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N S Zefirov

Publications and source records attributed to N S Zefirov.

At least 19 recordsLinked to original sources
PubMed2005

Highly diverse, massive organic data as explored by a composite QSPR strategy: an advanced study of boiling point.

An improved strategy of quantitative structure-property relationship (QSPR) studies of diverse and inhomogeneous organic datasets has been proposed. A molecular connectivity term was successively corrected for different structural features encoded in fragmental descriptors. The so-called solvation index 1chis (a weighted Randic index) was used as a "leading" variable and standardized molecular fragments were employed as "corrective" class-specific variables. Performance of the new approach was illustrated by modelling a dataset of experimental normal boiling points of 833 organic compounds belonging to 20 structural classes. Firstly, separate QSPR models were derived for each class and for eight groups of structurally similar classes. Finally, a general model formed by combining all the classes together was derived (r2=0.957, s=12.9degreesC). The strategy outlined can find application in QSPR analyses of massive, highly diverse databases of organic compounds.

Linear Models↗
PubMed2004

Effect of intramolecular interactions on circular dichroism of ortho-substituted 1-phenethylamines.

The synthesis of ortho-substituted (S)-1-phenethylamines via ortho-lithiation of its N,N-dimethyl derivative followed by reactions with different reagents is described. Circular dichroism spectra of synthesized compounds were measured. It is shown that the observed short-wave Cotton effects greatly depend on the existence of cyclic structure due to possible interactions such as hydrogen bond or electrostatic interaction.

Journal Article↗
PubMed2002

An approach to the interpretation of backpropagation neural network models in QSAR studies.

An approach to the interpretation of backpropagation neural network models for quantitative structure-activity and structure-property relationships (QSAR/QSPR) studies is proposed. The method is based on analyzing the first and second moments of distribution of the values of the first and the second partial derivatives of neural network outputs with respect to inputs calculated at data points. The use of such statistics makes it possible not only to obtain actually the same characteristics as for the case of traditional "interpretable" statistical methods, such as the linear regression analysis, but also to reveal important additional information regarding the non-linear character of QSAR/QSPR relationships. The approach is illustrated by an example of interpreting a backpropagation neural network model for predicting position of the long-wave absorption band of cyane dyes.

Adsorption↗
PubMed2002

A new scheme for electronegativity equalization as a source of electronic descriptors: application to chemical reactivity.

Recently, we have proposed a new unconventional scheme of electronegativity equalization. We assume that atomic electronegativities are equalized in a molecule in the same manner as electrical potentials in the nodes of a closed electrical network, with the molecule being represented by a molecular graph (MG). Computational procedure includes several operations over the matrices associated with MG. The only parameter used is the atomic electronegativity (EN). The method is very fast and easy-to-implement. With the help of the method one can generate a family of electronic descriptors (equalized or "effective" ENs and atomic charges) which are applicable to the treatment of some types of chemical reactivity. Quite good correlations of the descriptors obtained are observed for such thermodynamic and kinetic data as proton affinity and Taft's inductive sigma* constants. The EN equalization scheme suggested can be used as an independent tool for molecular electrostatics modeling, or can be implemented into an integrated QSAR software.

Electricity↗
PubMed2001

The learned symmetry concept in revealing quantitative structure-activity relationships with artificial neural networks.

A method to build QSAR models based on substituent constants for congeneric sets of compounds having several topologically equivalent substituent positions was proposed. The approach is based on the application of artificial neural networks (learning to construct nonlinear structure-activity relationships taking into account necessary symmetry properties of training set structures) to a training set expanded by adding the copies of compounds with the same activity values but with permuted assignment of equivalent substituent positions. The better predictive power of these constructed models, as compared with the performances of neural network models for non-expanded sets was demonstrated for the calcium channel blockers of 1,4-dihydropyridine type and for hallucinogenic phenylalkylamines.

Calcium Channel Blockers↗
PubMed2001

Versatile computerized system for tracking and analysis of water maze tests.

A crucial step in the estimation of properties of compounds in behavioral experiments is the quantification and description of the different effects observed. The goal of the present work was the automation of the Morris water maze test, one of the most popular behavioral methods for the study of animal memory. An original system was developed that provides fast and accurate tracking of animals, storage of the results in the database and video archive and a means of analyzing the results. This computerized version of the Morris water maze test permits the quantification of such vague characteristics of cognitive function as the "directionality" of search of the hidden platform after a standard training series. The suggested parameters made it possible to discriminate cognitive properties of the novel compounds from other behavioral effects affecting escape latency. The effectiveness of this system was demonstrated in two experiments with neurochemically lesioned and drug-treated rats.

Analysis of Variance↗
PubMed2000

Fragmentation of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones under electron ionization.

A series of 3,7-dialkyl-1,5-diphenyl-3,7-diazabicyclo[3.3. 1]nonan-9-ones was prepared, and the details of their fragmentation under electron ionization (EI) were elucidated. The molecular ions of each compound under consideration were quite abundant in their EI spectra. Full-scan spectra exhibited a number of fragment ions which were clearly assigned using MS/MS and accurate mass measurements. The basic fragmentation of 3,7-dialkyl-1,5-diphenylbispidinones was due to the cleavage of C(1)-C(2) bond followed by a hydrogen migration similar to an odd-electron McLafferty rearrangement. Alternatively, the C(1)-C(2) bond cleavage was followed by the elimination of an imine molecule, Alk-N=CH(2). Further fragmentation resulted in ions at m/z 234 and 103, present in the spectra of all the compounds under study. The fragmentation pathways proposed in this paper are based on the substituent shifts, accurate mass measurements and collision-induced dissociation spectra of selected ions. The results of the present work can be useful in selecting the fragment ions suitable for identification and quantitation of bispidinones in biological matrices.

Anesthetics, Local↗
PubMed1990

[Formation of models of the interaction between organophosphate compound structure and their ability to inhibit cholinesterase].

On the basis of a discrete-regression model earlier proposed by the authors, computer modelling of relationships between structure of organophosphorous compounds and their anticholinesterase activity was carried out. Values of kinetic constants of reversible and irreversible inhibition of human erythrocyte acetylcholinesterase and horse serum butyrylcholinesterase by more than 240 phosphoryl and thiophosphoryl compounds (from own and literature data) were used as initial basis. For description of these compounds' structure informational-topological, physico-chemical and donor-acceptor descriptors were used. By means of procedures of discriminant, regression and cluster analysis, the compounds studied were divided into groups according to the structure, and quantitative structure--activity correlations were found in most of the clusters. This study revealed some functional peculiarities of these compounds and allowed for rationalisation of search of effective compounds with anticholinesterase activity.

Acetylcholinesterase↗
PubMedDate not supplied

QSAR for boiling points of "small" sulfides. Are the "high-quality structure-property-activity regressions" the real high quality QSAR models?

Our investigation was motivated by a recent paper concerning "high-quality structure-property-activity regressions" (J. Chem. Inf. Comput. Sci. 2000, 40, 899-905) for boiling points of small sulfides using variable connectivity indices. We performed QSAR study of the same data set using a logically preselected solvation index and obtained a very good one-parameter regression. The structures of the whole possible set of small sulfides (C2-C6) were generated and the statistics were proven by real prediction using an external test set of sulfides. The variants of extended prediction with extrapolated data and QSAR using an expanded training set were also performed, and all these data also revealed the preference of the solvation index. A general problem of descriptive vs predictive QSAR is discussed.

Journal Article↗