Spectrophotometric and 27-Al NMR Characterization of Aluminum(III) Complexes with L-Histidine Predrag Djurdjevic Faculty of Science, Institute of Chemistry, Kragujevac, Yugoslavia Mirjana Cvijovic The Copper Mill, Sevojno, Uzice, Yugoslavia Vesna Pavelkic Institute of Nuclear Sciences, Vinca, Belgrade, Yugoslavia Joanna Zakrzewska Institute of General and Physical Chemistry, Belgrade, Yugoslavia Abstract: The complex formation between L-histidine (HHis) and aluminum(III) ion in water solutions was studied by UV spectrophotometric and 27-Al NMR measure- ments at 298 K. UV spectra were measured on solutions in which the total concen- tration of histidine was from 15.0 to 50.0 mmol/dm 3 and the concentration ratio of histidine to aluminum was varied from 3 : 1 to 10 : 1 in the pH range between 4.2 and 6.0. The spectra were taken in the wavelength interval 240 – 340 nm. Nonlinear least-squares treatment of the spectrophotometric data indicates the formation of the complexes Al(HHis) 3þ , Al(His) 2þ , Al(HHis)His 2þ , and Al 2 (OH)His 4þ with the overall formation constants b p,q,r : log b 1,1,1 ¼ 11.90 + 0.04, log b 1,1,0 ¼ 7.25 + 0.08, log b 1,2,1 ¼ 20.1 + 0.1, and log b 2,1,1 ¼ 5.92 + 0.12 (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively). 27 Al-NMR spectra were taken on solutions with the concentration of aluminum 50 mmol/dm 3 and that of histidine 250 mmol/dm 3 . Received 12 December 2004, Accepted 17 March 2005 Address correspondence to Predrag Djurdjevic, Faculty of Science, Institute of Chemistry, P.O. Box 60, Kragujevac 34000, Yugoslavia. E-mail: preki@knez.kg.ac.yu Spectroscopy Letters, 38: 617–634, 2005 Copyright # Taylor & Francis, Inc. ISSN 0038-7010 print/1532-2289 online DOI: 10.1081/SL-200062968 617