USE OF MOMENT OF INERTIA IN COMPARATIVE MOLECULAR-FIELD ANALYSIS TO MODEL CHROMATOGRAPHIC RETENTION OF NONPOLAR SOLUTES

A quantitative structure-retention relationship (QSRR) was developed f rom chromatographic data on 31 unsubstituted 3-6-ring polycyclic aroma tic hydrocarbons (PAHs) using the 3D-QSAR method known as comparative molecular held analysis (CoMFA). The resulting CoMFA model gave an exc ellent correlation to high-performance liquid chromatography retention data for these PAHs yielding r(2) values of 0.947 (conventional) and 0.865 (cross-validated). The steric and electrostatic contributions to the CoMFA model were 100% and 0%, respectively. A unique feature of t his study was the use of moment of inertia, I, as a basis for CoMFA al ignment of the PAH molecules. The moment of inertia also provided an a lternative method for calculating the solute length-to-breadth ratio ( L/B), which has been applied in previous QSRR studies as a molecular d escriptor for PAH retention. By virtue of its mathematical simplicity and lack of ambiguity, the present derivation of L/B from I offers sev eral advantages over other geometry-based schemes. Finally, I-x was ev aluated for use as a molecular descriptor in QSRR regression analysis to predict the log of the retention index (log I) for these PAHs. The correlation with PAH retention was weak when the moment of inertia was considered alone but improved dramatically (r(2) = 0.928) when the mo ment of inertia and connectivity index chi were used in combination as descriptors.