Application of the Recognizing Ability for L-Cysteine Residue to Peptide-Analysis using the Trigonal-Bipyramidal Palladium(II) Complex

The high selectivity for the thiolato sulfur atom in the axial position of the five-coordinate trigonal-bipyramidal palladium(II) complexes with tris (2-(diphenylphosphino) -ethyi)phosphine (pp_3 ) was confirmed. In order to apply such a selectivity to separation of amino acids, an acetonitrile solution of [Pd(pp_3)(CH_3CN)](BF_4)_2 was added to a weakly basic aqueous solution containing four amino acids, L-alanine, L-methionine, L-penicillamine, L-cysteine, and the resultant complex is extracted with chloroform, The chloroform solution showed only the ^P NMR signals for the L-cysteinato complex which was newly isolated. The preference for L-cysteine over L-methionine and L-penicillamine is explained by the electronic and steric reasons. Furthermore, we have applied the selectivity to detection of the L-cysteine residue in glutathione and to determination of the reduced form of glutathione. The pp_3 palladium(II) complex did not react to form a throlato complex with the oxidized form of glutathione. Such a discriminating ability for the oxidation state is quite useful for investigation of the biological redox system. It was also indicated that the glutathionato complex is useful for discrimination of the organotin compounds.