Title

Breaking Aggregation and Driving the Keto-to-gem-Diol Equilibrium of the N,N'-Dimethyl-2,6-diaza-9,10-anthraquinonediium Dication to the Keto Form by Intercalation in Cucurbit[7]uril

Abstract

1H NMR, ESI-MS, and DFT calculations with the M062X/6-31G* method show that, in water, the bistetrafluoroborate salt of N,N'-dimethyl-2,6-diaza-9,10-anthraquinonediium dication (DAAQ·2BF4-) exists in equilibrium with both its gem-diol and several aggregates (from dimers to at least octamers). with high concentrations of HCl (e.g., 1.2–1.5 M), all aggregates break up and the keto-to-gem-diol equilibrium is shifted quantitatively toward the quinone form. the same effect is observed with 1.5 mol equiv of cucurbit[7]uril, CB[7], with which all equilibria are shifted toward the quinone form, which undergoes slow exchange with the CB[7] cavity as both the free and the CB[7]-intercalated quinone (DAAQ@CB[7]) are observed simultaneously by 1H NMR. the affinity of DAAQ for the CB[7] cavity (Keq = 4 × 106 M–1) is in the range found for tricyclic dyes (0.4–5.4 × 106 M–1), and among the highest observed to date. a computational comparative study of the corresponding CB[7] complex of the N,N'-dimethyl-4,4'-bipyridinium dication (N,N'-dimethyl viologen, MeV) suggests that the higher binding constant for intercalation of DAAQ may be partially attributed to a lesser distortion of CB[7] (required to maximize favorable nonbonding interactions) as a result of the flat geometry of DAAQ.

Department(s)

Chemistry

International Standard Serial Number (ISSN)

223263

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2013 American Chemical Society (ACS), All rights reserved.


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