Multiple molecular dynamics simulations have been performed to explore the transport properties of single methane, methanol, and ethanol molecules through the water-filled transmembrane cyclic peptide nanotube (CPNT) of 8 × (WL)₄-POPE, as well as the potential application of this CPNT in the separation of an alcohol/water mixture. Molecular size and hydrophilicity/hydrophobicity were found to significantly influence molecular diffusion behavior in the channel. Methane and ethanol display more explicit distributions in midplane regions, while methanol mainly occurs in α-plane zones. Methane and ethanol drift faster near an α-plane zone, whereas methanol diffuses uniformly throughout the whole transmembrane region. The dipole orientation of channel methanol is significantly affected by the bare carbonyl groups at the tube mouths and flips mainly in gap 4, whereas the rotation of ethanol is blocked. Ball-shaped hydrophobic methane experiences more flips in gap 4. The PMF (potential of mean force) profiles of the three organic molecules disclose their different diffusion behaviors in the CPNT. Amphiphilic alcohols are able to form direct H-bonds with channel water and the tube. Both single and double water bridges with the tube were observed in the methanol and ethanol systems. The different adsorption behaviors of the alcohols and water in the dehydrated CPNT may lead to the potential application of the CPNT as a means of separating alcohols from water.
The similarities and differences of pnicogen and tetrel bonds formed by carbenes CX2 with H3AsO and H3SiCN were investigated by carrying out ab initio calculations in association with topological analysis of electron density.
The properties of some types of noncovalent interactions formed by triplet diphenylcarbene (DPC 3 ) have been investigated by means of density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) studies. The DPC 3 •••LA (LA = AlF 3 , SiF 4 , PF 5 , SF 2 , ClF) complexes have been analyzed from their equilibrium geometries, binding energies, charge transfer and properties of electron density. The triel bond in the DPC 3 •••AlF 3 complex exhibits a partially covalent nature, with the binding energy − 65.7kJ/mol. The tetrel bond, pnicogen bond, chalcogen bond and halogen bond in the DPC 3 •••LA (LA = SiF 4 , PF 5 , SF 2 , ClF) complexes show the character of a weak closed-shell noncovalent interaction.Polarization plays an important role in the formation of the studied complexes. The strength of intermolecular interaction decreases in the order LA = AlF 3 > ClF > SF 2 > SiF 4 > PF 5 . In the process of complexation, the charge transferrs from DPC 3 to the antibonding orbital of AlF 3 /SF 2 /ClF, the quantity of charge transfer is very small between DPC 3 and SiF 4 /PF 5 . The electron spin density transferrs from the radical DPC 3 to ClF and SF 2 in the formation of halogen bond and chalcogen bond, but for the DPC 3 •••AlF 3 /SiF 4 /PF 5 complexes, the transfer of electron spin density is minimal.
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