Preparation and study of amino acid ( DL-leucine, L-isoleucine, L-histidine) Schiff bases with ethyl-α-ketocyclopentylcarboxylate and the corresponding copper( II) complexes

Abstract

Amino acid Schiff bases with ester function K(Rleu)·2H 2O ( 1), K(Rile)·2H 2O ( 2), K(Rhis)·H 2O ( 3) (Rleu, Rile and Rhis represent the Schiff base of DL-leucine, L-isoleucine and L-histidine, and ethyl-α-ketocyclopentylcarboxylate) were synthesized. Compounds 1, 2 and 3 were characterized by 1H NMR spectroscopy. The copper(II) complexes, Cu(Rleu′)·H 2O ( 4), Cu[Rile′]·H 2O ( 5) andCu(Rhis′)·2H 2O ( 6), were obtained with the N-deprotonated Schiff bases (Rleu′, Rile′ and Rhis′). The COO stretching bands in their IR spectra suggest that the carboxylate acts as a monodentate group when binding with copper. The temperature dependence of the susceptibility for 6 may be fit to the Curie-Weiss expression χ=O.32/(T-26.2) emu mol −1 K −1 The dehydration process of 6 leads to the anhydrous compound, enthalpy (53±2kJ mol −1) and activation energy (82±5 kJ mol −1).