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Two-dimensional (2D) pulsed electron paramagnetic resonance study of VO2+-triphosphate interactions: Evidence for tridentate triphosphate coordination, and relevance to bone uptake and insulin enhancement by vanadium pharmaceuticals

TitleTwo-dimensional (2D) pulsed electron paramagnetic resonance study of VO2+-triphosphate interactions: Evidence for tridentate triphosphate coordination, and relevance to bone uptake and insulin enhancement by vanadium pharmaceuticals
Publication TypeJournal Article
Year of Publication2002
AuthorsDikanov, SA, Liboiron, BD, Orvig, C
JournalJournal of the American Chemical Society
Volume124
Pagination2969-2978
Date PublishedMar
Type of ArticleArticle
ISBN Number0002-7863
KeywordsAQUEOUS-SOLUTION, DIABETES-MELLITUS, DISORDERED-SYSTEMS, ECHO ENVELOPE MODULATION, HYSCORE SPECTROSCOPY, {2-DIMENSIONAL ESEEM
Abstract

Two- and four-pulse electron spin echo envelope modulation (ESEEM) and four-pulse two-dimensional hyperfine sublevel correlation (HYSCORE) spectroscopies have been used to determine the solution structure of a 3:1 triphosphate:vanadyl solution at pH 5.0. Limited quantitative data were extracted from the two pulse spectra; however, HYSCORE proved to be more useful in the detection and interpretation of the P-31 and H-1 couplings. Three sets of cross-peaks were observed for each nucleus. For the P-31 couplings, three sets of cross-peaks were observed in the HYSCORE spectrum, and contour line shape analysis yielded coupling constants of approximately 15, 9, and 1 MHz. HYSCORE cross-peaks in the proton region were partially overlapping; however, interpretation of the proton coupling was simplified through the use of one-dimensional four-pulse ESEEM and subsequent analysis of the sum combination peaks. Comparison of the derived isotropic and anisotropic coupling constants with results from earlier ESEEM and electron nuclear double resonance (ENDOR) studies was consistent with the presence of at least one, and most likely two, water molecules coordinated in the equatorial plane of the vanadyl cation. The vanadyl-triphosphate system was shown to be an accurate model of the in vivo vanadyl-phosphate coupling constants determined in an earlier study (Dikanov, S. A.; Liboiron, B. D.; Thompson, K. H.; Vera, E.; Yuen, V. G.; McNeill, J. H.; Orvig, C. J. Am. Chem. Soc. 1999, 121,11004.) Comparison of these values to those found in previous spectroscopic studies of vanadyl-triphosphate interactions, along with a detailed structural interpretation, are presented, This work represents the first detection of tridentate polyphosphate coordination to the vanadyl ion, and the first observation of an axial phosphate interaction not previously reported in earlier ENDOR and pulsed electron paramagnetic resonance studies.

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