Biomedical subjects

Qing-Sen Yu

Publications and source records attributed to Qing-Sen Yu.

5 recordsLinked to original sources

PubMed2006

QSPR/QSAR models for prediction of the physicochemical properties and biological activity of polybrominated diphenyl ethers.

Polybrominated diphenyl ethers (PBDEs) are a group of important persistent organic pollutants. In the present study, geometrical optimization and electrostatic potential calculations have been performed for all 209 PBDE congeners at the HF/6-31G level of theory. A number of statistically-based parameters have been obtained. Linear relationships between gas-chromatographic relative retention time (RRT), n-octanol/air partition coefficient (lgK(OA)), 298 K supercooled liquid vapour pressures (lgp(L)), Henry's law constant (lgH) and Ah receptor binding affinity (-lgRBA) of PBDEs and the structural descriptors have been established by multiple regression method. The result shows that the quantities derived from electrostatic potential V(s,max),V(s,min),Pi, Sigma V+(S), V-(S) , nu, sigma 2(tot), and N-(v), together with the molecular volume (Vmc) can be well used to express the quantitative structure-property relationships of PBDEs, which proves the general applicability of this parameter set to a great extent. Good predictive capabilities have also been demonstrated. Based on these equations, the predicted values have been presented for those PBDE congeners whose experimentally determined physicochemical properties are unavailable. The QSAR model for the Ah receptor binding affinity is relatively poor, which can be ascribed to the complexity of factors which affect biological activity and the limitations of the present parameter set in describing steric characters of the molecule.

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PubMed2006

Proton exchanges between phenols and ammonia or amines: a computational study.

Density functional theory calculations at the B3LYP/6-31+G(d,p) level of theory have been performed to explore proton exchanges between phenols and ammonia or amines, which can be used to account for previous NMR experiments. For the parent phenol-NH(3) system, a transition state with a symmetric phenolate-NH(4)(+)-like structure, which lies about 35 kcal mol(-1) in energy above the hydrogen-bonded complex, has been successfully located. An intrinsic reaction coordinate (IRC) analysis indicates that the proton exchange is a concerted process, which can be roughly divided into four continuous subprocesses. A series of para-substituted phenol-NH(3) systems have been considered to investigate the substituent effect. Whereas introduction of an electron-withdrawing group on the phenol appreciably reduces the barrier, an opposite effect is observed for an electron-donating group. Moreover, it has been disclosed that there exists a good linear correlation between the activation barriers and the interaction energies between the phenols and NH(3), indicating the important role of proton transfer (or hydrogen bonding) in determining the proton exchange. Also considered are the proton exchanges between phenol and amines and those for some sterically hindered systems. The results show that the phenol tends to exchange hydrogen with the amines, preferably the secondary amines, and that the steric effect is favorable for the proton exchange, which imply that, as the IRC analysis suggested, besides the proton transfer, the flip of the ammonium-like moiety may play a significant role in the course of proton exchange. For all of these systems, we investigated the solvent effects and found that the barrier heights of proton exchange decrease remarkably as compared to those in a vacuum due to the ion pair feature of the transition state. Finally, we explored the phenol radical cation-NH(3) system; the barrierless proton transfer and remarkably low barrier (5.2 kcal mol(-1)) of proton exchange provide further evidence for the importance of proton transfer in the proton exchange.

Amines↗

PubMed2006

Electrochemical characteristics of gatifloxacin and its interaction with DNA.

The electrochemical behavior of gatifloxacin (GTFX) and its interaction with natural calf thymus DNA (ctDNA) is investigated by differential pulse voltammetry (DPV) on a carbon paraffined electrode. According to the suggested electrochemical equation, a binding constant of 1.7058 x 10(5) (mol L(-1))(-1) and binding sizes s = 3.09 (base pairs) of GTFX with ctDNA are obtained by nonlinear fit analysis of electrochemical data. The results demonstrate that GTFX has the properties of an intercalative binder.

Animals↗

PubMed2005

Ab initio study of the complexes of halogen-containing molecules RX (X=Cl, Br, and I) and NH3: towards understanding the nature of halogen bonding and the electron-accepting propensities of covalently bonded halogen atoms.

Ab initio calculations have been performed on a series of complexes formed between halogen-containing molecules and ammonia to gain a deeper insight into the nature of halogen bonding. It appears that the dihalogen molecules form the strongest halogen-bonded complexes with ammonia, followed by HOX; the charge-transfer-type contribution has been demonstrated to dominate the halogen bonding in these complexes. For the complexes involving carbon-bound halogen molecules, our calculations clearly indicate that electrostatic interactions are mainly responsible for their binding energies. Whereas the halogen-bond strength is significantly enhanced by progressive fluorine substitution, the substitution of a hydrogen atom by a methyl group in the CH(3)X...NH(3) complex weakened the halogen bonding. Moreover, remote substituent effects have also been noted in the complexes of halobenzenes with different para substituents. The influence of the hybridization state of the carbon atom bonded to the halogen atom has also been examined and the results reveal that halogen-bond strengths decrease in the order HC triple bond CX > H(2)C=CHX approximately O=CHX approximately C(6)H(5)X > CH(3)X. In addition, several excellent linear correlations have been established between the interaction energies and both the amount of charge transfer and the electrostatic potentials corresponding to an electron density of 0.002 au along the R-X axis; these correlations provide good models with which to evaluate the electron-accepting abilities of the covalently bonded halogen atoms. Finally, some positively charged halogen-bonded systems have been investigated and the effect of the charge has been discussed.

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PubMed2004

Binding interaction of gatifloxacin with bovine serum albumin.

The binding of gatifloxacin to bovine serum albumin (BSA) in aqueous solution was studied using fluorescence spectroscopy and absorbance spectra, Further, the interactions influenced by Fe3+ and Cu2+ were also explored in this work. Based on Scatchard's site-binding model and florescence quenching, practical formulas for small molecule ligands to bio-macromolecules have been proposed. The binding parameters were measured according to suggested models, and the binding distance and the transfer efficiency of energy between gatifloxacin and BSA were also obtained in view of the Förster theory of non-radiation energy transfer. The effect of gatifloxacin on the conformation of BSA has also been analyzed using synchronous fluorescence spectroscopy.

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