The effect of hydrogen bonding on the diffusion of water in n-alkanes and n-alcohols measured with a novel single microdroplet method.

While the Stokes-Einstein (SE) equation predicts that the diffusion coefficient of a solute will be inversely proportional to the viscosity of the solvent, this relation is commonly known to fail for solutes, which are the same size or smaller than the solvent. Multiple researchers have reported that for small solutes, the diffusion coefficient is inversely proportional to the viscosity to a fractional power, and that solutes actually diffuse faster than SE predicts. For other solvent systems, attractive solute-solvent interactions, such as hydrogen bonding, are known to retard the diffusion of a solute. Some researchers have interpreted the slower diffusion due to hydrogen bonding as resulting from the effective diffusion of a larger complex of a solute and solvent molecules. We have developed and used a novel micropipette technique, which can form and hold a single microdroplet of water while it dissolves in a diffusion controlled environment into the solvent. This method has been used to examine the diffusion of water in both n-alkanes and n-alcohols. It was found that the polar solute water, diffusing in a solvent with which it cannot hydrogen bond, closely resembles small nonpolar solutes such as xenon and krypton diffusing in n-alkanes, with diffusion coefficients ranging from 12.5x10(-5) cm(2)/s for water in n-pentane to 1.15x10(-5) cm(2)/s for water in hexadecane. Diffusion coefficients were found to be inversely proportional to viscosity to a fractional power, and diffusion coefficients were faster than SE predicts. For water diffusing in a solvent (n-alcohols) with which it can hydrogen bond, diffusion coefficient values ranged from 1.75x10(-5) cm(2)/s in n-methanol to 0.364x10(-5) cm(2)/s in n-octanol, and diffusion was slower than an alkane of corresponding viscosity. We find no evidence for solute-solvent complex diffusion. Rather, it is possible that the small solute water may be retarded by relatively longer residence times (compared to non-H-bonding solvents) as it moves through the liquid.

Maladaptive trauma appraisals mediate the relation between attachment anxiety and PTSD symptom severity.

OBJECTIVE: In a large sample of community-dwelling older adults with histories of exposure to a broad range of traumatic events, we examined the extent to which appraisals of traumatic events mediate the relations between insecure attachment styles and posttraumatic stress disorder (PTSD) symptom severity. METHOD: Participants completed an assessment of adult attachment, in addition to measures of PTSD symptom severity, event centrality, event severity, and ratings of the A1 PTSD diagnostic criterion for the potentially traumatic life event that bothered them most at the time of the study. RESULTS: Consistent with theoretical proposals and empirical studies indicating that individual differences in adult attachment systematically influence how individuals evaluate distressing events, individuals with higher attachment anxiety perceived their traumatic life events to be more central to their identity and more severe. Greater event centrality and event severity were each in turn related to higher PTSD symptom severity. In contrast, the relation between attachment avoidance and PTSD symptoms was not mediated by appraisals of event centrality or event severity. Furthermore, neither attachment anxiety nor attachment avoidance was related to participants' ratings of the A1 PTSD diagnostic criterion. CONCLUSION: Our findings suggest that attachment anxiety contributes to greater PTSD symptom severity through heightened perceptions of traumatic events as central to identity and severe. (PsycINFO Database Record