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Substituent Effects on Energetics of Peptide-Carboxylate Hydrogen Bonds as Studied by ^1H NMR Spectroscopy: Implications for Enzyme Catalysis

Emenike, Bright U. and Liu, Albert Tianxiang and Naveo, Elsy P. and Roberts, John D. (2013) Substituent Effects on Energetics of Peptide-Carboxylate Hydrogen Bonds as Studied by ^1H NMR Spectroscopy: Implications for Enzyme Catalysis. Journal of Organic Chemistry . ISSN 0022-3263. http://resolver.caltech.edu/CaltechAUTHORS:20131204-111551936

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Abstract

Substituent effects in N–H···O hydrogen bonds were estimated by comparing the acidities of two series of model compounds: N-benzoylanthranilic acids (A) and 4-benzoylamidobenzoic acids (B). Intramolecular N–H···O hydrogen bonds were found to be present in the A series of compounds, while B acids were used as control models. The respective pK_a values for A and B acids were determined experimentally in DMSO solution using proton NMR spectroscopy. With X = H, the pK_a for A and B acids were observed to be 7.6 and 11.6, respectively, a difference of 4.0 units (ΔpK_a). However, with X = p-NO_2, the ΔpK_a value between A and B acids increased to 4.7 units: the pK_a values for A and B acids were determined as 6.7 and 11.4, respectively. The ΔpK_a values between A and B acids as a function of the X substituents were studied in 10 other examples. The effects of X substituents in A acids could be predicted on the basis of the observed linear Hammett correlations, and the sensitivity of each substituent effect was found to be comparable to those observed for the ionization of substituted benzoic acids (ρ = 1.04 for A acids, and ρ = 1.00 for benzoic acids).


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http://dx.doi.org/10.1021/jo401762mDOIArticle
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Additional Information:© 2013 American Chemical Society. Received: August 15, 2013. Publication Date (Web): October 15, 2013. Acknowledgement is made to the National Science Foundation under Grants CHE-0841550, TG-CHE1000106, and to the donors of the Petroleum Research Fund administered by the American Chemical Society for support for this research. Other important support came from the Summer Undergraduate Research Fellowship Program (SURF) at the California Institute of Technology, the Senior Scientist Mentor Program of the Camille and Henry Dreyfus Foundation, and the NORAC Grant to Caltech by Dr. and Mrs, Chester M. McCloskey. We are indebted to Merck and Company, Dr. David J. Mathre, and Edith M. Roberts for their helpful financial assistance. The facilities of the MCS used in these studies were established with grants from DURIP-ONR and DURIP-ARO, with additional support from ONR, ARO, NSF, NIH, DOE, Chevron, Nissan, Dow Corning, Intel, Pfizer, Boehringer-Ingelheim, and Sanofi-Aventis. The authors declare no competing financial interest.
Funders:
Funding AgencyGrant Number
NSFCHE-0841550
NSFTG-CHE1000106
American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Camille and Henry Dreyfus Foundation Senior Scientist Mentor ProgramUNSPECIFIED
DURIP-ONRUNSPECIFIED
DURIP-AROUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Army Research Office (ARO)UNSPECIFIED
NSFUNSPECIFIED
NIHUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
ChevronUNSPECIFIED
NissanUNSPECIFIED
Dow CorningUNSPECIFIED
IntelUNSPECIFIED
PfizerUNSPECIFIED
Boehringer-IngelheimUNSPECIFIED
Sanofi-AventisUNSPECIFIED
Record Number:CaltechAUTHORS:20131204-111551936
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20131204-111551936
Official Citation: Substituent Effects on Energetics of Peptide-Carboxylate Hydrogen Bonds as Studied by 1H NMR Spectroscopy: Implications for Enzyme Catalysis Bright U. Emenike, Albert Tianxiang Liu, Elsy P. Naveo, and John D. Roberts The Journal of Organic Chemistry Article ASAP
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42826
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:04 Dec 2013 21:11
Last Modified:04 Dec 2013 21:11

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