Molecular dynamics simulations with polarizable potentials were carried out to investigate the n-alkane/water interface, including sodium-halide ion distributions. A new polarizable force field was developed for n-alkanes, which gave good agreement with experiment for liquid densities and heats of vaporization for different n-alkanes at different temperatures. Also, good agreement with experiment was found for alkane/water interfacial tensions for a variety of alkanes. Alkane/water interfaces with linear alkanes of different chain lengths had fairly similar properties, except that with longer alkanes, the interfacial width decreased. Water induced dipoles were reduced at the alkane/water interface in comparison with the bulk, but their induced dipoles were greater at the alkane/water interface than at the air/water interface. Furthermore, the water structure expanded at the alkane/water interface in comparison with the bulk, but this expansion was not as significant as at the air/water interface. Sodium-halide concentrated solutions at the n-octane/water interface were simulated and compared with the air/water interface. Iodide had a similar interfacial concentration at both interfaces, while bromide and chloride showed significantly reduced interfacial concentration at the alkane/water interface. Iodide’s differing behavior was linked to the fact that it has favorable hydrophobic interactions with alkanes that were not as strong for bromide and chloride with the alkanes.

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New molecular models that incorporated polarizable interactions with electrostatic damping were developed to better understand the interfacial properties of aqueous electrolyte systems. The models were parameterized to give free energies of aqueous solvation and the change in activity with respect to concentration in agreement with experiment. Specifically, we investigated NaCl, NaBr, and NaI systems, finding anion propensity for the air-water interface was reduced in comparison with previously developed polarizable models. This coincided with a more negative surface excess than that given by previously developed polarizable models. Furthermore, we investigated the interfacial properties of SrCl2 aqueous systems, finding that strontium had a moderate enhancement in interfacial density in comparison with bulk, while still having a fairly large negative surface excess, in agreement with experimental results.

Poklis and Backer published a survey of the concentrations of fentanyl and norfentanyl that could be expected in urine from patients using Duragesic, a transdermal fentanyl patch. That study employed a relatively small number of patient data points and analysis by Gas Chromatography/Mass Spectrometry. This work examines a larger population of patient positives for fentanyl and norfentanyl to determine whether more than a decade later the original report remains accurate in predicting the range and median levels of fentanyl and norfentanyl concentrations physicians can expect to see from their patients. Additionally, these data were transformed to develop a model that results in a near Gaussian distribution of urine drug test results. This retrospective approach was developed to transform and normalize urine drug testing results to provide a historical picture of expected patient values for this important analgesic. The resulting near Gaussian distribution is dose independent and as such should be of value to physicians in quickly assessing whether their patient is consistent with this historical population in the broad terms of this model. While this comparison alone is not definitive for adherence with a treatment regimen, together with patient interviews, prescription history and other clinical criteria, it can add an idea of expected patient values from urine drug testing.