Cyclic voltammetric behaviour of the O2/O2− redox couple at a HMDE and its interaction with nisoldipine

New bi-phosphonate derivative: Synthesis, characterization, antioxidant activity in vitro and via cyclic voltammetry mode and evaluation of its inhibition of SARS-CoV-2 main protease

In this study, we have synthesized a new molecule labeled HBPA. Its molecular structure was determined by spectroscopic methods such as: FT-IR, NMR (¹H, ¹³C and ³¹P); our compound is subjected to two antioxidant activities assays: DPPH scavenging and ferric reducing antioxidant power (FRAP); in the results, HBPA was expanded remarkable inhibition when compared especially to standard BHT with values of 14.936±0.808 and 7.1486±0.0645 μg/ml, respectively; in addition to the scavenging test of superoxide anion integrated in electrochemical process, it elucidated a strongly stable interaction towards the radical by evaluating the thermodynamic descriptors (Gibbs free energy ΔG° and the binding constant K_b). Besides, the electrochemical behavior of HBPA was distinguished by an irreversible system and for the electrochemical regime adopted at the surface of the electrode; a diffusion governed by a slow charge transfer was deduced. The molecular docking of HBPA was conducted beside Chloroquine and the obtained results were indicated a significant binding with active sites of the SARS-CoV-2 main protease (M^pro).

Redox process is crucial for inhibitory properties of aurintricarboxylic acid against activity of YopH: virulence factor of Yersinia pestis

YopH is a bacterial protein tyrosine phosphatase, which is essential for the viability and pathogenic virulence of the plague-causing Yersinia sp. bacteria. Inactivation of YopH activity would lead to the loss of bacterial pathogenicity. We have studied the inhibitory properties of aurintricarboxylic acid (ATA) against YopH phosphatase and found that at nanomolar concentrations ATA reversibly decreases the activity of YopH. Computational docking studies indicated that in all binding poses ATA binds in the YopH active site. Molecular dynamics simulations showed that in the predicted binding pose, ATA binds to the essential Cys403 and Arg409 residues in the active site and has a stronger binding affinity than the natural substrate (pTyr). The cyclic voltammetry experiments suggest that ATA reacts remarkably strongly with molecular oxygen. Additionally, the electrochemical reduction of ATA in the presence of a negative potential from −2.0 to 2.5 V generates a current signal, which is observed for hydrogen peroxide. Here we showed that ATA indicates a unique mechanism of YopH inactivation due to a redox process. We proposed that the potent inhibitory properties of ATA are a result of its strong binding in the YopH active site and in situ generation of hydrogen peroxide near catalytic cysteine residue.

Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by (3)O2 if the solution is exposed to sunlight. The driving force for the photoinduced electron transfer is calculated from electrochemical and spectroscopic data. The outcome of the reaction depends on the light intensity and the concentration of O2. In the solid state the heterocyclic hydroperoxide is stable; in solution it is involved in further reactions.

Analyses by GC–MS and GC–MS–MS of the hantzsch synthesis products using hydroxy- and methoxy-aromatic aldehydes

EI mass spectra of products of the dihydropyridine Hantzsch synthesis using hydroxy and methoxy aldehydes as starting materials are reported. The reaction products (C-4 hydroxy- and methoxyphenyl-1,4-dihydropyridines and chromeno[3,4,c]-pyridines) were derivatized with N-methyl-N-(trimethylsilyl)-trifluoracetamide to be analyzed by gas chromatographic techniques. Fragmentation pathways for 1,4-dihydropyridines and chromeno-pyridines are proposed. The study provides (mainly through MS-MS technique) useful data for the confirmation of the structure of the compounds and also is a valuable tool for further analytical purposes to follow both photostability and reactivity studies with free radicals for these types of compounds.

Eccentric Phenomena at Liquid Mercury Electrode/Solution Interfaces: Upward, Downward, and Circular Motions

The present paper describes a visualization of unidirectional and circular motions triggered by an electrochemical redox reaction at a charged, bent, and streamed liquid electrode/liquid solution interface. The novel circular motion that induces a conversion of electrochemical energy into mechanical energy could be visualized for the first time at a hanging mercury drop electrode (HMDE)/dimethyl sulfoxide (DMSO) solution interface via the electrochromic reaction of 2,1,3-benzothiadiazole (BTD) by using a CCD-color video camera. The observed motions are self-insisting in nature and are tunable into upward, downward, clockwise, and anticlockwise ones by an appropriate choice of the experimental conditions. This circular motion is visualized for the first time as the cause of the well-known cyclic voltammetric anodic current oscillation at the HMDE. Several small perturbations, for example, surface tension, surface motion, bulk motion, diffusional mass transport, and surface electrochemical potential are considered to be endlessly amplified by their coupling in a cyclic chain, resulting in such macroscopic motions at the electrode/solution interface. All of the phenomena can be explained on the basis of the modern theory proposed by Aogaki et al. for the polarographic streaming maxima of the first kind.

Reactivity of 1,4-dihydropyridines toward alkyl, alkylperoxyl radicals, and ABTS radical cation

A series of C4-substituted 1,4-dihydropyridines (DHP) with either secondary or tertiary nitrogen in the dihydropyridine ring were synthesized. All of these compounds together with some commercial DHP derivatives were tested for potential scavenger effects toward alkyl, alkylperoxyl radicals, and ABTS radical cation in aqueous media at pH 7.4. Kinetic rate constants were assessed either by UV/vis spectroscopy or GC/MS techniques. Tested compounds reacted faster toward alkylperoxyl radicals and ABTS radical cation than alkyl ones. N-Ethyl-substituted DHPs showed the lowest reactivity. Kinetic results were compared with either trolox or nisoldipine. Using deuterium kinetic isotope effect studies, we have proved that the hydrogen of the 1-position of the DHP ring is involved in the proposed mechanism. This fact is mostly noticeable in the case of alkyl radicals. In all cases, the respective pyridine derivative was detected as the main product of the reaction.