NMR Investigation of Quaternary Ammonium Dimeric Surfactant C16-4-C16·2Br Micelles
季铵盐型双子表面活性剂16-4-16聚集状态的NMR研究

Conformation of Gemini 16-4-16 in heavy water solutions at concentrations close to the critical micellar concentration (cmc) was studied by NMR relaxation, self-diffusion and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). In forming micelles, the protons of the spacer group and a part of hydrophobic protons next to the polar head group are involved in the surface layer of the micellar core. The hydrophobic protons away from the polar head group are situated internal in the micellar core. The motion of the molecules are relatively more restricted than their monomeric homologue CTAB. 2D NOESY experiments show cross peaks between the protons in or close to the spacer group. The inter-proton distances thus calculated show deviation from those of the intra-molecular ones, calculated by HYPERCHEM. Therefore, inter-molecular interaction is responsible for these strong cross peaks. The corresponding proton pairs are in near vicinity. Accordingly we postulate a special arrangement of the molecules in the spherical 16-4-16 micelles.