A kinetic and mechanistic investigation of the alcoholysis of phenyl isocyanate using 1-propanol as the alcohol was undertaken. A molecular mechanism of urethane formation in both alcohol and isocyanate excess is explored using a combination of an accurate fourth generation Gaussian thermochemistry (G4MP2) with the Solvent Model Density (SMD) implicit solvent model. These mechanisms were analyzed from an energetic point of view. According to the newly proposed two-step mechanism for isocyanate excess, allophanate is an intermediate towards urethane formation via six-centered transition state (TS) with a reaction barrier of 62.6 kJ/mol in the THF model. In the next step, synchronous 1,3-H shift between the nitrogens of allophanate and the cleavage of the C–N bond resulted in the release of the isocyanate and the formation of a urethane bond via a low-lying TS with 49.0 kJ/mol energy relative to the reactants. Arrhenius activation energies of the stoichiometric, alcohol excess and the isocyanate excess reactions were experimentally determined by means of HPLC technique. The activation energies for both the alcohol (measured in our recent work) and the isocyanate excess reactions were lower compared to that of the stoichiometric ratio, in agreement with the theoretical calculations.

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1,4-dioxane is a cytotoxic B2 type human carcinogen, a serious water pollutant produced solely by industrial activity. The effect of 1,4-dioxane on phospholipid membrane models composed by DPPC and its branched isomer (IPPC) was investigated using MD simulations. Clear and polluted membranes were compared by membrane parameters such as APL, VPL, compressibility modulus, membrane thickness and orderliness of lipid tails. While neat systems significantly differ from each other, the presence of the pollutant has the same effect on both types of lipid membranes: high density of dioxane appears at the vicinity of ester groups which pushes away lipid headgroups from each other, leading to an overall change in lipid structure: APL and VPL grows, while the orderliness of lipid tails, membrane thickness and compressibility modulus decreases. Orientational preferences of water and dioxane molecules were also investigated and different membrane regions have been specified according to the stance of water molecules. Free energy profile for 1,4-dioxane penetration mechanism into DPPC membranes was carried out using metadynamics for two different concentrations of the pollutant (c 1 =7.51 g/dm 3 , c 2 =75.10 g/dm 3), which showed that the higher the concentration is, the lower the free energy of penetration gets. Only a small free energy barrier was found in the headgroup region and accumulation of dioxane is thermodynamically unfavored in the middle of the bilayer. The penetration mechanism has been described in detail based on the orientational preference of 1,4-dioxane molecules and the free energy profiles.

The presence of industrially produced chemicals in water is often not monitored while their passive transport and accumulation can cause serious damage in living cells. Molecular dynamics simulations make an...

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