Insights into the binding of paclitaxel to human serum albumin: multispectroscopic studies

The interaction of paclitaxel with human serum albumin (HSA) was studied using fluorescence, resonance light scattering, ultraviolet‐visible, circular dichroism and Fourier transform infrared spectroscopy at pH 7.4. Fluorescence data revealed that the fluorescence quenching of HSA by paclitaxel was a static quenching procedure. Time‐resolved fluorescence data also confirmed the quenching mode, which present a constant decay time of about 5 ns. The binding sites were approximately 1 and the binding constant suggested a weak association (324/M at 298 K), which is helpful for the release of the drug to targeted organs. The thermodynamic parameters, ΔG^○, ΔH° and ΔS° were calculated as – 1.06 × 10⁴ J/mol, 361 J/mol per K and 9.7 × 10⁴ J/mol respectively at 298 K, suggesting that binding was spontaneous and was driven mainly by hydrophobic interactions. The binding distance between HSA and paclitaxel was determined to be 2.23 nm based on the Förster theory. Analysis of circular dichroism, ultraviolet‐visible, three‐dimensional fluorescence, Fourier transform infrared and resonance light scattering spectra demonstrated that HSA conformation was slightly altered in the presence of paclitaxel and dimension of the individual HSA molecules were larger after interacting with paclitaxel. These results were confirmed by a molecular docking study. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of binding properties of dicationic styrylimidazo[1,2‐a]pyridinium dyes to human serum albumin by spectroscopic techniques

The binding interaction between two dicationic styrylimidazo[1,2‐a]pyridinium dyes and human serum albumin (HSA) was investigated at physiological conditions using fluorescence, UV–vis absorption, and circular dichroism (CD) spectroscopies. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by these dyes was static. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that hydrogen bonding and van der Waals forces played a major role in the formation of the dye–HSA complex. Binding distances (r) between dyes and HSA were calculated according to Förster's non‐radiative energy transfer theory. Studies of conformational changes of HSA using CD measurements indicate that the α‐helical content of the protein decreased upon binding of the dyes. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Investigation on the Interaction of Norgestrel with Human Serum Albumin Using Spectroscopy and Molecular‐Docking Method

The interaction of norgestrel with human serum albumin (HSA) was investigated by spectroscopy and molecular‐docking methods. Results of spectroscopy methods suggested that the quenching mechanism of norgestrel on HSA was static quenching and that the quenching process was spontaneous. Negative values of thermodynamic parameters (ΔG, ΔH, and ΔS) indicated that hydrogen bonding and van der Waals forces dominated the binding between norgestrel and HSA. Three‐dimensional fluorescence spectrum and circular dichroism spectrum showed that the HSA structure was slightly changed by norgestrel. Norgestrel mainly bound with Sudlow site I based on a probe study, as confirmed by molecular‐docking results. Competition among similar structures indicated that ethisterone and norethisterone affected the binding of norgestrel with HSA. CH₃ in R₁ had little effect on norgestrel binding with HSA. The surface hydrophobicity properties of HSA, investigated using 8‐anilino‐1‐naphthalenesulfonic acid, was changed with norgestrel addition.     

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.     

Interaction of 3'-azido-3'-deamino daunorubicin with DNA: multispectroscopic and molecular modeling

In this paper, 3'-azido-3'-deamino daunorubicin (ADNR) was synthesized and the interaction of ADNR and calf thymus DNA (ctDNA) was investigated for the first time by using multi-spectroscopic techniques and molecular modeling study in vitro under simulated physiological conditions. Hypochromicity of the absorption spectra of ADNR were observed in the presence of ctDNA, and the fluorescence of ADNR was strongly quenched through static mechanism with the addition of ctDNA. Moreover, the fluorescence polarization was increased when ctDNA was added. From the experimental results, conclusion can be drawn that the binding mode of ADNR with ctDNA was an intercalative binding, and the calculated thermodynamic parameters suggested that the binding of ADNR to ctDNA was driven mainly by hydrogen bonding force. Furthermore, the results obtained from computational modeling further proved the experimental results obtained from spectroscopic investigations.     

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.     

Binding of daunorubicin to human serum albumin using molecular modeling and its analytical application

This study was designed to examine the interaction of daunorubicin with human serum albumin (HSA) for the first time by fluorescence spectroscopy in combination with UV absorption and molecular modeling under simulative physiological conditions. The quenching mechanism was suggested to be static quenching according to the fluorescence measurement and the linearity of Scatchard plot indicated that daunorubicin bound to a single class of binding sites on HSA. The thermodynamic parameters, enthalpy change (DeltaH) and entropy change (DeltaS) were calculated to be -16.13 kJ/mol and 27.86 J/(molK), according to the Vant'Hoff equation. These data suggested that hydrophobic interaction was the predominant intermolecular forces stabilizing the complex, which was in good agreement with the results of molecular modeling study. In addition, the effects of common ions on the binding constant of daunorubicin-HSA complex were also discussed at room temperature. Moreover, the synchronous fluorescence technique was successfully employed to determine the total proteins in serum, urine and saliva samples at room temperature under the optimum conditions with a wide linear range and satisfactory results.     

Studies on the interactions of 3,6‐diaminoacridine derivatives with human serum albumin by fluorescence spectroscopy

This study reports the preparation and investigation of the modes of binding of the two symmetric 3,6‐diaminoacridine derivatives obtained from proflavine, which are 3,6‐diphenoxycarbonyl aminoacridine and 3,6‐diethoxycarbonyl aminoacridine to human serum albumin (HSA). The interaction of HSA with the derivatives was investigated using fluorescence quenching and ultraviolet‐visible absorption spectra at pH 7.2 and different temperatures. The results suggest that the derivatives used can interact strongly with HSA and are the formation of HSA‐derivative complexes and hydrophobic interactions as the predominant intermolecular forces in stabilizing for each complex. The Stern‐Volmer quenching constants, binding constants, binding sites and corresponding thermodynamic parameters ΔH, ΔS and ΔG were calculated at different temperatures. The binding distance (r) ~ 3 nm between the donor (HSA) and acceptors (3,6‐diethoxycarbonyl aminoacridine, 3,6‐diphenoxycarbonyl aminoacridine and proflavine) was obtained according to Förster's non‐radiative energy transfer theory. Moreover, the limit of detection and limit of quantification of derivatives were calculated in the presence of albumin. Copyright © 2014 John Wiley & Sons, Ltd.     

In vitro studies on the interaction between human serum albumin and fosfomycin disodium salt,an antibiotic drug by multi-spectroscopic and molecular docking methods

The interaction between the human serum albumin (HSA) and drug, fosfomycin disodium salt (FOS) has been studied by different spectroscopic techniques. The experimental results showed a static quenching mechanism in the interaction of FOS with HSA. The number of binding sites, n and observed binding constant K _a were measured by fluorescence quenching method. The thermodynamic parameters ΔG°, ΔH° and ΔS° were calculated according to van’t Hoff equation. The calculated distance r between FOS and the protein is evaluated according to the theory of Förster energy transfer. A change in the secondary structure of the protein was evident from the circular dichroism measurements, synchronous fluorescence and three-dimensional fluorescence spectra.     

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     

Binding of the bioactive component jatrorrhizine to human serum albumin

The interaction between Jatrorrhizine with human serum albumin (HSA) were studied by fluorescence quenching technique, circular dichroism (CD) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K) are 7.278 x 10(4), 6.526 x 10(4), and 5.965 x 10(4) L.mol(-1) at 296, 303, and 310 K, respectively. The CD spectra and FT-IR spectra have proved that the protein secondary structure changed in the presence of Jatrorrhizine in aqueous solution. The effect of common ions on the binding constants was also investigated. In addition, the thermodynamic functions standard enthalpy (DeltaH(0)) and standard entropy (DeltaS(0)) for the reaction were calculated to be -10.891 kJ.mol(-1) and 56.267 J.mol(-1) K(-1), according to the van't Hoff equation. These data indicated that hydrophobic and electrostatic interactions played a major role in the binding of Jatrorrhizine to HSA. Furthermore, the displacement experiments indicated that Jatrorrhizine could bind to the site I of HSA, which was also in agreement with the result of the molecular modeling study.     

Experimental and computational studies on the binding of diazinon to human serum albumin

In the present research, the binding properties of diazinon (DZN), as an organophosphorus herbicide, to human serum albumin (HSA) were investigated using combination of spectroscopic, electrochemistry, and molecular modeling techniques. Changes in the UV–Vis and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. The obtained results from spectroscopic and electrochemistry experiments along with the computational studies suggest that DZN binds to residues located in subdomains IIA of HSA with binding constant about 1410.9 M^?1 at 300 K. From the thermodynamic parameters calculated according to the van’t Hoff equation, the enthalpy change ΔH° and entropy change ΔS° were found to be ?16.695 and 0.116 KJ/mol K, respectively. The primary binding pattern is determined by hydrophobic interaction and hydrogen binding occurring in so-called site I of HSA. DZN could slightly alter the secondary structure of HSA. All of experimental results are supported by computational techniques such as docking and molecular dynamics simulation using a HSA crystal model.     

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.     

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.     

The binding characteristics of the interaction between 3-(2-cyanoethyl) cytosine and human serum albumin

The binding characteristics of the interaction between 3-(2-cyanoethyl) cytosine (CECT) and human serum albumin (HSA) were investigated using fluorescence, UV absorption spectroscopic and molecular modeling techniques under simulative physiological conditions. The intrinsic fluorescence intensity of HSA was decreased with the addition of CECT. The fluorescence data handled by Stern–Volmer equation proved that the quenching mechanism of the interaction between CECT and HSA was a static quenching procedure. The binding constants evaluated utilizing the Lineweaver–Burk equation at 17, 27 and 37?°C, were 2.340?×?10⁴, 2.093?×?10⁴ and 1.899?×?10⁴?L?mol^?1, respectively. The thermodynamic parameters were calculated according to van’t Hoff equations. Negative enthalpy (ΔH) and positive entropy (ΔS) values indicated that both hydrogen bond and hydrophobic force played a major role in the binding process of CECT to HSA, which was consistent with the results of the molecular modeling study. In addition, the effect of other ions on the binding constant of CECT-HSA was examined.     

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.     

Interaction of cyproheptadine hydrochloride with human serum albumin using spectroscopy and molecular modeling methods

The interaction between cyproheptadine hydrochloride (CYP) and human serum albumin (HSA) was investigated by fluorescence spectroscopy, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and molecular modeling at a physiological pH (7.40). Fluorescence of HSA was quenched remarkably by CYP and the quenching mechanism was considered as static quenching since it formed a complex. The association constants K_a and number of binding sites n were calculated at different temperatures. According to Förster's theory of non‐radiation energy transfer, the distance r between donor (human serum albumin) and acceptor (cyproheptadine hydrochloride) was obtained. The effect of common ions on the binding constant was also investigated. The effect of CYP on the conformation of HSA was analyzed using FT‐IR, synchronous fluorescence spectroscopy and 3D fluorescence spectra. The thermodynamic parameters ΔH and ΔS were calculated to be ?14.37 kJ mol^?1 and 38.03 J mol^?1 K^?1, respectively, which suggested that hydrophobic forces played a major role in stabilizing the HSA‐CYP complex. In addition, examination of molecular modeling indicated that CYP could bind to site I of HSA and that hydrophobic interaction was the major acting force, which was in agreement with binding mode studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of the interaction between 2′-deoxyuridine and human serum albumin

The binding of 2′-deoxyuridine to human serum albumin (HSA) was investigated by fluorescence spectroscopy in combination with molecular modeling under simulation of physiological conditions. The quenching mechanism was suggested to be static according to the fluorescence measurement. The thermodynamic parameters: enthalpy change (ΔH) and entropy change (ΔS) were calculated to be −18.87 kJ/mol and 24.00 J/(mol K) according to the Vant’Hoff equation. These data suggest that hydrophobic interactions are the predominant intermolecular forces stabilizing the complex. Experimental results are in agreement with the results obtained by molecular modeling study. In addition, the effects of common ions on the binding constants were also studied at room temperature.     

Interaction of (-)-epigallocatechin-3-gallate with human serum albumin: fluorescence, fourier transform infrared, circular dichroism, and docking studies

(-)-Epigallocatechin-3-gallate (EGCG), the major constituent of green tea has been reported to prevent many diseases by virtue of its antioxidant properties. The binding of EGCG with human serum albumin (HSA) has been investigated for the first time by using fluorescence, circular dichroism (CD), Fourier transform infrared (FTIR) spectroscopy, and protein-ligand docking. We observed a quenching of fluorescence of HSA in the presence of EGCG. The binding parameters were determined by a Scatchard plot and the results were found to be consistent with those obtained from a modified Stern-Volmer equation. From the thermodynamic parameters calculated according to the van't Hoff equation, the enthalpy change deltaH degrees and entropy change deltaS degrees were found to be -22.59 and 16.23 J/mol K, respectively. These values suggest that apart from an initial hydrophobic association, the complex is held together by van der Waals interactions and hydrogen bonding. Data obtained by fluorescence spectroscopy, CD, and FTIR experiments along with the docking studies suggest that EGCG binds to residues located in subdomains IIa and IIIa of HSA. Specific interactions are observed with residues Trp 214, Arg 218, Gln 221, Asn 295 and Asp 451. We have also looked at changes in the accessible surface area of the interacting residues on binding EGCG for a better understanding of the interaction.