Factors Affecting the Formation of 2:1 Host:Guest Inclusion Complexes of 2-[(R-Phenyl)amine]-1,4-naphthalenediones (PAN) in ß- and γ-Cyclodextrins.

ABSTRACT

The molecular hosts cyclodextrins form inclusion complexes with a wide variety of guests, resulting in complexes with various hostguest stoichiometries. In the case of a series of 19 1,4-naphthoquinolines as guests with either ß- or γ-cyclodextrin studied using electrospray mass spectroscopy, in most cases only 11 complexes were observed, with 21 hostguest complexes observed in just 6 out of 38 hostguest combinations. It is shown that these higher-order complexes were observed only in the case of small (or no) electronically withdrawing substituents, and were much less likely in the case of the larger γ-cyclodextrin host. The size and electronic properties of the substituents involved shows that both steric and electronic factors must be taken into account in predicting which cyclodextrin hostguest stoichiometries will be stable enough to form (or once formed, be robust enough to be observed in the ESI-MS experiments). It is clear that the prediction of host-guest stoichiometry for a specific host-guest pair is complicated, and involves a subtle interplay of both electronic and steric factors. However, there are definite trends, which can be used to help predict hostguest stoichiometry for a given host-guest pair.