Dynamic spreading of a nanosized droplet on a solid in an electric field.

Molecular dynamic simulations are performed for the dynamic spreading of a nanosized water droplet subject to a parallel electric field. The results show that the droplet spreads asymmetrically in a weak field but symmetrically in a strong field. The initial conditions affect the dynamic spreading behavior but not the final equilibrium shapes.

Molecular dynamics simulation of the electrically induced spreading of an ionically conducting water droplet.

Molecular dynamics simulations are applied to study the spreading behavior of a nanosized water droplet that contains freely moving Na(+)/Cl(-) ions subject to an imposed electric field parallel to a solid surface. Results show that the positive and negative ions move relatively freely in response to an applied electric field, whereas polar water molecules realign themselves. These localized behaviors of the ions and the polar molecules are affected by both the applied electric field strength and the ion concentration, which in turn determine the deformation and spreading of the droplet on a solid substrate. The presence of the freely moving ions causes the ion-containing droplet to spread differently from a droplet of pure water. In a weak electric field of 0.05 V/Å, a droplet of a lower ion concentration spreads asymmetrically and the spreading asymmetry is considerably smaller than that associated with a pure water droplet of the same size. In a stronger field of 0.1 V/Å, a droplet of a higher ion concentration spreads symmetrically and completely wets the solid surface whereas a less ionically conducting droplet undergoes an asymmetric-to-symmetric transition in spreading until it reaches equilibrium.

Molecular dynamics simulation of nanosized water droplet spreading in an electric field.

Molecular dynamics (MD) simulations are performed for the spreading of a nanosized water droplet on a solid substrate subject to a parallel electric field. A combined electrostatic and Lennard-Jones potential is employed to represent the intermolecular interactions. Results show that in response to the applied field, polar water molecules realign themselves and this microscopic reorientation of molecular dipoles combines with the intermolecular forces to produce a macroscopic deformation of a free spherical water droplet into an ellipsoid. The applied field has a strong effect on the spreading of the water droplet on a solid substrate. For a weaker parallel field, the droplet spreading is asymmetric with the leading contact angle being greater than the trailing contact angle. With an increase in field strength, this asymmetry continues to increase, culminates, and then decreases until it disappears. The symmetric spreading remains with a further increase in the field strength until the saturation point is reached. This transition from the asymmetric to symmetric spreading is a manifestation of the interaction of the electric field with polar water molecules and the intermolecular forces within the droplet and between the water and solid; the interaction also leads to a change in hydrogen bonds along the droplet surface. The dynamics of the droplet spreading is entailed by the electrically induced motion of molecules along the liquid surface toward the solid substrate and is controlled by a competing mechanism among the electric, water-water, and water-solid intermolecular forces.

Single sevoflurane exposure decreases neuronal nitric oxide synthase levels in the hippocampus of developing rats.

BACKGROUND: The use of general anaesthetics in young children and infants has raised concerns regarding the adverse effects of these drugs on brain development. Sevoflurane might have harmful effects on the developing brain; however, these effects have not been well investigated. METHODS: Postnatal day 7 (P7) Sprague-Dawley rats were continuously exposed to 2.3% sevoflurane for 6 h. We used the Fox battery test and Morris water maze (MWM) to examine subsequent neurobehavioural performance. Cleaved caspase-3 and neuronal nitric oxide synthase (nNOS) were quantified by immunoblotting, and the Nissl staining was used to observe the histopathological changes in the hippocampus. RESULTS: A single 6 h sevoflurane exposure at P7 rats resulted in increased cleaved caspase-3 expression and decreased nNOS levels in the hippocampus, and induced the loss of pyramidal neurones in the CA1 and CA3 subfields of the hippocampus at P7-8. These changes were accompanied by temporal retardation of sensorimotor reflexes. However, neither the Fox battery test at P1-21 nor the MWM test at P28-32 showed differences between the air- and sevoflurane-treated groups. CONCLUSIONS: Although early exposure to sevoflurane increases activated caspase-3 expression and neuronal loss and decreases nNOS in the neonatal hippocampus, it does not affect subsequent neurobehavioural performances in juvenile rats.

Intrathecal application of short interfering RNA knocks down c-jun expression and augments spinal motoneuron death after root avulsion in adult rats.

The immediate-early gene, c-jun, is expressed in spinal motoneurons after spinal root avulsion. The expression of c-jun was suggested to be necessary for motoneuron survival and regeneration after avulsion. In the present study, a small interfering RNA (siRNA) was delivered intrathecally to the injured spinal segments immediately after root avulsion in rats to knock down expression of the c-jun gene in injured spinal motoneurons so as to explore the role of c-jun in the motoneurons in vivo. Our results showed that the siRNA not only inhibited the expression of both c-jun mRNA and protein but also augmented the death of injured motoneurons at day 14 post-injury. These findings indicated that induction of c-jun gene expression plays a pivotal role in the survival of injured motoneurons. Meanwhile, these results suggest that siRNAs applied intrathecally can effectively mediate the expression of the c-jun gene in injured motoneurons.

Chemical constituents of the brown alga Dictyopteris divaricata.

A novel sesquiterpene-substituted benzoic acid, named dictyvaric acid (1), together with nine known compounds (2-10), have been isolated from the brown alga Dictyopteris divaricata Okam. The structure of 1 was elucidated as 3-[(decahydro-2-hydroxy-2,5,5,8a-tetramethyl-1-naphthalenyl)-methyl]-4-hydroxybenzoic acid by spectroscopic methods, including IR, FABMS, HR-FABMS, 1D and 2D NMR techniques. All compounds were obtained from this species for the first time.