The First Example of Positive Allosterism in an Aqueous Saccharide-Binding System Designed on a Ce(IV) Bis(porphyrinate) Double Decker Scaffold

The first example of a positive, homotropic system in aqueous saccharide-binding has been achieved using a Ce(IV) bis(porphyrinate) double decker scaffold bearing two pairs of boronic acid groups (compound 2). In this system, the binding of the first guest (1:2 saccharide/boronic acid complex) suppresses the rotational freedom of the two porphyrin planes, which facilitates the binding of the second guest. As a result, two pairs of boronic acid groups in 2 can autoacceleratively bind these guests and yield CD-active species. The analyses of CD intensity–guest concentration plots according to the Hill equation resulted in K=3.7×104 M−2 and n=2.0 for d-fructose and K=9.6×105 M−2 and n=1.6 for d-glucose. The present system which is in action even in aqueous media is widely applicable to allosteric control of drug release, catalytic reaction, information transduction, etc. of saccharide-containing guest molecules.