Binding of puerarin to human serum albumin: a spectroscopic analysis and molecular docking

Novel vanadyl complexes synthesis, characterization and interactions with bovine serum albumin-effects on STZ- diabetes rats

Drug-protein interactions are essential since most administered drugs bind abundantly and reversibly to serum albumin and are delivered mainly as a complex with protein. The nature and strength of drug-protein interactions have a big impact on how a drug works biologically. The binding parameters are useful in studying the pharmacological response of drugs and the designing of dosage forms. Serum albumin is regarded as optimal model for in vitro research on drug-protein interaction since it is the main protein that binds medicines and other physiological components. In this perspective, binary complex have been synthesized and characterized, from vanadium metal and acetylacetone(4,4,4-trifluoro-1-(2-theonyl)-1,3-butanedione). Imidazole, 2-Methyl-imidazole, and 2-Ethyl-imidazole auxiliary ligands were employed for the synthesis of ternary complexes. Additionally, UV absorption and fluorescence emission spectroscopy were used to examine the binding interactions between vanadium complexes and Bovine Serum Albumin. The outcomes of the binding studies and spectral approaches were in strong agreement with one another. These complexes upon inoculation into diabetes-induced Wistar rats stabilized their serum glucose levels within 3 days. From various studies, it was discovered that the ordering of glucose-lowering actions of these metal complexes were equivalent. The vanadium ternary metal complex derived from (4,4,4-trifluoro-1-(2-theonyl)-1,3-butanedione) and imidazole as ligands is the best among the other metal vanadium complexes.

Synthesis of bioactive hemoglobin-based oxygen carrier nanoparticles via metal-phenolic complexation

The transfusion of donor red blood cells (RBCs) is seriously hampered by important drawbacks that include limited availability and portability, the requirement of being stored in refrigerated conditions, a short shelf life or the need for RBC group typing and crossmatching. Thus, hemoglobin (Hb)-based oxygen (O2) carriers (HBOCs) which make use of the main component of RBCs and the responsible protein for O2 transport, hold a lot of promise in modern transfusion and emergency medicine. Despite the great progress achieved, it is still difficult to create HBOCs with a high Hb content to attain the high O2 demands of our body. Herein a metal-phenolic self-assembly approach that can be conducted in water and in one step to prepare nanoparticles (NPs) fully made of Hb (Hb-NPs) is presented. In particular, by combining Hb with polyethylene glycol, tannic acid (TA) and manganese ions, spherical Hb-NPs with a uniform size around 350-525 nm are obtained. The functionality of the Hb-NPs is preserved as shown by their ability to bind and release O2 over multiple rounds. The binding mechanism of TA and Hb is thoroughly investigated by UV-vis absorption and fluorescence spectroscopy. The binding site number, apparent binding constant at two different temperatures and the corresponding thermodynamic parameters are identified. The results demonstrate that the TA-Hb interaction takes place through a static mechanism in a spontaneous process as shown by the decrease in Gibbs free energy. The associated increase in entropy suggests that the TA-Hb binding is dominated by hydrophobic interactions.

Comparative investigation on interaction between potent antimalarials and human serum albumin using multispectroscopic and computational approaches

This study performed a comparative investigation to explore the interaction mechanisms between two potential antimalarial compounds, JMI 346 and JMI 105, and human serum albumin (HSA), a vital carrier protein responsible for maintaining important biological functions. Our aim was to assess the pharmacological efficiency of these compounds while comprehensively analyzing their impact on the dynamic behavior and overall stability of the protein. A comprehensive array of multispectroscopic techniques, including UV-Vis. spectroscopy, steady-state fluorescence analysis, synchronous fluorescence spectroscopy, three-dimensional fluorescence and circular dichroism spectroscopy, docking studies, and molecular dynamics simulations, were performed to probe the intricate details of the interaction between the compounds and HSA. Our results revealed that both JMI 346 and JMI 105 exhibited promising pharmacological effectiveness within the context of malaria therapy. However, JMI 346 was found to exhibit a significantly higher affinity and only minor altered impact on HSA, suggesting a more favorable interaction with the protein on the dynamic behavior and overall stability of the protein in comparison to JMI 105. Further studies can build on these results to optimize the drug-protein interaction and enable the development of more potent and targeted antimalarial treatments.

Digital Database of Absorption Spectra of Diverse Flavonoids Enables Structural Comparisons and Quantitative Evaluations

Flavonoids play diverse roles in plants, comprise a non-negligible fraction of net primary photosynthetic production, and impart beneficial effects in human health from a plant-based diet. Absorption spectroscopy is an essential tool for quantitation of flavonoids isolated from complex plant extracts. The absorption spectra of flavonoids typically consist of two major bands, band I (300-380 nm) and band II (240-295 nm), where the former engenders a yellow color; in some flavonoids the absorption tails to 400-450 nm. The absorption spectra of 177 flavonoids and analogues of natural or synthetic origin have been assembled, including molar absorption coefficients (109 from the literature, 68 measured here). The spectral data are in digital form and can be viewed and accessed at http://www.photochemcad.com. The database enables comparison of the absorption spectral features of 12 distinct types of flavonoids including flavan-3-ols (e.g., catechin, epigallocatechin), flavanones (e.g., hesperidin, naringin), 3-hydroxyflavanones (e.g., taxifolin, silybin), isoflavones (e.g., daidzein, genistein), flavones (e.g., diosmin, luteolin), and flavonols (e.g., fisetin, myricetin). The structural features that give rise to shifts in wavelength and intensity are delineated. The availability of digital absorption spectra for diverse flavonoids facilitates analysis and quantitation of these valuable plant secondary metabolites. Four examples are provided of calculations─multicomponent analysis, solar ultraviolet photoprotection, sun protection factor (SPF), and Förster resonance energy transfer (FRET)─for which the spectra and accompanying molar absorption coefficients are sine qua non.

A flaw in applying the FRET technique to evaluate the distance between ligands and tryptophan residues in human serum albumin: Proposal of correction

Due to its primordial function as a drug carrier, human serum albumin (HSA) is extensively studied regarding its binding affinity with developing drugs. Förster resonance energy transfer (FRET) is frequently applied as a spectroscopic molecular ruler to measure the distance between the binding site and the ligand. In this work, we have shown that most of the published results that use the FRET technique to estimate the distance from ligands to the binding sites do not corroborate the crystallography data. By comparing the binding affinity of dansyl-proline with HSA and ovotransferrin, we demonstrated that FRET explains the quenching provoked by the interaction of ligands in albumin. So, why does the distance calculation via FRET not corroborate the crystallography data? We have shown that this inconsistency is related to the fact that a one-to-one relationship between donor and acceptor is not present in most experiments. Hence, the quenching efficiency used for calculating energy transfer depends on distance and binding constant, which is inconsistent with the correct application of FRET as a molecular ruler. We have also shown that the indiscriminate attribution of 2/3 to the relative orientation of transition dipoles of the acceptor and donor (κ²) generates inconsistencies. We proposed corrections based on the experimental equilibrium constant and theoretical orientation of transition dipoles to correct the FRET results.

Elucidation of the binding mechanism of astragaloside IV derivative with human serum albumin and its cardiotoxicity in zebrafish embryos

LS-102 is a new derivative of astragaloside IV (AGS IV) that has been shown to possess potentially significant cardioprotective effects. However, there are no reports concerning its interaction with human serum albumin (HSA) and toxicology in vertebrates. The present investigation was undertaken to characterize the interaction of AGS IV and LS-102 with HSA using equilibrium dialysis and UHPLC-MS/MS methods, along with computational methods. Notably, the effects of AGS IV and LS-102 were studied in vivo using the zebrafish embryo model. Markers related to embryonic cardiotoxicity and thrombosis were evaluated. We showed that the plasma protein binding rate of AGS IV (94.04%–97.42%) was significantly higher than that of LS-102 (66.90%–69.35%). Through site marker competitive experiments and molecular docking, we found that AGS IV and LS-102 were located at the interface of subdomains IIA and IIIA, but the site I might be the primary binding site. Molecular dynamics revealed that AGS IV showed a higher binding free energy mainly due to the stronger hydrophobic and hydrogen bonding interactions. Moreover, the secondary structure implied no obvious effect on the protein structure and conformation during the binding of LS-102. LS-102 significantly ameliorated the astramizole-induced heart rate slowing, increased SV-BA spacing, and prevented arachidonic acid-induced thrombosis in zebrafish. To our knowledge, we are the first to reveal that LS-102 binds to HSA with reversible and moderate affinity, indicating its easy diffusion from the circulatory system to the target tissue, thereby providing significant insights into its pharmacokinetic and pharmacodynamic properties when spread in the human body. Our results also provide a reference for the rational clinical application of LS-102 in the cardiovascular field.

Comparative study of the binding between chlorogenic acid and four proteins by isothermal titration calorimetry, spectroscopy and docking methods

As a polyphenolic compound, chlorogenic acid has antioxidant, anti-inflammatory, antiviral, anti-obesity and other effects. Based on the interactions between chlorogenic acid and the proteins (human serum albumin (HSA), pepsin (Pep), trypsin (Try), fat mass and obesity-associated protein (FTO)), results will provide clues for screening effective inhibitors. The interaction between chlorogenic acid and the four proteins (HSA, Pep, Try, FTO) was analyzed by the aid of fluorescence quenching, synchronous fluorescence, three-dimensional fluorescence, isothermal titration calorimetry, and molecular docking. It can be concluded that there is no obvious interaction between chlorogenic acid and FTO. The binding affinity between chlorogenic acid and three proteins is HSA > Try > Pep. The binding process is spontaneous, and the quenching type is static quenching. Hydrophobic interaction and hydrogen bonding is observed in the binding process. This study provides valuable information for understanding the interaction mechanism between chlorogenic acid and proteins, and provides clues for screening inhibitors.

Chebulinic and chebulagic acid binding with serum proteins: biophysical and molecular docking approach

Chebulinic acid (CHN) and chebulagic acid (CHG) have been known for centuries for their anti-cancer, anti-diabetes, HIV and anti-inflammatory properties. In this study, the interaction of these phytochemicals CHN/CHG, with the two major transport proteins for various drugs, human serum albumin (HSA) and α-1-acid glycoprotein (AGP), was unraveled by using several spectroscopic techniques and computational methods. The binding of CHN/CHG quenches the HSA/AGP fluorescence intensities, and also these phytochemicals are bound strongly to HSA/AGP proteins. An apparent decrease in fluorescence intensities of CHN/CHG-HSA and CHN/CHG-AGP complex showed the static mode of fluorescence quenching. Furthermore, the intrinsic fluorescence and using site-specific markers ibuprofen competing with these molecules, thereby replacing it in the binding site of subdomain IIIA. The computational methods substantiated the experimental findings, revealing that CHN interacted with Lys414A, Glu492A, Glu492A and Lys413A residues of subdomain IIIA of HSA and for CHG showed the interaction with Lys545A and Lys413A residues of subdomain IIIA of HSA. Fluorescence and surface plasmon resonance data unveiled a previously unreported binding event between CHN/CHG and HSA; the determined binding affinities of both compounds were slightly higher for HSA than AGP. A change in functionality of protein confirmed the esterase-like activity of HSA in the presence of CHG/CHN upon binding with CHG/CHN. Displacement and circular dichroism (CD) experiments analysis showed that the two CHN/CHG and binding specifically to IIIA subdomain on HSA results in the conformational changes in the HSA. Thus, CD revealed a few conformational changes in HSA due to CHN/CHG. The binding of these two phytochemicals to the plasma proteins would give a path to develop new inspired drug molecules for chronic diseases.Communicated by Ramaswamy H. Sarma.

In Vitro Investigation of Binding Interactions between Albumin–Gliclazide Model and Typical Hypotensive Drugs

Type 2 diabetes management usually requires polytherapy, which increases the risk of drug-to-drug interactions. Among the multiple diabetes comorbidities, hypertension is the most prevalent. This study aimed to investigate the binding interactions between the model protein, bovine albumin, and the hypoglycemic agent gliclazide (GLICL) in the presence of typical hypotensive drugs: quinapril hydrochloride (QUI), valsartan (VAL), furosemide (FUR), amlodipine besylate (AML), and atenolol (ATN). Spectroscopic techniques (fluorescence quenching, circular dichroism) and thermodynamic experiments were employed. The binding of the gliclazide to the albumin molecule was affected by the presence of an additional drug ligand, which was reflected by the reduced binding constant of the BSA–DRUG–GLICL system. This may indicate a possible GLICL displacement and its enhanced pharmacological effect, as manifested in clinical practice. The analysis of the thermodynamic parameters indicated the spontaneity of the reaction and emphasized the role of hydrogen bonding and van der Waals forces in these interactions. The secondary structure of the BSA remained almost unaffected.

Interaction of Conazole Pesticides Epoxiconazole and Prothioconazole with Human and Bovine Serum Albumin Studied Using Spectroscopic Methods and Molecular Modeling

The interactions of epoxiconazole and prothioconazole with human serum albumin and bovine serum albumin were investigated using spectroscopic methods complemented with molecular modeling. Spectroscopic techniques showed the formation of pesticide/serum albumin complexes with the static type as the dominant mechanism. The association constants ranged from 3.80 × 104-6.45 × 105 L/mol depending on the pesticide molecule (epoxiconazole, prothioconazole) and albumin type (human or bovine serum albumin). The calculated thermodynamic parameters revealed that the binding of pesticides into serum albumin macromolecules mainly depended on hydrogen bonds and van der Waals interactions. Synchronous fluorescence spectroscopy and the competitive experiments method showed that pesticides bind to subdomain IIA, near tryptophan; in the case of bovine serum albumin also on the macromolecule surface. Concerning prothioconazole, we observed the existence of an additional binding site at the junction of domains I and III of serum albumin macromolecules. These observations were corroborated well by molecular modeling predictions. The conformation changes in secondary structure were characterized by circular dichroism, three-dimensional fluorescence, and UV/VIS absorption methods.

Fluorescence spectroscopy and molecular docking analysis of the binding of Lactobacillus acidophilus GIM1.208 β-glucosidase with quercetin glycosides

Lactobacillus acidophilus is an important probiotic. The β-glucosidase produced by L. acidophilus GIM1.208 can transform quercetin glycosides of Rosa roxburghii Tratt to release quercetin and improve the functional activity of raw materials. Understanding the interaction and the characteristics of the two will lay a theoretical foundation for the site-directed transformation and functional application of the catalytic active site of enzymes. In our study, using the heterologously expressed and highly stable, purified L. acidophilus GIM1.208 BGL as the strain, the representative quercetin in β-glucosidase and Rosa roxburghii Tratt was preliminarily predicted and explored using ultraviolet-visible absorption spectroscopy. Fluorescence spectroscopy combined with molecular docking was used to determine the interaction characteristics of the glycoside substrates, rutin (Rut) and isoquercitrin (Iso). Results from molecular docking showed that Asp159, Arg56, Iso294, Phe292, and Gly25 were the main residues of β-glucosidase and Rut. Arg56 was found to be the most crucial residue of β-glucosidase and isoquercitrin; the interaction between Rut and Iso and β-glucosidase was mainly driven by hydrogen bonding. The combined free energy of β-glucosidase and Iso was found to be -182.10 kcal/mol, while that of β-glucosidase and Rut was -32.37 kcal/mol. The results of fluorescence spectroscopy showed that the fluorescence intensity of β-glucosidase decreased with an increase in Rut and Iso concentrations. This interaction made β-glucosidase quench endogenous fluorescence, which was static quenching. The binding constants of Rut and Iso with β-glucosidase were determined to be 0.50×10⁷ and 0.31×10⁷ L/mol, respectively, indicating that rutin had a stronger affinity when interacting with β-glucosidase. These findings were consistent with our prediction results determined using molecular docking studies.

Mono- and bis-pyrazolophthalazines: Design, synthesis, cytotoxic activity, DNA/HSA binding and molecular docking studies

In an attempt to find new potent cytotoxic compounds, several mono- and bis-pyrazolophthalazines 4a-m and 6a-h were synthesized through an efficient, one-pot, three- and pseudo five-component synthetic approach. All derivatives were evaluated for their in vitro cytotoxic activities against four human cancer cell lines of A549, HepG2, MCF-7, and HT29. Compound 4e showed low toxicity against normal cell lines (MRC-5 and MCF 10A, IC₅₀ > 200 µM) and excellent cytotoxic activity against A549 cell line with IC₅₀ value of 1.25 ± 0.19 µM, which was 1.8 times more potent than doxorubicin (IC₅₀ = 2.31 ± 0.13 µM). In addition, compound 6c exhibited remarkable cytotoxic activity against A549 and MCF-7 cell lines (IC₅₀ = 1.35 ± 0.12 and 0.49 ± 0.01 µM, respectively), more than two-fold higher than that of doxorubicin. The binding properties of the best active mono- and bis-pyrazolophthalazine (4e and 6c) with HSA and DNA were fully evaluated by various techniques including UV-Vis absorption, circular dichroism (CD), Zeta potential and dynamic light scattering analyses indicating interaction of the compounds with the secondary structure of HSA and significant change of DNA conformation, presumably via a groove binding mechanism. Additionally, molecular docking and site-selective binding studies confirmed the fundamental interaction of compounds 4e and 6c with base pairs of DNA. Compounds 4e and 6c showed promising features to be considered as potential lead structures for further studies in cancer therapy.

Repurposing of genistein as anti-sickling agent: elucidation by multi spectroscopic, thermophoresis, and molecular modeling techniques

Sickle cell disease (SCD) is a major medical problem in which mono-therapeutic interventions have so far shown only limited effectiveness. We studied the repurpose of genistein, which could prevent sickle hemoglobin from polymerizing under hypoxic conditions in this disease. Genistein an important nutraceutical molecule found in soybean. The present study examines the repurposing genistein as an anti- sickling agent. Genistein shows inhibition of Hb S polymerization as well as a sickle reversal. Also, we have explored the interaction of the genistein with sickle hemoglobin (Hb S), using fluorescence, far-UV-CD spectroscopy, MicroScale Thermophoresis (MST), FTIR, combined with molecular modeling computations. The quenching constant decreases with increasing temperature, a characteristic that coincides with the static type of quenching mechanism. Temperature-dependent fluorescence measurements and molecular modeling studies reveal that apart from the hydrogen bonding, electrostatic interactions also play a crucial role in genistein and Hb S complex formation. In silico, distribution prediction of adsorption, digestion, metabolism, excretion, and toxicity (ADME/Tox) based on physical and chemical properties show that genistein is nontoxic and has ideal drug properties. The helicity and thermophoretic mobility of Hb S was a change in the presence of genistein, which leads to the destabilizing the Hb S polymer was examined using CD and MST, respectively. Our results open up the possibility for a promising therapeutic approach for the SCD by repurposed genistein as an anti-sickling agent.Communicated by Ramaswamy H. Sarma.

Characterizing the Binding of Angiotensin Converting Enzyme I Inhibitory Peptide to Human Hemoglobin: Influence of Electromagnetic Fields

Background:

Drug-protein complexes is one of the crucial factors when analyzing the pharmacokinetics and pharmacodynamics of a drug because they can affect the excretion, distribution, metabolism and interaction with target tissues.

Objectives:

The aim of this study was to investigate the interaction of human hemoglobin (Hb) and angiotensin I converting enzyme inhibitory peptide (ACEIP) in the absence and presence of different- frequency electromagnetic fields (EMF).

Methods:

Various spectroscopic methods like fluorescence spectroscopy, ultraviolet, circular dichroism and conductometry techniques were applied to investigate Hb-ACEIP interaction in the absence and presence of EMF.

Result:

The presented spectroscopic studies indicated that EMF changed the interaction between Hb and ACEIP. The a-helix content of Hb decreased upon binding to ACEIP and conductivity of the solution enhanced upon binding. Based on Stern-Volmer equations, it could be stated that the Hb-ACEIP affinity was higher in the presence of EMF.

Conclusion:

It can be concluded that for patients who use the drug to control blood pressure, a low-frequency electromagnetic field would have a positive effect on the uptake of the drug.

Comparative studies on the interaction of nine flavonoids with trypsin

In this study, the interaction between nine classic flavonoids (including baicalin, quercetin, myricetin, rutin, puerarin, daidzein, liquiritin and isoliquiritin) and trypsin was investigated by fluorescence spectroscopy and molecular modeling methods. The results reveal that all flavonoids can interact with trypsin to form flavonoid-trypsin complexes. The binding parameters obtained from the data at different temperatures indicate that all flavonoids can spontaneously bind with trypsin with one binding site. The binding constants of trypsin with nine classic flavonoids are in the following order as: baicalin > myricetin > rutin > isoliquiritin > hesperidin > puerarin > quercetin > daidzein > liquiritin. The interaction forces between flavonoids and trypsin may be electrostatic forces (except for rutin/puerarin/daidzein), hydrophobic interactions as well as van der Waals forces. Synchronous fluorescence spectroscopy shows that the interaction between flavonoids and trypsin changes the hydrophobicity of the microenvironment of tryptophan (Trp) residues. All flavonoids close to tyrosine (Tyr) residues but have no effect on the microenvironment around Tyr residues except for hesperidin and liquiritin. Molecular modeling displays that all flavonoids bind directly into trypsin cavity site and lead to a decrease in enzyme activity.

Z-Acrylonitrile Derivatives: Improved Synthesis, X-ray Structure, and Interaction with Human Serum Albumin

AIMS AND OBJECTIVE

In the synthesis of heterocyclic compounds, acrylonitrile derivatives are the most important and appropriate precursors. These compounds are the most important intermediates and subunits for the enhancement of molecules having pharmaceutical or biological interests. Nitrogen-containing compounds have received extensive consideration in the literature over the years.

MATERIALS AND METHODS

A facile, economic and efficient method has been developed for the synthesis of acrylonitrile derivatives using p-nitrophenylacetonitrile and aromatic/heterocyclic aldehydes in the presence of zinc chloride at room temperature. Spectroscopic data were obtained using the following instruments: Fourier transform infrared spectra (KBr discs, 4000-400 cm-1) by Shimadzu IR-408 Perkin-Elmer 1800 instrument; 1H NMR and 13C NMR spectra by Bruker Avance-II 400 MHz using DMSO-d6 as a solvent containing TMS as the internal standard.

RESULTS

To continue our ongoing studies to synthesize heterocyclic and pharmaceutical compounds by mild, facile and efficient protocols, herein we wish to report our experimental results on the synthesis of acrylonitrile derivatives, using various aromatic/heterocyclic aldehydes and p-nitrophenylacetonitrile in the presence of zinc chloride in ethanolic media at room temperature. Some of the new compounds were tested for their human serum albumin activity (HSA) while a study of interaction with HSA protein was performed for compounds 3a and 3b. The results show that compound 3b binds tightly to HSA as compared to compound 3a.

CONCLUSION

It can be concluded that acrylonitrile derivatives can be synthesized by an efficient method via the reaction of p-nitrophenylacetonitrile with aromatic/heterocyclic aldehydes by the use of zinc chloride as an effective solid catalyst. The remarkable features of this procedure include excellent yields (90-95%), short reaction period (30 min.), moderate reaction environment, easy workup procedure and managing of the catalyst. This method may find a wide significance in organic synthesis for the synthesis of the Z-acrylonitrile.

The effect of heparan sulfate on promoting amyloid fibril formation by β-casein and their binding research with multi-spectroscopic approaches

As a molecular chaperone, β-casein is difficult to form amyloid fibrils under physiological conditions due to its chaperone activity. Heparan sulfate (HS) has drawn attention of technologists all over the word because of its relation to amyloid deposits in some amyloidosis diseases. For better understanding the relationship between the β-casein and HS, the multi-spectroscopic studies were employed. The data of thioflavin T (ThT) binding assay, transmission electron microscopy (TEM) and circular dichroism (CD) demonstrated that HS promoted fibril formation by β-casein in the amount and the growth speed. The results of steady-state UV-vis absorption spectra, fluorescence spectroscopy and fluorescence lifetime revealed that the β-casein-HS complexes were formed and HS quenched the fluorescence of β-casein by a static quenching mechanism. On the basis of fluorescence analysis, the value of binding constant was equal to 1.17 × 10⁷ L mol^-1 at 338.15 K and there was about one binding site between them. According to thermodynamic parameters obtained, it was deduced that a spontaneous reaction happened, and protein-ligand complex was stabilized by hydrogen bonds and hydrophobic interaction. Furthermore, using fluorescence resonance energy transfer (FRET) assay, the value of binding distance between HS and Trp143 of β-casein was calculated to be 0.93 nm. Finally, on the basis of synchronous fluorescence experiment, the polarity increasing and hydrophobicity decreasing around Trp143 occurred during the period of fibril formation by β-casein.

Fungicide Tebuconazole Influences the Structure of Human Serum Albumin Molecule

Studies of interactions between pesticides and target mammalian proteins are important steps toward understanding the pesticide's toxicity. Using calorimetric and spectroscopic methods, the interaction between triazole fungicide tebuconazole and human serum albumin has been investigated. The spectroscopic techniques showed that fluorescence quenching of human serum albumin by tebuconazole was the result of the formation of tebuconazole/human serum albumin complex with the static type as the dominant mechanism. The association constant was found to be 8.51 × 103 L/mol. The thermodynamic parameters were obtained as ΔH = -56.964 kJ/mol, ΔS = -115.98 J/mol·K. The main active interactions forming the tebuconazole/human serum albumin complex were identified as the interplay between hydrogen bonds and/or van der Waals forces, based on thermodynamic experiments. These binding modes were corroborated well by the predictions of molecular modeling. Hydrogen bonding of tebuconazole with Arg222, Ala215 and Ala291 of human serum albumin played a relevant role in binding. The conformation changes in secondary structure were characterized by circular dichroism and 3D fluorescence spectra.

Potential of isoquercitrin as antisickling agent: a multi-spectroscopic, thermophoresis and molecular modeling approach

Sickle cell disease is an inherited disease caused by point mutation in hemoglobin (β-globin gene). Under oxygen saturation, sickle hemoglobin form polymers, leading to rigid erythrocytes. The transition of the blood vessels is altered and initiated by the adhesion of erythrocytes, neutrophils and endothelial cells. Sickle Hemoglobin (HbS) polymerization is a major cause in red blood cells (RBC), promoting sickling and destruction of RBCs. Isoquercitrin, a medicinal bioactive compound found in various medicinal plants, has multiple health benefits. The present study examines the potential of isoquercitrin as an anti-sickle agent, showing a significant decrease in the rate of polymerization as well as sickling of RBCs. Isoquercitrin-induced graded alteration in absorbance and fluorescence of HbS, confirmed their interaction. A negative value of ΔG° strongly suggests that it is a spontaneous exothermic reaction induced by entropy. Negative ΔH° and positive ΔS° predicted that hydrogen and hydrophobic binding forces interfered with a hydrophobic microenvironment of β6Val leading to polymerization inhibition of HbS. HbS-Isoquercitrin complex exhibits helical structural changes leading to destabilization of the HbS polymer as confirmed by CD spectroscopy. MST and DSC results indicate greater changes in thermophoretic mobility and thermal stability of sickle hemoglobin in the presence of isoquercitrin, respectively. These findings were also supported by molecular simulation studies using DOCK6 and GROMACS. Hence, we can conclude that isoquercitrin interacts with HbS through hydrogen bonding, which leads to polymerization inhibition. Consequently, isoquercitrin could potentially be used as a medication for the treatment of sickle cell disease.Communicated by Ramaswamy H. Sarma.

Experimental and theoretical investigations of novel oxidovanadium(IV) juglone complex: DNA/HSA interaction and cytotoxic activity

A new oxidovanadium(IV) complex VO(L)(Jug) (HL = 5-methoxy-1,3-bis (1-methyl-1H-benzo[d]imidazol-2-yl)benzene, Jug = juglone) was synthesized and characterized. Interactions of the V(IV) complex with calf thymus DNA (CT DNA) and human serum albumin were studied using different techniques such as UV-vis and fluorescence emission spectroscopy. The experimental results were confirmed by the molecular docking study. The oxidovanadium(IV) complex can efficiently cleave pUC19 DNA in the presence of Hydrogen peroxide. Also, the in vitro cytotoxicity properties of the oxidovanadium(IV) complex was evaluated against MCF-7, HPG-2 and HT-29 cancer cell lines and HEK293 non-malignant fibroblasts were evaluated and compared with free ligands, VOSO₄ and cisplatin as reference drugs.Communicated by Ramaswamy H. Sarma.

Synthesis and characterization of new unsymmetrical Schiff base Zn (II) and Co (II) complexes and study of their interactions with bovin serum albumin and DNA by spectroscopic techniques

Two novel tetra-coordinated Cobalt(II) and Zinc (II) chelate series with the general formula of [Co (L)·2H₂O] (1) and [Zn (L)] (2) [L=N-2-hydroxyacetophenon-N'-2-hydroxynaphthaldehyde-1,2 phenylenediimine)] with biologically active Schiff base ligands were synthesized and recognized by elemental analysis and multi-nuclear spectroscopy (IR and ¹H and ¹³C NMR); then, their biological activities including DNA and protein interactions were studied. The interaction of the synthesized compounds with bovine serum albumin (BSA) was investigated via fluorescence spectroscopy, showing the affinity of the complexes for these proteins with relatively high binding constant values and the changed secondary BSA structure in the presence of the complexes. The interaction of these compounds with CT-DNA was considered by UV-Vis technique, emission titration, viscosity measurements, helix melting methods, and circular dichroism (CD) spectroscopy, confirming that the complexes were bound to CT-DNA by the intercalation binding mode. Furthermore, the complexes had the capability to displace the DNA-bound MB, as shown by the competitive studies of these complexes with methylene blue (MB), thereby suggesting the intercalation mode for the competition. Finally, the theoretical studies carried out by the docking method were performed to calculate the binding constants and recognize the binding site of the BSA and DNA by the complexes. In addition, in vitro and in silico studies showed that the compounds were degradable by bacterial and fungal biodegradation activities.

Binding of naringin and naringenin with hen egg white lysozyme: A spectroscopic investigation and molecular docking study

The interactions of naringenin (NG) and naringin (NR) with Hen Egg White Lysozyme (HEWL) in aqueous medium have been investigated using UV-vis spectroscopy, steady-state fluorescence, circular dichroism (CD), Fourier Transform infrared spectroscopy (FT-IR) and molecular docking analyses. Both NG and NR can quench the intrinsic fluorescence of HEWL via static quenching mechanism. At 300K, the value of binding constant (K_b) of HEWL-NG complex (5.596±0.063×10⁴M^-1) was found to be greater than that of HEWL-NR complex (3.404±0.407×10⁴M^-1). The negative ΔG° values in cases of both the complexes specify the spontaneous binding. The binding distance between the donor (HEWL) and acceptor (NG/NR) was estimated using the Försters theory and the possibility of non-radiative energy transfer from HEWL to NG/NR was observed. The presence of metal ions (Ca²⁺, Cu²⁺ and Fe²⁺) decreased the binding affinity of NG/NR towards HEWL. Synchronous fluorescence studies indicate the change in Trp micro-environment due to the incorporation of NG/NR into HEWL. CD and FT-IR studies indicated that the α-helicity of the HEWL was slightly enhanced due to ligand binding. NG and NR inhibited the enzymatic activity of HEWL and exhibited their affinity for the active site of HEWL. Molecular docking studies revealed that both NG and NR bind in the close vicinity of Trp 62 and Trp 63 residues which is vital for the catalytic activity.

Exposure of carbendazim induces structural and functional alteration in garlic phytocystatin: An in vitro multi-spectroscopic approach

Carbendazim is a broad spectrum benzimidazole fungicide which is used to ensure plants' protection from pest and pathogens' invasion. The present work describes the impact of carbendazim (CAR) on garlic phytocystatin (GPC) which is a crucial plant regulatory protein. Interaction of carbendazim with GPC has been investigated through various biophysical techniques viz. UV absorption, fluorescence spectroscopy, isothermal titration calorimetry, far-UV circular dichroism and FTIR spectroscopy which showed binding between them with consequent modulatory effects. Functional activity of GPC was monitored by the anti-papain inhibitory assay which suggests that incubation of GPC with the higher concentration of CAR disrupts the inhibitory function of GPC. UV spectroscopy confirmed the formation of GPC-CAR complex. Intrinsic fluorescence suggests binding of CAR to GPC which reflects the changes in microenvironment around tryptophan residues of GPC. Isothermal titration calorimetry suggests that interaction of CAR to GPC is an exothermic reaction. Secondary structure analysis was also performed which confirmed that binding of CAR decreases the alpha-helical content of GPC. Collectively, these results demonstrated that GPC exhibited significant structural and functional alteration upon interaction with carbendazim. Since GPC is involved in various regulatory processes, therefore, its structural or functional alteration may lead to disruption of physiological and biological balance within the plant. Hence, our study signifies that exposure of carbendazim to plant exerts physicochemical alteration within the plant.