Insight into the interaction of antitubercular and anticancer compound clofazimine with human serum albumin: spectroscopy and molecular modelling

The binding of clofazimine to human serum albumin (HSA) was investigated by applying optical spectroscopy and molecular docking methods. Fluorescence quenching data revealed that clofazimine binds to protein with binding constant in the order of 10⁴ M^?1, and with the increase in temperature, Stern–Volmer quenching constants gradually decreased indicating quenching mode to be static. The UV–visible spectra showed increase in absorbance upon interaction of HSA with clofazimine which further reveals formation of the drug–albumin complex. Thermodynamic parameters obtained from fluorescence data indicate that the process is exothermic and spontaneous. Forster distance (R_o) obtained from fluorescence resonance energy transfer is found to be 2.05 nm. Clofazimine impelled rise in α-helical structure in HSA as observed from far-UV CD spectra while there are minor alterations in tertiary structure of the protein. Clofazimine interacts strongly with HSA inducing secondary structure in the protein and slight alterations in protein topology as suggested by dynamic light scattering results. Moreover, docking results indicate that clofazimine binds to hydrophobic pocket near to the drug site II in HSA.     

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.     

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.     

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).     

Interaction of a tyrosine kinase inhibitor,vandetanib with human serum albumin as studied by fluorescence quenching and molecular docking

Interaction of a tyrosine kinase inhibitor, vandetanib (VDB), with the major transport protein in the human blood circulation, human serum albumin (HSA), was investigated using fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking analysis. The binding constant of the VDB–HSA system, as determined by fluorescence quenching titration method was found in the range, 8.92–6.89?×?10^3?M^?1 at three different temperatures, suggesting moderate binding affinity. Furthermore, decrease in the binding constant with increasing temperature revealed involvement of static quenching mechanism, thus affirming the formation of the VDB–HSA complex. Thermodynamic analysis of the binding reaction between VDB and HSA yielded positive ΔS (52.76 J?mol^?1 K^?1) and negative ΔH (?6.57?kJ?mol^?1) values, which suggested involvement of hydrophobic interactions and hydrogen bonding in stabilizing the VDB–HSA complex. Far-UV and near-UV CD spectral results suggested alterations in both secondary and tertiary structures of HSA upon VDB-binding. Three-dimensional fluorescence spectral results also showed significant microenvironmental changes around the Trp residue of HSA consequent to the complex formation. Use of site-specific marker ligands, such as phenylbutazone (site I marker) and diazepam (site II marker) in competitive ligand displacement experiments indicated location of the VDB binding site on HSA as Sudlow’s site I (subdomain IIA), which was further established by molecular docking results. Presence of some common metal ions, such as Ca²⁺, Zn²⁺, Cu²⁺, Ba²⁺, Mg²⁺, and Mn²⁺ in the reaction mixture produced smaller but significant alterations in the binding affinity of VDB to HSA.     

Probing the intermolecular interactions into serum albumin and anthraquinone systems: a spectroscopic and docking approach

Intermolecular interaction study of human serum albumin (HSA) with two anthraquinones i.e. danthron and quinizarin has been performed through fluorescence, UV-vis and CD spectroscopy along with docking analysis. The titration of drugs into HSA solution brought about the quenching of fluorescence emission by way of complex formation. The binding constants were found to be 1.51 × 10⁴ L mol^?1 and 1.70 × 10⁴ L mol^?1 at λ_exc = 280 nm while at λ_exc = 295 nm, the values of binding constants were 1.81 × 10⁴ L mol^?1 and 1.90 × 10⁴ L mol^?1 which hinted toward binding of both the drugs in the vicinity of subdomain IIA. Different temperature study revealed the presence of static quenching mechanism. Moreover, more effective quenching of the fluorescence emission was observed at λ_exc = 295 nm which also suggested that both the drug molecule bind nearer to Trp-214. Thermodynamic parameters showed that hydrophobic interaction was the major force behind the binding of drugs. The UV-vis spectroscopy testified the formation of complex in both the systems and primary quenching mechanism as static one. The changes in secondary structure and α-helicity in both the systems were observed by circular dichroism spectroscopy. Furthermore, molecular docking analysis predicted the probable binding site of drugs in subdomain IIA of HSA molecule. The types of amino acid residues surrounding the drug molecule advocated that van der Waals forces, hydrophobic forces and electrostatic forces played a vital role in the stabilization of drug-protein complex formed.     

Spectroscopic and molecular modeling approaches to investigate the binding of proton pump inhibitors to human serum albumin

The interaction between two proton pump inhibitors viz., omeprazole (OME) and esomeprazole (EPZ) with human serum albumin (HSA) was studied by fluorescence, absorption, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), voltammetry, and molecular modeling approaches. The Stern–Volmer quenching constants (K_sv) for OME-HSA and EPZ-HSA systems obtained at different temperatures revealed that both OME and EPZ quenched the intensity of HSA through dynamic mode of quenching mechanism. The binding constants of OME-HSA and EPZ-HSA increased with temperature, indicating the increased stability of these systems at higher temperatures. Thermodynamic parameters viz., ?H^°, ?S^°, and ?G^° were determined for both systems. These values revealed that both systems were stabilized by hydrophobic forces. The competitive displacement and molecular docking studies suggested that OME/EPZ was bound to Sudlow’s site I in subdomain IIA in HSA. The extent of energy transfer from HSA to OME/EPZ and the distance of separation in tryptophan (Trp214) Trp214-OME and Trp214-EPZ was determined based on the theory of fluorescence resonance energy transfer. UV absorption, 3D fluorescence, and CD studies indicated that the binding of OME/EPZ to HSA has induced micro environmental changes around the protein which resulted changes in its secondary structure.     

Combination mode of antimalarial drug mefloquine and human serum albumin: Insights from spectroscopic and docking approaches

The interaction between mefloquine (MEF), the antimalarial drug, and human serum albumin (HSA), the main carrier protein in blood circulation, was explored using fluorescence, absorption, and circular dichroism spectroscopic techniques. Quenching of HSA fluorescence with MEF was characterized as static quenching and thus confirmed the complex formation between MEF and HSA. Association constant values for MEF-HSA interaction were found to fall within the range of 3.79-5.73 × 10⁴ M^˗1 at various temperatures (288, 298, and 308 K), which revealed moderate binding affinity. Hydrogen bonds and hydrophobic interactions were predicted to connect MEF and HSA together in the MEF-HSA complex, as deduced from the thermodynamic data (ΔS = +133.52 J mol⁻¹ K⁻¹ and ΔH = +13.09 kJ mol⁻¹) of the binding reaction and molecular docking analysis. Three-dimensional fluorescence spectral analysis pointed out alterations in the microenvironment around aromatic amino acid (tryptophan and tyrosine) residues of HSA consequent to the addition of MEF. Circular dichroic spectra of HSA in the wavelength ranges of 200-250 and 250-300 nm hinted smaller changes in the protein's secondary and tertiary structures, respectively, induced by MEF binding. Noncovalent conjugation of MEF to HSA bettered protein thermostability. Site marker competitive drug displacement results suggested HSA Sudlow's site I as the MEF binding site, which was also supported by molecular docking analysis.     

Experimental and computational studies on the binding of diazinon to human serum albumin

In the present research, the binding properties of diazinon (DZN), as an organophosphorus herbicide, to human serum albumin (HSA) were investigated using combination of spectroscopic, electrochemistry, and molecular modeling techniques. Changes in the UV–Vis and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. The obtained results from spectroscopic and electrochemistry experiments along with the computational studies suggest that DZN binds to residues located in subdomains IIA of HSA with binding constant about 1410.9 M^?1 at 300 K. From the thermodynamic parameters calculated according to the van’t Hoff equation, the enthalpy change ΔH° and entropy change ΔS° were found to be ?16.695 and 0.116 KJ/mol K, respectively. The primary binding pattern is determined by hydrophobic interaction and hydrogen binding occurring in so-called site I of HSA. DZN could slightly alter the secondary structure of HSA. All of experimental results are supported by computational techniques such as docking and molecular dynamics simulation using a HSA crystal model.     

Binding of methacycline to human serum albumin at subdomain IIA using multispectroscopic and molecular modeling methods

This study was designed to examine the interaction of methacyline (METC) with human serum albumin (HSA) by multispectroscopy and a molecular modeling method under simulative physiological conditions. The quenching mechanism was suggested to be static quenching based on fluorescence and ultraviolet–visible (UV–Vis) spectroscopy. According to the Vant' Hoff equation, the values of enthalpy (?H) and entropy change (?S) were calculated to be ?95.29 kJ/mol and ?218.13 J/mol/K, indicating that the main driving force of the interaction between HSA and METC were hydrogen bonds and van der Waals's forces. By performing displacement measurements, the specific binding of METC in the vicinity of Sudlow's site I of HSA was clarified. An apparent distance of 3.05 nm between Trp214 and METC was obtained via the fluorescence resonance energy transfer (FRET) method. Furthermore, the binding details between METC and HSA were further confirmed by molecular docking studies, which revealed that METC was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, polar forces, hydrogen bonding, etc. The results of three‐dimensional fluorescence and Fourier transform infrared (FTIR) spectroscopy showed that METC caused conformational and some microenvironmental changes in HSA and reduced the α‐helix significantly in the range of 52.3?40.4% in HSA secondary structure. Moreover, the coexistence of metal ions such as Ca²⁺, Al³⁺, Fe³⁺, Zn²⁺, Cu²⁺, Cr³⁺ and Cd²⁺ can decrease the binding constants of METC–HSA. Copyright © 2012 John Wiley & Sons, Ltd.     

Interactive association between RhoA transcriptional signaling inhibitor,CCG1423 and human serum albumin: Biophysical and in silico studies

Multiple spectroscopic techniques, such as fluorescence, absorption, and circular dichroism along with in silico studies were used to characterize the binding of a potent inhibitor molecule, CCG1423 to the major transport protein, human serum albumin (HSA). Fluorescence and absorption spectroscopic results confirmed CCG1423–HSA complex formation. A strong binding affinity stabilized the CCG1423–HSA complex, as evident from the values of the binding constant (K_a = 1.35 × 10⁶–5.43 × 10⁵ M^?1). The K_SV values for CCG1423–HSA system were inversely correlated with temperature, suggesting the involvement of static quenching mechanism. Thermodynamic data anticipated that CCG1423–HSA complexation was mainly driven by hydrophobic and van der Waals forces as well as hydrogen bonds. In silico analysis also supported these results. Three-dimensional fluorescence and circular dichroism spectral analysis suggested microenvironmental perturbations around protein fluorophores and structural (secondary and tertiary) changes in the protein upon CCG1423 binding. CCG1423 binding to HSA also showed some protection against thermal denaturation. Site-specific marker-induced displacement results revealed CCG1423 binding to Sudlow’s site I of HSA, which was also confirmed by the computational results. A few common ions were also found to interfere with the CCG1423–HSA interaction.     

Insights into the binding of paclitaxel to human serum albumin: multispectroscopic studies

The interaction of paclitaxel with human serum albumin (HSA) was studied using fluorescence, resonance light scattering, ultraviolet‐visible, circular dichroism and Fourier transform infrared spectroscopy at pH 7.4. Fluorescence data revealed that the fluorescence quenching of HSA by paclitaxel was a static quenching procedure. Time‐resolved fluorescence data also confirmed the quenching mode, which present a constant decay time of about 5 ns. The binding sites were approximately 1 and the binding constant suggested a weak association (324/M at 298 K), which is helpful for the release of the drug to targeted organs. The thermodynamic parameters, ΔG^○, ΔH° and ΔS° were calculated as – 1.06 × 10⁴ J/mol, 361 J/mol per K and 9.7 × 10⁴ J/mol respectively at 298 K, suggesting that binding was spontaneous and was driven mainly by hydrophobic interactions. The binding distance between HSA and paclitaxel was determined to be 2.23 nm based on the Förster theory. Analysis of circular dichroism, ultraviolet‐visible, three‐dimensional fluorescence, Fourier transform infrared and resonance light scattering spectra demonstrated that HSA conformation was slightly altered in the presence of paclitaxel and dimension of the individual HSA molecules were larger after interacting with paclitaxel. These results were confirmed by a molecular docking study. Copyright © 2013 John Wiley & Sons, Ltd.     

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).     

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.     

Multi-spectroscopic and molecular modelling approach to investigate the interaction of riboflavin with human serum albumin

Riboflavin (RF) plays an important role in various metabolic redox reactions in the form of flavin adenine dinucleotide and flavin mononucleotide. Human serum albumin (HSA) is an important protein involved in the transportation of drugs, hormones, fatty acid and other molecules which determine the biodistribution and physiological fate of these molecules. In this study, we have investigated the interaction of riboflavin RF with HSA under simulative physiological conditions using various biophysical, calorimetric and molecular docking techniques. Results demonstrate the formation of riboflavin–HSA complex with binding constant in the order of 10⁴ M^?1. Fluorescence spectroscopy confirms intermediate strength having a static mode of quenching with stoichiometry of 1:1. Experimental results suggest that the binding site of riboflavin mainly resides in sub-domain IIA of HSA and that ligand interaction increases the α-helical content of HSA. These parameters were further verified by isothermal titration calorimetry ITC which confirms the thermodynamic parameters obtained by fluorescence spectroscopy. Molecular docking was employed to suggest a binding model. Based on thermodynamic, spectroscopic and computational observations it can be concluded that HSA-riboflavin complex is mainly stabilized by various non-covalent forces with binding energy of ?7.2 kcal mol^?1.     

Probing the binding of two 19‐nortestosterone derivatives to human serum albumin: insights into the interactions of steroid hormone drugs with functional biomacromolecule

Norethindrone acetate (NETA) is a fatty acid ester of norethindrone (NET) that can convert to its more active parent compound NET when orally administered. To study the interactions of NETA and NET with human serum albumin (HSA), we applied fluorescence spectroscopy, circular dichroism (CD), and molecular docking. The effects of metal ions on the HSA–NETA/NET system were also explored. Fluorescence data showed that the quenching mechanism of HSA by NETA and NET was consistent with a static model and that the binding constant of NETA was higher than that of NET. Thermodynamic parameters indicated that hydrogen bonds and van der Waals forces were the main forces maintaining the stability of the HSA–NETA/NET complex. Molecular modeling studies revealed that NETA and NET were bound within subdomain IIA of HSA, in accordance with the site probe results. Synchronous fluorescence spectroscopy, CD, and three‐dimensional fluorescence spectroscopy further confirmed that the binding of NETA/NET to HSA changed the secondary structure of the protein. All other metal ions, except for Ca²⁺, decreased the K value of the HSA–NETA/NET system with enhancement of the maximum effectiveness of NETA/NET. Three commercially available steroid hormone drugs influenced the binding ability of NETA on HSA to different extents. This study provides novel insights into the interactions between HSA and NETA/NET, as well as a solid foundation for future research on drug pharmacokinetics and pharmacodynamics. Copyright © 2016 John Wiley & Sons, Ltd.     

Binding forces between a novel Schiff base palladium(II) complex and two carrier proteins: human serum albumi and β-lactoglobulin

Ligand binding studies on carrier proteins are crucial in determining the pharmacological properties of drug candidates. Here, a new palladium(II) complex was synthesized and characterized. The in vitro binding studies of this complex with two carrier proteins, human serum albumin (HSA), and β-lactoglobulin (βLG) were investigated by employing biophysical techniques as well as computational modeling. The experimental results showed that the Pd(II) complex interacted with two carrier proteins with moderate binding affinity (K_b ≈ .5 × 10⁴ M^?1 for HSA and .2 × 10³ M^?1 for βLG). Binding of Pd(II) complex to HSA and βLG caused strong fluorescence quenching of both proteins through static quenching mechanism. In two studied systems hydrogen bonds and van der Waals forces were the major stabilizing forces in the drug-protein complex formation. UV–Visible and FT-IR measurements indicated that the binding of above complex to HSA and βLG may induce conformational and micro-environmental changes of two proteins. Protein–ligand docking analysis confirmed that the Pd(II) complex binds to residues located in the subdomain IIA of HSA and site A of βLG. All these experimental and computational results suggest that βLG and HSA might act as carrier protein for Pd(II) complex to deliver it to the target molecules.     

Cytotoxicity and comparative binding mechanism of piperine with human serum albumin and α-1-acid glycoprotein

Human serum albumin (HSA) and α-1-acid glycoprotein (AGP) (acute phase protein) are the plasma proteins in blood system which transports many drugs. To understand the pharmacological importance of piperine molecule, here, we studied the anti-inflammatory activity of piperine on mouse macrophages (RAW 264.7) cell lines, which reveals that piperine caused an increase in inhibition growth of inflammated macrophages. Further, the fluorescence maximum quenching of proteins were observed upon binding of piperine to HSA and AGP through a static quenching mechanism. The binding constants obtained from fluorescence emission were found to be K_piperine?=?5.7 ± .2 × 10⁵ M^?1 and K_piperine = 9.3± .25 × 10⁴ M^?1 which correspond to the free energy of ?7.8 and ?6.71 kcal M^?1at 25 °C for HSA and AGP, respectively. Further, circular dichrosim studies revealed that there is a marginal change in the secondary structural content of HSA due to partial destabilization of HSA–piperine complexes. Consequently, inference drawn from the site-specific markers (phenylbutazone, site I marker) studies to identify the binding site of HSA noticed that piperine binds at site I (IIA), which was further authenticated by molecular docking and molecular dynamic (MD) studies. The binding constants and free energy corresponding to experimental and computational analysis suggest that there are hydrophobic and hydrophilic interactions when piperine binds to HSA. Additionally, the MD studies have showed that HSA–piperine complex reaches equilibration state at around 3 ns, which prove that the HSA–piperine complex is stable in nature.     

Characterization of human serum albumin's interactions with safranal and crocin using multi-spectroscopic and molecular docking techniques

Interaction mechanisms of human serum albumin (HSA) with safranal and crocin were studied using UV–Vis absorption, fluorescence quenching and circular dichroism (CD) spectroscopies as well as molecular docking techniques. Changes in absorbance and fluorescence of HSA upon interactions with both compounds were attributed to their binding to amino acid chromophores located in subdomains IIA and IIIA. Fluorescence secondary inner filter effect was excluded using 278 nm and 340 nm as the wavelengths of HSA's excitation and fluorescence while safranal and crocin absorbed at 320 nm and 445 nm, respectively. Stern-Volmer model revealed a static quenching mechanism involve the formation of non-fluorescent ground state complexes. Stern-Volmer, Hill, Benesi-Hilbrand and Scatchard models gave apparent binding constants ranged in 4.25 × 10³ - 2.15 × 10⁵ for safranal and 7.67 × 10³ - 4.23 × 10⁵ L mol^?1 for crocin. CD measurements indicated that 13 folds of safranal and crocin unfolded the α-helix structure of HSA by 7.47–21.20%. In-silico molecular docking revealed selective exothermic binding of safranal on eight binding sites with binding energies ranged in ?3.969 to ?6.6.913 kcal/mol. Crocin exothermally bound to a new large pocket located on subdomain IIA (sudlow 1) with binding energy of ?12.922 kcal/mol.These results confirmed the formation of HSA stable complexes with safranal and crocin and contributed to our understanding for their binding characteristics (affinities, sites, modes, forces … etc.) and structural changes upon interactions. They also proved that HSA can solubilize and transport both compounds in blood to target tissues. The results are of high importance in determining the pharmacological properties of the two phytochemical compounds and for their future developments as anticancer, antispasmodic, antidepressant or aphrodisiac therapeutic agents.     

Exploring the interactions of a Tb(III)–quercetin complex with serum albumins (HSA and BSA): spectroscopic and molecular docking studies

Serum albumins (human serum albumin (HSA) and bovine serum albumin (BSA), two main circulatory proteins), are globular and monomeric macromolecules in plasma that transport many drugs and compounds. In the present study, we investigated the interactions of the Tb(III)–quercetin (Tb–QUE) complex with HSA and BSA using common spectroscopic techniques and a molecular docking study. Fluorescence data revealed that the inherent fluorescence emission of HSA and BSA was markedly quenched by the Tb–QUE complex through a static quenching mechanism, confirming stable complex formation (a ground‐state association) between albumins and Tb–QUE. Binding and thermodynamic parameters were obtained from the fluorescence spectra and the related equations at different temperatures under biological conditions. The binding constants (K_b) were calculated to be 0.8547 × 10³ M^?1 for HSA and 0.1363 × 10³ M^?1 for BSA at 298 K. Also, the number of binding sites (n) of the HSA/BSA–Tb–QUE systems was obtained to be approximately 1. Thermodynamic data calculations along with molecular docking results indicated that electrostatic interactions have a main role in the binding process of the Tb–QUE complex with HSA/BSA. Furthermore, molecular docking outputs revealed that the Tb–QUE complex has high affinity to bind to subdomain IIA of HSA and BSA. Binding distances (r) between HSA–Tb–QUE and BSA–Tb–QUE systems were also calculated using the Forster (fluorescence resonance energy transfer) method. It is expected that this study will provide a pathway for designing new compounds with multiple beneficial effects on human health from the phenolic compounds family such as the Tb–QUE complex.