One of the major simplifications of CG models is the representation of the solvent, which is either implicit or modeled explicitly as a van der Waals particle. The effect of polarization, and thus
a proper screening of interactions depending on the local environment, is absent. Given the important role of water as a ubiquitous solvent in biological systems, its treatment is crucial selleck chemicals to the properties derived from simulation studies. Here, we parameterize a polarizable coarse-grained water model to be used in combination with the CG MARTINI force field. Using a three-bead model to represent four water molecules, we show that the orientational polarizability of real water can be effectively accounted for. This has the consequence that the dielectric screening of bulk water is reproduced. At the same time, we parameterized our new water model such that bulk water density and oil/water partitioning data remain at the same level of accuracy as for the standard MARTINI force field. We apply the new model to two cases for which current CG force fields are inadequate. First, we address the transport of ions across a lipid membrane. The computed potential of mean force shows that the ions now naturally feel the change in dielectric medium when moving from the high dielectric aqueous phase toward Selleckchem GSK461364 the low dielectric membrane interior. In the second
application we consider the electroporation process of both an oil slab and a lipid bilayer. The electrostatic field drives the
formation of water filled pores in both cases, following a similar mechanism as seen with atomistically detailed models.”
“Using electric field-induced second harmonic Cediranib cost generation (EFISHG) measurements, we directly probed a time-varying space charge field responsible for carrier injection followed by radiative recombination (electroluminescence; EL). Experiments using tetracene as the active layer of a top-contact field-effect transistor with application of a pulsed voltage showed that a space charge field remained around the source electrode-caused by injected holes, but not by electrons. Observing the time-varying EFISHG intensity at the electrodes clearly showed that the space charge field formed in the vicinity of the electrodes made a dominant contribution to the opposite-polarity carrier injection, directly leading to EL around the electrodes by carrier recombination. We concluded that EFISHG measurement is useful for probing carrier behavior in luminescent materials, by eliminating two-photon excited photoluminescence from the material induced using an incident laser. (C) 2011 American Institute of Physics. [doi:10.1063/1.3554835]“
“Background: Switching warfarin for heparin has been a practice for managing periprocedural anticoagulation in high-risk patients undergoing device-related procedures.