Investigation of the interaction of aurantio‐obtusin with human serum albumin by spectroscopic and molecular docking methods

The interaction between human serum albumin (HSA) and aurantio‐obtusin was investigated by spectroscopic techniques combined with molecular docking. The Stern–Volmer quenching constants (K_SV) decreased from 8.56 × 10⁵ M^?1 to 5.13 × 10⁵ M^?1 with a rise in temperatures from 289 to 310 K, indicating that aurantio‐obtusin produced a static quenching of the intrinsic fluorescence of HSA. Time‐resolved fluorescence studies proved again that the static quenching mechanism was involved in the interaction. The sign and magnitude of the enthalpy change as well as the entropy change suggested involvement of hydrogen bonding and hydrophobic interaction in aurantio‐obtusin–HSA complex formation. Aurantio‐obtusin binding to HSA produced significant alterations in secondary structures of HSA, as revealed from the time‐resolved fluorescence, Fourier transform infrared (FT‐IR) spectroscopy, three‐dimensional (3D) fluorescence and circular dichroism (CD) spectral results. Molecular docking study and site marker competitive experiment confirmed aurantio‐obtusin bound to HSA at site I (subdomain IIA).     

Interaction of cyproheptadine hydrochloride with human serum albumin using spectroscopy and molecular modeling methods

The interaction between cyproheptadine hydrochloride (CYP) and human serum albumin (HSA) was investigated by fluorescence spectroscopy, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and molecular modeling at a physiological pH (7.40). Fluorescence of HSA was quenched remarkably by CYP and the quenching mechanism was considered as static quenching since it formed a complex. The association constants K_a and number of binding sites n were calculated at different temperatures. According to Förster's theory of non‐radiation energy transfer, the distance r between donor (human serum albumin) and acceptor (cyproheptadine hydrochloride) was obtained. The effect of common ions on the binding constant was also investigated. The effect of CYP on the conformation of HSA was analyzed using FT‐IR, synchronous fluorescence spectroscopy and 3D fluorescence spectra. The thermodynamic parameters ΔH and ΔS were calculated to be ?14.37 kJ mol^?1 and 38.03 J mol^?1 K^?1, respectively, which suggested that hydrophobic forces played a major role in stabilizing the HSA‐CYP complex. In addition, examination of molecular modeling indicated that CYP could bind to site I of HSA and that hydrophobic interaction was the major acting force, which was in agreement with binding mode studies. Copyright © 2012 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.     

Elucidation of the interaction of human serum albumin with anti‐cancer sipholane triterpenoid from the Red Sea sponge

A sipholane triterpenoid, named sipholenone A, with anti‐cancer properties was isolated from the Red Sea sponge Siphonochalina siphonella and characterized by proton and carbon‐13 nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectroscopies. The goal of this study was to visualize the binding of this triterpenoid with human serum albumin (HSA) and to determine its binding site on the biomacromolecule. The interaction was visualized using fluorescence quenching, synchronous fluorescence, far‐ and near‐UV circular dichroism (CD), UV–visible and Fourier transform‐infrared (FT‐IR) spectroscopies. UV–visible spectroscopy indicated the formation of a ground‐state complex as a result of the interaction. Sipholenone A quenches the fluorescence of HSA via a static quenching mechanism. A small blue shift in the fluorescence quenching profiles suggested the involvement of hydrophobic forces in the interaction. Sipholenone A binding takes place at site I of subdomain II A with a 1:1 binding ratio, as revealed by displacement binding studies using warfarin, ibuprofen and digitoxin. Far‐UV CD and FT‐IR studies showed that the binding of sipholenone A to HSA also had a small effect on the protein's secondary structure with a slight decrease in the α‐helical content. Several thermodynamic parameters were calculated, along with Forster's radiative energy transfer analysis.     

Interaction of human serum albumin with novel imidazole derivatives studied by spectroscopy and molecular docking

This study was a detailed characterization of the interaction of a series of imidazole derivatives with a model transport protein, human serum albumin (HSA). Fluorescence and time‐resolved fluorescence results showed the existence of a static quenching mode for the HSA–imidazole derivative interaction. The binding constant at 296 K was in the order of 10⁴ M^–1, showing high affinity between the imidazole derivatives and HSA. A site marker competition study combined with molecular docking revealed that the imidazole derivatives bound to subdomain IIA of HSA (Sudlow's site I). Furthermore, the results of synchronous, 3D, Fourier transform infrared, circular dichroism and UV–vis spectroscopy demonstrated that the secondary structure of HSA was altered in the presence of the imidazole derivatives. The specific binding distance, r, between the donor and acceptor was obtained according to fluorescence resonance energy transfer. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic and molecular modelling analysis of the interaction between ethane‐1,2‐diyl bis(N,N‐dimethyl‐N‐hexadecylammoniumacetoxy)dichloride and bovine serum albumin

Several spectroscopic approaches namely fluorescence, time‐resolved fluorescence, UV‐visible, and Fourier transform infra‐red (FT‐IR) spectroscopy were employed to examine the interaction between ethane‐1,2‐diyl bis(N,N‐dimethyl‐N‐hexadecylammoniumacetoxy)dichloride (16‐E2‐16) and bovine serum albumin (BSA). Fluorescence studies revealed that 16‐E2‐16 quenched the BSA fluorescence through a static quenching mechanism, which was further confirmed by UV–visible and time‐resolved fluorescence spectroscopy. In addition, the binding constant and the number of binding sites were also calculated. The thermodynamic parameters at different temperatures (298 K, 303 K, 308 K and 313 K) indicated that 16‐E2‐16 binding to BSA is entropy driven and that the major driving forces are electrostatic interactions. Decrease of the α‐helix from 53.90 to 46.20% with an increase in random structure from 22.56 to 30.61% were also observed by FT‐IR. Furthermore, the molecular docking results revealed that 16‐E2‐16 binds predominantly by electrostatic and hydrophobic forces to some residues in the BSA sub‐domains IIA and IIIA. Copyright © 2015 John Wiley & Sons, Ltd.     

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH = 7.4) was investigated using UV–vis absorption spectroscopy (UV–vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT‐IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady‐state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >10¹⁰ L mol^?1 sec^?1. This result indicates that the ENPL–BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG ⁰), enthalpic change (ΔH ⁰) and entropic change (ΔS ⁰). The binding of ENPL with BSA is an enthalpy‐driven process due to |ΔH °| > |T ΔS °| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub‐domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α‐helical secondary structure.     

Studies on the interaction between vincamine and human serum albumin: a spectroscopic approach

The interaction between vincamine (VCM) and human serum albumin (HSA) has been studied using a fluorescence quenching technique in combination with UV/vis absorption spectroscopy, Fourier transform infrared (FT–IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling under conditions similar to human physiological conditions. VCM effectively quenched the intrinsic fluorescence of HSA via static quenching. The binding constants were calculated from the fluorescence data. Thermodynamic analysis by Van't Hoff equation revealed enthalpy change (ΔH) and entropy change (ΔS) were ?4.57 kJ/mol and 76.26 J/mol/K, respectively, which indicated that the binding process was spontaneous and the hydrophobic interaction was the predominant force. The distance r between the donor (HSA) and acceptor (VCM) was obtained according to the Förster's theory of non‐radiative energy transfer and found to be 4.41 nm. Metal ions, viz., Na⁺, K⁺, Li⁺, Ni²⁺, Ca²⁺, Zn²⁺ and Al³⁺ were found to influence binding of the drug to protein. The 3D fluorescence, FT–IR and CD spectral results revealed changes in the secondary structure of the protein upon interaction with VCM. Furthermore, molecular modeling indicated that VCM could bind to the subdomain IIA (site I) of HSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Molecular investigation of the interaction between ionic liquid type gemini surfactant and lysozyme: A spectroscopic and computational approach

Herein, we are reporting the interaction of ionic liquid type gemini surfactant, 1,4‐bis(3‐dodecylimidazolium‐1‐yl) butane bromide ([C₁₂?4‐C₁₂im]Br₂) with lysozyme by using Steady state fluorescence, UV‐visible, Time resolved fluorescence, Fourier transform‐infrared (FT‐IR) spectroscopy techniques in combination with molecular modeling and docking method. The steady state fluorescence spectra suggested that the fluorescence of lysozyme was quenched by [C₁₂?4‐C₁₂im]Br₂ through static quenching mechanism as confirmed by time resolved fluorescence spectroscopy. The binding constant for lysozyme‐[C₁₂?4‐C₁₂im]Br₂ interaction have been measured by UV‐visible spectroscopy and found to be 2.541 × 10⁵M^?1. The FT‐IR results show conformational changes in the secondary structure of lysozyme by the addition of [C₁₂?4‐C₁₂im]Br₂. Moreover, the molecular docking study suggested that hydrogen bonding and hydrophobic interactions play a key role in the protein‐surfactant binding. Additionally, the molecular dynamic simulation results revealed that the lysozyme‐[C₁₂?4‐C₁₂im]Br₂ complex reaches an equilibrium state at around 3 ns. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 406–415, 2015.     

Exploration of interaction of canthaxanthin with human serum albumin by spectroscopic and molecular simulation methods

The interaction between the food colorant canthaxanthin (CA) and human serum albumin (HSA) in aqueous solution was explored by using fluorescence spectroscopy, three‐dimensional fluorescence spectra, synchronous fluorescence spectra, UV–vis absorbance spectroscopy, circular dichroism (CD) spectra and molecular docking methods. The thermodynamic parameters calculated from fluorescence spectra data showed that CA could result in the HSA fluorescence quenching. From the K_SV change with the temperature dependence, it was concluded that HSA fluorescence quenching triggered by CA is the static quenching and the number of binding sites is one. Furthermore, the secondary structure of HSA was changed with the addition of CA based on the results of synchronous fluorescence, three‐dimensional fluorescence and CD spectra. Hydrogen bonds and van der Waals forces played key roles in the binding process of CA with HSA, which can be obtained from negative standard enthalpy (ΔH) and negative standard entropy (ΔS). Furthermore, the conclusions were certified by molecular docking studies and the binding mode was further analyzed with Discovery Studio. These conclusions can highlight the potential of the interaction mechanism of food additives and HSA.     

Assessment of the interaction procedure between Pt(IV) prodrug [Pt(5,5′-dmbpy)Cl4 and human serum albumin: Combination of spectroscopic and molecular modeling technique

In this study, a cytotoxic Pt(IV) complex [Pt(5,5′-dmbpy)Cl₄ (5,5′-dmbpy is 5,5′-dimethyl-2,2′-bipyridine) was selected to investigate its affinity to human serum albumin (HSA) by spectroscopy and molecular docking methods. This complex has a bidentate nitrogen donor ligand with four chloride anions attached to a Pt(IV) metal in a distorted octahedral environment. The ?uorescence data showed this complex quench the intrinsic ?uorescence of HSA through a static quenching mechanism. The binding constant (K_b) and the number of binding sites (n) were obtained based on the results of fluorescence measurements. UV–vis, circular dichroism spectroscopy, and three-dimensional fluorescence spectroscopy proved that the Pt(IV) complex could slightly change the secondary structure of protein. Thermodynamic parameters show that the Pt(IV) complex binds to HSA through electrostatic and Vander Waals interactions with one binding site. The molecular docking results confirmed the spectroscopic results and showed that Pt(IV) complex is embedded into subdomain IIA of protein. The aim of this study is to describe the performance of effective anti-cancer drugs when faced with proteins such as HSA.     

Binding interaction study on human serum albumin with bactericidal gold nanoparticles synthesized from a leaf extract of Musa balbisiana: a multispectroscopic approach

This study describes the eco‐friendly, low‐cost and room‐temperature synthesis of gold nanoparticles from Musa balbisiana leaf extract, which acts as both reducing and stabilizing agent, and characterized by ultraviolet?visible (UV–vis) light spectroscopy, fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE‐SEM), analytical transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDAX) and dynamic light scattering (DLS) instruments. These nanoparticles showed an average diameter of 33.83 ± 3.39 nm, which was confirmed from the size distribution histogram. The bactericidal activity of these nanoparticles was confirmed using bacteria Escherichia coli and Staphylococcus aureus at 1 and 2 nM minimum inhibitory concentrations, respectively. The interaction between nanoparticles and human serum albumin (HSA) was investigated, as this plays significant roles in biological systems. The nature of interaction, binding parameters and structural variation of HSA in the presence of these nanoparticles have been evaluated using several useful spectroscopic approaches such as UV–vis, FTIR, time‐resolved and steady‐state fluorescence, and circular dichroism in addition to the measurement of zeta potential. This interaction study revealed that static quenching occurs in this process with minimal alteration in the secondary structure, but the native structure of HSA remained unaltered. The binding constant and thermodynamic parameters of this interaction process were also evaluated.     

Study of the Enantioselective Interaction of Diclofop and Human Serum Albumin by Spectroscopic and Molecular Modeling Approaches In Vitro

In this contribution, the enantioselective interactions between diclofop (DC) and human serum albumin (HSA) were explored by steady‐state and 3D fluorescence, ultraviolet‐visible spectroscopy (UV‐vis), and molecular modeling. The binding constants between R‐DC and HSA were 0.9213 × 10⁵, 0.9118 × 10⁵, and 0.9009 × 10⁵ L · mol^‐1 at 293, 303, 313 K, respectively. Moreover, the binding constants of S‐DC for HSA were 1.4766 × 10⁵, 1.2899 × 10⁵, and 1.0882 × 10⁵ L · mol^‐1 at 293, 303, and 313 K individually. Such consequences markedly implied the binding between DC enantiomers and HSA were enantioselective with higher affinity for S‐DC. Steady‐state fluorescence study evidenced the formation of DC‐HSA complex and there was a single class of binding site on HSA. The thermodynamic parameters (ΔH, ΔS, ΔG) of the reaction clearly indicated that hydrophobic effects and H‐bonds contribute to the formation of DC‐HSA complex, which was in excellent agreement with molecular simulations. In addition, both site‐competitive replacement and molecular modeling suggested that DC enantiomers were located within the binding pocket of Sudlow's site II. Furthermore, the alterations of HSA secondary structure in the presence of DC enantiomers were verified by UV‐vis absorption and 3D fluorescence spectroscopy. This study can provide important insight into the enantioselective interaction of physiological protein HSA with chiral aryloxyphenoxy propionate herbicides and gives support to the use of HSA for chiral pesticides ecotoxicology and environmental risk assessment. Chirality 25:719–725, 2013. © 2013 Wiley Periodicals, Inc.     

Probing the mechanism of interaction of metoprolol succinate with human serum albumin by spectroscopic and molecular docking analysis

In the present work, the mechanism of the interaction between a β1 receptor blocker, metoprolol succinate (MS) and human serum albumin (HSA) under physiological conditions was investigated by spectroscopic techniques, namely fluorescence, Fourier transform infra‐red spectroscopy (FT‐IR), fluorescence lifetime decay and circular dichroism (CD) as well as molecular docking and cyclic voltammetric methods. The fluorescence and lifetime decay results indicated that MS quenched the intrinsic intensity of HSA through a static quenching mechanism. The Stern–Volmer quenching constants and binding constants for the MS–HSA system at 293, 298 and 303 K were obtained from the Stern–Volmer plot. Thermodynamic parameters for the interaction of MS with HSA were evaluated; negative values of entropy change (ΔG°) indicated the spontaneity of the MS and HSA interaction. Thermodynamic parameters such as negative ΔH° and positive ΔS° values revealed that hydrogen bonding and hydrophobic forces played a major role in MS–HSA interaction and stabilized the complex. The binding site for MS in HSA was identified by competitive site probe experiments and molecular docking studies. These results indicated that MS was bound to HSA at Sudlow's site I. The efficiency of energy transfer and the distance between the donor (HSA) and acceptor (MS) was calculated based on the theory of Fosters' resonance energy transfer (FRET). Three‐dimensional fluorescence spectra and CD results revealed that the binding of MS to HSA resulted in an obvious change in the conformation of HSA. Cyclic voltammograms of the MS–HSA system also confirmed the interaction between MS and HSA. Furthermore, the effects of metal ions on the binding of MS to HSA were also studied.     

Spectroscopic and molecular simulation studies on the interaction of di‐(2‐ethylhexyl) phthalate and human serum albumin

Di‐(2‐ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in industrial production, but may have a potential health risk. In this study, the binding characteristics of DEHP with human serum albumin (HSA) in aqueous solution at pH 7.4 were determined using UV/vis absorption, fluorescence, Fourier transform infrared (FTIR) spectroscopy and circular dichroism (CD), along with a molecular simulation technique. Analysis of the fluorescence titration data at different temperatures suggested that the fluorescence quenching mechanism of HSA by DEHP was static. The calculated thermodynamic parameters indicated that hydrophobic forces played a predominant role in formation of the DEHP–HSA complex, but hydrogen bonds could not be omitted. Site marker competitive experiments and denaturation studies showed that the binding of DEHP to HSA primarily took place in subdomain IIA of HSA, and molecular docking results further corroborated the binding sites. The synchronous fluorescence, UV/vis absorption, FTIR and CD spectra revealed that the addition of DEHP induced changes in the secondary structure of HSA. Protein surface hydrophobicity (PSH) tests indicated that DEHP binding to HSA caused an increase in the PSH. Moreover, the effects of some metal ions on the binding constant of DEHP − HSA interaction were also investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Insights into In Vitro Binding of Parecoxib to Human Serum Albumin by Spectroscopic Methods

Herein, we report the effect of parecoxib on the structure and function of human serum albumin (HSA) by using fluorescence, circular dichroism (CD), Fourier transforms infrared (FTIR), three‐dimensional (3D) fluorescence spectroscopy, and molecular docking techniques. 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 parecoxib binds spontaneously with HSA through van der Waals forces and hydrogen bonds with binding constant of 3.45 × 10⁴ M^?1 at 298 K. It can be seen from far‐UV CD spectra that the α‐helical network of HSA is disrupted and its content decreases from 60.5% to 49.6% at drug:protein = 10:1. Protein tertiary structural alterations induced by parecoxib were also confirmed by FTIR and 3D fluorescence spectroscopy. The molecular docking study indicated that parecoxib is embedded into the hydrophobic pocket of HSA.     

Comparison of interactions between human serum albumin and silver nanoparticles of different sizes using spectroscopic methods

Three different sizes (15.9 ± 2.1 nm, 26.4 ± 3.2 nm and 39.8 ± 4.0 nm, respectively) of citrate‐coated silver nanoparticles (SNPs) have been synthesized and characterized. The interactions of the synthesized SNPs with human serum albumin (HSA) at physiological pH have been systematically studied by UV‐vis absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The results indicate that the SNPs can bind to HSA with high affinity and quench the intrinsic fluorescence of HSA. The binding constants and quenching rate constants were calculated. The apparent association constants (K_app) values are 2.14 × 10⁴ M^–1 for 15.9 nm SNP, 1.65 × 10⁴ M^–1 for 26.4 nm SNP and 1.37 × 10⁴ M^–1 for 39.8 nm SNP, respectively. The values of binding constant obtained from the fluorescence quenching data match well with that determined from the absorption spectral changes. These results suggest that the smaller SNPs have stronger interactions to HSA than the larger ones at the same concentrations. Synchronous fluorescence, three‐dimensional fluorescence and CD spectroscopy studies show that the synthesized SNPs can induce slight conformational changes in HSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation on the Interaction of Hydroxyethyl Starch 130/0.4 (Voluven) and Serum Albumin for Pharmacokinetic and Toxicological Implications

The interaction of hydroxyethyl starch 130/0.4 (Voluven) with human serum albumin (HSA) has been investigated by fluorescence (steady state and synchronous), Fourier transforms infrared (FT‐IR), and circular dichroism (CD) spectroscopies. Analysis of the fluorescence quenching data of HSA by Voluven using the Stern–Volmer method revealed the formation of 1:1 ground‐state complex. Evaluation of binding parameters and binding energy indicated that the binding reaction was exothermic. On the basis of fluorescence measurements, it was concluded that electrostatic forces play a crucial role in stabilizing the complex. The binding distance was calculated by using Förster resonance energy transfer (FRET) theory. The conformational changes of HSA were obtained qualitatively as well as quantitatively using synchronous fluorescence, FT‐IR, and CD. The HSA underwent partial unfolding in the presence of Voluven.     

Multi-spectroscopic,thermodynamic and molecular docking studies to investigate the interaction of eplerenone with human serum albumin

The binding of small molecular drugs with human serum albumin (HSA) has a crucial influence on their pharmacokinetics. The binding interaction between the antihypertensive eplerenone (EPL) and HSA was investigated using multi-spectroscopic techniques for the first time. These techniques include ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), native fluorescence spectroscopy, synchronous fluorescence spectroscopy and molecular docking approach. The fluorescence spectroscopic study showed that EPL quenched HSA inherent fluorescence. The mechanism for quenching of HSA by EPL has been determined to be static in nature and confirmed by UV absorption and fluorescence spectroscopy. The modified Stern–Volmer equation was used to estimate the binding constant (K_b) as well as the number of bindings (n). The results indicated that the binding occurs at a single site (K_b = 2.238 × 10³ L mol⁻¹at 298 K). The enthalpy and entropy changes (∆H and ∆S) were 58.061 and 0.258 K J mol⁻¹, respectively, illustrating that the principal intermolecular interactions stabilizing the EPL–HSA system are hydrophobic forces. Synchronous fluorescence spectroscopy revealed that EPL binding to HSA occurred around the tyrosine (Tyr) residue and this agreed with the molecular docking study. The Förster resonance energy transfer (FRET) analysis confirmed the static quenching mechanism. The esterase enzyme activity of HSA was also evaluated showing its decrease in the presence of EPL. Furthermore, docking analysis and site-specific markers experiment revealed that EPL binds with HSA at subdomain IB (site III).     

Binding of Janus kinase inhibitor tofacitinib with human serum albumin: multi-technique approach

In this report, we have investigated the binding affinity of tofacitinib with human serum albumin (HSA) under simulated physiological conditions by using UV–visible spectroscopy, fluorescence quenching measurements, dynamic light scattering (DLS), differential scanning calorimetry (DSC) and molecular docking methods. The obtained results demonstrate that fluorescence intensity of HSA gets quenched by tofacitinib and quenching occurs in static manner. Binding parameters calculated from modified Stern–Volmer equation shows that the drug binds to HSA with a binding constant in the order of 10⁵. Synchronous fluorescence data deciphered the change in the microenvironment of tryptophan residue in HSA. UV spectroscopy and DLS measurements deciphered complex formation and reduction in hydrodynamic radii of the protein, respectively. Further DSC results show that tofacitinib increases the thermo stability of HSA. Hydrogen bonding and hydrophobic interaction are the main binding forces between HSA and tofacitinib as revealed by docking results.