SUGAR SENSING UTILIZING AGGREGATION PROPERTIES OF BORONIC-ACID-APPENDED PORPHYRINS AND METALLOPORPHYRINS

It has been shown that saccharides in water can be sensitively detecte d by a boronic-acid-appended porphyrin (1) and its metal complexes (2M (2+)). The idea is based on the phenomenon that absorption and fluores cence spectra of porphyrins change sensitively in response to a shift in the aggregation-deaggregation equilibrium and that the self-associa tion of saccharides with boronic acids in water affects this equilibri um. Among four monosaccharides tested in detail, the spectral change o ccurs in the order D-fructose > D-arabinose > D-mannose > D-glucose. I n 2M(2+) the saccharide-binding process is detectable visually through the colour change. The saccharide-induced fluorescence changes are ve ry large because 1 and 2M(2+) aggregates are almost non-fluorescent wh ereas monomeric 1 and 2M(2+) generated by saccharide-binding are stron gly fluorescent. This is a novel method for sugar sensing, useful in a n aqueous system.