ULTRAVIOLET-ABSORPTION CHARACTERISTICS AND CALCULATED SEMIEMPIRICAL PARAMETERS AS CHEMICAL DESCRIPTORS IN MULTIVARIATE MODELING OF POLYCHLORINATED-BIPHENYLS

The structural variation within the polychlorinated biphenyls (PCBs) w as characterized by using principal component analysis (PCA). A multiv ariate model was evolved from 52 physicochemical descriptors including measured ultraviolet (UV) absorption spectra, calculated semiempirica l parameters (AM1) and properties captured from the literature. Parame ters calculated by using the AM1-Hamiltonian were e.g. heat of formati on, dipole moments, ionization potential and the barrier of internal r otation. The UV spectra were measured and digitized in the range 200-3 00 nm. The multivariate model revealed that most of the information wi thin the set of physicochemical parameters was related to molecular si ze. Descriptors depending on size were e.g. GC retention times, partit ion coefficients and a subset of semiempirically derived energy terms. Important also were parameters reflecting differences in substitution patterns and related to electronic and steric properties, such as UV absorption in the wavelength region 245-300 nm, the barrier of interna l rotation and the ionization potential. The developed model describes the large variation in physicochemical characteristics within the PCB s. The importance of a broad chemical characterization is illustrated by a quantitative structure-activity relationship (QSAR) for the poten cy of inhibition of intercellular communication for 27 structurally di verse tetra- to heptachlorinated PCBs.