Conformational Preferences of N,N-Dimethylsuccinamate as a Function of Alkali and Alkaline Earth Metal Salts: Experimental Studies in DMSO and Water As Determined by ^1H NMR Spectroscopy

Abstract

The fraction of gauche conformers of N,N-dimethylsuccinamic acid (1) and its Li^+, Na^+, K^+, Mg^(2+), Ca^(2+), and N(Bu)_4^+ salts were estimated in DMSO and D_2O 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 D_2O, 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.