The investigation of the interaction between edaravone and bovine serum albumin by spectroscopic approaches

The fluorescence and ultraviolet spectroscopies were explored to study the interaction between edaravone (EDA) and bovine serum albumin (BSA) under imitated physiological condition. The experimental results show that the fluorescence quenching mechanism between EDA and BSA is a combined quenching (dynamic and static quenching). The binding constants, binding sites, and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction system were calculated at different temperatures. According to Förster non-radiation energy transfer theory, the binding distance between EDA and BSA was calculated to be 3.10 nm. The effect of EDA on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effects of some common metal ions Mg²⁺, Ca²⁺, Cu²⁺, and Ni²⁺ on the binding constant between EDA and BSA were examined.     

Characterize the interaction between naringenin and bovine serum albumin using spectroscopic approach

Naringenin, a flavanone compound highly enriched in grapefruits, has been identified as a possible inhibitor of cell proliferation; and thus has the potential to act as an antitumorigenic agent. In this study, the binding of naringenin to bovine serum albumin (BSA) was studied at the physiological conditions (pH=7.40) by fluorescence and UV-vis spectroscopy. Naringenin strongly quenches the intrinsic fluorescence of BSA, and a decrease in the fluorescence quenching constant was observed together with an increase in temperature, which indicates that the fluorescence quenching of BSA by naringenin is a result of the formation of naringenin-BSA complex. Binding parameters calculating from Stern-Volmer method and Scatchard method showed that naringenin bind to BSA with the binding affinities of the order 10⁴ L mol⁻¹. Thermodynamic parameters such as ΔG, ΔH and ΔS, were calculated at different temperatures, showing that electrostatic interactions were mostly responsible for the binding of naringenin to BSA. Site marker competitive displacement experiments demonstrating that naringenin bind with high affinity to site I (subdomain IIA) of BSA. Furthermore, the effect of metal ions to naringenin-BSA system was studied, and the specific binding distance r (3.30 nm) between donor (Trp-212) and acceptor (naringenin) was obtained according to fluorescence resonance energy transfer (FRET).     

Interaction of the flavonoid hesperidin with bovine serum albumin: A fluorescence quenching study

The interaction between the flavonoid hesperidin and bovine serum albumin (BSA) was investigated by fluorescence and UV/Vis absorption spectroscopy. The results revealed that hesperidin caused the fluorescence quenching of BSA through a static quenching procedure. The hydrophobic and electrostatic interactions play a major role in stabilizing the complex. The binding site number n, and apparent binding constant K_A, corresponding thermodynamic parameters ΔG^o, ΔH^o, ΔS^o at different temperatures were calculated. The distance r between donor (BSA) and acceptor (hesperidin) was obtained according to fluorescence resonance energy transfer. The effect of Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, and Mn²⁺ on the binding constants between hesperidin and BSA were studied. The effect of hesperidin on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy and UV/Vis absorption spectroscopy.     

Fluorescence Study on the Interaction of Bovine Serum Albumin with P-Aminoazobenzene

In this paper, the interaction between p-aminoazobenzene (PAAB) and BSA was investigated mainly by fluorescence quenching spectra, circular dichroism (CD) and three-dimensional fluorescence spectra under simulative physiological conditions. It was proved that the fluorescence quenching of BSA by PAAB was mainly a result of the formation of a PAAB-BSA complex. The modified Stern-Volmer quenching constant K _a and the corresponding thermodynamic parameters ΔH, ΔG and ΔS at different temperatures were calculated. The results indicated that van der Waals interactions and hydrogen bonds were the predominant intermolecular forces in stabilizing the complex. The distance r?=?4.33 nm between the donor (BSA) and acceptor (PAAB) was obtained according to Förster’s non-radioactive energy transfer theory. The synchronous fluorescence, CD and three-dimensional fluorescence spectral results showed that the hydrophobicity of amino acid residues increased and the losing of α-helix content (from 63.57 to 51.83%) in the presence of PAAB. These revealed that the microenvironment and conformation of BSA were changed in the binding reaction.     

Spectroscopic studies of 7, 8-dihydroxy-4-methylcoumarin and its interaction with bovine serum albumin

The absorption and fluorescence spectra of 7, 8-dihydroxy-4-methylcoumarin (DHMC) in ethanol-water (1:9 v/v) solution at varying pH values were investigated . The interaction between DHMC and bovine serum albumin (BSA) was investigated by fluorescence, FT-IR, and circular dichroism (CD) spectroscopy. The Stern-Volmer quenching constant (K_SV), the quenching rate constant of the bimolecular reaction (K_q), the binding constant, and number of binding sites (n) of DHMC with BSA were evaluated. The results showed that DHMC quenches the fluorescence intensity of BSA through a static quenching process. Positive value of entropy change (ΔS) and negative value of enthalpy change (ΔH) of the BSA-DHMC interaction were obtained according to the van't Hoff equation. The interaction between DHMC and BSA was driven mainly by hydrophobic forces. The binding process was spontaneous and exothermic. The binding distance between the tryptophan residue in BSA and the DHMC was found to be about 2.6 nm based on the Förster theory of non-radiation energy transfer.     

Interactions between imazethapyr and bovine serum albumin: Spectrofluorimetric study

The interaction between imazethapyr (IMA) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. The Stern–Volmer quenching constant (K_SV) at three temperatures was evaluated in order to determine the quenching mechanism. The dependence of fluorescence quenching on viscosity was also evaluated for this purpose. The results showed that IMA quenches the fluorescence intensity of BSA through a static quenching process. The values of the binding constant for the formed BSA–IMA complex and the number of binding sites were found to be 1.51×10⁵ M^?1 and 0.77, respectively, at room temperature. Based on the calculated thermodynamic parameters, the forces that dominate the binding process are hydrogen bonds and van der Waals forces, and the binding process is spontaneous and exothermic. The quenching of protein fluorescence by iodide ion was used to probe the accessibility of tryptophan residues in BSA and the change in accessibility induced by the presence of IMA. According to the obtained results, the BSA–IMA complex is formed in the site where the Trp-134 is located, causing it to become less exposed to the solvent.     

Study on the conjugation mechanism of colistin sulfate with bovine serum albumin and effect of the metal ions on the reaction

Colistin sulfate (CS) can quench the fluorescence of bovine serum albumin (BSA) in an aqueous solution at pH 7.40. The static fluorescence-quenching process between BSA and CS was confirmed and the binding constant, the number of binding sites and thermodynamic data for the interaction between BSA and CS were also obtained. Results showed that the order of magnitude of binding constant (K_a) was 10⁴, and the number of binding site (n) in the binary system was approximately equal to 1; electrostatic force played an important role on the conjugation reaction between BSA and CS. On the basis of the Förster theory of the resonance energy transfer, the binding distance (r) between CS and BSA was less than 7 nm. Comparing the quenching of protein fluorescence excited at 280 nm and 295 nm and from the site marker replacement experiments, it was shown that the primary CS binding site was located in the sub-domain IIA (site I) of BSA. Synchronous fluorescence spectra clearly revealed that the binding of CS with BSA can induce conformation changes in BSA. In addition, the effects of common metal ions on the binding constants of CS–BSA complex were also discussed. It was shown that, except Cu²⁺, the high metal ion concentrations improved the CS efficacy.     

Fluorometric investigation of the interaction between nitrophenols and 7-hydroxy-4-azidomethylcoumarin

The interaction between nitrophenols and 7-hydroxy-4-azidomethylcoumarin has been investigated by fluorescence and UV-vis absorbance spectroscopy. Quenching mechanisms have been evaluated by fluorescence measurements at different temperatures. Stern-Volmer quenching constant K_sv and corresponding thermodynamic parameters ΔH⁰, ΔG⁰ and ΔS⁰ were calculated. Binding studies concerning the number of binding sites ‘n’ and apparent binding constant ‘K’ were performed by fluorescence quenching method.     

Studies on the interaction between scopoletin and two serum albumins by spectroscopic methods

The interactions of scopoletin to bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated by spectroscopic methods. The fluorescence tests indicated that the formation mechanism of scopoletin–BSA/HSA complexes belonged to the static quenching. The displacement experiments suggested that scopoletin primarily bound to tryptophan residues of BSA/HSA within site I (subdomain IIA). The binding distance of scopoletin to BSA/HSA was 2.38/2.34 nm. The thermodynamic parameters (ΔG, ΔH and ΔS) calculated on the basis of different temperatures revealed that the binding of BSA–scopoletin was mainly depended on van der Waals interaction and hydrogen bond, and yet the binding of HSA–scopoletin was strongly relied on the hydrophobic interaction and electrostatic interaction. The results of synchronous fluorescence, 3D fluorescence, UV–vis absorption, and FT-IR spectra showed that the conformations of BSA and HSA altered with the addition of scopoletin. In addition, the effects of some common ions on the binding constants of scopoletin to proteins were also investigated.     

Investigation of the interaction between trazodone hydrochloride and bovine serum albumin

In this paper, the binding of trazodone hydrochloride (TZH) to bovine serum albumin (BSA) was investigated by spectroscopic (fluorescence, spectrophotometry and circular dichroism) techniques under simulative physiological conditions. A strong fluorescence quenching reaction of TZH to BSA was observed and the quenching mechanism was suggested as dynamic quenching according to the Stern-Volmer equation. The binding constants of TZH with BSA at 288, 302 and 309 K were calculated as (1.56±0.003)×10⁴, (2.31±0.002)×10⁴ and (5.44±0.004)×10⁴ M⁻¹, respectively. The thermodynamic parameters, ΔH⁰ and ΔS⁰ were obtained to be 39.86±0.008 kJ mol⁻¹ and 217.89±0.011 J mol⁻¹ K⁻¹, respectively, which indicated the presence of hydrophobic forces between TZH and BSA. The spectral results observed showed that the binding of TZH to BSA induced conformational changes in BSA. Based on the Förster's theory of non-radiation energy transfer, the binding average distance, r between donor (BSA) and acceptor (TZH) was found to be 2.4 nm. The effect of common ions on binding of TZH to BSA was also examined.     

Study on the interaction of La with bovine serum albumin at molecular level

The interaction of La³⁺ to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra, and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by La³⁺ was a static quenching process and the binding constant is 1.75×10⁴ L mol⁻¹ and the number of binding sites is 1 at 289 K. The thermodynamic parameters (ΔH=−20.055 kJ mol⁻¹, ΔG=−23.474 kJ mol⁻¹, and ΔS=11.831 J mol⁻¹ K⁻¹) indicate that electrostatic effect between the protein and the La³⁺ is the main binding force. In addition, UV-vis, CD, and synchronous fluorescence results showed that the addition of La³⁺ changed the conformation of BSA.     

Study on the interaction between tabersonine and human serum albumin by optical spectroscopy and molecular modeling methods

The mechanism of interaction between tabersonine (TAB) and human serum albumin (HSA) was investigated by the methods of fluorescence spectroscopy, UV–vis absorption spectroscopy and molecular modeling under simulative physiological conditions. Results obtained from analysis of fluorescence spectrum and fluorescence intensity indicated that TAB has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding site number n and apparent binding constant K_a, corresponding thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were calculated. The distance r between donor (human serum albumin) and acceptor (tabersonine) was obtained according to the Förster theory of non-radiation energy transfer. The effect of common ions on binding constant was also investigated. The synchronous fluorescence and three-dimensional fluorescence spectra were used to investigate the structural change of HSA molecules with addition of TAB. Furthermore, the study of molecular modeling indicated that TAB could bind to the site I of HSA and hydrophobic interaction was the major acting force, which was in agreement with the binding mode study.     

Study on the interaction between promethazine hydrochloride and bovine serum albumin by fluorescence spectroscopy

The interaction between promethazine hydrochloride (PMT) and bovine serum albumin (BSA) in vitro was investigated by means of fluorescence spectroscopy and absorption spectroscopy. The fluorescence of BSA was quenched remarkably by PMT and the quenching mechanism was considered as static quenching by forming a complex. The association constants K_a and the number of binding sites n were calculated at different temperatures. The BSA-PMT binding distance was determined to be less than 8 nm, suggesting that energy transfer from BSA to PMT may occur. The thermodynamic parameters of the interaction between PMT and BSA were measured according to the van’t Hoff equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be −23.62 kJ mol⁻¹ and −0.10 J mol⁻¹ K⁻¹, respectively, which indicated that the interaction of PMT with BSA was driven mainly by van der Waals forces and hydrogen bonds. The binding process was a spontaneous process in which Gibbs free energy change (ΔG) was negative. In addition, the results of synchronous fluorescence spectra and three-dimensional fluorescence spectra showed that binding of PMT with BSA can induce conformational changes in BSA.     

Mechanistic and conformational studies on the interaction of anti-inflammatory drugs, isoxicam and tenoxicam with bovine serum albumin

The mechanism of interaction of the non-steroidal anti-inflammatory drugs, isoxicam (IXM) and tenoxicam (TXM) with bovine serum albumin (BSA) has been studied using spectroscopic techniques, viz., spectrofluorescence, circular dichroism (CD), UV-visible absorption and FT-IR under simulative physiological conditions. Stern-Volmer analysis of fluorescence quenching data shows the presence of the static quenching mechanism. Thermodynamic parameters (negative ΔH⁰ and positive ΔS⁰ values obtained in the present study) revealed that the hydrophobic interactions played a major role in the interaction of these drugs with BSA. The distance, r between the donor (BSA) and acceptor (IXM/TXM) was calculated based on the Forster’s theory of non-radiation energy transfer and the values were observed to be 3.85 nm and 2.60 nm in IXM-BSA and TXM-BSA system, respectively. CD and FT-IR studies indicated that the binding of IXM/TXM to BSA induced conformational changes in BSA. The effect of common ions on the binding of IXM/TXM to BSA has been investigated.     

Characterization of the interaction between human lactoferrin and lomefloxacin at physiological condition: Multi-spectroscopic and modeling description

The interaction between lomefloxacin (LMF) and human lactoferrin (Hlf) was studied by using fluorescence, circular dichroism (CD) spectroscopic and molecular modeling measurements. By the fluorescence quenching results, it was found that the binding constant K_A=8.69×10⁵ L mol⁻¹, and number of binding sites n=1.75 at physiological condition. Experimental results observed showed that the binding of LMF to Hlf induced conformational changes of Hlf. The participation of tyrosyl and tryptophanyl residues of protein was also estimated in the drug-Hlf complex by synchronous fluorescence. The quantitative analysis data of far-UV CD spectra from that of the α-helix 37.4% in free Hlf to 30.2% in the LMF-Hlf complex further confirmed that secondary structure of the protein was changed by LMF. Near-UV CD showed perturbations around tryptophan and tyrosine residues which involves perturbations of tertiary structure. The thermodynamic parameters like, ΔH° and ΔS°, have been calculated to be 63.411 kJ mol⁻¹ and 231.104 J mol⁻¹ K⁻¹, respectively. Thermodynamic analysis showed that hydrophobic interactions were the main force in the binding site but the hydrogen bonding and electrostatic interaction could not be excluded which in agreement with the result of molecular docking study. The distance r between donor and acceptor was obtained according to fluorescence resonance energy transfer (FRET) and found to be 1.78 nm. The interaction between LMF and Hlf has been verified as consistent with the static quenching procedure and the quenching mechanism is related to the energy transfer. Furthermore, the study of molecular modeling that LMF could bind to the α-helixes between Pro145-Asn152 and Phe167-Gln172 regions and hydrophobic interaction was the major acting force for the binding site, which was in agreement with the thermodynamic analysis.     

Investigation of proton pump inhibitors binding with bovine serum albumin and their relationship to molecular structure

The interactions of three proton pump inhibitors (PPIs), omeprazole, pantoprazole and ilaprazole with bovine serum albumin (BSA) have been investigated by fluorescence, synchronous fluorescence, ultraviolet–visible (UV–vis) and circular dichroism (CD). Various binding parameters have been calculated at various temperatures. The results indicated that omeprazole, pantoprazole and ilaprazole had a strong ability to quench the intrinsic fluorescence of BSA with static quenching mechanism, and the binding affinities were significantly affected by different substituents and polarities as the order ilaprazole>pantoprazole>omeprazole. The site marker competitive experiments indicated that the binding of omeprazole, pantoprazole and ilaprazole to BSA primarily took place in subdomain IIA. The results of thermodynamic parameters ΔG, ΔH and ΔS indicated that electrostatic interaction played a major role for PPIs–BSA association. The distance r between PPIs and BSA was evaluated according to the theory of Förster's energy transfer. The quantitative analysis of synchronous fluorescence and CD spectra showed the change in secondary structure of the BSA upon interaction with PPIs by a reduction of α-helix. All the above results many have relevant insight into the PPIs' availability and distribution.     

Investigation of three flavonoids binding to bovine serum albumin using molecular fluorescence technique

The three flavonoids including naringenin, hesperetin and apigenin binding to bovine serum albumin (BSA) at pH 7.4 was studied by fluorescence quenching, synchronous fluorescence and UV–vis absorption spectroscopic techniques. The results obtained revealed that naringenin, hesperetin and apigenin strongly quenched the intrinsic fluorescence of BSA. The Stern–Volmer curves suggested that these quenching processes were all static quenching processes. At 291 K, the value and the order of the binding constant were K_{A (naringenin)}=4.08×10⁴<K_{A (hesperetin)}=5.40×10⁴≈K_{A (apigenin)}=5.32×10⁴ L mol^?1. The main binding force between the flavonoid and BSA was hydrophobic and electrostatic force. According to the Förster theory of non-radiation energy transfer, the binding distances (r₀) were obtained as 3.36, 3.47 and 3.30 nm for naringenin–BSA, hesperetin–BSA and apigenin–BSA, respectively. The effect of some common ions such as Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺ and Ca²⁺ on the binding was also studied in detail. The competition binding was also performed. The apparent binding constant (K′_A) obtained suggested that one flavonoid had an obvious effect on the binding of another flavonoid to protein when they coexisted in BSA solution.     

Probing the interaction of flower-like CdSe nanostructure particles targeted to bovine serum albumin using spectroscopic techniques

The interaction between flower-like CdSe nanostructure particles (CdSe NP) and bovine serum albumin (BSA) was investigated from a spectroscopic angle under simulative physiological conditions. Under pH 7.4, CdSe NP could effectively quench the intrinsic fluorescence of BSA via static quenching. The binding constant (K_A) was 6.38, 3.27, and 1.90×10⁴ M⁻¹ at 298, 304, and 310 K, respectively and the number of binding sites was 1.20. According to the Van't Hoff equation, the thermodynamic parameters (ΔH°=−77.48 kJ mol⁻¹, ΔS°=−168.17 J mol⁻¹ K⁻¹) indicated that hydrogen bonds and van der Waals forces played a major role in stabilizing the BSA−CdSe complex. Besides, UV-vis and circular dichroism (CD) results showed that the addition of CdSe NP changed the secondary structure of BSA and led to a decrease in α-helix. These results suggested that BSA underwent substantial conformational changes induced by flower-like CdSe nanostructure particles.     

Study of Interaction of Silver Nanoparticles with Bovine Serum Albumin Using Fluorescence Spectroscopy

The interaction between silver nanoparticles (SNPs) and Bovine Serum Albumin (BSA) was investigated at physiological pH in an aqueous solution using fluorescence spectroscopy. The analysis of fluorescence spectrum and fluorescence intensity indicates that SNPs have a strong ability to quench the intrinsic fluorescence of BSA by both static and dynamic quenching mechanisms. Resonance light scattering (RLS) spectra indicated the formation of a complex between BSA and SNP. The number of binding sites ‘n’ and binding constants ‘K’ were determined at different temperatures based on fluorescence quenching. The thermodynamic parameters namely ∆H^°, ∆G^°, ∆S^° were calculated at different temperatures and the results indicate that hydrophobic forces are predominant in the SNP-BSA complex. Negative ∆G^° values imply that the binding process is spontaneous. Synchronous fluorescence spectra showed a blue shift which is indicative of increasing hydrophobicity.     

胡椒碱与牛血清白蛋白的相互作用

采用荧光光谱技术研究了胡椒碱与牛血清白蛋白（BSA）的相互作用。根据测定不同温度下胡椒碱对BSA的猝灭常数,证实了荧光猝灭过程为静态猝灭,由热力学参数焓变（ΔH）小于零和熵变（ΔS）大于零,推断出胡椒碱与BSA之间主要靠静电引力相结合,生成自由能变（ΔG）为负值,表明胡椒碱与BSA的作用过程是一个自发过程;并应用同步荧光光谱技术考察了胡椒碱对BSA构象的影响。