A Novel Sugar Sensing System Designed with a Cooperative Action of a Boronic-Acid-Appended Zinc Porphyrin and a 3-Pyridylboronic Acid Axial Ligand

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Abstract
The cooperative action of two boronic acids is indispensable to the selective binding of saccharides in aqueous solution and the binding process can be spectrophotometrically monitored by using porphyrins as a chromophoric probe. It is not so easy, however, to synthesize porphyrins that satisfy these prerequisites, i.e., porphyrins bearing two appropriately-arranged boronic acid groups within a molecule. In this paper, we report that such a diboronic-acid-based porphyrin receptor can be easily designed by utilizing the self-assembling nature of a Zn(II) porphyrin and an axial ligand: That is, a mixture of boronic-acid-appended Zn(II) porphyrin (1-Zn) and 3-pyridylboronic acid (2) self-organizes to create a novel diboronic acid system for saccharide (S) recognition. Thus, the 1-Zn·2·S ternary complexes give the CD spectral pattern inherent to saccharide absolute configuration. The present study is a new example for sugar sensing using a boronic acid-porphyrin self-assembly system.