Separation of chloroform from a dilute solution using a cyclic peptide nanotube: A molecular dynamics study.

This work firstly explored the potential application of a cyclic peptide nanotube (CPNT) in the separation of chloroform from a dilute solution. Four hydrophobic CPNTs of 8 × (WL)4,5 and 8 × (AL)4,5 all exhibit excellent adsorption characteristics to chloroform. The CPNT diameter, side chain structures and the concentration of chloroform in a solution all affect the adsorption characteristics of chloroform. CHCl3 molecules are overwhelmingly adsorbed on the surfaces of these CPNTs as a cluster, and sporadically reside inside the channels, consistent with the chloroform's potentials of mean force (PMFs) inside and outside the channels. The distribution characteristics, molecular orientations and interactions with the surroundings of chloroform inside and outside four CPNTs embedded in individual dilute CHCl3/water solutions were analyzed in detail, providing referable information of the adsorption characteristics of a hydrophobic CPNT to chloroform.

Transport properties of simple organic molecules in a transmembrane cyclic peptide nanotube.

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.

[Application of miniscrew for extraction of mesially impacted wisdom tooth adjacent to the inferior alveolar nerve canal].

PURPOSE: To study the value of miniscrew for extraction of mesially impacted wisdom tooth adjacent to the inferior alveolar nerve canal. METHODS: Fourteen mesially impacted wisdom teeth were proven to be adjacent to the inferior alveolar nerve canal by means of cone-beam CT scan. The treatment began with the miniscrew traction of the wisdom teeth. After 2-5 months, they were moved away from the canal and then extracted. RESULTS: After extraction, all 14 cases did not show any obvious side effect. CONCLUSIONS: Application of miniscrew traction is a valuable method for minimally invasive extraction of mesially impacted wisdom tooth that is adjacent to the inferior alveolar nerve canal.

Cyclo-hexa-peptides at the water/cyclohexane interface: a molecular dynamics simulation.

Molecular dynamic (MD) simulations have been performed to study the behaviors of ten kinds of cyclo-hexa-peptides (CHPs) composed of amino acids with the diverse hydrophilic/hydrophobic side chains at the water/cyclohexane interface. All the CHPs take the "horse-saddle" conformations at the interface and the hydrophilicity/hydrophobicity of the side chains influences the backbones' structural deformations. The orientations and distributions of the CHPs at the interface and the differences of interaction energies (ΔΔE) between the CHPs and the two liquid phases have been determined. RDF analysis shows that the H-bonds were formed between the O(C) atoms of the CHPs' backbones and H(w) atoms of water molecules. N atoms of the CHPs' backbones formed the H-bonds or van der Waals interactions with the water solvent. It was found that there is a parallel relationship between ΔΔE and the lateral diffusion coefficients (D ( xy )) of the CHPs at the interface. The movements of water molecules close to the interface are confined to some extent, indicating that the dynamics of the CHPs and interfacial water molecules are strongly coupled.

Investigation on the micro-mechanisms of Al(3+) interfering the reactivities of aspartic acid and its biological processes with Mg(2+).

Density functional theory (DFT) has been applied to study the micro-mechanisms of Al3+ interfering the reactivities of aspartic acid (H2asp) and its biological processes with Mg2+. All the 46 stable conformers of Hasp- and 3 of asp2- have been determined at the B3LYP/6-311++G** level, showing that the 7 most stable conformers of Hasp- all present a very strong and linear O-H...O H-bond between carboxyl and carboxylic acid groups with the bond energy high up to 162 kJ mol(-1). The reaction thermodynamics and micro-mechanism between Al3+ and Hasp- (or asp2-) in aqueous phase have been investigated by the combined application of supramolecular model and polarizable continuum IEFPCM solvent model, firstly revealing Al3+ interfering in the biological processes of aspartic acid. The substitution thermodynamics and mechanisms of Mg2+ by Al3+ in the biological processes between the species of aspartic acid and Mg2+ in aqueous phase were probed, revealing the facile displacement of Mg2+ by Al3+. These results may provide a reasonable mechanism of Al3+ biological toxicity at the microscopic level.

Theoretical insight into the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of aldol reactions.

Density functional theory has been applied to study the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of the (S)-proline-catalyzed direct aldol reactions. Reaction scenarios of three kinds of aliphatic aldehydes were investigated. Four transition states associated with the stereocontrolling step of each reaction have been obtained. They are corresponding to the syn and anti arrangements of enamine intermediates and the si and re attacks to the carbonyl group of an aldehyde. The solvent effect of DMSO was investigated using self-consistent reaction field method based on the polarizable continuum model. The computed energies of transition states explain the origin of the catalysis and enantioselectivities for these (S)-proline-catalyzed aldol reactions and reveal the influences of alpha-substituents in aliphatic aldehydes on the enantioselectivities of these reactions.