Two chiral salen-Co(II) complexes, (R)-7 and (R)-8 bearing two boronic acid groups were synthesized. The saccharide-binding event was conveniently monitored by a spectral change in UV-vis absorption spectroscopy arising from saccharide-boronic acids complexation. Since the distance between the two boronic acid groups is shorter than other diboronic acid-based receptors, the saccharide selectivity is quite different from other systems: the largest association constant was observed for fructose and the next for talose. In addition, chiral recognition was achieved for certain saccharides: the largest discrimination was 2.1 observed for (R)-7 with D/L-allose. These results indicate that the salen-metal complexes provide an excellent basic skeleton for designing the chiral sugar sensing systems.
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