Amino acid/diphosphine ruthenium complexes, of general formula [Ru(AA-H)(dppb)(bipy)]PF6 [AA = amino acid: glycine (gly), L-alanine (ala), L-tyrosine (tyr), L-methionine (met), L-leucine (leu), L-valine (val), L-serine (ser), L-tryptophan (trp), and L-lysine(lys); dppb = 1,4-bis(diphenylphosphino)butane; bipy = 2,2'-bipyridine], were synthesized and characterized. The X-ray structures of the glycine and leucine complexes showed that the amino acids are coordinated to the metal center through the carboxylate and amine groups. The complexes, except for the glycine ligand, form two different conformational isomers, as suggested by X-ray structure determination of the complex with leucine, and shown by 31P{1H} NMR analysis. The cyclic and differential pulse voltammograms of the complexes exhibited an oxidation potential (RuII/RuIII) close to 1.0 V, against Ag/AgCl. Toxicity tests against the MDA-MB-231 and DU 145 human tumor cell lines and the Ehrlich mouse cell line indicated a high degree of cytotoxicity for the amino acid complexes. The intrinsic binding constants (Kb) for the amino acid complexes were determined and found to be in the range of 1.40 x '10 POT. 4' - 1.80 x '10 POT. 4' M-1, suggesting weak interactions of the complexes with DNA. ; CAPES ; CNPq ; FAPESP (12/06013-4)