Specific interaction of 4′-O-(a-l-Cladinosyl) daunorubicin with human serum albumin: The binding site II on HSA molecular using spectroscopy and modeling

Influence of diimine bidentate ligand in the nitrosyl and nitro terpyridine ruthenium complex on the HSA/DNA interaction and antiviral activity

Nitric oxide (NO) acts in different physiological processes, such as blood pressure control, antiparasitic activities, neurotransmission, and antitumor action. Among the exogenous NO donors, ruthenium nitrosyl/nitro complexes are potential candidates for prodrugs, due to their physicochemical properties, such as thermal and physiological pH stability. In this work, we proposed the synthesis and physical characterization of the new nitro terpyridine ruthenium (II) complexes of the type [RuII(L)(NO2)(tpy)]PF6 where tpy = 2,2':6',2″-terpyridine; L = 3,4-diaminobenzoic acid (bdq) or o-phenylenediamine (bd) and evaluation of influence of diimine bidentate ligand NH.NHq-R (R = H or COOH) in the HSA/DNA interaction as well as antiviral activity. The interactions between HSA and new nitro complexes [RuII(L)(NO2)(tpy)]+ were evaluated. The Ka values for the HSA-[RuII(bdq)(NO2)(tpy)]+ is 10 times bigger than HSA-[RuII(bd)(NO2)(tpy)]+. The sites of interaction between HSA and the complexes via synchronous fluorescence suppression indicate that the [RuII(bdq)(NO2)(tpy)]+ is found close to the Trp-241 residue, while the [RuII(bd)(NO2)(tpy)]+ complex is close to Tyr residues. The interaction with fish sperm fs-DNA using direct spectrophotometric titration (Kb) and ethidium bromide replacement (KSV and Kapp) showed weak interaction in the system fs-DNA-[RuII(bdq)(NO)(tpy)]+. Furthermore, fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+ system showed higher intercalation constant. Circular dichroism spectra for fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+, suggest semi-intercalative accompanied by major groove binding interaction modes. The [RuII(bd)(NO2)(tpy)]+ and [RuII(bd)(NO)(tpy)]3+ inhibit replication of Zika and Chikungunya viruses based in the nitric oxide release under S-nitrosylation reaction with cysteine viral.

Calorimetric and spectroscopic detection of the interaction between a diazo dye and human serum albumin

Dye effluents are one of the main causes of water pollution. Azo dyes, the most widely applied colorants, are particularly difficult to degrade. Exposure of such dyes to the aquatic environment is hazardous to human health and biota due to their intrinsic harmful mutagenic and carcinogenic properties. Congo Red (CR) is an anionic and synthetic diazo dye, which is recalcitrant to the biodegradative process and metabolizes to produce a potential carcinogen. Research on the interaction of this toxic dye with serum albumin, as a transport protein, is of paramount significance because the physiological and toxicological behaviours of the dye in vivo are associated with its interactive characteristics with the proteins. In this regard, a detailed binding profile of CR with human serum albumin (HSA) was studied using isothermal titration calorimetry (ITC) along with various spectroscopic and microscopic methods. The thermodynamic results from ITC indicated that the CR-HSA non-covalent interaction occured primarily due to favorable entropy and unfavorable enthalpy with a Ka of 106 M-1 at lower concentrations and 105 M-1 at higher concentrations. Steady-state fluorescence data revealed that the intrinsic fluorescence of HSA was quenched in the presence of CR via the static quenching mechanism. Using Förster's non-radioactive energy transfer theory (FRET), the specific binding distance r (2.73 nm) between the donor (Trp-214 from HSA) and the acceptor (CR) was calculated. Our preliminary results indicated that CR had a high affinity to HSA, which can have significant implications in the distribution and elimination of this toxic dye upon exposure.

Investigation of the binding and simultaneous quantifications of propanil and bromoxynil herbicide concentrations in human serum albumin

This study reported the use of UV-visible and fluorescence spectroscopy and partial-least-square (PLS) multivariate regression for accurate and simultaneous quantifications of two widely used herbicides, propanil, 3',4'-dichloropropionanilide (PPL) and bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile (BXL) in human serum albumin (HSA) at physiological conditions. The binding affinity and thermodynamic properties of PPL-HSA and BXL-HSA complexes were also investigated. Partial-least-square (PLS) regression was used to collate the variability in the absorption or emission spectra of PPL-HSA and BXL-HSA complexes with PPL and/or BXL concentrations in HSA samples. The binding constants of 7.66× 10⁸ M^-1 for PPL-HSA and 4.88× 10⁶ M^-1 for BXL-HSA complexes were calculated at physiological conditions (temperature, 310 K; pH 7.4). Thermodynamic parameter values: enthalpy (ΔH) (13.99 kJ mol^-1), entropy (ΔS) (0.078 kJ mol^-1 K^-1), and Gibbs free energy (ΔG) (-10.19 kJ mol^-1) were determined for PPL-HSA complexation at physiological conditions. However, differences in thermodynamic property values of: ΔH (-214.3 kJ mol^-1), ΔS (-0.563 kJ mol^-1 K^-1), and ΔG (-39.70 kJ mol^-1) were observed for BXL-HSA complexes. The binding constants and negative ΔG values indicated strong binding affinity and thermodynamically favorability of PPL-HSA and BXL-HSA complex formation. Results of the PLS regression calibration showed good linearity (R² ≥ 0.998289), high sensitivity, and impressive low limit-of-detections (LODs) of 1.38× 10^-8 M for PPL and 1.68× 10^-8 M for BXL that are comparable and/or lower than many previously reported LODs for herbicide and pesticide analyses. Most importantly, PLS regression is capable of simultaneous quantifications of PPL and BXL concentrations in HSA samples with good accuracy and low errors of 3.66%. UV-visible spectrophotometers and spectrofluorometers are fairly inexpensive, easy to use, and are readily available in almost every laboratory, making this protocol excellent and affordable for routine analysis of weed/pest control chemical residues in humans. The results of this study are significant and remarkable that will provide critical insight into the binding mechanism of herbicide toxicity in humans and non-target organisms, which are of special interest in the area of biomedical study, environmental risk assessment, and ecotoxicology.

Interactions of cephalexin with bovine serum albumin: displacement reaction and molecular docking

Introduction: The drug-plasma protein interaction is a fundamental issue in guessing and checking the serious drug side effects related with other drugs. The purpose of this research was to study the interaction of cephalexin with bovine serum albumin (BSA) and displacement reaction using site probes.

Methods: The interaction mechanism concerning cephalexin (CPL) with BSA was investigated using various spectroscopic methods and molecular modeling method. The binding sites number, n, apparent binding constant, K, and thermodynamic parameters, ΔG⁰, ΔH⁰, and ΔS⁰ were considered at different temperatures. To evaluate the experimental results, molecular docking modeling was calculated.

Results: The distance, r=1.156 nm between BSA and CPL were found in accordance with the Forster theory of non-radiation energy transfer (FRET) indicating energy transfer occurs between BSA and CPL. According to the binding parameters and ΔG⁰= negative values and ΔS⁰= 28.275 j mol^-1K^-1, a static quenching process is effective in the CPL-BSA interaction spontaneously. ΔG⁰ for the CPL-BSA complex obtained from the docking simulation is -28.99 kj mol^-1, which is close to experimental ΔG of binding, -21.349 kj mol^-1 that indicates a good agreement between the results of docking methods and experimental data.

Conclusion: The outcomes of spectroscopic methods revealed that the conformation of BSA changed during drug-BSA interaction. The results of FRET propose that CPL quenches the fluorescence of BSA by static quenching and FRET. The displacement study showed that phenylbutazon and ketoprofen displaced CPL, indicating that its binding site on albumin is site I and Gentamicin cannot be displaced from the binding site of CPL. All results of molecular docking method agreed with the results of experimental data.

α-Mangostin Extraction from the Native Mangosteen (Garcinia mangostana L.) and the Binding Mechanisms of α-Mangostin to HSA or TRF

In order to obtain the biological active compound, α-mangostin, from the traditional native mangosteen (Garcinia mangostana L.), an extraction method for industrial application was explored. A high yield of α-mangostin (5.2%) was obtained by extraction from dried mangosteen pericarps with subsequent purification on macroporous resin HPD-400. The chemical structure of α-mangostin was verified mass spectrometry (MS), nuclear magnetic resonance (¹H NMR and ¹³C NMR), infrared spectroscopy (IR) and UV-Vis spectroscopy. The purity of the obtained α-mangostin was 95.6% as determined by HPLC analysis. The binding of native α-mangostin to human serum albumin (HSA) or transferrin (TRF) was explored by combining spectral experiments with molecular modeling. The results showed that α-mangostin binds to HSA or TRF as static complexes but the binding affinities were different in different systems. The binding constants and thermodynamic parameters were measured by fluorescence spectroscopy and absorbance spectra. The association constant of HSA or TRF binding to α-mangostin is 6.4832×10⁵ L/mol and 1.4652×10⁵ L/mol at 298 K and 7.8619×10⁵ L/mol and 1.1582×10⁵ L/mol at 310 K, respectively. The binding distance, the energy transfer efficiency between α-mangostin and HSA or TRF were also obtained by virtue of the Förster theory of non-radiation energy transfer. The effect of α-mangostin on the HSA or TRF conformation was analyzed by synchronous spectrometry and fluorescence polarization studies. Molecular docking results reveal that the main interaction between α-mangostin and HSA is hydrophobic interactions, while the main interaction between α-mangostin and TRF is hydrogen bonding and Van der Waals forces. These results are consistent with spectral results.

Synthesis, characterization and biological application of four novel metal-Schiff base complexes derived from allylamine and their interactions with human serum albumin: Experimental, molecular docking and ONIOM computational study

Novel metal-based drug candidate including VOL2, NiL2, CuL2 and PdL2 have been synthesized from 2-hydroxy-1-allyliminomethyl-naphthalen ligand and have been characterized by means of elemental analysis (CHN), FT-IR and UV-vis spectroscopies. In addition, (1)H and (13)C NMR techniques were employed for characterization of the PdL2 complex. Single-crystal X-ray diffraction technique was utilized to characterise the structure of the complexes. The Cu(II), Ni(II) and Pd(II) complexes show a square planar trans-coordination geometry, while in the VOL2, the vanadium center has a distorted tetragonal pyramidal N2O3 coordination sphere. The HSA-binding was also determined, using fluorescence quenching, UV-vis spectroscopy, and circular dichroism (CD) titration method. The obtained results revealed that the HSA affinity for binding the synthesized compounds follows as PdL2>CuL2>VOL2>NiL2, indicating the effect of metal ion on binding constant. The distance between these compounds and HSA was obtained based on the Förster's theory of non-radiative energy transfer. Furthermore, computational methods including molecular docking and our Own N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) were carried out to investigate the HSA-binding of the compounds. Molecular docking calculation indicated the existence of hydrogen bond between amino acid residues of HSA and all synthesized compounds. The formation of the hydrogen bond in the HSA-compound systems leads to their stabilization. The ONIOM method was utilized in order to investigate HSA binding of compounds more precisely in which molecular mechanics method (UFF) and semi empirical method (PM6) were selected for the low layer and the high layer, respectively. The results show that the structural parameters of the compounds changed along with binding to HSA, indicating the strong interaction between the compounds and HSA. The value of binding constant depends on the extent of the resultant changes. This should be mentioned that both theoretical methods calculated the Kb values in the same sequence and are in a good agreement with the experimental data.

A combined spectroscopic, docking and molecular dynamics simulation approach to probing binding of a Schiff base complex to human serum albumin

The molecular mechanism of a Schiff base complex ((E)-((E)-2-(3-((E)-((E)-3(mercapto (methylthio) methylene)cyclopentylidene) amino) propylimino) cyclopentylidene) (methylthio) methanethiol) binding to Human Serum Albumin (HSA) was investigated by fluorescence quenching, absorption spectroscopy, molecular docking and molecular dynamics (MD) simulation procedures. The fluorescence emission of HSA was quenched by this Schiff base complex that has been analyzed for estimation of binding parameters. The titration of Schiff base solution by various amount of HSA was also followed by UV-Vis absorption spectroscopy and the corresponding data were analyzed by suitable models. The results revealed that this Schiff base has an ability to bind strongly to HSA and formed 1:1 complex. Energy transfer mechanism of quenching was discussed and the value of 5.45 ± 0.06 nm was calculated as the mean distance between the bound complex and the Trp residue. This is implying the high possibility of energy transfer from HSA to this Schiff base complex. Molecular docking results indicated that the main active binding site for this Schiff base complex is site III in subdomain IB. Moreover, MD simulation results suggested that this Schiff base complex can interact with HSA, without affecting the secondary structure of HSA but probably with a slight modification of its tertiary structure. MD simulations, molecular docking and experimental data reciprocally supported each other.

Synthesis, characterization and interaction of N,N'-dipyridoxyl (1,4-butanediamine) Co(III) salen complex with DNA and HSA

Co(III) salen complex with N,N'-dipyridoxyl (1,4-butanediamine) Schiff-base ligand as tetradentate ligand was synthesized and characterized by the elemental and spectroscopic analysis. The interaction of this complex with calf thymus DNA (ct DNA) has been investigated in vitro using UV absorption, fluorescence spectroscopy, thermal denaturation and gel electrophoresis techniques. The binding constant has been estimated to be 1×10(4)M(-1) using UV absorption. The addition of ct DNA to Co(III) salen solution resulted in a fluorescence quenching. The binding constant and site size binding have been calculated in connection with other experimental observations show that the interactive model between Co(III) salen and ct DNA is an intercalative one. The interaction between plasmid DNA (pTZ57R DNA) and this complex is confirmed by gel electrophoresis studies. Furthermore, the interaction between HSA and Co(III) salen complex was investigated by UV absorption, fluorescence spectroscopy and molecular modeling. The binding constant for the interaction of this complex with HSA were found to be 3.854×10(4)M(-1) using UV absorption, which was in good agreement with the binding constant obtained from fluorescence method (3.866×10(4)M(-1)). The binding distance between HSA and this complex was estimated to be 2.48nm according to Förster theory of non-radioactive energy transfer. Molecular modeling studies suggested that hydrophobic interaction was the predominant intermolecular forces stabilizing Co(III) complex-HSA system.

Probing the interaction of human serum albumin with bilirubin in the presence of aspirin by multi-spectroscopic, molecular modeling and zeta potential techniques: insight on binary and ternary systems

Here, we report on the effect of aspirin (ASA), on the binding parameters with regard to bilirubin (BR) to human serum albumin (HSA). Two different classes of binding sites were detected. Binding to the first and second classes of the binding sites was dominated by hydrophobic forces in the case of HSA-BR, whereas in the case of the ternary system, binding to the first and second classes of the binding sites was achieved by electrostatic interaction. The binding constant (K(a)) and number of binding site (n) obtained were 1.6 × 10(6)M(-1) and 0.98, respectively, for the primary binding site in the case of HSA-BR, and 3.7 × 10(6)M(-1) and 0.84, respectively, in the presence of ASA (ternary complex) at λ(ex)= 280 nm. The progressive quenching of the protein fluorescence as the BR concentration increased indicated an arrangement of the domain IIA in HSA. Changes in the environment of the aromatic residues were also observed by synchronous fluorescence spectroscopy (SFS). Changes of the secondary structure of HSA involving a decrease of α-helical and β-sheet contents and increased amounts of turns and unordered conformations were mainly found at high concentrations of BR. For the first time, the relationship between the structural parameters of HSA-BR by RLS for determining the critical induced aggregation concentration (C(CIAC)) of BR in the absence and presence of ASA was investigated, and there was a more significant enhancement in the case of the ternary mixture as opposed to the binary one. Changes in the zeta potential of HSA and the HSA-ASA complex in the presence of BR demonstrated a hydrophobic adsorption of this anionic ligand onto the surface of HSA in the binary system as well as both electrostatic and hydrophobic adsorption in the case of the ternary complex. By performing docking experiments, it was found that the acting forces between BR and HSA were mainly hydrophobic > hydrogen bonding > electrostatic interactions, and consequently BR had a long storage time in blood plasma, especially in the presence of ASA. This was due to the electrostatic interaction force between the BR and HSA being stronger in (HSA-ASA) BR than in the HSA-BR complex. In addition, it was demonstrated that, in the presence of ASA, the first binding site of BR on HSA was altered, but the parameters of binding did not become significantly modified, and thus the affinity of BR barely changed with and without ASA.

The binding characteristics of the interaction between 3-(2-cyanoethyl) cytosine and human serum albumin

The binding characteristics of the interaction between 3-(2-cyanoethyl) cytosine (CECT) and human serum albumin (HSA) were investigated using fluorescence, UV absorption spectroscopic and molecular modeling techniques under simulative physiological conditions. The intrinsic fluorescence intensity of HSA was decreased with the addition of CECT. The fluorescence data handled by Stern-Volmer equation proved that the quenching mechanism of the interaction between CECT and HSA was a static quenching procedure. The binding constants evaluated utilizing the Lineweaver-Burk equation at 17, 27 and 37 °C, were 2.340 × 10(4), 2.093 × 10(4) and 1.899 × 10(4) L mol(-1), respectively. The thermodynamic parameters were calculated according to van't Hoff equations. Negative enthalpy (ΔH) and positive entropy (ΔS) values indicated that both hydrogen bond and hydrophobic force played a major role in the binding process of CECT to HSA, which was consistent with the results of the molecular modeling study. In addition, the effect of other ions on the binding constant of CECT-HSA was examined.

Investigation of the behavior of HSA upon binding to amlodipine and propranolol: Spectroscopic and molecular modeling approaches

The interaction between human serum albumin (HSA) and two drugs - amlodipine and propranolol - was investigated using fluorescence, UV absorption and circular dichroism (CD) spectroscopy. In addition, the binding site was established by applying molecular modeling technique. Fluorescence data suggest that amlodipine will quench the intrinsic fluorescence of HSA; whereas propranolol enhances the fluorescence of HSA. The binding constants for the interaction of amlodipine and propranolol with HSA were found to be 3.63×10(5)M(-1) and 2.29×10(4)M(-1), respectively. The percentage of secondary structure feature of each one of the HSA-bound drugs, i.e. the α-helix content, was estimated empirically by circular dichroism. The results indicated that amlodipine causes an increase, and that propranolol leads to a decrease in α-helix content of HSA. The spectroscopic analysis indicates that the binding mechanisms of the two drugs are different from each other. The data obtained by the molecular modeling study indicated that these drugs bind, with different affinity, to different sites located in subdomain IIA and IIIA.

Binding of engeletin with bovine serum albumin: insights from spectroscopic investigations

In this paper, several spectroscopic techniques were used to investigate the interaction of engeletin (ELN) with bovine serum albumin (BSA). The analysis of UV-Vis absorption and fluorescence spectra revealed that ELN and BSA formed a static complex ELN-BSA, and ELN quenched the fluorescence of BSA effectively. According to the thermodynamic parameters ΔS(0) = 47.27 J·mol(-1)·K(-1) and ΔΗ(0) = -10.34 kJ·mol(-1), the hydrophobic and hydrogen bond interactions were suggested to be the major interaction forces between ELN and BSA. Raman spectroscopy indicated that the binding of ELN slightly changed the conformations and microenviroment of BSA and decreased the α-helix content of BSA.