A 200 ps molecular dynamics simulation of a membrane bilayer consisting of 202 dilauroylphosphatidylethanolamine molecules and 8108 water molecules at 315 K is conducted. Distribution functions of lipid groups, order parameters, and other properties of the lipid bilayer are calculated and compared with experimental measurements. A detailed analysis is conducted for the structure at the membrane-water interface. Water polarization profile, membrane dipole potential profile, and susceptibility profile are calculated. Simulation results suggest that the polarization of water is determined mainly by the distribution of lipid head groups in the interfacial region. The membrane dipole potential is mainly due to the ester groups linked to the glycerol backbone, while the contribution due to the phosphatidylethanolamine head groups is almost completely cancelled by the contribution due to oriented water molecules. The susceptibility profile suggests a dielectric constant around 30 for the head group-water interface and a dielectric constant around 10 for the ester group region. The ammonium groups of the DLPE membrane are found to form hydrogen bonds with water molecules, while no orientational preference is observed for water molecules around the choline groups of a previously simulated POPC ( 1 -palmitoyl-2-oleoyl-sn-glycerol-3-phosphatidylcholine) membrane. Correlations of the membrane surface charge density are also analyzed. The simulations which involved 32 808 atoms included Coulombic forces between all atom pairs evaluated by means of the fast multipole algorithm. Effects of cutting off Coulombic forces at a distance of 8 A are discussed.

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Lead-free perovskites have recently been successfully applied in radiation detection and light emitting devices.

Single chain Janus nanoparticles (SCJNPs) (tadpole-like Janus nanoparticles) with a PEO (poly(ethylene oxide)) chain as the “tail” and a cross-linked PCEMA (poly(2-cinnamoyloxyethyl methacrylate)) chain as the “head” were synthesized conveniently and efficiently by directly photo-cross-linking PCEMA block of PEO-b-PCEMA diblock copolymer in the common solvent DMF; intramolecular cross-linking occurred dominantly at a relatively high concentration of the copolymer when the cross-linking speed is relatively low, leading to SCJNPs. In selective solvent for the “tails”, the rigid “heads” aggregated into superparticles. It is significant that under a gentle ultrasonic treatment (40 kHz for 10 min) the spherical superparticles formed in DMF/ethanol (1/4, v/v) dissociated into individual SCJNPs. It is also demonstrated that even in pure water in which the superparticles have a more closely aggregated structure, there are still hydrophilic channels within the superparticles connecting the surrounding medium and the inside of the superparticles, which allows rapid transport of hydrophilic small molecules within the superparticles, as demonstrated by the fast acid quench of fluorescence of the encapsulated ANS (8-anilino-1-naphthalenesulfonate). These features should make the superparticles promising in the applications as templates for biomimetic mineralization, highly efficient microreactors for interfacial chemical reactions, and ultrasound responsive nanovehicles for controlled drug release.

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The desolvation of lipid molecules in a complex of the enzyme human synovial phospholipase A2 with a lipid membrane is investigated as a mechanism that enhances the overall activity of the enzyme. For this purpose the interaction of the enzyme phospholipase A2 with a dilauryl‐phosphatityl‐ethanolamin (DLPE) membrane monolayer surface has been studied by means of molecular dynamics simulations. Two enzyme‐membrane complexes, a loose and a tight complex, are considered. For comparison, simulations are also carried out for the enzyme in aqueous solution. The conformation, dynamics, and energetics of the three systems are compared, and the interactions between the protein and lipid molecules are analyzed. Free energies of solvation are calculated for the lipid molecules in the enzyme–membrane interface. Along with the calculated dielectric susceptibility at this interface, the results show the desolvation of lipids in a tightly bound, but not in a loosely bound protein‐membrane complex. The desolvated lipids are found to interact mainly with hydrophobic protein residues, Including Leu‐2, Val‐3, Ala‐18, Leu‐19, Phe‐24, Val‐31, and Phe‐70. The results also explain why the turnover rate of phospholipase A2 complexed to a membrane is enhanced after a critical amount of negatively charged reaction product is accumulated. © 1996 Wiley‐Liss, Inc.

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