Kinetic description of water transport during spontaneous emulsification induced by Span 80.

Spontaneous emulsification is a phenomenon that forms nanometer-sized droplets (nanodroplets) without the application of any external force, and the mechanism has been actively studied for application to various technologies. In this study, we analyzed the kinetics of spontaneous emulsification induced by Span 80. The measurement of water concentration in Span 80 hexadecane solution indicated that the chemical potential of water in the nanodroplets decreased as the amount of water in the nanodroplets decreased. Based on this result, water transport between the aqueous phase and nanodroplets in which the chemical potential of water was controlled was quantitatively investigated by using a microfluidic device. The results demonstrate that the kinetics of water transport during spontaneous emulsification induced by Span 80 was described by a model of osmotic transport through an organic liquid film between the aqueous phase and nanodroplets.

Free-Energy Analysis of Peptide Binding in Lipid Membrane Using All-Atom Molecular Dynamics Simulation Combined with Theory of Solutions.

All-atom molecular dynamics (MD) simulations are performed to examine the stabilities of a variety of binding configurations of alamethicin, a 20-amino-acid amphipathic peptide, in the bilayers of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1,2-dimyristoyl- sn-glycero-3-phosphatidylcholine (DMPC). The binding free energy of alamethicin is calculated through a combination of MD simulation and the energy-representation theory of solutions, and it is seen that the transmembrane configuration is stable in both membranes. A surface-bound state is also found to be stable due to the balance between the attractive and repulsive interactions of the peptide with lipid and water, and the key role of water is pointed out for the stability in the interfacial region. A difference between the POPC and DMPC systems is noted when the polar C-terminal domain is buried in the hydrophobic region of the membrane. In POPC, the peptide is unfavorably located with that configuration due to the loss of electrostatic interaction between the peptide and lipid.

[A Case of Sigmoid Colon Cancer Identified by Gastric Perforation].

We report a case of sigmoid colon cancer that was incidentally found using CT that was performed for upper abdominal pain. An 83-year-old man with a long history of lung tuberculosis and idiopathic pulmonary fibrosis presented with upper abdominal pain. CT findings revealed free gas around the stomach. He was diagnosed with upper gastrointestinal perforation and his condition improved after undergoing conservative treatment. Upper endoscopy revealed an irregular ulcer at the angular incisure of the stomach with thickened folds, but biopsy resulted in a Group 1 classification. CT findings also incidentally revealed sigmoid colonic wall thickness, and colonoscopy showed a type Ⅰ lesion in the sigmoid colon, which biopsy resulted in Group 5, and we performed sigmoidectomy for sigmoid colon cancer under a combination of spine-subarachnoid and epidural anesthesia because of his respiratory dysfunction.

Critical nucleus size for crystallization of supercooled liquids in two dimensions.

Using molecular dynamics simulations, we study the crystallization of supercooled liquids in two dimensions in which particles interact with other particles via the Lennard-Jones-Gauss potential. We first prepare supercooled liquids at various temperatures by rapid quenching from the melt. The simulations are performed with a crystalline seed inserted at the center of the initial system. We investigate the time evolution of the inserted nucleus and its surroundings and determine the critical nucleus size n_{c} defined as the smallest nucleus which survives. The results show that n_{c} scales as ∼(T_{m}-T)^{-2} with the melting temperature T_{m}, as expected in the classical nucleation theory. We also obtain the crystallization time at various temperatures as a function of nucleus size and show that the presence of a crystalline seed significantly affects the crystallization time when the temperature is higher than the characteristic temperature T^{*} at which the crystallization time becomes the shortest. This indicates that the crystallization is controlled by thermodynamics in this temperature range. When the temperature is lower than T^{*}, the effect of the inserted nucleus on crystallization is less significant, which indicates that crystallization is controlled by emergence and merging of small crystalline nuclei.

Glass formation and crystallization of a simple monatomic liquid.

A simple monatomic system in two dimensions with a double-well interaction potential is investigated in a wide range of temperatures by molecular-dynamics simulation. The system is melted and equilibrated well above the melting temperature, and then it is quenched to a temperature 88% below the melting temperature at several cooling rates to produce an amorphous state. Various thermodynamic quantities are measured as functions of temperature while the system is heated at a constant rate. The glass transition is observed with a sudden increase in the energy and the glass transition temperature is shown to be an increasing function of the cooling rate in the preparation process of the amorphous state. In a relatively high-temperature region, the system gradually transforms into crystals, and the time-temperature-transformation curve shows a typical nose shape. It is found that the transformation time to a crystalline state is the shortest at a temperature 14-15 % below the melting temperature and that at sufficiently low temperatures the system does not transform into a crystalline state within an observation time in our simulation. This indicates that a long-lived glassy state is realized.