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.     

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.     

Study of the interaction between tosufloxacin tosylate and bovine serum albumin by multi-spectroscopic methods

The interaction of tosufloxacin tosylate (TSFX) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, UV–vis spectroscopy and FT-IR spectroscopy. The results indicated that the intrinsic fluorescence of BSA was quenched by TSFX through a static quenching mechanism, and the effective binding constants (K_a) were obtained by means of the modified Stern–Volmer equation. Thermodynamic parameters showed that electrostatic interaction was mostly responsible for the binding of TSFX to BSA. The binding distance (r) between TSFX and Trp-212 was determined to be 3.90 nm according to Föster non-radiative energy transfer theory. BSA had a single class of binding site at Sudlow' site I in subdomain IIA for TSFX. The effects of TSFX on the conformation of BSA were analyzed by synchronous fluorescence spectra and three-dimensional fluorescence spectra, and the results exhibited that the hydrophobicity of tryptophan microenvironment was decreased. In FT-IR spectra, Fourier self-deconvolution, secondary derivative and the curve-fitting process were carried out to obtain the components of BSA secondary structure at 298 K and 310 K. The full basic data indicated that the presence of TSFX resulted in α-helix and β-sheet changing into β-turn and random, which displayed that TSFX induced the unfolding of the polypeptides of BSA.     

A study on the binding interaction between the imidazole derivative and bovine serum albumin by fluorescence spectroscopy

The interaction between the imidazole derivative 2-(2,4-difluorophenyl)-1-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (dfppip) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. From the experimental results, it was found that the imidazole derivative has strong ability to quench the intrinsic fluorescence of BSA by forming complexes. Electrostatic interactions play an important role to stabilize the complex. The binding constants and the number of binding sites have been determined in detail. The distance (r) between the donor and the acceptor was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence spectroscopy. The effect of metal ions such as Cu²⁺, Zn²⁺, Ca²⁺, Mg²⁺, Ni²⁺, Co²⁺ and Fe²⁺ on the binding constants between the imidazole derivative and BSA were also studied.     

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.     

The Application of Two-dimensional Fluorescence Correlation Spectroscopy on the Interaction Between Bovine Serum Albumin and Paeonolum in the Presence of Fe(III)

The effect of Fe³⁺ on the interaction between bovine serum albumin (BSA) and paeonolum (PAL), which was extracted from the traditional Chinese herb, Paeonia suffruticosa Andr, was investigated by UV and fluorescence spectroscopy. Two-dimensional correlation spectroscopy was applied to the analysis of fluorescence spectra. The results of spectroscopic measurements suggested that PAL had a strong ability to quench the intrinsic fluorescence of BSA through static quenching procedure in the presence of Fe(III). Thermodynamic parameter enthalpy changes (ΔH) and entropy changes (ΔS) were calculated. The binding parameters including binding constant (K), and the distance (r) between PAL and BSA were evaluated on the basis of the theory of Föster energy transfer. Owing to the spectral resolution enhancement in 2D correlation spectroscopy, the structure change of PAL–Fe³⁺ can be observed.     

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 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.     

Spectroscopic studies on the binding of barbital to bovine serum albumin

In this paper, the interaction between barbital and bovine serum albumin (BSA) was investigated by the method of fluorescence spectroscopy under simulative physiological conditions. Fluorescence data revealed that the fluorescence quenching of BSA by barbital was the result of the formation of BSA-barbital complex, and the effective quenching constants (K_a) were 1.468×10⁴, 1.445×10⁴ and 1.403×10⁴ M⁻¹ at 297, 303 and 310 K, respectively. The thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS) for the reaction were calculated to be −2.679 kJ mol⁻¹ and 70.76 J mol⁻¹ K⁻¹, respectively, according to the van’t Hoff equation. The results indicated that hydrophobic and electrostatic interactions were the dominant intermolecular force in stabilizing the complex. The results of synchronous fluorescence spectra showed that binding of barbital with BSA can induce conformational changes in BSA. In addition, the effects of Cu²⁺ and Zn²⁺ on the constants of BSA-barbital complex were also discussed.     

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.     

Study on the interaction between methyl blue and human serum albumin by fluorescence spectrometry

The interaction of methyl blue (MB) with human serum albumin (HSA) was studied by fluorescence and absorption spectroscopy. The intrinsic fluorescence of HSA was quenched by MB, which was rationalized in terms of the static quenching mechanism. The number of binding sites and the apparent binding constants at different temperatures were obtained from the Stern-Volmer analysis of the fluorescence quenching data. The thermodynamic parameters determined by the van’t Hoff analysis of the binding constants (ΔH°=39.8 kJ mol⁻¹ and ΔS°=239 J mol⁻¹ K⁻¹) clearly indicate that binding is absolutely entropy-driven and enthalpically disfavored The efficiency of energy transfer and the distance between the donor (HSA) and the acceptor (MB) were calculated as 60% and 2.06 nm from the Förster theory of non-radiation energy transfer.     

Complexes between C.I. Acid Orange 6 and human serum albumin, a multi-spectroscopic approach to investigate the binding behavior

The interaction mechanism of Acid Orange 6 (AO6) with human serum albumin (HSA) was investigated firstly by using fluorescence quenching technique, UV absorbance, circular dichroism (CD), Fourier transform infrared (FT-IR), three-dimensional fluorescence spectroscopy in combination with molecular modeling method under simulative physiological conditions. Fluorescence data indicated that there is a single class of binding sites between AO6 and HSA, and the alterations of HSA secondary structure in the presence of AO6 was confirmed by synchronous fluorescence, UV, CD, FT-IR and three-dimensional fluorescence spectra. The efficiency of fluorescence resonance energy transfer provided the binding distance (r) of 2.83 nm for AO6-HSA system. Furthermore, the thermodynamic parameters enthalpy change (ΔH⁰) and entropy change (ΔS⁰) for the reaction were calculated to be −5.77 kJ mol⁻¹ and 109.42 J mol⁻¹ K⁻¹, respectively, according to Van't Hoff equation, these data suggested that both hydrophobic forces and hydrogen bonding play a major role in the binding of AO6 to HSA, which agrees well with the results of molecular modeling study. Experimental results showed that the interaction between AO6 and HSA induced a conformational change of HSA, which was proved by the qualitative and quantitative analysis data of different spectroscopic techniques under simulative physiological conditions.     

Spectrophotometric studies on the interaction between myricetin and lysozyme in the absence or presence of Cuor Fe

The binding of myricetin to lysozyme (Lys) in aqueous solution was investigated by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy (UV) and circular dichroism (CD) spectra under physiological conditions. There are also many metal ions present in body, thus the research about the effect of metal ions on the interaction of drugs with proteins is crucial. In this study, we have investigated the effect of both familiar metal ions Cu²⁺ and Fe³⁺ on the interaction between myricetin and Lys by using spectroscopy technique at pH 7.40, for the first time. Spectrophotometric observations are rationalized in terms of a static quenching process in a static quenching way. The cause of showing upward curvy patterns in Stern-Volmer plots was analyzed. The binding constants and binding sites of myricetin with Lys with or without Cu²⁺ and Fe³⁺ at different concentrations of myricetin were calculated. UV/vis measurements on the enzymatic activity of Lys with or without Cu²⁺ in the absence or presence of myricetin indicated that the interaction between myricetin and Lys led to a reduction in the activity of Lys. Furthermore, the effect of pH on the binding constant of myricetin with Lys was also examined.     

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.     

Probing the binding of vitexin to human serum albumin by multispectroscopic techniques

The interaction between vitexin and human serum albumin (HSA) has been studied by using different spectroscopic techniques viz., fluorescence, UV-vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy under simulated physiological conditions. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of vitexin to HSA. The binding constants (K_a) between vitexin and HSA were obtained according to the modified Stern-Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were calculated to be -57.29 kJ mol⁻¹ and -99.01 J mol⁻¹ K⁻¹ via the van't Hoff equation, which indicated that the interaction of vitexin with HSA was driven mainly by hydrogen bond and van der Waals forces. Fluorescence anisotropy data showed that warfarin and vitexin shared a common binding site I corresponding to the subdomain IIA of HSA. The binding distance (r) between the donor (HSA) and the acceptor (vitexin) was 4.16 nm based on the Förster theory of non-radioactive energy transfer. In addition, the results of synchronous fluorescence, CD and FT-IR spectra demonstrated that the microenvironment and the secondary structure of HSA were changed in the presence of vitexin.     

Interaction of Salicylic Acid with Bovine Hemoglobin and Effect of the Coexistent Metal Ion on the Reaction

The interaction between bovine hemoglobin (BHb) and salicylic acid (SA) was investigated at different temperatures by fluorescence spectroscopy, as was the effect of common metal ions (Mg²⁺, Zn²⁺, Cu²⁺, Co²⁺, Fe³⁺, Ni²⁺) on the BHb–SA system. Results showed that the quenching mechanism of SA on BHb was a static quenching process. The electrostatic force played an important role in the conjugation reaction between BHb and SA. Besides, the values of Hill's coefficients were approximately equal to 1. Synchronous and CD spectra revealed that the microenvironment and the conformation of BHb were changed during the binding reaction.     

Methylene blue as a DNA probe for a comparative study of Cd, Pb and Cr ions binding to calf thymus DNA

Methylene blue (MB) was developed as a sensitive DNA probe for a comparative study of Cd²⁺, Pb²⁺ and Cr³⁺ ions binding with calf thymus DNA (ctDNA). The fluorescence intensity of the MB-ctDNA system increased dramatically when heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺ ions) were added, which indicated that some of the bound MB molecules were released from the ctDNA base pairs. To compare the binding affinity of these three different heavy metal ions with ctDNA, the relationships between the fluorescence intensity of the MB-ctDNA-M (Metal ions) system and the concentration ratio of [M]/[DNA(p)] were investigated. The results showed that the order of the binding affinity of heavy metal ions with ctDNA had the following sequence: Cr³⁺> Cd²⁺>Pb²⁺. This order was further proved by the effects of heavy metal ions on the number of MB bound to ctDNA, the measurements of binding constants of these heavy metal ions to ctDNA, and the effects of heavy metal ions on the absorption of the MB-ctDNA system. In addition, the interaction mechanisms of Cd²⁺, Pb²⁺ and Cr³⁺ ions with ctDNA were also discussed in detail. These results indicated that their interaction mechanisms are related to the concentration ratios of heavy metal ions to DNA.     

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.     

Interaction of the docetaxel with human serum albumin using optical spectroscopy methods

Docetaxel is a semi-synthetic product derived from the needles of the European yew. It is an antineoplastic agent belonging to the taxoid family. The interaction between docetaxel and human serum albumin (HSA) has been investigated systematically by the fluorescence quenching technique, synchronous fluorescence spectroscopy, ultraviolet (UV)-vis absorption spectroscopy, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) under physiological conditions. Our fluorescence data showed that HSA had only one docetaxel binding site and the binding process was a static quenching procedure. According to the Van’t Hoff equation, the thermodynamic parameters standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) were calculated to be −41.07 KJ mol⁻¹ and −49.72 J mol⁻¹ K⁻¹. These results suggested that hydrogen bond was the predominant intermolecular force stabling the docetaxel-HSA complex. The data from the CD, FT-IR and UV-vis spectroscopy supported the change in the secondary structure of protein caused by the interaction of docetaxel with HSA.     

Study of the interaction between fluoxetine hydrochloride and bovine serum albumin in the imitated physiological conditions by multi-spectroscopic methods

The mechanism of interaction of an antidepressant, fluoxetine hydrochloride (FLX) with bovine serum albumin (BSA) has been studied by different spectroscopic techniques under physiological conditions. FLX was found to quench the intrinsic fluorescence of protein by static quenching mechanism. The binding constant ‘K’ was found to be 7.06×10³ M⁻¹ at 296 K. The value of ‘n’ close to unity revealed that the BSA has a single class of binding site for FLX. Based on thermodynamic parameters, hydrogen bonding and van der Waals forces were proposed to operate between BSA and FLX. The change in conformation of protein was noticed upon its interaction with the drug. From displacement studies it was concluded that the FLX bound to protein at site I. The effects of various common metals ions on the binding were also investigated.