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As the major stabilizer for crude oil emulsion in petroleum industry, asphaltene has been concerned more widespread with the increasing demand of energy in the world. The in-depth understanding on its properties at crude oil-water interface has some beneficial effect on dealing with the emulsion in oil industry. To investigate these interfacial properties at molecular level, molecular dynamics (MD) simulation was utilized. The results show that asphaltene molecules tend to different orientation between them at this interface so as to decrease the repulsive force of aggregation process. Moreover, the contributors to asphaltene stability at crude oil-water interface also were discussed. It mainly includes hydrogen bond networks around asphaltene polar group. The hydrogen bond networks behave like an anchor to grab hold of asphaltene at the interface. The aggregation properties of asphaltene at oil-water interface were obtained by using the umbrella sampling method. The results indicate that aggregation state is most stable for asphaltene molecules at oil-water interface and the system free energy will increase after the aggregate be broken. [ABSTRACT FROM AUTHOR]

Bioaccumulation of perfluoroalkyl and polyfluoroalkyl substances (PFASs) is an important indicator of their hazard. Partitioning to membrane phospholipids is one of the pathways for their bioaccumulation. However, the molecular mechanism on PFASs uptake into membrane phospholipids is not yet to be fully understood. In this work, we used molecular dynamics (MD) simulations to study the uptake processes of PFOS and its alternatives (6:2 Cl-PFESA and OBS) into DPPC bilayers, and to evaluate their interaction with DPPC bilayers and their effect on properties of DPPC bilayers. The result of free energy changes shows that a barrier of 2–3 kcal mol−1 exists when these adsorbed PFASs on the surface are absorbed into DPPC bilayers. After incorporating into DPPC bilayers, three DPPC molecules interact with and thus stabilize a PFOS (or 6:2 Cl-PFESA or OBS) molecule. And another role of the three DPPC molecules is to shield these PFASs from exposure to water environment. These PFASs have the similar condensing effect on the model membrane. The molecular-level study is beneficial for understanding the bioaccumulation and toxicity of PFOS and its alternatives. [Display omitted] • The uptake of PFOS, 6:2 Cl-PFESA and OBS into DPPC bilayers is easy to happen. • A barrier of 2–3 kcal mol−1 needs to be overcome during the uptake processes. • Three DPPC molecules interact with a PFOS (or 6:2 Cl-PFESA or OBS) molecule. • A role of three DPPC molecules is to shield PFASs from exposure to water molecules. • PFOS, 6:2 Cl-PFESA and OBS have the similar condensing effect on DPPC bilayers. [ABSTRACT FROM AUTHOR]

H 2 SO 4 is an important pollutant in the atmosphere, and it mainly be formed through the oxidation of SO 2. SO 3 produced from the oxidation of SO 2 is a precursor of H 2 SO 4. Considering that understanding of SO 3 hydration reaction at the air-water interface is limited, we combined the classical molecular dynamics simulations (classical MD) with Born–Oppenheimer MD simulations and ab initio calculations to study the SO 3 reaction with H 2 O at air-water interface. The free energy and impinging results indicate that the SO 3 molecules can easily be trapped by water droplets. After uptake by the interface, the SO 3 can react rapidly with water molecules to form the ion pair of HSO 4 − and H 3 O+ or H 2 SO 4 within a few picoseconds. In the interfacial hydration mechanism, the loop-structure formation is not prerequisite of the hydration reaction, which is obviously different from the corresponding gas-phase hydration reaction of SO 3. The work is meaningful for understanding the heterogeneous formation of H 2 SO 4 and the contribution of interfacial reaction to the new particle formation. • SO 3 can easily be trapped by water droplets. • The SO 3 hydration mechanism at the air-water interface was considered. • The loop-structure formation is not prerequisite of interfacial hydration of SO 3. [ABSTRACT FROM AUTHOR]