Speciation of gold(III)-L-histidine complex: a multi-instrumental approach

The formation and structure of gold (III)-L-histidine complex was investiga ted with the use of carbon (C-13) and proton (H-1) nuclear magnetic resonan ce (NMR), infrared (IR) spectroscopy, capillary electrophoresis (CE), capil lary electrophoresis-inductively coupled plasma-mass spectroscopy (CE-ICP-M S), X-ray fluorescence spectroscopy (XRF), matrix-assisted laser desorption /ionization (MALDI), and laser desorption mass spectroscopy (LDMS). It was found that two L-histidine molecules and one gold ion slowly form a complex in acidic solution. Each L-histidine molecule provided two nitrogen ligand s; one was the alpha-amino group and the other from the imidazole ring. The Au(III)-bis-L-histidine complex precipitates after deprotonation of the fr ee carboxylic group, resulting in an increase in the solution acidity. Dete rmination of the exact sequence of events and the identity of the complex w as a comprehensive instrumental analysis problem involving the above techni ques.