title: IRMPD spectroscopic study of microsolvated [Na(GlyAla)]+ and [Ca(GlyAla-H)]+ and the blue shifting of the hydrogen-bonded amide stretch with each water addition.
abstract: In this study, the structures of [Na(GlyAla)(H2O)](+) and [Ca(GlyAla-H)(H2O)n](+), (n = 1-3) solvated ion-molecule complexes (as well as the AlaGly isomers) were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and with computational methods. Calculations showed that in the calcium clusters, the lowest-energy complex is the one in which the peptide is deprotonated at the carboxylic acid end and that Ca(2+) binds to both carboxylate oxygen atoms as well as the amide carbonyl oxygen. For the microsolvated structures, all three water molecules also bind directly to Ca(2+). For the singly, doubly, and triply solvated complexes, these structures are supported by experimental IRMPD spectra. For the [Na(GlyAla)(H2O)](+) complex, both carbonyl oxygen atoms, one from the intact carboxylic acid and one from the amide group, as well as the water molecule were found to be bound to the Na(+). In all of the spectra, a strong band is observed between 3300 and 3400 cm(-1) and is assigned to the amide N-H stretch, which is red-shifted due to hydrogen bonding with the amine nitrogen. The position of the hydrogen-bonded amide N-H stretch is experimentally and theoretically found to be sensitive to the number of water molecules; it is shown to blue shift upon successive hydrations.
authors.affiliation: Department of Chemistry, Memorial University, St. John's, Newfoundland and Labrador, Canada A1B 3X7 Canada.
authors.forename: Maryam B
authors.initials: MB
authors.lastname: Moghaddam
authors.forename: Travis D
authors.initials: TD
authors.lastname: Fridgen
mesh_terms: D000577:Amides / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D003116:Color; D004151:Dipeptides / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D008968:Molecular Conformation; D017785:Photons; D012964:Sodium / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D000577:Amides; D004151:Dipeptides; D012997:Solvents; D014867:Water; D012964:Sodium; D002118:Calcium