Fluorescence spectroscopic studies on the interaction of Gemini surfactant 14‐6‐14 with bovine serum albumin

The interaction of the cationic Gemini surfactant hexamethylene‐1,3‐bis (tetradecyldimethylammonium bromide) (14‐6‐14) with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectra and three‐dimensional (3D) fluorescence spectra. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters ΔH, ΔG and ΔS have been estimated by the fluorescence quenching method. The results indicated that hydrophobic forces were the predominant intermolecular forces between BSA and the surfactant. Competitive experiments and the number of binding sites calculation show that 14‐6‐14 can be inserted in site‐II (in subdomain IIIA) of BSA. The effect of 14‐6‐14 on the conformation of BSA was evaluated by synchronous fluorescence spectroscopy and 3D fluorescence spectral methods. The results show that the conformation of BSA was changed dramatically in the presence of 14‐6‐14, by binding to the Trp and Try residues of BSA. The investigation provides interaction between BSA and 14‐6‐14 as a model for molecular design and industrial research. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Study of the interaction between 8-azaguanine and bovine serum albumin using optical spectroscopy and molecular modeling methods

The interaction between 8-azaguanine (8-Azan) and bovine serum albumin (BSA) in Tris-HCl buffer solutions at pH 7.4 was investigated by means of fluorescence and ultraviolet-visible (UV-Vis) spectroscopy. At 298 K and 310 K, at a wavelength of excitation (λ _ex) of 282 nm, the fluorescence intensity decreased significantly with increasing concentrations of 8-Azan. Fluorescence static quenching was observed for BSA, which was attributed to the formation of a complex between 8-Azan and BSA during the binding reaction. This was illuminated further by the UV-Vis absorption spectra and the decomposition of the fluorescence spectra. The thermodynamic parameters ∆G, ∆H, ∆S were calculated. The results showed that the forces acting between 8-Azan and BSA were typical hydrophobic forces, and that the interaction process was spontaneous. The interaction distance r between 8-Azan and BSA, evaluated according to fluorescence resonance energy transfer theory, suggested that there is a high possibility of energy transfer from BSA to 8-Azan. Theoretical investigations based on homology modeling and molecular docking suggested that binding between 8-Azan and BSA is dominated by hydrophilic forces and hydrogen bonding. The theoretical investigations provided a good structural basis to explain the phenomenon of fluorescence quenching between 8-Azan and BSA.     

Molecular interaction of cationic gemini surfactant with bovine serum albumin: A spectroscopic and molecular docking study

Herein, we report the effect of N,N′-bis(dodecyloxycarbonylmethyl)-N,N,N′,N′-tetramethyl-1,2-ethanediammonium dibromide (dodecyl betainate gemini or DBG) on the structure and function of bovine serum albumin (BSA) by using fluorescence, time resolved fluorescence, circular dichroism and dynamic light scattering techniques. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters viz ΔH, ΔG and ΔS have been estimated by the fluorescence quenching method. The results indicated that DBG binds spontaneously with BSA through hydrophobic interaction. Time resolved fluorescence data show that the quenching follows the static mechanism pathway. It can be seen from far-UV CD spectra that the α-helical network of BSA is disrupted and its content increases from 71% to 79% at lower concentrations which again decreases to 38% at higher concentration. DLS measurements suggested that hydrodynamic radius (R_h) decreases in the presence of 30 and 40 μM of DBG while it increases when the concentration of DBG was 70 and 100 μM. The molecular docking study indicated that DBG is embedded into subdomain IIA of BSA and binds with the R-914, R-195 and R-217 residues by hydrogen bonding and by hydrophobic interaction.     

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.     

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.     

A Spectroscopic Approach to Investigate the Molecular Interactions between the Newly Approved Irreversible ErbB blocker "Afatinib" and Bovine Serum Albumin

The interaction of afatinib (AFB) with bovine serum albumin (BSA) was examined via fluorescence and UV-Vis spectroscopy. Spectrofluorimetric measurements revealed that AFB can strongly quench the BSA intrinsic fluorescence through producing a non-fluorescent complex. This quenching mechanism was thoroughly investigated with regard to the type of quenching, binding constant, number of binding locations and the fundamental thermodynamic parameters. Subsequently, the association constant of AFB with BSA was computed at three different temperatures and was found to range from 7.34 to 13.19 x10⁵ L mol^-1. Thermodynamic parameters calculations demonstrated a positive ΔS^Ɵvalue with both negative ΔH^ϴand ΔG^ϴvalues for AFB–BSA complex, which in turn infers thata spontaneous binding is taking place with both electrostatic bonding and hydrophobic interactions participating in the binding of AFB and BSA. Similarly, the UV absorption spectra of AFB-BSA system were studied and confirmed the interaction. Conformational alteration of the protein upon binding to AFB was elaborated with the aid of three dimensional fluorescence measurements as well as synchronous fluorescence spectra.     

Micelle formation in the presence of photosystem I

The correlation between membrane protein solubilisation and detergent aggregation in aqueous solution is studied for a series of n-alkyl-β-d-maltosides (C_xG₂ with x = 10, 11, 12 being the number of carbon atoms in the alkyl chain) using the trimeric photosystem I core complex (PSIcc) of oxygenic photosynthesis from Thermosynechococcus elongatus as model protein. While protein solubilisation is monitored via the turbidity of the solution, the aggregation behavior of the detergent is probed via the fluorescence spectrum of the polycyclic aromatic hydrocarbon pyrene. In addition, changes of the fluorescence spectrum of PSIcc in response to formation of the detergent belt surrounding its hydrophobic surface are investigated. Solubilisation of PSIcc and aggregation of detergent into micelles or belts are found to be strictly correlated. Both processes are complete at the critical solubilisation concentration (CSC) of the detergent, at which the belts are formed. The CSC depends on the concentration of the membrane protein, [prot], and is related to the critical micelle concentration (CMC) by the empirical law ln(CSC/CMC) = n¯₀ [prot], where the constant n¯₀ = (2.0 ± 0.3) μM⁻¹ is independent of the alkyl chain length x. Formation of protein-free micelles below the CSC is not observed even for x = 10, where a significant excess of detergent is present at the CSC. This finding indicates an influence of PSIcc on micelle formation that is independent of the binding of detergent to the hydrophobic protein surface. The role of the CSC in the optimisation of membrane protein crystallisation is discussed.     

The interaction of mequitazine with phospholipid model membranes

The effect of increasing concentrations of mequitazine, a quinuclidinylmethyl-phenothiazine, on the phase transition temperature (T_c), the broadening of the transition peak, the enthalpy and entropy of transition of dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholine (DPPC) liposomes was studied. Pest critical micelle concentrations of mequitazine (CMC = 5.23 X 10^?2M), caused broadening of the transition peak and lowering of the T_c of pure liposomes. The ratio of peak heights from the nuclear magnetic resonance (NMR) spectra of egg phosphatidycholine liposomes was used as a criterion for assessing the interaction of the drug with phospholipid membranes. Mequitazine interacts with both the polar head groups and hydrophobic membrane interior.     

Physical chemical studies of short-chain lecithin homologues. I. Influence of the chain length of the fatty acid ester and of electrolytes on the critical micelle concentration

The critical micelle concentration (CMC) of four synthetic phosphatidylcholines (containing two hexanoyl, heptanoyl, octanoyl or nonanoyl residues respectively) in aqueous solutions have been determined by surface tension measurements. The dependence of the CMC on the chain length is discussed on the basis of the mass action model for micelle formation. For the three higher homologues a contribution of 1.08 kT per CH₂ group to the standard free energy of micellisation is found. The change in this free energy in going from the dihexanoyl- to the diheptanoyllecithin is somewhat larger (1.2 kT per CH₂ group).The influence of high concentrations (several moles per liter) of simple electrolytes on the CMC is interpreted as a salting-out of nonpolar solutes in water. Contrary to expectations the effects of NaCl and Lil on the CMC of dioctanoyllecithin are not additive.     

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

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

Interaction of indole and tryptophan derivatives with sodium dodecyl sulfate micelles measured with ultraviolet absorption and fluorescence quenching

The distribution of indole and tryptophan derivatives between sodium dodecyl sulfate (SDS) micellar and aqueous phases was analyzed using conventional methods of ultraviolet (UV) absorption spectroscopy and measurement of fluorescence quenching by succinimide. On the assumption of a simple pseudo-phase equilibrium between both phases the distribution coefficient was easily obtained by the measurement of the ratioR _pv of the absorbance intensity in the peak to that in the valley of the UV spectra or the fluorescence quenching constant K_sv. The possibilities and limitations of utilizing the ratio of the collisional quenching constant estimating from theK _sv value in the micellar phase to that in the aqueous phase for a measure of the polarity of the microenvironment around the tryptophan derivatives in the SDS micelle is discussed in comparison with theR _pv values for the UV spectra. The indole ring in the derivatives in the SDS micelle is localized near or on the micelle-water interface with its imino group directed toward the aqueous phase. Thus it can serve as a feasible model for interpreting the distribution coefficients andR _pv values obtained for the various indole and tryptophan derivatives.Abbreviations UV ultraviolet - SDS sodium dodecyl sulfate - ATEE N-acetyl-l-tryptophan ethyl ester - ATA N-acetyl-l-tryptophan-amide - CMC critical micelle concentration     

Multispectroscopic exploration and molecular docking analysis on interaction of eriocitrin with bovine serum albumin

Eriocitrin is a flavanone glycoside, which exists in lemon or lime citrus fruits. It possesses antioxidant, anticancer, and anti‐allergy activities. In order to investigate the pharmacokinetics and pharmacological mechanisms of eriocitrin in vivo, the interaction between eriocitrin and bovine serum albumin (BSA) was studied under the simulated physiological conditions by multispectroscopic and molecular docking methods. The results well indicated that eriocitrin and BSA formed a new eriocitrin‐BSA complex because of intermolecular interactions, which was demonstrated by the results of ultraviolet‐visible (UV‐vis) absorption spectra. The intrinsic fluorescence of BSA was quenched by eriocitrin, and static quenching was the quenching mechanism. The number of binding sites (n) and binding constant (K_b) at 310 K were 1.22 and 2.84 × 10⁶ L mol^?1, respectively. The values of thermodynamic parameters revealed that the binding process was spontaneous, and the main forces were the hydrophobic interaction. The binding distance between eriocitrin and BSA was 3.43 nm. In addition, eriocitrin changed the conformation of BSA, which was proved by synchronous fluorescence and circular dichroism (CD) spectra. The results of site marker competitive experiments suggested that eriocitrin was more likely to be inserted into the subdomain IIA (site I), which was further certified by molecular docking studies.     

Self-assembly and interactions of short antimicrobial cationic lipopeptides with membrane lipids: ITC,FTIR and molecular dynamics studies

In this work, the self-organization and the behavior of the surfactant-like peptides in the presence of biological membrane models were studied. The studies were focused on synthetic palmitic acid-containing lipopeptides, C₁₆–KK–NH₂ (I), C₁₆–KGK–NH₂ (II) and C₁₆–KKKK–NH₂ (III). The self-assembly was explored by molecular dynamics simulations using a coarse-grained force field. The critical micellar concentration was estimated by the surface tension measurements. The thermodynamics of the peptides binding to the anionic and zwitterionic lipids were established using isothermal titration calorimetry (ITC). The influence of the peptides on the lipid acyl chain ordering was determined using FTIR spectroscopy. The compounds studied show surface-active properties with a distinct CMC over the millimolar range. An increase in the steric and electrostatic repulsion between polar head groups shifts the CMC toward higher values and reduces the aggregation number. An analysis of the peptide–membrane binding revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions enabling the lipopeptides to interact with the lipid bilayer. In the case of C₁₆–KKKK–NH₂ (III), compensation of the electrostatic and hydrophobic interactions upon binding to the anionic membrane has been suggested and consequently no overall binding effects were noticed in ITC thermograms and FTIR spectra.     

The interaction between cepharanthine and two serum albumins: multiple spectroscopic and chemometric investigations

The binding modes of cepharanthine (CEPT) with bovine serum albumin (BSA) and human serum albumin (HSA) have been established by reproducing physiological conditions, which is very important to understand the pharmacokinetics and toxicity of CEPT. These spectral data were further analyzed by the multivariate curve resolution‐alternating least squares method. Moreover, the concentration profiles and pure spectra of three species (BSA/HSA, CEPT and CEPT–BSA/HSA) and the apparent equilibrium constants K_app were evaluated. The experimental results showed that CEPT could quench the fluorescence intensity of BSA/HSA by a combined quenching (static and dynamic) procedure. The binding constant (K), the thermodynamic parameters (ΔG, ΔH and ΔS) and binding subdomain were measured, and indicated that CEPT could spontaneously bind to BSA/HSA on subdomain IIA through the hydrophobic interactions. The effect of CEPT on the secondary structure of proteins has been analyzed by circular dichroism, 3D fluorescence and Fourier transform infrared spectra. The binding distance between CEPT and tryptophan of BSA/HSA was 2.305/1.749 nm, which is based on the Förster resonance energy transfer theory. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigations on the interactions of DiAmsar with serum albumins: Insights from spectroscopic and molecular docking techniques

Diamine‐sarcophagine (DiAmsar) binding to human serum albumin (HSA) and bovine serum albumin (BSA) was investigated under simulative physiological conditions. Fluorescence spectra in combination with Fourier transform infrared (FT‐IR), UV‐visible (UV–vis) spectroscopy, cyclic voltammetry (CV), and molecular docking method were used in the present work. Experimental results revealed that DiAmsar had an ability to quench the HSA and BSA intrinsic fluorescence through a static quenching mechanism. The Stern–Volmer quenching rate constant (K_sv) was calculated as 0.372 × 10³ M^‐1 and 0.640 × 10³ M^‐1 for HSA and BSA, respectively. Moreover, binding constants (K_a), number of binding sites (n) at different temperatures, binding distance (r), and thermodynamic parameters (?H°, ?S°, and ?G°) between DiAmsar and HSA (or BSA) were calculated. DiAmsar exhibited good binding propensity to HSA and BSA with relatively high binding constant values. The positive ?H° and ?S° values indicated that the hydrophobic interaction is main force in the binding of the DiAmsar to HSA (or BSA). Furthermore, molecular docking results revealed the possible binding site and the microenvironment around the bond. Copyright © 2014 John Wiley & Sons, Ltd.     

Role of surfactant on the proteolysis of aqueous bovine serum albumin

Nonionic and ionic surfactants diminish the initial rate of proteolysis of aqueous bovine serum albumin (BSA) by subtilisin Carlsberg. Surfactants studied include: nonionic tetraethylene glycol monododecyl ether (C12E4); anionic sodium dodecyl sulfate (SDS), anionic sodium dodecylbenzenesulfonate (SDBS), and cationic dodecyltrimethylamonium bromide (DTAB). Kinetic data are obtained using fluorescence emission. Special attention is given to enzyme kinetic specificity determined by fitting initial-rate data to the Michaelis-Menten model. All surfactants reduce the rate of proteolysis, most strongly at concentrations near and above the critical micelle concentration (CMC). Circular dichroism (CD), tryptophan/tyrosine fluorescence spectra, and tryptophan fluorescence thermograms indicate that BSA partially unfolds at ionic surfactant concentrations near and above the CMC. Changes in BSA conformation are less apparent at ionic surfactant concentrations below the CMC and for the nonionic surfactant C12E4. Subtilisin Carlsberg activity against the polypeptide, succinyl-Ala-Ala-Pro-Phe-p-nitroanilide, decreased due to enzyme-surfactant interaction. At the concentrations and time frames studied, there was no enzyme autolysis. Importantly, aqueous proteolysis rates are significantly reduced at high surfactant concentrations where protein-micellar-surfactant aggregates occur. To explain the negative effect of surfactant on subtilisin Carlsberg proteolytic activity against BSA, we propose that micelle/protein complexes hinder enzyme access.     

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 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.     

Effect of triazole‐tryptophan hybrid on the conformation stability of bovine serum albumin

The effect of a potent antimicrobial compound bearing 1,2,3‐triazole core and a tryptophan tail, triazole‐tryptophan hybrid (TTH), with bovine serum albumin (BSA) have been explored using various spectroscopic and molecular docking methods. Studies revealed that TTH strongly quenches the intrinsic fluorophore of BSA by a static quenching mechanism. Time‐resolved fluorescence spectra further confirmed the involvement of static quenching for TTH–BSA system. The calculated thermodynamic parameters; ΔH, ΔS, and ΔG showed that the binding process was spontaneous, exothermic and entropy driven. Synchronous fluorescence, three‐dimensional (3D) fluorescence and circular dichroism data revealed that TTH induces the structural alteration in BSA and enhances its stability. In silico study of TTH–BSA system showed that it binds with BSA at the site I of subdomain IIA. Both the experimental and in silico study showed that the hydrophobic and electrostatic interactions play a major role in TTH–BSA binding.