An analysis of the antibacterial activities of 15 terpenoids, eleven of which werepreviously described by us and four were extracted from the literature, suggested twostructural requirements for activity of these and related compounds: a hydrophobic moiety,consisting of a substituted decalin skeleton, and a hydrophilic region possessing onehydrogen-bond-donor group. These structural requirements are responsible for an optimalinsertion of these and related compounds into cell membranes, as suggested by the resultsof docking some of these compounds into a model phospholipid bilayer.

The solvatochromic shifts of the two isomeric title betaines 4 and 5, built up from the unsubstituted pyridinio acceptor and phenoxide donor fragments, were recorded in twelve solvents and the data compared with results from semi-empirical (AM1) and ab initio (HF/6-311G and B3LYP/6-311G) calculations.