eprintid: 17229 rev_number: 24 userid: 1419 dir: disk0/00/01/72/29 datestamp: 2013-02-08 21:05:08 lastmod: 2021-06-12 23:55:30 status_changed: 2013-02-08 21:05:08 type: article metadata_visibility: show item_issues_count: 0 eprint_status: archive creators_name: Myshakina, NS creators_name: Ahmed, Z creators_name: Asher, SA creators_email: creators_email: creators_email: asher@pitt.edu creators_id: creators_id: creators_id: ASHER title: Dependence of amide vibrations on hydrogen bonding ispublished: pub divisions: sch_as_chemistry full_text_status: public abstract: The effect of hydrogen bonding on the amide group vibrational spectra has traditionally been rationalized by invoking a resonance model where hydrogen bonding impacts the amide functional group by stabilizing its [ -O-C=NH+] structure over the [O=C-NH] structure. However, Triggs and Valentini's UV-Raman study of solvation and hydrogen bonding effects on e-caprolactum, N,N-dimethylacetamide (DMA), and N-methylacetamide (NMA) (Triggs, N. E.; Valentini, J. J. J. Phys. Chem. 1992, 96, 6922-6931) casts doubt on the validity of this model by demonstrating that, contrary to the resonance model prediction, carbonyl hydrogen bonding does not impact the AmII′ frequency of DMA. In this study, we utilize density functional theory (DFT) calculations to examine the impact of hydrogen bonding on the C=O and N-H functional groups of NMA, which is typically used as a simple model of the peptide bond. Our calculations indicate that, as expected, the hydrogen bonding frequency dependence of the AmI vibration predominantly derives from the C=O group, whereas the hydrogen bonding frequency dependence of the AmII vibration primarily derives from N-H hydrogen bonding. In contrast, the hydrogen bonding dependence of the conformation-sensitive AmIII band derives equally from both C=O and N-H groups and thus, is equally responsive to hydrogen bonding at the C=O or N-H site. Our work shows that a clear understanding of the normal mode composition of the amide vibrations is crucial for an accurate interpretation of the hydrogen bonding dependence of amide vibrational frequencies. © 2008 American Chemical Society. date: 2008-09-25 date_type: published publication: Journal of Physical Chemistry B volume: 112 number: 38 pagerange: 11873 - 11877 refereed: TRUE issn: 1520-6106 id_number: 10.1021/jp8057355 other_id: NLM NIHMS86297 other_id: NLM PMC2633779 pmcid: PMC2633779 pmid: 18754632 mesh_headings: Acetamides--chemistry mesh_headings: Amides--chemistry mesh_headings: Hydrogen Bonding mesh_headings: Models, Chemical mesh_headings: Vibration mesh_headings: Water--chemistry chemical_names: Acetamides chemical_names: Amides chemical_names: Water chemical_names: dimethylacetamide chemical_names: N-methylacetamide citation: Myshakina, NS and Ahmed, Z and Asher, SA (2008) Dependence of amide vibrations on hydrogen bonding. Journal of Physical Chemistry B, 112 (38). 11873 - 11877. ISSN 1520-6106 document_url: http://d-scholarship-dev.library.pitt.edu/17229/1/licence.txt