The flexible host molecule 1 displays induced-fitting behavior due to atropisomeric interconversion upon binding to guest molecules, especially ubiquinone derivatives, such as 2,3,5,6-tetramethoxy-p-benzoquinone. In the presence of the quinone, the proportion of the best-fitting αααα-isomer increases from 11 % to 78% through the formation of multiple hydrogen bonds. This dynamic process can be fully accounted for by two parameters: a rate constant of internal rotation about the C(porphyrin)–C(aryl) bonds and the association constants between the individual atropisomers and the quinone.
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Hayashi et al. (1998) studied this question.