A number of unanswered questions occurred to us upon reading a communication by Yam and Kai (ref. 16) which had reported optical sensing properties of a boronic-acid-appended Re1 complex for saccharides. Careful re-examination has disclosed that the pKa-value proposed by them (5.9) is wrong and that the saccharide-binding mode at pH above the pKa is totally different from that at pH below the pKa. The absorption spectral change, which reflects an sp2-to-sp3 boron hybridisation change induced by the saccharide complexation, was observed only at pH below the pKa, and the CD band, which reflects the formation of 1:1 cyclic complexes, appeared only at pH above the pKa. The results imply that the optimum pH should be carefully selected for the precise optical sensing of saccharides.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Perkin Transactions 1|
|Publication status||Published - Jan 1 2000|
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