The hi&dine complexes of pentaammineruthenium in the (II) and (III) oxidation states have been prepared and characterized. Spectral data shows that hi&dine is bound through the imidazoIe-N-3. The ruthenium (II) ion rearrangg in acidic solution to give a tetrammineruthenium complex of hi&dine in which the histidine is bound through the imidazoIe-C-2 atom. The spectral properties of this linkage isomer are described. The potential biological significance of hi&dine N-C linkage isomerism is discussed.
In view of the ability of imidazole and certain of its simple alky1 derivatives to adopt both nitrogen-bound and carbon-bound coordination in
ruthenium ammine complexes, [I, 21 it was of interest t.o examine hi&dine complexes of ruthenium in search of the same behavior. In this paper we report t.he isolat.ion and complexes of ruthenium. certain properties of carbon-bound histidine EXPERIlWZNTAL Pe~taaminehistidineruthetium(IXI) Trichloride DLHistidine (620 mg) was dissolved in 20 ml of 0.100 N HCl and diluted to 40 ml total volume. This solution was placed in a flask equipped for continuous argon purge. Solid chloropentaammineruthenium dichloride 133 (292 mg) was added followed by several pieces of freshly amalgamated mossy zinc. Reaction was allowed to proceed for 3 hours with a continuous argon purge, during which time all the solid ruthenium salt dissolved and a yellow solution was formed. This solution was t.hen diluted to about @ American EXsevier Publishing Company, Inc., 1973 100 ml totai volume and subjected to a vigorous air stream for 1 hour. The resulting red solution nas acidified to pH ~1 with hydrochloric acid. The product was isolated by ion exchange chromatography using purified Dowex SOW-X2 resin supplied by Bio-Rad Laboratories. It was eluted as an orange band by 3 N HC1. The hydrochloric acid solution was evaporated to dryness using a rotary evaporator at < 1 mm and the residual solid wss crystahized from acetone-water giving a 40% yield of the product as a monohydrate.
Anal. CaIc. for CsH&13N80~Ru~H~O: