Binding interaction of harpagoside and bovine serum albumin: spectroscopic methodologies and molecular docking / 中国中药杂志

Scrophularia ningpoensis has exhibited a variety of biological activities and been used as a pharmaceutical product for the treatment of inflammatory ailment, rheumatoid arthritis, osteoarthritis and so on. Harpagoside (HAR) is considerer as a main bioactive compound in this plant. Serum albumin has important physiological roles in transportation, distribution and metabolism of many endogenous and exogenous substances in body. It is of great significance to study the interaction mechanism between HAR and bovine serum albumin (BSA). The mechanism of interaction between HAR and BSA was investigated using 2D and 3D fluorescence, synchronous florescence, ultraviolet spectroscopy and molecular docking. According to the analysis of fluorescence spectra, HAR could strongly quench the fluorescence of BSA, and the static quenching process indicated that the decrease in the quenching constant was observed with the increase in temperature. The magnitude of binding constants (KA) was more than 1×10⁵ L·mol⁻¹, and the number of binding sites(n) was approximate to 1. The thermodynamic parameters were calculated through analysis of fluorescence data with Stern-Volmer and Van't Hoff equation. The calculated enthalpy change (ΔH) and entropy change (ΔS) implied that the main interaction forces of HAR with BSA were the bonding interaction between van der Waals forces and hydrogen. The negative values of energy (ΔG) demonstrated that the binding of HAR with BSA was a spontaneous and exothermic process. The binding distance(r) between HAR and BSA was calculated to be about 2.80 nm based on the theory of Frster's non-radiation energy transfer, which indicated that energy is likely to be transfer from BSA to HAR. Both synchronous and 3D florescence spectroscopy clearly revealed that the microenvironment and conformation of BSA changed during the binding interaction between HAR and BSA. The molecular docking analysis revealed HAR is more inclined to BSA and human serum albumin (HSA) in subdomain ⅡA (Sudlow's site I). This study will provide valuable information for understanding the action mechanism of HAR.

Multi-spectroscopic characterization of bovine serum albumin upon interaction with atomoxetine / 药物分析学报

The quenching interaction of atomoxetine (ATX) with bovine serum albumin (BSA) was studied in vitro under optimal physiological condition (pH=7.4) by multi-spectroscopic techniques. The mechanism of ATX-BSA system was a dynamic quenching process and was confirmed by the fluorescence spectra and lifetime measurements. The number of binding sites, binding constants and other binding characteristics were computed. Thermodynamic parameters ΔH0 and ΔS0 indicated that intermolecular hydrophobic forces predominantly stabilized the drug-protein system. The average binding distance between BSA and ATX was studied by F?rsters theory. UV-absorption, Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD), synchronous spectra and three-dimensional (3D) fluorescence spectral results revealed the changes in micro-environment of secondary structure of protein upon the interaction with ATX. Displacement of site probes and the effects of some common metal ions on the binding of ATX with BSA interaction were also studied.

Fluorescence Excitation-Emission Matrix Spectra Coupled with Physic and Mathematic Isolation to Study Composition of Dissolved Organic Matter / 分析化学

Combunung wuth fluorescence excutatuon-emussuon matrux ( EEM ) spectra and parallel factor analysus, suze exclusuon chromatography ( SEC ) equupped wuth multu-excutatuon/emussuon scan model fluorescence detector was used for the analysus of the composutuon of dussolved organuc matter ( DOM) usolated from landfull leachates wuth dufferent ages. The analytucal results showed that the two leachate-deruved DOMs both comprused proteun- and humuc-luke substances. However, there were four kunds of proteun-luke matter un young landfull leachates, u. e. , proteun wuth hugh molecular weught, proteun-luke matter bound to humuc-luke substances wuth hugh or low molecular weught, and peptude/amuno acuds. Whule there were only two kunds of proteun-luke matter un old landfull leachates, u. e. , proteun wuth hugh molecular weught and proteun-luke matter bound to humuc-luke substances wuth hugh molecule weught. Compared wuth SEC, EEM spectra coupled wuth parallel factor analysus could udentufy the proteun-luke matter bound wuth humuc-luke substances or those presented as non-humuc-luke substances, though ut could not udentufy the proteun-luke matter presented as proteun and that presented as peptude/ amuno acuds. The experumental results demonstrated that EEM spectra coupled wuth PARAFAC analysus and SEC could be used to characteruze proteun- and humuc-luke matter presented as dufferent specues.

Characterization and Investigation of Reduction Capacity of Hydrophilic Organic Matter from Compost and its Influence Factors / 分析化学

Reduction capacity ( RC ) is an important index to evaluate the redox ability of dissolved organic matter. In order to determine the RC, hydrophilic organic fractions ( HyI ) isolated from dissolved organic matter extracted from the uncomposted and composted samples were used as electron donators and mediators, and three kinds of irons were chosen as electron acceptors. The results showed that, the RC values from the composted sample were 15. 88, 13. 41 and 51. 45 mmol e -/mol C for the electron acceptors Fe2(SO4)3, Fe(NO3)3 and FeCit, respectively, which were higher than the corresponding values (13. 45, 11. 77 and 43. 16 mmol e-/mol C) from the uncomposted sample. The electron acceptor type shows a dramatic influence on the RC value of HyI. The RC value determined by FeCit was obviously higher than that measured using Fe2( SO4 ) 3 and Fe( NO3 ) 3 , and the microbial reducing capacity of the HyI was lower than the corresponding native reducing capacity. By analyzing the special absorbencies ( SUVA254 and SUVA280 ) , absorbance ratios ( A2/A3 and A4/A6 ) and integrated area from UV-vis spectra, it can be found that the RC was affected by aromatic degree, unsaturated conjugated structure, and molecular weight. Excitation-emission matrix spectra coupled with regional integration analysis showed that the relative content of humic-like substances ( humic-like acids and fulvic-like acids) was the main factor influencing the RC value of HyI. The results obtained can be used to characterize the redox properties of HyI, and reveal its role in the transformation and degradation of pollutants during composting.

Spectroscopic study on interaction of quercitrin with human serum albumin / 中草药

Objective: To study the interaction of quercitrin with human serum albumin (HSA) and the influence of glucose. Methods: To investigate the interaction mechanism between quercitrin and HSA by spectroscopic method; to calculate the binding constants, binding sites, and binding distance according to double logarithmic plot and Föster's energy transfer theory, respectively; to explain the type of interaction force between quercitrin with HSA by thermodynamic parameters; to discuss the conformation change of HSA via synchronous fluorescence spectra. Results: The fluorescence quenching mechanism of quercitrin to HSA was static quenching; The binding constants and the number of binding sites decreased with the increasing of temperature and glucose; The distance between the donor and acceptor was less than 7 nm; The hydrophobic forces played a major role in stabilizing quercetrin and HSA complex; The binding reaction had changed the micro-environmention of tryptophan residues. Conclusion: Quercetrin could bind with HSA and change the conformation of HSA; The physiological concentration of glucose increases the binding constants and the number of binding sites of quercetrin with HSA.

Study on the Mechanism of DNA Conformation Change Induced by Cr(Ⅵ)-GSH Complex / 环境与健康杂志

Objective To study the interaction between Cr(Ⅵ)-GSH complex and DNA and to understand the mechanism of DNA conformation change induced by Cr(Ⅵ)-GSH complex. Methods Chromium(Ⅵ) reacts on glutathione forms the chromium (Ⅴ) intermediate complex, and the intermediate complex can induce the conformation change of DNA, in the present paper, ultraviolet and fluorescence spectra, Scatchard equation, fluorescence quenching curve, and fluorescence probe method using ethidium bromide (EB) as a fluorescence probe were employed. Results The chromium (Ⅴ) intermediate complex formed rapidly after the reaction between Cr(Ⅵ) and GSH in Hepes buffer solution at pH=7.4, the complex did not insert into the base pairs on the DNA duplex strand and developed electrostatic binding with the phosphate backbone of DNA, but induced a conformation change of DNA leading to a disruption of duplex structure. In the following time, the complex decomposed and the end product was Cr(Ⅲ), Cr(Ⅲ) can cross-link with DNA, the whole process needs about an hour. Conclusion The chromium(Ⅴ) intermediate complex of the conformation change reaction of chromium(Ⅵ) and glutathione may play an important role in inducing the DNA.