Coordination complexes of amino acids:isomerism and dimorphism of the copper(II) complexes of phenylalanine and tyrosine

Abstract

(D-Phenylalaninato)(L-phenylalaninato)copper(II) has been obtained in two isomeric forms which, from their diffuse reflectance spectra, are designated as the cis and trans forms. The trans isomer is converted into the cis on suspension in hot water. An unstable monohydrate was also isolated. Under similar conditions only the trans form of bis(L- phenylalaninato)copper(II) was obtained. The aqueous solution spectra in the visible region of all forms were identical. Blue trans-(D-tyrosinato)(L-tyrosinato)copper(II) is converted into a mauve coloured form when suspended in hot water. The diffuse reflectance spectrum of this latter form indicates that it is 4-coordinate and possibly cis in configuration. A second, unstable, trans complex of different crystalline form was also obtained. Two crystalline forms of bis(~-tyrosinato)copper(II) were isolated. Spectral differences between the two can be attributed to a difference in coordination number and their different crystalline forms. The solution spectra in the visible region of all forms were identical. No isomerism or dimorphism was found for the complexes of DL- and L-tryptophan.