Determination of the specific interaction between palmatine and bovine serum albumin

The binding of palmatine to bovine serum albumin (BSA) was studied under physiological conditions (pH = 7.40) by molecular spectroscopic approach. It was proved that the fluorescence quenching of BSA by palmatine is a result of the formation of palmatine–BSA complex. Binding parameters were determined using the modified Stern–Volmer equation and Scatchard equation, to measure the specific binding between palmatine and BSA. The thermodynamic parameters calculated, ∆G°, ∆H° and ∆S° indicate that the electrostatic interactions play a major role in the palmatine–BSA association. Site marker competitive displacement experiments demonstrated that palmatine binds with specific affinity to site II (subdomain IIIA) of BSA. Furthermore, the specific binding distance r (3.36 nm) was obtained according to fluorescence resonance energy transfer. The results of synchronous fluorescence spectra and UV–Visible absorption spectra show that the conformation of bovine serum albumin has been changed.     

Multispectroscopic exploration and molecular docking analysis on interaction of eriocitrin with bovine serum albumin

Eriocitrin is a flavanone glycoside, which exists in lemon or lime citrus fruits. It possesses antioxidant, anticancer, and anti‐allergy activities. In order to investigate the pharmacokinetics and pharmacological mechanisms of eriocitrin in vivo, the interaction between eriocitrin and bovine serum albumin (BSA) was studied under the simulated physiological conditions by multispectroscopic and molecular docking methods. The results well indicated that eriocitrin and BSA formed a new eriocitrin‐BSA complex because of intermolecular interactions, which was demonstrated by the results of ultraviolet‐visible (UV‐vis) absorption spectra. The intrinsic fluorescence of BSA was quenched by eriocitrin, and static quenching was the quenching mechanism. The number of binding sites (n) and binding constant (K_b) at 310 K were 1.22 and 2.84 × 10⁶ L mol^?1, respectively. The values of thermodynamic parameters revealed that the binding process was spontaneous, and the main forces were the hydrophobic interaction. The binding distance between eriocitrin and BSA was 3.43 nm. In addition, eriocitrin changed the conformation of BSA, which was proved by synchronous fluorescence and circular dichroism (CD) spectra. The results of site marker competitive experiments suggested that eriocitrin was more likely to be inserted into the subdomain IIA (site I), which was further certified by molecular docking studies.     

Fluorescence spectroscopic studies on the interaction of Gemini surfactant 14‐6‐14 with bovine serum albumin

The interaction of the cationic Gemini surfactant hexamethylene‐1,3‐bis (tetradecyldimethylammonium bromide) (14‐6‐14) with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectra and three‐dimensional (3D) fluorescence spectra. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters ΔH, ΔG and ΔS have been estimated by the fluorescence quenching method. The results indicated that hydrophobic forces were the predominant intermolecular forces between BSA and the surfactant. Competitive experiments and the number of binding sites calculation show that 14‐6‐14 can be inserted in site‐II (in subdomain IIIA) of BSA. The effect of 14‐6‐14 on the conformation of BSA was evaluated by synchronous fluorescence spectroscopy and 3D fluorescence spectral methods. The results show that the conformation of BSA was changed dramatically in the presence of 14‐6‐14, by binding to the Trp and Try residues of BSA. The investigation provides interaction between BSA and 14‐6‐14 as a model for molecular design and industrial research. Copyright © 2011 John Wiley & Sons, Ltd.     

Studies on the interaction between benzophenone and bovine serum albumin by spectroscopic methods

The interaction between benzophenone (BP) and bovine serum albumin (BSA) was investigated by the methods of fluorescence spectroscopy combined with UV–Vis absorption and circular dichroism (CD) measurements under simulative physiological conditions. The experiment results showed that the fluorescence quenching of BSA by BP was resulted from the formation of a BP–BSA complex and the corresponding association constants (K _a) between BP and BSA at four different temperatures had been determined using the modified Stern–Volmer equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be –43.73 kJ mol⁻¹ and −53.05 J mol⁻¹ K⁻¹, respectively, which suggested that hydrogen bond and van der Waals force played major roles in stabilizing the BP–BSA complex. Site marker competitive experiments indicated that the binding of BP to BSA primarily took place in site I (sub-domain IIA). The conformational investigation showed that the presence of BP decreased the α-helical content of BSA and induced the slight unfolding of the polypeptides of protein, which confirmed some micro-environmental and conformational changes of BSA molecules.     

Study on the synthesis of sulfonamide derivatives and their interaction with bovine serum albumin

Three sulfonamide derivatives (SAD) were first synthesized from p‐hydroxybenzoic acid and sulfonamides (sulfadimidine, sulfamethoxazole and sulfachloropyridazine sodium) and were characterized by elemental analysis, ¹H NMR and MS. The interaction between bovine serum albumin (BSA) and SAD was studied using UV/vis absorption spectroscopy, fluorescence spectroscopy, time‐resolved fluorescence spectroscopy and circular dichroism spectra under imitated physiological conditions. The experimental results indicated that SAD effectively quenched the intrinsic fluorescence of BSA via a static quenching process. The thermodynamic parameters showed that hydrogen bonding and van der Waal's forces were the predominant intermolecular forces between BSA and two SADs [4‐((4‐(N‐(4,6‐dimethylpyrimidin‐2‐yl)sulfamoyl)phenyl)carbamoyl)phenyl acetate and 4‐((4‐(N‐(5‐methylisoxazol‐3‐yl)sulfamoyl)phenyl)carbamoyl)phenyl acetate], but hydrophobic forces played a major role in the binding process of BSA and 4‐((4‐(N‐(6‐chloropyridazin‐3‐yl)sulfamoyl)phenyl) carbamoyl)phenyl acetate. In addition, the effect of SAD on the conformation of BSA was investigated using synchronous fluorescence spectroscopy and circular dichroism spectra. Molecular modeling results showed that SAD was situated in subdomain IIA of BSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic study on the interaction of bovine serum albumin with zinc(II) phthalocyanine

The interaction between the photosensitive antitumour drug, 2(3),9(10),16(17),23(24)‐tetra‐(((2‐aminoethylamino)methyl)phenoxy)phthalocyaninato‐zinc(II) (ZnPc) and bovine serum albumin (BSA) has been investigated using various spectroscopic methods. This work may provide some useful information for understanding the interaction mechanism of anticancer drug–albumin binding and gain insight into the biological activity and metabolism of the drug in blood. Based on analysis of the fluorescence spectra, ZnPc could quench the intrinsic fluorescence of BSA and the quenching mechanism was static by forming a ground state complex. Meanwhile, the Stern–Volmer quenching constant (K_SV), binding constant (K_b), number of binding sites (n) and thermodynamic parameters were obtained. Results showed that the interaction of ZnPc with BSA occurred spontaneously via hydrogen bond and van der Waal's force. According to Foster's non‐radioactive energy transfer theory, the energy transfer from BSA to ZnPc occurred with high possibility. Synchronous fluorescence and circular dichroism (CD) spectra also demonstrated that ZnPc induced the secondary structure of and conformation changes in BSA, especially α helix. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and study on the binding of thiazol‐2(3H)‐ylidine derivative with human serum albumin using spectroscopic and molecular docking methods

In this article, a facile and convenient synthesis of thiazol‐2(3H)‐ylidine derivatives of fatty acid ( 3a – c ) is described. The binding of N′‐(4,5‐dimethyl‐3‐penylthiazol‐2(3H)‐ylidine)octadec‐9‐enehydrazide ( 3a ) with human serum albumin (HSA) is explored using various spectral methods and molecular docking. Fluorescence quenching results show that 3a induces conformational changes in HSA and the polarity around the tryptophan residues is increased. Stern–Volmer quenching plots at different temperatures (298, 305 and 312 K) show that the fluorescence quenching mechanism is static quenching. Synchronous fluorescence, 3D fluorescence spectra, circular dichroism and Fourier transform infrared spectroscopy are used to determine the structural change in HSA on interaction with 3a . Förster resonance energy transfer analysis shows that the binding distance (r₀ = 2.78 nm) between HSA (Trp214) and 3a is within the of range 2–8 nm for quenching to occur. The molecular docking study also confirms that 3a is located in subdomain IIA (site I) of HSA and is stabilized by hydrogen bonding and hydrophobic forces.     

Experimental,computational and chemometrics studies of BSA-vitamin B6 interaction by UV–Vis,FT-IR,fluorescence spectroscopy,molecular dynamics simulation and hard-soft modeling methods

The interaction of pyridoxine (Vitamin B6) with bovine serum albumin (BSA) is investigated under pseudo-physiological conditions by UV–Vis, fluorescence and FTIR spectroscopy. The intrinsic fluorescence of BSA was quenched by VB6, which was rationalized in terms of the static quenching mechanism. According to fluorescence quenching calculations, the bimolecular quenching constant (k_q), dynamic quenching (K_SV) and static quenching (K_LB) at 310 K were obtained. The efficiency of energy transfer and the distance between the donor (BSA) and the acceptor (VB6) were calculated by Foster’s non-radiative energy transfer theory and were equal to 41.1% and 2.11 nm.The collected UV–Vis and fluorescence spectra were combined into a row-and column-wise augmented matrix and resolved by multivariate curve resolution-alternating least squares (MCR-ALS). MCR-ALS helped to estimate the stoichiometry of interactions, concentration profiles and pure spectra for three species (BSA, VB6 and VB6-BSA complex) existed in the interaction procedure. Based on the MCR-ALS results, using mass balance equations, a model was developed and binding constant of complex was calculated using non-linear least squares curve fitting. FT-IR spectra showed that the conformation of proteins was altered in presence of VB6. Finally, the combined docking and molecular dynamics (MD) simulations were used to estimate the binding affinity of VB6 to BSA. Five-nanosecond MD simulations were performed on bovine serum albumin (BSA) to study the conformational features of its ligand binding site. From MD results, eleven BSA snapshots were extracted, at every 0.5 ns, to explore the binding affinity (GOLD score) of VB6 using a docking procedure. MD simulations indicated that there is a considerable flexibility in the structure of protein that affected ligand recognition. Structural analyses and docking simulations indicated that VB6 binds to site I and GOLD score values depend on the conformations of both BSA and ligand. Molecular modeling results showed that VB6–BSA complex formed not only on the basis of electrostatic forces, but also on the basis of π–π staking and hydrogen bond. There was an excellent agreement between the experimental and computational results. The results presented in this paper, will offer a reference for detailed and systematic studies on the biological effects and action mechanism of small molecules with proteins.     

Using resonance light scattering and UV/vis absorption spectroscopy to study the interaction between gliclazide and bovine serum albumin

At different temperatures (298, 310 and 318 K), the interaction between gliclazide and bovine serum albumin (BSA) was investigated using fluorescence quenching spectroscopy, resonance light scattering spectroscopy and UV/vis absorption spectroscopy. The first method studied changes in the fluorescence of BSA on addition of gliclazide, and the latter two methods studied the spectral change in gliclazide while BSA was being added. The results indicated that the quenching mechanism between BSA and gliclazide was static. The binding constant (K_a), number of binding sites (n), thermodynamic parameters, binding forces and Hill's coefficient were calculated at three temperatures. Values for the binding constant obtained using resonance light scattering and UV/vis absorption spectroscopy were much greater than those obtained from fluorescence quenching spectroscopy, indicating that methods monitoring gliclazide were more accurate and reasonable. In addition, the results suggest that other residues are involved in the reaction and the mode ‘point to surface’ existed in the interaction between BSA and gliclazide. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of the interaction between sodium salts of (2E)‐3‐(4'‐halophenyl)prop‐2‐enoyl sulfachloropyrazine and bovine serum albumin by fluorescence spectroscopy

Three sodium salts of (2E)‐3‐(4'‐halophenyl)prop‐2‐enoyl sulfachloropyrazine (CCSCP) were synthesized and their structures were determined by ¹H and ¹³C NMR, LC‐MS and IR. The binding properties between CCSCPs and bovine serum albumin (BSA) were studied using fluorescence spectroscopy in combination with UV–vis absorbance spectroscopy. The results indicate that the fluorescence quenching mechanisms between BSA and CCSCPs were static quenching at low concentrations of CCSCPs or combined quenching (static and dynamic) at higher CCSCP concentrations of 298, 303 and 308 K. The binding constants, binding sites and corresponding thermodynamic parameters (ΔH, ΔS, ΔG) were calculated at different temperatures. All ΔG values were negative, which revealed that the binding processes were spontaneous. Although all CCSCPs had negative ΔH and positive ΔS, the contributions of ΔH and ΔS to ΔG values were different. When the 4'‐substituent was fluorine or chlorine, van der Waals interactions and hydrogen bonds were the main interaction forces. However, when the halogen was bromine, ionic interaction and proton transfer controlled the overall energetics. The binding distances between CCSCPs and BSA were determined using the Förster non‐radiation energy transfer theory and the effects of CCSCPs on the conformation of BSA were analyzed by synchronous fluorescence spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd.     

The investigation of the interaction between orientin and bovine serum albumin by spectroscopic analysis

In this paper, the interaction between orientin and bovine serum albumin (BSA) was examined using fluorescence and absorbance spectroscopy. The analysis of the quenching mechanism was done using Stern–Volmer plots which exhibit upward (positive) deviation. A linear response to orientin was shown in the concentration range between 3 and 50 μM. The experimental results showed the presence of a static quenching process between orientin and BSA. The thermodynamic parameters ΔH, ΔS and ΔG were also calculated and suggested that the hydrophobic and electrostatic interactions played an important role in the interaction between orientin and BSA. Furthermore, the distances between BSA and orientin were determined according to Förster non‐radiation energy transfer theory. In addition, the results of the synchronous fluorescence obtained indicated that the binding of orientin with BSA could affect conformation in BSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectroscopic investigation into the interaction of a diazacyclam‐based macrocyclic copper(ii) complex with bovine serum albumin

Cyclam‐based ligands and their complexes are known to show antitumor activity. This study was undertaken to examine the interaction of a diazacyclam‐based macrocyclic copper(II) complex with bovine serum albumin (BSA) under physiological conditions. The interactions of different metal‐based drugs with blood proteins, especially those with serum albumin, may affect the concentration and deactivation of metal drugs, and thereby influence their availability and toxicity during chemotherapy. In this vein, several spectral methods including UV–vis absorption, fluorescence and circular dichroism (CD) spectroscopy techniques were used. Spectroscopic analysis of the fluorescence quenching confirmed that the Cu(II) complex quenched BSA fluorescence intensity by a dynamic mechanism. In order to further determine the quenching mechanism, an analysis of Stern–Volmer plots at various concentrations of BSA was carried out. It was found that the K_SV value increased with the BSA concentration. It was suggested that the fluorescence quenching process was a dynamic quenching rather than a static quenching mechanism. Based on Förster's theory, the average binding distance between the Cu(II) complex and BSA (r) was found to be 4.98 nm; as the binding distance was less than 8 nm, energy transfer from BSA to the Cu(II) complex had a high possibility of occurrence. Thermodynamic parameters (positive ΔH and ΔS values) and measurement of competitive fluorescence with 1‐anilinonaphthalene‐8‐sulphonic acid (1,8‐ANS) indicated that hydrophobic interaction plays a major role in the Cu(II) complex interaction with BSA. A Job's plot of the results confirmed that there was one binding site in BSA for the Cu(II) complex (1:1 stoichiometry). The site marker competitive experiment confirmed that the Cu(II) complex was located in site I (subdomain IIA) of BSA. Finally, CD data indicated that interaction of the Cu(II) complex with BSA caused a small increase in the α‐helical content. Copyright © 2016 John Wiley & Sons, Ltd.     

The Interactions of Glutathione-Capped CdTe Quantum Dots with Trypsin

Due to their unique fluorescent properties, quantum dots present a great potential for biolabelling applications; however, the toxic interactions of quantum dots with biopolymers are little known. The toxic interactions of glutathione-capped CdTe quantum dots with trypsin were studied in this paper using synchronous fluorescence spectroscopy, fluorescence emission spectra, and UV–vis absorption spectra. The interaction between CdTe quantum dots and trypsin resulted in structure changes of trypsin and inhibited trypsin's activity. Fluorescence emission spectra revealed that the quenching mechanism of trypsin by CdTe quantum dots was a static quenching process. The binding constant and the number of binding sites at 288 and 298 K were calculated to be 1.98 × 10⁶ L mol⁻¹ and 1.37, and 6.43 × 10⁴ L mol⁻¹ and 1.09, respectively. Hydrogen bonds and van der Waals' forces played major roles in this process.     

In vitro study on binding interaction of quinapril with bovine serum albumin (BSA) using multi-spectroscopic and molecular docking methods

The binding interaction between quinapril (QNPL) and bovine serum albumin (BSA) in vitro has been investigated using UV absorption spectroscopy, steady-state fluorescence spectroscopic, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and molecular docking methods for obtaining the binding information of QNPL with BSA. The experimental results confirm that the quenching mechanism of the intrinsic fluorescence of BSA induced by QNPL is static quenching based on the decrease in the quenching constants of BSA in the presence of QNPL with the increase in temperature and the quenching rates of BSA larger than 10¹⁰ L mol^?1 s^?1, indicating forming QNPL–BSA complex through the intermolecular binding interaction. The binding constant for the QNPL–BSA complex is in the order of 10⁵ M^?1, indicating there is stronger binding interaction of QNPL with BSA. The analysis of thermodynamic parameters together with molecular docking study reveal that the main binding forces in the binding process of QNPL with BSA are van der Waal’s forces and hydrogen bonding interaction. And, the binding interaction of BSA with QNPL is an enthalpy-driven process. Based on Förster resonance energy transfer, the binding distance between QNPL and BSA is calculated to be 2.76 nm. The results of the competitive binding experiments and molecular docking confirm that QNPL binds to sub-domain IIA (site I) of BSA. It is confirmed there is a slight change in the conformation of BSA after binding QNPL, but BSA still retains its secondary structure α-helicity.     

Fluorescent bovine serum albumin interacting with the antitussive quencher dextromethorphan: a spectroscopic insight

The interaction of dextromethorphan hydrobromide (DXM) with bovine serum albumin (BSA) is studied by using fluorescence spectra, UV–vis absorption, synchronous fluorescence spectra (SFS), 3D fluorescence spectra, Fourier transform infrared (FTIR) spectroscopy and circular dichroism under simulated physiological conditions. DXM effectively quenched the intrinsic fluorescence of BSA. Values of the binding constant, K_A, are 7.159 × 10³, 9.398 × 10³ and 16.101 × 10³ L/mol; the number of binding sites, n, and the corresponding thermodynamic parameters ΔG°, ΔH° and ΔS° between DXM and BSA were calculated at different temperatures. The interaction between DXM and BSA occurs through dynamic quenching and the effect of DXM on the conformation of BSA was analyzed using SFS. The average binding distance, r, between the donor (BSA) and acceptor (DXM) was determined based on Förster's theory. The results of fluorescence spectra, UV–vis absorption spectra and SFS show that the secondary structure of the protein has been changed in the presence of DXM. Copyright © 2015 John Wiley & Sons, Ltd.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH = 7.4) was investigated using UV–vis absorption spectroscopy (UV–vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT‐IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady‐state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >10¹⁰ L mol^?1 sec^?1. This result indicates that the ENPL–BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG ⁰), enthalpic change (ΔH ⁰) and entropic change (ΔS ⁰). The binding of ENPL with BSA is an enthalpy‐driven process due to |ΔH °| > |T ΔS °| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub‐domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α‐helical secondary structure.     

A Spectroscopic Approach to Investigate the Molecular Interactions between the Newly Approved Irreversible ErbB blocker "Afatinib" and Bovine Serum Albumin

The interaction of afatinib (AFB) with bovine serum albumin (BSA) was examined via fluorescence and UV-Vis spectroscopy. Spectrofluorimetric measurements revealed that AFB can strongly quench the BSA intrinsic fluorescence through producing a non-fluorescent complex. This quenching mechanism was thoroughly investigated with regard to the type of quenching, binding constant, number of binding locations and the fundamental thermodynamic parameters. Subsequently, the association constant of AFB with BSA was computed at three different temperatures and was found to range from 7.34 to 13.19 x10⁵ L mol^-1. Thermodynamic parameters calculations demonstrated a positive ΔS^Ɵvalue with both negative ΔH^ϴand ΔG^ϴvalues for AFB–BSA complex, which in turn infers thata spontaneous binding is taking place with both electrostatic bonding and hydrophobic interactions participating in the binding of AFB and BSA. Similarly, the UV absorption spectra of AFB-BSA system were studied and confirmed the interaction. Conformational alteration of the protein upon binding to AFB was elaborated with the aid of three dimensional fluorescence measurements as well as synchronous fluorescence spectra.     

Synthesis of Morin–Zinc(II) Complex and its Interaction with Serum Albumin

A morin–zinc(II) complex (MZ) was synthesized and its interaction with bovine serum albumin (BSA) were studied by molecular spectroscopy including fluorescence emission spectra, UV-visible spectra, circular dichroism (CD) spectra, three-dimensional fluorescence spectra, and synchronous fluorescence spectra. The interaction mechanism of BSA and MZ was discussed by fluorescence quenching method and Förster non-radiation energy transfer theory. The thermodynamic parameters ΔH ^θ, ΔG ^θ, ΔS ^θ at different temperatures were calculated and the results indicate the interaction is an exothermic as well as entropy-driven process. Hydrogen bond forces played the most important role in the reaction. The fluorescence probe experiment showed that the binding site of MZ is in subdomain IIA of BSA and the distance between BSA and MZ is 3.17 nm at normal body temperature. The conformation changes of BSA in presence of MZ were investigated by CD spectra and three-dimensional fluorescence spectra.     

Studies on the interaction between tetraphenylporphyrin compounds and bovine serum albumin.

The interaction of three porphyrin compounds with bovine serum albumin (BSA) was examined by fluorescence emission spectra at the excitation wavelength 280 nm and in UV-Vis absorption spectra. Through fluorescence quenching experiments, it was confirmed that the combination of three porphyrin compounds with BSA was a single static quenching process. The binding constant K(A), the thermodynamic parameters enthalpy change (DeltaH(0)), Gibbs free energy change (DeltaG(0)) and entropy change (DeltaS(0)) were obtained. It was found that hydrophobic interaction played a main role in tetraphenylporphyrin (TPP) or tetraparacholophenylporphyrin (TClPP) binding to BSA, while tetraparamethoxyphenylporphyrin (TMEOPP) mainly based on van der Waals' force. According to F?ster energy transfer, the separate distance r, the energy transfer efficiency E and F?ster radium R(0) were calculated. The results obtained from the above experiments showed that three porphyrin compounds were tightly bound to BSA.