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Methylguanidinium is an important molecular ion which also serves as the model compound for arginine side chain. We studied the structure and dynamics of methylguanidium ion at the air/water interface by molecular dynamics simulations employing the Drude polarizable force field. We found out that methylguanidinium accumulate on the interface with a majority adopting tilted conformations. We also demonstrated that methylguanidinium and guanidinium ions have different preference towards the air/water interface. Our results illustrate the importance to explicitly include the electronic polarization effects in modeling interfacial properties. File list (2)download file view on ChemRxiv mguan.v2.pdf (6.67 MiB) download file view on ChemRxiv si. mguan.v2.pdf (8.42 MiB)

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Adopting BYLP method in Density Functional Theory (DFT), we make theoretical study on the ozonide-orthophenylphenol, parachlorophenol, orthobenzoquinone and parabenzoquinone in the two reaction routes of phenol oxidizing into benzoquinone with ozone. We get the geometric configuration of molecules, charge distribution of atoms, thermodynamical properties and frontier orbit energy. Natural Bond Orbital(NBO)charge calculation shows that compared with orthobenzoquinone and parabenzoquinone molecules, phenol, orthophenylphenol and parachlorophenol molecules have stronger reactivity and they are more likely to have electrophilic substitution reaction. Thermodynamic properties indicate that phenol is easy to have oxidation reaction and produce orthophenylphenol which is easily to oxidize into orthobenzoquinone no matter at low temperature, room temperature or high temperature. Another reaction pathwaycalculation shows that in thermodynamics, phenol will not easily ozonize into parachlorophenol; while parachlorophenol will easily ozonize into parabenzoquinone. Frontier orbit energy calculation shows that phenol, orthophenylphenol, and parachlorophenol show similar stability. Orthobenzoquinone and parabenzoquinone have the strongest stability.