Dependence of the Elastic Properties of H5-Chondrites (NWA 12370) on Pressure

Doklady Physics - The mechanical properties of NWA 12370 chondrite, petrological type H5, depending on the external hydrostatic pressure were studied using ultrasonic waves. This meteorite is a...     

Quantum-chemical parameters of 2-substituted 5-nitrofuran derivatives

Quantum-chemical parameters of molecules of 2-substituted 5-nitrofuran derivatives were calculated using the GAMESS software package and their correlation with the antibacterial activity of the compounds was analyzed. Regression analysis technique was employed to find linear relationships between the logarithm of the average inhibiting concentration of 5-nitrofuran derivatives and the quantum-chemical parameters. The largest correlation coefficient (0.932) was found for the dependence of the antibacterial activity on the amount of charge on the nitrogen atom of the nitro group. The results obtained are in agreement with modern concepts about the nature of the antibacterial activity of 2-substituted 5-nitrofuran derivatives.     

Structure–reactivity relationship in Diels–Alder reactions obtained using the condensed reaction graph approach

By the structural representation of a chemical reaction in the form of a condensed graph a model allowing the prediction of rate constants (logk) of Diels–Alder reactions performed in different solvents and at different temperatures is constructed for the first time. The model demonstrates good agreement between the predicted and experimental logk values: the mean squared error is less than 0.75 log units. Erroneous predictions correspond to reactions in which reagents contain rarely occurring structural fragments. The model is available for users at https://cimm.kpfu.ru/predictor/.     

Effect of copper(I) on the conformation of the thiacalixarene platform in azide-alkyne cycloaddition

New lower-rim tetrasubstituted p-tert-butylthiacalix[4]arene derivatives bearing alkyl, propargyl, or triazole-containing substituents were synthesized. The structures of these compounds were determined by 1D and 2D NMR spectroscopy in solution and by X-ray diffraction in the solid phase. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) of azides to a mixture of 1,3-alternate–partial cone stereoisomers of dipropargyl derivatives of thiacalix[4]arene affords triazole-containing products exclusively in the 1,3-alternate conformation.     

Structure–reactivity relationship in bimolecular elimination reactions based on the condensed graph of a reaction

By means of a structural representation of the chemical reactivity as a condensed graph a model predicting rate constants of the bimolecular elimination reaction is derived for the first time. The model developed enables the prediction of rate constants of reactions proceeding in different solvents or water-organic mixtures at different temperatures. It demonstrates a good predictive performance: a mean square deviation of predicted values from experimental ones is less than 0.7 logarithmic units. An outlier analysis shows that prediction errors are mainly due to the imperfection of the training data containing unique reactions. The model is available for users at arsole.u-strasbg.fr.     

Structure of 16-hydroxyisosteviol-derived dicarboxylic acid esters

Dielcometry, method of dipole moments, IR spectroscopy, and computer simulation were used to show that dicarboxylic acid esters derived from 16-hydroxyisosteviol (ent-16-hydroxybeyeran-19-oic acid) exist in CCl₄ solutions as tweezer-like or open-chain structures, or dimers with various steric structures, depending on the degree of dilution. Concentrations at which both the esters and parent dicarboxylic acids undergo structural rearrangement were established. The structure of three esters was confirmed by X-ray diffraction.     

Azocalix[4]arene-Rhodamine Supramolecular Hypoxia-Sensitive Systems: A Search for the Best Calixarene Hosts and Rhodamine Guests

A potential hypoxia-sensitive system host-guest complex of three calixarenes (including two with four anionic carboxyl and sulphonate azo fragments on the upper rim and a newly synthesized bis-azo adduct of calixarene in the cone configuration with azo fragments on the lower rim with the most widespread cationic and zwitterionic rhodamine dyes (123, 6G and B)) was studied using UV-VIS spectrometry and fluorescence as well as 1D and 2D NMR techniques. It was found that all three calixarenes form a complex with rhodamine dyes with a 1:1 composition. The association constants of calixarene-dye complexes with sulfonate calixarenes, especially in the case of tetra-anionic calixarene, turned out to be higher compared with carboxyl calixarene due to the more intense electrostatic interactions. For the first time using an HRESI MS technique, it was shown that the treatment of rhodamine 6G and 123 with sodium dithionite (SDT) produces a non-fluorescent leuco form of the dye, and only rhodamine B can be used with SDT without the occurrence of a side reduction. Moreover, it was identified that in addition to the reduction in the azo groups, SDT causes partial cleavage of the aryl ether bonds. The found features of SDT should be taken into account when SDT is used as an azoreductase mimic.     

Using semantic analysis of texts for the identification of drugs with similar therapeutic effects

Russian Chemical Bulletin - Semantic analysis of text collections was used to identify drugs with similar therapeutic activity. Natural language processing methods were applied to analyse >...