ConformationalPreferences of NN-Dimethylsuccinamateas a Function of Alkali and AlkalineEarth Metal Salts: Experimental Studies in DMSO and Water As Determinedby 1H NMR Spectroscopy

摘要

The fraction of gauche conformers of N,N-dimethylsuccinamic acid (>1) and its Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and N(Bu)4⁺ salts were estimated in DMSO and D2O solution by comparing the experimental vicinal proton–proton couplings determined by ¹H NMR spectroscopy with those calculated using the Haasnoot, de Leeuw, and Altona (HLA) equation. In DMSO, the gauche preferences were found to increase with decreasing Ahrens ionic radius of the metal counterion. The same trend was not seen in D2O, where the gauche fraction for all of the metallic salts were estimated to be approximately statistical or less. This highlights the importance of metal chelation on the conformation of organic molecules in polar aprotic media, which has implications for protein folding.