Atomic-level molecular modeling of the nonionic surfactant Triton X-100: the OPE9 component in vacuum and water.

The commercially available nonionic surfactant Triton X-100 is a mixture of polyoxyethylene tert-octylphenyl ethers (OPEn) with an average of n = 9.5 oxyethylene (OE) units in the molecules, and the population maximum at n = 9. Thus, the OPEn = 9 component was chosen to be studied by atomic level molecular modeling, using second-generation force fields. The 1,000 conformers generated via random sampling of torsional angles around single bonds yielded 11 clusters based on geometrical similarity. Representatives of geometrically distinctly different clusters with significant populations were chosen from a narrow energy range around the most probable energy to be analyzed for interaction with water. The effect of water on the conformation of the OE chain was found to be modest, similar to the situation that had been reported earlier for the anionic surfactant Aerosol-OT (AOT). The number of bound water molecules is strongly dependent on the conformation of the OE chain and is affected by electrostatic as well as steric effects. Unlike the case of AOT, for which the length of the hydrophobic tail was found to govern the size of reverse micelles in CCl4, the size of reverse micelles of OPEn = 9 cannot be predicted from the dimensions of the hydrophilic tail.

Age-dependent changes in the osmotic behavior of rat brain and liver.

Osmotic potential of liver and brain tissue has been determined by measuring swelling or shrinkage of the tissues in anoxic Ringer solution the osmotic concentration of which was rendered hypo- or hyperosmotic by dilution or addition of polyethylene glycol (PEG 6000), respectively. The percentages of volume change were fitted to an exponential equation permitting the calculation of the initial speed of volume change. The age-dependent increase of the intracellular dry mass content was also taken into consideration. It has been established that initial velocity of the volume change displays an age-dependent decline in all kinds of media tested; however, the slope of this decrease is steeper in the diluted Ringer solution than in the other ones. Calculations show that the colloid osmotic pressure (mmHg) of the intracellular mass decreases between 1 and 26 months of age from 810 to 596 and from 2,477 to 904 in the brain and liver, respectively. The results may be interpreted as consequences of a decreased colloid dispersity which may be related to an oxygen free radical induced intermolecular cross-linking.