Monopeptide versus Monopeptoid: Insights on Structure and Hydration of Aqueous Alanine and Sarcosine via X-ray Absorption Spectroscopy Page: 2 of 30
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Abstract:
Despite the obvious significance, the aqueous interactions of peptides remain incompletely
understood. Their synthetic analogues called peptoids (poly-N-substituted glycines), have
recently emerged as a promising biomimetic material, particularly due to their robust
secondary structure and resistance to denaturation. We describe comparative near-edge x-
ray absorption fine structure (NEXAFS) spectroscopy studies of aqueous sarcosine, the
simplest peptoid, and alanine, its peptide isomer, interpreted by density functional theory
calculations. The sarcosine nitrogen K-edge spectrum is blue-shifted with respect to that of
alanine, in agreement with our calculations; we conclude that this shift results primarily
from the methyl group substitution on the nitrogen of sarcosine. Our calculations indicate
that the nitrogen K-edge spectrum of alanine differs significantly between dehydrated and
hydrated scenarios, while that of the sarcosine zwitterion is less affected by hydration. In
contrast, the computed sarcosine spectrum is greatly impacted by conformational
variations, while the alanine spectrum is not. This relates to a predicted solvent dependence
for alanine, as compared to sarcosine. Additionally, we show the theoretical nitrogen K-
edge spectra to be sensitive to the degree of hydration, indicating that experimental X-ray
spectroscopy may be able to distinguish between bulk and partial hydration, such as found
in confined environments near proteins and in reverse micelles.
Keywords: NEXAFS, alanine, sarcosine, DFT, XCH9
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Uejio, Janel S.; Schwartz, Craig P.; Duffin, Andrew M.; England, Alice; Prendergast, David & Saykally, Richard J. Monopeptide versus Monopeptoid: Insights on Structure and Hydration of Aqueous Alanine and Sarcosine via X-ray Absorption Spectroscopy, article, November 19, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1013229/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.