No abstract

Combination of commercial QSPR (quantitative structure−property relationship) software with an evaluated database creates a powerful tool for development of thermophysical property correlations. By using data quality codes in the DIPPR relational database, a training set of property values within a desired accuracy level can be obtained for use in QSPR regression software. Moreover, additional database queries can be used to restrict the training set to specified families or functional groups and further refine the molecular descriptors that are used to correlate the property. This provides a good basis for rapid development of QSPR correlations of known uncertainty and chemical domain. This procedure is illustrated by its application to the extension of the Macleod−Sugden (Trans. Faraday Soc. 1923, 19, 38. Chem. Soc. 1924, 125, 32.) correlation for surface tension based upon the parachor. Quayle (Chem. Rev. 1953, 53, 439−591.) correlated the parachor in terms of additive atomic and structural increments but used a training set limited in temperature and scope. In this work, new molecular descriptors were selected consistent with the accuracy of the training set extracted from the DIPPR database, and their additive increments to the parachor were regressed from 8697 surface tension values of uncertainty less than 5% for 649 different compounds. This produced a correlation with an average absolute deviation (AAD) of 3.2%. This can be compared with an AAD of 6.9% using the Quayle descriptors for the same set.

Using periodic boundary conditions and a constant applied field, we have simulated current flow through an 8.125-A internal diameter, rigid, atomistic channel with polar walls in a rigid membrane using explicit ions and extended simple point charge water. Channel and bath currents were computed from 10 10-ns trajectories for each of 10 different conditions of concentration and applied voltage. An electric field was applied uniformly throughout the system to all mobile atoms. On average, the resultant net electric field falls primarily across the membrane channel, as expected for two conductive baths separated by a membrane capacitance. The channel is rarely occupied by more than one ion. Current-voltage relations are concentration dependent and superlinear at high concentrations.

The flash point is an important indicator of the flammability of a chemical. For safety purposes, many data compilations report the lowest value and not the most likely. This practice, combined with improper documentation and poor data storage methods, has resulted in compilations filled with fire-hazard data that are inconsistent with related properties and between members of homologous chemical series. In this study, the flash points reported in the DIPPR 801 database and more than 1,400 other literature values were critically reviewed based on measurement method, inter-property relations, and trends in chemical series. New measurements for seven compounds illustrate the differences between experimental flash points and data commonly found in fire-hazard compilations. With a critically reviewed set of experimental data, published predictive methods for the flash point were evaluated for accuracy.

We investigate the interfacial electrochemical properties of an aqueous electrolyte solution with discrete water molecules in slab geometry between charged atomistic electrodes. Long-range intermolecular Coulombic interactions are calculated using the particle-particle-particle-mesh method with a modification to account for the slab geometry. Density distribution profiles and potential drops across the double layer are given for 0, 0.25, and 1 M aqueous electrolyte solutions each at 0, Ϯ0.1, Ϯ0.2, and Ϯ0.3 C/m 2 electrode surface charges. Results are compared qualitatively with experimental x-ray scattering findings, other computer simulation results, and traditional electrochemistry theory. The interfacial fluid structure characteristics are generally in good qualitative agreement with the conclusions obtained in some integral equation theories and in the experimental x-ray study. The potential in the simulations shows an oscillatory behavior near the electrode, which theories that do not include the molecular nature of water cannot reproduce for the given conditions. Surprisingly, the results also show that the water structure near the electrode is dominated by the charge on the electrode and is fairly insensitive to the ion concentrations. Except at large electrode charge, the potential drop across the double layer does not depend significantly upon the concentration of the ions.