Interaction between cucurbituril and viologen derivatives
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The interaction between cucurbituril (Q) and a series of symmetric viologen derivatives having aliphatic substituents of variable length [N,N′-dialkyl-4,4′-bipyridinium dianions; alkyl = CH3(CH2) n –, n = 0 (MV2+), 1 (EV2+), 2 (PV2+), 3 (BV2+), 4 (FV2+), 5 (HV2+) or 6 (SV2+); BPY2+ = diprotonated 4,4-bipyridine], determined by 1H NMR and electronic absorption spectroscopy methods, is described. Some different binding models were observed in this work when compared to the interactions between cucurbituril (Q) and these guests. The experimental results revealed that the binding site of the guests by Q depended strongly on the length of the aliphatic substituents on the 4,4′-bipyridinium nucleus. While a 1:2 complex was observed for Q-BPY2+ under acidic conditions, a 1:1 complex was formed for Q-viologen derivatives with chains shorter than four carbon atoms. However, multiple Q molecules could be threaded on the longer-chain FV2+, HV2+ or SV2+ molecules to form 2:1 and even possibly 3:1 complexes.
KeywordsCucurbituril Viologen derivatives Binding models 1H NMR spectroscopy Electronic absorption spectroscopy
Support of the National Natural Science Foundation of China (NSFC; No. 20662003), the International Collaborative Project Fund of the Chinese Ministry of Science and Technology (Grant No. 2003DF000030), the “Chun-Hui” Fund and the America and Pacific Region Research Collaboration Fund of the Chinese Ministry of Education, the Science and Technology Fund of Guizhou Province (Grant No. J-2005-2012) and the Governor Foundation of Guizhou Province, P.R. China, are gratefully acknowledged.
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