engleski

UV-Vis spectra of 1-[N-(tert-butoxycarbonyl)amino]-2-hydroxymethylcyclopropane-1-carboxylic acid complexes with copper(II)

1-Aminocyclopropane-1-carboxylic acid (ACC) is a precursor of the plant hormone ethylene and its derivatives are used in peptide synthesis as the spots of the great strain, originating from the cyclopropane ring. N-protected amino acids have a lowered affinity of nitrogen to bind metal ions, so it is to be expected that N-protected ACC derivatives would bind preferentially through carboxylate group. The complexes of copper(II) with enantiomeric 1-[N-(tert-butoxycarbonyl)amino]-2-hydroxymethylcyclopropane-1-carboxylic acid were studied by UV-Vis spectrophotometric titration (pH=3.4 - 11.9) in water. UV-Vis spectra in water and organic solvents showed that the ligand formed "red" (ƒÜmax=420-490 nm), "blue" (ƒÜmax=630-640 nm), and "green" (ƒÜmax=690-750 nm) complexes. The "red" species having maximum at 430 nm was isolated from water by chloroform extraction, and the green solid was isolated with chloroform from the crude residue obtained by the reaction of ligand with Cu(OH)2. UV-Vis spectrum of the dissolved crude residue in water showed a maximum at 640 nm. The isolated green solid seems to have a binuclear (Ą§acetato likeĄ¨) structure. UV-Vis spectrum of the green complex dissolved in chloroform showed a maximum at 690 nm. In water the binuclear species is destroyed. The IR spectrum of the green solid showed bands of Cu-O stretching, but the bands of Cu-N stretching were missing. The bands at 2357 and 2327 cm-1 strongly suggest the additional binding of the side chain carbonyl group to the copper(II) apical position.

amino acid; coordination compouds; hydroxy acids; hydrogen bond; molecular mechanics

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