title: Generation of [La(peptide)]3+ complexes in the gas phase: determination of the number of binding sites provided by dipeptide, tripeptide, and tetrapeptide ligands.
abstract: Gas-phase complexes [La(peptide)](3+) containing 2-4 amino-acid residues have been investigated by electrospraying solutions containing La(3+) and the peptide; only complexes in which the peptide contained an arginine residue were observed. Using the coordination number of eight for La(3+) [Shi, T.; Hopkinson, A. C.; Siu, K. W. M. Chem. Eur. J. 2007, 13, 1142-1151] and the relative abundances of the hydrates [La(peptide)(H(2)O)(n)](3+), the number of binding sites provided by the peptides was deduced: Leu-Trp-Met-Arg, 7; Met-Arg-Phe-Ala, 6; Gly-Arg-Gly, 4; Gly-Gly-Arg 4; and Met-Arg, 4. Density Functional Theory calculations show that the zwitterionic form of Gly-Gly-Arg preferentially binds La(3+) through four coordination sites-the two amide oxygens and the two carboxy oxygens.
authors.affiliation: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada.
authors.forename: Tujin
authors.initials: T
authors.lastname: Shi
authors.forename: K W Michael
authors.initials: KW
authors.lastname: Siu
authors.forename: Alan C
authors.initials: AC
authors.lastname: Hopkinson
mesh_terms: D001665:Binding Sites; D005740:Gases; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D005740:Gases; D028581:Lanthanoid Series Elements; D008024:Ligands; D009842:Oligopeptides