THE DETERMINATION OF SOLVATION DESCRIPTORS FOR TERPENES, AND THE PREDICTION OF NASAL PUNGENCY THRESHOLDS

We have previously put forward two solvation equations for the correla tion of chemical and biochemical phenomena, including nasal pungency t hresholds (NPT) in man. In order to make use of these equations, a num ber of descriptors need to be assigned to any given solute, viz. pi(2) (H) the dipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2) (H) the overall hydrogen-bond acidity and basicity, and log L-16 where L-16 is the solute gas;hexadecane partition coefficient. We show that these descriptors can be obtained from data from a number of processe s, including gas-liquid chromatography, high performance liquid chroma tography, gas-water partitions, gas-solvent partitions and water-solve nt partitions. In this way, the above descriptors have been obtained f or eleven terpenes, including hydrocarbons, aldehydes, ketones, alcoho ls and an ether. The pi(2)(H), Sigma alpha(2)(H) and log L-16 descript ors have also been obtained for a further 21 terpenes, but Sigma beta 2(H) now has to be estimated. Through our previously reported equation , we have predicted NPT values for the total 32 terpenes. Small hydroc arbons such as alpha-pinene are predicted to have large NPT values, bu t aldehydes (cg. geranial) and ketones (e.g. camphor) are predicted to have moderate values, and alcohols (cg. menthol and borneol) and thei r acetates are predicted to have very small NPT values.