Studies of interaction between colchicine and bovine serum albumin by fluorescence quenching method

The effects and mechanism of flavonoid-rePON1 interactions. Structure-activity relationship study

Flavonoids are plant phenolic secondary metabolites that are widely distributed in the human diet. These antioxidants have received much attention because of their neuroprotective, cardioprotective, and chemopreventive actions. While a major focus has been on the flavonoids' antioxidant properties, there is an emerging view that many of the potential health benefits of flavonoids and their in vivo metabolites are due to modulatory actions in cells through direct interactions with proteins, and not necessarily due to their antioxidant function. This view relies on the observations that flavonoids are present in the circulation at very low concentrations, which are not sufficient to exert effective antioxidant effects. The enzyme paraoxonase 1 (PON1) is associated with high-density lipoprotein (HDL), and is responsible for many of HDLs' antiatherogenic properties. We previously showed that the flavonoid glabridin binds to rePON1 and affects the enzyme's 3D structure. This interaction protects the enzyme from inhibition by an atherogenic component of the human carotid plaque. Here, we broadened our study to an investigation of the structure-activity relationships (SARs) of 12 flavonoids from different subclasses with rePON1 using Trp-fluorescence quenching, modeling calculations and Cu(2+)-induced low-density lipoprotein (LDL) oxidation methods. Our findings emphasize the 'protein-binding' mechanism by which flavonoids exert their beneficial biological role toward rePON1. Flavonoids' capacity to interact with the enzyme's rePON1 hydrophobic groove mostly dictates their pro/antioxidant behavior.

Synthesis, spectroscopic investigations, antimicrobial and DNA binding studies of a new charge transfer complex of o-phenylenediamine with 3,5-dinitrosalicylic acid

A charge transfer complex of o-phenylenediamine (OPD) as donor with 3,5-dinitrosalicylic acid (DNSH) as acceptor, was synthesized and characterized by FTIR, (1)H NMR, (13)C NMR, mass spectroscopy, elemental analysis and X-ray crystallography. The structural investigations exhibit that the cation and anion are joined together by strong N(+)H⋯O(-) type hydrogen bonds and stoichiometry of CT complex was found to be 1:1. The CT (charge transfer) complex shows remarkable interaction with Calf thymus DNA, and the CT complex was also screened for its microbial activity such as antimicrobial and antifungal activities. A molecular frame work through H-bonding interactions via n→π(*) transitions between neighboring moieties is found which is responsible for high melting point of resulting CT complex. This has been attributed to the formation of 1:1 CT complex.

Oroxylin A inhibits hemolysis via hindering the self-assembly of α-hemolysin heptameric transmembrane pore

Alpha-hemolysin (α-HL) is a self-assembling, channel-forming toxin produced by most Staphylococcus aureus strains as a 33.2-kDa soluble monomer. Upon binding to a susceptible cell membrane, the monomer self-assembles to form a 232.4-kDa heptamer that ultimately causes host cell lysis and death. Consequently, α-HL plays a significant role in the pathogenesis of S. aureus infections, such as pneumonia, mastitis, keratitis and arthritis. In this paper, experimental studies show that oroxylin A (ORO), a natural compound without anti-S. aureus activity, can inhibit the hemolytic activity of α-HL. Molecular dynamics simulations, free energy calculations, and mutagenesis assays were performed to understand the formation of the α-HL-ORO complex. This combined approach revealed that the catalytic mechanism of inhibition involves the direct binding of ORO to α-HL, which blocks the conformational transition of the critical “Loop” region of the α-HL protein thereby inhibiting its hemolytic activity. This mechanism was confirmed by experimental data obtained from a deoxycholate-induced oligomerization assay. It was also found that, in a co-culture system with S. aureus and human alveolar epithelial (A549) cells, ORO could protect against α-HL-mediated injury. These findings indicate that ORO hinders the lytic activity of α-HL through a novel mechanism, which should facilitate the design of new and more effective antibacterial agents against S. aureus.

The mechanism controlling protein-ligand interactions is one of the most important processes in rational drug design. X-ray crystallography is a traditional tool used to investigate the interaction of ligands and proteins in a complex. However, protein crystallography is inefficient, and the development of crystal technology and research remains unequally distributed. Thus, it seems impractical to explore the structure of the α-hemolysin-ORO monomer complex by crystallography. Therefore, we used molecular dynamics simulations to investigate the receptor-ligand interaction in the α-HL-ORO monomer complex. In this study, we found that oroxylin A (ORO), a natural compound with little anti-S. aureus activity, can inhibit the hemolytic activity of α-HL at low concentrations. Through molecular docking and molecular dynamics simulations, we determined the potential binding mode of the protein-ligand interaction. The data revealed that ORO directly binds to α-HL, an interaction that blacks the conformational transition of the critical “Loop” region in α-HL and thus prevents the formation of the α-HL heptameric transmembrane pore, which ultimately inhibits the hemolytic activity of α-HL. This mechanism was confirmed by experimental data. Furthermore, we demonstrated that ORO could protect against α-HL-mediated injury in human alveolar epithelial (A549) cells.

Molecular insight into the inhibition mechanism of cyrtominetin to α-hemolysin by molecular dynamics simulation

The protein α-hemolysin (α-HL) is a self-assembling exotoxin that binds to the membrane of a susceptible host cell. In this paper, experimental studies show that cyrtominetin (CTM) can inhibit the hemolytic activity of α-HL. To understand how CTM can affect hemolytic activity, molecular dynamics simulations were carried out for α-HL-CTM complex and these results were compared with the crystal structure of monomeric α-HL. With this approach, the analysis revealed that the inhibition of CTM involves CTM directly binding to α-HL. Due to the binding of CTM, the conformation of the critical "Loop" region was restrained. This mechanism was confirmed by the experimental data. These findings indicate that CTM hinders the lysis activity of α-HL through a novel mechanism.

Spectroscopic analyses on interaction of Naphazoline hydrochloride with bovine serum albumin

The fluorescence and ultraviolet spectroscopy were explored to study the interaction between Naphazoline hydrochloride (Naphcon) and bovine serum albumin (BSA) at three different temperatures (292, 301, and 310 K) under imitated physiological conditions. The quenching mechanism of BSA by Naphacon was interpreted using the Stern-Volmer mechanism, and 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 BSA and Naphcon was found to be 4.71 nm. Synchronous fluorescence spectroscopy showed the conformation of BSA changed in the presence of Naphacon. In addition, the effect of some common metal ions (Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Fe(2+)) on the binding constant between Naphcon and BSA was examined.

Spectroscopic studies on the interactions between CdTe quantum dots coated with different ligands and human serum albumin

This paper investigates the interactions between human serum albumin (HSA) and CdTe quantum dots (QDs) with nearly identical hydrodynamic size, but capped with four different ligands (MPA, NAC, and GSH are negatively charged; CA is positively charged) under physiological conditions. The investigation was carried out using fluorescence spectroscopy, circular dichroism (CD) spectra, UV-vis spectroscopy, and dynamic light scattering (DLS). The results of fluorescence quenching and UV-vis absorption spectra experiments indicated the formation of the complex of HSA and negatively charged QDs (MPA-CdTe, NAC-CdTe, and GSH-CdTe), which was also reconfirmed by the increasing of the hydrodynamic radius of QDs. The K(a) values of the three negatively charged QDs are of the same order of magnitude, indicating that the interactions are related to the nanoparticle itself rather than the ligands. ΔH<0 and ΔS>0 implied that the electrostatic interactions play predominant roles in the adsorption process. Furthermore, it was also proven that QDs can induce the conformational changes of HSA from the CD spectra and the three-dimensional fluorescence spectra of HSA. However, our results demonstrate that the interaction mechanism between the positively charged QDs (CA-CdTe) and HSA is significantly different from negatively charged QDs. For CA-CdTe QDs, both the static and dynamic quenching occur within the investigated range of concentrations. According to the DLS results, some large-size agglomeration also emerged.

Investigation on the site-selective binding of bovine serum albumin by erlotinib hydrochloride

The purpose of this study was to investigate the site-selective binding of erlotinib hydrochloride (ET), a targeted anticancer drug, to bovine serum albumin (BSA) through 1H NMR, spectroscopic, thermodynamic, and molecular modeling methods. The fluorescence quenching of BSA by ET was a result of the formation of BSA-ET complex with high binding affinity. The site marker competition study combined with isothermal titration calorimetry experiment revealed that ET binds to site II of BSA mainly through hydrogen bond and van der Waals force. Molecular docking was further applied to define the specific binding site of ET to BSA. The conformation of BSA was changed in the presence of ET, revealed by synchronous fluorescence, circular dichroism, and three-dimensional fluorescence spectroscopy results. Further, NMR analysis of the complex revealed that the binding capacity contributed by the aromatic protons in the binding site of BSA might be greater than the aliphatic protons. An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:26.

BSA binding and antimicrobial studies of branched polyethyleneimine-copper(II)bipyridine/phenanthroline complexes

The interaction of two water soluble branched polyethyleneimine-copper(II) complexes containing bipyridine/phenanthroline with bovine serum albumin (BSA) was studied by, UV-Visible absorption, fluorescence, lifetime measurements and circular dichroism spectroscopic techniques. The polymer-copper(II) complexes strongly quench the intrinsic fluorescence of BSA is the static quenching mechanism through hydrogen bonds and van der Waal's attraction. The distance r, between the BSA and the complexes seems to be less than 2 nm indicating that the energy transfer between the donor and acceptor occurs with high probability. Synchronous fluorescence studies indicate the binding of polymer-copper(II) complexes with BSA mostly changes the polarity around tryptophan residues rather than tyrosine residues. The circular dichroism studies indicate that the binding has induced considerable amount of conformational changes in the protein. The complexes also show some antibacterial and antifungal properties.

Spectroscopic investigation on the interaction of 9-aminoacridine with certain dyes

The fluorescence quenching of 9-Aminoacridine (9-AA) by various dyes were probed in aqueous medium using steady state and time resolved fluorescence spectroscopic techniques. From these techniques, we had rationalized the interaction of 9-AA with various dyes via ground state complex formation. The binding constant (K) and number of binding sites (n) were calculated from the relevant fluorescence quenching data. The fluorescence emission of 9-Aminoacridine was quenched by the dyes through static quenching followed by the mechanism of energy transfer. The static quenching mechanism was confirmed by lifetime measurements. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The results showed that Van der Waals interaction or hydrogen bond formation played a major role in the binding of 9-AA with these dyes.

Potential toxicity of sulfanilamide antibiotic: binding of sulfamethazine to human serum albumin

Antibiotics are widely used in daily life but their abuse has posed a potential threat to human health. The interaction between human serum albumin (HSA) and sulfamethazine (SMZ) was investigated by capillary electrophoresis, fluorescence spectrometry, and circular dichroism. The binding constant and site were determined to be 1.09×10(4) M(-1) and 1.14 at 309.5 K. The thermodynamic determination indicated that the interaction was driven by enthalpy change, where the electrostatic interaction and hydrogen bond were the dominant binding force. The binding distance between SMZ and tryptophan residue of HSA was obtained to be 3.07 nm according to Fǒrster non-radioactive energy transfer theory. The site marker competition revealed that SMZ bound into subdomain IIA of HSA. The binding of SMZ induced the unfolding of the polypeptides of HSA and transferred the secondary conformation of HSA. The equilibrium dialysis showed that only 0.13 mM SMZ decreased vitamin B(2) by 38% transported on the HSA. This work provides a new quantitative evaluation method for antibiotics to cause the protein damage.

Spectroscopic studies on the interaction of bovine serum albumin with surfactants and apigenin

The binding of apigenin (Ap) to bovine serum albumin (BSA) has been studied using the methods of fluorescence spectroscopy and UV-vis absorption spectroscopy. The spectroscopic analysis of the quenching mechanism indicates that the quenching constants are inversely correlated with the temperatures and the quenching process could result from a static interaction. The type of interaction force was discussed and the binding site of Ap was in site I (subdomain IIA) of BSA. The thermodynamic parameters ΔH and ΔS are -42.02kJ mol(-1) and -48.31J mol(-1)K(-1), respectively and the negative ΔG implying that the binding interaction was spontaneous. The distance r between BSA and Ap was calculated according to Förster's theory and the value is 3.44nm. The synchronous and three-dimensional fluorescence spectra show that the binding of Ap to BSA could lead to the changes in the conformation and microenvironment of BSA. At the same time, the effects of ionic surfactants on the interaction of Ap and BSA have also been investigated.

Study on the interaction between novel spiro pyrrolidine and bovine serum albumin by spectroscopic techniques

Spiro pyrrolidines, which were proved with diverse and potent biological activities and they were discovered widespread in nature. In this paper, using fluorescence and ultraviolet spectroscopy, we investigated the interactions between novel spiro pyrrolidine (NSP) and bovine serum albumin (BSA) under the imitated physiological condition. The results show that the NSP binds to BSA molecules. Static quenching and non-radiation energy transfer are the main reasons for fluorescence quenching. We calculated the binding constant (K(a)) and binding sites (n) at different temperatures and obtained the binding distance between the tryptophan residue in BSA and the NSP based on the Förster theory of non-radiation energy transfer. In addition, using synchronous fluorescence spectra, we demonstrated conformation changes of BSA caused by NSP. The comparison of binding potency of NSP and BSA suggests that the substituent on the benzene ring influences the binding ability of NSP and BSA.

Synthesis, spectroscopic characterization, DNA interaction and antibacterial study of metal complexes of tetraazamacrocyclic Schiff base

The template condensation reaction between benzil and 3,4-diaminotoulene resulted mononuclear 12-membered tetraimine macrocyclic complexes of the type, [MLCl(2)] [M=Co(II), Ni(II), Cu(II) and Zn(II)]. The synthesized complexes have been characterized on the basis of the results of elemental analysis, molar conductance, magnetic susceptibility measurements and spectroscopic studies viz. FT-IR, (1)H and (13)C NMR, FAB mass, UV-vis and EPR. An octahedral geometry has been envisaged for all these complexes, while a distorted octahedral geometry has been noticed for Cu(II) complex. Low conductivity data of all these complexes suggest their non-ionic nature. The interactive studies of these complexes with calf thymus DNA showed that the complexes are avid binders of calf thymus DNA. The in vitro antibacterial studies of these complexes screened against pathogenic bacteria proved them as growth inhibiting agents.

4-alkoxyethoxy-N-octadecyl-1,8-naphthalimide fluorescent sensor for human serum albumin and other major blood proteins: design, synthesis and solvent effect

A series of 4-alkoxyethoxy-N-octadecyl-1,8-naphthalimides with intense blue fluorescence were designed and synthesized as polarity and spectrofluorimetric probes for the determination of proteins. In solvents of different polarities, the Stokes shifts of two dyes increased with increasing solvent polarity and fluorescence quantum yields decreased significantly, suggesting that electronic transiting from ground to excited states was π-π(*) in character. Dipole moment changes were estimated from solvent-dependent Stokes shift data using a solvatochromic method based on bulk solvent polarity functions and the microscopic solvent polarity parameter (E(T)N). These results were generally consistent with semi-empirical molecular orbital calculations and were found to be quite reliable based on the fact that the correlation of the solvatochromic Stokes shifts with E(T)N was superior to that obtained using bulk solvent polarity functions. Fluorescence data revealed that the fluorescence quenching of human serum albumin (HSA) by dyes was the result of the formation of a Dye-HSA complex. The method was applied to the determination of total proteins (HSA + immunoglobulins) in human serum samples and results were in good agreement with those reported by the research institute.

Nickel(II)-Schiff base complex recognizing domain II of bovine and human serum albumin: spectroscopic and docking studies

It has been spectroscopically monitored that a mononuclear nickel(II)-Schiff base complex {[NiL]·CH(3)OH=NSC} exhibits greater binding affinity for bovine serum albumin (BSA) than that of its human counterpart (HSA). Moreover the modes of binding of NSC with the two serum albumins also differ significantly. Docking studies predict a relatively rare type of 'superficial binding' of NSC at domain IIB of HSA with certain mobility whereas for BSA such phenomena has not been detected. The mobile nature of NSC at domain IIB of HSA has been well correlated with the spectroscopic results. It is to be noted that thermodynamic parameters for the NSC interaction also differ for the two serum albumins. Occurrence of energy transfer between the donor (Trp of BSA and HSA) and acceptor (NSC) has been obtained by means of Förster resonance energy transfer (FRET). The protein stability on NSC binding has also been experimented by the GuHCl-induced protein unfolding studies. Interestingly it has been found that NSC-HSA interaction enhances the protein stability whereas NSC-BSA binding has no such impact. Such observations are indicative of the fact that the conformation of NSC is responsible in recognizing the two serum albumins and selectively enhancing protein stability.

Optical spectroscopic exploration of binding of Cochineal Red A with two homologous serum albumins

Cochineal Red A is a negatively charged synthetic azo food colorant and a potential carcinogen. We present here the study of binding of Cochineal Red A with two homologous serum albumins, human (HSA) and bovine (BSA), in aqueous pH 7.4 buffer by optical spectroscopic techniques. Protein intrinsic fluorescence quenching by Cochineal Red A occurs through ground-state static interaction and its binding with BSA is stronger than with HSA. The magnitudes of thermodynamic parameters suggest that dye binding occurs principally via electrostatic complexation. Site-marker competitive binding shows that Cochineal Red A binds primarily to site I of serum albumins. Circular dichroic spectra indicate that dye binding results in some conformational modification of serum albumins. Increased ionic strength of the medium results in lowering of binding. This study provides an important insight into possible means of removal of dye toxicity.

Glabridin protects paraoxonase 1 from linoleic acid hydroperoxide inhibition via specific interaction: a fluorescence-quenching study

The enzyme paraoxonase 1 (PON1) binds to high-density lipoprotein (HDL) and is responsible for many of HDL's antiatherogenic properties. We previously showed that recombinant PON1 is inhibited by linoleic acid hydroperoxide (LA-OOH) present in the lipid fraction of the human carotid plaque (LLE) via oxidation of the enzyme's Cys284 thiol. Here we explore the effect of glabridin, an isoflavan isolated from licorice root, on preventing LA-OOH's inhibitory effect on rePON1 using the tryptophan-fluorescence-quenching technique and modeling calculations. Glabridin significantly prevented rePON1 inhibition by LLE or oxidized linoleic acid (by 22% and 15%, respectively), whereas ascorbic acid and Trolox, strong antioxidants, had no effect. Glabridin quenched the intrinsic fluorescence of rePON1 in a concentration-dependent manner. Binding parameters and modeling calculations demonstrated a major role for hydrophobic forces in the rePON1-glabridin interaction, indicating that it is not the antioxidant capacity of glabridin that protects rePON1 from LA-OOH inhibition, but rather its specific interaction with the enzyme.

Investigations on photoinduced interaction of 9-aminoacridine with certain catechols and rutin

The fluorescence quenching of 9-aminoacridine by certain biologically important catechols and rutin was investigated using absorption, steady state and time resolved fluorescence measurements. The in vitro-antioxidant activities of the above compounds were studied using deoxyribose degradation assay and nitric oxide scavenging assay. The experimental results showed that the fluorescence of 9-aminoacridine was quenched by quencher molecules via forming ground state complex. The bimolecular quenching rate constant k(q), binding constant (K) and number of binding sites (n) were calculated at different temperatures from relevant fluorescence data. Static quenching mechanism was supported by lifetime measurement. The free energy change (ΔG(et)) for electron transfer process was calculated by Rehm-Weller equation. The binding distance of 4-nitrocatechol with 9-aminoacridine was obtained according to Forster's non-radiative energy transfer theory. Nature of binding forces and their interactions was probed based on thermodynamic parameters.

Photoinduced electron-transfer from imidazole derivative to nano-semiconductors

Bioactive imidazole derivative absorbs in the UV region at 305 nm. The interaction of imidazole derivative with nanoparticulate WO3, Fe2O3, Fe3O4, CuO, ZrO2 and Al2O3 has been studied by UV-visible absorption, FT-IR and fluorescence spectroscopies. The imidazole derivative adsorbs strongly on the surfaces of nanosemiconductor, the apparent binding constants for the association between nanomaterials and imidazole derivative have been determined from the fluorescence quenching. In the case of nanocrystalline insulator, fluorescence quenching through electron transfer from the excited state of the imidazole derivative to alumina is not possible. However, a possible mechanism for the quenching of fluorescence by the insulator is energy transfer, that is, energy transferred from the organic molecule to the alumina lattice. Based on Forster's non-radiation energy transfer theory, the distance between the imidazole derivative and nanoparticles (r0∼2.00 nm) as well as the critical energy transfer distance (R0∼1.70 nm) has been calculated. The interaction between the imidazole derivative and nanosurfaces occurs through static quenching mechanism. The free energy change (ΔGet) for electron transfer process has been calculated by applying Rehm-Weller equation.

Characterization of the interaction between 4-(tetrahydro-2-furanmethoxy)-N-octadecyl-1,8-naphthalimide and human serum albumin by molecular spectroscopy and its analytical application

A novel 4-(tetrahydro-2-furanmethoxy)-N-octadecyl-1,8-naphthalimide (TNN) was synthesized as a spectrofluorimetric probe for the determination of proteins. The effect of different solvents on the spectral characteristics of TNN was investigated. The results showed that TNN displayed dependent solvent polarity properties due to the effect of internal charge transfer. The interactions between TNN and human serum albumin (HSA) were studied by fluorescence and absorption spectroscopy. Fluorescence data revealed that the fluorescence quenching of HSA by TNN was the result of the formation of TNN-HSA complex. The binding parameters of interactions between TNN and HSA at different temperatures were obtained according to the Stern-Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), for the interactions were calculated to be -7.31 kJ mol(-1) and 72.75 J mol(-1) K(-1) according to the van't Hoff equation, indicating that the hydrogen bonds and hydrophobic interactions were the dominant intermolecular force in stabilizing the complex. The effect of TNN on the conformation of HSA was analyzed by circular dichroism and synchronous fluorescence spectroscopy. Furthermore, the results of displacement experiments using warfarin indicated that TNN could bind to site I of HSA. The fluorescence of TNN could be largely quenched by HSA, based on which a new fluorometric method for detecting HSA in the HCl-Tris buffer solution (pH = 7.4) was developed. The linear ranges of the calibration curves were 0.1~14.2 μM for HSA, 0.1~13.0 μM for bovine serum albumin (BSA), 0.2~9.7 μM for γ-globulin, and 0.3~11.3 μM for hemoglobin (Hb), with detection limits (3σ) of 1.37 × 10(-10) M for HSA, 1.84 × 10(-10) M for BSA, 3.14 × 10(-10) M for γ-globulin, and 6.86 × 10(-10) M for Hb. The effect of metal cations on the fluorescence spectra of TNN in ethanol was also investigated. The method has been applied to the determination of total proteins in human serum samples collected from the hospital and the results were in good agreement with those reported by the hospital.

Interaction of avelox with bovine serum albumin and effect of the coexistent drugs on the reaction

The interaction between Avelox and bovine serum albumin (BSA) was investigated at different temperatures by fluorescence spectroscopy. Results showed that Avelox could quench the intrinsic fluorescence of BSA strongly, and the quenching mechanism was a static quenching process with Förester spectroscopy energy transfer. The electrostatic force played an important role on the conjugation reaction between BSA and Avelox. The order of magnitude of binding constants (K_a) was 10⁴, and the number of binding site (n) in the binary system was approximately equal to 1. The binding distance (r) was less than 3 nm and the primary binding site for Avelox was located in subdomain IIA of BSA. Synchronous fluorescence spectra clearly revealed that the microenvironment of amino acid residues and the conformation of BSA were changed during the binding reaction. In addition, the effect of some antibiotics on the binding constant of Avelox with BSA was also studied.

In vitro investigation of the interaction between pentachlorophenol and alkaline phosphatase by spectroscopic methods

The interaction characteristics of alkaline phosphatase (ALP) with pentachlorophenol (PCP) were investigated using fluorescence, UV-vis absorption, and circular dichroism (CD) techniques. Results obtained from analysis of fluorescence intensity indicated that PCP has a strong ability to quench the intrinsic fluorescence of ALP through a static quenching procedure. The thermodynamic parameters ΔH and ΔS were observed to be -4.60kJmol(-1) and 54.59Jmol(-1)K(-1), respectively, and the value of ΔG was negative. These results indicate that the binding reactions were spontaneous, and both hydrophobic and electrostatic forces were involved in the interaction of PCP and ALP. Based on Forster's theory of non-radiation energy transfer, the binding distance, r, between the ALP and PCP was evaluated to be 2.50nm and the critical distance R(0) was 2.26nm. The CD spectra results showed that the α-helicity was decreased from 49.68% in native ALP to 47.28% in PCP-ALP systems, which indicate the secondary structure of ALP was changed slightly in the presence of PCP.

Spectroscopic studies on the interaction between an anticancer drug ampelopsin and bovine serum albumin

The interaction between bovine serum albumin (BSA) and the anticancer drug molecule ampelopsin (AMP) was investigated using fluorescence spectroscopy, circular dichroism (CD) spectra, and time-resolved spectra under simulated physiological conditions. Fluorescence data showed that the intrinsic fluorescence of BSA was strongly quenched by AMP in terms of a dynamic quenching process. Binding constants and binding sites were calculated. The thermodynamic parameters indicated that the hydrogen bonding and weak van der Waals force played a major role in the interaction. The site marker competitive experiments suggested that the binding site of AMP and BSA was probably located on site III. Based on the Förster's theory, the average binding distance between AMP and BSA was obtained (r=5.47nm). The binding of AMP and BSA leaded to conformational changes of BSA according to synchronous fluorescence spectra, CD data and mean fluorescence lifetime values.

Study on the interaction between isoniazid and bovine serum albumin by fluorescence spectroscopy: the effect of dimethylsulfoxide

The investigation of the binding between isoniazid (or isonicotinic acid hydrazide, INH) and serum albumin is of crucial importance to reveal the reason of resistant Mycobacterium tuberculosis strains towards INH and to increase the anti-tuberculous activity of INH. The interaction between INH and bovine serum albumin (BSA) was studied by fluorescence, UV and FT-IR spectroscopy methods. The analysis of the emission quenching at different temperatures revealed that the quenching mechanism corresponds to a static process and, as consequence; a complex INH-BSA is formed. The modified Stern-Volmer quenching constant K (a) and the corresponding thermodynamic parameters ΔH, ΔG and ΔS were calculated. The distance, r, between donor (BSA) and acceptor (INH) was calculated to be 2.14 nm based on Förster's non-radiative energy transfer theory (FRET). The results obtained on the basis of fluorescence study of BSA solutions at the presence of dimethylsulfoxide (DMSO) were discussed in terms of the hydration properties and competitive intermolecular interactions between BSA and solvent components. The dependence of binding constant on the concentration of added DMSO as a solvent component showed non monotonous behavior. The conformational changes of BSA and its secondary structure alterations at the presence of INH were revealed.

Luminescent study on the binding interaction of bioactive imidazole with bovine serum albumin-A static quenching mechanism

Novel bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. The interaction between the imidazole derivative and bovine serum albumin (BSA) was investigated by fluorescence and UV-vis absorption spectroscopy. The fluorescence quenching of BSA by the imidazole derivatives may be due to the formation of imidazole-BSA complex. The fluorescence quenching mechanism of BSA by imidazole was analyzed and the binding constant has been calculated. The binding distance between imidazole and BSA was obtained based on Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant between imidazole and BSA was also examined.

Binding interaction of bioactive imidazole with bovine serum albumin--a mechanistic investigation

A novel Y-shaped imidazole derivative 4-((E)-2-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)vinyl)phenol has been synthesized and characterised by IR, UV-vis, mass and NMR spectral techniques. The mutual interaction of this imidazole derivative (DPTIV) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by DPTIV was analyzed and the binding constant has been calculated. The binding distance between DPTIV and BSA was obtained based on the theory of Forester's non-radiation energy transfer. The effect of some common ions on the binding constant between DPTIV and BSA was also examined.

The fluorescence spectroscopic study on the interaction between imidazo[2,1-b]thiazole analogues and bovine serum albumin

The interaction between imidazo[2,1-b]thiazole (IMTZ) and bovine serum albumin (BSA) was analyzed by fluorescence and ultraviolet spectroscopy at 302 and 310 K under simulative physiological conditions. The results show that IMTZ can effectively quench the intrinsic fluorescence of BSA via static and dynamic quenching. The binding constant, binding sites of IMTZ with BSA were calculated. According to the Förster non-radiation energy transfer theory, the average binding distance between IMTZ and BSA was obtained. What's more, the synchronous fluorescence spectra indicated that the conformation of BSA has been changed. The results provided the information for the binding of IMTZ to BSA, and the influences of substituent group on the interaction were also discussed.

Interaction of sodium benzoate with trypsin by spectroscopic techniques

The toxicity of sodium benzoate to trypsin was investigated by fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-visible absorption spectroscopy and circular dichroism (CD) spectroscopy under mimic physiological conditions. Sodium benzoate could unfold trypsin by decreasing the β-sheet structure, which leads to more exposure of internal amino acid groups and the obvious intrinsic fluorescence quenching with the rising concentration of sodium benzoate. The results of spectroscopic measurements indicated that sodium benzoate changed the internal microenvironment of trypsin and induced the alteration of the whole molecule, which were performed toxic effects on the organism. Trypsin and sodium benzoate interacted with each other to produce a substance by van der Waals forces and hydrogen bond, the model of which was shown by AutoDock software.

Stereo-selectivity of human serum albumin to enantiomeric and isoelectronic pollutants dissected by spectroscopy, calorimetry and bioinformatics

1-naphthol (1N), 2-naphthol (2N) and 8-quinolinol (8H) are general water pollutants. 1N and 2N are the configurational enantiomers and 8H is isoelectronic to 1N and 2N. These pollutants when ingested are transported in the blood by proteins like human serum albumin (HSA). Binding of these pollutants to HSA has been explored to elucidate the specific selectivity of molecular recognition by this multiligand binding protein. The association constants (K(b)) of these pollutants to HSA were moderate (10(4)-10(5) M(-1)). The proximity of the ligands to HSA is also revealed by their average binding distance, r, which is estimated to be in the range of 4.39-5.37 nm. The binding free energy (ΔG) in each case remains effectively the same for each site because of enthalpy-entropy compensation (EEC). The difference observed between ΔC(p) (exp) and ΔC(p) (calc) are suggested to be caused by binding-induced flexibility changes in the HSA. Efforts are also made to elaborate the differences observed in binding isotherms obtained through multiple approaches of calorimetry, spectroscopy and bioinformatics. We suggest that difference in dissociation constants of pollutants by calorimetry, spectroscopic and computational approaches could correspond to occurrence of different set of populations of pollutants having different molecular characteristics in ground state and excited state. Furthermore, our observation of enhanced binding of pollutants (2N and 8H) in the presence of hemin signifies that ligands like hemin may enhance the storage period of these pollutants in blood that may even facilitate the ill effects of these pollutants.

Study on the structural changes of bovine serum albumin with effects on polydatin binding by a multitechnique approach

Polydatin is a traditional Chinese medicine which shows effective biological activity as antimicrobial and antiviral agent. The secondary structure changes of bovine serum albumin (BSA) were investigated by the methods of Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD) and Raman spectroscopy. The experimental results indicated that polydatin changed the secondary structure of BSA. The presence of polydatin decreased α-helix content of BSA. The conformations of disulfide bridges and the microenvironment of Tyr, Trp residues were also changed.