Conformational Freeze for the Ethylene Glycol Backbone of 1,2-Ethylene-di-N-n-propylcarbamate in the Triton X-100 Mixed Micelle

Abstract

For the first time, four (eclipsed-(O,O)-, gauche-, anti-, and eclipsed-(O,H)-) conformations of the ethylene glycol backbone of 1,2-ethylene-di-N-n- propylcarbamate (1) are detected in the mixed micelle of Triton X-100 and compound 1 from 600 MHz 1H NMR. Compound 1 is synthesized as a short-chain analog of glycerol lipid to probe the conformation of the ethylene glycol backbone of compound 1 in the Triton X-100 mixed micelle. From the 600 MHz 1H NMR study, the singlet at 4.26 ppm for the ethylene protons of compound 1 splits into four signals (3.68 and 3.70 (AX), 4.15 (quartet), 4.26 (singlet), and 4.30 (singlet)) after formation of the mixed micelle with Triton X-100. These four signals are assigned as the ethylene protons of the eclipsed-(O,H)-, gauche-, anti-, and eclipsed- (O,O)-conformations of the ethylene glycol backbone of compound 1 in the Triton X-100 mixed micelles, respectively. The population of gauche and anti conformations depends on the concentration of compound 1 in the Triton X-100 mixed micelle. Furthermore, the population of anti conformation is proportional but that of the gauche conformation is inversely proportional to the concentration of compound 1 in the Triton X-100 mixed micelle. Therefore, these four conformers of compound 1 are apparently trapped in the Triton X-100 mixed micelle. Alternatively, the major conformation of the ethylene glycol backbones of Triton X-100 is proposed as the gauche conformation in the mixed micelle because most ethylene glycol moieties of Triton X-100 curl in the mixed micelle and show a quartet at 3.65 ppm.