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 (2M(2+)). 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 2M(2+) the saccharide-binding process is detectable visually through the colour change. The saccharide-induced fluorescence changes are very large because 1 and 2M(2+) aggregates are almost non-fluorescent whereas monomeric 1 and 2M(2+) generated by saccharide-binding are strongly fluorescent. This is a novel method for sugar sensing, useful in an aqueous system.