A number of unanswered questions occurred to us upon reading a communication by Yam and Kai (ref. ) which had reported optical sensing properties of a boronic-acid-appended ReI 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.
在阅读Yam和Kai(参考文献)关于附有
硼酸的ReI配合物在
糖类光学传感特性的报道时,我们产生了若干未解之谜。仔细重新检查发现,他们提出的pKa值(5.9)是不正确的,并且在pH高于pKa与pH低于pKa时,糖结合模式完全不同。仅在pH低于pKa时观察到吸收光谱变化,这反映了由
糖类配位引起的sp2到sp3
硼杂化变化;而仅在pH高于pKa时观察到CD谱带,这反映了1:1环状配合物的形成。这些结果意味着,在精确光学传感
糖类时,应仔细选择最佳pH。