Chemometrics in QSAR

Quantitative Structure-Activity Relationships (QSARs) and Quantitative Structure-Property Relationships (QSPRs) are scientific fields in which the use of chemometric methods is of outstanding importance. Indeed, chemometric methods, as well as statistics and chemoinformatics, are the basic tools for finding mathematical meaningful relationships between the molecular structure and biological activities, physicochemical, toxicological, and environmental properties of chemicals.Three main topics are involved in the QSAR/QSPR approach to the scientific research: the concept of molecular structure, the definition of molecular descriptors, and the chemometric tools.After a short historical presentation, QSAR modeling approaches, both those based on the classical chemometric methods and those defined by some peculiar strategies, are presented. Then, after an introduction to molecular descriptors, some basic modeling methodologies based on the variable descriptor selection are described. Finally, the general principles for QSAR/QSPR analysis are reported, paying special attention to the concept of applicability domain (AD) and model validation. These principles have been recently received from the Organization for Economic Co-operation and Development (OECD) as the principles for accepting QSAR models for regulatory purposes and adopted as guidelines for the new European Community Regulation on Chemicals (Registration, Evaluation and Authorisation of Chemicals (REACH))