as TX100) is extensively used to solubilize membrane phos-The polarized infrared spectra of water in the middle phase pholipids and to purify membrane-bound proteins and enzymes of Triton X100 aqueous solution were compared with those of without loss of their biological activity (1, 2). Moreover, this poly(ethylene oxide) in the crystalline state. The oxyethylene amphipathic surfactant is widely employed in industry as a chain of TX100 orients approximately perpendicular to the direcdetergent, solubilizer, and emulsifier.
tion of the stream (parallel to the direction of growth of the liquid
The size and shape of the micelle and mesophase of crystal), while that of poly(ethylene oxide) orients parallel to the TX100 have been extensively studied by various methods stretching direction. However, in both cases the water molecule such as viscometry (3), X-ray (4, 5), light scattering (6), prefers the perpendicular orientation of its bisector to the oxyethy-Raman (7-9), and NMR (10-13) analysis. However, lene chain. The OH stretching frequency of water in Triton X100 sharply increases with increasing water content up to about 10 knowledge about the manner of hydration and the role of wt% and decreases suddenly up to about 40 wt%, after which it water upon the formation of micelles and mesophases is still stays constant. The initial increment in the OH stretching frevery incomplete. We have great interest in the process of quency is due to the progression of the hydrogen bonding between hydration of TX100, since we detected drastic coagulation water and the ether oxygen in the oxyethylene groups of Triton of TX100 in a limited range during the dilution of TX100. X100 and the subsequent reduction is the result of the linkage Infrared spectra are quite sensitive for the presence of between the waters. On the other hand, the increase in intensity hydrogen bonds, detected as variations in frequency, bandand the decrease in band-width of the 949 cm 01 band up to a width, and integrated intensity. Detailed studies of the OH constant value at about 40 wt% H 2 O suggest the progression of stretching and CH 2 rocking bands at various concentrations, the ordered GTTG helical conformation in the oxyethylene group therefore, provide some useful information about the hydraof Triton X100. The appearance of the middle phase of Triton tion and conformation of the oxyethylene chain in the differ-X100 results in the formation of the hydrogen-bonding network of the (2:1) complex at about 40 wt% H 2 O. In the middle phase ent environments. In order to understand the detailed segof 40-60 wt% H 2 O, water added in excess gradually dissolves the mental environments of TX100 under various concentralinkage among the adjacent oxyethylene chains, but the system tions, we also used the 13 C NMR technique. partially remains in the liquid crystal phase. Above 60 wt% H 2 O
The number of bound waters at the hydrophilic part of (water:oxyethylene ร
5:1), the water added in excess interrupts TX100 has been estimated by many workers, but the estithe hydrogen-bond linkage of the 2:1 complex and destroys the mates have been widespread. In the present work, the results middle phase. However, the helical conformation resides in this of IR and NMR measurements gave two hydrated water aqueous solution, because the oxyethylene group prefers the helical molecules per one oxyethylene unit. conformation in the aqueous solution rather than in the neat or Finally, assuming the structure of the tetrahedral water molten state. The 13 C chemical shifts ensured the concurrence of network to be that of ice I h , we propose a reasonable replehydration to the various oxygen atoms in the oxyethylene chain tion model for the water/TX100 complex. and the existence of the helical conformation. In the middle phase, the weak orientation of water and TX100 is due to the directional distributions of the helical axis in the quasi-spherical micelle. EXPERIMENTAL