Divalent Metal-Ion Complexes with Dipeptide Ligands Having Phe and His Side-Chain Anchors: Effects of Sequence, Metal Ion, and Anchor.
Conformational preferences have been surveyed for divalent metal cation complexes with the dipeptide ligands AlaPhe, PheAla, GlyHis, and HisGly. Density functional theory results for a full set of complexes are presented, and previous experimental infrared spectra, supplemented by a number of newly recorded spectra obtained with infrared multiple photon dissociation spectroscopy, provide experimental verification of the preferred conformations in most cases. The overall structural features of these complexes are shown, and attention is given to comparisons involving peptide sequence, nature of the metal ion, and nature of the side-chain anchor. A regular progression is observed as a function of binding strength, whereby the weakly binding metal ions (Ba(2+) to Ca(2+)) transition from carboxylate zwitterion (ZW) binding to charge-solvated (CS) binding, while the stronger binding metal ions (Ca(2+) to Mg(2+) to Ni(2+)) transition from CS binding to metal-ion-backbone binding (Iminol) by direct metal-nitrogen bonds to the deprotonated amide nitrogens. Two new sequence-dependent reversals are found between ZW and CS binding modes, such that Ba(2+) and Ca(2+) prefer ZW binding in the GlyHis case but prefer CS binding in the HisGly case. The overall binding strength for a given metal ion is not strongly dependent on the sequence, but the histidine peptides are significantly more strongly bound (by 50-100 kJ mol(-1)) than the phenylalanine peptides.
Chemistry Department, Case Western Reserve University , Cleveland, Ohio 44106, United States.
Robert C
RC
Dunbar
Radboud University, Institute for Molecules and Materials, FELIX Laboratory , Toernooiveld 7c, 6525ED Nijmegen, The Netherlands.
Giel
G
Berden
Radboud University, Institute for Molecules and Materials, FELIX Laboratory , Toernooiveld 7c, 6525ED Nijmegen, The Netherlands.
Jonathan K
JK
Martens
Radboud University, Institute for Molecules and Materials, FELIX Laboratory , Toernooiveld 7c, 6525ED Nijmegen, The Netherlands.|University of Amsterdam , Science Park 904, 1098XH Amsterdam, The Netherlands.
Jos
J
Oomens
D002264:Carboxylic Acids / Q000737:chemistry / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry* / Q000378:metabolism; D002414:Cations, Monovalent / Q000737:chemistry* / Q000378:metabolism; D056831:Coordination Complexes / Q000737:chemistry* / Q000378:metabolism; D004151:Dipeptides / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010649:Phenylalanine / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013816:Thermodynamics
D002264:Carboxylic Acids; D002413:Cations, Divalent; D002414:Cations, Monovalent; D056831:Coordination Complexes; D004151:Dipeptides; D010649:Phenylalanine; D006639:Histidine