Exploration of interaction of canthaxanthin with human serum albumin by spectroscopic and molecular simulation methods

The interaction between the food colorant canthaxanthin (CA) and human serum albumin (HSA) in aqueous solution was explored by using fluorescence spectroscopy, three‐dimensional fluorescence spectra, synchronous fluorescence spectra, UV–vis absorbance spectroscopy, circular dichroism (CD) spectra and molecular docking methods. The thermodynamic parameters calculated from fluorescence spectra data showed that CA could result in the HSA fluorescence quenching. From the K_SV change with the temperature dependence, it was concluded that HSA fluorescence quenching triggered by CA is the static quenching and the number of binding sites is one. Furthermore, the secondary structure of HSA was changed with the addition of CA based on the results of synchronous fluorescence, three‐dimensional fluorescence and CD spectra. Hydrogen bonds and van der Waals forces played key roles in the binding process of CA with HSA, which can be obtained from negative standard enthalpy (ΔH) and negative standard entropy (ΔS). Furthermore, the conclusions were certified by molecular docking studies and the binding mode was further analyzed with Discovery Studio. These conclusions can highlight the potential of the interaction mechanism of food additives and HSA.     

Investigation on the Interaction of Hydroxyethyl Starch 130/0.4 (Voluven) and Serum Albumin for Pharmacokinetic and Toxicological Implications

The interaction of hydroxyethyl starch 130/0.4 (Voluven) with human serum albumin (HSA) has been investigated by fluorescence (steady state and synchronous), Fourier transforms infrared (FT‐IR), and circular dichroism (CD) spectroscopies. Analysis of the fluorescence quenching data of HSA by Voluven using the Stern–Volmer method revealed the formation of 1:1 ground‐state complex. Evaluation of binding parameters and binding energy indicated that the binding reaction was exothermic. On the basis of fluorescence measurements, it was concluded that electrostatic forces play a crucial role in stabilizing the complex. The binding distance was calculated by using Förster resonance energy transfer (FRET) theory. The conformational changes of HSA were obtained qualitatively as well as quantitatively using synchronous fluorescence, FT‐IR, and CD. The HSA underwent partial unfolding in the presence of Voluven.     

Investigations with spectroscopy, zeta potential and molecular modeling of the non-cooperative behaviour between cyclophosphamide hydrochloride and aspirin upon interaction with human serum albumin: binary and ternary systems from multi-drug therapy

The interaction between cyclophosphamide hydrochloride (CYC) and aspirin (ASA) with human serum albumin (HSA) was studied by various kind of spectroscopic, ζ potential and molecular modeling under physiological conditions. The fluorescence data showed that the binding of drugs to proteins caused strong static fluorescence quenching. The analysis of the fluorescence quenching of HSA in the binary and ternary systems displayed that ASA was affected by the complex formed between CYC and HSA. Moreover, CYC was influenced by the HSA-ASA complex. The inherent binding information, including the quenching mechanism, binding constants, number of binding sites, effective quenching constant, fraction of the initial fluorescence and thermodynamic parameters were measured by the fluorescence quenching technique at various temperatures. In addition, according to the synchronous fluorescence spectra of HSA, the results showed that the fluorescence quenching of HSA originated from the Trp and Tyr residues, and indicated a conformational change of HSA with the addition of the drugs. Far-UV CD spectra of HSA were recorded before and after the addition of ASA and CYC as binary and ternary systems. An increase in intensity of the positive CD peak of HSA was observed in the presence of the drugs. The results were interpreted by excited interactions between the aromatic residues of the HSA binding sites and the drugs bound to them. The distance r between donor and acceptor was obtained by the Forster energy according to fluorescence resonance energy transfer (FRET) and found to be 2.35 nm and 1.78 nm for CYC and ASA, respectively. This confirmed the existence of static quenching for proteins in the presence of CYC and ASA. Furthermore, docking studies pointed at a reduction of the affinity of each of the drug compounds to the protein in the presence of the other in meaningful amounts. Pre-binding of any of the said compounds forced the second to bind in a non-optimized location and orientation. The potential at the electrokinetic shear surface of the protein-drug solution were measured at several concentrations of the drugs by the ζ potential technique, which confirmed experimental and theoretical results.     

Combined multispectroscopic and molecular docking investigation on the interaction between strictosamide and human serum albumin

The interaction between strictosamide (STM) and human serum albumin (HSA) was investigated by fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy, ultraviolet‐visible absorption spectroscopy, circular dichroism spectroscopy and molecular modeling under physiological pH 7.4. STM effectively quenched the intrinsic fluorescence of HSA via static quenching. The binding site number n and apparent binding constant K_a were determined at different temperatures by fluorescence quenching. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) for the reaction were calculated as ?3.01 kJ/mol and 77.75 J/mol per K, respectively, which suggested that the hydrophobic force played major roles in stabilizing the HSA–STM complex. The distance r between donor and acceptor was obtained to be 4.10 nm according to Förster's theory. After the addition of STM, the synchronous fluorescence and three‐dimensional fluorescence spectral results showed that the hydrophobicity of amino acid residues increased and the circular dichroism spectral results showed that the α‐helix content of HSA decreased (from 61.48% to 57.73%). These revealed that the microenvironment and conformation of HSA were changed in the binding reaction. Furthermore, the study of molecular modeling indicated that STM could bind to site I of HSA and the hydrophobic interaction was the major acting force, which was in agreement with the binding mode study. Copyright © 2013 John Wiley & Sons, Ltd.     

Interaction of cromolyn sodium with human serum albumin: a fluorescence quenching study

The interaction between cromolyn sodium (CS) and human serum albumin (HSA) was investigated using tryptophan fluorescence quenching. In the discussion of the mechanism, it was proved that the fluorescence quenching of HSA by CS is a result of the formation of a CS–HSA complex. Quenching constants were determined using the Sterns–Volmer equation to provide a measure of the binding affinity between CS and HSA. The thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated. The distance r between donor (Trp²¹⁴) and acceptor (CS) was obtained according to fluorescence resonance energy transfer (FRET). Furthermore, synchronous fluorescence spectroscopy data and UV–vis absorbance spectra have suggested that the association between CS and HSA changed the molecular conformation of HSA and the electrostatic interactions play a major role in CS–HSA association.     

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.     

Deciphering the binding of carbendazim (fungicide) with human serum albumin: A multi-spectroscopic and molecular modelling studies

Carbendazim is a benzimidazole fungicide used to control the fungal invasion. However, its exposure might lead to potential health problems. The present study evaluates the interaction of carbendazim (CAR) with human serum albumin (HSA) which is an important drug carrier protein and plays a very crucial role in the transportation of small molecules. A number of biophysical techniques were employed to investigate the binding of CAR with HSA. The increased UV-absorption of HSA on titrating with CAR suggests the formation of HSA–CAR complex and it could be due to the exposure of aromatic residues. The fluorescence study confirmed that CAR quenches the fluorescence of HSA and showed the static mode of quenching. CAR (50 µM) quenches around 56.14% of the HSA fluorescence. The quenching constant, binding constant, number of binding site and free energy change was calculated by fluorescence quenching experiment. Competitive displacement assay showed Sudlow’s site I as the primary binding site of CAR on HSA. The synchronous fluorescence study revealed the perturbation in the microenvironment around tyrosine and tryptophan residues upon binding of CAR to HSA. The circular dichroism results suggested that the binding of CAR to HSA altered its secondary structure. Molecular docking experiment demonstrated the binding of CAR to Sudlow’s site I of HSA. Docking studies suggested that the hydrogen bonding, van der Waals and pi-alkyl are playing role in the interaction of CAR with HSA. The study confirmed the conformational changes within HSA upon binding of CAR.     

Comparative studies on the interaction of cefixime with bovine serum albumin by fluorescence quenching spectroscopy and synchronous fluorescence spectroscopy

Under simulated physiological conditions, the reaction mechanism between cefixime and bovine serum albumin at different temperatures (293, 303 and 310 K) was investigated using a fluorescence quenching method and synchronous fluorescence method, respectively. The results indicated that the fluorescence intensity and synchronous fluorescence intensity of bovine serum albumin decreased regularly on the addition of cefixime. In addition, the quenching mechanism, binding constants, number of binding sites, type of interaction force and energy‐transfer parameters of cefixime with bovine serum albumin obtained from two methods using the same equation were consistent. The results indicated that the synchronous fluorescence spectrometry could be used to study the binding mechanism between drug and protein, and was a useful supplement to the conventional method. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

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。     

Molecular interactions of isoxazolcurcumin with human serum albumin: spectroscopic and molecular modeling studies

Curcumin is a nontoxic natural product with diverse pharmacological potencies. We report the interaction of a potent synthetic derivative of curcumin, isoxazolcurcumin (IOC) with human serum albumin (HSA) using various biophysical methods. The observed fluorescence quenching of HSA by IOC is due to a complex formation by a static quenching process with a quenching constant of the order of 10(5) M(-1). The binding affinity and the number of binding sites were obtained from a Scatchard analysis. Thermodynamics reveals that the interaction is entropy driven with predominantly hydrophobic forces. From the observed F?rster-type fluorescence resonance energy transfer (FRET), the donor (Trp 214 in HSA) to acceptor (IOC) distance is calculated to be 3.2 nm. The conformational changes of HSA due to the interaction were investigated qualitatively from synchronous fluorescence spectra along with a quantitative estimation of the secondary structure from Fourier Transform Infrared (FTIR) and circular dichroism (CD) spectroscopies. Molecular docking studies were performed to obtain information on the possible residues involved in the interaction process, and changes in accessible surface area of the interacting residues were calculated. The preferred binding site of IOC was analyzed by ligand displacement experiments with 1-anilino-8-naphthalenesulfonate (ANS) and warfarin-bound HSA.     

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.     

Characterizing the interaction between pyrogallol and human serum albumin by spectroscopic and molecular docking methods

In the present study, the interaction of Pyrogallol (PG) with human serum albumin (HSA) was investigated by UV, fluorescence, Circular dichroism (CD), and molecular docking methods. The results of fluorescence experiments showed that the quenching of intrinsic fluorescence of HSA by PG was due to a static quenching. The calculated binding constants (K) for PG-HSA at different temperatures were in the order of 10⁴?M ^?1, and the corresponding numbers of binding sites, n were approximately equal to unity. The thermodynamic parameters, ΔH and ΔS were calculated to be negative, which indicated that the interaction of PG with HSA was driven mainly by van der Waals forces and hydrogen bonds. The negative value was obtained for ΔG showed that the reaction was spontaneous. In addition, the effect of PG on the secondary structure of HSA was analyzed by performing UV–vis, synchronous fluorescence, and CD experiments. The results indicated that PG induced conformational changes in the structure of HSA. According to Förster no-radiation energy transfer theory, the binding distance of HSA to PG was calculated to be 1.93?nm. The results of molecular docking calculations clarified the binding mode and the binding sites which were in good agreement with the results of experiments.

Communicated by Ramaswamy H. Sarma     

Fluorescence spectroscopy and molecular simulation on the interaction of caffeic acid with human serum albumin

Fluorescence spectroscopy and molecular simulation were explored to study the interaction between caffeic acid and human serum albumin (HSA). The experimental results indicated that the fluorescence quenching mechanism between caffeic acid and HSA is a static quenching, which was proved again by the analysis of fluorescence lifetime by time‐correlated single photon counting. The binding process is spontaneous and the hydrophobic force is the main force between caffeic acid and HSA. In addition, the binding of caffeic acid to HSA was modeled by molecular dynamics simulations. The root mean square deviations, root mean square fluctuations, radius of gyration and the number of hydrogen bonds of the molecular dynamic (MD) simulation process were analyzed. Both experimental and modeling results demonstrated strong binding between HSA and caffeic acid. HSA had a slight conformational change when it binds with caffeic acid. The obtained information is useful for HSA drug design. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparison of the binding behavior of FCCP with HSA and HTF as determined by spectroscopic and molecular modeling techniques

The interaction of carbonylcyanide p‐(trifluoromethoxy) phenylhydrazone (FCCP) with human serum albumin (HSA) and human transferrin (HTF) was investigated using multiple spectroscopy, molecular modeling, zeta‐potential and conductometry measurements of aqueous solutions at pH 7.4. The fluorescence, UV/vis and polarization fluorescence spectroscopy data disclosed that the drug–protein complex formation occurred through a remarkable static quenching. Based on the fluorescence quenching, two sets of binding sites with distinct affinities for FCCP existed in the two proteins. Steady‐state and polarization fluorescence analysis showed that there were more affinities between FCCP and HSA than HTF. Far UV‐CD and synchronous fluorescence studies indicated that FCCP induced more structural changes on HSA. The resonance light scattering (RLS) and zeta‐potential measurements suggested that HTF had a greater resistance to drug aggregation, whereas conductometry measurements expressed the presence of free ions improving the resistance of HSA to aggregation. Thermodynamic measurements implied that a combination of electrostatic and hydrophobic forces was involved in the interaction between FCCP with both proteins. The phase diagram plots indicated that the presence of second binding site on HSA and HTF was due to the existence of intermediate structures. Site marker competitive experiments demonstrated that FCCP had two distinct binding sites in HSA which were located in sub‐domains IIA and IIIA and one binding site in the C‐lobe of HTF as confirmed by molecular modeling. The obtained results suggested that both proteins could act as drug carriers, but that the HSA potentially had a higher capacity for delivering FCCP to cancerous tissues. Copyright © 2013 John Wiley & Sons, Ltd.     

A concise approach to 1,11-didechloro-6-methyl-4'-O-demethyl rebeccamycin and its binding to human serum albumin: fluorescence spectroscopy and molecular modeling method

1,11-Didechloro-6-methyl-4'-O-demethyl rebeccamycin (JDC-108), a rebeccamycin analog possessing potent anti-tumor activities, was prepared via a concise one-pot strategy in good yield. The interaction between JDC-108 and human serum albumin (HSA) was studied by spectroscopic methods including fluorescence spectroscopy, UV-vis absorption spectrum, and molecular modeling. The quenching mechanism of fluorescence of HSA by JDC-108 was discussed. The number of binding sites n and apparent binding constant K were measured by fluorescence quenching method. The thermodynamic parameters DeltaH, DeltaG, DeltaS at different temperatures were calculated and the results indicated the binding reaction was mainly entropy-driven and hydrophobic forces played major role in the reaction. The distance r between donor (HSA) and acceptor (JDC-108) was obtained according to F?rster theory of non-radiation energy transfer. Synchronous fluorescence and UV-vis absorption spectrum were used to investigate the molecular conformation of HSA molecules with addition of JDC-108 and the result indicated that molecular conformation of HSA molecules was changed in the presence of JDC-108 and the hydrophobic interaction played a major role in JDC-108-HSA association, which was in good agreement with the results of molecular modeling study. In addition, the effect of common ions on the binding constants of JDC-108-HSA complex was also discussed.     

Comparison of interactions between human serum albumin and silver nanoparticles of different sizes using spectroscopic methods

Three different sizes (15.9 ± 2.1 nm, 26.4 ± 3.2 nm and 39.8 ± 4.0 nm, respectively) of citrate‐coated silver nanoparticles (SNPs) have been synthesized and characterized. The interactions of the synthesized SNPs with human serum albumin (HSA) at physiological pH have been systematically studied by UV‐vis absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The results indicate that the SNPs can bind to HSA with high affinity and quench the intrinsic fluorescence of HSA. The binding constants and quenching rate constants were calculated. The apparent association constants (K_app) values are 2.14 × 10⁴ M^–1 for 15.9 nm SNP, 1.65 × 10⁴ M^–1 for 26.4 nm SNP and 1.37 × 10⁴ M^–1 for 39.8 nm SNP, respectively. The values of binding constant obtained from the fluorescence quenching data match well with that determined from the absorption spectral changes. These results suggest that the smaller SNPs have stronger interactions to HSA than the larger ones at the same concentrations. Synchronous fluorescence, three‐dimensional fluorescence and CD spectroscopy studies show that the synthesized SNPs can induce slight conformational changes in HSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic analysis of the interaction between amphotericin B and human serum albumin using surface plasmon resonance and fluorescence spectroscopy.

The binding interaction between amphotericin B and human serum albumin (HSA) has been studied using surface plasmon resonance (SPR) spectroscopy combined with a fluorescence quenching method to confirm the binding kinetic results. In this paper, the SPR method used to study the drug-protein interaction has been described in detail. The association rate constant, dissociation rate constant and the equilibrium association constant of amphotericin B binding to HSA were obtained using this method. To confirm the feasibility of the SPR method, a fluorescence quenching method was performed to obtain the equilibrium constant. In order to obtain more accurate results, experiment design was used to optimize the fluorescence quenching process. The two equilibrium association constants obtained using the two methods were 4.017 x 10(4) M(-1) (SPR) and 3.656 x 10(4) M(-1) (fluorescence quenching method) respectively.     

Spectroscopic and molecular simulation studies on the interaction of di‐(2‐ethylhexyl) phthalate and human serum albumin

Di‐(2‐ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in industrial production, but may have a potential health risk. In this study, the binding characteristics of DEHP with human serum albumin (HSA) in aqueous solution at pH 7.4 were determined using UV/vis absorption, fluorescence, Fourier transform infrared (FTIR) spectroscopy and circular dichroism (CD), along with a molecular simulation technique. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by DEHP was static. The calculated thermodynamic parameters indicated that hydrophobic forces played a predominant role in formation of the DEHP–HSA complex, but hydrogen bonds could not be omitted. Site marker competitive experiments and denaturation studies showed that the binding of DEHP to HSA primarily took place in subdomain IIA of HSA, and molecular docking results further corroborated the binding sites. The synchronous fluorescence, UV/vis absorption, FTIR and CD spectra revealed that the addition of DEHP induced changes in the secondary structure of HSA. Protein surface hydrophobicity (PSH) tests indicated that DEHP binding to HSA caused an increase in the PSH. Moreover, the effects of some metal ions on the binding constant of DEHP − HSA interaction were also investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Interaction of human serum albumin with novel imidazole derivatives studied by spectroscopy and molecular docking

This study was a detailed characterization of the interaction of a series of imidazole derivatives with a model transport protein, human serum albumin (HSA). Fluorescence and time‐resolved fluorescence results showed the existence of a static quenching mode for the HSA–imidazole derivative interaction. The binding constant at 296 K was in the order of 10⁴ M^–1, showing high affinity between the imidazole derivatives and HSA. A site marker competition study combined with molecular docking revealed that the imidazole derivatives bound to subdomain IIA of HSA (Sudlow's site I). Furthermore, the results of synchronous, 3D, Fourier transform infrared, circular dichroism and UV–vis spectroscopy demonstrated that the secondary structure of HSA was altered in the presence of the imidazole derivatives. The specific binding distance, r, between the donor and acceptor was obtained according to fluorescence resonance energy transfer. Copyright © 2015 John Wiley & Sons, Ltd.