Pergamon 0277-5387(95)00586-2 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON Polyhedron zyxwvutsrqponmlkjihgfedc Vol. l5,No. 11,pp. 2887-2894. 1996 CopyrIght c; 1996 Elsewer Saence Ltd Prmted m Great Britam All nghts reserved 0277 5387196 $15.00+0.00 zyxwvutsrq CHARACTERIZATION OF a-AMINO ACIDATO CHROMIUM(II1) COMPLEXES BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY TERESA M. SANTOS” and JirLIO D. PEDROSA DE JESUS Inorganic and Materials Group, Department of Chemistry, University of Aveiro, 3800-Aveiro, Portugal and FRANCISCO M. L. AMADO, PEDRO M. DOMINGUES, M. GRACA SANTANA- MARQUES and A. J. FERRER-CORREIA Mass Spectrometry Laboratory, Department of Chemistry, University of Aveiro, 3800-Aveiro, Portugal zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM (Received 29 September 1995 ; accepted 7 December 1995) Abstract-Circular dichroism and fast atom bombardment mass spectrometry were used to characterize several chromium(Il1) complexes with u-amino acids. Five structures, reported previously, supported on elemental analysis and/or on different spectroscopic data were confirmed on the basis of both their circular dichroism and mass spectrometric properties, and three new structures are proposed from mass spectrometry results. Copyright 0 1996 Elsevier Science Ltd The coordination chemistry of chromium(II1) with natural a-amino acids has received considerable attention for a long time.“’ Recent work on the biological role of chromium(II1) in chromate tox- icity” has given a new importance to the study of the chemistry of such compounds. One particular difficulty in the syntheses of chromium(II1) com- plexes with a cc-amino acids is that several types of compounds are produced.2,3.7,9 Tris-chelates, bis- chelated mixed complexes and dimers can be obtained under apparently similar experimental conditions. The possibility of the formation of mix- tures, the inapplicability of NMR methods for the characterization of paramagnetic chromium(II1) complexes and, in many cases, the lack of crystals suitable for X-ray diffraction analysis, make the determination of the structures of chromium(II1) coordination compounds very difficult. This means that, quite commonly, characterization relies on the * Author to whom correspondence should be addressed. results of elemental analysis and/or on electronic spectroscopic results, including circular dichroism (CD).2,3,5.6,9.‘2Mass spectrometry techniques, and particularly fast atom bombardment mass spec- trometry (FAB-MS) are now used, for the first time, in an attempt to provide better structural charac- terization of the complexes formed by the reaction of chromium(II1) with a-amino acids. In the present work, FAB-MS is used to study several chromium(II1) complexes with L-alanine, L- valine, L-leucine and L-isoleucine and the results are correlated with those from CD experiments with the same samples. It is demonstrated that FAB-MS can provide valuable information about the nature of these type of compounds. The potential of this technique as a powerful tool for structural studies of chromium(II1) species is also discussed. EXPERIMENTAL Material and methods Cr(NO,), *9Hz0 was obtained from Fluka, and L-alanine, L-valine, L-leucine, L-isoleucine, NaOH 2887