Charge relay at the peptide bond. A proton magnetic resonance study of solvation effects on the amide electron density distribution. [Alumichrome and alumichrome C]
The proton magnetic resonance (/sup 1/H NMR) manifestations of amide solvation in polypeptides have been studied using alumichrome and alumichrome C as model compounds. The extreme structural rigidity of the alumichromes allowed the investigation to center on the chemical shifts of the amides as conformational drifts are precluded. The data have been analyzed primarily in terms of two main events: H bonding of the amide nitrogen to basic solvents (Me/sub 2/SO, DMF, and pyridine), and protonation of the amide carbonyl by Bronsted acids (chloroform, TFE, and TFA). The two solvent types cause a low-field shift of the amide proton resonance which in the first case arises from a direct effect, while in the second case, consistent with an earlier suggestion of Schwyzer and Ludescher, the deshielding would result from the extreme electronic lability of the peptide link which permits an electron density flow to the carbonyl. The solvent-induced chemical shift is shown to depend on the extent of exposure of the pertinent hydrogen and oxygen atoms so that the magnitude and direction of the effect reflect conformational features of the molecule at the amide sites. (auth)
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 7365395
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 97:16
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
POLYPEPTIDES
NUCLEAR MAGNETIC RESONANCE
AMIDES
CHARGE EXCHANGE
CHEMICAL SHIFT
CHLOROFORM
DMSO
ELECTRON DENSITY
MONOCARBOXYLIC ACIDS
ORGANIC ACIDS
PYRIDINES
SOLVATION
TEMPERATURE DEPENDENCE
WATER
AZINES
CARBOXYLIC ACIDS
CHLORINATED ALIPHATIC HYDROCARBONS
HALOGENATED ALIPHATIC HYDROCARBONS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
MAGNETIC RESONANCE
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
PEPTIDES
PROTEINS
RESONANCE
SULFOXIDES
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)