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

• Published in: Molecules (Basel, Switzerland) Switzerland), 2016-11, Vol.21 (11), p.1568-1568
• Main Authors: Jankowski, Christopher K, Lamouroux, Christine, Jiménez-Estrada, Manuel, Arseneau, Sebastien, Wagner, Brian D
• Format: Article
• Language: English
• Subjects: beta-Cyclodextrins - chemistry; cyclodextrin inclusion complexes; cyclodextrins; ESI-MS; gamma-Cyclodextrins - chemistry; host-guest inclusion; host-guest stoichiometry; Models, Molecular; molecular modeling; Molecular Structure; Naphthoquinones - chemistry; Spectrometry, Mass, Electrospray Ionization - methods
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules21111568

The molecular hosts cyclodextrins form inclusion complexes with a wide variety of guests, resulting in complexes with various host:guest stoichiometries. In the case of a series of 19 1,4-naphthoquinolines as guests with either β- or γ-cyclodextrin studied using electrospray mass spectroscopy, in most cases only 1:1 complexes were observed, with 2:1 host:guest complexes observed in just 6 out of 38 host:guest 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 host:guest 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 host:guest stoichiometry for a given host-guest pair.