Induced Chirality in Sulfasalazine by Complexation With Albumins: Theoretical and Experimental Study.

Through molecular recognition, drugs can interact and complex with macromolecules circulating in the body. The serum albumin transport protein, found in several mammals, has several interaction sites where these molecules can be located. The drug sulfasalazine (SSZ) is known in the literature to complex at drug site 1 (DS1) in human serum (HSA) and bovine serum (BSA) proteins. This complexation can be studied using various spectroscopic techniques. With the techniques used in this work, absorption in the ultraviolet and visible regions (UV-Vis) and electronic circular dichroism (ECD), a significant difference was observed in the results involving HSA and BSA. The application of theoretical methodologies, such as TD-DFT and molecular docking, suggests that the conformation that SSZ assumes in DS1 of the two proteins is different, which exposes it to different amino acid residues and different hydrophobicities. This difference in conformation may be related to the location of DS1 where the drug interacts or to the possibility of SSZ moving in the BSA site, due to its larger size, and moving less freely in HSA.

Circular dichroism spectrum of (R)-(+)-3,3'-dibromo-1,1'-bi-2-naphthol in albumin: Alterations caused by complexation-Experimental and in silico investigation.

This study describes the interaction of human serum albumin (HSA) with the binol derivative (R)-(+)-3,3'-dibromo-1,1'-bi-2-naphthol (R-BrB), which has its optical activity based on the prohibitive energetic barrier for conversion into the enantiomer (S)-(+)-3,3'-dibromo-1,1'-bi-2-naphthol (S-BrB). The objective was to assess the ability of HSA to differentiate axial enantiomers based on their binding efficiency and their impact on the CD spectra. We discovered that both enantiomers were effective ligands, and the CD signal disappeared when equimolar amounts of R-BrB and S-BrB were simultaneously added, indicating no preference for either enantiomer. The complexation resulted in a significant signal increase at 250 nm and a bathochromic effect at 370 nm. Molecular docking simulations were performed, and the lower energy pose of R-BrB was selected for DFT calculations. The theoretical CD spectra of free and complexed R-BrB were obtained and showed alterations corroborating the experimental results. By comparing the difference spectrum (HSA:R-BrB minus HSA) with the spectrum of free RBrB in water or ethyl alcohol, we concluded that the CD signal intensification was due to the increased solubilization of R-BrB upon binding to HSA.

Theoretical study of the interaction between the antibiotic linezolid and the active site of the 50S ribosomal subunit of the bacterium Haloarcula marismortui.

First antibiotic in the oxazolidinone class, linezolid fights gram-positive multiresistant bacteria by inhibiting protein synthesis through its interaction with the 50S subunit of the functional bacterial ribosome. For its antimicrobial action, it is necessary that its chiral carbon located in the oxazolidinone ring is in the S-conformation. Computational calculation at time-dependent density functional theory methodology, ultraviolet-visible (UV-Vis), and electronic circular dichroism spectra was obtained for noncomplexed and complexed forms of linezolid to verify the possible chirality of nitrogen atom in the acetamide group of the molecule. The molecular system has two chiral centers. So, there are now four possible configurations: RR, RS, SR, and SS. For a better understanding of the system, the electronic spectra at the PBE0/6-311++G(3df,2p) level of theory were obtained. The complexed form was obtained from the crystallographic data of the ribosome, containing the S-linezolid molecular system. The computational results obtained for the electronic properties are in good agreement with the experimental crystallographic data and available theoretical results.

Methyl divanillate: redox properties and binding affinity with albumin of an antioxidant and potential NADPH oxidase inhibitor.

Vanillic acid is a widely used food additive (flavouring agent, JECFA number: 959) with many reported beneficial biological effects. The same is true for its ester derivative (methyl vanillate, JECFA number: 159). Based on the increasing evidence that diapocynin, the dimer of apocynin (NADPH oxidase inhibitor), has some improved pharmacological properties compared to its monomer, here the dimer of methyl vanillate (MV), i.e., methyl divanillate (dimer of methyl vanillate, DMV) was synthesized and studied in the context of its redox properties and binding affinity with human serum albumin (HSA). We found that the antioxidant potency of DMV was significantly increased compared to MV. In this regard, the reduction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical by DMV was 30-fold more effective compared to MV. Ferric ion reduction was 4-fold higher and peroxyl radical reduction was 2.7-fold higher. The interaction with HSA was significantly improved (Stern-Vomer constants, 3.8 × 105 mol-1 L and 2.3 × 104 mol-1 L, for DMV and MV, respectively). The complexation between DMV and HSA was also evidenced by induced circular dichroism (ICD) signal generation in the former due to its fixation in the asymmetric protein pocket. Density-functional calculations (TD-DFT) showed that the ICD spectrum was related to a DMV conformation bearing a dihedral angle of approximately -60°. Similar dihedral angles were obtained in the lowest and most populated DMV cluster poses obtained by molecular docking simulations. The computational studies and experimental displacement studies revealed that DMV binds preferentially at site I. In conclusion, besides being a powerful antioxidant, DMV is also a strong ligand of HSA. This is the first study on the chemical and biophysical properties of DMV, a compound with potential beneficial biological effects.

Induction of axial chirality in divanillin by interaction with bovine serum albumin.

Vanillin is a plant secondary metabolite and has numerous beneficial health applications. Divanillin is the homodimer of vanillin and used as a taste enhancer compound and also a promissory anticancer drug. Here, divanillin was synthesized and studied in the context of its interaction with bovine serum albumin (BSA). We found that divanillin acquires axial chirality when complexed with BSA. This chiroptical property was demonstrated by a strong induced circular dichroism (ICD) signal. In agreement with this finding, the association constant between BSA and divanillin (3.3 x 105 mol-1L) was higher compared to its precursor vanillin (7.3 x 104 mol-1L). The ICD signal was used for evaluation of the association constant, demonstration of the reversibility of the interaction and determination of the binding site, revealing that divanillin has preference for Sudlow's site I in BSA. This property was confirmed by displacement of the fluorescent markers warfarin (site I) and dansyl-L-proline (site II). Molecular docking simulation confirmed the higher affinity of divanillin to site I. The highest scored conformation obtained by docking (dihedral angle 242°) was used for calculation of the circular dichroism spectrum of divanillin using Time-Dependent Density Functional Theory (TDDFT). The theoretical spectrum showed good similarity with the experimental ICD. In summary, we have demonstrated that by interacting with the chiral cavities in BSA, divanillin became a atropos biphenyl, i.e., the free rotation around the single bound that links the aromatic rings was impeded. This phenomenon can be explained considering the interactions of divanillin with amino acid residues in the binding site of the protein. This chiroptical property can be very useful for studying the effects of divanillin in biological systems. Considering the potential pharmacological application of divanillin, these findings will be helpful for researchers interested in the pharmacological properties of this compound.

Taurine Bromamine: Reactivity of an Endogenous and Exogenous Anti-Inflammatory and Antimicrobial Amino Acid Derivative.

Taurine bromamine (Tau-NHBr) is produced by the reaction between hypobromous acid (HOBr) and the amino acid taurine. There are increasing number of applications of Tau-NHBr as an anti-inflammatory and microbicidal drug for topical usage. Here, we performed a comprehensive study of the chemical reactivity of Tau-NHBr with endogenous and non-endogenous compounds. Tau-NHBr reactivity was compared with HOBr, hypochlorous acid (HOCl) and taurine chloramine (Tau-NHCl). The second-order rate constants (k2) for the reactions between Tau-NHBr and tryptophan (7.7 × 10² M(-1)s(-1)), melatonin (7.3 × 10³ M(-1)s(-1)), serotonin (2.9 × 10³ M(-1)s(-1)), dansylglycine (9.5 × 10¹ M(-1)s(-1)), tetramethylbenzidine (6.4 × 10² M(-1)s(-1)) and H2O2 (3.9 × M(-1)s(-1)) were obtained. Tau-NHBr demonstrated the following selectivity regarding its reactivity with free amino acids: tryptophan > cysteine ~ methionine > tyrosine. The reactivity of Tau-NHBr was strongly affected by the pH of the medium (for instance with dansylglycine: pH 5.0, 1.1 × 104 M(-1)s(-1), pH 7.0, 9.5 × 10 M(-1)s(-1) and pH 9.0, 1.7 × 10 M(-1)s(-1)), a property that is related to the formation of the dibromamine form at acidic pH (Tau-NBr2). The formation of singlet oxygen was observed in the reaction between Tau-NHBr and H2O2. Tau-NHBr was also able to react with linoleic acid, but with low efficiency compared with HOBr and HOCl. Compared with HOBr, Tau-NHBr was not able to react with nucleosides. In conclusion, the following reactivity sequence was established: HOBr > HOCl > Tau-NHBr > Tau-NHCl. These findings can be very helpful for researchers interested in biological applications of taurine haloamines.

Hypobromous acid, a powerful endogenous electrophile: Experimental and theoretical studies.

Hypobromous acid (HOBr) is an inorganic acid produced by the oxidation of the bromide anion (Br(-)). The blood plasma level of Br(-) is more than 1,000-fold lower than that of chloride anion (Cl(-)). Consequently, the endogenous production of HOBr is also lower compared to hypochlorous acid (HOCl). Nevertheless, there is much evidence of the deleterious effects of HOBr. From these data, we hypothesized that the reactivity of HOBr could be better associated with its electrophilic strength. Our hypothesis was confirmed, since HOBr was significantly more reactive than HOCl when the oxidability of the studied compounds was not relevant. For instance: anisole (HOBr, k2=2.3×10(2)M(-1)s(-1), HOCl non-reactive); dansylglycine (HOBr, k2=7.3×10(6)M(-1)s(-1), HOCl, 5.2×10(2)M(-1)s(-1)); salicylic acid (HOBr, k2=4.0×10(4)M(-1)s(-1), non-reactive); 3-hydroxybenzoic acid (HOBr, k2=5.9×10(4)M(-1)s(-1), HOCl, k2=1.1×10(1)M(-1)s(-1)); uridine (HOBr, k2=1.3×10(3)M(-1)s(-1), HOCl non-reactive). The compounds 4-bromoanisole and 5-bromouridine were identified as the products of the reactions between HOBr and anisole or uridine, respectively, i.e. typical products of electrophilic substitutions. Together, these results show that, rather than an oxidant, HOBr is a powerful electrophilic reactant. This chemical property was theoretically confirmed by measuring the positive Mulliken and ChelpG charges upon bromine and chlorine. In conclusion, the high electrophilicity of HOBr could be behind its well-established deleterious effects. We propose that HOBr is the most powerful endogenous electrophile.