Erin Duffy

Intramolecular Hydrogen Bonding Motifs in Deprotonated Glycine Peptides by Cryogenic Ion Infrared Spectroscopy

The infrared spectra of deprotonated glycine peptides, (Gn-H)(-) with n = 1-4, in the 1200-3500 cm(-1) spectral region are presented. Comparisons between the experimental and calculated spectra reveal the chain length dependent hydrogen bonding motifs that define the geometries of these species. First, an interaction between the terminal carboxylate and the neighboring amide N-H is present in all the peptide structures. This interaction is strong enough to align this amide group in the same plane as the carboxylate. However, we found that the vibrational frequency shift of this hydrogen bonded N-H group is not well reproduced in the calculations. Second, in the longer (G3-H)(-) and (G4-H)(-) species, the peptide chain folds such that the terminal NH2 group also interacts with the carboxylate. Both of these folded structures display an interaction between the terminal NH2 and the neighboring N-H as well. Lastly, an amide-amide interaction is observed in the longest (G4-H)(-) structure. Analysis of the N-H peak positions reveals the interplay among the different hydrogen bonds, especially around the negatively charged carboxylate moiety.

Vibrational Characterization of Microsolvated Electrocatalytic Water Oxidation Intermediate: [Ru(tpy)(bpy)(OH)]2+(H2O)0–4

The infrared predissociation spectra of the mass-selected electrocatalytic water oxidation intermediate [Ru(tpy)(bpy)(OH)]2+(H2O)0-4 are reported. The [Ru(tpy)(bpy)(OH)]2+ species is generated by passing a solution of [Ru(tpy)(bpy)(H2O)](ClO4)2 through an electrochemical flow cell held at 1.2 V and is immediately introduced into the gas phase via electrospray ionization (ESI). The microsolvated clusters are formed by reconstructing the water network in a cryogenic ion trap. Details of the hydrogen bonding network in these clusters are revealed by the infrared predissociation spectra in the OH stretch region. This improved method for capturing microsolvated clusters yielded colder complexes with much better resolved IR features than previous studies. The analysis of these spectra, supported by electronic structure calculations and compared to previous results on [Ru(tpy)(bpy)(H2O)]2+(H2O)0-4 clusters, reveals the nature of the Ru-OH bond and the effect of hydrogen bonding on facilitating the subsequent oxidation to [Ru(tpy)(bpy)(O)]2+ in the proposed catalytic cycle. Particularly, the hydrogen bonding interaction in [Ru(tpy)(bpy)(OH)]2+(H2O)1 is much weaker than that in the corresponding [Ru(tpy)(bpy)(H2O)]2+(H2O)1 and thus is less effective at activating the hydroxyl ligand for further oxidation via proton coupled electron transfer (PCET). Furthermore, the results here reveal that the Ru-OH bond, though formally described as an Ru3+/OH- interaction, has more covalent bond character than ionic bond character.