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pH-Dependent Nuclear Magnetic Resonance Spectra of ^(15)N-Enriched Glycine. Line Shape and Relaxation Studies

Cooper, Robert A. and Lichter, Robert L. and Roberts, John D. (1973) pH-Dependent Nuclear Magnetic Resonance Spectra of ^(15)N-Enriched Glycine. Line Shape and Relaxation Studies. Journal of the American Chemical Society, 95 (11). pp. 3724-3729. ISSN 0002-7863. doi:10.1021/ja00792a042.

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The influence of pH on the line shapes, chemical shifts, and relaxation times of the ^(15)N resonances in aqueous solutions of 95%-enriched ^(15)N glycine is discussed. Below pH 6.4, the observed ^(15)N and ^1H spectra of glycine clearly reflect chemical-exchange modulation of the ^(15)N-^1H scalar interaction. The observed increase in the scalar relaxation, as well as the concomitant decrease in the nuclear Overhauser enhancement of the ^(15)N resonance as the pH increases, can also be explained on the basis of chemical exchange. A comparative study of ^(15)N enriched glycine and ethyl glycinate shows that the ^(15)N chemical-shift changes found for glycine in the acid region reflect the electronic changes at the carbonyl function. Furthermore, the observed differences in the line shapes for the two compounds correlate well with the differences in pK_a's for the ^+NH_3 group. The changes in line shape for both the decoupled and undecoupled ^(15)N spectra of glycine and its ethyl ester above pH 6.4 suggest that ^(15)N chemical-shift averaging occurs as the result of exchange between the protonated and deprotonated forms.

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Additional Information:© 1973 American Chemical Society. Received September 7, 1972. Supported by the Public Health Service, Research Grant No. GM-11072 from the Division of General Medical Sciences, and the National Science Foundation; National Institutes of Health Postdoctoral Fellow, 1971-1972.
Funding AgencyGrant Number
U.S. Public Health Service (USPHS)GM-11072
NIH Postdoctoral FellowshipUNSPECIFIED
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Caltech Gates and Crellin Laboratories of Chemistry4522
Issue or Number:11
Record Number:CaltechAUTHORS:20151009-133522833
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Official Citation:pH-Dependent nuclear magnetic resonance spectra of nitrogen-15-enriched glycine. Line shape and relaxation studies Robert A. Cooper, Robert L. Lichter, and John D. Roberts Journal of the American Chemical Society 1973 95 (11), 3724-3729 DOI: 10.1021/ja00792a042
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60943
Deposited By: Ruth Sustaita
Deposited On:16 Oct 2015 01:37
Last Modified:10 Nov 2021 22:42

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