title: Effects of transition metal ion identity and π-cation interactions in metal-bis(peptide) complexes containing phenylalanine.
abstract: Electrospray ionization-tandem mass spectrometry was used to study the effects of the metal ion identity and π-cation interactions on the dissociation pathways of metal-bis(peptide) complexes, where the metal is either Mn(2+), Co(2+), Ni(2+), Cu(2+), or Zn(2+); and the peptide is either FGGF, GGGG, GF, or GG, where G is glycine and F is phenylalanine. The [(FGGF)(FGGF-H) + M(2+)](+) and [(GGGG)(GGGG-H) + M(2+)](+) complexes dissociated by losing one FGGF or GGGG, respectively. Relative binding affinities were measured using the crossover points, where the parent and product ions were equal in ion abundance and a normalized-collision energy scale. The results indicate the relative binding affinities for FGGF and GGGG follow the same order with respect to the transition metal ion identity: Cu(2+) < Ni(2+) < Mn(2+) ≈ Zn(2+) < Co(2+), and the π-cation interactions in the FGGF complex have a measureable stabilizing effect. In contrast, the main fragmentation channels of [(GF)(GF-H) + M(2+)]+ and [(GG)(GG-H) + M(2+)](+) are loss of CO(2) and 2CO(2) with the [(GF)(GF-H) + M(2+)](+) complex also exhibiting cinnamic acid ,GF, residual glycine, cinnamate and styrene loss.
authors.affiliation: Department of Chemistry, Texas A&M University-Commerce, Texas 75429, USA.
authors.forename: Brandon
authors.initials: B
authors.lastname: Utley
authors.forename: Laurence A
authors.initials: LA
authors.lastname: Angel
mesh_terms: D001665:Binding Sites; D002412:Cations; D007477:Ions; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D011485:Protein Binding; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D002412:Cations; D007477:Ions; D008670:Metals; D010455:Peptides; D028561:Transition Elements; D010649:Phenylalanine