15N NMR spectroscopy 28—solvent effects on the 15N13C coupling constants of amides, imides, ureas and polypeptides

The 15N13C coupling constants of 15N-enriched acetamide, N-acetylglycine anilide, phthalimide, α,α′-bisphthalimido-p-xylene, N-methyl-N′-phenylurea, poly-L-alanine and poly-L-valine were measured in various solvents. It was found that the 15N13C coupling constants depend largely on the nature of the solvent. Increasing acidity leads to higher one-bond and lower two-bond coupling constants. A change of concentration does not have any influence on the 15N13C couplings while a large increase in temperature leads to a slightly lower 1J(NC). It is concluded that solvent effects may limit the use of 15N13C coupling constants for the elucidation of solvent-induced conformational changes.

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