Phase structures, water binding, and molecular dynamics in liquid crystalline and frozen states of the system Triton X-100-D 2O : A deuteron and carbon NMR study

Abstract

The phase diagram of the system Triton X-100-deuterium oxide was constructed with the aid of deuterium nuclear magnetic resonance. Two liquid crystalline phases were detected. Oriented samples of these mesophases exhibited spectra consistent with cylindrical and lamellar structures, in agreement with the common features of middle neat phases, respectively. The hydration of Triton X-100 by D 2O was studied over a wide temperature and concentration range. The solvent binding capacity of the polyoxyethylene moiety of this detergent was determined by the method of nonfreezable water. The molar ratios D 2O/Triton were almost independent of the Triton concentration after freezing of the bulk solvent. On the other hand, the amount of nonfreezable water decreased considerably with temperature. This behavior was interpreted in terms of transference of water molecules to the ice phase. Comparison of 2H-NMR relaxation times and 13C-NMR line widths in the liquid crystalline states of the Triton-water system suggested that the mobility of the Triton molecule is most restricted at the hydrophilic-hydrophobic interface. The mobility gradient was found to persist at low temperatures when the bulk solvent is frozen. Fourier transform 2H-NMR spectra revealed that macroscopic freezing of micellar and hexagonal (middle phase) samples obviously causes a rearrangement of the detergent molecules. A lamellar phase structure adopted by Triton in the ice could explain these observations.