Vol 72, No 5 (2017)

A quantum chemical study of the mechanism and determination of the activation barriers of intramolecular η⁶,η⁶-inner-ring haptotropic rearrangements (IHR), consisting in moving a chromium tricarbonyl group Cr(CO)₃ from one six-membered aromatic ring to another, are carried out using the density functional theory (DFT) for the respective η⁶-complexes of coronene I and kekulene II. The stationary states on the potential energy surface, determining the mechanism of η⁶,η⁶-IHR, have a lower hapticity, which is of interest for catalysis because of the possibility of coordinating an additional substrate and reagent around the transition metal during the rearrangement. The processes of η⁶,η⁶-IHR complexes I and II occur with similar energy barriers (ΔG^≠ ≈ 20–25 kcal/mol) that are lower than the barriers (ΔG^≠ ≈ 30 kcal/mol) of similar transformations previously calculated or measured for naphthalene complexes and a number of small polyaromatic hydrocarbons.

D-amino acid oxidase (DAAO) is an FAD-containing oxidoreductase that stereospecifically oxidases D-amino acids to produce α-keto-acids, an ammonium ion, and hydrogen peroxide. The most important biotechnological process involving DAAO is the production of 7-amino cephalospranic acid (7-ACA) from cephalosporin C. The reaction product, 7-ACA, is then used as a precursor for the synthesis of cephalosporin antibiotics of different generations. We previously obtained mutant DAAOs from the yeast Trigonopsis variabilis (TvDAAO). The mutants with point amino acid substitutions were characterized by either an increased thermal stability or improved catalytic properties in the oxidation of cephalosporin C. In the present study, we obtained two new mutant TvDAAOs with two and four amino acid substitutions, respectively. The catalytic constants of these mutant TvDAAOs for the oxidation of cephalosporin C were 1.8 and 4 times higher than the respective parameter of the wild-type enzyme (wt-TvDAAO). The combination of substitutions increased the thermal stabilities of both mutant TvDAAOs by a factor of 2–3 as compared with the wt- TvDAAO.

The results are presented of the detection of volatile organic compounds, that is, degradation products of polymers, under the influence of UV radiation decomposition of polymer films from oxobiodegradable polyethylene on samples using an “electronic-nose” gas analyzer based on other selective piezosensors. The polymer films were obtained using different prooxidants: d2w, carboxylate, and iron stearate. The dependence of the composition of the films of the compounds was related to the treatment time, the power of the UV radiation, and the nature of the additives.

A technique for preparing enriched glauconite on the basis of a natural mineral from the Beloozyorskoe field of Saratov oblast has been developed. The results of a study of the chemical composition, surface structure, and certain physicochemical properties of the samples of the sorbent are presented. The sorption of ambroxol hydrochloride ions from aqueous solutions has been studied using natural and enriched glauconite. The sorption isotherms, are approximated by the Langmuir equation, have been obtained, and the values of the maximum sorptive capacities have been calculated. Based on the obtained data, conclusions have been drawn on using the studied natural mineral sorbents to extract the above-mentioned substance from aqueous solutions.