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Vanillin is a phenolic aldehyde widely used as a flavouring agent in the food industry. Vanillin has many health benefits and has gained attention in pharmacological industries also, due to its antioxidant properties and non-toxic nature. The interaction of vanillin with human hemoglobin (hHb), an abundant tetrameric heme protein, was investigated by several spectroscopic techniques and molecular modeling methods. UV-visible spectra showed that the binding of vanillin to hHb induces structural changes due to alterations in the micro-environment of hHb. Vanillin quenches the intrinsic fluorescence of hHb by the dynamic mechanism, which was confirmed by both temperature dependent and time resolved fluorescence studies. Vanillin binds spontaneously to hHb at a single site and the binding is stabilized by hydrogen bonds and hydrophobic interactions. The circular dichroism spectra showed that the binding of vanillin altered the secondary structure of hHb due to change in its alpha-helical content. Molecular docking identified the amino acids of hHb involved in binding to vanillin and also that the free energy change of the binding reaction is -5.5 kcal/mol. Thus, our results indicate that vanillin binds spontaneously to hHb at a single site and alters its secondary structure. This will help in understanding the potential use of vanillin and related antioxidants as therapeutic agents in various hematological disorders., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Isoprenaline hydrochloride is a potential cardiovascular drug helps in the smooth functioning of the heart muscles. So, we have performed the binding study of ISO with BSA. This study was investigated by UV absorption, fluorescence, synchronous fluorescence, circular dichroism, etc. The analysis of intrinsic fluorescence data showed the low binding affinity of ISO. The binding constant K b was 2.8 × 103 M-1 and binding stoichiometry (n) was approximately one and the Gibb's free energy change at 310 K was determined to be -8.69 kcal mol -1 . Negative Gibb's free energy change shows the spontaneity of the BSA and ISO interaction. We have found ISO-induced alternation in the UV absorption, synchronous fluorescence and CD spectra in the absence and presence of the quencher indicates the complex formation. In synchronous fluorescence, red shift was obtained because of the complex formation of BSA and ISO. The distance (r) between the BSA (donor) and ISO (acceptor) was 2.89 nm, determined by FRET. DLS measurements interpreted complex formation due to the reduction in hydrodynamic radii of the protein in the presence of the drug. The binding site of ISO was found to be nearer to Trp 134 with the help of molecular docking and the ΔG° was found to be -10.2 kcal mol -1 . The esterase activity result suggests that ISO acts as competitive inhibitor. Thus, this study would help to determine the binding capacity of the drug to the protein which may indicate the efficiency of diffusion of ISO into the blood for the treatment of heart diseases.

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Background: Triptolide is a major active constituent isolated from Tripterygiumwilfordii Hook F, a Chinese herbal medicine. This study investigated the intermolecular interaction between triptolide and bovine serum albumin (BSA)., Materials and Methods: The fluorescence, circular dichroism (CD) and molecular docking methods were used to investigate the intermolecular interaction between triptolide and BSA. The binding constant, the number of binding sites, binding subdomain and the thermodynamic parameters were measured., Results: The results of this experiment revealed that the intrinsic fluorescence of BSA was effectively quenched by triptolide via static quenching. The experimental results of synchronous fluorescence and CD spectra showed that the conformation of BSA was changed in the presence of triptolide., Conclusion: It indicated that triptolide could spontaneously bind on site II (subdomain IIIA) of BSA mainly via hydrogen bonding interactions and Van der Waals force.

The human palate can discern multiple tastes; however, it predominantly perceives five fundamental flavors: sweetness, saltiness, sourness, bitterness, and umami. Sweetness is primarily mediated through the sweet taste receptor, a membrane-bound heterodimeric structure comprising T1R2-T1R3. However, unraveling the structural and mechanistic intricacies of the sweet taste receptor has proven challenging. This study aimed to address this knowledge gap by expressing an extracellular N-terminal domain encompassing the cysteine-rich domain of human hT1R3 (hT1R3-TMD) in Escherichia coli. The expressed protein was obtained as inclusion bodies, purified by metal affinity chromatography, and refolded using the dilution-refolding method. Through rigorous analysis, we confirmed the successful refolding of hT1R3-TMD and elucidated its structural characteristics using circular dichroism spectroscopy. Notably, the refolded protein was found to exist as either a monomer or a dimer, depending on its concentration. A tryptophan fluorescence quenching assay revealed that the dissociation constants for sucrose, sucralose, and brazzein were >9500 μM, 2380 μM and 14.3 μM, respectively. Our findings highlight the utility of this E. coli expression system for producing functional hT1R3-TMD for investigations and demonstrate the efficacy of the tryptophan fluorescence quenching assay in revealing complex interactions between sweet taste receptors and various sweeteners. [ABSTRACT FROM AUTHOR]

The interaction between linamarin (LIN), a cyanogenic glycoside, and human serum albumin (HSA) was studied by multiple spectroscopic techniques and molecular docking simulation. All measurements were performed under physiological conditions. The obtained results (including the binding constants, effective quenching constant and a number of binding sites) showed that the complex of HSA‐LIN is formed. The values of Stern‐Volmer constants (6.70×103, 5.53×103 and 1.95×103) indicate that fluorescence quenching of HSA was static. Results of site marker experiments showed that the binding site of LIN is mainly located in site I (subdomain IIA) of HSA. The thermodynamic parameters showed that binding process occurs spontaneously through hydrophobic interactions. Molecular docking results are in good agreement with experimental data. Furthermore, computational results revealed LIN binds in the cavity of TRP 214, that is, subdomain IIA (site I) of HSA. This comprehensive study provides a deeper insight into ligand binding in HSA which may be useful in drug design and pharmacology. [ABSTRACT FROM AUTHOR]

BACKGROUND: Phyllanthus emblica Linn. (PE) is rich in polyphenols, which can be categorized into free and bound phenolics (PEFP and PEBP). This study evaluated the inhibitory effect of PEFB and PEBP on α‐amylase for the first time. The mechanism of the inhibition effect of PEFP and PEBP on α‐amylase was investigated by enzyme inhibition kinetics, multispectral analysis, thermodynamics, and molecular docking. RESULTS: Free and bound phenolics inhibited α‐amylase activity effectively in a mixed type of inhibition. Fluorescence quenching and thermodynamic analyses showed that the binding of PEFP and PEBP to α‐amylase occurred through a static quenching process (Kq = 6.94 × 10¹² and 5.74 × 10¹² L mol−1 s−1), which was accompanied by a redshift (λem from 343 to 347 nm), leading to a change in the microenvironment. This process was found to be a spontaneous exothermic reaction (ΔG < 0). Circular dichroism (CD) analysis confirms that the secondary structure of α‐amylase was altered, in particular a decrease in α‐helixes and an increase in random coils. Molecular docking studies showed that PEFP and PEBP interacted with α‐amylase through hydrogen bonding and hydrophobic interactions. CONCLUSION: The present study provides valuable insights into the mechanism of action of PEFP and PEBP on α‐amylase, which will provide a theoretical basis for their possible use as novel natural α‐amylase inhibitors. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The unique structure of G4.0 PAMAM dendrimers allows a drug to be enclosed in internal spaces or immobilized on the surface. In the conducted research, the conditions for the formation of the active G4.0 PAMAM complex with doxorubicin hydrochloride (DOX) were optimized. The physicochemical properties of the system were monitored using dynamic light scattering (DLS), circular dichroism (CD), and fluorescence spectroscopy. The Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) method was chosen to determine the preferential conditions for the complex formation. The highest binding efficiency of the drug to the cationic dendrimer was observed under basic conditions when the DOX molecule was deprotonated. The decrease in the zeta potential of the complex confirms that DOX immobilizes through electrostatic interaction with the carrier's surface amine groups. The binding constants were determined from the fluorescence quenching of the DOX molecule in the presence of G4.0 PAMAM. The two-fold way of binding doxorubicin in the structure of dendrimers was visible in the Isothermal calorimetry (ITC) isotherm. Fluorescence spectra and release curves identified the reversible binding of DOX to the nanocarrier. Among the selected cancer cells, the most promising anticancer activity of the G4.0-DOX complex was observed in A375 malignant melanoma cells. Moreover, the preferred intracellular location of the complexes concerning the free drug was found, which is essential from a therapeutic point of view. [ABSTRACT FROM AUTHOR]

The diterpene cafestol represents the most potent cholesterol-elevating compound known in the human diet, being responsible for more than 80% of the effect of coffee on serum lipids, with a mechanism still not fully clarified. In the present study, the interaction of cafestol and 16-O-methylcafestol with the stabilized ligand-binding domain (LBD) of the Farnesoid X Receptor was evaluated by fluorescence and circular dichroism. Fluorescence quenching was observed with both cafestol and 16-O-methylcafestol due to an interaction occurring in the close environment of the tryptophan W454 residue of the protein, as confirmed by docking and molecular dynamics. A conformational change of the protein was also observed by circular dichroism, particularly for cafestol. These results provide evidence at the molecular level of the interactions of FXR with the coffee diterpenes, confirming that cafestol can act as an agonist of FXR, causing an enhancement of the cholesterol level in blood serum. [ABSTRACT FROM AUTHOR]

[Display omitted] • We developed chiral quasi-two-dimensional perovskites for H 2 S detection and E. coli antibacterial. • Bio(R/S-PEA) 2 CsPb 2 Br 7 as probes exhibit fast and sensitive responses to H 2 S. • Bio(R/S-PEA) 2 CsPb 2 Br 7 have a significant effect as antibacterial agents in inhibiting the growth of E. coli. • This work provides ideas for biological applications of aqueous-phase dual-functional perovskite materials. Perovskite nanocrystals (PNCs) have attracted extensive attention for their potential applications in biology. However, only a handful of PNCs have been scrutinized in the biological domain due to issues such as instability, poor dispersion, and size inhomogeneity in polar solvents. The development of dual-functional perovskite nanomaterials with hydrogen sulfide (H 2 S) sensing and antibacterial capabilities is particularly intriguing. In this study, we prepared chiral quasi-two-dimensional (quasi-2D) perovskite nanomaterials, Bio(S-PEA) 2 CsPb 2 Br 7 and Bio(R-PEA) 2 CsPb 2 Br 7 , that were uniformly dispersed in aqueous media. The effective encapsulation of methoxypolyethylene glycol amine (mPEG-NH 2) improved water stability and uniformity of particle size. Circular dichroism (CD) signals were created by the successful insertion of chiral cations. These perovskites as probes showed a rapid and sensitive fluorescence quenching response to H 2 S, and the effect of imaging detection was observed at the Escherichia coli (E. coli) level. As antibacterial agents, their pronounced positive charge properties facilitated membrane lysis and subsequent E. coli death, indicating a significant antibacterial effect. This work has preliminary explored the application of chiral perovskites in biology and provides insight into the development of bifunctional perovskite nanomaterials for biological applications. [ABSTRACT FROM AUTHOR]

In this study, we determined the interaction of piperine and calf thymus DNA (ct DNA) in Tris-HCl buffer solution at pH = 6.8 and also evaluated the binding mechanism through the data of multi-spectroscopic techniques along with thermal melting and viscosity measurements. The outcomes of fluorescence quenching confirmed the occurrence of interactions between piperine and ctDNA and pointed out the role of piperine as the quencher. In addition, the KSV values were measured at three different temperatures of 298, 303, and 308 K to be 4.5 × 107 M−1, 5.65 × 107 M−1, and 9.36 × 107 M−1, respectively, which suggested the dominance of dynamic mechanism as the fluorescence quenching of piperine-ctDNA. The thermodynamic parameters revealed the predominance of hydrophobic forces in the interaction of ctDNA with piperine. According to the resonance light scattering data, the formation of a complex between piperine and ctDNA led to the creation of a larger particle. Ethidium bromide (EB) and acridine orange (AO) displacement studies, along with the ionic effects of NaCl and KI assessments, confirmed the interaction of piperine-ctDNA through a groove binding mode. The melting temperature assay of ctDNA upon the addition of piperine concentration indicated the probable groove binding of piperine to ctDNA, which was affirmed by relative viscosity measurement as well. The lack of detecting any alterations in the circular dichroism (CD) spectrum of CD investigation verified as a characteristic sign of groove binding mechanism and also confirmed all the experimental results with regard to the binding of piperine-ctDNA complex. Next to observing a concentration and time-dependent cytotoxicity in MDA-MB-231 cells, the impact of piperine on increasing lipid peroxidation and decreasing the activity of superoxide dismutase was also noticed. Apparently, piperine is capable of inducing caspase-3 activity as well. [ABSTRACT FROM AUTHOR]

Soluble starch (SS) could significantly accelerate the process of bovine serum albumin (BSA) cold-set gelation by glucono-δ-lactone (GDL) and microbial transglutaminase (MTGase) coupling inducers, and enhance the mechanical properties. Hardness, WHC, loss modulus (G″) and storage modulus (G′) of the gel increased significantly, along with the addition of SS, and gelation time was also shortened from 41 min (SS free) to 9 min (containing 4.0% SS); the microstructure also became more and more dense. The results from FTIR, fluorescence quenching and circular dichroism (CD) suggested that SS could bind to BSA to form their composites, and the hydrogen bond was probably the dominant force. Moreover, the ability of SS to bind the original free water in BSA gel was relatively strong, thereby indirectly increasing the concentration of BSA and improving the texture properties of the gel. The acceleration of gelling could also be attributed to the fact that SS reduced the negative charge of BSA aggregates and further promoted the rapid formation of the gel. The embedding efficiency (EE) of quercetin in BSA-SS cold-set gel increased from 68.3% (SS free) to 87.45% (containing 4.0% SS), and a controlled-released effect was detected by simulated gastrointestinal digestion tests. The work could put forward new insights into protein gelation accelerated by polysaccharide, and provide a candidate for the structural design of new products in the food and pharmaceutical fields. [ABSTRACT FROM AUTHOR]

The binding of ligands to G-quadruplex (G4) structures at the ends of human telomeric DNA induces thermal stabilization, which interferes with telomere maintenance by disrupting the association of telomeres with the telomerase enzyme—an important marker for cancer. Understanding the binding mode of the ligand-G quadruplex DNA complex is imperative for evaluating the relative efficacy and specificity of their interaction. We focused on the interaction of 1,5-Bis(3-piperidino propionamido) anthracene-9,10-dione with human telomeric DNA sequences using surface plasmon resonance, absorbance, fluorescence (steady-state and lifetime), and circular dichroism spectroscopy techniques. The ligand binding with HTel22 (Kb = 8.4 × 105 M−1) induced cell toxicity with an IC50 value of ∼ 8.64 µM in MCF-7 cancer cell lines. Significant hypochromism (59 %), fluorescence quenching (97 %), no change in fluorescence lifetime and absence of induced Circular Dichroism (CD) band upon addition of G4 DNA to ligand, suggest a groove/external binding mode. CD spectral changes reflect rearrangement in parallel and antiparallel strands to accommodate the ligand. Docking results reveal specific short contacts of the ligand's side chain, including 9CO, 13N, 14NH, and 11CO, with the grooves of the G4 DNA, without making any contact with the loops, favoring an energetically more favorable conformation. Thermal denaturation profiles, obtained by Differential Scanning Calorimetry and CD, show the stabilization of wHTel26 and HTel22 G4 DNA in K+ and Na+ rich solutions by 21.2 and 17.6 °C, respectively, which may restrict the access of telomerase to telomeres. The findings indicate the potential of modifying anthraquinone substituent groups for therapeutic applications.

Human serum albumin (HSA) efficiently transports drugs in vivo: most are organic. Therefore, it is important to delineate the binding of small molecules to HSA. Here, for the first time, we show that HSA binding depends not only on the identity of the d8 metal ion, NiII or PdII, of their complexes with bis(pyrrole-imine), H2PrPyrr, but on the pH level as well. Fluorescence quenching data for native and probe-bound HSA showed that sites close to Trp-214 (subdomain IIA) are targeted. The affinity constants, Ka, ranged from ~3.5 × 103 M−1 to ~1 × 106 M−1 at 37 °C, following the order Pd(PrPyrr) > Ni(PrPyrr) at pH levels of 4 and 7; but Ni(PrPyrr) > Pd(PrPyrr) at a pH level of 9. Ligand uptake is enthalpically driven, dependent mainly on London dispersion forces. The induced CD spectra for the protein-bound ligands could be simulated by hybrid QM:MM TD-DFT methods, allowing us to delineate the binding site of the ligands and to prove that the metal chelates neither decompose nor demetallate after uptake by HSA. The transport and delivery of the metal chelates by HSA in vivo is therefore feasible. [ABSTRACT FROM AUTHOR]

Chiral aggregation‐induced emission (AIE) molecules have drawn attention for their helical self‐assembly and special optical properties. The helical self‐assembly of AIE‐active chiral non‐linear main‐chain polymers can produce some desired optical features. In this work, a series of V‐shaped chiral AIE‐active polyamides P1‐C3, P1‐C6, P1‐C12 and linear P2‐C3, P2‐C6, bearing n‐propyl/hexyl/dodecyl side‐chains, based on tetraphenylbutadiene (TPB), were prepared. All target main‐chain polymers exhibit distinct AIE characteristics. The polymer P1‐C6 with moderate length alkyl chains shows better AIE properties. The V‐shaped main‐chains and the chiral induction of (1R,2R)‐(+)‐1,2‐cyclohexanediamine in each repeating unit promote the polymer chains display helical conformation, and multiple helical polymer chains induce nano‐fibers helicity when the polymer chains aggregate and self‐assemble in THF/H2O mixtures. Simultaneously, the helical conformation polymer chains and helical nano‐fibers cause P1‐C6 produce strong circular dichroism (CD) signals with positive Cotton effect. Moreover, P1‐C6 could also occur fluorescence quenching response to Fe3+ selectively with a low detection limit of 3.48 μmol/L. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the interaction between parecoxib and p38MAPK under simulated physiological conditions. Methods: The interaction between parecoxib and p38MAPK was studied under simulated physiological conditions using spectroscopy-based methods. The effect of parecoxib on the microenvironment and conformation of p38MAPK chromophore was studied by synchronous fluorescence spectroscopy, three)dimensional fluorescence, time-resolved fluorescence spectroscopy, circular dichroism spectroscopy, and ultraviolet-visible absorption spectroscopy. Results: Synchronous fluorescence spectroscopy showed that addition of parecoxib changed the structure of p38MAPK and destroyed the original stable structure. Three-dimensional fluorescence spectroscopy showed that the hydrophilicity of the microenvironment in which the fluorescent chromophore is located was enhanced, and the polarity increased such that the serum protein macromolecules tend to be unfolded, and the alpha-helix content reduced. Time-resolved fluorescence spectroscopy showed that the presence of parecoxib hardly affected the fluorescence quenching of p38MAPK, and the combination of parecoxib and p38MAPK forms a stable complex (static quenching). Circular dichroism spectroscopy revealed the combined parecoxib change, the secondary structure of p38MAPK and reduced the alpha-helix content. Ultraviolet-visible absorption spectroscopy revealed changes in the microenvironment of the three amino acid residues as well as the tertiary structure of the protein. Conclusion: The results shows that parecoxib has a significant effect on the structure of p38MAPK. In addition to explicitly inhibiting COX-2 and blocking arachidonic acid synthesis of prostaglandins, it inhibits the pathway involved in p38MAPK. [ABSTRACT FROM AUTHOR]

Given the ubiquitous and multifaceted role of copper ions in various biological processes, we report herein the one-pot facile synthesis, X-ray structure, Hirshfeld surface analysis, enzyme-like activities, and biomolecular interactions of three mononuclear copper(II) complexes, [Cu(L)(X)] (1–3) with a tridentate quinoline-based salicylaldimine Schiff base (LH) having an N2O donor set where X denotes NCS, N3, and NO3 for complexes 1, 2, and 3, respectively. Single-crystal X-ray study, spectroscopic techniques, DFT, and TD-DFT calculations were all used to fully characterize the complexes. The bio-inspired catalytic activities of the synthesized complexes were spectrophotometrically evaluated for the aerial oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) and 2-aminophenol (OAPH) in acetonitrile. The results of ESI mass spectrometry, EPR analysis of the reaction mixture, and DFT computations established that the aforementioned oxidation is metal-mediated and radical-driven, leading us to propose a viable mechanistic scheme. In complex 3, coordinated nitrate probably confers greater lability, allowing it to be the most effective enzyme for catecholase and phenoxazane-synthase activities. The biological activity of complexes 1–3 and the ligand LH towards calf thymus DNA and proteins (bovine serum albumin (BSA)) was explored using absorption and fluorescence spectral titrations, which affirmed that the compounds underwent avid binding with DNA, with high binding affinities (Kb) of approximately 104–105 M−1. The observed DNA binding constants and viscosity measurement data suggested an intercalative mode of DNA binding with the copper(II) complexes. Spectral evidence also supports the high binding propensity (on the order of approximately 105 M−1) of the complexes with the protein. They actively suppressed the protein's intrinsic fluorescence in a static quenching mode, as further determined by fluorescence lifetime titration of protein with the complexes. Circular dichroism and synchronous spectroscopic experiments supported the protein's conformational alterations mediated by copper(II) complexes (1–3) in the microenvironment of the tryptophan residue of the protein. The typical binding distance between BSA and complexes was also computed using fluorescence resonance energy transfer. Of the three complexes (1–3), complex 3 stands out as the most efficacious. [ABSTRACT FROM AUTHOR]

In this study, sweet potato β-amylase (SPA) was modified by methoxy polyethylene glycol maleimide (molecular weight 5000, Mal-mPEG5000) to obtain the Mal-mPEG5000-SPA modified β-amylase and the interaction mechanism between SPA and Mal-mPEG5000 was investigated. the changes in the functional groups of different amide bands and modifications in the secondary structure of enzyme protein were analyzed using infrared spectroscopy and circular dichroism spectroscopy. The addition of Mal-mPEG5000 transformed the random curl in the SPA secondary structure into a helix structure, forming a folded structure. The Mal-mPEG5000 improved the thermal stability of SPA and protected the structure of the protein from breaking by the surrounding. The thermodynamic analysis further implied that the intermolecular forces between SPA and Mal-mPEG5000 were hydrophobic interactions and hydrogen bonds due to the positive values of ΔHθ and ΔSθ. Furthermore, the calorie titration data showed that the binding stoichiometry for the complexation of Mal-mPEG5000 to SPA was 1.26, and the binding constant was 1.256 × 107 mol/L. The binding reaction resulted from negative enthalpy, indicating that the interaction of SPA and Mal-mPEG5000 was induced by the van der Waals force and hydrogen bonding. The UV results showed the formation of non-luminescent material during the interaction, the Fluorescence results confirmed that the mechanism between SPA and Mal-mPEG5000 was static quenching. According to the fluorescence quenching measurement, the binding constant (KA) values were 4.65 × 104 L·mol−1 (298K), 5.56 × 104 L·mol−1 (308K), and 6.91 × 104 L·mol−1 (318K), respectively. [ABSTRACT FROM AUTHOR]

The reactions of copper chloride and 4′-(4′-substituted-phenyl)-2,2′:6′,2′′-terpyridine ligands bearing nitro (L1), methyl (L2), phenyl (L3), tolyl (L4) and carboxyl (L5) gave five copper compounds (1–5) which have mononuclear structures with their Cu(II) ions five-coordinate in the irregular square pyramidal geometries. Their in vitro biological properties were evaluated by CCK-8 assay, which show remarkable proliferation inhibitive properties on the cancer cell lines including A549, Eca-109, and Bel-7402, and two human normal cell lines (HL-7702 and HLF). The values of IC50 indicate better anticancer activities of these compounds than that of cisplatin. Compound 2 with methyl group exhibits the best anticancer activity, with IC50 value < 2.5 µM on all the tested cancer cells. The interactions of the compounds with DNA were evaluated using UV–Vis absorption titrations, circular dichroism spectroscopy, and DNA viscosity. The complexes show significant insertion binding with DNA sequences and strong intercalator binding mode with DNA sequences. Compounds 1–5 interact with the functional groups of DNA through π···π stacking, van der Waals interactions, hydrophobic interactions, and hydrogen bonds as determined by molecular docking. In addition, strong binding interactions between the five copper(II) complexes and bovine serum albumin (BSA) were studied by fluorescence titration and circular dichroism spectroscopy. [ABSTRACT FROM AUTHOR]

Flavonoids have potential applications in the nutraceutical, medicinal, pharmaceutical and cosmetic fields. The binding of flavonoids with DNA could unravel essential information required for the design of novel and effective chemical agents. The present paper describes the interaction of a flavonoid and a potent anticancer drug, galangin (GAL) with calf thymus DNA (ct-DNA) by fluorescence, UV absorption, melting studies, viscosity measurements and molecular docking studies. A hyperchromic effect was noticed in the absorption spectra of ct-DNA in the presence of the GAL system, indicating the presence of a groove mode of binding. Furthermore, GAL persuaded the minor changes in ct-DNA viscosity, indicating a non-intercalative mode of binding. Fluorescence studies revealed that the GAL quenched the fluorescence intensity of ct-DNA-Hoechst, thereby indicating the interaction between GAL and ct-DNA. Fluorescence results obtained at 298, 308 and 318 K revealed that the fluorescence quenching of ct-DNA-Hoechst-GAL occurred through the static quenching mechanism. Thermodynamic parameters for ct-DNA-Hoechst-GAL were computed and suitable conclusions were drawn. The changes noticed in the conformation of ct-DNA upon interaction with GAL were evaluated in terms of molar ellipticity. It indicated a plausible interaction between ct-DNA and GAL. The molecular docking studies also confirmed the groove mode of binding in the ct-DNA-GAL system. Thus, this work helped to unravel the binding mechanism between GAL and ct-DNA. [ABSTRACT FROM AUTHOR]

The current therapeutic approach for gout is through the inhibition of the xanthine oxidase (XO) enzyme. Allopurinol, a clinically used XO inhibitor, causes many side effects. This study aimed to investigate the interaction between XO and inhibitors identified from Chrysanthemum morifolium by using computational simulation and multispectroscopic methods. The crude extract, petroleum ether, ethyl acetate (EtOAc), and residual fractions were subjected to an XO inhibitory assay and 1H NMR analysis. The EtOAc fraction was shown to be strongly correlated to the XO inhibitory activity by using PLS biplot regression analysis. Kaempferol, apigenin, homovanillic acid, and trans-cinnamic acid were suggested to contribute to the XO inhibitory activity. Molecular docking showed that kaempferol and apigenin bound to the active site of XO with their benzopyran moiety sandwiched between Phe914 and Phe1009, interacting with Thr1010 and Arg880 by hydrogen bonding. Kaempferol showed the lowest binding energy in molecular dynamic simulation. The residues that contributed to the binding energy were Glu802, Arg880, Phe 914, and Phe 1009. A fluorescence quenching study showed a combination of static and dynamic quenching for all four inhibitors binding to XO. Circular dichroism spectroscopy revealed that there was no major change in XO conformation after binding with each inhibitor. [ABSTRACT FROM AUTHOR]

4-Fluoro- N -(thiazol-2-yl)benzenesulfonamide (3) is a novel fluorinated compound, containing various biological activities. Therefore, absorption spectroscopy, fluorescence quenching, molecular docking, and molecular simulation were employed to investigate the interaction between 3 and human serum albumin (HSA). Firstly, compound 3 meets all criteria for drug-likeness prediction. UV absorption spectra revealed the interaction of 3 with HSA altered the microenvironment of protein, as well as circular dichroism spectroscopic analysis indicated slightly conformational changes and a reduction in α-helical content. The binding parameters of the HSA– 3 complex suggested that fluorescence quenching is driven by combined static and dynamic processes. Additionally, the stability of the complex is attributed to conventional hydrogen and hydrophobic bonding interactions. Furthermore, esterase-like activity indicated that the binding of 3 might disrupt HSA's bond networks, leading to structural alterations. Consequently, the strong binding constant (K a ≈ 1.204 × 106 M–1) aligns with the predicted unbound fraction (0.28) in serum, indicating that thiazole 3 has good bioavailability in plasma and can be effectively transported to target sites, thereby exerting its pharmaceutical effects. However, careful dosage management is essential to prevent potential adverse effects. Overall, these findings highlight the potential of 3 as a therapeutic agent, emphasizing the need for further research to optimize its uses. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Binding interaction of BSA with a therapeutic drug (4BHC) is studied. • 4BHC quenched the intrinsic fluorescence of BSA by static quenching mechanism. • The binding constant between BSA and 4BHC is ∼ 104 M−1. • The dominant interaction force is hydrophobic in nature. • 4BHC changes the microenvironment of BSA around the Trp residue. The interaction of biomacromolecules with each other or with the ligands is essential for biological activity. In this context, the molecular recognition of bovine serum albumin (BSA) with 4-(Benzo[1,3]dioxol-5-yloxymethyl)-7-hydroxy-chromen-2-one (4BHC) is explored using multispectroscopic and computational techniques. UV–Vis spectroscopy helped in predicting the conformational variations in BSA. Using fluorescence spectroscopy, the quenching behaviour of the fluorophore upon interaction with the ligand is examined, which is found to be a static type of quenching; fluorescence lifetime studies further verify this. The binding constant is discovered to be in the range of 104 M−1 , which indicates the moderate type of association that results in reversible binding, where the transport and release of ligands in the target tissue takes place. Fourier-transform infrared spectroscopy (FT-IR) measurements validate the secondary structure conformational changes of BSA after complexing with 4BHC. The thermodynamic factors obtained through temperature-dependent fluorescence studies suggest that the dominant kind of interaction force is hydrophobic in nature, and the interaction process is spontaneous. The alterations in the surrounding microenvironment of the binding site and conformational shifts in the structure of the protein are studied through 3D fluorescence and synchronous fluorescence studies. Molecular docking and molecular dynamics (MD) simulations agree with experimental results and explain the structural stability throughout the discussion. The outcomes might have possible applications in the field of pharmacodynamics and pharmacokinetics. [ABSTRACT FROM AUTHOR]

Inhibition of pancreatic lipase (PL) is a strategy to prevent obesity. The inhibitory effects of Flos Sophorae Immaturus (FSI) extract and its main flavonoid components, rutin and quercetin, on PL were investigated. The contents of rutin and quercetin in FSI extract were 44.10 ± 1.33 % and 6.07 ± 1.62 %, respectively. The IC 50 values of FSI extract, rutin and quercetin on PL were 322, 258 and 71 μg/mL, respectively. Rutin and quercetin inhibited PL in a reversible and noncompetitive manner. The combination of rutin and quercetin exhibited synergistic inhibitory effects at low concentration. The binding of rutin/quercetin with PL caused the fluorescence quenching of protein. Fluorescence titration showed the binding affinity of quercetin with PL protein was stronger than that of rutin. Circular dichroism analysis showed the binding changed the secondary structure of PL with an increase in random coil and a decrease in α-Helix and β-Sheet. Molecular docking revealed that rutin and quercetin could interact with the amino acid residues around the catalytic site through multiple secondary interactions. In vivo studies showed that FSI extract can reduce fat absorption and promote fecal fat excretion through inhibition of PL activity, and the effects were mainly due to rutin and quercetin. • FSI extract with main components of rutin and quercetin exhibited inhibition on lipase. • Rutin and quercetin exhibited synergistic inhibitory effects. • The binding of rutin/quercetin with lipase was investigated by different methods. • FSI extract reduced fat absorption and promoted fecal fat excretion in rat. [ABSTRACT FROM AUTHOR]

The interaction between di-n-butyl phthalate (DBP) and bovine serum albumin (BSA) in physiological Tris-HCl buffer at pH 7.4 was investigated by fluorescence quenching technique. By analyzing the fluorescence spectrum and intensity, it was observed that the DBP had a strong ability to quench the intrinsic fluorescence of BSA through a static quenching procedure. The binding constants K and the number of binding sites n of DBP with BSA were calculated to be 0.11 × 102 L·mol−1 and 0.52 at 298 K, respectively. The thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) were also calculated to be positive showing that hydrophobic forces might play a major role in the binding of DBP to BSA. The binding process was spontaneous in which Gibbs free energy change (ΔG) was negative. The distance (r) between the donor (BSA) and acceptor (DBP) was calculated to be 2.02 nm based on Forster's non-radiative energy transfer theory, which indicated that the energy transfer from BSA to DBP occurs with a high possibility. The synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectra showed that the binding of di-n-butyl phthalate to BSA induced conformational changes in BSA. The interaction between DBP and BSA can help researchers better understand the nature of poisons and serve people in the right way with first aid and detoxification. [ABSTRACT FROM AUTHOR]

In this study, we examined the interaction process of human serum albumin (HSA) with a water‐soluble zinc(II) complex of dichloro {2‐[N‐(2‐hydroxyethylammonioethyl) imino methyl] phenol} at pH=7.4 and in vitro utilizing molecular docking modeling and spectral techniques. In the multi‐temperature fluorescence test, the consecutive and gradual addition of the zinc(II) complex to the HSA‐containing cell resulted in fluorescence quenching, and it showed that the zinc(II) complex‐protein interaction is associated with a static quenching mechanism; also, the number of binding sites (n) and the binding constant (Kb) were computed by this test. The evaluation of thermodynamic data showed spontaneous progression, and the involvement of hydrogen bonding/van der Waals forces in protein‐zinc(II)complex formation. The site markers competition studies using two drugs, warfarin and ibuprofen, indicated that zinc(II) complex binds to the protein via site I/sub‐domain IIA. The albumin‐zinc(II) complex interaction and the structural alterations in the serum albumin were proved by electronic absorption technique and circular dichroism spectroscopy. Job′s curve exhibited a stoichiometric ratio of 1 : 1 in the HSA‐zinc(II) complex adduct. The accuracy of the results obtained from experimental findings on the interaction between HSA and zinc(II) complex was checked by molecular docking simulation, which illustrated a good agreement between experimental and theoretical data. [ABSTRACT FROM AUTHOR]

In this study, high pressure processing (HPP) and thermal treatment were comparatively evaluated by examining their impacts on the binding behavior and interaction between α-lactalbumin (α-La) and pelargonium-3-glucoside (P3G) under pH values of 6.0, 7.4, and 8.0. The methods of circular dichroism spectroscopy, fluorescence quenching, dynamic light scattering, and molecular simulation were used to characterize the effects of processing-induced changes in protein structure, size distribution, binding site conformation, and residue charges on their binding characteristics between them. The results indicated that the thermal treatments significantly increased the quenching constants of the complex at pH 7.4/8.0 and 60/80 °C, as well as the accessible fraction of protein at pH 8.0/80 °C. Both HPP and thermal treatments increased the random coil content and showed limited effects on the α-helix and β-sheet contents of α-La and caused the aggregation of the complex to varying degrees. Molecular dynamic simulation and docking analyses revealed that the binding site of the complex did not change under different processing conditions, but the solvent-accessible surface area varied under different conditions. [ABSTRACT FROM AUTHOR]

Various spectroscopic techniques involving fluorescence spectroscopy, circular dichroism (CD), and computational approaches were used to elucidate the molecular aspects of interaction between the antiepileptic drug topiramate and the multifunctional transport protein bovine serum albumin (BSA) under physiological conditions. Topiramate quenched BSA fluorescence in a static quenching mode, according to the Stern‐Volmer quenching constant (Ksv) data derived from fluorescence spectroscopy for the topiramate‐BSA complex. The binding constant was also used to calculate the binding affinity for the topiramate‐BSA interaction. Fluorescence and circular dichroism experiments demonstrate that the protein's tertiary structure is affected by the microenvironmental alterations generated by topiramate binding to BSA. To establish the exact binding site, interacting residues, and interaction forces involved in the binding of topiramate to BSA, molecular modeling and simulation approaches were used. According to the Molecular Mechanics Poisson‐Boltzmann Surface Area (MMPBSA) calculations, the average binding energy between topiramate and BSA is −421.05 kJ/mol. Topiramate was discovered to have substantial interactions with BSA, changing the structural dynamic and Gibbs free energy landscape patterns. [ABSTRACT FROM AUTHOR]

Biomolecular binding of a potential drug, ezetimibe (EZT) with bovine serum albumin (BSA) was investigated by spectroscopic and electrochemical methods besides molecular modeling studies. Fluorescence measurements showed that the fluorescence intensity of BSA was quenched by EZT with a slight blue shift in the emission wavelength (from 346 to 340 nm). The values of binding constant, number of binding molecules and Stern–Volmer quenching constant of EZT-BSA system was calculated at different temperatures. The values of Stern–Volmer quenching constant increased with temperature indicating the presence of dynamic quenching mechanism. The probable location of EZT within the protein cavity (subdomain IIIA) was explored by docking studies and displacement experiments. Based on the values of free energy change, enthalpy change and entropy change, hydrophobic interaction was proposed to be the main factor that stabilized the EZT-BSA interaction. Studies on zeta potential of BSA unraveled the role of electrostatic interaction between EZT and BSA. In addition, synchronous fluorescence and circular dichroism spectral studies revealed the conformational changes occurred in BSA upon binding of EZT. [ABSTRACT FROM AUTHOR]

Interactions between bovine γ‐globulin (BGG) and borohydride‐capped silver nanoparticles (BAgNPs) were studied using dynamic light scattering (DLS) and spectroscopic techniques such as UV–vis spectroscopy, fluorescence, and circular dichroism. The results were compared with earlier reported interactions between γ‐globulin and citrate‐coated AgNPs (CAgNPs). BAgNPs were synthesized and characterized. Irrespective of the coating on AgNPs, nanoparticles had formed ground‐state complexes with the protein. CAgNPs, as well as BAgNPs had caused static quenching of tryptophan (Trp) fluorescence of the protein. The change in the capping agent from citrate to borohydride weakened the binding of nanoparticles with the protein. But the same change in capping agent had increased the fluorescence quenching efficiency of AgNPs. Hydrogen bonding and van der Waals interactions were involved in BGG–BAgNPs complex similar to the CAgNPs complex with γ‐globulin. Polarity of the Trp microenvironment in BGG was not altered using BAgNPs as opposed to CAgNPs, as supported using synchronous and three‐dimensional fluorescence. Resonance light scattering experiments also suggested nano‐bio conjugation. Far‐UV and near‐UV circular dichroism (CD) spectra respectively pointed towards changes in the secondary and tertiary structure of BGG by BAgNPs, which was not observed for CAgNPs. [ABSTRACT FROM AUTHOR]

Abstract Diabetes is among the top ten deadly diseases in the world. It occurs either when the pancreas does not produce enough insulin (INS) or when the body cannot effectively use the insulin it produces. Phloretin (PHL) has a biological effect that can treat diabetes. A spectroscopic study was carried out to explore the interaction between phloretin and insulin. UV/Vis spectroscopy, fluorescence spectroscopy, and circular dichroism spectropolarimeter were used in the study. UV/Vis spectra showed that the interaction between PHL and INS produced strong absorption at a wavelength of 282 nm. The fluorescence analysis results showed that the excitation and emission occurred at 280-nm and 305-nm wavelengths, respectively. Temperature changes did not affect INS emissions. However, the interaction of PHL–INS caused a redshift at 305 to 317 nm. Temperature affected the binding constant (K a ) and the binding site (n). Ka decreased with increasing temperature and increased the binding site. The thermodynamic parameters such as enthalpy (ΔH 0) and entropy (ΔS 0) each had a value of − 16,514 kJ/mol and 22.65 J/mol·K. PHL and INS interaction formed hydrogen bonds and hydrophobic interaction. The free energy (ΔG0) recorded was negative. PHL and INS interactions took place spontaneously. The quenching effect was dynamic and static. K D values were greater than K S . The higher the temperature, the less was K D and K S . The appearance of two negative signals on circular dichroism (CD) spectropolarimeter implies that phloretin could induce regional configuration changes in insulin. The addition of PHL has revealed that the proportion of α-helix in the insulin stabilizes its structure. Phloretin’s stabilization and enhancement of the α-helix structural configuration in insulin indicate that phloretin can improve insulin resistance.

• β -lactoglobulin (β -LG) was used as fluorescence probe to detect pymetrozine (PYM). • The fluorescence of β -LG was statically quenched by PYM. • The sensitive detection of PYM was realized based on Stern-Volmer equation. • The LOD for PYM was lower as 0.03 μg mL−1. • The recoveries in apple and pear samples were satisfactory. A method was developed for the detection of pymetrozine (PYM) using β -lactoglobulin (β -LG) as a probe. The interaction between PYM and β -LG was studied by fluorescence spectra, circular dichroism spectra (CD), synchronous fluorescence spectra, ultraviolet visible spectra (UV–vis), fourier transform infrared (FT-IR) and molecular docking. The fluorescence quenching type between PYM and β -LG was demonstrated to be static by Stern-Volmer analysis and time-resolved fluorescence. The binding constant (K a) was 2.95 × 104 L mol−1 at 293 K. The electrostatic attraction was confirmed to be the primary binding force by Ross theory, and the binding distance was 2.02 nm by fluorescence Resonance Energy Transfer (FRET) theory. Based on the interaction between β -LG and PYM, a fluorescence detection method for PYM was established. Under optimal experimental conditions, the standard equations were established in the range of 0.43 – 10.68 μg mL−1. The limit of detection (LOD) for PYM was 0.03 μg mL−1. The method was successfully applied to apple and pear fruit samples. Recoveries of PYM in these samples were 97.44 % – 102.29 %, the relative standard deviation (RSD) of these samples were 0.24 % – 0.88 % (n = 3). [Display omitted] [ABSTRACT FROM AUTHOR]

Human serum albumin (HSA) effectively binds to compounds having different molecular weight and thus facilitates their distribution in the living organisms. Thus, the binding interactions between a potential antibacterial drug (levofloxacin) and synthesized choline based levofloxacinate conjugates with HSA have been explored. The binding efficacy and mechanism were explored by utilizing different spectroscopic techniques; UV–Visible, steady state fluorescence, time resolved fluorescence and esterase-like activity. The interactions between the ligands and protein were electrostatic as well as hydrophobic in nature. The influence of different ligands having different alkyl chain shows quenching of the fluorescence emission of HSA. The spontaneous binding/quenching of HSA with ligands was static in nature, validated by steady state and time resolved fluorescence spectroscopy. Also, the impact of these ligands on the conformation of the native HSA structure was evaluated by using circular dichroism spectroscopy. In combination to the structural change study, the native protein functionality was observed (in terms of 'esterase-like activity') which has been found to be on lower side due to ligand binding. Further, we have performed the reverse study to check the impact of HSA on the fluorescent fluoroquinolone drug. The current study may prove helpful in elucidating the chemico-biological interactions which may prove useful in the pharmaceuticals, pharmacology, and different biochemistry fields. Graphical abstract [Display omitted] [ABSTRACT FROM AUTHOR]

• Carboxyl-pycy-3-gluc exhibits remarkable stability against β-glycosidase. • Carboxylpyranoanthocyanins display limited affinity for binding with β-glycosidase. • Introducing carboxyl-pycy-3-gluc induces subtle changes in β-glycosidase's structure. • Incorporating carboxyl-pycy-3-gluc enriches food with vividness and enduring color. Anthocyanins are susceptible to degradation by β-glycosidase, resulting in color loss. This study analyzed the impact of β-glycosidase on carboxylpyranocyanidin-3-O-glucoside (Carboxyl-pycy-3-gluc) and its precursor cyanidin-3-O-glucoside (Cy-3-gluc). Carboxyl-pycy-3-gluc exhibited enhanced stability upon treatment with β-glucosidase. Ultraviolet–visible and circular dichroism spectroscopy revealed slight changes in the microenvironment and secondary structure of β-glycosidase when carboxyl-pycy-3-gluc was present. The fluorescence experiment indicated that anthocyanins quench the fluorescence of β-glycosidase through static quenching via hydrophobic interactions. Molecular docking of six types of carboxylpyranoanthocyanins and their precursors with β-glycosidase revealed that carboxylpyranoanthocyanins exhibited lower binding affinity than their precursors, consistent with the enzyme kinetic experiment results. The incorporation carboxyl-pycy-3-gluc into Sanhua Plum Juice and Wine endowed them with vivid and stable coloration. The study illustrated that carboxyl-pycy-3-gluc exhibits low binding affinity with β-glycosidase, thereby maintaining stability and confirming its potential as a colorant. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the impact of cytosine 5’-monophosphate (5’-CMP), guanosine 5’-monophosphate (5’-GMP), and uridine 5’-monophosphate (5’-UMP), along with their disodium salts, in combination with D-mannitol (D-M), on the conformation and fluorescence properties of interferon α-2b (IFN), and to determine the energy parameters governing these interactions. Methods: Spectroscopic techniques including time-resolved spectroscopy, circular dichroism, and fluorescence spectroscopy, along with isothermal nanocalorimetry, were employed. Results: The nucleotide monophosphates (5’-rNMFs) in their acidic form, particularly when complexed with D-mannitol, exhibited stronger binding to interferon α-2b compared to their salt forms. Interaction between IFN α-2b and 5’-rNMFs, especially in the presence of D-mannitol, was found to be exothermic and induced changes in the conformational flexibility of IFN α-2b, increasing the proportion of disordered regions. Conversely, interaction with disodium salts of NMPs was characterized by an endothermic process, potentially enhancing the conformational rigidity of IFN α-2b and improving the efficiency of non-radiative energy transfer to acidic 5’-rNMFs, likely due to the reduced intermolecular distances. Conclusions: Overall, the interactions involving 5’-nucleoside monophosphate acids, their salts, and IFN α-2b are influenced by a nucleotide type (purine vs. pyrimidine), the presence of mannitol, and chemical form (acid vs. salt). These interactions significantly affect fluorescence quenching, binding affinity, thermodynamics, energy transfer efficiency, and secondary structure alterations of IFN α-2b. [ABSTRACT FROM AUTHOR]

• The interactions between HSA and Dox in the presence of Cyp have been studied. • Results of theoretical calculations together with fluorescence and CD spectroscopy findings, were presented and discussed. • The HSA fluorescence is quenched through a static quenching mechanism. • The presence of the Cyp in the Sudlow II of protein influence the mode of the HSA-Dox binding. The interaction of human serum albumin (HSA) with doxorubicin and cyclophosphamide was analysed by using fluorescence and circular dichroism (CD) spectroscopy, electrophoretic light scattering (ELS) and molecular modelling. Based on the fluorescence quenching results we can assume the existence of HSA-Cyp-Dox complex in the solution. The K sv and K a values for the system obtained under physiological conditions were 1.603·104M−1 and 4.574·104M−1, respectively and proved only one binding site for the drugs. The reaction is spontaneous and hydrophobic or ionic interactions are predominant in the process. Results of circular dichroism spectroscopy exhibit that the presence of cyclophosphamide and doxorubicin in the binding center of the protein induce insubstantial alteration in their secondary structure. The Forster theory was employed to determine the donor – acceptor distance in the HSA system and it was found to be 3.67 nm. Zeta potential analysis confirmed existence of the hydrophobic interaction and some instability of the system under physiological conditions. According to molecular docking study in both cases doxorubicin binds to the same site of albumin with very similar free energy of biding. However, the origins of stabilization and the binding modes of Dox in the Sudlow site I of HSA are different. [ABSTRACT FROM AUTHOR]

[Display omitted] • Obovatol's role as α-glucosidase (α-Glu) and α-amylase (α-Amy) inhibitor was assessed. • Synthesis of ten obovatol analogous for α-Glu and α-Amy inhibition. • Compounds 1 , 11 , 22 , 26 and 27 were effective inhibitors and were tested for cytotoxicity. • Interaction with the enzyme was studied by CD analysis, SPR imaging and molecular docking studies. • Obovatol-based neolignans are promising structures for developing novel hypoglycemic drugs. Diabetes mellitus is a metabolic disease characterized by hyperglycemia, which can be counteracted by the inhibition of α-glucosidase (α-Glu) and α-amylase (α-Amy), enzymes responsible for the hydrolysis of carbohydrates. In recent decades, many natural compounds and their bioinspired analogues have been studied as α-Glu and α-Amy inhibitors. However, no studies have been devoted to the evaluation of α-Glu and α-Amy inhibition by the neolignan obovatol (1). In this work, we report the synthesis of 1 and a library of new analogues. The synthesis of these compounds was achieved by implementing methodologies based on: phenol allylation, Claisen/Cope rearrangements, methylation, Ullmann coupling, demethylation, phenol oxidation and Michael-type addition. Obovatol (1) and ten analogues were evaluated for their in vitro inhibitory activity towards α-Glu and α-Amy. Our investigation highlighted that the naturally occurring 1 and four neolignan analogues (11 , 22 , 26 and 27) were more effective inhibitors than the hypoglycemic drug acarbose (α-Amy: 34.6 µM; α-Glu: 248.3 µM) with IC 5O value of 6.2–23.6 µM toward α-Amy and 39.8–124.6 µM toward α-Glu. Docking investigations validated the inhibition outcomes, highlighting optimal compatibility between synthesized neolignans and both the enzymes. Concurrently circular dichroism spectroscopy detected the conformational changes in α-Glu induced by its interaction with the studied neolignans. Detailed studies through fluorescence measurements and kinetics of α-Glu and α-Amy inhibition also indicated that 1 , 11 , 22 , 26 and 27 have the greatest affinity for α-Glu and 1 , 11 and 27 for α-Amy. Surface plasmon resonance imaging (SPRI) measurements confirmed that among the compounds studied, the neolignan 27 has the greater affinity for both enzymes, thus corroborating the results obtained by kinetics and fluorescence quenching. Finally, in vitro cytotoxicity of the investigated compounds was tested on human colon cancer cell line (HCT-116). All these results demonstrate that these obovatol-based neolignan analogues constitute promising candidates in the pursuit of developing novel hypoglycemic drugs. [ABSTRACT FROM AUTHOR]

The interaction mechanism between 3-biotinylate-6-benzimidazole B-nor-cholesterol analogs and ct-DNA was studied by spectroscopic (ultraviolet spectroscopy (UV), fluorescence spectroscopy, and circular dichroism spectroscopy (CD)), viscosity, and molecular docking technology methods. The UV spectra showed that these compounds induced a color enhancement effect on ct-DNA. The fluorescence spectra verified that the compounds and ct-DNA were bound in the grooves, and the fluorescence quenching process was static quenching. The CD spectra revealed that these compounds did not change the positive peak of the ct-DNA base pair accumulation, while the negative peak of the ct-DNA right-hand helix exhibited a slight hyperchromic effect. The viscosity test indicated that the reaction between these compounds and ct-DNA did not significantly change the viscosity. According to the molecular docking results, the three compounds mainly interacted with the ct-DNA via the groove mode, and all of them expressed a weak electrostatic effect, which was slightly stronger for compound 3. [ABSTRACT FROM AUTHOR]

The present work demonstrates comprehensive spectrofluorometric characterization of interaction of a bioactive flavonoid quercetin (QCT) with the transport protein human hemoglobin (Hb) by protein‐induced quenching phenomenon. Interaction between such a pharmacologically essential drug and Hb has been enlightened by means of steady‐state and time‐resolved fluorescence spectroscopy. The protein‐induced Stern–Volmer quenching study of QCT depicts an upward curvature that cannot be an outcome of only the static quenching arising from ground‐state complexation. Therefore, an extensive time‐resolved fluorescence characterization of the quenching process has been performed to discern the actuating quenching mechanism. However, the estimated value of bimolecular quenching constant (kq) from the diffusion‐controlled quenching study hints for dynamic quenching phenomenon. Finally, the significant amplification of the average lifetime of QCT as a function of protein concentration aids to resolve this conflict affirming the quenching phenomenon to be an exquisite drug–protein binding interaction. Not only the quenching mechanism has been established, but also the binding parameters and location of binding within the microheterogeneous cavity of Hb has been explicated. AutoDock‐based "blind docking" simulation has been employed to conquer probable binding location of the drug within protein cavity. Nevertheless, circular dichroism (CD) spectroscopy depicts the modification of the native conformation of Hb, which is indicative of this binding phenomenon. [ABSTRACT FROM AUTHOR]

Berberine is separated from medical plants and food raw materials, and shows excellent anti‐diabetic activity and could be used as a food additive in some countries and regions. However, its inhibitory mechanisms on α‐amylase and α‐glucosidase have hardly ever been revealed in vitro. In this study, enzymatic reaction kinetics, fluorescence quenching, circular dichroism spectroscopy, and molecular docking are used to study the inhibitory effects of berberine on α‐amylase and α‐glucosidase. Berberine has great inhibitory effects on α‐amylase and α‐glucosidase (IC50 = 50.83 µg mL–1, IC50 = 198.4 µg mL–1, respectively), and inhibition types of α‐amylase and α‐glucosidase are non‐competitive inhibition and competitive inhibition, respectively. Fluorescence spectra show that there is static quenching between berberine and α‐amylase or α‐glucosidase. Besides, hydrophobic interaction is the main interaction type. These results are further evidenced and visualized by molecular docking. This study provides a different theoretical basis for berberine in anti‐diabetic activity in vitro and expands interaction research about hydrophobic compounds and α‐amylase as well as α‐glucosidase. [ABSTRACT FROM AUTHOR]

The compound [Ru2O(keto)2(py)6](PF6)2, keto=ketoprofen and py=pyridine, interacts with calf thymus‐DNA with Kb=1.08×104 M−1. It efficiently quenches HSA fluorescence in different temperatures, with Ksv values in the 104–105 M−1 range, both by dynamic and static mechanisms. The data provided by the double logarithmic and van't Hoff approximations indicated a moderate (Kb≈104 M−1) and spontaneous (ΔG<0) interaction, being enthalpically driven (ΔH=−27.1 kJ mol−1 and ΔS=−5.3 J mol−1 K−1). Molecular docking calculations confirmed that the binuclear compound interacts with HSA more strongly than with DNA. The occurrence of a high contribution from electrostatic forces was observed, fully consistent with the bicationic nature of [Ru2O(keto)2(py)6](PF6)2. The molecular docking results also revealed that the interaction occurs in an external subdomain, explaining the lack of significant conformational changes in the protein, as probed by circular dichroism spectra. [ABSTRACT FROM AUTHOR]

Background and aims: The objective of the present study was to collect the spectroscopic results obtained from previous studies to determine how exogenous toxic ligands can alter the structural and functional properties of human hemoglobin (HHb). Methods: Using spectroscopic techniques, English published articles (from January 2009 to June 2020) on HHb were systematical reviewed by searching several databases such as PubMed, ScienceDirect databases, and Google Scholar. In this regard, some keywords were searched, including (human hemoglobin) AND (spectroscopy) OR (spectroscopic analysis) OR (spectroscopic studies) AND (environmental pollutants) OR (food additives) OR (dyes) OR (fuel additives) OR (radioactive metal ions) OR (insecticides) OR (food colorants). After screening full text articles, we extracted relevant data according to our subject from included articles. Results: Finally, 17 studies were found to be related to the subject of this study. Analysis of investigations suggested that after exposure of HHb to each exogenous ligand, we could observe heme hydrophobic pocket alteration, fluorescence quenching, and polarity alteration around aromatic residues of protein, indicating that the structural properties of HHb were changing. Lack of some spectroscopic techniques in some articles could place some minor limitations on the obtained evidence. Conclusion: Considering the impacts of the exogenous ligands on characteristics of HHb, in the first step, it is the responsibility of governments to exercise strict control over the manufacturing sectors and then industry owners to investigate the effects of chemical products on the living organisms before commercializing them. [ABSTRACT FROM AUTHOR]

The current therapeutic approach for gout is through the inhibition of the xanthine oxidase (XO) enzyme. Allopurinol, a clinically used XO inhibitor, causes many side effects. This study aimed to investigate the interaction between XO and inhibitors identified from Chrysanthemum morifolium by using computational simulation and multispectroscopic methods. The crude extract, petroleum ether, ethyl acetate (EtOAc), and residual fractions were subjected to an XO inhibitory assay and 1H NMR analysis. The EtOAc fraction was shown to be strongly correlated to the XO inhibitory activity by using PLS biplot regression analysis. Kaempferol, apigenin, homovanillic acid, and trans-cinnamic acid were suggested to contribute to the XO inhibitory activity. Molecular docking showed that kaempferol and apigenin bound to the active site of XO with their benzopyran moiety sandwiched between Phe914 and Phe1009, interacting with Thr1010 and Arg880 by hydrogen bonding. Kaempferol showed the lowest binding energy in molecular dynamic simulation. The residues that contributed to the binding energy were Glu802, Arg880, Phe 914, and Phe 1009. A fluorescence quenching study showed a combination of static and dynamic quenching for all four inhibitors binding to XO. Circular dichroism spectroscopy revealed that there was no major change in XO conformation after binding with each inhibitor.

Diabetes is among the top ten deadly diseases in the world. It occurs either when the pancreas does not produce enough insulin (INS) or when the body cannot effectively use the insulin it produces. Phloretin (PHL) has a biological effect that can treat diabetes. A spectroscopic study was carried out to explore the interaction between phloretin and insulin. UV/Vis spectroscopy, fluorescence spectroscopy, and circular dichroism spectropolarimeter were used in the study. UV/Vis spectra showed that the interaction between PHL and INS produced strong absorption at a wavelength of 282 nm. The fluorescence analysis results showed that the excitation and emission occurred at 280-nm and 305-nm wavelengths, respectively. Temperature changes did not affect INS emissions. However, the interaction of PHL–INS caused a redshift at 305 to 317 nm. Temperature affected the binding constant (Ka) and the binding site (n). Ka decreased with increasing temperature and increased the binding site. The thermodynamic parameters such as enthalpy (ΔH0) and entropy (ΔS0) each had a value of − 16,514 kJ/mol and 22.65 J/mol·K. PHL and INS interaction formed hydrogen bonds and hydrophobic interaction. The free energy (ΔG0) recorded was negative. PHL and INS interactions took place spontaneously. The quenching effect was dynamic and static. KD values were greater than KS. The higher the temperature, the less was KD and KS. The appearance of two negative signals on circular dichroism (CD) spectropolarimeter implies that phloretin could induce regional configuration changes in insulin. The addition of PHL has revealed that the proportion of α-helix in the insulin stabilizes its structure. Phloretin's stabilization and enhancement of the α-helix structural configuration in insulin indicate that phloretin can improve insulin resistance. [ABSTRACT FROM AUTHOR]

Tetrapeptides containing a Cys-Gly-Cys motif and a propensity to adopt a reverse-turn structure were synthesized to evaluate how O-, N-, H-, and aromatic π donor groups might contribute to mercury(II) complex formation. Tetrapeptides Xaa-Cys-Gly-Cys, where Xaa is glycine, glutamate, histidine, or tryptophan, were prepared and reacted with mercury(II) chloride. Their complexation with mercury(II) was studied by spectroscopic methods and computational modeling. UV-vis studies confirmed that mercury(II) binds to the cysteinyl thiolates as indicated by characteristic ligand-to-metal-charge-transfer transitions for bisthiolated S-Hg-S complexes, which correspond to 1 : 1 mercury-peptide complex formation. ESI-MS data also showed dominant 1 : 1 mercury-peptide adducts that are consistent with double deprotonations from the cysteinyl thiols to form thiolates. These complexes exhibited a strong positive circular dichroism band at 210 nm and a negative band at 193 nm, indicating that these peptides adopted a β-turn structure after binding mercury(II). Theoretical studies confirmed that optimized 1 : 1 mercury-peptide complexes adopt β-turns stabilized by intramolecular hydrogen bonds. These optimized structures also illustrate how specific N-terminal side-chain donor groups can assume intramolecular interactions and contribute to complex stability. Fluorescence quenching results provided supporting data that the indole donor group could interact with the coordinated mercury. The results from this study indicate that N-terminal side-chain residues containing carboxylate, imidazole, or indole groups can participate in stabilizing dithiolated mercury(II) complexes. These structural insights on peripheral mercury-peptide interactions provide additional understanding of the chemistry of mercury(II) with side-chain donor groups in peptides. [ABSTRACT FROM AUTHOR]

This study was conducted to examine the binding of a newly synthesized Schiff base derived from 2-hydroxy-1-naphthaldehyde and 5-amino-2-mercaptobenzimidazole with human serum albumin (HSA) employing various biophysical techniques. The thermal-based fluorescence quenching data indicated that static quenching occurred between the ligand and HSA. The fluorescence results expose that ligand quenches the intrinsic fluorescence of HSA through a static quenching procedure. The thermodynamic parameters of the binding interaction, obtained using van't Hoff equation indicated the spontaneity of the reaction. The stability of the HSA–ligand complex resulted from hydrogen bonding and hydrophobic interactions, which afforded a substantial binding affinity between ligand and HSA. UV–Vis and circular dichroism data indicated that ligand binding induced conformational changes in HSA. The energy transfer efficiency determined according to Fӧorster's theory. Absorption, distribution, metabolism, and excretion (ADME) and Lipinski's drug likeness of the ligand was predicted, revealing that it had auspicious physicochemical properties for oral bioavailability. Furthermore, molecular modeling was also employed to determine the location of the ligand in HSA binding sites, which revealed that the ligand interacted with polar and apolar residues of site I (subdomain IIA) of HSA, predominantly through hydrophobic and hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interaction of enzalutamide with α 2 M decreases the antiproteolytic activity of protein. • The far UV-CD spectrum reveals slight alteration in the secondary structure of α 2 M. • The intrinsic fluorescence spectrum shows static quenching of fluorescence intensity. • The K b was found to be 1.23 × 104M−1 suggesting strong binding. • The synchronous fluorescence indicates changes in microenvironment around Tyr. • The interaction was found to be exothermic and spontaneous in nature. The drug pharmacokinetics is affected upon binding with proteins, thus making drug-protein interactions crucial. This study investigated the interaction between enzalutamide and human major antiproteinase alpha-2-macroglobulin (α 2 M) by using multi spectroscopic and calorimetric techniques. The spectroscopic techniques such as circular dichroism (CD), intrinsic fluorescence, and UV–visible absorption were used to determine the mechanism of enzalutamide-α 2 M interaction. Studies on the quenching of fluorescence at three different temperatures showed that the enzalutamide-α 2 M complex is formed through static quenching mechanism. The change in microenvironment around tyrosine residues in protein was detected through synchronised fluorescence. The secondary structure of α 2 M was slightly altered by enzalutamide according to far UV-CD spectral analysis. Changes in position of amide I band in FTIR spectra further confirm the secondary structural alteration in α 2 M. According to thermodynamic characteristics such as fluorescence quenching and isothermal titration calorimetry (ITC), hydrogen bonds and hydrophobic interactions were involved in the interaction machanism. The ITC reiterated the exothermic and spontaneous nature of the interaction. The lower proteinase inhibitory activity of the α 2 M-enzalutamide conjugate as reflects the disruption of the native α 2 M structure upon interaction with enzalutamide. [ABSTRACT FROM AUTHOR]

Jacalin, the jackfruit seed lectin, exhibits high specificity for the tumor-specific T-antigen and is used in various biomedical and biotechnological applications. Here, we report biophysical studies on the thermal unfolding of jacalin and the effect of pH and temperature on its secondary structure. Differential scanning calorimetric (DSC) studies revealed that native jacalin unfolds at ∼60 °C and that carbohydrate binding stabilizes the protein structure. Circular dichroism spectroscopic studies indicated that the secondary structure of jacalin remains mostly unaffected over pH 2.0–9.0, whereas considerable changes were observed in the tertiary structure. DSC experiments demonstrated that jacalin exhibits two overlapping transitions between pH 2 and 5, which could be attributed to dissociation of the tetrameric protein into subunits and their unfolding. Interestingly, only one transition between pH 6 and 9 was observed, suggesting that the subunit dissociation and unfolding occur simultaneously. While quenching of the protein intrinsic fluorescence by acrylamide increased significantly upon carbohydrate binding, quenching by succinimide is essentially unaffected. We attribute this difference to increased exposure of Trp-123 in the α-chain as it is involved in carbohydrate binding. Both acrylamide and succinimide gave biphasic Stern-Volmer plots, consistent with differential accessibility of the two tryptophan residues of jacalin to them. [Display omitted] • Secondary structure of jacalin is stable over a wide range of pH (2–9) and temperature. • The unfolding temperature of jacalin increases from 60 °C to 63 °C upon sugar binding. • Two unfolding transitions of jacalin at pH 2–5 are assigned to subunit dissociation and unfolding. • A single transition is observed at pH 6–9 indicating simultaneous subunit dissociation and unfolding. • The two Trp residues of jacalin show different accessibilities to acrylamide and succinimide. [ABSTRACT FROM AUTHOR]

[Display omitted] • Floxuridine (FUDR) spontaneously forms a complex with human serum albumin (HSA). • FUDR induces quenching in the protein fluorescence in a static mode. • Hydrogen bonds, hydrophobic and van der Waals forces promote complex formation. • FUDR-HSA binding leads to a slight change in the protein conformation. • Site I of HSA is recognized as the preferred site in the FUDR-HSA complex. The binding mode of antineoplastic antimetabolite, floxuridine (FUDR), with human serum albumin (HSA), the leading carrier in blood circulation, was ascertained using multi-spectroscopic, microscopic, and computational techniques. A static fluorescence quenching was established due to decreased K sv values with rising temperatures, suggesting FUDR-HSA complexation. UV–vis absorption spectral results also supported this conclusion. The binding constant, K a values, were found within 9.7–7.9 × 103 M−1 at 290, 300, and 310 K, demonstrating a moderate binding affinity for the FUDR-HSA system. Thermodynamic data (ΔS = +46.35 J.mol−1.K−1 and ΔH = −8.77 kJ.mol−1) predicted the nature of stabilizing forces (hydrogen-bonds, hydrophobic, and van der Waals interactions) for the FUDR-HSA complex. Circular dichroism spectra displayed a minor disruption in the protein's 2° and 3° structures. At the same time, atomic force microscopy images proved variations in the FUDR-HSA surface morphology, confirming its complex formation. The protein's microenvironment around Trp/Tyr residues was also modified, as judged by 3-D fluorescence spectra. FUDR-bound HSA showed better resistance against thermal stress. As disclosed from ligand displacement studies, the FUDR binding site was placed in subdomain IIA (Site I). Further, the molecular docking analysis corroborated the competing displacement studies. Molecular dynamics evaluations revealed that the complex achieved equilibrium during simulations, confirming the FUDR–HSA complex's stability. [ABSTRACT FROM AUTHOR]

The function and application of β‐glucosidase attract attention nowadays. β‐glucosidase was confirmed of transforming ginsenoside Rb1 to rare ginsenoside, but the interaction mechanism remains not clear. In this work, β‐glucosidase from GH1 family of Paenibacillus polymyxa was selected, and its gene sequence bglB was synthesized by codon. Then, recombinant plasmid was transferred into Escherichia coli BL21 (DE3) and expressed. The UV–visible spectrum showed that ginsenoside Rb1 decreased the polarity of the corresponding structure of hydrophobic aromatic amino acids (Trp) in β‐glucosidase and increased new π‐π* transition. The fluorescence quenching spectrum showed that ginsenoside Rb1 inhibited intrinsic fluorescence, formed static quenching, reduced the surface hydrophobicity of β‐glucosidase, and KSV was 8.37 × 103 L/M (298K). Circular dichroism (CD) showed that secondary structure of β‐glucosidase was changed by the binding action. Localized surface plasmon resonance (LSPR) showed that β‐glucosidase and Rb1 had strong binding power which KD value was 5.24 × 10–4 (±2.35 × 10–5) M. Molecular docking simulation evaluated the binding site, hydrophobic force, hydrogen bond, and key amino acids of β‐glucosidase with ginsenoside Rb1 in the process. Thus, this work could provide basic mechanisms of the binding and interaction between β‐glucosidase and ginsenoside Rb1. [ABSTRACT FROM AUTHOR]