Baiba Turovska

Natural-Antioxidant-Inspired Benzo[b]selenophenes: Synthesis, Redox Properties, and Antiproliferative Activity.

The cyclization of arylalkynes under selenobromination conditions, combined with an acid-induced 3,2-aryl shift, was elaborated as a general synthetic pathway for the preparation of polyhydroxy-2- and -3-arylbenzo[b]selenophenes from the same starting materials. The redox properties, free-radical-scavenging ability, and cytotoxicity against malignant cell lines (MCF-7, MDA-MB-231, HepG2, and 4T1) of the synthesized compounds were explored, and the obtained results were used to consider the structure-activity relationships (SARs) in these compounds. Consequently, the structural features that were responsible for the highly potent peroxyl-radical-scavenging activity were established.

Electrochemical oxidation of hydrogenated indolizines and their precursors in chemical synthesis—quaternized pyridyldihydropyridines

The course of electrochemical and chemical oxidation of quaternized pyridyl dihydropyridines has been compared. The splitting off of the carboxylato group from the betaine structure as the substituent in position 4 of 1,4-dihydropyridine ring seems to be the decisive factor in the intramolecular cycloaddition forming indolizines during oxidation. The mechanisms of the electrochemical oxidation in acetonitrile of both tetrahydro- and dihydroindolizines have been studied using rrde voltammetry.

Electrochemical study of intramolecular charge transfer complexes derived from 1,4-naphthoquinone. Part 2. Electro-oxidation of 2-substituted 3-arylamino-1,4-naphthoquinone autocomplexes

Abstract Electrochemical oxidation of intramolecular charge transfer complexes (ICTs) derived from 1,4-naphthoquinone has been studied in acetonitrile using cyclic voltammetry and RRDE. The anodic oxidation of 2-substituted 3-arylamino-1,4-naphthoquinone autocomplexes AC I proceeds in one quasi-reversible stage. The ICT conformation is preserved not only during the electron transfer, but also in the cation radicals formed. The results, obtained from electro-oxidation of AC, confirm the marked electron acceptor properties of die arylamino moiety, at the same time acting as an electron donor in the intramolecular donor-acceptor (D-A) bond. A relationship between redox potentials and ICT electron transfer energy has been found in the case of AC I reversible electrochemical redox reactions.

Electrochemical study of intramolecular charge transfer complexes derived from 1,4-naphthoquinone Part 1. Electroreduction

Abstract Electrochemical investigations (polarography, cyclic voltammetry, rotating ring-disk electrode voltammetry) of intramolecular charge transfer complexes (AC) derived from 1,4-naphthoquinone were performed in acetonitrile. It is concluded that in the first one-electron stage of its electrochemical reduction the AC is in a complexed form. At the same time the amino moiety, which shows a marked inductive (−I) effect, acts as an electron donor in the donor-acceptor (D-A) interaction. Facilitation of the reduction of the quinone part by the aryl amine residue is compensated by the D-A interaction, which makes the electroreduction more difficult. By using ultramicroelectrodes it was shown that the primary reaction products (naphthosemiquinone anions) easily form ion pairs with the tetrabutylammonium ion (TBA + ).

Rational computing of energy levels for organic electronics: the case of 2-benzylidene-1,3-indandiones

Device engineering in organic electronics, an active area of research, requires knowledge of the energy levels of organic materials (traditionally but ambiguously denoted as HOMO and LUMO). These can be effectively determined by electrochemical investigation, but yet more effective would be quantum chemical (QC) computation of these quantities. However, there is no consensus on the computational method in the research community. Ongoing discussions often focus on choosing the right density functional method, but neglect other model parameters, in particular, the basis set. This study considers comparison of various methodologies and parameters for predicting ionization energy I and electron affinity A. Our aim was to outline a QC ‘recipe’ used in the search of new structures with desired energy levels for application in the field of organic electronics. Validation of calculated results to electrochemically determined values through linear regression and effect decomposition were used for compiling the recipe, ensuring trend-descriptive and resource–effective combination of QC model parameters. In particular, accounting for solvation by the medium is found to be essential and hardly consuming any additional CPU time. Basis set extension with extra valence functions is found to be much more effective than by adding diffuse functions. Among explored methods, B3LYP/6-311G(d) + CPCM is the recommended one for ionization energy, providing experimental quality results suitable for screening purposes. CAM-B3LYP is deemed more efficient for electron affinity, though by far not achieving the desired quality. Correction by computed reference redox pair potential is also found to be overall advantageous.

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

Summary Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by 3O2 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.