4}, year = {1999}, note = {ISI Document Delivery No.: 262ZHTimes Cited: 65Cited Reference Count: 27}, month = {Sep}, pages = {251-257}, type = {Article}, abstract = {Vanadium has well-documented blood-glucose-lowering properties both in vitro and in vivo. The design of new oxovanadium(IV) coordination compounds, intended for use as insulin-enhancing agents in the treatment of diabetes mellitus, can potentially benefit from a synergistic approach, in which the whole complex has more than an additive effect from its component parts. Biguanides, most importantly metformin, are oral hypoglycemic agents used today to treat type 2 diabetes mellitus. In this study, biguanide, metformin, and phenformin, all biguanides, were coordinated to oxovanadium(IV) to form potential insulin-enhancing compounds. Highly colored, air-stable, bis(biguanidato)oxovanadium(IV), [VO(big)(2)], bis(N{\textquoteright},N{\textquoteright}-dimethylbiguanidato)oxovanadium(IV) [VO(metf)(2)], and bis(beta-phenethyl-biguanidato)oxovanadium(IV), [VO(phenf)(2)], were prepared. Solvation with dimethylsulfoxide occurred with VO(metf)(2) to form a six-coordinate complex. Precursor ligands and oxovanadium(IV) coordination complexes were characterized by infrared spectroscopy, mass spectrometry, elemental analyses, magnetic susceptibility, and, where appropriate, H-1 NMR spectroscopy. Biological testing with VO(metf)(2), a representative compound, for insulin-enhancing potential included acute (72 h) administration, both by intraperitoneal (i.p.) injection and by oral gavage (p.o,) in streptozotocin (STZ)-diabetic rats. VO(metf)(2) administration resulted in significant blood-glucose lowering at doses of 0.12 mmol kg(-1) i.p. and 0.60 mmol kg(-1) p.o. (previously established as ED50 doses for organically chelated oxovanadium(IV) complexes); however, no positive associative effects due to the presence of biguanide in the complex were apparent. (C) 1999 Elsevier Science Inc. All rights reserved.}, keywords = {biguanide, BIS(MALTOLATO)OXOVANADIUM(IV), BMOV, coordination complex, GLUCOSE-LOWERING PROPERTIES, insulin mimic, MECHANISM, METFORMIN, MIMETIC AGENT, MUSCLE, RATS, VANADIUM}, isbn = {0162-0134}, url = {://000084097800010}, author = {Woo, L. C. Y. and Yuen, V. G. and Thompson, K. H. and McNeill, J. H. and Orvig, Chris} } @article {4245, title = {Applications of collision dynamics in quadrupole mass spectrometry}, journal = {Journal of the American Society for Mass Spectrometry}, volume = {9}, number = {2}, year = {1998}, note = {ISI Document Delivery No.: YT841Times Cited: 50Cited Reference Count: 44}, month = {Feb}, pages = {101-113}, type = {Article}, abstract = {Some applications of collision dynamics in the field of quadrupole mass spectrometry are presented. Previous data on the collision induced dissociation of ions in triple quadrupole mass spectrometers is reviewed. A new method to calculate the internal energy distribution of activated ions directly from the increase in the cross section for dissociation with center of mass energy is presented. This method, although approximate, demonstrates explicitly the high efficiency of transfer of translational to internal energy of organic ions. It is argued that at eV center of mass energies, collisions between protein ions and neutrals such as Ar are expected to be highly inelastic. The discovery and application of collisional cooling in radio frequency quadrupoles is reviewed. Some previously unpresented data on fragment ion energies in triple quadrupole tandem mass spectrometry are shown that demonstrate directly the loss of kinetic energy of fragment ions in the cooling process. The development of the energy loss method to measure collision cross sections of protein ions in triple quadrupole instruments is reviewed along with a new discussion of the effects of inelastic collisions in these experiments and related ion mobility experiments. (C) 1998 American Society for Mass Spectrometry.}, keywords = {ACTIVATION, BOND-ENERGIES, GAS-PHASE, INDUCED DISSOCIATION, ION FRAGMENTATION, IONS, MECHANISM, MOLECULES, POLYATOMIC, SIZE, TRIPLE QUADRUPOLE}, isbn = {1044-0305}, url = {://000071650400001}, author = {Douglas, D. J.} } @article {4298, title = {Epimerization via carbon-carbon bond cleavage. L-ribulose-5-phosphate 4-epimerase as a masked class II aldolase}, journal = {Biochemistry}, volume = {37}, number = {16}, year = {1998}, note = {ISI Document Delivery No.: ZM208Times Cited: 32Cited Reference Count: 35}, month = {Apr}, pages = {5746-5754}, type = {Article}, abstract = {Studies indicating that the E. coli L-ribulose-5-phosphate 4-epimerase employs an "aldolase-like" mechanism are reported. This NAD(+)-independent enzyme epimerizes a steseocenter that does not bear an acidic proton and therefore it cannot utilize a simple deprotonation-reprotonation mechanism. Sequence similarities between the epimerase and the class II L-fuculose-1-phosphate aldolase suggest that the two may be evolutionarily related and that the epimerization may occur via carbon-carbon bond cleavage and re-formation. Conserved residues thought to provide the metal ion ligands of the epimerase have been modified using site-directed mutagenesis. The resulting mutants show low k(cat) values in addition to a reduced affinity for Zn2+. These observations serve to establish that there is a structural link between between the active site geometry of the epimerase and the aldolase. In addition, the H97N mutant was found to catalyze the condensation of dihydroxyacetone and glycolaldehyde phosphate to produce a mixture of L-ribulose-5-phosphate and D-xylulose-5-phosphate. This observation of aldolase activity establishes that the epimerase active site is capable of promoting carbon-carbon bond cleavage. Furthermore, glycolaldehyde phosphate was shown to be a competitive inhibitor of the mutant enzyme (K-t = 0.37 mM) but not of the wild-type enzyme. The mutation apparently causes the epimerase to become "leaky" and enables it to bind/generate the normal reaction intermediates from the unbound aldol cleavage products.}, keywords = {ENZYMES, ESCHERICHIA-COLI, L-FUCULOSE-1-PHOSPHATE ALDOLASE, MECHANISM, MUTAGENESIS, ORGANIC-SYNTHESIS, PCR, PURIFICATION, SEQUENCE, SITE}, isbn = {0006-2960}, url = {://000073515500048}, author = {Johnson, A. E. and Tanner, M. E.} } @article {4418, title = {Structural, spectroscopic, thermodynamic and kinetic properties of copper(II) complexes with tripodal tetraamines}, journal = {Inorganic Chemistry}, volume = {37}, number = {16}, year = {1998}, note = {ISI Document Delivery No.: 110GETimes Cited: 87Cited Reference Count: 38}, month = {Aug}, pages = {4022-4029}, type = {Article}, abstract = {Spectroscopic, thermodynamic, and kinetic measurements have been made on aqueous solutions of copper(II) complexes of hexamethylated tren and trimethylated tren (one methylation per primary amine group of tren) with the objective of correlating: the influence of geometry (trigonal bipyramidal, evident from UV/vis spectroscopy) and N-alkyl substitution in the ligand on these inherent properties. At 25.0 degrees C the protonation constants of Me(3)tren are not significantly different from those of tren and Me(6)tren, and the stability constant for the Cu(II) complex is of the same order of magnitude as that for the [Cu(tren)(H2O)](2+) complex ion; The pK(a) for deprotonation of the coordinated water molecule of [Cu(Me(3)tren)(H2O)](2+) is intermediate between the values for the complexes containing the unsubstituted and the fully substituted tren ligand. Substitution (pyridine for water) kinetics measurements employing stopped-flow and temperature-jump methods revealed different patterns of reactivity: pyridine replaces water in [Cu(Me(3)tren)(H2O)](2+) with a second-order rate constant of (4.4 +/- 0.8) x 10(2) M-1 s(-1) at 25.0 degrees C, whereas the corresponding process for [Cu(Me(6)tren)(H2O)](2+) is relatively complex and is discussed in more detail. Substitution in the former complex ion is characterized in the forward and reverse directions, by Delta H-double dagger = 60 +/- 8 and 51.9 +/- 0.9 kJ mol(-1), Delta S-double dagger = 5 +/- 27 and -23 +/- 3 J mol(-1) K-1, and Delta V-double dagger = -8.7 +/- 4.6 and -6.2 +/- 1.1 cm(3) mol(-1), respectively, It is concluded that this reaction follows an I-a mechanism, similar to that reported for the comparable reaction of [Cu(tren)(H2O)](2+). An X-ray structural determination on a crystal of [Cu-2(Me(3)tren)(2)(CN)] (ClO4)(3) . 2CH(3)CN demonstrated trigonal bipyramidal geometry about each copper(II) center. As has been found in comparable complexes of tren and Me(6)tren, the axial nitrogen to copper bond is shorter than the equatorial nitrogen-copper bonds, and the angle made by N(axial)-Cu-N(equatorial) is less than 90 degrees (84.6-85.4 degrees), signifying that each copper ion lies below the plane of the equatorial nitrogen atoms.}, keywords = {AQUEOUS-SOLUTION, CRYSTAL-STRUCTURE, ELECTRONIC-PROPERTIES, IMIDAZOLE, ION, MECHANISM, PHENANTHROLINE, PRESSURE-DEPENDENCE, RESONANCE, SUBSTITUTION KINETICS}, isbn = {0020-1669}, url = {://000075371200019}, author = {Thaler, F. and Hubbard, C. D. and Heinemann, F. W. and vanEldik, R. and Schindler, S. and Fabian, I. and Dittler-Klingemann, A. M. and Hahn, F. E. and Orvig, Chris} } @article {4028, title = {Cytochrome c folding kinetics studied by time-resolved electrospray ionization mass spectrometry}, journal = {Biochemistry}, volume = {36}, number = {18}, year = {1997}, note = {ISI Document Delivery No.: WY063Times Cited: 82Cited Reference Count: 46}, month = {May}, pages = {5554-5559}, type = {Article}, abstract = {A new method for studying the folding kinetics of proteins is described. The method combines a continuous flow mixing technique with an electrospray mass spectrometer. Different protein conformations in solution are detected by the different charge states they produce during electrospray ionization. Unfolded proteins generally have more accessible protonation sites and give higher charge states than native proteins. The method is applied to study the refolding of acid-denatured cytochrome c. Global data analysis is used to obtain the exponential lifetimes which are associated with the refolding process. The kinetics can be described by two lifetimes of 0.17 +/- 0.02 and 8.1 +/- 0.9 s which are in accordance with the results of stopped flow experiments previously described in the literature. These lifetimes are associated with roughly 90 and 10\% of the total intensity changes in the mass spectrum, respectively, and most likely reflect fast and slow refolding subpopulations of cytochrome c in solution.}, keywords = {COMPLEX, denaturation, FERRICYTOCHROME-C, IRON BLEOMYCIN, LIGANDS, MECHANISM, PATHWAYS, PROBING CONFORMATIONAL-CHANGES, PROTEINS, SPECTRA}, isbn = {0006-2960}, url = {://A1997WY06300029}, author = {Konermann, L. and Collings, B. A. and Douglas, D. J.} } @article {3933, title = {Mechanistic aspects of the oxidation of phosphines and related substrates by trans-Ru-VI(TMP)(O)(2); TMP equals dianion of 5,10,15,20-tetramesitylporphyrin}, journal = {Journal of Molecular Catalysis a-Chemical}, volume = {117}, number = {1-3}, year = {1997}, note = {ISI Document Delivery No.: WN736Times Cited: 11Cited Reference Count: 34Proceedings of the 6th International Symposium on the Activation of Dioxygen and Homogeneous Catalytic OxidationAPR 14-19, 1996NOORDWIJKERHOUT, NETHERLANDSRoyal Netherlands Chem Soc}, month = {Mar}, pages = {91-102}, type = {Proceedings Paper}, abstract = {The stoichiometric oxidations of some Pt (p-X-C6H4)(3) compounds (X=OMe, Me, H, F, Cl and CF3), AsPh(3) and SbPh(3) by trans-Ru-VI(TMP)(O)(2) (1) in benzene solution generate the corresponding oxides and Ru-II(TMP)(L) species (L=P(p-X-C6H4)(3), AsPh(3), SbPh(3)). Stopped-flow kinetic data are consistent with a mechanism involving formation (within a k(1) step) of Ru-IV(TMP)(O)(OL) which then reversibly dissociates the OL ligand to generate Ru-IV(TMP)(O); this disproportionates to Ru-VI(TMP)(O)(2) and Ru-II(TMP), which forms Ru-II(TMP)(L). Delta H-1 double dagger values for the phosphine systems vary from 18 to 21 kJ mol(-1), increasing with decreasing electron density at the phosphorus, while Delta S-1 double dagger values become more favorable (-94 to -78 J mol(-1) K-1) with increasing molecular mass of the substituent. Preliminary kinetic data on the O-2-oxidations of the substrates catalyzed by (1) under 1 atm of air are presented.}, keywords = {5-COORDINATE, DINITROGEN COMPLEXES, MECHANISM, models, OXYGEN-TRANSFER, phosphine oxidation, PORPHYRIN COMPLEX, REACTIVITY, ruthenium, RUTHENIUM PORPHYRIN}, isbn = {1381-1169}, url = {://A1997WN73600009}, author = {Cheng, S. Y. S. and James, Brian R.} } @article {3918, title = {Unusual ligand-induced reductive elimination in Cp*W(NO)(H)[eta(2)-PPh(2)C(6)H(4)]: A route to the extremely strong pi-donor fragment Cp*W(NO)(PPh(3))}, journal = {Journal of the American Chemical Society}, volume = {119}, number = {5}, year = {1997}, note = {ISI Document Delivery No.: WG232Times Cited: 25Cited Reference Count: 39}, month = {Feb}, pages = {1139-1140}, type = {Article}, keywords = {ACTIVATION, ALKYL, CARBON HYDROGEN-BONDS, COMPLEXES, hydride, ISOCYANIDE, MECHANISM, REACTIVITY, rhenium, TUNGSTEN}, isbn = {0002-7863}, url = {://A1997WG23200042}, author = {Burkey, D. J. and Debad, J. D. and Legzdins,Peter} } @article {3832, title = {Phosphinate inhibitors of the D-glutamic acid-adding enzyme of peptidoglycan biosynthesis}, journal = {Journal of Organic Chemistry}, volume = {61}, number = {5}, year = {1996}, note = {ISI Document Delivery No.: TZ997Times Cited: 66Cited Reference Count: 31}, month = {Mar}, pages = {1756-1760}, type = {Article}, abstract = {We report the synthesis and initial evaluation of the first effective inhibitors of the D-glutamic acid-adding enzyme (UDP-N-acetylmuramoyl-L-alanine:D-glutamate ligase or MurD). This enzyme plays a key role in bacterial peptidoglycan biosynthesis and is therefore a target for antibiotic design. Phosphinic acid 3 is a dipeptide analog linked to uridine diphosphate by a hydrophobic spacer. It is a good inhibitor of the enzyme (IC50 = 0.68 mu M) as it closely resembles the tetrahedral intermediate that is presumed to form in the ligation reaction. Compound 4 lacks the terminal UMP group, and compound 5 lacks both the linker and UDP functionalities. These are less effective inhibitors of the enzyme with IC50 values of 29 mu M and > 1 mM, respectively. Preincubation of the enzyme in the presence of inhibitor 3 and ATP does not result in irreversible inhibition or in the formation of a slowly decomplexing species, suggesting that the phosphinic acid is not phosphorylated in the active site.}, keywords = {(AMINOALKYL)PHOSPHINATE, ATP, D-ALANINE LIGASE, ESCHERICHIA-COLI, INACTIVATION, MECHANISM, PHOSPHINOTHRICIN, PURIFICATION, RAPID-QUENCH, SYNTHETASE}, isbn = {0022-3263}, url = {://A1996TZ99700030}, author = {Tanner, M. E. and Vaganay, S. and vanHeijenoort, J. and Blanot, D.} } @article {3102, title = {ALKYL-FOR-IODIDE METATHESIS INITIATED BY DISSOCIATION OF THE PHOSPHINE LIGAND FROM CPCR(NO)(PPH3)I}, journal = {Journal of the American Chemical Society}, volume = {116}, number = {17}, year = {1994}, note = {ISI Document Delivery No.: PD697Times Cited: 6Cited Reference Count: 20}, month = {Aug}, pages = {7700-7705}, type = {Article}, abstract = {{The alkyl-for-iodide metathesis reaction that occurs when CpCr(NO)(PPh(3))I (1) is treated with 2 equiv of Me(3)SiCH(2)MgCl in THF to form CpCr(NO)(PPh(3))(CH(2)SiMe(3)) (6) has been investigated in some detail. The conversion is initiated by loss of the phosphine ligand from the chromium atom{\textquoteright}s coordination sphere, the most compelling evidence for this step being that addition of excess phosphine (e.g. 4 equiv) to the initial reaction mixture completely inhibits the reaction. Four intermediate complexes which are formed sequentially on the reaction path from 1 to 6 have been detected by IR and ESR spectroscopy. These complexes have been identified as CpCr(NO)(THF)I (2), CpCr-(NO{\textendash}>Mg{CH(2)SiMe(3)})Cl)(THF)I (3), CpCr(NO{\textendash}>Mg{CH(2)SiMe(3)}Cl)(THF)(CH(2)SiMe(3)) (4), and CpCr(NO) (THF)(CH(2)SiMe(3)) (5). Complexes 3 and 4 have also been detected spectroscopically during the reaction of CpCr(NO)(THF)I (2) with Me(3)SiCH(2)MgCl which produces CpCr(NO)(THF)(CH(2)SiMe(3)) (5). This understanding of the mechanistic pathway has resulted in the development of a general synthetic route to previously inaccessible 17-valence-electron CpCr(NO)(L)R complexes (L = C5H11N Or NH(2)CMe(3)}, keywords = {COMPLEXES, MECHANISM, MO, MOLYBDENUM, ORGANOMETALLIC NITROSYL CHEMISTRY, TUNGSTEN}, isbn = {0002-7863}, url = {://A1994PD69700029}, author = {Legzdins,Peter and Shaw, M. J.} } @article {3175, title = {THE SYNTHESIS AND STABILITY OF AZIRIDINO-GLUTAMATE, AN IRREVERSIBLE INHIBITOR OF GLUTAMATE RACEMASE}, journal = {Tetrahedron Letters}, volume = {35}, number = {24}, year = {1994}, note = {ISI Document Delivery No.: NR716Times Cited: 37Cited Reference Count: 17}, month = {Jun}, pages = {4073-4076}, type = {Article}, abstract = {Aziridino-glutamate (2-(2-carboxyethyl)aziridine-2-carboxylic acid, (+/-)4) was synthesized by heating alpha-fluoromethylglutamate in base. In neutral solution, 4 was shown to cyclize to the gamma-lactone 5 with a half life of 4 minutes. Aziridino-glutamate was shown to irreversibly inactivate glutamate racemase by alkylating an active site cysteine residue, Electrospray mass spectrometry was used to establish that a covalent bond had famed and that this bond protects one of the enzyme{\textquoteright}s two cysteine residues from reacting with iodoacetate under denaturing conditions.}, keywords = {ACID, EPIMERASE, ESCHERICHIA-COLI, MECHANISM, PEDIOCOCCUS-PENTOSACEUS}, isbn = {0040-4039}, url = {://A1994NR71600007}, author = {Tanner, M. E. and Miao, S. C.} } @article {2871, title = {SYNTHESES OF 2-DEOXY-2-FLUORO MONOSACCHARIDE AND OLIGOSACCHARIDE GLYCOSIDES FROM GLYCALS AND EVALUATION AS GLYCOSIDASE INHIBITORS}, journal = {Carbohydrate Research}, volume = {249}, number = {1}, year = {1993}, note = {ISI Document Delivery No.: MD387Times Cited: 41Cited Reference Count: 34}, month = {Oct}, pages = {77-90}, type = {Article}, abstract = {Several fluorinated oligosaccharides, including 2-deoxy-2-fluoro derivatives of cellobiose, maltose, and maltotriose were synthesized by the action of fluorine or acetyl hypofluorite on the corresponding glycal peracetates. Temperature effects on the stereoselectivities of these reactions were examined. Addition of acetyl hypofluorite to several 2-substituted glycals in the gluco or galacto series gave 2,2-disubstituted arabino- or lyxo-hexose derivatives; 3,4,6-tri-O-acetyl-2-fluoro-D-glucal or the analogous galactal yielded 2-deoxy-2,2-difluoro arabino- or lyxo-hexose peracetates, whereas 2-acetoxy-3,4,6-tri-O-acetyl-D-glucal or the analogous galactal gave 2(R)-2-acetoxy-2-fluoro-arabino- or lyxo-hexose peracetates, respectively. 2-Acetamido-3,4,6-tri-O-acetyl-D-glucal gave 2(R)-2-acetamido-2-acetoxy-3,4,6-tri-O-acetyl-alpha-D-arabino-hexopyrano syl fluoride. 2,4-Dinitrophenyl 2-deoxy-2-fluoro-beta-cellobioside was an inactivator of the exoglucanase from Cellulomonas fimi while 2-deoxy-2-fluoro-alpha-maltosyl and alpha-maltotriosyl fluorides were slow substrates of human pancreatic alpha-amylase and rabbit muscle glycogen debranching enzyme, respectively.}, keywords = {ACETYL HYPOFLUORITE, beta-glucosidase, CATALYTIC FLEXIBILITY, DERIVATIVES, ENZYME, GLYCOSYLASES, hydration, INTERMEDIATE, MECHANISM}, isbn = {0008-6215}, url = {://A1993MD38700007}, author = {McCarter, J. D. and Adam,Michael J. and Braun, C. and Namchuk, M. and Tull, D. and Withers, S. G.} } @article {7233, title = {SYNTHESIS AND REACTIVITY OF THE IRIDIUM VINYLIDENE IR=C=CH2[N(SIME2CH2PPH2)2] - FORMATION OF CARBON-CARBON BONDS VIA MIGRATORY INSERTION OF A VINYLIDENE UNIT}, journal = {Organometallics}, volume = {11}, number = {9}, year = {1992}, note = {ISI Document Delivery No.: JN066Times Cited: 75Cited Reference Count: 42}, month = {Sep}, pages = {2979-2990}, type = {Article}, abstract = {{The synthesis of the 16-electron iridium vinylidene complex Ir=C=CH2[N(SiMe2CH2PPh2)2] is described by starting from the cyclooctene derivative Ir(eta-2-C8H14)[N(SiMe2CH2PPh2)2] with addition of acetylene. This vinylidene complex reacts with a variety of electrophiles; thus, reaction with AlR3 (R = Me, Et) or GaMe3 leads to the formation of the new derivatives Ir(ER2)CR=CH2[N(SiMe2CH2PPh2)2] (E = Al}, keywords = {ACETYLIDE COMPLEXES, ALKYNE, CARBENE, COMPLEX, FISCHER-TROPSCH REACTION, LIGAND, MECHANISM, PHOTOINDUCED RING EXPANSION, REARRANGEMENT, SATURATED CARBON, TRANSITION-METAL}, isbn = {0276-7333}, url = {://A1992JN06600009}, author = {Fryzuk,Michael D. and Huang, L. and McManus, N. T. and Paglia, P. and Rettig, S. J. and White, G. S.} } @article {7272, title = {SYNTHESIS, CHARACTERIZATION AND REACTIVITY OF SOME MONONUCLEAR AND DINUCLEAR CHLORORUTHENIUM COMPLEXES CONTAINING CHELATING DITERTIARY PHOSPHINES (P-P) WITH P-PRU = 1}, journal = {Inorganica Chimica Acta}, volume = {198}, year = {1992}, note = {ISI Document Delivery No.: JK243Times Cited: 72Cited Reference Count: 92}, month = {Aug-Oct}, pages = {283-296}, type = {Article}, abstract = {{Mixed-valence complexes of the type (P-P)ClRu(mu-Cl)3RuCl(P-P), and the [RuCl(P-P)]2(mu-Cl)2 products formed by their reduction with H2, are synthesized, where P-P is a chelating ditertiary phosphine Ph2P(CH2)nPPh2 (n = 3-6) or some related chiral analogues such as diop, chiraphos, dppcp, dpcycp, bdpp, binap, phenop or norphos (diop = Ph2PCH2CHOCMe2OCHCH2PPh2; chiraphos = Ph2PCH(Me)CH(Me)PPh2; dppcp = Ph2PCH(CH2)3CHPPh2; dpcycp = (C6H11)2PCH(CH2)3CHP(C6H11)2; bdpp(skewphos) = Ph2PCH(Me)CH2CH(Me)PPh2; binap = 2,2{\textquoteright}-bis(diphenylphosphine)-1,1{\textquoteright}-binaphthyl; phenop = Ph2PN(Et)CH(CH2Ph)CH2OPPh2; norphos = Ph2PCHCHCH=CHCH(CH2)CHPPh2). The [RuCl(binap)]2(mu-Cl)2 species is also formed in solution by dissociation of PPh3 from RuCl2(binap)(PPh3) which is synthesized by phosphine exchange with RuCl2(PPh3)3. From the [RuCl(P-P)]2(mu-Cl)2 complex (P-P = Ph2P(CH2)4PPh2), a range of L(P-P)Ru(mu-Cl)3RuCl(P-P) species is readily formed, where L includes an amine, acetone, NN-dimethylacetamide, Mel, PhCN, CO, N2 or H2; the L = NEt3 adduct is made also from RUCl2(dppb)(PPh3), while the corresponding dimethyl sulfoxide adduct (L = DMSO), 17e, is synthesized directly from cis-RuCl2(DMSO)4 and the phosphine. P-31{H-1} NMR data are presented for the Ru(II) species, while characterization of 17e includes an X-ray_crystallographic analysis that confirms the trichloro-bridged formulation. Crystal data are as follows: triclinic, P1BAR}, keywords = {1{\textquoteright}-BINAPHTHYL, 2, 2{\textquoteright}-BIS(DIPHENYLPHOSPHINO)-1, ASYMMETRIC HYDROGENATION, BINAP-RUTHENIUM(II) COMPLEXES, CATALYSTS, COMPLEXES, CRYSTAL-STRUCTURE, DICARBOXYLATE, MECHANISM, ROUTE, RUTHENIUM(II) COMPLEXES, UNSATURATED CARBOXYLIC-ACIDS}, isbn = {0020-1693}, url = {://A1992JK24300031}, author = {Joshi, A. M. and Thorburn, I. S. and Rettig, S. J. and James, Brian R.} } @article {7320, title = {SYNTHESIS OF 2-DEOXY-2-[F-18]-FLUORO-BETA-MANNOSYL [F-18] FLUORIDE AS A POTENTIAL IMAGING PROBE FOR GLYCOSIDASES}, journal = {Journal of Labelled Compounds \& Radiopharmaceuticals}, volume = {31}, number = {12}, year = {1992}, note = {ISI Document Delivery No.: KA889Times Cited: 6Cited Reference Count: 10}, month = {Dec}, pages = {1005-1009}, type = {Article}, abstract = {The mechanism-based glycosidase inhibitor 2-deoxy-2-[F-18]-fluoro-beta-mannosyl [F-18]-fluoride was synthesized and its covalent binding to Agrobacterium beta-glucosidase was demonstrated in vitro.}, keywords = {BETA-GLYCOSIDASE, F-18, glycosyl fluoride, MECHANISM}, isbn = {0362-4803}, url = {://A1992KA88900006}, author = {McCarter, J. D. and Adam,Michael J. and Withers, S. G.} } @article {7038, title = {HYDRIDO THIOLATO AND THIOLATO COMPLEXES OF RUTHENIUM(II) CARBONYL PHOSPHINES}, journal = {Inorganic Chemistry}, volume = {30}, number = {24}, year = {1991}, note = {ISI Document Delivery No.: GR813Times Cited: 52Cited Reference Count: 76}, month = {Nov}, pages = {4617-4627}, type = {Article}, abstract = {{Oxidative addition of RSH (R = H, alkyl, aryl) or RSSR (R = aryl) to Ru(CO)2L3 (L = PPh3, 1) yields respectively cct-RuH(SR)(CO)2L2 (type 2) (cct = cis,cis,trans) or cct-Ru(SR)2(CO)2L2 (type 3); a hydrido selenolate species is made similarly using PhSeH. Methods for in situ formation of corresponding mixed bis(thiolate) species are also given. 1 is generally unreactive toward thioethers, although with propylene sulfide cct-Ru(eta-2-S2) (CO)2L2 is produced. Metathesis reactions of cct-RuCl2(CO)2L2 with NaSR salts yield 3 (R = aryl) or, when R = Et, cct-RuCl(SEt)(CO)2L2 or [L(CO)2Ru(mu-2-SEt)2(mu-3-SEt)Na(THF)]2 (4), depending on reaction conditions. The complexes are characterized by IR spectroscopy, H-1, P-31, and, in some cases, C-13 NMR spectroscopy, and for 2g and 3g (R = SC6H4pMe) and 4, X-ray crystallography. All three complexes crystallized in the space group P1BAR. For 2g}, keywords = {CHEMISTRY, DERIVATIVES, MECHANISM, METHYLDISULFIDO-LIGAND, MOLECULAR-STRUCTURE, NUCLEAR MAGNETIC-RESONANCE, OSMIUM, REACTIVITY, TRANSITION-METALS, X-RAY CRYSTAL}, isbn = {0020-1669}, url = {://A1991GR81300031}, author = {Jessop, P. G. and Rettig, S. J. and Lee, C. L. and James, Brian R.} } @article {7005, title = {ORGANOMETALLIC NITROSYL CHEMISTRY .43. SYNTHESIS AND CHARACTERIZATION OF CHIRAL MOLYBDENUM AND TUNGSTEN NEUTRAL COMPLEXES CONTAINING ETA-2-BENZYL LIGANDS}, journal = {Organometallics}, volume = {10}, number = {8}, year = {1991}, note = {ISI Document Delivery No.: GA275Times Cited: 44Cited Reference Count: 48}, month = {Aug}, pages = {2857-2870}, type = {Article}, abstract = {{Reaction of Cp{\textquoteright}M(NO)Cl2 (Cp{\textquoteright} = Cp (eta-5-C5H5) or Cp* (eta-5-C5Me5); M = Mo or W) with 2 equiv of p-XylMgCl (p-Xyl = p-MeC6H4CH2) affords the corresponding bis(p-xylyl) complexes in good yields. Subsequent treatment of the Cp{\textquoteright}M(NO)(CH2Ar)2 compounds (CH2Ar = CH2Ph or p-Xyl) with HCl produces the new isolable Cp{\textquoteright}M(NO)(CH2Ar)Cl species. These, in turn, undergo metathesis reactions with RMgCl or R2Mg(dioxane)2 reagents and convert to Cp{\textquoteright}M(NO)(CH2Ar)R (R = CH2SiMe3, CH2CMe3 (Npt), or C6H4CH3 (p-Tol)). All new complexes isolated during this work have been fully characterized by conventional spectroscopic methods. Single-crystal X-ray crystallographic analyses have been performed on two prototypal complexes, namely Cp*Mo(NO)(CH2Ph)Cl and Cp*Mo(NO)(CH2Ph)(CH2SiMe3). Crystal data for Cp*Mo(NO)(CH2Ph)Cl: a = 9.3451 (16) angstrom}, keywords = {allyl, BARRIERS, BENZYL COMPLEXES, COMPLEXES, CRYSTAL-STRUCTURE, DYNAMICS, ETA-5-C5H5, ISOMERS, MECHANISM, MOLECULAR-STRUCTURE, OXIDE}, isbn = {0276-7333}, url = {://A1991GA27500061}, author = {Dryden, N. H. and Legzdins,Peter and Trotter, J. and Yee, V. C.} } @article {7005, title = {ORGANOMETALLIC NITROSYL CHEMISTRY .43. SYNTHESIS AND CHARACTERIZATION OF CHIRAL MOLYBDENUM AND TUNGSTEN NEUTRAL COMPLEXES CONTAINING ETA-2-BENZYL LIGANDS}, journal = {Organometallics}, volume = {10}, number = {8}, year = {1991}, note = {ISI Document Delivery No.: GA275Times Cited: 44Cited Reference Count: 48}, month = {Aug}, pages = {2857-2870}, type = {Article}, abstract = {{Reaction of Cp{\textquoteright}M(NO)Cl2 (Cp{\textquoteright} = Cp (eta-5-C5H5) or Cp* (eta-5-C5Me5); M = Mo or W) with 2 equiv of p-XylMgCl (p-Xyl = p-MeC6H4CH2) affords the corresponding bis(p-xylyl) complexes in good yields. Subsequent treatment of the Cp{\textquoteright}M(NO)(CH2Ar)2 compounds (CH2Ar = CH2Ph or p-Xyl) with HCl produces the new isolable Cp{\textquoteright}M(NO)(CH2Ar)Cl species. These, in turn, undergo metathesis reactions with RMgCl or R2Mg(dioxane)2 reagents and convert to Cp{\textquoteright}M(NO)(CH2Ar)R (R = CH2SiMe3, CH2CMe3 (Npt), or C6H4CH3 (p-Tol)). All new complexes isolated during this work have been fully characterized by conventional spectroscopic methods. Single-crystal X-ray crystallographic analyses have been performed on two prototypal complexes, namely Cp*Mo(NO)(CH2Ph)Cl and Cp*Mo(NO)(CH2Ph)(CH2SiMe3). Crystal data for Cp*Mo(NO)(CH2Ph)Cl: a = 9.3451 (16) angstrom}, keywords = {allyl, BARRIERS, BENZYL COMPLEXES, COMPLEXES, CRYSTAL-STRUCTURE, DYNAMICS, ETA-5-C5H5, ISOMERS, MECHANISM, MOLECULAR-STRUCTURE, OXIDE}, isbn = {0276-7333}, url = {://A1991GA27500061}, author = {Dryden, N. H. and Legzdins,Peter and Trotter, J. and Yee, V. C.} } @article {6996, title = {VERATRYL ALCOHOL AS A MEDIATOR IN LIGNIN MODEL-COMPOUND BIODEGRADATION}, journal = {Holzforschung}, volume = {45}, number = {1}, year = {1991}, note = {ISI Document Delivery No.: FC210Times Cited: 7Cited Reference Count: 22}, month = {Feb}, pages = {31-35}, type = {Article}, abstract = {Veratryl alcohol and 1,4-dimethoxybenzene were found to be ineffective mediators for the oxidation of anisyl alcohol by the lignin peroxidase model, iron meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrin chloride (TDCSPPFeCl). However, veratryl alcohol can mediate the electrochemical oxidation of the polymeric dye Poly B-411. The TDCSPPFeCl catalyzed reactions of lignin model compounds were found to be dependent on pH and the solvent being used. The importance of the mediating role of veratryl alcohol in lignin degradation is discussed.}, keywords = {APPROACH, BASIDIOMYCETE PHANEROCHAETE-CHRYSOSPORIUM, BIOMIMETIC, BURDS, C BOND-CLEAVAGE, DEGRADATION, ENZYME, IRON PORPHYRINS, LIGNIN, MECHANISM, MEDIATOR, OXIDATION, PEROXIDASE, PORPHYRIN, SYSTEM, VERATRYL ALCOHOL}, isbn = {0018-3830}, url = {://A1991FC21000006}, author = {Cui, F. T. and Dolphin, D.} }