Sugar sensing utilizing aggregation properties of boronic-acid-appended porphyrins and metalloporphyrins

It has been shown that saccharides in water can be sensitively detected by a boronic-acid-appended porphyrin (1) and its metal complexes (2M2+). The idea is based on the phenomenon that absorption and fluorescence spectra of porphyrins change sensitively in response to a shift in the aggregation–deaggregation equilibrium and that the self-association of saccharides with boronic acids in water affects this equilibrium. Among four monosaccharides tested in detail, the spectral change occurs in the order D-fructose > D-arabinose > D-mannose > D-glucose. In 2M2+ the saccharide-binding process is detectable visually through the colour change. The saccharide-induced fluorescence changes are very large because 1 and 2M2+ aggregates are almost non-fluorescent whereas monomeric 1 and 2M2+ generated by saccharide-binding are strongly fluorescent. This is a novel method for sugar sensing, useful in an aqueous system.