Simulations of membranes and other interfacial systems using P2(1) and Pc periodic boundary conditions. (9/102)

We demonstrate the ease and utility of simulating heterogeneous interfacial systems with P2(1) and Pc periodic boundary conditions which allow, for example, lipids in a membrane to switch leaflets. In preliminary tests, P2(1) was shown to yield equivalent results to P1 in simulations of bulk water, a water/vacuum interface, and pure DPPC bilayers with an equal number of lipids per leaflet; equivalence of Pc and P1 was also demonstrated for the former two systems. P2(1) was further tested in simulations involving the spreading of an octane film on water, and equilibration of a DPPC bilayer from an initial condition containing different numbers of lipids in the two leaflets. Lastly, a simulation in P2(1) of a DOPC/melittin membrane showed significant passage of lipids to the melittin-containing leaflet from the initial distribution, and lends insight into the condensation of lipids by melittin.  (+info)

Circular dichroic properties and average dimensions of DNA-containing reverse micellar aggregates. (10/102)

With the aim of investigating the compartmentation of nucleic acids and surfactant aggregates, we have studied the circular dichroic properties of DNA solubilized in reverse micelles. DNA incorporated in AOT/isooctane reverse micelles (AOT=bis-2-ethyl-hexyl sodium sulfosuccinate) assumes an anomalous circular dichroism (CD) spectrum with the characteristic features of a psi spectrum. Older literature observations could therefore be confirmed that attribute these spectral changes to the fact that the reverse micelles induce the formation of a condensed form of DNA. A dynamic light scattering (DLS) characterization of the DNA-containing micellar solutions was carried out, and three populations of aggregates in a polar solvent are observed, with an average radius centered at 5, 100 and 1000 nm, respectively, all three containing DNA. Several forms of DNA, including a plasmid, have been investigated. The formation of 1 microm-large aggregates depends on the DNA concentration and such aggregates disappear in the course of a few hours. Conversely, the 100 nm aggregates are stable for at least 1 day and contain DNA in a normal spectral state at low concentration and in a condensed form-it is the characteristic psi spectrum-in a higher concentration range. The solubilization of DNA in reverse micelles brings about unexpected larger structures in hydrocarbon solution, and whereas the very large component can be with all likelihood be attributed to clusters of smaller reverse micelles, the components at 100 nm radius appear to be a quite stable and characteristic feature of DNA-containing reverse micelles.  (+info)

Molecular dynamics investigation of membrane-bound bundles of the channel-forming transmembrane domain of viral protein U from the human immunodeficiency virus HIV-1. (11/102)

Molecular dynamics (MD) simulations have been carried out on bundles of the channel-forming transmembrane (TM) domain of the viral protein U (VPU(1-27) and VPU(6-27)) from the human immunodeficiency virus (HIV-1). Simulations of hexameric and pentameric bundles of VPU(6-27) in an octane/water membrane mimetic system suggested that the pentamer is the preferred oligomer. Accordingly, an unconstrained pentameric helix bundle of VPU(1-27) was then placed in a hydrated palmitoyl-oleyl-3-n-glycero-phosphatidylethanolamine (POPE) lipid bilayer and its structural properties calculated from a 3-ns MD run. Some water molecules, initially inside the channel lumen, were expelled halfway through the simulation and the bundle adopted a conical structure reminiscent of previous MD results obtained for VPU(6-27) in an octane/water system. The pore constriction generated may correspond to a closed state of the channel and underlies the relocation of the W residue toward the pore lumen. The relative positions of the helices with respect to the bilayer and their interactions with the lipids are discussed. The observed structure is stabilized via specific interactions between the VPU helices and the carbonyl oxygen atoms of the lipid molecules, particularly at the Q and S residues.  (+info)

A new route to (+)-estrone using a bicyclo[3.2.1]octane chiral building block. (12/102)

A new route to (+)-estrone has been developed starting from the chiral building block having a bicyclo[3.2.1]octane framework based on the inherent stereochemical chemical nature of the chiral building block.  (+info)

Synthesis of new n-substituted cyclic imides with expected anxiolytic activity. XXI. Derivatives of 1-acetyldibenzo-[e.h]-bicyclo[2.2.2]-octane-2,3-dicarboximide. (13/102)

The preparation of a number of new N-substituted derivatives of 1-acetyldibenzo-[e.h]-bicyclo[2.2.2]-octane-2,3-dicarboximide with an expected anxiolytic activity is described.  (+info)

Synthesis of new n-substituted cyclic imides with potential anxiolytic activity. XXIII. Derivatives of 2'-chlorodibenzo[e.h]bicyclo[2.2.2]octane-2,3-dicarboximide. (14/102)

The preparation of a number of derivatives of dibenzo[e.h]bicyclo[2.2.2]octane-2,3-dicarboximide with an expected anxiolytic activity is described.  (+info)

Synthetic study of optically active 3-azabicyclo[3.3.0]octane-2,6,8-tricarboxylic acid. (15/102)

Synthesis of (1R,2S,5S,6R,8S)-3-azabicyclo[3.3.0]octane-2,6,8-tricarboxylic acid (2) from trans-4-hydroxy-L-proline (5) was attempted. A Diels-Alder reaction of 3,4-dehydroproline derivative 9 and cyclopentadiene afforded a single stereoisomer 11. The Diels-Alder adduct was smoothly converted to the hydrochloride of 2 (24) via RuO(4) oxidation. Although some racemization of the material or product was observed during the synthetic processes, the amino acid 24 proved to be optically pure.  (+info)

Preparation of gelatin microbeads with a narrow size distribution using microchannel emulsification. (16/102)

The purpose of this study was to prepare monodisperse gelatin microcapsules containing an active agent using microchannel (MC) emulsification, a novel technique for preparing water-in-oil (W/O) and oil-in-water (O/W) emulsions. As the first step in applying MC emulsification to the preparation of monodisperse gelatin microcapsules, simple gelatin microbeads were prepared using this technique. A W/O emulsion with a narrow size distribution containing gelatin in the aqueous phase was created as follows. First, the aqueous disperse phase was fed into the continuous phase through the MCs at 40 degrees C (operating pressure: 3.9 kPa). The emulsion droplets had an average particle diameter of 40.7 microm and a relative standard deviation of 5.1%. The temperature of the collected emulsion was reduced and maintained at 25 degrees C overnight. The gelatin microbeads had a smooth surface after overnight gelation; the average particle diameter was calculated to be 31.6 microm, and the relative standard deviation, 7.3%. The temperature was then lowered to 5 degrees C by rapid air cooling and finally dried. The gelatin beads were dried and could be resuspended well in iso-octane. They had an average particle diameter of 15.6 microm, and a relative standard deviation of 5.9%. Using MC emulsification, we were able to prepare gelatin microbeads with a narrow size distribution. Since this emulsification technique requires only a low-energy input, it may create desirable experimental conditions for microencapsulation of unstable substances such as peptides and proteins. This method is promising for making monodisperse microbeads.  (+info)