Basicity and metal ion binding capability of amine-carboxyboranes, R3N·BH2COOH, boron analogs of glycine and N-methylated glycines

Ionization of the carboxylic acid proton from net zero charged amine-carboxyboranes, where amine = NH3, CH3NH2, (CH3)2NH, and (CH3)3N, occurs with pKa values of 8.33, 8.23, 8.14, and 8.38, respectively, at 0.5 M ionic strength and 21 °C. There is no evidence for amine nitrogen deprotonation in the first three compounds at pH < 11. In contrast to glycine and its mono- and di-N-methylated derivatives, the boron analogs do not chelate Zn²⁺ or Cu²⁺. Up to pH 11, both metal ions coordinate to the four amine-carboxyboranes only through the carboxylate group. For the binding of Zn²⁺, the respective stability constants logarithms are : 2.47, 2.43, 2.32, and 2.67. © 1982.

Duke Scholars

Author Andrew T. McPhail Chemistry