Spectroscopic investigation of water‐soluble alloyed QDs with bovine serum albumin

We present here a systematic investigation on the interaction between a water‐soluble alloyed semiconductor quantum dot and bovine serum albumin using various spectroscopic techniques i.e. fluorescence quenching, resonance light scattering and synchronous fluorescence spectroscopy. The analysis of fluorescence spectrum and fluorescence intensity indicates that the intrinsic fluorescence of bovine serum albumin (BSA) gets quenched by both static and dynamic quenching mechanism. The Stern‐Volmer quenching constants, energy transfer efficiency parameters, binding parameters and corresponding thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) have been evaluated by using van 't Hoff equation at different temperatures. A positive entropy change with a positive enthalpy change was observed suggesting that the binding process was an entropy‐driven, endothermic process associated with the hydrophobic effect. The intermolecular distance (r) between donor (BSA) and acceptor (CdSeS/ZnS quantum dots) was estimated according to Förster's theory of non‐radiative energy transfer. The synchronous fluorescence spectra revealed a blue shift in the emission maxima of tryptophan which is indicative of increasing hydrophobicity. Negative ΔG⁰ values implied that the binding process was spontaneous. It was found that hydrophobic forces played a role in the quenching process. Copyright © 2016 John Wiley & Sons, Ltd.     

A study on the interaction between 3‐spiro‐piperidones and bovine serum albumin using spectroscopic approaches

The interaction between 3‐spiro‐2′‐pyrrolidine‐3′‐spiro‐3″‐piperidine‐2,3″‐dione (PPD) and bovine serum albumin (BSA) in aqueous solution was studied using fluorescence and UV–vis spectroscopy. Fluorescence emission data revealed that BSA (1.00 × 10^‐5 mol/L) fluorescence was statically quenched by PPD at various concentrations, which implies that a PPD–BSA complex was formed. The binding constant (K_A), the number of binding sites (n) and the specific binding site of the PPD with BSA were determined. Energy‐transfer efficiency parameters were determined and the mechanism of the interaction discussed. The thermodynamic parameters, ΔG, ΔH and ΔS, were obtained according to van't Hoff's equation, showing the involvement of hydrophobic forces in these interactions. The effect of PPD acting on the BSA conformation was detected by synchronous fluorescence. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of triazole‐tryptophan hybrid on the conformation stability of bovine serum albumin

The effect of a potent antimicrobial compound bearing 1,2,3‐triazole core and a tryptophan tail, triazole‐tryptophan hybrid (TTH), with bovine serum albumin (BSA) have been explored using various spectroscopic and molecular docking methods. Studies revealed that TTH strongly quenches the intrinsic fluorophore of BSA by a static quenching mechanism. Time‐resolved fluorescence spectra further confirmed the involvement of static quenching for TTH–BSA system. The calculated thermodynamic parameters; ΔH, ΔS, and ΔG showed that the binding process was spontaneous, exothermic and entropy driven. Synchronous fluorescence, three‐dimensional (3D) fluorescence and circular dichroism data revealed that TTH induces the structural alteration in BSA and enhances its stability. In silico study of TTH–BSA system showed that it binds with BSA at the site I of subdomain IIA. Both the experimental and in silico study showed that the hydrophobic and electrostatic interactions play a major role in TTH–BSA binding.     

Good use of fruit wastes: eco‐friendly synthesis of silver nanoparticles,characterization, BSA protein binding studies

A simple and eco‐friendly methodology for the green synthesis of silver nanoparticles (AgNPs) using a mango seed extract was evaluated. The AgNPs were characterized by ultraviolet‐visible spectrophotometry, Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and X‐ray diffraction. The interaction between the green synthesized AgNPs and bovine serum albumin (BSA) in an aqueous solution at physiological pH was examined by fluorescence spectroscopy. The results confirmed that the AgNPs quenched the fluorophore of BSA by forming a ground state complex in aqueous solution. This fluorescence quenching data were also used to determine the binding sites and binding constants at different temperatures. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) suggest that the binding process occurs spontaneously through the involvement of electrostatic interactions. The synchronous fluorescence spectra showed a blue shift, indicating increasing hydrophobicity. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Biomolecular interaction study of hydralazine with bovine serum albumin and effect of β‐cyclodextrin on binding by fluorescence, 3D,synchronous, CD,and Raman spectroscopic methods

Spectrofluoremetric technique was employed to study the binding behavior of hydralazine with bovine serum albumin (BSA) at different temperatures. Binding study of bovine serum albumin with hydralazine has been studied by ultraviolet–visible spectroscopy, fluorescence spectroscopy and confirmed by three‐dimensional, synchronous, circular dichroism, and Raman spectroscopic methods. Effect of β‐cyclodextrin on binding was studied. The experimental results showed a static quenching mechanism in the interaction of hydralazine with bovine serum albumin. The binding constant and the number of binding sites are calculated according to Stern–Volmer equation. The thermodynamic parameters ?H^o, ?G^o, ?S^o at different temperatures were calculated. These indicated that the hydrogen bonding and weak van der Waals forces played an important role in the interaction. Based on the Förster's theory of non‐radiation energy transfer, the binding average distance, r, between the donor (BSA) and acceptor (hydralazine) was evaluated and found to be 3.95 nm. Spectral results showed that the binding of hydralazine to BSA induced conformational changes in BSA. The effect of common ions on the binding of hydralazine to BSA was also examined. Copyright © 2016 John Wiley & Sons, Ltd.     

Intermolecular interaction of fosinopril with bovine serum albumin (BSA): The multi‐spectroscopic and computational investigation

The intermolecular interaction of fosinopril, an angiotensin converting enzyme inhibitor with bovine serum albumin (BSA), has been investigated in physiological buffer (pH 7.4) by multi‐spectroscopic methods and molecular docking technique. The results obtained from fluorescence and UV absorption spectroscopy revealed that the fluorescence quenching mechanism of BSA induced by fosinopril was mediated by the combined dynamic and static quenching, and the static quenching was dominant in this system. The binding constant, K_b, value was found to lie between 2.69 × 10³ and 9.55 × 10³ M^?1 at experimental temperatures (293, 298, 303, and 308 K), implying the low or intermediate binding affinity between fosinopril and BSA. Competitive binding experiments with site markers (phenylbutazone and diazepam) suggested that fosinopril preferentially bound to the site I in sub‐domain IIA on BSA, as evidenced by molecular docking analysis. The negative sign for enthalpy change (ΔH⁰) and entropy change (ΔS⁰) indicated that van der Waals force and hydrogen bonds played important roles in the fosinopril‐BSA interaction, and 8‐anilino‐1‐naphthalenesulfonate binding assay experiments offered evidence of the involvements of hydrophobic interactions. Moreover, spectroscopic results (synchronous fluorescence, 3‐dimensional fluorescence, and Fourier transform infrared spectroscopy) indicated a slight conformational change in BSA upon fosinopril interaction.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction between lisinopril and bovine serum albumin

To further understand the mode of action and pharmacokinetics of lisinopril, the binding interaction of lisinopril with bovine serum albumin (BSA) under imitated physiological conditions (pH 7.4) was investigated using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD) and molecular docking methods. The results showed that the fluorescence quenching of BSA near 338 nm resulted from the formation of a lisinopril–BSA complex. The number of binding sites (n) for lisinopril binding on subdomain IIIA (site II) of BSA and the binding constant were ~ 1 and 2.04 × 10⁴ M^–1, respectively, at 310 K. The binding of lisinopril to BSA induced a slight change in the conformation of BSA, which retained its α‐helical structure. However, the binding of lisinopril with BSA was spontaneous and the main interaction forces involved were van der Waal's force and hydrogen bonding interaction as shown by the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ for the binding of lisinopril with BSA. It was concluded from the molecular docking results that the flexibility of lisinopril also played an important role in increasing the stability of the lisinopril–BSA complex. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of fluorescence interaction and conformational changes of bovine serum albumin with histamine H1‐receptor–drug epinastine hydrochloride by spectroscopic and time‐resolved fluorescence methods

The fluorescence, ultraviolet (UV) absorption, time resolved techniques, circular dichroism (CD), and infrared spectral methods were explored as tools to investigate the interaction between histamine H₁ drug, epinastine hydrochloride (EPN), and bovine serum albumin (BSA) under simulated physiological conditions. The experimental results showed that the quenching of the BSA by EPN was static quenching mechanism and also confirmed by lifetime measurements. The value of n close to unity indicated that one molecule of EPN was bound to protein molecule. The binding constants (K) at three different temperatures were calculated (7.1 × 10⁴, 5.5 × 10⁴, and 3.9 × 10⁴M⁻¹). Based on the thermodynamic parameters (ΔH⁰, ΔG⁰, and ΔS⁰), the nature of binding forces operating between drug and protein was proposed. The site of binding of EPN in the protein was proposed to be Sudlow's site I based on displacement experiments using site markers viz, warfarin, ibuprofen, and digitoxin. Based on the Förster's theory of non‐radiation energy transfer, the binding average distance, r between the donor (BSA) and acceptor (EPN) was evaluated and found to be 4.48 nm. The UV–visible, synchronous fluorescence, CD, and three‐dimensional fluorescence spectral results revealed the changes in secondary structure of the protein upon its interaction with EPN. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 646–657, 2015.     

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.     

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.     

Probing into the binding interaction between medroxyprogesterone acetate and bovine serum albumin (BSA): spectroscopic and molecular docking methods

To further understand the mechanism of action and pharmacokinetics of medroxyprogesterone acetate (MPA), the binding interaction of MPA with bovine serum albumin (BSA) under simulated physiological conditions (pH 7.4) was studied using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, circular dichroism and molecular docking methods. The experimental results reveal that the fluorescence of BSA quenches due to the formation of MPA–BSA complex. The number of binding sites (n) and the binding constant for MPA–BSA complex are ~1 and 4.6 × 10³ M^?1 at 310 K, respectively. However, it can be concluded that the binding process of MPA with BSA is spontaneous and the main interaction forces between MPA and BSA are van der Waals force and hydrogen bonding interaction due to the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ in the binding process of MPA with BSA. MPA prefers binding on the hydrophobic cavity in subdomain IIIA (site II′′) of BSA resulting in a slight change in the conformation of BSA, but BSA retaining the α‐helix structure. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization of intermolecular interaction between cyanidin‐3‐glucoside and bovine serum albumin: Spectroscopic and molecular docking methods

The intermolecular interaction between cyanidin‐3‐glucoside (Cy‐3‐G) and bovine serum albumin (BSA) was investigated using fluorescence, circular dichroism and molecular docking methods. The experimental results revealed that the fluorescence quenching of BSA at 338 nm by Cy‐3‐G resulted from the formation of Cy‐3‐G–BSA complex. The number of binding sites (n) for Cy‐3‐G binding on BSA was approximately equal to 1. The experimental and molecular docking results revealed that after binding Cy‐3‐G to BSA, Cy‐3‐G is closer to the Tyr residue than the Trp residue, the secondary structure of BSA almost not change, the binding process of Cy‐3‐G with BSA is spontaneous, and Cy‐3‐G can be inserted into the hydrophobic cavity of BSA (site II′) in the binding process of Cy‐3‐G with BSA. Moreover, based on the sign and magnitude of the enthalpy and entropy changes (ΔH⁰ = – 29.64 kcal/mol and ΔS⁰ = – 69.51 cal/mol K) and the molecular docking results, it can be suggested that the main interaction forces of Cy‐3‐G with BSA are Van der Waals and hydrogen bonding interactions. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Molecular interactions of thymol with bovine serum albumin: Spectroscopic and molecular docking studies

Thymol is the main monoterpene phenol present in the essential oils which is used in the food industry as flavoring and preservative agent. In this study, the interaction of thymol with the concentration range of 1 to 6 μM and bovine serum albumin (BSA) at fixed concentration of 1 μM was investigated by fluorescence, UV‐vis, and molecular docking methods under physiological‐like condition. Fluorescence experiments were performed at 5 different temperatures, and the results showed that the fluorescence quenching of BSA by thymol was because of a static quenching mechanism. The obtained binding parameters, K, were in the order of 10⁴ M^?1, and the binding number, n, was approximately equal to unity indicating that there is 1 binding site for thymol on BSA. Calculated thermodynamic parameters for enthalpy (ΔH), entropy (ΔS), and Gibb's free energy (ΔG) showed that the reaction was spontaneous and hydrophobic interactions were the main forces in the binding of thymol to BSA. The results of UV‐vis spectroscopy and Arrhenius' theory showed the complex formation in the interaction of thymol and BSA. Negligible conformational changes in BSA by thymol were observed in fluorescence experiments, and the same results were also obtained from UV‐vis studies. Results of molecular docking indicated that the subdomain IA of BSA was the binding site for thymol.     

Characterization of interactions of simvastatin,pravastatin, fluvastatin,and pitavastatin with bovine serum albumin: multiple spectroscopic and molecular docking

The binding interactions of simvastatin (SIM), pravastatin (PRA), fluvastatin (FLU), and pitavastatin (PIT) with bovine serum albumin (BSA) were investigated for determining the affinity of four statins with BSA through multiple spectroscopic and molecular docking methods. The experimental results showed that SIM, PRA, FLU, and PIT statins quenched the intrinsic fluorescence of BSA through a static quenching process and the stable stains–BSA complexes with the binding constants in the order of 10⁴ M^?1 at 298 K were formed through intermolecular nonbond interaction. The values of ΔH⁰, ΔS⁰ and ΔG⁰ in the binding process of SIM, PRA, FLU, and PIT with BSA were negative at the studied temperature range, suggesting that the binding process of four statins and BSA was spontaneous and the main interaction forces were van der Waals force and hydrogen-bonding interactions. Moreover, the binding of four statins with BSA was enthalpy-driven process due to |ΔH°|>|TΔS°| under the studied temperature range. From the results of site marker competitive experiments and molecular docking, subdomain IIIA (site II) was the primary binding site for SIM, PRA, FLU, and PIT on BSA. The results of UV–vis absorption, synchronous fluorescence, 3D fluorescence and FT-IR spectra proved that the slight change in the conformation of BSA, while the significant changes in the conformation of SIM, PRA, FLU, and PIT drug in statin–BSA complexes, indicating that the flexibility of statin molecules plays an important role in increasing the stability of statin–BSA complexes.     

Electronic and fluorescent studies on the interaction of DNA and BSA with a new ternary praseodymium complex containing 2,9-dimethyl 1,10-phenanthroline and antibacterial activities testing

In this study, fluorescence emission spectra, UV–vis absorption spectra, ethidium bromide (EB)-competition experiment, and iodide quenching experiment were used for the interaction study of the Fish salmon DNA (FS-DNA) with [Pr(dmp)2Cl3(OH2)] where dmp is 2,9-dimethyl 1,10-phenanthroline. The binding constant and the number of binding sites of the complex with FS-DNA were 6.09?±?0.04 M^?1 and 1.18, respectively. The free energy, enthalpy, and entropy changes (ΔG°, ΔH°, and ΔS°) in the binding process of the Pr(III) complex with FS-DNA were –8.02?kcal mol^?1, +39.44?kcal mol^?1, and +159.56?cal mol^?1 K^?1, respectively. Based on these results, the interaction process between FS-DNA with [Pr(dmp)2Cl3(OH2)] was spontaneous and the main binding interaction force was groove binding mode. Also, Fluorescence and electronic absorption spectroscopy were used in order to evaluate the binding characteristics, stoichiometry, and interaction mode of praseodymium(III) (Pr(III)) complex with bovine serum albumin (BSA). Title complex showed good binding propensity to BSA presenting moderately high Kb values. The fluorescence quenching of BSA by Pr(III) complex has been observed to be the static process. The positive ΔH° and ΔS° values showed that the hydrophobic interaction is the main force in the binding of Pr(III) complex and BSA. Eventually, the average aggregation number, <J>, of BSA potentially induced by title complex confirmed the 1:1 stoichiometry for title complex-BSA adducts. In vitro, antimicrobial activity of title complex was indicated that the complex is more active against both Escherichia coli and Enterococcus faecalis bacterial strains than Staphylococcus aureus, and Pseudomonas aeruginosa.

Communicated by Ramaswamy H. Sarma     

Micronomicin/tobramycin binding with DNA: fluorescence studies using of ethidium bromide as a probe and molecular docking analysis

Two aminoglycosides, micronomicin (MN), and tobramycin (TB), binding with DNA were studied using various spectroscopic techniques including fluorescence, UV–Vis, FT-IR, and CD spectroscopy coupled with relative viscosity and molecular docking. Studies of fluorescence quenching and time-resolved fluorescence spectroscopy all revealed that MN/TB quenching the fluorescence of DNA–EB belonged to static quenching. The binding constants and binding sites were obtained. The values of ΔH, ΔS, and ΔG suggested that van der Waals force or hydrogen bond might be the main binding force. FT-IR and CD spectroscopy revealed that the binding of MN/TB with DNA had an effect on the secondary structure of DNA. Binding mode of MN/TB with DNA was groove binding which was ascertained by viscosity measurements, CD spectroscopy, ionic strength, melting temperature (T_m), contrast experiments with single stranded (ssDNA), and double stranded DNA (dsDNA). Molecular docking analysis further confirmed that the groove binding was more acceptable result.     

Fluorometric probing on the binding of hematoxylin to serum albumin

The binding of a cell nucleus stain, hematoxylin (HTL), to bovine serum albumin (BSA) was studied by spectroscopy including fluorescence spectra, UV–Visible absorption, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra. The results indicated that the binding had led to static fluorescence quenching, with non-radiation energy transfer happening within single molecule. The observed binding constant was calculated to be 10^5.588 l mol^?1 at 311 K and one binding site had formed. The thermodynamic parameters of the interaction complied with ΔG ^θ < 0, ΔH ^θ < 0, ΔS ^θ < 0 and the results indicate that hydrogen bonds played major role in the reaction. The distance r between donor (BSA) and acceptor (HTL) was obtained according to the Förster theory of non-radiation energy transfer. The structural change of BSA molecules with addition of HTL was analyzed and the optimized geometry of HTL–BSA was investigated by fluorescence probe method.     

Study on the interaction between anti‐tuberculosis drug ethambutol and bovine serum albumin: multispectroscopic and cyclic voltammetric approaches

The binding of bovine serum albumin (BSA) to ethambutol (EMB) was investigated using spectroscopic methods, viz., fluorescence, Fourier transform infrared (FTIR), ultraviolet (UV)/vis absorption and cyclic voltammetry techniques. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of serum albumin by EMB is static, which was also confirmed by lifetime measurements. The number of binding sites, n, and binding constant, K, were obtained at various temperatures. The distance, r, between EMB and the protein was evaluated according to the Förster energy transfer theory. Based on displacement experiments using site probes, viz., warfarin, ibuprofen and digitoxin, the site of binding of EMB in BSA was proposed to be Sudlow's site I. The effect of EMB on the conformation of BSA was analyzed by using synchronous fluorescence spectra (SFS) and 3D fluorescence spectra. The results of fluorescence, UV/vis absorption and FTIR spectra showed that the conformation of BSA was changed in the presence of EMB. The thermodynamic parameters including enthalpy change (ΔH⁰), entropy change (ΔS⁰) and free energy change (ΔG⁰) for BSA–EMB were calculated according to the van't Hoff equation and are discussed.