Human serum albumin–malathion complex study in the presence of silver nanoparticles at different sizes by multi spectroscopic techniques

The binding of malathion to human serum albumin (HSA) in the presence of silver nanoparticles (AgNPs) was investigated for the first time by multiple spectroscopic methods such as fluorescence quenching, fluorescence resonance energy transfer (FRET), circular dichroism, red-edge excitation shift (REES), synchronous fluorescence and three dimensional fluorescence spectroscopy under physiological conditions .The results indicated that binding of malathion to HSA induced fluorescence quenching through static mechanism. The number of binding sites was calculated by double logarithmic equation. Changes in the micro-environment of the fluorophore residues were also probed by synchronous fluorescence spectroscopy and REES. Changes of secondary structure of HSA in HSA–malathion complex was verified by circular dichroism approach in the presence of AgNPs that showed the electrostatic interaction changes in the protein structure. The binding average distance (r) between the donor (HSA) and the acceptor (malathion) was measured and found to be 1.63?nm according to the Forster’s theory of non-radiation energy transfer which was <7?nm confirmed the existence of static quenching in the presence of AgNPs. The conformational changes of HSA by three-dimensional fluorescence spectroscopy were studied. By comparing the resonance light scattering in the binary and ternary systems, we could estimate the effect of AgNPs on the precipitation of the malathion on the HSA. Generally we have discussed the toxicity reduction effect of malathion in food industrial by the results of spectroscopy techniques.     

Effect of CdTe Quantum Dots Size on the Conformational Changes of Human Serum Albumin: Results of Spectroscopy and Isothermal Titration Calorimetry

Quantum dots (QDs) are recognized as some of the most promising candidates for future applications in biomedicine. However, concerns about their safety have delayed their widespread application. Human serum albumin (HSA) is the main protein component of the circulatory system. It is important to explore the interaction of QDs with HSA for the potential in vivo application of QDs. Herein, using spectroscopy and isothermal titration calorimetry (ITC), the effect of glutathione-capped CdTe quantum dots of different sizes on the HSA was investigated. After correction for the inner filter effect, the fluorescence emission spectra and synchronous fluorescence spectra showed that the microenvironment of aromatic acid residues in the protein was slightly changed when the glutathione (GSH)–cadmium telluride (CdTe) QDs was added, and GSH–CdTe QDs with larger particle size exhibited a much higher effect on HSA than the small particles. Although a ground-state complex between HSA and GSH–CdTe QDs was formed, the UV–vis absorption and circular dichroism spectroscopic results did not find appreciable conformational changes of HSA. ITC has been used for the first time to characterize the binding of QDs with HSA. The ITC results revealed that the binding was a thermodynamically spontaneous process mainly driven by hydrophobic interactions, and the binding constant tended to increase as the GSH–CdTe QDs size increased. These findings are helpful in understanding the bioactivities of QDs in vivo and can be used to assist in the design of biocompatible and stable QDs.     

Investigation of the interaction between quercetin and human serum albumin by multiple spectra,electrochemical impedance spectra and molecular modeling

Quercetin (Qu), a flavonoid compound, exists widely in the human diet and exhibits a variety of pharmacological activities. This work is aimed at studying the effect of Qu on the bioactive protein, human serum albumin (HSA) under simulated biophysical conditions. Multiple spectroscopic methods (including fluorescence and circular dichroism), electrochemical impedance spectra (EIS) and molecular modeling were employed to investigate the interaction between Qu and HSA. The fluorescence quenching and EIS experimental results showed that the fluorescence quenching of HSA was caused by formation of a Qu–HSA complex in the ground state, which belonged to the static quenching mechanism. Based on the calculated thermodynamic parameters, it concluded that the interaction was a spontaneous process and hydrogen bonds combined with van der Waal's forces played a major role in stabilizing the Qu–HSA complex. Molecular modeling results demonstrated that several amino acids participated in the binding process and the formed Qu–HSA complex was stabilized by H‐bonding network at site I in sub‐domain IIA, which was further confirmed by the site marker competitive experiments. The evidence from circular dichroism (CD) indicated that the secondary structure and microenvironment of HSA were changed. Alterations in the conformation of HSA were observed with a reduction in the amount of α helix from 59.9% (free HSA) to 56% (Qu–HSA complex), indicating a slight unfolding of the protein polypeptides. Copyright © 2014 John Wiley & Sons, Ltd.     

Binding of Janus kinase inhibitor tofacitinib with human serum albumin: multi-technique approach

In this report, we have investigated the binding affinity of tofacitinib with human serum albumin (HSA) under simulated physiological conditions by using UV–visible spectroscopy, fluorescence quenching measurements, dynamic light scattering (DLS), differential scanning calorimetry (DSC) and molecular docking methods. The obtained results demonstrate that fluorescence intensity of HSA gets quenched by tofacitinib and quenching occurs in static manner. Binding parameters calculated from modified Stern–Volmer equation shows that the drug binds to HSA with a binding constant in the order of 10⁵. Synchronous fluorescence data deciphered the change in the microenvironment of tryptophan residue in HSA. UV spectroscopy and DLS measurements deciphered complex formation and reduction in hydrodynamic radii of the protein, respectively. Further DSC results show that tofacitinib increases the thermo stability of HSA. Hydrogen bonding and hydrophobic interaction are the main binding forces between HSA and tofacitinib as revealed by docking results.     

Spectroscopic investigation of the effects of aqueous‐phase prepared CdTe quantum dots on protein hemoglobin at the molecular level

3‐Mercaptopropionic Acid‐modified CdTe quantum dots (QDs) were synthesized and characterized by infrared, fluorescence, and ultraviolet–visible absorption spectra and Nano‐ZetaSizer measurements. Then the interaction between QDs and hemoglobin was studied to investigate the effects of QDs on the structure and function of hemoglobin by using a variety of spectroscopy methods and isothermal titration calorimetry. The results showed van der Waals forces and hydrogen bonding predominantly played major roles in the binding. The intrinsic fluorescence of hemoglobin was quenched with changes to the microenvironment of tyrosine and tryptophan residues and complex conformational changes of hemoglobin were induced with the loosening and unfolding skeleton. However, the heme in hemoglobin was still stable, indicating that the main physiological function of hemoglobin might not be significantly inhibited. This study will provide a new strategy to study the biological toxicity of QDs at the molecular level.     

Comparison of molecular interactions of Ag2Te and CdTe quantum dots with human serum albumin by spectroscopic approaches

Ag₂Te quantum dots (QDs) have attracted great attention in biological applications due to their superior photoluminescence qualities and good biocompatibility, but their potential biotoxicity at a molecular biology level has been rarely discussed. In order to better understand the basic behavior of Ag₂Te QDs in biological systems and compare their biotoxicity to cadmium‐containing QDs, a series of spectroscopic measurements was applied to reveal the molecular interactions of Ag₂Te QDs and CdTe QDs with human serum albumin (HSA). Ag₂Te QDs and CdTe QDs statically quenched the intrinsic fluorescence of HSA by electrostatic interactions, but Ag₂Te QDs exhibited weaker quenching ability and weaker binding ability compared with CdTe QDs. Electrostatic interactions were the main binding forces and Sudlow's site I was the primary binding site during these binding interactions. Furthermore, micro‐environmental and conformational variations of HSA were induced by their binding interactions with two QDs. Ag₂Te QDs caused less secondary structural and conformational change in HSA, illustrating the lower potential biotoxicity risk of Ag₂Te QDs. Our results systematically indicated the molecular binding mechanism of Ag₂Te QDs with HSA, which provided important information for possible toxicity risk of these cadmium‐free QDs to human health.     

Conformation, thermodynamics and stoichiometry of HSA adsorbed to colloidal CdSe/ZnS quantum dots

Water-soluble luminescent colloidal quantum dots (QDs) have attracted great attention in biological and medical applications. In particular, for any potential in vivo application, the interaction of QDs with human serum albumin (HSA) is crucial. As a step toward the elucidation of the fate of QDs introduced to organism, the interactions between QDs and HSA were systematically investigated by various spectroscopic techniques under the physiological conditions. It was proved that binding of QDs and HSA is a result of the formation of QDs-HSA complex and electrostatic interactions play a major role in stabilizing the complex. The modified Stern-Volmer quenching constant K(a) at different temperatures and corresponding thermodynamic parameters DeltaH, DeltaG and DeltaS were calculated. Furthermore, the site marker competitive experiments revealed that the binding location of QDs with HSA is around site I, centered at Lys199. The conformational changes of HSA induced by QDs have been analyzed by means of CD and FT-IR. The results suggested that HSA underwent substantial conformational changes at both secondary and tertiary structure levels. The stoichiometry of HSA attached to QDs was obtained by dynamic light scattering (DLS) and zeta-potential.     

Binding of amifostine to human serum albumin: A biophysical study

The aim of this present work is to investigate the interaction between amifostine and human serum albumin (HSA) in simulated physiological conditions by spectroscopic methods to reveal potential toxic effects of the drug. The results reflected that amifostine caused fluorescence quenching of HSA through a static quenching process, which was further confirmed by the electrochemical experiments. The binding constants at 290, 297 and 304 K were obtained as 2.53 × 10⁵/M, 8.13 × 10⁴/M and 3.59 × 10⁴/M, respectively. There may be one binding site of amifostine on HSA. The thermodynamic parameters indicated that the interaction between amifostine and HSA was driven mainly by hydrogen bonding and electrostatic forces. Synchronous fluorescence spectra, circular dichroism and Fourier transform infrared spectroscopy results showed amifostine binding slightly changed the conformation of HSA with secondary structural content changes. Förster resonance energy transfer study revealed high possibility of energy transfer with amifostine‐Trp‐214 distance of 3.48 nm. The results of the present study may provide valuable information for studying the distribution, toxicological and pharmacological mechanisms of amifostine in vivo. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular interaction of some cardiovascular drugs with human serum albumin at physiological‐like conditions: A new approach

In the present study, the interaction of human serum albumin (HSA) with some cardiovascular drugs (CARs) under physiological conditions was investigated via the fluorescence spectroscopic and Fourier transform infrared spectroscopy. The CAR included Captopril, Timolol, Propranolol, Atenolol, and Amiodarone. Cardiovascular drugs can effectively quench the endogenous fluorescence of HSA by static quenching mechanism. The fluorescence quenching of HSA is mainly caused by complex formation of HSA with CAR. The binding reaction of CAR with HSA can be concluded that hydrophobic and electrostatic interactions are the main binding forces in the CAR‐HSA system. The results showed that CAR strongly quenched the intrinsic fluorescence of HSA through a static quenching procedure, and nonradiation energy transfer happened within molecules. Fourier transform infrared spectroscopy absorption studies showed that the secondary structure was changed according to the interaction of HSA and CAR. The binding reaction of CAR with HSA can be concluded that hydrophobic and electrostatic interactions are the main binding forces in the CAR‐HSA system. The results obtained herein will be of biological significance in pharmacology and clinical medicines.     

Insights into the interaction of methotrexate and human serum albumin: A spectroscopic and molecular modeling approach

In this study, fluorescence spectroscopy and molecular modeling approaches were employed to investigate the binding of methotrexate to human serum albumin (HSA) under physiological conditions. From the mechanism, it was demonstrated that fluorescence quenching of HSA by methotrexate results from the formation of a methotrexate/HSA complex. Binding parameters calculated using the Stern–Volmer method and the Scatchard method showed that methotrexate binds to HSA with binding affinities in the order 10⁴ L·mol^?1. Thermodynamic parameter studies revealed that the binding reaction is spontaneous, and that hydrogen bonds and van der Waals interactions play a major role in the reaction. Site marker competitive displacement experiments and a molecular modeling approach demonstrated that methotrexate binds with appropriate affinity to site I (subdomain IIA) of HSA. Furthermore, we discuss some factors that influence methotrexate binding to HSA.     

Investigation into the interaction of methylparaben and erythromycin with human serum albumin using multispectroscopic methods

In this paper, the interaction of methylparaben and erythromycin with human serum albumin (HSA) was studied for the first time using spectroscopic methods including Fourier transform infrared (FTIR) spectroscopy and UV absorption spectroscopy in combination with fluorescence quenching under physiological conditions. The binding parameters were evaluated using a fluorescence quenching method. Based on Förster's theory of non‐radiation energy transfer, the binding average distance, r between the donor (HSA) and the acceptor (methylparaben and erythromycin) was evaluated. UV/vis absorption, FTIR, synchronous and 3D spectral results showed that the conformation of HSA was changed in the presence of methylparaben and erythromycin. The thermodynamic parameters were calculated according to the van't Hoff equation and are discussed. The effect of some biological metal ions and site probes on the binding of methylparaben and erythromycin to HSA were further examined. Copyright © 2015 John Wiley & Sons, Ltd.     

Interaction of human serum albumin with 10-hydroxycamptothecin: spectroscopic and molecular modeling studies

In this work, fluorescence spectroscopy in combination with circular dichroism spectroscopy and molecular modeling was employed to investigate the binding of 10-hydroxycamptothecin (HCPT) to human serum albumin (HSA) under simulative physiological conditions. The experiment results showed that the fluorescence quenching of HSA by HCPT was a result of the formation of HCPT–HSA complex. The corresponding association constants (K _a) between HCPT and HSA at four different temperatures were determined according to the modified Stern–Volmer equation. The results of thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrogen bonds and van der Waals forces played major roles for HCPT–HSA association. Site marker competitive displacement experiment indicated that the binding of HCPT to HSA primarily took place in sub-domain IIA (site I). Molecular docking study further confirmed the binding mode and the binding site obtained by fluorescence and site marker competitive experiments. The conformational investigation showed that the presence of HCPT decreased the α-helical content of HSA and induced the slight unfolding of the polypeptides of protein, which confirmed some micro-environmental and conformational changes of HSA molecules.     

罗丹明类荧光分子探针与血清白蛋白之间相互作用的研究

本研究旨在对罗丹明类荧光探针ZM-6与人血清白蛋白(HSA)的相互作用进行研究。采用了荧光光谱法、三维荧光光谱法、同步荧光光谱法以及CD光谱法在模拟生理条件下对二者的相互作用以及HSA的构象进行了研究。研究结果表明,探针与ZM-6之间的猝灭机理主要是静态猝灭方式。根据热力学数据确定了二者之间的作用力,类型为范德华力和氢键。二者之间的结合距离为4.45 nm。同时得出,ZM-6对HSA的构象产生了影响。此研究对于探针分子的设计以及修饰提供有效的数据以及理论支持。     

Interactions between antimalarial indolone-N-oxide derivatives and human serum albumin

The binding affinity of human serum albumin (HSA) to three antimalarial indolone-N-oxide derivatives, INODs, was investigated under simulated physiological conditions using fluorescence spectroscopy in combination with UV-vis absorption and circular dichroism (CD) spectroscopy. Analysis of fluorescence quenching data of HSA by these compounds at different temperatures using Stern-Volmer and Lineweaver-Burk methods revealed the formation of a ground state indolone-HSA complex with binding affinities of the order 10(4) M(-1). The thermodynamic parameters ΔG, ΔH, and ΔS, calculated at different temperatures, indicated that the binding reaction was endothermic and hydrophobic interactions play a major role in this association. The conformational changes of HSA were investigated qualitatively using synchronous fluorescence and quantitatively using CD. Site marker competitive experiments showed that the binding process took place primarily at site I (subdomain IIA) of HSA. The number of binding sites and the apparent binding constants were also studied in the presence of different ions.     

Comparison and analysis on the serum‐binding characteristics of aspirin–zinc complex and aspirin

This study was designed to compare the protein‐binding characteristics of aspirin–zinc complex (AZN) with those of aspirin itself. AZN was synthesized and interacted with a model transport protein, human serum albumin (HSA). Three‐dimensional fluorescence, ultraviolet–visible and circular dichroism (CD) spectra were used to characterize the interaction of AZN with HSA under physiological conditions. The interaction mechanism was explored using a fluorescence quenching method and thermodynamic calculation. The binding site and binding locality of AZN on HSA were demonstrated using a fluorescence probe technique and Förster non‐radiation energy transfer theory. Synchronous fluorescence and CD spectra were employed to reveal the effect of AZN on the native conformation of the protein. The HSA‐binding results for AZN were compared with those for aspirin under consistent experimental conditions, and indicated that aspirin acts as a guide in AZN when binding to Sudlow's site I, in subdomain IIA of the HSA molecule. Moreover, compared with aspirin, AZN showed greater observed binding constants with, but smaller changes in the α‐helicity of, HSA, which proved that AZN might be easier to transport and have less toxicity in vivo.     

An improved synthetic approach to 7-[3-amino-4-O-(α-l-mycarosyl)-2,3,6-trideoxy-α-l-lyxo-hexopyranosyl]daunorubicinone and its interaction with human serum albumin

An improved synthetic approach to 7-[3-amino-4-O-(α-l-mycarosyl)-2,3,6-trideoxy-α-l-lyxo-hexopyranosyl]daunorubicinone (α1) with high stereoselectivity and good yield was developed. The feature of its binding to human serum albumin (HSA) was also investigated under simulative physiological conditions via fluorescence and UV-vis absorption spectroscopy and molecular modeling methods. The results revealed that α1 caused the fluorescence quenching of HSA by the formation of α1-HSA complexes. Hydrophobic interactions played a major role in stabilizing the complex, which was in good agreement with the results of the molecular modeling study. In addition, the effect of common ions on the binding constants of α1-HSA complexes at room temperature was also discussed. All the experimental results and theoretical data indicated that α1 bound to HSA and was effectively transported and eliminated in the body. Such findings may provide useful guidelines for further drug design.     

Probing the mechanism of interaction of metoprolol succinate with human serum albumin by spectroscopic and molecular docking analysis

In the present work, the mechanism of the interaction between a β1 receptor blocker, metoprolol succinate (MS) and human serum albumin (HSA) under physiological conditions was investigated by spectroscopic techniques, namely fluorescence, Fourier transform infra‐red spectroscopy (FT‐IR), fluorescence lifetime decay and circular dichroism (CD) as well as molecular docking and cyclic voltammetric methods. The fluorescence and lifetime decay results indicated that MS quenched the intrinsic intensity of HSA through a static quenching mechanism. The Stern–Volmer quenching constants and binding constants for the MS–HSA system at 293, 298 and 303 K were obtained from the Stern–Volmer plot. Thermodynamic parameters for the interaction of MS with HSA were evaluated; negative values of entropy change (ΔG°) indicated the spontaneity of the MS and HSA interaction. Thermodynamic parameters such as negative ΔH° and positive ΔS° values revealed that hydrogen bonding and hydrophobic forces played a major role in MS–HSA interaction and stabilized the complex. The binding site for MS in HSA was identified by competitive site probe experiments and molecular docking studies. These results indicated that MS was bound to HSA at Sudlow's site I. The efficiency of energy transfer and the distance between the donor (HSA) and acceptor (MS) was calculated based on the theory of Fosters' resonance energy transfer (FRET). Three‐dimensional fluorescence spectra and CD results revealed that the binding of MS to HSA resulted in an obvious change in the conformation of HSA. Cyclic voltammograms of the MS–HSA system also confirmed the interaction between MS and HSA. Furthermore, the effects of metal ions on the binding of MS to HSA were also studied.     

The specific binding of chlorogenic acid to human serum albumin

Chlorogenic acid (CGA) is one of the most abundant polyphenol compounds in human diet. It is also an active component in traditional Chinese medicines which are used to treat various diseases. In this study, fluorescence spectroscopy in combination with UV–Vis absorption spectroscopy was employed to investigate the specific binding of CGA to human serum albumin (HSA) under the physiological conditions. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by CGA is a result of the formation of CGA–HSA complex. Binding parameters calculating from Stern–Volmer method and Scatchard method showed that CGA bind to HSA with the binding affinities of the order 10⁴ l mol⁻¹. The thermodynamic parameters studies revealed that the binding was characterized by negative enthalpy and positive entropy changes and the electrostatic interactions play a major role for CGA–HSA association. Site marker competitive displacement experiments demonstrated that CGA specific bind to site I (subdomain IIA) of HSA. The binding distance r (3.10 nm) between donor (Trp-214) and acceptor (CGA) was obtained according to fluorescence resonance energy transfer. Furthermore, the effect of metal ions on CGA–HSA system was studied.     

Comparative studies on the interactions of baicalein and Al(III)–baicalein complex with human serum albumin

A new potential drug aluminum(III)–baicalein complex (ALBC) was synthesized and characterized. The binding mechanisms of baicalein (BC) and ALBC to human serum albumin (HSA) under simulative physiological conditions were investigated, in order to understand the pharmacokinetics of BC and ALBC. Fluorescence spectroscopy results suggested that the binding level of BC is higher than that of ALBC. Results of UV–vis, synchronous fluorescence, 3D fluorescence, circular dichroism and Fourier transform infrared spectroscopic analyses consistently demonstrated that the conformation of HSA was altered when bound to BC or ALBC. The distance between HSA as a donor and BC (or ALBC) as an acceptor was determined via fluorescence resonance energy transfer. The results of competitive experiments and molecular docking studies indicated that BC was located in site I (subdomain IIA) on HSA and that ALBC was bound to HSA mainly within site II (subdomain IIIA). Copyright © 2015 John Wiley & Sons, Ltd.     

Specific interaction of chalcone-protein: cardamonin binding site II on the human serum albumin molecule

Cardamonin (2',4'-dihydroxy-6'-methoxychalcone), one of the main constituents from the seeds of Alpinia katsumadai Hayata, belongs to chalcone with its antibacterial, antiinflammatory and other important therapeutic activities of significant potency and low systemic toxicity. In this article, the interaction of cardamonin to human serum albumin (HSA) has been studied for the first time by spectroscopic methods including Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD), and UV-absorption spectroscopy in combination with fluorescence quenching under physiological conditions with drug concentrations of 0.67-4.0 microM. The results of the spectroscopic measurements and the thermodynamic parameters obtained (the enthalpy change DeltaH(0) and the entropy change DeltaS(0) were calculated to be -25.312 and 7.040 J.mol(-1).K(-1) according to the van't Hoff equation) suggest that hydrophobic interaction is the predominant intermolecular forces stabilizing the complex, which is also in good agreement with the results of the molecule modeling study. The alterations of protein secondary structure in the presence of cardamonin in aqueous solution were quantitatively calculated by the evidence from CD and FTIR spectroscopes with reductions of alpha-helices of about 20%, decreases of beta-sheet structures of about 14%, and increases of beta-turn structures of about 15%. The quenching mechanism and the number of binding sites (n approximately 1) were obtained by fluorescence titration data. Fluorescent displacement measurements confirmed that cardamonin binds HSA on site II. In addition, the effects of common ions on the constants of the cardamonin-HSA complex were also discussed.