摘要:

The characterization of molecular structure using structural invariants has increased greatly over the last ten years. Specifically, topological indices have become more widely used in the quantification of molecular structure for use in quantitative structure-activity relationship studies, chemical documentation, and molecular similarity studies. The basis, calculation, and utility of topological indices has been examined, with an eye to the specific advantages and problems in their use. In addition, variable clustering and principal component analysis are examinee as two potential solutions to the problem of index intercorrelation.

ISSN:1062-936X    

DOI:10.1080/10629369708039122

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The development of molecular complexity measures is reviewed. Two novel sets of indices termedtopological complexitiesare introduced proceeding from the idea that topological complexity increases with theoverall connectivityof the molecular graph. The latter is assessed as the connectivity ofallconnected subgraphs in the molecular graph, including the graph itself. First-order, second-order, third-order, etc., topological complexitiesiTCare defined as the sum of the vertex degrees in the connected subgraphs with one, two, three, etc., edges, respectively. Zero-order complexity is also specified for the simplest subgraphs–the graph vertices. The overall topological complexityTCis then defined as the sum of the complexities of all orders. These new indices mirror the increase in complexity with the increase in the number of atoms and, at a constant number of atoms, with the increase in molecular branching and cyclicity. Topological complexities compare favorably to molecular connectivities of Kier and Hall, as demonstrated in detail for the classical QSPR test-the boiling points of alkanes. Related to the wide application of molecular connectivities to QSAR studies, a similar importance of the new indices is anticipated.

ISSN:1062-936X    

DOI:10.1080/10629369708039123

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An efficient algorithm for deriving QSPR/QSAR models with nonorthogonal and ordered orthogonal descriptors, based on orthogonalization of topological indices, is presented. It is applied to structure-boiling point modeling of nonanes as the test case. The selection of the best descriptors from multivariate linear regression modeling is carried out using descriptors which are first orthogonalized. It is shown that such an algorithm is applicable for the selection of the best descriptors in a multivariate linear regression model even to very large sets of descriptors. A computationally-effective method for the (ordered) orthogonalization of topological indices is also introduced. By the use of an ordered orthogonalization procedure it is possible to select the best order of descriptors for orthogonalization. The orthogonalization in the selected order of descriptors produces models with a smaller number of significant descriptors. The comparison between QSPR/QSAR models with nonorthogonal and ordered orthogonal topological indices favors the latter models. It is also shown that the enlarging of the basis set results in better QSPR/QSAR models, but it is not possible to know in advance whether it is better to use a nonlinear transformation of the smaller basis or to compute additional descriptors.

ISSN:1062-936X    

DOI:10.1080/10629369708039124

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A number of recently graph matrices encoding in various ways the topological information is presented. Four graph operators are used to compute 19 topological indices for a set of 306 alkanes. The intercorrelation coefficients of the 19 topological indices are computed and used to identify highly intercorrelated indices.

ISSN:1062-936X    

DOI:10.1080/10629369708039125

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

WHIM descriptors are 3-dimensional molecular indices that represent different sources of chemical information. WHIM descriptors contain information about the whole 3D-molecular structure in terms of size, shape, symmetry and atom distribution. These indices are calculated from (x, y, z)-coordinates of a molecule within different weighting schemes in a straightforward manner and represent a very general approach to describe molecules in a unitary conceptual framework. A set of 40 simple heterogeneous compounds is used to show the main characteristics, some properties and the modelling power of WHIM descriptors by using simple scatter plots of the descriptors. These descriptors have been used to search for quantitative structure-activity and structure-property relationships for several classes of environmental relevant compounds. Comparisons with other sets of descriptors have also been performed.

ISSN:1062-936X    

DOI:10.1080/10629369708039126

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Four classes of theoretical structural parameters, viz., topostructural, topochemical, geometrical and quantum chemical descriptors, have been used in the development of quantitative structure-activity relationship (QSAR) models for a set of sixty-nine benzene derivatives. None of the individual classes of parameters was very effective in predicting toxicity. A hierarchical approach was followed in using a combination of the four classes of indices in QSAR model development. The reslults show that the hierarchical QSAR approach using the algorithmically derived molecular descriptors can estimate the LC50values of the benzene derivatives reasonably well.

ISSN:1062-936X    

DOI:10.1080/10629369708039127

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Quantitative Structure-Activity Relationships (QSAR) studies are powerful tools to rationalize complex systems where physico-chemical properties and biological activities of compounds of environmental and toxicological interest are involved. In these fields, due to costs, time, and difficulties in obtaining experimental measures, one of the main objectives is to fill the need for general predictive models. The challenge is to describe and represent, on a quantitative basis, all the molecular structural features in order to use them as descriptors in quantitative structure-activity models.

ISSN:1062-936X    

DOI:10.1080/10629369708039128

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A backpropagation neural network model, implemented in AUTOLOGP (Version 4.0), was developed for estimating then-octanol/water partition coefficient of organic molecules from their structure described by means of a modified autocorrelation method. The advantages of the autocorrelation method, which allows the description of any kind of molecules by means of computerized molecular descriptors presenting a physicochemical meaning, were emphasized through the simulation performances obtained with AUTOLOGP (Version 4.0) and from a comparative study involving two regression models derived from various topological indices.

ISSN:1062-936X    

DOI:10.1080/10629369708039129

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In environmental and ecotoxicological problems, the need for more general predictive models is one of the aims of the science. To reach this objective, the models, even if capable of producing more approximate values, must be applicable to the huge number of chemicals put on the market that are discharged in the environment, at least for setting priority lists among potentially hazardous substances.

ISSN:1062-936X    

DOI:10.1080/10629369708039130

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The values of logP(n-octanol/water partition coefficient) for 1449 chemicals were calculated from the fragmental/regression model of Klopman and co-workers (J. Chem. Inf. Comput. Sci.1994, 34, 752-781) and from the autocorrelation/backpropagation neural network model implemented in AUTOLOGPTM(Version 4.0). Both models provided good simulation results but the superiority of the latter was demonstrated.

ISSN:1062-936X    

DOI:10.1080/10629369708039131

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor