Non-covalent binding analysis of sulfamethoxazole to human serum albumin:Fluorescence spectroscopy,UV-vis,FT-IR,voltammetric and molecular modeling

This study was designed to examine the interaction of sulfamethoxazole （SMZ） with human serum albumin（HSA）. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of human serum albumin by SMZ was static mechanism. The binding constant values for the SMZ-HSA system were obtained to be 22,500 L/mol at 288 K, 15,600 L/mol at 298 K, and 8500 L/mol at 308 K. The distance r between donor and acceptor was evaluated according to the theory of Foster energy transfer. The results of spectroscopic analysis and molecular modeling techniques showed that the conformation of human serum albumin had been changed in the presence of SMZ. The thermodynamic parameters, namely enthalpy change （ΔH^0） - 36.0 kJ/mol, entropy change （ΔS^0） - 41.3 Jim01 K and free energy change （ΔG^0） - 23.7 kJ/ mol, were calculated by using van＇t Hoff equation. The effect of common ions on the binding of SMZ to HSA was tested.

Fluorescence spectroscopy of osthole binding to human serum albumin

The interaction of human serum albumin （HSA） with osthole was investigated by fluorescence spectroscopy. Osthole can quench the fluorescence of HSA and the quenching mechanism is a static process. The binding site number n and apparent binding constant K were measured at different temperatures. The thermodynamic parameters △H^0, △G^0 and △S^0 were calculated at different temperatures. The results indicated that electrostatic forces played a major role in the interaction of osthole with HSA. Results of osthole synchronous fluorescence and UV absorption spectra showed that the microenvironment and conformation of HSA were changed.

Fluorescence Spectroscopy and Molecular Docking Approach to Probe the Interaction between Dehydroeburicoic Acid and Human Serum Albumin

The interaction between dehydroeburicoic acid (DeEA), a triterpene purified from medicinal fungi and the major transport protein, human serum albumin (HSA), were systematically studied by fluorescence spectroscopy, synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy and molecular docking approach under simulated physiological conditions. The intrinsic fluorescence of HSA was quenched through the combination of static and dynamic quenching mechanism. DeEA cannot be stored and carried by HSA in the body at higher temperature. The hydrogen bonding, hydrophobic force and van der Waals force were major acting forces. The site II was the major binding site. The energy transfer could occur with high probability and the binding distance was 3.29 nm. The binding process slightly changed the conformation and microenvironment of HSA. The DeEA molecule entered the hydrophobic cleft of HSA and formed the hydrogen bonding with Glu-492 and Lys-545.

Study on the secondary structure and hydration effect of human serum albumin under acidic pH and ethanol perturbation with IR/NIR spectroscopy

Human serum albumin(HSA)is the most abundant protein in plasma and plays an essential physiological role in the human body.Ethanol precipitation is the most widely used way to obtain HSA,and pH and ethanol are crucial factors affecting the process.In this study,infrared(IR)spectroscopy and near-infrared(NIR)spectroscopy in combination with chemometrics were used to investigate the changes in the secondary structure and hydration of HSA at acidic pH(5.6-3.2)and isoelectric pH when ethanol concentration was varied from 0%to 40%as a perturbation.IR spectroscopy combined with the two-dimensional correlation spectroscopy(2DCOS)analysis for acid pH system proved that the secondary structure of HSA changed significantly when pH was around 4.5.What's more,the IR spectroscopy and 2DCOS analysis showed different secondary structure forms under different ethanol concentrations at the isoelectric pH.For the hydration effect analysis,NIR spectroscopy combined with the McCabe-Fisher method and aquaphotomics showed that the free hydrogen-bonded water fluctuates dynamically,with ethanol at 0-20%enhancing the hydrogen-bonded water clusters,while weak hydrogen-bonded water clusters were formed when the ethanol concentration increased continuously from 20%to 30%.These measurements provide new insights into the structural changes and changes in the hydration behavior of HSA,revealing the dynamic process of protein purification,and providing a theoretical basis for the selection of HSA alcoholic precipitation process parameters,as well as for further studies of complex biological systems.

Combined fluorescence and electrochemical investigation on the binding interaction between organic acid and human serum albumin

Human serum albumin （HSA） is a plasma protein responsible for the binding and transport of fatty acids and a variety of exogenous chemicals such as drugs and environmental pollutants. Such binding plays a crucial role in determining the ADME （absorption, distribution, metabolism, and excretion） and bioavailability of the pollutants. The binding interaction between HSA and acetic acid （C2）, octanoic acid （C8） and dodecanoic acid （C12） has been investigated by the combination of site-specific fluorescent probe, tryptophan intrinsic fluorescence and tyrosine electrochemistry. For the study of the fatty acid interaction with the two drug-binding sites on HSA, two fluorescent probes, dansylamide and dansyl-L-proline were employed in the displacement measurements. Intrinsic fluorescence of tryptophan in HSA was monitored upon addition of the fatty acids into HSA. Electrocatalyzed response of the tyrosine residues in HSA by a redox mediator was used to investigate the binding interaction. Qualitatively, observations from these three approaches were very similar. HSA did not show any change in the fluorescence and electrochemical experiments after mixing with C2, suggesting there is no significant interaction with the short-chain fatty acid. For C8, the measured signal dropped in a single-exponential mode, indicating an independent and non-cooperative binding. The calculated association constant and binding ratio were 3.1 × 10^6 L/mol and 1 with drug binding Site Ⅰ, 1.1 × 107 L/mol and 1 with Site Ⅱ, and 7.0× 0^4 L/mol and 4 with the tryptophan site, respectively. The measurements with C12 displayed multiple phases of fluorescence change, suggesting cooperativity and allosteric effect of the C12 binding. These results correlate well with those obtained by the established methods, and validate the new approach as a viable tool to study the interactions of environmental pollutants with biological molecules.

Investigation of binding behaviour of procainamide hydrochloride with human serum albumin using synchronous,3D fluorescence and circular dichroism

Interaction of procainamide hydrochloride（PAH） with human serum albumin（HSA） is of great significance in understanding the pharmacokinetic and pharmacodynamic mechanisms of the drug. Multi-spectroscopic techniques were used to investigate the binding mode of PAH to HSA and results revealed the presence of static type of quenching mechanism. The number of binding sites, binding constants and thermodynamic parameters were calculated. The results showed a spontaneous binding of PAH to HSA and hydrophobic interactions played a major role. In addition, the distance between PAH and the Trp–214 was estimated employing the F？rster＇s theory. Site marker competitive experiments indicated that the binding of PAH to HSA primarily took place in subdomain IIA（Sudlow＇s site I）. The influence of interference of some common metal ions on the binding of PAH to HSA was studied. Synchronous fluorescence spectra（SFS）, 3D fluorescence spectra and circular dichroism（CD） results indicated the conformational changes in the structure of HSA.

Study of <i>in Vitro</i>Interaction of Sildenafil Citrate with Bovine Serum Albumin by Fluorescence Spectroscopy

In vitro interaction of sildenafil citrate (SC) with bovine serum albumin (BSA) was investigated at two excitation wavelengths of BSA (280 nm and 293 nm) at two different temperatures (298 K and 308 K) by fluorescence emission spectroscopy. The study showed that quenching of BSA fluores-cence by sildenafil citrate was the result of formation BSA-SC complex with probable involvement of both tryptophan and tyrosine residues of BSA. Fluorescence quenching constant was determined from Stern-Volmer equation, and both static quenching and dynamic quenching were showed for BSA by SC at the conditions. Van’t Hoff equation was used to measure the thermodynamic parameters ΔG, ΔH, and ΔS at the temperatures which indicated that the hydrogen bond and the hydrophobic forces played major roles for BSA-SC complexation. The binding number (n) was found to be ≈1 indicating that one mole BSA bound with one mole SC. The binding affinity of SC to BSA was calculated at different temperatures. The binding constant was decreased with increasing temperatures indicating that stability of BSA-SC complex decreased with increasing temperatures.

Characterization of Gallic Acid Interaction with Human Serum Albumin by Spectral and Molecular Modeling Methods

The binding of drugs with human serum albumin（HSA） is a crucial factor influencing the distribution and bioactivity of drugs in the body.To understand the action mechanisms between gallic acid（GA,3,4,5-trihydroxybenzoic acid） and HSA,the binding of GA with HSA was investigated by a combined experimental and computational approach.The fluorescence properties of HSA and the binding parameters of GA collectively indicate that the binding is characterized by static quenching mechanism at one high affinity binding site.According to the estimated molecular distance between the donor（HSA） and the acceptor（GA）,the binding is related to the fluorescence resonance energy transfer.As indicated by the thermodynamic parameters,hydrophobic interaction plays a major role in the GA-HSA complex.Further,the experimental results reveal that GA is bound in the large hydrophobic cavity of subdomain IIA in the site I of HSA,which is well approved by molecular docking.

Study on the Interaction between Human Serum Albumins and Methyl Pheophorbide-a-Gd

The binding reaction between methyl pheophorbide-a-Gd (MPA-Gd) and Human Serum Albumins (HSA) was studied by fluorescence and UV-Vis absorption spectra. The results indicated that the binding reaction of them was a single static quenching process, MPA-Gd strongly bound HSA, the binding equilibrium constant K0=2.298×105 L·mol-1 at 25 ℃. The shortest binding distance(r) and energy transfer efficiency(E) between donor (HSA) and acceptor (MPA-Gd) was obtained by Frster′s nonradiative energy transfer mechanism as follows: r=4.03 nm, E=0.12. The enthalpy change (ΔH) and entropy change (ΔS) were calculated at 25 and 37 ℃. The results indicated that the hydrogen bonds played major role in the reaction. Furthermore, the displacement experiments indicated that MPA-Gd could bind to the site Ⅱof HSA.

Interaction between a novel intramolecular charge transfer fluorescent probe PFEP and human serum albumin

The interaction mechanism between human serum albumin(HSA) and 1-phenyl-3(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2- pyrazoline(PFEP) was investigated by fluorescence and absorption titration techniques in combination with molecular modeling method.Stern-Volmer plots at different temperatures proved that PFEP could quench the intrinsic fluorescence of HSA attributed to a static quenching procedure.The association constants were calculated in the range of 1×10~5-8×10~5mol^(-1) at different pH conditions,a...

Analysis of Binding Interaction between Captopril and Human Serum Albumin

The interaction between captopril, an inhibitor of angiotensin converting enzyme and human serum albumin, a principal plasma protein in the liver has been investigated in vitro under a simulated physiological condition by UV-vis spectrophotometry and fluorescence spectrometry. The intrinsic fluorescence intensity of human serum albumin was strongly quenched by captopril. The binding constants and the number of binding sites can be calculated from the data obtained from fluorescence quenching experiments. The negative value of ΔG0 reveals that the binding process is a spontaneous process. According to the van’t Hoff equation, the standard enthalpy change (ΔH0) and standard entropy change (ΔS0) for the reaction were calculated to be 35.98 KJ●mol-1 and 221.25 J●mol-1 K. It indicated that the hydrophobic interactions play a main role in the binding of captopril to human serum albumin. In addition, the distance between captopril (acceptor) and tryptophan residues of human serum albumin (donor) was estimated to be 1.05 nm according to the F?rster’s resonance energy transfer theory. The results obtained herein will be of biological significance in pharmacology and clinical medicine.

Insight into the interaction of inhaled corticosteroids with human serum albumin: A spectroscopic-based study

It is well known that the safety and efficacy profile of an inhaled cortocosteroid(ICS) is influenced by the pharmacokinetic properties and associated pharmacodynamic effects of the drug. Freely circulating,protein unbound, and active ICS can cause systemic adverse effects. Therefore, a detailed investigation of drug-protein interaction could be of great interest to understand the pharmacokinetic behaviour of corticosteroids and for the design of new analogues with effective pharmacological properties. In the present work, the interaction between some corticosteroids and human serum albumin(HSA) has been studied by spectroscopic approaches. UV–Vis spectroscopy confirmed that all the investigated corticosteroids can bind to HSA forming a protein-drug complex. The intrinsic fluorescence of HSA was quenched by all the investigated drugs, which was rationalized in terms of a static quenching mechanism. The thermodynamic parameters determined by the Van't Hoff analysis of the binding constants(negative ΔH and ΔS values) clearly indicate thathydrogen bonds and van der Waals forces play a major role in the binding process between albumin and betamethasone, flunisolide and prednisolone, while hydrophobic forces may play a major role in stabilizing albumin-triamcinolone complexes.

Binding interactions of pefloxacin mesylate with bovine lactoferrin and human serum albumin

The binding of pefloxacin mesylate (PFLX) to bovine lactoferrin (BLf) and human serum albumin (HSA) in dilute aqueous solution was studied using fluorescence spectra and absorbance spectra. The binding constant K and the binding sites n were obtained by fluorescence quenching method. The binding distance r and energy-transfer efficiency E between pefloxacin mesylate and bovine lactoferrin as well as human serum albumin were also obtained according to the mechanism of F?rster-type dipole-dipole nonradiative energy-transfer. The effects of pefloxacin mesylate on the conformations of bovine lactoferrin and human serum albumin were also analyzed using synchronous fluorescence spectroscopy.

Preparation of （2E）-3-（4＇-Halophenyl）prop-2-enoyl Sulfachlorpyridazine Sodium Salts and Their Interaction with Bovine Serum Albumin by Fluorescence Spectroscopy

Three （2E）-3-（4＇-halophenyl）prop-2-enoyl sulfachlorpyridazine sodium salts（XPSCA） were synthesized. Their chemical structures were confirmed by IH NMR and 13C NMR, electrospray ionization mass spectrometry （ESI-MS）, and infrared（IR） spectroscopy. The interactions between XPSCA and bovine serum albumin（BSA） were investigated under imitated physiological condition by fluorescence quenching technique and UV-Vis absorption spectroscopy according to the Stern-Volmer equation. The results from the emission quenching at different tempera- tures indicate that the quenching mechanism of serum albumin by XPSCA was static quenching mechanism at low XPSCA concentrations or a combined quenching（static and dynamic） mechanism at higher XPSCA concentrations. At different temperatures, the binding constant and the binding sites of XPSCA with BSA were investigated, and the distances were evaluated according to F6rster non-radiative resonance energy transfer theory. The thermodynamic parameters were calculated according to van＇t Hoff equation, which implies that both van der Waals interaction and hydrogen bond played major roles in stabilizing the XPSCA-BSA complexes, whereas hydrophobic interactions were secondary. Moreover, the conformational changes in BSA were analyzed by synchronous fluorescence spectra.

Investigation of the Interaction between Isoflavonoids and Bovine Serum Albumin by Fluorescence Spectroscopy

The interactions of bovine serum albumin （BSA） with three structurally related isoflavonoids, genistein, puerarin and daidzein, were studied under physiological conditions by fluorescence spectroscopic technique. The quenching mechanism of these compounds with BSA was suggested as static quenching and the binding constants were determined at different temperatures based on the fluorescence quenching results. The transfer efficiency of energy and distance between the acceptor and BSA were investigated on the basis of the mechanism of the Forster energy transference. According to the thermodynamic parameters it has been suggested that the acting force be mainly hydrophobic force. The comparison of binding potency of the three isoflavonoids to BSA showed that the substitution by 5-OH and 8-Glc could enhance the binding affinity. All these obtained in the work can make us better understand the mode of the action and pharmacological activities of the isoflavonoids.

Studies on the binding of vinpocetine to human serum albumin by molecular spectroscopy and modeling

The interaction between vinpocetine（VPC） and human serum albumin（HSA） in physiological buffer（pH 7.40） was investigated by fluorescence,FT-IR,UV-vis absorption and molecular modeling.VPC effectively quenched the intrinsic fluorescence of HSA via static quenching.The binding site number n and apparent binding constant K_a,corresponding thermodynamic parametersΔG,ΔH andΔS at different temperatures were calculated.The synchronous fluorescence and FT-IR spectra were used to investigate the structural change of HSA molecules with addition of VPC.Molecular modeling indicated that VPC could bind to the site I of HSA and hydrophobic interaction was the major acting force,which was in agreement with the binding mode study.

Effect of bovine serum albumin on the micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers in aqueous solutions by fluorescence spectroscopy

Effect of bovine serum albumin (BSA) on the temperature-dependent association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers was investigated using pyrene fluorescence spectroscopy. The critical micellization temperature (CMT) of pluronics in aqueous solution was increased by the addition of BSA. A closed association model was used to obtain the standard free energies (△G0), enthalpies (△H 0), and entropies (△S 0) of micellization. The standard enthalpy and entropy of micellization for pluronic polymers in water were decreased with an increase of the BSA content. The more PPO component in the pluronic polymer, the higher the changed values of micellization enthalpy and entropy. The hydrophobic part of the pluronics, PPO, was responsible for the interaction between pluronics and BSA. Hydrophobic interaction between PPO and BSA was correlated to the alternation of the PPO-PPO interaction by the addition of BSA, which would shift the CMT toward higher temperature and alter the thermodynamic parameters of micellization for pluronics in aqueous solutions.

Spectroscopic Investigation of the Interaction between Human Serum Albumins and 10-Hydroxycamptothecin

The binding reaction between 10-hydroxycamptothecin （10-HCPT） and human serum albumins （HSA） is studied by means of fluorescence spectroscopy, UV-Vis absorption spectrum, IH NMR spectrum, and molecular simulation. The results indicate that the binding reaction of 10-HCPT and HSA is a single static quenching process, and the binding equilibrium constant for 10-HCPT binding with HSA is estimated K0-4.93×10^4 L · mol-I at 25 ℃ with the molar ratio of I ： 1. The distance （r） and energy transfer efficiency（E） between donor （HSA） and acceptor （10-HCPT） are obtained as follows, r=3.51 nm; E-0.27. The enthalpy change （△Hφ） and entropy change （△Sφ） are calcu- lated at different temperatures, and the hydrophobic force and shidipole force are the functions in the reaction. The results show that 10-HCPT binds within the subdomain II A of HSA by the hydrophobic force, and the 10-OH and 20-OH of 10-HCPT bind with both residue Leu-238 of HSA and Ala 291 of HSA by hydrogen bonds.

Spectroscopic Study on Interaction of Lomefloxacin with Human Serum Albumin in the Presence of Copper Ion

The interaction of lomefloxacin （LMF） with human serum albumin （HSA） in the presence of copper ions in a physiological medium and its thermodynamic characteristics were investigated by multi-spectroscopy. The experimental results showed that both LMF and LMF-Cu^2＋ could quench the fluorescence of HSA with a static quenching mechanism, indicating that LMF or LMF-Cu^2＋ could react with HSA. The apparent binding constants/numbers of binding sites were estimated as 4.924± 105 Lomol 1/1.473 for LMF-HSA, 8.990± 104 L·mol^-1/1.785 for LMF- Cu^2＋-HSA, 1.10± 105 L·mol^-1/1.21 for LMF-Cu^2＋ and 7.30± 102 L·mol^-1/0.82 for HSA-Cu^2＋, respectively. AH and AS for LMF-HSA system were calculated to be --2.189 kJ·mol^-1 and 61.25 J·mol^-1·K^-1, while those for LMF-Cu^2＋-HSA system were -7.401 kJ·mol^-1 and 47.63 J·mol^-1·K^-1 Although the values of AH and AS in these two systems were different, the treads were similar, which indicated that electrostatic interactions in these two systems played a major role. According to Forster theory, the distances were given as 5.006 nm for HSA-LMF and 4.709 nm for HSA-LMF-Cu^2＋. Synchronous fluorescence and circular dichroism spectra confirmed further that the conformations of human serum albumin before and after interacting with LMF or LMF-Cu^2＋ were different. All the results revealed that copper ions promoted the interaction of lomefloxacin with human serum albumin.

Analysis of curcumin interaction with human serum albumin using spectroscopic studies with molecular simulation

BACKGROUND： Curcumin has emerged to be utilized as a superb beneficial agent, due to its naturally occurring anti-oxidant, anti-inflammatory and anti-carcinogenic property. METHODS： The interaction of curcumin with human serum albumin, the main in vivo transporter of exogenous substances, was investigated using absorption spectroscopy, steady-state fluorescence, excited state life-time studies and circular dichroism spectroscopy.RSULTS：Isothermal titration calorimetry techniques inferred one class of binding site with binding constant -1.74 × 10^5 M ^-1 revealing a strong interaction. The binding profile was analyzed through the evaluation of the thermodynamic parameters, which indicated the involvement of hydrophobic interactions （burial of non-polar group）. Fluorescence lifetime of tryptophan residue was observed to decrease to 1.94 ns from 2.84 ns in presence of Curcumin. Percentage of ct helicity of human serum albumin was also reduced significantly upon binding with curcumin as evidenced by circular dichroism measurement leading to conformational modification of the protein molecule. CONCLUSIONS： On the basis of such complementary results, it may be concluded that curcumin shows strong binding affinity for human serum albumin, probably at the hydrophobic cavities of the protein and at or around the tryptophan residue. Molecular Docking analysis of liSA and curcumin provided light on the number of binding sites at an atomic level, which were already determined at a molecular level in spectroscopic measurements. Our study unfolds the modes of interaction of curcumin with human serum albumin in the light of different biophysical techniques and molecular modeling analysis.