Probing the interaction between 7-O-β-d-glucopyranosyl-6-(3-methylbut-2-enyl)-5,4′-dihydroxyflavonol with bovine serum albumin (BSA)

Synthesis, Characterization, and BSA Binding Properties of Carboxylated Merocyanine-Based Fluorophores

This study describes the synthesis of new carboxylated merocyanine dyes by Knoevenagel condensation between 4-carboxybenzaldehyde and indolium/benzoindolium- and benzothiazolium-based coupling compounds. The condensations were performed in the presence of ammonium acetate, and the products were obtained in good yields after simple purification. These merocyanines exhibit UV-A-to-blue absorption and blue-to-green fluorescence emission, characterized by relatively large Stokes shift values (∼5000 cm-1). In addition, quantum chemical calculations were conducted to better explore the electronic and photophysical properties of the merocyanines under study. Thermal analysis via thermogravimetric analysis (TGA) revealed distinct decomposition stages for the merocyanines, with stability up to 200 °C. Cyclic voltammetry revealed irreversible waves for donor oxidation and acceptor reduction. On the basis of the onset potentials, the highest occupied molecular orbital (HOMO) energies were estimated to be between -5.38 and -5.47 eV, and the lowest unoccupied molecular orbital (LUMO) energies were calculated to range from -3.20 to -3.24 eV. These values suggest a narrow electrochemical band gap of 2.07 to 2.13 eV. Finally, fluorescence quenching experiments using the intrinsic fluorescence of the Trp residues in BSA were successfully applied to these compounds, indicating strong interactions with this protein via a static mechanism. The docking simulations corroborated the interaction between the merocyanines and BSA.

Vanadium(V) complexes derived from triphenylphosphonium and hydrazides: cytotoxicity evaluation and interaction with biomolecules

The development of coordination compounds with antineoplastic therapeutic properties is currently focused on non-covalent interactions with deoxyribonucleic acid (DNA). Additionally, the interaction profiles of these compounds with globular plasma proteins, particularly serum albumin, warrant thorough evaluation. In this study, we report on the interactions between biomolecules and complexes featuring hydrazone-type imine ligands coordinated with vanadium. The potential to enhance the therapeutic efficiency of these compounds through mitochondrial targeting is explored. This targeting is facilitated by the derivatization of ligands with triphenylphosphonium groups. Thus, this work presents the synthesis, characterization, interactions, and cytotoxicity of dioxidovanadium(V) complexes (C1-C5) with a triphenylphosphonium moiety. These VV-species are coordinated to hydrazone-type iminic ligands derived from (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride ([AH]Cl) and aromatic hydrazides ([H2L1]Cl-[H2L5]Cl). The structures of the five complexes were elucidated through single-crystal X-ray diffraction and vibrational spectroscopies, confirming the presence of dioxidovanadium(V) species in various geometries with degrees of distortion (τ = 0.03-0.50) and highlighting their zwitterionic characteristics. The molecular structural stability of C1-C5 in solution was ascertained using 1H, 19F, 31P, and 51V-nuclear magnetic resonance. Moreover, their interactions with biomolecules were evaluated using diverse spectroscopic methodologies and molecular docking, indicating moderate interactions (Kb ≈ 104 M-1) with calf thymus DNA in the minor groove and with human serum albumin, predominantly in the superficial IB subdomain. Lastly, the cytotoxic potentials of these complexes were assessed in keratinocytes of the HaCaT lineage, revealing that C1-C5 induce a reduction in metabolic activity and cell viability through apoptotic pathways.

Influence of para-substituted benzaldehyde derivatives with different push/pull electron strength groups on the conformation of human serum albumin and toxicological effects in zebrafish

Excessive intake of benzaldehyde and its derivatives can cause irreversible damage to living organisms. Hence, benzaldehyde derivatives with different para-substitutions of push/pull electronic groups were chosen to investigate the effect of different substituent properties on the structure of human serum albumin (HSA). The binding constants, number of binding sites, major interaction forces, protein structural changes, and binding sites of benzaldehyde (BzH) and its derivatives (4-BzHD) with HSA in serum proteins were obtained based on multispectral and molecular docking techniques. The mechanism of BzH/4-BzHD interaction on HSA is mainly static quenching and is accompanied by the formation of a ground state complex. BzH/4-BzHD is bound to HSA in a 1:1 stoichiometric ratio. The interaction forces for the binding of BzH/4-BzHD to HSA are mainly hydrogen bonding and hydrophobic interaction, which are also accompanied by a small amount of electrostatic interactions. The effect of BzH/4-BzHD on HSA conformation follows: 4-Diethylaminobenzaldehyde (4-DBzH) > 4-Nitrobenzaldehyde (4-NBzH) > 4-Hydroxybenzaldehyde (4-HBzH) > 4-Acetaminobenzaldehyde (4-ABzH) > BzH, which means that the stronger push/pull electronic strength of the para-substituted benzaldehyde derivatives has a greater effect on HSA conformation. Furthermore, the concentration-lethality curves of different concentrations for BzH/4-BzHD on zebrafish verified above conclusion. This work provides a scientific basis for the risk assessment of benzaldehyde and its derivatives to the ecological environment and human health and for the environmental toxicological studies of benzaldehyde derivatives with different strengths of push/pull electron substitution.

Increasing the polarity of β-lapachone does not affect its binding capacity with bovine plasma protein

Despite ortho-quinones showing several biological and pharmacological activities, there is still a lack of biophysical characterization of their interaction with albumin - the main carrier of different endogenous and exogenous compounds in the bloodstream. Thus, the interactive profile between bovine serum albumin (BSA) with β-lapachone (1) and its corresponding synthetic 3-sulfonic acid (2, under physiological pH in the sulphonate form) was performed. There is one main binding site of albumin for both β-lapachones (n ≈ 1) and a static fluorescence quenching mechanism was proposed. The Stern-Volmer constant (KSV) values are 104 M-1, indicating a moderate binding affinity. The enthalpy (-3.41 ± 0.45 and - 8.47 ± 0.37 kJ mol-1, for BSA:1 and BSA:2, respectively) and the corresponding entropy (0.0707 ± 0.0015 and 0.0542 ± 0.0012 kJ mol-1 K-1) values indicate an enthalpically and entropically binding driven. Hydrophobic interactions and hydrogen bonding are the main binding forces. The differences in the polarity of 1 and 2 did not change significantly the affinity to albumin. In addition, the 1,2-naphthoquinones showed a similar binding trend compared with 1,4-naphthoquinones.

Photoactive glycoconjugates with a very large Stokes shift: synthesis, photophysics, and copper(II) and BSA sensing

This study presents the synthesis of novel glycoconjugates by connecting benzazole and carbohydrate units with a 1,2,3-triazole linker. A simple synthetic route employing a copper(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) was utilized. The synthesized compounds exhibit excited-state intramolecular proton transfer (ESIPT), resulting in longer wavelength emission with a significantly large Stokes shift (∼10 000 cm-1). These compounds show potential as chemical sensors due to their ability to detect Cu2+ ions, causing a decrease in fluorescence emission (turn-off effect). Additionally, they demonstrate strong interaction with proteins, exemplified by their interaction with bovine serum albumin (BSA) as a model protein.

A binuclear Cu(I)-phosphine complex as a specific HSA site I binder: synthesis, X-ray structure determination, and a comprehensive HSA interaction analysis

In this research, we present a method for synthesis and a detailed description of geometry characterization of a novel binuclear Cu(I) phosphine complex, along with analysis of its interaction with HSA using spectroscopic and simulation methods. The Cu atoms are coordinated in a tetrahedral geometry, which results in coordination by two nitrogen atoms from the N,N'-(ethane-1,2-diyl)bis(1-(pyridin-2-yl)methanimine ligand (L), a chloride, and a PPh3. The complex binding constant to HSA in a biochemical environment was determined to be ∼106, which is indicative of a strong interaction. The fluorescence of HSA is significantly quenched by binding to the complex via a static mechanism, whereas the microenvironment of the tryptophan residue remains unchanged. A spontaneous binding process was indicated by a negative value for ΔG. Thermodynamic signatures reflect the dominance of hydrophobic forces during the interaction. The site marker competitive experiment combined with docking simulation analysis revealed the closeness position of the complex binding site to warfarin location in specific ligand site I of HSA. The information generated in the present study would be valuable to understand the interaction mechanistic and pharmacological behavior of Cu(I) complexes.Communicated by Ramaswamy H. Sarma.

Characterization of sulfasalazine-bovine serum albumin and human serum albumin interaction by spectroscopic and theoretical approach

The interaction of sulfasalazine (SZ) with the carrier proteins bovine serum albumin (BSA) and human serum albumin (HSA) was explored by fluorescence, absorption and circular dichroism (CD) spectroscopy along within silicotechniques. The spectral alteration observed in fluorescence, absorption and CD spectra upon the addition of SZ confirmed the complex formation of SZ with BSA and HSA. The inverse temperature dependence behaviour of theK_svvalues as well as the increase in the protein's absorption signals after the addition of SZ indicate that SZ triggered quenching of BSA/HSA fluorescence as the static quenching. The binding affinity (k_b) of the order of 10⁶ M^-1 was reported towards the BSA-SZ and HSA-SZ association process. Interpretation of thermodynamic data (enthalpy change = -93.85 kJ mol^-1and entropy change = -200.81 J mol^-1K^-1for BSA-SZ system; enthalpy change = -74.12 kJ mol^-1and entropy change = -123.90 J mol^-1K^-1for HSA-SZ system) anticipated that hydrogen bond and van der Waals forces were the main intermolecular forces in the complex stabilization. Inclusion of SZ to BSA/HSA produced microenvironmental perturbations around Tyr and Trp residues. The UV, synchronous and 3D analysis confirmed the structural alteration of proteins after SZ binding, which was supported by CD results. The binding location of SZ in BSA/HSA was detected in Sudlow's site I (subdomain IIA) and the same was revealed by competitive site-marker displacement investigations. Density functional theory study was done to comprehend the feasibility of the analysis and to optimize the structure and energy gap that validated the experimental results. This study is expected to provide deep information about the pharmacology of SZ with its pharmacokinetic properties.

Physicochemical mechanism of BSA, Hb, and dsDNA biomacromolecules with aq-NaCMC at 298.15-310.15 K interfaced with UV-vis fluorescence circular dichroism spectroscopy and in-silico for interacting activities

The 0.2-0.8mg% @ 0.2 mg% bovine serum albumin (BSA 66), hemoglobin (Hb 64.5), and double stranded deoxyribonucleic acid (dsDNA 130 kDa) with water and 0.25, 0.50, and 1.00 g% aqueous carboxymethyl cellulose sodium salt (NaCMC) thermodynamically, kinetically, and tentropically stable homogeneous solutions via resonating energy transfer were designed. Density (ρ), viscosity (η), surface tension (γ), friccohesity (σ), Gibbs free energy (ΔG_b), chemical potential (μ), frictional volume (ϕ), apparent molar volume (V₂), hydrodynamic radius (R_h), and isentropic compressibility (k_sϕ) at 298.15, 304.15, and 310.15 K were studied. UV-Vis spectrophotometry, fluorescence spectroscopy, circular dichroism (CD), MALDI TOF, and in-silico study via reorientational activities have elucidated structural recognition. The ρ, η, γ, σ, ΔG_b, μ, V₂, ϕ, R_h, and k_sϕ physicochemical properties (PCPs) have studied the interacting activities of salt bridges (peptide bonds) of proteins and base pairs (adenine, thymine, cytosine, guanine) of dsDNA on developing nanohydration sphere (NHS) with water and 0.25, 0.50, and 1.00 g% aq-NaCMC. Regression constants of PCPs have elaborated the interacting mechanism of internal linkages of BSA, Hb, and dsDNA for solubilizing them without unfolding assisted by glycosidic bonds of glucopyranose units of NaCMC. Magnitudes of regression constants analyse the inner salt bridges, electrostatic dipoles, and hydrogen bonds (HB) to interact with H₂O dipoles and NaCMC affecting solubilization of biomolecules (biomols) in areas of biochemical, biophysical, bioengineering, tissue, and genetic engineering. PCPs, UV-Vis, fluorescence, CD, and in-silico study analyse their structurally interacting abilities with NaCMC via respective NHS to be extended to pharmaceutical and cosmetic processes by minimizing quantum energy barrier (QEB) as Newtonian behaviour of structural sensors.

Biophysical Characterization of the Interaction between a Transport Human Plasma Protein and the 5,10,15,20-Tetra(pyridine-4-yl)porphyrin

The interaction between human serum albumin (HSA) and the non-charged synthetic photosensitizer 5,10,15,20-tetra(pyridine-4-yl)porphyrin (4-TPyP) was evaluated by in vitro assays under physiological conditions using spectroscopic techniques (UV-vis, circular dichroism, steady-state, time-resolved, synchronous, and 3D-fluorescence) combined with in silico calculations by molecular docking. The UV-vis and steady-state fluorescence parameters indicated a ground-state association between HSA and 4-TPyP and the absence of any dynamic fluorescence quenching was confirmed by the same average fluorescence lifetime for HSA without (4.76 ± 0.11 ns) and with 4-TPyP (4.79 ± 0.14 ns). Therefore, the Stern-Volmer quenching (K_SV) constant reflects the binding affinity, indicating a moderate interaction (10⁴ M^-1) being spontaneous (ΔG°= -25.0 kJ/mol at 296 K), enthalpically (ΔH° = -9.31 ± 1.34 kJ/mol), and entropically (ΔS° = 52.9 ± 4.4 J/molK) driven. Binding causes only a very weak perturbation on the secondary structure of albumin. There is just one main binding site in HSA for 4-TPyP (n ≈ 1.0), probably into the subdomain IIA (site I), where the Trp-214 residue can be found. The microenvironment around this fluorophore seems not to be perturbed even with 4-TPyP interacting via hydrogen bonding and van der Waals forces with the amino acid residues in the subdomain IIA.

Bis-triazolylchalcogenium-Functionalized Benzothiadiazole Derivatives as Light-up Sensors for DNA and BSA

A range of bis-triazolylchalcogenium-BTD 3 was synthesized by a copper-catalyzed azide-alkyne cycloaddition of azido arylchalcogenides 1 and 4,7-diethynylbenzo[c][1,2,5]thiadiazole 2. Eight new compounds were obtained in moderate to good yields using 1 mol % of copper(II) acetate monohydrate under mild reaction conditions. In addition, the synthesized bis-triazolylchalcogenium-BTD 3a-3h were investigated regarding their photophysical, electrochemical, and biomolecule binding properties in solution. In general, compounds presented strong absorption bands at the 250-450 nm region and cyan to green emission properties. The redox process attributed to the chalcogen atom was observed by electrochemical analysis (CV techniques). In addition, spectroscopic studies by UV-vis, steady-state emission fluorescence, and molecular docking calculations evidenced the ability of each derivative to establish interactions with calf-thymus DNA (CT-DNA) and bovine serum albumin (BSA). The behavior presented for this new class of compounds makes them a promising tool as optical sensors for biomolecules.

Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue–green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (K_q~10¹² L·mol⁻¹·s⁻¹). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.

Helical water-soluble NiII complexes with pyridoxal ligand derivatives: Structural evaluation and interaction with biomacromolecules

This article deals with the synthesis of Schiff-based bis-azomethine-based ligands derived from pyridoxal and aliphatic dihydrazides and the synthesis of nickel(II) complexes C1-C4. The synthesized complexes had their structures elucidated by monocrystal X-ray diffraction and were characterized by vibrational and absorption spectroscopy. The synthesized ligands have characteristics that allow the formation of self-assembly processes, thus, the flexibility or rigidity of the coordination of organic molecules added to the orbitals of the Ni^II cation leads to the formation of helical complexes with double helix and a dinucler nickel(II) complex. Moreover, compounds was their interactions with CT-DNA and HSA absorption and emission analysis and molecular docking calculations.

Fluorescent pyrene moiety in fluorinated C6F5-corroles increases the interaction with HSA and CT-DNA

Two fluorinated meso-C6F5-corroles (5,15-bis(pentafluorophenyl)-10-(phenyl)corrole and 5,15-bis(pentafluorophenyl)-10-(1-pyrenyl)corrole) were biologically evaluated in terms of binding affinity to human serum albumin (HSA) and calf-thymus DNA (CT-DNA) via multiple spectroscopic techniques under physiological conditions combined with molecular docking calculations. The HSA:corrole interaction is spontaneous and moderate via static binding, disturbing both secondary and tertiary albumin structures at high fluorinated corrole concentrations. The competitive binding studies indicated positive cooperativity or allosteric activation, while molecular docking calculations suggested that both fluorinated corroles bind preferentially inside subdomains IIA and IB (sites I and III, respectively). The experimental CT-DNA binding assays indicated that fluorinated corroles interact spontaneously by non-classical modes in the minor groove of the CT-DNA strands via static fluorescence quenching mechanism. Molecular docking results also showed the minor groove as the main binding site for CT-DNA. Overall, the pyrene moiety increased the interaction with HSA and CT-DNA, which is probably due to the planarity and volume that favors the pyrene unit to be buried inside the biomacromolecule pockets.

Modified pyrazole platinum(II) complex can circumvent albumin and glutathione: Synthesis, structure and cytotoxic activity

The synthesis and structural characterization of novel platinum complexes ([Pt^II(Pz)₂Cl₂] - C1, C2 and C3) featuring diphenyl-pyrazole derived ligands: para-fluorophenyl and para-substituted phenyl (CH₃, F and Cl for L1, L2 and L3, respectively) were reported and it was also evaluated their potential antitumor activity. The elemental, molar conductivity and thermogravimetric analysis combined with FTIR, UV-vis, NMR and mass spectrometry are in agreement with the chemical structure indicated by single-crystal X-ray diffraction. The antiproliferative activities were assessed against tumor (B16F10 and 4T1) and non-tumor (BHK21) cell lines, and the cytotoxicity of the compounds was strongly increased after metal complexation displaying promising activity. It was also assessed the ability of extracellular bovine serum albumin (BSA) and glutathione (GSH) to decrease the cytotoxicity of the complexes against B16F10. It was highlighted that only the C3 activity was not disturbed in those conditions, being confirmed by flow cytometry using Anexin-V/PI to evaluate interferences in the apoptosis process, even it was not predicted by molecular docking simulations. The interaction of the synthesized compounds with calf-thymus DNA (ctDNA) and bovine serum albumin (BSA) was also investigated through spectrophotometric assays and molecular docking simulations, indicating that C1 and C2 presented better interaction with the biomacromolecules than the corresponding ligands. In addition, agarose gel electrophoresis with plasmid DNA revealed that C1-C3 are capable of interaction with DNA and modify its electrophoretic mobility.

Privileged Scaffold Chalcone: Synthesis, Characterization and Its Mechanistic Interaction Studies with BSA Employing Spectroscopic and Chemoinformatics Approaches

Chalcone, a privileged structure, is considered as an effective template in the field of medicinal chemistry for potent drug discovery. In the present study, a privileged template chalcone was designed, synthesized, and characterized by various spectroscopic techniques (NMR, high-resolution mass spectrometry, Fourier transform infrared (FT-IR) spectroscopy, UV spectroscopy, and single-crystal X-ray diffraction). The mechanism of binding of chalcone with bovine serum albumin (BSA) was determined by multispectroscopic techniques and computational methods. Steady-state fluorescence spectroscopy suggests that the intrinsic fluorescence of BSA was quenched upon the addition of chalcone by the combined dynamic and static quenching mechanism. Time-resolved spectroscopy confirms complex formation. FT-IR and circular dichroism spectroscopy suggested the presence of chalcone in the BSA molecule microenvironment and also the possibility of rearrangement of the native structure of BSA. Moreover, molecular docking studies confirm the moderate binding of chalcone with BSA and the molecular dynamics simulation analysis shows the stability of the BSA-drug complex system with minimal deformability fluctuations and potential interaction by the covariance matrix. Moreover, pharmacodynamics and pharmacological analysis show good results through Lipinski rules, with no toxicity profile and high gastrointestinal absorptions by boiled egg permeation assays. This study elucidates the mechanistic profile of the privileged chalcone scaffold to be used in therapeutic applications.

Synthesis, photophysics and biomolecule interactive studies of new hybrid benzo-2,1,3-thiadiazoles

New hybrid molecules containing benzo-2,1,3-thiadiazole, benzofuran and arylselanyl moieties were synthesized and their photophysics and biomolecule interactive studies were performed.

In vitro and in vivo cytotoxic activity and human serum albumin interaction for a methoxy-styryl-thiosemicarbazone

Thiosemicarbazone is a class of compounds with potential applications in medicine, presenting high capacity to inhibit the growth of cancer cells as well as low toxicity. Because of high interest in anticancer studies involving thiosemicarbazones as new chemotherapeutic agents, a synthetic thiosemicarbazone derivative, 4-N-(2'-methoxy-styryl)-thiosemicarbazone (MTSC) was evaluated in vivo against Ehrlich carcinoma in an animal model. In vivo results demonstrated that MTSC treatment induced the survival of mice and altered significantly the body weight of the surviving mice 12 days after tumor inoculation. Treatment with 30 mg/kg of MTSC exhibited effective cytotoxic activity with T/C values of 150.49% (1 dose) and 278% (2 doses). Its interaction with human serum albumin (HSA), which plays a crucial role in the biodistribution of a wide variety of ligands, was investigated by multiple spectroscopic techniques at 296 K, 303 K, and 310 K, as well as by theoretical calculations. The interaction between HSA and MTSC occurs via ground-state association in the subdomain IIA (Sudlow's site I). The binding is moderate (K_a ≈ 10⁴ M^-1), spontaneous, entropically, and enthalpically driven. Molecular docking results suggested hydrogen bonding and hydrophobic interactions as the main binding forces. Overall, the interaction HSA:MTSC could provide therapeutic benefits, improving its cytotoxic efficacy and tolerability.

Regulating the alky chain length of fatty acid-didanosine prodrugs and evaluating its role in albumin binding

Rational design of prodrugs for efficient albumin binding shows distinct advantages in drug delivery in terms of drug availability, systemic circulation, and potential targeting effect. And fatty acids are good candidates due to their high affinity to albumin. However, how the alkyl chain length of fatty acids affects the binding dynamics between prodrugs and albumin, despite its importance, is still unclear. In the present study, three prodrugs of didanosine (DDI) and fatty acids were designed and synthesized to evaluate the effect of the alkyl chain length on prodrug-albumin binding process, including capric acid-didanosine (CA-DDI), myristic acid-didanosine (MA-DDI), and stearic acid-didanosine (SA-DDI). The binding dynamics between these prodrugs with bovine serum albumin (BSA) were studied by fluorometry, circular dichroism (CD), UV analysis, and molecular docking. It turned out that DDI itself showed poor binding affinity to BSA. In contrast, CA-DDI, MA-DDI, and SA-DDI demonstrated significantly improved binding affinity. Interestingly, the binding affinity between DDI prodrugs and BSA was correlated with the alkyl chain length of fatty acids, and the binding constant significantly increased with the extension of alkyl chain length (K_CA-DDI = 5.86 × 103 M^-1, K_MA-DDI = 8.57 × 103 M^-1, and K_SA-DDI = 11.42 × 103 M^-1 at 298 K).

Multi-Spectroscopic and Theoretical Analysis on the Interaction between Human Serum Albumin and a Capsaicin Derivative-RPF101

The interaction between the main carrier of endogenous and exogenous compounds in the human bloodstream (human serum albumin, HSA) and a potential anticancer compound (the capsaicin analogue RPF101) was investigated by spectroscopic techniques (circular dichroism, steady-state, time-resolved, and synchronous fluorescence), zeta potential, and computational method (molecular docking). Steady-state and time-resolved fluorescence experiments indicated an association in the ground state between HSA:RPF101. The interaction is moderate, spontaneous (ΔG° < 0), and entropically driven (ΔS° = 0.573 ± 0.069 kJ/molK). This association does not perturb significantly the potential surface of the protein, as well as the secondary structure of the albumin and the microenvironment around tyrosine and tryptophan residues. Competitive binding studies indicated Sudlow’s site I as the main protein pocket and molecular docking results suggested hydrogen bonding and hydrophobic interactions as the main binding forces.

Novel piperonal 1,3,4-thiadiazolium-2-phenylamines mesoionic derivatives: Synthesis, tyrosinase inhibition evaluation and HSA binding study

A novel series of piperonal mesoionic derivatives (PMI 1-6) was synthesized. Tyrosinase inhibition in the presence of PMI-1, -2, -3, -4, -5 and -6 as well as human serum albumin (HSA) binding studies with PMI-5 and PMI-6 were done by spectroscopic and theoretical methods. The mesoionic compound PMI-5 is the most promising tyrosinase inhibitor with a noncompetitive inhibitory mechanism and an IC₅₀=124μmolL^-1. In accordance with the kinetic profile, molecular docking results show that PMI-5 is able to interact favorably with the tyrosinase active site containing the substrate molecule, L-DOPA, interacting with Val-247, Phe-263 and Val-282 residues. The spectroscopic results for the interaction HSA:PMI-5 and HSA:PMI-6 indicated that these mesoionic compounds can associate with HSA in the ground state and energy transfer can occur with high probability. The binding was moderate, spontaneous and can perturb significantly the secondary structure of the albumin. The molecular docking results suggest that PMI-5 and PMI-6 are able to be accommodated inside the Sudlow's site I in HSA, interacting with hydrophobic and hydrophilic amino acid residues.