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Stepwise microhydration of aromatic amide cations: water solvation networks revealed by the infrared spectra of acetanilide+–(H2O)n clusters (n ≤ 3)

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Abstract

The structure and activity of peptides and proteins strongly rely on their charge state and the interaction with their hydration environment. Here, infrared photodissociation (IRPD) spectra of size-selected microhydrated clusters of cationic acetanilide (AA+, N-phenylacetamide), AA+–(H2O)n with n ≤ 3, are analysed by dispersion-corrected density functional theory calculations at the ωB97X-D/aug-cc-pVTZ level to determine the stepwise microhydration process of this aromatic peptide model. The IRPD spectra are recorded in the informative X–H stretch (νOH, νNH, νCH, amide A, 2800–3800 cm−1) and fingerprint (amide I–II, 1000–1900 cm−1) ranges to probe the preferred hydration motifs and the cluster growth. In the most stable AA+–(H2O)n structures, the H2O ligands solvate the acidic NH proton of the amide by forming a hydrogen-bonded solvent network, which strongly benefits from cooperative effects arising from the excess positive charge. Comparison with neutral AA–H2O reveals the strong impact of ionization on the acidity of the NH proton and the topology of the interaction potential. Comparison with related hydrated formanilide clusters demonstrates the influence of methylation of the amide group (H → CH3) on the shape of the intermolecular potential and the structure of the hydration shell.

Graphical abstract: Stepwise microhydration of aromatic amide cations: water solvation networks revealed by the infrared spectra of acetanilide+–(H2O)n clusters (n ≤ 3)

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Publication details

The article was received on 11 Jul 2017, accepted on 01 Sep 2017 and first published on 04 Sep 2017


Article type: Paper
DOI: 10.1039/C7CP04659F
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    Stepwise microhydration of aromatic amide cations: water solvation networks revealed by the infrared spectra of acetanilide+–(H2O)n clusters (n ≤ 3)

    J. Klyne, M. Schmies, M. Miyazaki, M. Fujii and O. Dopfer, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C7CP04659F

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