Study on the binding of cerium to bovine serum albumin

The interaction of Ce(3+) 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 Ce(3+) was a static quenching process, the binding constant is 6.70 × 10(5) , and the number of binding site is 1. The thermodynamic parameters (ΔH = -29.94 kJ mol(-1) , ΔG = -32.38 kJ mol(-1) , and ΔS = 8.05 J mol(-1) K(-1) ) indicate that electrostatic effect between the protein and the Ce(3+) is the main binding force. In addition, UV-vis, CD, and synchronous fluorescence results showed that the addition of Ce(3+) changed the conformation of BSA.     

Characterization of the interaction between reserpine and bovine serum albumin: spectroscopic approaches

The characteristics of the interaction between reserpine and bovine serum albumin (BSA) were studied by fluorescence, UV-vis absorption and Fourier transform infrared (FT-IR) spectroscopy. Spectroscopic analysis revealed that fluorescence quenching of BSA by reserpine was through a static quenching procedure. The binding constant K(A) of reserpine with BSA at 293, 301 and 309 K was 1.63, 1.78 and 2.35 x 10(5) moL(-1) L respectively, which indicated degree of binding force between reserpine and BSA. There was one binding site between reserpine and BSA. The entropy and enthalpy changes were positive, indicating that interaction of reserpine and BSA was driven mainly by hydrophobic forces. The average binding distance between the donor (BSA) and the acceptor (reserpine) was about 3.84 nm based on the Forster non-radiation energy transfer theory. Results of synchronous fluorescence and FT-IR spectra indicated that the conformation and microenvironment of BSA were changed by the binding of reserpine. The results may provide important insights into the physiological activity of reserpine.     

Interactions of some modified mono- and bis-beta-cyclodextrins with bovine serum albumin

Two mono-substituted beta-cyclodextrins and two bridged bis-beta-cyclodextrins, that is, mono(6-(2-aminoethylamino)-6-deoxy)-beta-cyclodextrin (1), mono(6-(2-(2-aminoethylamino)ethylamino)-6-deoxy)-beta-cyclodextrin (2), ethylene-1,2-diamino bis-6-(6-deoxy-beta-cyclodextrin) (3), and iminodiethylene-2,2'-diamino bis-6-(6-deoxy-beta-cyclodextrin) (4), were prepared from beta-cyclodextrin. Their binding ability with bovine serum albumin as a model protein was investigated through proton magnetic resonance (1H NMR), ultraviolet visible spectroscopy (UV-vis), circular dichroism (CD), and fluorescence spectroscopy. In the 1H NMR spectra of the modified cyclodextrins, the resolution of proton signals decreases after the addition of BSA. From the UV and CD spectra, it is found that both the UV absorption and the alpha-helix content of BSA increase with the concentration of the modified cyclodextrins. The protein-ligand interactions cause a fluorescence quenching. The quenching constants are determined using the Stern-Volmer equation to provide an observation of the binding affinity between modified cyclodextrins and BSA. All these results indicate that the modified cyclodextrins can interact with BSA and the bridged bis(beta-cyclodextrin)s (3 and 4) have much stronger interactions than the mono-substituted beta-cyclodextrins (1 and 2). The strong binding stability of bis-cyclodextrins should be attributed to the cooperative effect of two adjacent cyclodextrin moieties. Job's plot shows that the complex stoichiometries of BSA to the modified cyclodextrins were 1:4 for 1 and 2, as well as 1:3 for 3 and 4, respectively.     

Evaluation of binding and thermodynamic characteristics of interactions between a citrus flavonoid hesperitin with protein and effects of metal ions on binding

The mechanism of interaction of a non-glycosidic citrus flavonoid, hesperitin (HES) with bovine serum albumin (BSA) was studied by UV-vis absorption, fluorescence, FT-IR, circular dichroism, fluorescence anisotropy and synchronous fluorescence spectroscopy in phosphate buffer of pH 7.4. Fluorescence data revealed that the fluorescence quenching of BSA by HES was the result of the formed complex of HES-BSA. The binding constants and thermodynamic parameters at four different temperatures, the location of binding, and the nature of binding force were determined. The hydrogen bonds interactions were found to be the predominant intermolecular forces to stabilize the complex. The conformation of BSA was discussed by synchronous fluorescence and CD methods. The alterations of protein secondary structure upon complexation with HES were evident from the gradual decrease in α-helicity. The distance between the donor (BSA) and acceptor (flavonoid) was calculated from the fluorescence resonance energy transfer and found to be 1.978 nm. Common ions viz., Zn(2+), K(+), Cu(2+), Ni(2+), Mn(2+) and Co(2+) were found to influence the binding of flavonoid to protein.     

Intermolecular interaction of nickel (ii) phthalocyanine tetrasulfonic acid tetrasodium salt with bovine serum albumin: A multi-technique study

The interaction of nickel (II) phthalocyanine tetrasulfonic acid tetrasodium salt with bovine serum albumin (BSA) has been investigated by combination of fluorescence, UV-vis absorption, Fourier transform infrared (FT-IR), and circular dichorism (CD) spectroscopies as well as through molecular docking. Fluorescence quenching and absorption spectra were investigated as a mean for estimating the binding parameters. Analysis of fluorescence quenching data at different temperatures was performed in order to specify the thermodynamics parameters for interactions of phthalocyanine complex with BSA. According to experimental data it was suggested that phthalocyanine had a significant binding affinity to BSA and the process was entropy driven. Based on the results of molecular docking it was indicated that the main active binding site for this phthalocyanine complex is site I in subdomain IIA of BSA. The results provide useful information for understanding the binding mechanism of anticancer drug-albumin and gives insight into the biological activity and metabolism of the drug in blood.     

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.     

Study on the Interaction Between {\mathrm{Cu}}{\left( {{\mathrm{phen}}} \right)}^{{2 + }}_{3} and Bovine Serum Albumin by Spectroscopic Methods

In this work, the interaction between ${\text{Cu}}\left( {{\text{phen}}} \right)_3^{\,\,2 + } In this work, the interaction between Cu(phen)(2+)(3) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV-vis absorption and circular dichroism (CD) spectroscopic techniques under physiological conditions. The fluorescence data proved that the fluorescence quenching of BSA by Cu(phen)(2+)(3) was the result of the Cu(phen)(2+)(3) -BSA complex formation. The binding constants (K (a)) between Cu(phen)(2+)(3) and BSA at four different temperatures were calculated according to the modified Stern-Volmer equation. The enthalpy change (DeltaH) and entropy change (DeltaS) were calculated to be 10.74 kJ mol(-1) and 54.35 J mol(-1) K(-1), respectively, which indicated that electrostatic interactions played a major role in the formation of Cu(phen)(2+)(3) -BSA complex. The distance r between the donor (BSA) and acceptor[Cu(phen)(2+)(3)] was obtained to be 3.55 nm based on F?rster's energy transfer theory. The synchronous fluorescence and CD spectroscopy results showed that the polarity of the residues increased and the lost of the alpha-helix content of BSA (from 59.84 to 53.70%). These indicated that the microenvironment and conformation of BSA were changed in the presence of Cu(phen)(2+)(3).     

Study on the interactions of mapenterol with serum albumins using multi‐spectroscopy and molecular docking

The interactions of mapenterol with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated systematically using fluorescence spectroscopy, absorption spectroscopy, circular dichroism (CD) and molecular docking techniques. Mapenterol has a strong ability to quench the intrinsic fluorescence of BSA and HSA through static quenching procedures. At 291 K, the binding constants, K_a, were 1.93 × 10³ and 2.73 × 10³ L/mol for mapenterol–BSA and mapenterol–HAS, respectively. Electrostatic forces and hydrophobic interactions played important roles in stabilizing the mapenterol–BSA/has complex. Using site marker competitive studies, mapenterol was found to bind at Sudlow site I on BSA/HSA. There was little effect of K⁺, Ca²⁺, Cu²⁺, Zn²⁺ and Fe³⁺ on the binding. The conformation of BSA/HSA was changed by mapenterol, as seen from the synchronous fluorescence spectra. The CD spectra showed that the binding of mapenterol to BSA/HSA changed the secondary structure of BSA/HSA. Molecular docking further confirmed that mapenterol could bind to Sudlow site I of BSA/HSA. According to Förster non‐radiative energy transfer theory (FRET), the distances r₀ between the donor and acceptor were calculated as 3.18 and 2.75 nm for mapenterol–BSA and mapenterol–HAS, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Photochemical studies on the binding of an organic fluoride to bovine serum albumin

The interaction of fipronil (FPN), a pesticide containing fluorine, to bovine serum albumin (BSA) was studied by spectroscopy including fluorescence spectra, UV–Visible absorption, scattering spectra, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra. The number of binding sites n and observed binding constant Kb was measured by fluorescence quenching method. The thermodynamic parameters ΔH, ΔG, ΔS at different temperatures were calculated and the results indicate that hydrophobic forces played major role in the reaction. The distance r between donor (BSA) and acceptor (FPN) was obtained according to the Förster theory of non-radiation energy transfer. The structural change of BSA molecules with addition of FPN was analyzed and the results may be helpful to biologists, chemists and therapeutists.     

Synthesis of Morin–Zinc(II) Complex and its Interaction with Serum Albumin

A morin–zinc(II) complex (MZ) was synthesized and its interaction with bovine serum albumin (BSA) were studied by molecular spectroscopy including fluorescence emission spectra, UV-visible spectra, circular dichroism (CD) spectra, three-dimensional fluorescence spectra, and synchronous fluorescence spectra. The interaction mechanism of BSA and MZ was discussed by fluorescence quenching method and Förster non-radiation energy transfer theory. The thermodynamic parameters ΔH ^θ, ΔG ^θ, ΔS ^θ at different temperatures were calculated and the results indicate the interaction is an exothermic as well as entropy-driven process. Hydrogen bond forces played the most important role in the reaction. The fluorescence probe experiment showed that the binding site of MZ is in subdomain IIA of BSA and the distance between BSA and MZ is 3.17 nm at normal body temperature. The conformation changes of BSA in presence of MZ were investigated by CD spectra and three-dimensional fluorescence spectra.     

Study on the interaction of chromate with bovine serum albumin by spectroscopic method

The interaction between two chromates [sodium chromate (Na₂CrO₄) and potassium chromate K₂CrO₄)] and bovine serum albumin (BSA) in physiological buffer (pH 7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that two chromates could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of chromate with BSA were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were negative, indicating that the interaction of two chromates with BSA was driven mainly by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (BSA) and acceptor (chromate) was calculated based on Forster’s non-radiative energy transfer theory. The results of UV–Vis absorption, synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra showed that two chromates induced conformational changes of BSA.     

Interaction between fasudil hydrochloride and bovine serum albumin: spectroscopic study

The interaction between fasudil hydrochloride (FSD) and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopy under imitated physiological conditions. The Stern–Volmer quenching model has been successfully applied and the results revealed that FSD could quench the intrinsic fluorescence of BSA effectively via static quenching. The binding constants and binding sites for the BSA–FSD system were evaluated. The corresponding thermodynamic parameters obtained at different temperatures indicated that hydrophobic force played a major role in the interaction of FSD and BSA. The distance between the donor (BSA) and the acceptor (FSD) was obtained according to fluorescence resonance energy transfer (FRET). Synchronous fluorescence spectroscopy and FT‐IR spectra showed that the conformation of BSA was changed in the presence of FSD. Copyright © 2015 John Wiley & Sons, Ltd.     

Biochemical evaluation of a synthesized isoflavone-selenium complex by molecular spectra

A coordination compound of 5, 7-dihydrox-4'-methoxyisoflavone and selenium was synthesized and its structure was identified by IR, LC-MS and (1)H-NMR. Its biochemical effects were investigated using bovine serum albumin (BSA) as a target protein molecule, in which process three-dimensional (3D) fluorescence spectra, ultraviolet spectra, circular dichroism (CD) spectra and fluorescence probe techniques were employed. The interaction of SEIF and BSA was discussed by fluorescence quenching method and F?rster non-radiation energy transfer theory. The thermodynamic parameters ΔH (θ), ΔG (θ), ΔS (θ) at different temperatures were calculated according to Van't Hoff isobaric equation and the results indicated the interaction was an exothermic as well as a spontaneous process. The binding site was explored by fluorescence probe method using warfarin and ibuprofen as markers. Intramolecular forces which are responsible for maintaining the binding were mainly hydrogen bond and van der Waals power. The average distance from the tryptophan residue in domain II of BSA (donor) to SEIF (acceptor) is 3.57 nm at body temperature. The conformation changes of BSA were investigated by 3D fluorescence and CD spectra.     

Spectral diagnostics of the interaction between pyridoxine hydrochloride and bovine serum albumin in vitro

The interaction between pyridoxine hydrochloride (VB6) and bovine serum albumin (BSA) were studied by spectroscopic methods including fluorescence spectroscopy and UV-visible absorption spectra. The quenching mechanism of fluorescence of BSA by VB6 was discussed. The number of binding sites n and observed binding constant K(b) was measured by fluorescence quenching method. The thermodynamic parameters DeltaH(theta), DeltaG(theta), DeltaS(theta) at different temperatures were calculated and the results indicate the binding reaction is mainly entropy-driven and hydrophobic interaction played major role in the reaction. The distance r between donor (BSA) and acceptor (VB6) was obtained according to FOrster theory of non-radiation energy transfer. Synchronous fluorescence and three-dimensional fluorescence spectra were used to investigate the structural change of BSA molecules with addition of VB6, the result indicates that the secondary structure of BSA molecules is changed in the presence of VB6.     

Binding of the environmental pollutant naphthol to bovine serum albumin

The interactions between naphthol and bovine serum albumin (BSA) were investigated by spectroscopy. Our results prove the formation of complex between naphthol and BSA. Hydrophobic interaction dominates in the association reaction. The isomers stack with the aromatic residues in their binding sites with different geometries. Effects of BSA on the excited-state proton transfer and fluorescence spectra of the isomers indicate the different characters of their binding sites. 1-Naphthol inserts deeply into a hydrophobic cavity whereas 2-naphthol is in a basic environment on the surface of BSA. Naphthol statically quenches the fluorescence of BSA in a concentration-dependent manner positively deviating from the linear Stern-Volmer equation. Naphthol binds near Trp-134 in the subdomain IA of the native BSA and is accessible to Trp-212 when BSA is unfolded by naphthol. The folding pattern of the main chain is altered at high naphthol concentration as revealed by the change in the secondary structure. The binding of 1-naphthol is more cooperative than that of 2-naphthol. The extent of cooperativity was estimated by the Hill equation.     

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.     

The investigation of the interaction between ribavirin and bovine serum albumin by spectroscopic methods

The interaction between ribavirin (RIB) with bovine serum albumin (BSA) has been investigated by fluorescence quenching technique in combination with UV–vis absorption and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The quenching of BSA fluorescence by RIB was found to be a result of the formation of RIB–BSA complex. The binding constants and the number of binding sites were calculated at three different temperatures. The values of thermodynamic parameters ?H, ?S, ?G at different temperatures indicate that hydrophobic and hydrogen bonds played important roles for RIB–BSA association. The binding distance r was obtained according to the theory of FÖrster’s non–radiation energy transfer. The displacement experiments was performed for identifying the location of the binding site of RIB on BSA. The effects of common ions on the binding constant of RIB and BSA were also examined. Finally, the conformational changes of BSA in the presence of RIB were also analyzed by CD spectra and Synchronous fluorescence spectra.     

The interaction of blood proteins with brucine

The features of brucine (BC) binding to two blood proteins, bovine hemoglobin (BHb), and bovine serum albumin (BSA), were investigated via fluorescence, circular dichroism and UV/Vis absorption spectroscopy. The results revealed that BC caused the fluorescence quenching of blood proteins by the formation of BC–protein complex. The corresponding thermodynamic parameters were measured at different temperatures. The process of binding BC molecule on protein was a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased. Hydrophobic and electrostatic interactions play a major role in stabilizing the complex. The molecular docking has been employed to explore the binding site of the BC in BHb and BSA on the Autodock 4.2. The distances r between BC and protein were calculated to be 4.93 and 5.08 nm for BHb, and BSA, respectively. The effect of BC on the conformation of blood proteins was analyzed using CD, synchronous fluorescence and three-dimensional fluorescence spectra.     

Study on the synthesis of sulfonamide derivatives and their interaction with bovine serum albumin

Three sulfonamide derivatives (SAD) were first synthesized from p‐hydroxybenzoic acid and sulfonamides (sulfadimidine, sulfamethoxazole and sulfachloropyridazine sodium) and were characterized by elemental analysis, ¹H NMR and MS. The interaction between bovine serum albumin (BSA) and SAD was studied using UV/vis absorption spectroscopy, fluorescence spectroscopy, time‐resolved fluorescence spectroscopy and circular dichroism spectra under imitated physiological conditions. The experimental results indicated that SAD effectively quenched the intrinsic fluorescence of BSA via a static quenching process. The thermodynamic parameters showed that hydrogen bonding and van der Waal's forces were the predominant intermolecular forces between BSA and two SADs [4‐((4‐(N‐(4,6‐dimethylpyrimidin‐2‐yl)sulfamoyl)phenyl)carbamoyl)phenyl acetate and 4‐((4‐(N‐(5‐methylisoxazol‐3‐yl)sulfamoyl)phenyl)carbamoyl)phenyl acetate], but hydrophobic forces played a major role in the binding process of BSA and 4‐((4‐(N‐(6‐chloropyridazin‐3‐yl)sulfamoyl)phenyl) carbamoyl)phenyl acetate. In addition, the effect of SAD on the conformation of BSA was investigated using synchronous fluorescence spectroscopy and circular dichroism spectra. Molecular modeling results showed that SAD was situated in subdomain IIA of BSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and spectroscopic characterization of 4-butoxyethoxy-N-octadecyl-1,8-naphthalimide as a new fluorescent probe for the determination of proteins

A novel 4-butoxyethoxy-N-octadecyl-1,8-naphthalimide (BON) was synthesized as a fluorescent probe for the determination of proteins. The interactions between BON and bovine serum albumin (BSA) were studied by fluorescence spectroscopy and UV-vis absorption spectroscopy. Fluorescence data revealed that the fluorescence quenching of BSA by BON was likely the result of the formation of the BON-BSA complex. According to the modified Stern-Volmer equation, the binding constants of BON with BSA at four different temperatures were obtained. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) for the reaction were calculated to be −23.27 kJ mol⁻¹ and 10.40 J mol⁻¹ K⁻¹ according to van’t Hoff equation, indicating that the hydrogen bonds and hydrophobic interactions played a dominant role in the binding of BON to BSA. Furthermore, displacement experiments using warfarin indicated that BON could bind to site I of BSA. The effect of BON on the conformation of BSA was also analyzed by synchronous fluorescence and three-dimensional fluorescence spectra. A new fluorescence quenching assay of the proteins BSA using BON in the HCl-Tris (pH 7.4) buffer solution was developed with maximum excitation and emission wavelengths of 373 and 489 nm, respectively. The linear range was 0.1-10.0 × 10⁻⁵ mol L⁻¹ with detection limits were determined to be 1.76 × 10⁻⁸ mol L⁻¹. The effect of metal cations on the fluorescence spectra of BON in ethanol was also investigated. Determination of protein in human serum by this method gave results which were very close to those obtained by using Coomassie Brilliant Blue G-250 colorimetry.