ALTERATIONS IN THE WATER STRUCTURE AND IN THE HYDROPHOBIC INTERACTIONS PRODUCED BY DISSOLUTIONS OF GASES AND SALTS

J.R. DE XAMMAR ORO

Montevideo-Uruguay

Congreso; 6 International Conference of Biological Physics and 5 Southern Cone Biophysics Congress; 2007

IUPAP – IUPAB – SAB - SUB

Viscosity measurements and cmc determination of solutions of SDS and TX-100 were performed in pure water previously ungasified and then saturated with nitrogen gas and also, in both cases, with 150 mM NaCl, the results show an important difference. The viscosity of the water increases with the content of gas and salts and the cmc of the ionic SDS in water saturated with nitrogen gas was lower than that for ungasified water. This difference was more important in presence of 150 mM NaCl. For the non-ionic TX-100 micelles a similar behavior was observed. These results are interpreted in terms of a cluster model for the water structure. The nitrogen molecules do not need to break hydrogen bonds, as they can easily fit inside the interstices of water lattice. Once in the interstices, they produce Van der Waals interactions with the nearer neighbors. As a result the water molecules lose mobility. Therefore a decrease of the entropy is produced and the enthalpy remains alm ost constant. The water structure is reinforced which increases the hydrophobic interactions. Thus, the cmc decreases. It must be pointed out that these results are also important for other phenomena like transport and selfdiffusion for which the microscopic structure of solvent is significant. This is particularly relevant for living systems in which presence of gases is normal. It may increase the hydrophobic interactions, viscosity, diffusion coefficient and also modify other transport properties. The viscosity measurements were performed with a Viscometer Ubbelohde 0c of capillary 0,46 mm of K = 0,003 with time controller "SCHOTT GERÄTE model AVS 300". For the SDS solution the cmc were determined by measuring conductivity. For the TX-100 solutions the cmc were determined by UV spectroscopy.