Dimethyl selenide complexes with compounds of Group IIIA elements: electron density redistribution and interaction energy partitioning

Molecular structures of dimethyl selenide complexes with AX₃ (A = B, Al, Ga, In; X = H, Me) compounds of Group IIIA elements were calculated by the PBE1PBE/Sapporo-TZ method. A complex approach to study the nature of interactions is proposed, which involves analysis of electron localization/delocalization characteristics and their influence on charge transfer and energy effects of complexation. It is shown that electron sharing is more important for stabilization of the complexes under study than electrostatic interaction between their fragments. It is demonstrated that analysis of local (topological) characteristics of the electron density distribution is insufficient to discover similarity/dissimilarity in the nature of some complexes. The energies of interaction in the complexes under study are mainly composed of the contributions of Se atom as active center of the donor molecule and the entire acceptor molecule. Energy characteristics of local interaction between Se atom and Group IIIA element atom are not representative.     

Estimation of the size of drug-like chemical space based on GDB-17 data

The goal of this paper is to estimate the number of realistic drug-like molecules which could ever be synthesized. Unlike previous studies based on exhaustive enumeration of molecular graphs or on combinatorial enumeration preselected fragments, we used results of constrained graphs enumeration by Reymond to establish a correlation between the number of generated structures (M) and the number of heavy atoms (N): logM = 0.584 × N × logN + 0.356. The number of atoms limiting drug-like chemical space of molecules which follow Lipinsky’s rules (N = 36) has been obtained from the analysis of the PubChem database. This results in M ≈ 10³³ which is in between the numbers estimated by Ertl (10²³) and by Bohacek (10⁶⁰).     

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.     

The synthesis and cytotoxic activity of N-unsubstituted 3-aryl-4-(trifluoromethyl)-4H-spiro[chromeno[3,4-c]pyrrolidine-1,11'-indeno[1,2-b]quinoxalines]

Chemistry of Heterocyclic Compounds - A method for a regio- and stereoselective synthesis of N-unsubstituted...     

Theoretical and experimental study on cyclic 6-methyl-2,3,4-tris(hydroxymethyl)pyridin-5-ol acetonides

Methods for the preparation of three cyclic 2,3,4-tris(hydroxymethyl)-6-methylpyridin-5-ol acetonides have been developed by variation of the reaction conditions. The six-membered acetonide turned out to be thermodynamically more stable than the seven-membered acetonide and bis-acetonide. The experimental data were consistent with the results of quantum-chemical calculations. The structure of the isolated compounds was proved by X-ray analysis.     

Exchange interaction mechanisms in 1,3,5,7-tetramethyl-2,6-diazaadamantane <Emphasis Type="Italic">N,N’</Emphasis>-dioxyl biradical

The exchange interaction parameters were calculated and the spin density distribution over the organic skeleton of the 1,3,5,7-tetramethyl-2,6-diazaadamantane N,N’-dioxyl biradical was studied based on the results of quantum chemical modeling of the biradical structure by the DFT method using various hybrid functionals (UB3LYP, LC-wPBE, UCAM-B3LYP, UHSEH1PBE) with the 6-311++G(2d,2p) basis set and by the UHF method with the same basis set. The characteristics of the direct orbital overlap between the N atoms of the two nitroxide groups were determined. The values of the J constant, obtained using different calculation methods, were found to be similar to each other. It was established that there is ferromagnetic exchange interaction between the radical sites in the system in question, which occurs predominantly according to the spin polarization mechanism in the 2,6-diazaadamantane core, and the various spin density transfer pathways through the C atoms of the organic skeleton were found to be nonequivalent. The direct overlap of the upper singly-occupied МОs with localization on the nitroxide groups led to a noticeable additional contribution of the antiferromagnetic exchange interaction. Despite the latter factor, the total contribution of these two mechanisms (spin polarization and direct through-space exchange) resulted in the triplet ground state in the biradical studied.     

Quantum-chemical investigation of structure and reactivity of pyrazol-5-ones and their thio- and seleno-analogs: X. Solvent effect on the chemical shifts of nuclei in the molecules of 3-methylpyrazol-5-ones and 1-phenyl-3-methylchalcogenepyrazol-5-ones and characteristics of tautomeric equilibrium in these compounds

By quantum-chemical DFT/GIAO method chemical shifts of all nuclei in the NMR spectra of 3-methylpyrazol-5-one and 1-phenyl-3-methylchalcogenopyrazol-5-ones in chloroform and dimethyl sulfoxide were calculated and analyzed using various solvation models. Low sensitivity to solvent of the chemical shfts of ¹³C and ¹H nuclei (except for “acidic” protons) calculated in the framework of various continuum models is revealed. Discrete and discrete-continuum models reflect well deshielding of the active centers of H-complexation and chemical shifts of “acidic” protons of the studied pyrazolones in solutions. Optimization of geometry of pyrazolones in solutions only slightly improves the agreement between the theoretically calculated and the experimental values. Shielding of nitrogen, oxygen, sulfur, and selenium atoms is more sensitive to the nature of solvent and to the nature of tautomeric forms. The methods of NMR spectroscopy allow to identify reliably the dominating tautomeric form but they are insufficient for the quantitative characterization of tautomeric equilibria.     

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 &gt;...     

Quantum chemical calculation of exchange interactions in supramolecularly arranged N,N′‐dioxy‐2,6‐diazaadamantane organic biradical

Quantum mechanical exchange effects in purely organic N,N′‐dioxy‐2,6‐diazaadamantane biradical derivatives with promesogenic substituents have been studied. To determine intermolecular exchange energies, packing conditions of the radical core units in layered liquid crystalline phases are simulated using the Gaussian 09 program. The broken symmetry approach gives J ≈ 7 cm^?1 for intramolecular ferromagnetic exchange interactions between nitroxyl radical centers in one molecule. Both ferromagnetic and antiferromagnetic intermolecular interactions are possible in this kind of systems according to the obtained calculation results. Depending on the mutual positioning and orientation of molecules, the intermolecular antiferromagnetic exchange constant can reach a value of ?50 cm^?1, and the intermolecular ferromagnetic constant a value of 10 cm^?1. The simultaneous presence of intramolecular and intermolecular exchange between spin‐carrying centers in this kind of supramolecularly ordered multispin systems is favorable for the formation of magnetically interacting chains and two‐dimensional networks. © 2016 Wiley Periodicals, Inc.