Spectroscopic Studies on the Interaction of Fluorine Containing Triazole with Bovine Serum Albumin

The binding of one fluorine including triazole (C₁₀H₉FN₄S, FTZ) to bovine serum albumin (BSA) was studied by spectroscopic techniques including fluorescence spectroscopy, UV–Vis absorption, and circular dichroism (CD) spectroscopy under simulative physiological conditions. Fluorescence data revealed that the fluorescence quenching of BSA by FTZ was the result of forming a complex of BSA–FTZ, and the binding constants (K _a) at three different temperatures (298, 304, and 310 K) were 1.516?×?10⁴, 1.627?×?10⁴, and 1.711?×?10⁴?mol L^?1, respectively, according to the modified Stern–Volmer equation. The thermodynamic parameters ΔH and ΔS were estimated to be 7.752 kJ mol^?1 and 125.217 J?mol^?1?K^?1, respectively, indicating that hydrophobic interaction played a major role in stabilizing the BSA–FTZ complex. It was observed that site I was the main binding site for FTZ to BSA from the competitive experiments. The distance r between donor (BSA) and acceptor (FTZ) was calculated to be 7.42 nm based on the Förster theory of non-radioactive energy transfer. Furthermore, the analysis of fluorescence data and CD data revealed that the conformation of BSA changed upon the interaction with FTZ.     

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

The interaction between bovine serum albumin (BSA) and benzidine (BD) in aqueous solution was investigated by fluorescence spectroscopy, circular dichroism (CD) spectra and UV–Vis spectroscopy, as well as resonance light scattering spectroscopy (RLS). It was proved from fluorescence spectra that the fluorescence quenching of BSA by BD was a result of the formation of BD–BSA complex, and the binding constants (K _a) were determined according to the modified Stern–Volmer equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?34.11 kJ mol^?1 and ?25.89 J mol^?1 K^?1, respectively, which implied that van der Waals force and hydrogen bond played predominant roles in the binding process. The addition of increasing BD to BSA solution caused the gradual enhancement in RLS intensity, exhibiting the forming of the aggregate. Moreover, the competitive experiments of site markers suggested that the binding site of BD to BSA was located in the region of subdomain IIA (sudlow site I). The distance (r) between the donor (BSA) and the acceptor (BD) was 4.44 nm based on the Förster theory of non–radioactive energy transfer. The results of synchronous fluorescence and CD spectra demonstrated the microenvironment and the secondary conformation of BSA were changed.     

Spectroscopic Studies on the Binding of Cobalt(II) 1,10-Phenanthroline Complex to Bovine Serum Albumin

The binding interaction of the cobalt(II) 1,10-phenanthroline complex (Co(phen) ₃ ²⁺ , phen = 1,10-phenanthroline) with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV–Vis absorption and circular dichroism measurements under simulative physiological conditions. The experiment results showed that the fluorescence intensity of BSA was dramatically decreased owing to the formation of Co(phen) ₃ ²⁺ –BSA complex. The corresponding association constants (K _a) between Co(phen) ₃ ²⁺ and BSA at four different temperatures were calculated according to the modified Stern–Volmer equation. The enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to be ?2.73 kJ mol^?1 and 82.27 J mol^?1?K^?1, respectively, which suggested that electrostatic interaction and hydrophobic force played major roles in stabilizing the Co(phen) ₃ ²⁺ –BSA complex. Site marker competitive experiments indicated that the binding of Co(phen) ₃ ²⁺ to BSA primarily took place in site I of BSA. A value of 4.11 nm for the average distance r between Co(phen) ₃ ²⁺ (acceptor) and tryptophan residues of BSA (donor) was derived from Förster’s energy transfer theory. The conformational investigation showed that the presence of Co(phen) ₃ ²⁺ resulted in the change of BSA secondary structure and induced the slight unfolding of the polypeptides of protein, which confirmed the microenvironment and conformational changes of BSA molecules.     

Multi-spectroscopic and voltammetric evidences for binding,conformational changes of bovine serum albumin with thiamine

The interaction between thiamine hydrochloride (TA) and bovine serum albumin (BSA) was investigated by fluorescence, FTIR, UV–vis spectroscopic and cyclic voltammetric techniques under optimised physiological condition. The fluorescence intensity of BSA is gradually decreased upon addition of TA due to the formation of a BSA–TA complex. The binding parameters were evaluated and their behaviour at different temperatures was analysed. The quenching constants (K_sv) obtained were 2.6 × 10⁴, 2.2 × 10⁴ and 2.0 × 10⁴ L mol^?1 at 288, 298 and 308 K, respectively. The binding mechanism was static-type quenching. The values of ΔH° and ΔS° were found to be 26.87 kJ mol^?1 and 21.3 J K^?1 mol^?1, and indicated that electrostatic interaction was the principal intermolecular force. The changes in the secondary structure of BSA upon interaction with TA were confirmed by synchronous and 3-D spectral results. Site probe studies reveal that TA is located in site I of BSA. The effects of some common metal ions on binding of BSA–TA complex were also investigated.     

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.     

Probing the behavior of bovine serum albumin upon binding to atenolol: insights from spectroscopic and molecular docking approaches

Molecular interaction of atenolol, a selective β₁ receptor antagonist with the major carrier protein, bovine serum albumin (BSA), was investigated under imitated physiological conditions (pH 7.4) by means of fluorescence spectroscopy, UV absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and molecular modeling studies. The steady-state fluorescence spectra manifested that static type, due to formation of the atenolol-BSA complex, was the dominant mechanism for fluorescence quenching. The characteristic information about the binding interaction of atenolol with BSA in terms of binding constant (K_b) were determined by the UV–vis absorption titration, and were found to be in the order of 10³ M^?1 at different temperatures, indicating the existence of a weak binding in this system. Thermodynamic analysis revealed that the binding process was primarily mediated by van der Waals force and hydrogen bonds due to the negative sign for enthalpy change (ΔH⁰), entropy change (ΔS⁰). The molecular docking results elucidated that atenolol preferred binding on the site II of BSA according to the findings observed in competitive binding experiments. Moreover, via alterations in synchronous fluorescence, three-dimensional fluorescence and FT-IR spectral properties, it was concluded that atenolol could arouse slight configurational and micro-environmental changes of BSA.     

Multi-spectroscopic studies on the interaction between traditional Chinese herb,helicid with pepsin

Study on the binding properties of helicid by pepsin systematically using multi-spectroscopic techniques and molecular docking method, and these interactions comprise biological recognition at molecular level and backbone of biological significance in medicine concerned with the uses, effects, and modes of action of drugs. We investigated the mechanism of interaction between helicid and pepsin by using various spectroscopic techniques viz., fluorescence spectra, UV–Vis absorption spectra, circular dichroism (CD), 3D spectra, synchronous fluorescence spectra and molecular docking methods. The quenching mechanism associated with the helicid–pepsin interaction was determined by performing fluorescence measurements at different temperatures. From the experimental results show that helicid quenched the fluorescence intensity of pepsin via a combination of static and dynamic quenching process. The binding constants (K_a) at three temperatures (288, 298, and 308 K) were 7.940?×?10⁷, 2.082?×?10⁵ and 3.199?×?10⁵ L mol^?1, respectively, and the number of binding sites (n) were 1.44, 1.14, and 1.18, respectively. The n value is close to unity, which means that there is only one independent class of binding site on pepsin for helicid. Thermodynamic parameters at 298 K were calculated as follows: ΔH^o (??83.85 kJ mol^?1), ΔG^o (??33.279 kJ mol^?1), and ΔS^o (??169.72 J K^?1 mol^?1). Based on thermodynamic analysis, the interaction of helicid with pepsin is driven by enthalpy, and Van der Waals’ forces and hydrogen bonds are the main forces between helicid and pepsin. A molecular docking study further confirmed the binding mode obtained by the experimental studies. The conformational changes in the structure of pepsin was confirmed by 3D fluorescence spectra and circular dichroism.     

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.     

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.     

Spectroscopic Investigation of the Interaction Between Copper (II) 2-oxo-propionic Acid Salicyloyl Hydrazone Complex and Bovine Serum Albumin

The interaction between copper (II) 2-oxo-propionic acid salicyloyl hydrazone (Cu^IIL) and bovine serum albumin (BSA) under physiological conditions was investigated by the methods of fluorescence spectroscopy, UV-Vis absorption, and circular dichroism spectroscopy. Fluorescence data showed that the fluorescence quenching of BSA by Cu^IIL was the result of the formation of the BSA–Cu^IIL complex. The apparent binding constants (K _a) between Cu^IIL and BSA at four different temperatures were obtained according to the modified Stern–Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), for the reaction were calculated to be ?80.79 kJ mol^?1 and ?175.48 J mol^?1 K^?1 according to van’t Hoff equation. The results indicated that van der Waals force and hydrogen bonds were the dominant intermolecular force in stabilizing the complex. The binding distance (r) between Cu^IIL and the tryptophan residue of BSA was obtained to be 4.1 nm according to Förster’s nonradioactive energy transfer theory. The conformational investigation showed that the application of Cu^IIL increased the hydrophobicity of amino acid residues and decreased the α-helical content of BSA (from 62.71% to 37.31%), which confirmed some microenvironmental and conformational changes of BSA molecules.     

Binding of anti-cardiovascular drug to serum albumin: an insight in the light of spectroscopic and computational approaches

Isoprenaline hydrochloride is a potential cardiovascular drug helps in the smooth functioning of the heart muscles. So, we have performed the binding study of ISO with BSA. This study was investigated by UV absorption, fluorescence, synchronous fluorescence, circular dichroism, etc. The analysis of intrinsic fluorescence data showed the low binding affinity of ISO. The binding constant K_b was 2.8 × 103 M-1 and binding stoichiometry (n) was approximately one and the Gibb’s free energy change at 310 K was determined to be -8.69 kcal mol^?1. Negative Gibb’s free energy change shows the spontaneity of the BSA and ISO interaction. We have found ISO-induced alternation in the UV absorption, synchronous fluorescence and CD spectra in the absence and presence of the quencher indicates the complex formation. In synchronous fluorescence, red shift was obtained because of the complex formation of BSA and ISO. The distance (r) between the BSA (donor) and ISO (acceptor) was 2.89 nm, determined by FRET. DLS measurements interpreted complex formation due to the reduction in hydrodynamic radii of the protein in the presence of the drug. The binding site of ISO was found to be nearer to Trp 134 with the help of molecular docking and the ΔG° was found to be –10.2 kcal mol^?1. The esterase activity result suggests that ISO acts as competitive inhibitor. Thus, this study would help to determine the binding capacity of the drug to the protein which may indicate the efficiency of diffusion of ISO into the blood for the treatment of heart diseases.     

Chemico-biological interaction of Etravirine and its β-Cyclodextrin complex with macromolecular targets

The interaction of etravirine with β-cyclodextrin is analyzed by UV–visible absorption, infrared, fluorescence, nuclear magnetic resonance, two-dimensional rotational frame nuclear Overhauser effect spectroscopy, and molecular modeling studies. The 4-hydroxy-3, 5-dimethylbenzonitrile moiety is found to take part in the binding. The stoichiometry of the inclusion complex of ET with β-CD is 1:1 with the binding constant of 2.03 × 10³ mol^?1 dm³. The binding of ET with calf thymus DNA (ctDNA) and bovine serum albumin (BSA) protein is investigated in the presence and the absence of β-CD. Fluorescence enhancement is observed during the binding of ET with ctDNA in the absence of β-CD, whereas in the presence of β-CD, fluorescence quenching is observed. The binding constants of the binding of ET and ET–β-CD to ctDNA are 7.84 × 10⁴ and 4.38 × 10⁴ mol^?1 dm³, respectively. The binding constant of the binding of ET and ET–β-CD to BSA are 3.14 × 10⁴ and 1.6396 × 10⁴ mol^?1 dm³, respectively. The apparent binding constants between ET–β-CD complex and ctDNA or BSA protein decreases significantly. The numbers of binding sites of interaction of ET with BSA protein and the binding distance between BSA protein and ET the absence and the presence of β-CD differ. β-CD modulates the binding of ET with the macromolecular targets.     

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.     

Preferential binding of fisetin to the native state of bovine serum albumin: spectroscopic and docking studies

We have investigated the binding of the biologically important flavonoid fisetin with the carrier protein bovine serum albumin using multi-spectroscopic and molecular docking methods. The binding constants were found to be in the order of 10⁴ M^?1 and the number of binding sites was determined as one. MALDI-TOF analyses showed that one fisetin molecule binds to a single bovine serum albumin (BSA) molecule which is also supported by fluorescence quenching studies. The negative Gibbs free energy change (?G°) values point to a spontaneous binding process which occurs through the presence of electrostatic forces with hydrophobic association that results in a positive entropy change (+51.69 ± 1.18 J mol^?1 K^?1). The unfolding and refolding of BSA in urea have been studied in absence and presence of fisetin using steady-state fluorescence and lifetime measurements. Urea denaturation studies indicate that fisetin is gradually released from its binding site on the protein. In the absence of urea, an increase in temperature that causes denaturation of the protein results in the release of fisetin from its bound state indicating that fisetin binds only to the native state of the protein. The circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopic studies showed an increase in % α-helix content of BSA after binding with fisetin. Site marker displacement studies in accordance with the molecular docking results suggested that fisetin binds in close proximity of the hydrophobic cavity in site 1 (subdomain IIA) of the protein. The PEARLS (Program of Energetic Analysis of Receptor Ligand System) has been used to estimate the interaction energy of fisetin with BSA and the results are in good correlation with the experimental findings.     

Molecular docking and experimental investigation of new indole derivative cyclooxygenase inhibitor to probe its binding mechanism with bovine serum albumin

The indole derivative 2-(5-methoxy-2-methyl-1H-indol-3-yl)-N'-[(E)-(3-nitrophenyl) methylidene]acetohydrazide (IND) was synthesized for its therapeutic potential to inhibit cyclooxygenase (COX)-II. Binding if IND to bovine serum albumin (BSA) was investigated was because most drugs bind to serum albumin in-vivo. Fluorescence, UV–vis spectrophotometry and molecular modeling methodologies were employed for studying the interaction mechanism. The intrinsic fluorescence of BSA was quenched by BSA and the quenching mechanism involved was static quenching. The binding constants between IND and BSA at the three studied temperatures (298, 301 and 306 K) were 1.09 × 10⁵, 4.36 × 10⁴ and 1.23 × 10⁴ L mol⁻¹ respectively. The most likely site for binding IND to BSA was Site I (subdomain IIA). The analysis of thermodynamic parameter revealed the involvement of hydrogen bonding and van der Waals forces in the IND-BSA interaction. Synchronous fluorescence spectroscopic (SFS) and UV–vis spectrophotometric studies suggested conformational change in BSA molecule post interaction to IND. Molecular docking and the experimental results corroborated one another. The study can prove as an insight for future IND drug development.     

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.     

Study on the interaction of fisetholz with BSA/HSA by multi-spectroscopic,cyclic voltammetric,and molecular docking technique

The interaction of fisetholz with bovine serum albumin (BSA) and human serum albumin (HSA) was investigated by multi-spectroscopic, cyclic voltammetric, and molecular docking technique. The results revealed that there was a static quenching of BSA/HSA induced by fisetholz. The binding constants (K_a) and binding sites (n) were calculated at different temperatures (293, 303, and 311?K). The enthalpy change (ΔH) were calculated to be –17.20?kJ mol^?1 (BSA) and –18.28?kJ mol^?1 (HSA) and the entropy change (ΔS) were calculated to be 35.41?J mol^?1 (BSA) and 24.02?J mol^?1 (HSA), respectively, which indicated that the interaction between fisetholz and BSA/HSA was mainly by electrostatic attraction. Based on displacement experiments using site probes, indomethacin and ibuprofen, the binding site of fisetholz to BSA/HSA was identified as sub-domain IIIA, which was further confirmed by molecular docking method. There was little effect of K⁺, Ca²⁺, Cu²⁺, Zn²⁺, and Fe³⁺ on fisetholz-BSA or fisetholz-HSA complex. The spectra of synchronous fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) all showed that fisetholz binding to BSA/HSA leads to secondary structures change of the two serum albumins. According to the Förster non-radiation energy transfer theory, the binding distance between fisetholz and BSA/HSA was 2.94/4.68?nm. The cyclic voltammetry as a supporting tool also indicated that fisetholz interacted with protein.

Communicated by Ramaswamy H. Sarma     

Study on the interaction between a water-soluble dinuclear nickel complex and bovine serum albumin by spectroscopic techniques

The interaction of a water-soluble dinuclear nickel(II) complex, [Ni₂(EGTB)(CH₃CN)₄](ClO₄)₄·4H₂O (EGTB = ethylene glycol-bis(β-aminoethyl ether) N,N,N′,N′-tetrakis(2-benzimidazoyl)) (1), and bovine serum albumin (BSA) was investigated under physiological conditions using fluorescence, synchronous fluorescence, UV–vis absorption and circular dichroism (CD). The experimental results suggested that the nickel(II) complex could bind to BSA with binding constant (K) ~ 10⁴ M^?1 and quench the intrinsic fluorescence of BSA through a static quenching mechanism. The thermodynamic parameters, ΔG°, ΔH°, and ΔS°, calculated at different temperatures, indicated that the binding reaction was spontaneous and electrostatic interactions played a major role in this association. Based on the number of binding sites, it was considered that one molecule of complex 1 could bind to a single site or two sites of the BSA molecule or the two binding modes coexisted. In view of the results of site marker competition experiments, the reactive sites of BSA to complex 1 mainly located in subdomain IIA (site I) and subdomain IIIA (site II) of BSA. Moreover, the binding distance, r, between donor (BSA) and acceptor (complex 1) was 5.13 nm according to Förster nonradiation energy transfer theory. Finally, as shown by the UV–vis absorption, synchronous fluorescence and CD, complex 1 could induce conformation and microenvironmental changes of BSA. The results obtained herein will be of biological significance in toxicology investigation and anticancer metallodrug design.     

Exploring the binding mode of donepezil with calf thymus DNA using spectroscopic and molecular docking methods

Donepezil (DNP) is one of approved drugs to treat Alzheimer's disease (AD). However, the potential effect of DNP on DNA is still unclear. Therefore, the interaction of DNP with calf thymus DNA (DNA) was studied in vitro using spectroscopic and molecular docking methods. Steady‐state and transient fluorescence experiments showed that there was a clear binding interaction between DNP and DNA, resulting from DNP fluorescence being quenched using DNA. DNP and DNA have one binding site between them, and the binding constant (K_b) was 0.78 × 10⁴ L·mol^?1 at 298 K. In this binding process, hydrophobic force was the main interaction force, because enthalpy change (ΔH) and entropy change (ΔS) of DNP–DNA were 67.92 kJ·mol^?1 and 302.96 J·mol^?1·K^?1, respectively. DNP bound to DNA in a groove‐binding mode, which was verified using a competition displacement study and other typical spectroscopic methods. Fourier transform infrared (FTIR) spectrum results showed that DNP interacted with guanine (G) and cytosine (C) bases of DNA. The molecular docking results further supported the results of spectroscopic experiments, and suggested that both Pi‐Sigma force and Pi‐Alkyl force were the major hydrophobic force functioning between DNP and DNA.     

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.