Dissipative particle dynamics (DPD) was carried out to study systems containing gold atoms, organic ether (oligohydroquinonyl ether terminated with a thiol group) and organic solvents. The components in the simulated system are very different in size and chemical nature. Our simulation showed that the reproduction of the macroscopic experimental phase separation, properly dividing the polymeric molecule into beads, selecting the size of gold bead, and choosing the appropriate interaction parameters between beads are crucial. In addition, the solvent effect was the dominant factor for the formation of spherical aggregates of Au atoms and organic ether molecules. We report the interaction strengths between the solvent and gold clusters. Our work has demonstrated that DPD methods can be applied to the study of complex meso-scale systems.

Beta-defensins are important part of innate immunity of fish, which are the first defense line against invading pathogens. In this study, the β-defensin (Lhβ-defensin) gene was cloned from spleen tissue of soiny mullet (Liza haematocheila). Lhβ-defensin cDNA was 747 bp in length, encoding 63 amino acids. Sequence alignment revealed that Lhβ-defensin contained six conserved cysteine residues and shared 97.5% sequence identities with grouper (Epinephelus coioides) β-defensin. Realtime PCR revealed that Lhβ-defensin was highest expressed in the immune related organs, such as spleen, kidney and gut of healthy fish. Following Streptococcus dysgalactiae infection, Lhβ-defensin was up-regulated in immune related organs, e.g. 17.6-fold in spleen and 10.87-fold in gut at 24 h post infection (hpi). Lhβ-defensin possessed a monomeric structure of a three-stranded anti-parallel β-sheet and an α-helix stabilized by three disulfide bonds formed by Cys30-Cys58, Cys36-Cys52, and Cys40-Cys59. In addition to the experimental work, computer simulation was also carried out to determine the possible conformation of β-defensin and its interaction with palmitoyloleoylphosphatidylglycerol (POPG), a model of bacteria membrane. The Lhβ-defensin was found to form dimeric structure stabilized by the van der Waals contacts of Leu35 and Cys37 in two anti-parallel β1-strands and the cation-π interaction between Tyr32 and Arg54 respectively in the two β1-strands. The most important interactions between β-defensin and membrane are the electrostatic interactions between Arg residues in β-defensin and head group of POPG bilayer as well as hydrogen bond interactions between them. Our results were useful for further understanding the potential mechanism of antimicrobial property of fish β-defensins.

The study conducted a molecular dynamics simulation based on a condensed-phase optimised molecular potentials for atomistic simulation studies force field model to investigate an anhydrous system of phosphoric acid-doped polybenzimidazole (poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole], PBI). Intermolecular pair correlation functions and corresponding coordination numbers were calculated to research the strengths for various types of hydrogen bonding. The results display that the strengths of the hydrogen bonding interactions are in the order of o1–h pair > o2–h pair > n2a–h pair > n3a–h pair, and most protons are located around the neighbourhood of H₂PO₄^– rather than that of PBI. The proton conductivities are 3.86 × 10⁻³ S cm⁻¹ at 298 K and 8.50 × 10⁻³ S cm⁻¹ at 413 K. Moreover, the value obtained from our simulation system at 413 K is within the same order of magnitude as the experimentally measured value 0.012 S cm⁻¹ at 420% doping level. The distribution of proton displacement exhibits that the displacement of most protons is about 1.25–2.5 Å. The displacement is over 3.0 Å only for a fraction of protons. In addition, the greatest displacement can approach 4.595 Å. The trajectory analyses of protons show that the most possible mechanisms of proton transfer come from three ways: (a) between two H₂PO₄^– anions, (b) between H₂PO₄^– anions and benzimidazole moieties and (c) between two benzimidazole moieties. The dynamics of polymer motion was studied by the trajectory analyses of ring flips. The large amplitude flips of rings in the polymer chains were found in the system. The flips between benzene and benzimidazole are more frequent than that between benzimidazole moieties.

Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.