@article {YANG2020120885,
	title = {Characterization of interaction between Bcl-2 oncogene promoter I-Motif DNA and flavonoids using electrospray ionization mass spectrometry and pressure-assisted capillary electrophoresis frontal analysis},
	journal = {Talanta},
	year = {2020},
	pages = {120885},
	abstract = {B-cell lymphoma 2 (Bcl-2) is an antiapoptotic protein which is believed to be a triggering factor in developing human tumors. The Bcl-2 C-rich promoter element has been shown to form the i-motif (IM) via cytosine-cytosine (C{\textendash}C+) base pair building blocks, which can be targeted through the binding of ligands associated with Bcl-2 expression modulation. In this work, we monitored IM development and thermodynamic stability within the Bcl-2 promoter via circular dichroism (CD) spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The results demonstrated that at an acidic pH, as well as in a crowded molecular environment, the Bcl-2 promoter element predominantly exists in a stable intramolecular IM folded state. We further explored the potential of targeting of the Bcl-2 IM to increase chemotherapeutic efficacy. We first used a rapid ESI-MS screening assay to identify possible ligands, finding that three natural flavonoids (P1, P5 and P6) exhibited a clear affinity for IM binding at 1:1 stoichiometry. Relative to P6, P1 and P5 were expected to form the more stable complexes with the Bcl-2 IM in gas phase according to MS/MS data. We further used ESI-MS and pressure-assisted capillary electrophoresis frontal analysis (PACE-FA) to assess the binding constants for these flavonoids in gas and liquid phases, respectively, with the latter considering both specific and non-specific binding. We found P5 and P6 to specifically bind the Bcl-2 IM with binding constants of \~{}104 M-1. P1 binding was confirmed to be due to both specific and nonspecific interactions, and the specific binding constant (8.67 {\texttimes} 103 M-1) was found much less significant than the binding constant in gas phase. Taken all these observations into consideration, the specific binding of selected flavonoids to the Bcl-2 IM may prove to be a potential ligand for modulating Bcl-2 gene expression.},
	keywords = {Bcl-2 oncogene, circular dichroism, Electrospray ionization mass spectrometry, Flavonoids, I-motif, Pressure-assisted capillary electrophoresis frontal analysis},
	issn = {0039-9140},
	doi = {https://doi.org/10.1016/j.talanta.2020.120885},
	url = {http://www.sciencedirect.com/science/article/pii/S0039914020301764},
	author = {Yang Yang and Hengqing Fu and Cheng Qian and Huihui Li and David D.Y. Chen}
}
@article {YANG2019,
	title = {Evaluation of the Binding of Natural Products with Thrombin Binding Aptamer G-Quadruplex Using Electrospray Ionization Mass Spectrometry and Spectroscopic Methods},
	journal = {Talanta},
	volume = {200},
	year = {2019},
	month = {08/2019},
	pages = {424-431},
	abstract = {<p>A 15-mer thrombin-binding aptamer (TBA) was discovered with specificity for thrombin. It forms a unique G-quadruplex (G4), which is postulated to be the molecular basis for its binding specificity. Many analytical methods make use of affinity binding between the thrombin and TBA as they form a very stable complex. We develope a strategy to stabilize TBA/G4\&$\#$39;s structure by introducing G4-interactive molecules, which may enhance its ability to recognize the target. Herein, a fast screening ESI-MS assay was employed to determine potential binding of natural products molecules with the TBA/G4 complex. The experimental results showed that four investigated natural alkaloids had apparent binding affinities. One of them, jatrorrhizine (L1), has been shown to bind strongly to the TBA/G4 mainly in 1:2 M ratio. Once the working conditions were established, the interaction of the jatrorrhizine with the TBA/G4 was explored using a combination of ESI-MS and spectroscopic techniques. Ligand-induced effects on TBA/G4 structure and its stability were examined by means of circular dichroism (CD). Jatrorrhizine inducing the G4 formation seems also to be the more effective in terms of thermal stabilization under the experimental conditions used. Both results of UV and fluorescence experiments undoubtedly showed a good binding affinity with the binding constant around 105L\&bull;mol\&minus;1. The stacking interactions of jatrorrhizine with the G-tetrads in TBA/G4 were further confirmed by competition experiment. ESI-MS was carried out to determine the coexistence of 1:1 and 1:2 complexes in TBA/G4-L1 system, and showed a dynamical shift from 1:1 to 1:2 complex in minutes.</p>},
	keywords = {Electrospray ionization mass spectrometry, fluorescence spectroscopy, jatrorrhizine, noncovalent interaction, Thrombin binding aptamer},
	issn = {0039-9140},
	doi = {https://doi.org/10.1016/j.talanta.2019.03.080},
	url = {http://www.sciencedirect.com/science/article/pii/S0039914019303376},
	author = {Pengfei Yang and Xinyi Wang and Zhenggui Gu and Huihui Li and David D.Y. Chen and Xiaodi Yang}
}
@article {FU2019,
	title = {Mass spectrometry and affinity capillary electrophoresis for characterization of host-guest interactions},
	journal = {Journal of Chromatography A},
	volume = {1589},
	year = {2019},
	month = {03/2019},
	pages = {182-190},
	abstract = {<p>Affinity capillary electrophoresis (ACE) in a free solution must be used to confirm the molecular interaction observed in electrospray ionization mass spectrometry (ESI-MS) for affinity binding analysis in the drug discovery process. In this article, the affinity of ibuprofen with three cyclodextrin species of different cavity sizes is investigated by both ESI-MS and ACE methods. Because the binding interactions are measured in different environments using ESI-MS (gas phase) and ACE (liquid phase), the experimental results show significant differences. To better illustrate the major factors influencing the binding constants in different environments, two types of simulations (molecular docking and molecular force field evaluation) are employed in the theoretical discussion. The molecular docking results were consistent with the ESI-MS experimental phenomena. Due to lack of the water molecules in the gas phase, a substantial difference in molecular interaction can contribute to a different binding affinity. By using the molecular modeling based on the force field evaluation with considering solvent molecules, β-CD is expected to form the most stable complex with ibuprofen in the liquid phase and the binding affinity of ibuprofen to γ-CD is much less significant than it is in gas phase. This prediction is in good agreement with the ACE results. Therefore, this work demonstrates that, by using ESI-MS in the first-step screening and ACE in the follow-up determination, a more accurate understanding can be achieved.</p>},
	keywords = {affinity capillary electrophoresis, Electrospray ionization mass spectrometry, Host-guest interaction, molecular modeling},
	issn = {0021-9673},
	doi = {https://doi.org/10.1016/j.chroma.2019.01.020},
	url = {http://www.sciencedirect.com/science/article/pii/S0021967319300202},
	author = {Hengqing Fu and Cheng Qian and Wenjun Tong and Huihui Li and David D.Y. Chen}
}
