Thermodynamic and physico-chemical descriptors of chloronaphthalenes: An attempt to select features explaining environmental behaviour and specific toxic effects of these compounds

35 physico-chemical descriptors were used to characterize all 75 congeners of chloronaphthalene in terms of their environmental stability and specific dioxin-like toxicity. A prepared basic thermodynamic and physico-chemical property data matrix of PCNs was interpreted using Principal Component Anal ysis (PCA). The PCA of the thermodynamic and physico-chemical data matrix c reated a four-dimensional model that explained 76% (58% + 9% + 5% + 4%) of the total variance. The loading plot shows that the first PC is influenced by variables describing degree of chlorination, molecular weight, polarizab ility and lipophilicity. The best positively correlated descriptors are: re tention time, standard molar entropy, heat capacity, a first-order molecula r connectivity index, logarithm of octanol-water partition coefficient, the Wiener Index, specific polarizability, a third order shape index for molec ules, the sum of absolute of the charges on each atom of the molecule, mole cular weight, polarizability, refractivity, solvent-accessible surface, van der Waals surface, solvent-accessible volume, van der Waals volume. Negati vely correlated descriptors are: standard enthalpy of formation and energy of HOMO. The second PC is strongly influenced by energy of LUMO, while subs titution pattern parameters, number of chlorine atoms at a-positions and vi cinal (adjacent) carbon atoms substitution pattern are less important param eters. The third PC depends on dipole moment and the largest negative charg e, and on substitution at position 2 of naphthalene nuclei, while the symme try group parameter is determined by PC4. There are small groups consisting of compounds which have similar values of LUMO energy and substitution pat tern. The congeners of CN substituted with chlorine at positions 1, 2, 3, 6 and 7 (Fv/Fv PCN congeners), and next those substituted at positions 1, 2, 3 and 6 or 7 (Fr/Fv PCB congeners) are considered to be most potent in ter ms of dioxin-like toxicity, and followed by those substituted at four posit ions (Fr[Fv), at three positions (Tr/Fv) and so on. The thermodynamic stabi lity of the congeners of CN depends on the number of attached chlorine and structure of the molecule. Among the 75 congeners of CN only a few, like PC N nos. 42, 52/60, 61, 66/67, are relatively resistant to biodegradation and biomagnify in animals occupying a higher position in the marine food web, and with a particular homologue group they are characterised by the lowest absolute values of energy of LUMO.