The interaction of DL-2,3-diaminopropionic acid and its methyl ester with metal ions. Part I. Formation constants

Abstract

Thermodynamic proton ionisation constants, pK_a^T, of the amino-groups of DL-2,3-diaminopropionic acid (DL-dap) and its methyl ester (DL-dapMe) have been determined by potentiometric titration at 25, 37, and 50 °C, and l= 0·1M. Formation constants for the following complexes [where E is the unprotonated form of DL-dapMe, A^– and AH are respectively the anionic and zwitterionic (protonated β-NH₂ group) forms of DL-dap] have been measured at 25 °C and l= 0·1M; CuE₂²⁺, CuE²⁺, CuEA⁺, CuE(AH)⁺, HgE₂²⁺, HgE²⁺. For CuE₂²⁺ and CuE²⁺, formation constants have been also been determined at 37 and 50 °C and the resulting thermodynamic parameters are discussed.

In addition, formation constants have been determined at 25 °C and l= 0·1M for the following complexes of DL-dap; MA₂, MA⁺, M(AH)²⁺, and MA(AH)⁺[M = copper(II), nickel(II), and mercury(II)]. Species M(AH)₂²⁺ and NiA(AH)⁺ were shown to be umimportant.