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Dependence of glycine CH<inf>2</inf> stretching frequencies on conformation, ionization state, and hydrogen bonding

Bykov, SV and Myshakina, NS and Asher, SA (2008) Dependence of glycine CH<inf>2</inf> stretching frequencies on conformation, ionization state, and hydrogen bonding. Journal of Physical Chemistry B, 112 (18). 5803 - 5812. ISSN 1520-6106

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We experimentally and theoretically examined the conformation, pH, and temperature dependence of the CH2 stretching frequencies of glycine (gly) in solution and in the crystalline state. To separate the effects of the amine and carboxyl groups on the CH2 stretching frequencies we examined the Raman spectra of 2,2,2-d3-ethylamine (CD 3-CH2-NH2) and 3,3,3-d3-propionic acid (CD3-CH2-COOH) in D2O. The symmetric (vsCH2) and asymmetric (vasCH2) stretching frequencies show a significant dependence on gly conformation. We quantified the relation between the frequency splitting (Δ = v asCH2 -vsCH2) and the ξ angle which determines the gly conformational geometry. This relation allows us to determine the conformation of gly directly from the Raman spectral frequencies. We observe a large dependence of the vsCH2 and v asCH2 frequencies on the ionization state of the amine group, which we demonstrate theoretically results from a negative hyperconjugation between the nitrogen lone pair and the C-H antibonding orbitais. The magnitude of this effect is maximized for C-H bonds trans to the nitrogen lone pair. In contrast, a small dependence of the CH2 stretching frequencies on the carboxyl group ionization state arises from derealization of electron density from carboxyl oxygen to C-H bonding orbitals. According to our experimental observations and theoretical calculations the temperature dependence of the vsCH2 and v asCH2 of gly is due to the change in the hydrogen-bonding strength of the amine/carboxyl groups to water. © 2008 American Chemical Society.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Bykov, SV
Myshakina, NS
Asher, SAasher@pitt.eduASHER
Date: 8 May 2008
Date Type: Publication
Journal or Publication Title: Journal of Physical Chemistry B
Volume: 112
Number: 18
Page Range: 5803 - 5812
DOI or Unique Handle: 10.1021/jp710136c
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Refereed: Yes
ISSN: 1520-6106
MeSH Headings: Amines--chemistry; Carbon--chemistry; Glycine--chemistry; Hydrogen--chemistry; Hydrogen Bonding; Ions--chemistry; Models, Molecular; Molecular Conformation; Propionic Acids--chemistry; Solutions; Spectrum Analysis, Raman; Temperature; Vibration
Other ID: NLM NIHMS239071, NLM PMC2952399
PubMed Central ID: PMC2952399
PubMed ID: 18447350
Date Deposited: 25 Sep 2012 14:21
Last Modified: 22 Jun 2021 12:56


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