ABSTRACT
Universidad Central de Las Villas, Santa Clara 54830, Villa Clara, Cuba
'That is not a regular rule, you invented it just now.' I t ’s the oldest rule in the book; said the K ing/ ‘Then it ought to be Number One; said Alice/
Lewis Carroll
INTRODUCTION
One of the main distinctive characteristics of modern chemistry is the use of theoretical tools for the molecular modeling of physicochemical processes, chemical reactions, medicinal and toxicological events, etc., in which chemicals are involved [1-8]. The success of the molecular modeling is judged by the insights that it offers on the nature of the processes studied, which permit a better comprehension and a rational modification of them. These properties, measured experimentally, are almost invariably expressed in quantitative terms, think for instance of boiling point, refraction index, transition state energy, percentage of inhibition of some enzymatic activity, lethal dose, and so forth. The paradigm for the modeling of such properties is the relationship that exists between them and the molecular structure of chemicals. This fact presupposes the first challenge for the molecular modeling: the properties are expressed as
numbers while the molecular structure is not [9-11]. The way to solve this problem is by using molecular descriptors, that are numbers representing information about different molecular features, to describe quantitatively the properties under study [12-14]. These models are known as quantitative structure-property (QSPR) and quantitative structureactivity relationships (QSAR), depending on the physicochemical or biological nature of the properties studied, respectively [15, 16].
