Conformational dependence of triton X-100 on environment studied by 2D NOESY and 1H NMR relaxation

Conformation of Triton X-100 (TX-100) in the bulk and in aqueous solutions at concentrations higher and lower than the critical micellar concentration (cmc) was studied by NMR relaxation, two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY), and molecular simulation by HYPERCHEM. Results show that motion of TX-100 in dilute solution (0.5 cmc) is in the extreme narrowing condition. Molecules are in the single molecular state with an extended polyoxyethylene chain. Tn forming micelles, these hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, coil, bend. and align along the surface of the TX-100 micellar core, forming a layer thick in dimension and loose in structure around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. The micelle is spherical at 10 cmc. Motions of all of the protons of TX-100 in the bulk, even of those on the polyoxyethylene chain, are more restricted than motions of those in the micellar core. Exponential decay of the proton spin - spin relaxation of TX-100 in the bulk shows the absence of oriented self-aggregation. Very short internuclear distances of the protons between hydrophilic and hydrophobic parts of TX-100 bulk measured from the 2D NOESY spectrum show that the molecules are arranged randomly, closely, and uniformly, which is the origin for the high viscosity of TX-100 bulk. Results are discussed in terms of inter- and intramolecular interactions.