Application of parallel processing techniques to improving the efficiency of MM2 molecular mechanics calculations

The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc.     

Fused lactones as a route to functionalized 1-substituted indoles

Indole lactones 8 and 14 were synthesized as a means of functionalizing the 1-isopropyl substituent of the indole nucleus. Lactone 8 , upon reduction with diisobutylaluminum hydride, produces lactol 9 which behaves like a masked hydroxy aldehyde and undergoes a Horner-Emmons reaction with triethyl phosphonoacteate to give α,β-unsaturated ester 3 which possesses a hydroxyl group on the 1-isopropyl moiety.     

The Enol of Acetone during Photochemical Reactions of 3-Hydroxy-3-methyl-2-butanone and of Acetone

The enol of acetone, formed by disproportionation reactions of 1-hydroxy-1-methylethyl radicals, is detected by NMR, spectroscopy during photoreactions of 3-hydroxy-3-methyl-2-butanone in acetonitrile and of acetone in 2-propanol and slowly tautomerizes to acetone. The photolysis of 3-hydroxy-3-methyl-2-butanone is shown to proceed via Type I cleavage, predominantly from an excited triplet state.     

Carbon dioxide emulsion assisted loading of polymer microspheres toward sustained release materials

An organic solvent-free method for encapsulating progesterone at high loadings within micron-sized inert latex polymer beads is reported. This approach makes use of a polymeric surfactant to emulsify carbon dioxide into an aqueous latex suspension. In this way, preformed approximately 4 microm polystyrene (PS) microparticles surface-grafted with poly(N-vinylpyrrolidone) (PVP) were plasticized and swollen followed by rapid partitioning of progesterone into the polymer matrix. The as-prepared polystyrene beads incorporated over 10% progesterone by weight while maintaining their initial size and morphological uniformity. Dissolution experiments were also carried out to obtain the release profile of progesterone entrapped within the PVP/PS particles.     

Novel heterocycles. 6. The condensation of ethyl o-fluorobenzoyl acetate with cyclic imino ethers

The reaction between ethyl o-fluorobenzoylacetate and cyclic imino ethers is described. The products, the corresponding 1,2-fused quinolines ( 13a-17a ), were isolated in good yields. In one instance the uncyclized condensation intermediate 18 was isolated and characterized.     

Self-assembly of phosphate fluorosurfactants in carbon dioxide

Anionic phosphodiester surfactants, possessing either two fluorinated chains (F/F) or one hydrocarbon chain and one fluorinated chain (H/F), were synthesized and evaluated for solubility and self-assembly in liquid and supercritical carbon dioxide. Several surfactants, of both F/F and H/F types and having varied counterions, were found to be capable of solubilizing water-in-CO2 (W/C), via the formation of microemulsions, expanding upon the family of phosphate fluorosurfactants already found to stabilize W/C microemulsions. Small-angle neutron scatteringwas used to directly characterize the microemulsion particles at varied temperatures, pressures, and water loadings, revealing behavior consistent with previous results on W/C microemulsions.     

Probing the molecular-scale lipid bilayer response to shear flow using nonequilibrium molecular dynamics

A nonequilibrium molecular dynamics simulation of the response of dimyristoylphosphatidylcholine (DMPC) bilayers to a solvent shear flow is presented. Application of shear flow to planar, stationary DMPC bilayers results in a redistribution of the membrane density profile along the bilayer normal due to the alignment of the lipids in the direction of flow and an increase in average lipid chain length. An increase in the intermolecular and intramolecular order of the lipids in response to the shear flow is also observed. This study provides groundwork for understanding the mechanism of the full response of lipid bilayers to externally imposed solvent shear flows, beginning with the response in the absence of collective lipid motions such as undulations and bilayer flow.     

Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada.

Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of < or = 1 microm and 5.9 microm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten.     

Fluorescence correlation spectroscopy of water-in-oil microemulsions: an application in specific characterisation of droplets containing biomolecules

Fluorescence correlation spectroscopy (FCS) has been successfully used to characterise water-in-oil (w/o) microemulsions. The investigated systems were stabilised by sodium bis-2-ethylhexyl sulphosuccinate (AOT) and the measured diffusion times have been related to the radii of the aggregated species, which for some systems, were separately determined by small-angle neutron scattering (SANS). We demonstrate that FCS is capable of measuring hydrodynamic radii of microemulsions rapidly and at surfactant concentrations lower than previously reported for other techniques. FCS was also used to specifically interrogate microemulsion droplets containing a fluorescently-labelled biomolecule, specifically phalloidin, a peptide fungal toxin from Amanita phalloides, and the enzyme -chymotrypsin (-CT). The microemulsion droplets are only marginally increased in size if a small peptide (phalloidin) is included in the water phase, whereas the droplet size is significantly increased when a larger protein (-CT) is included.     

The chemistry of 2H-3,1-benzoxazine-2,4(1H)-dione (isatoic anhydride). 10. Reactions with ester enolates. Synthesis of 4-hydroxy-1-methyl-3-prenyl-2(1H)-quinolinones,Crucial intermediates in the synthesis of quinoline alkaloids

N-Methylisatoic anhydride reacts with the lithium enolates of esters to produce β-ketoesters 4 in nearly quantitative yield. Thermal cyclization of these relatively unstable intermediates afford the corresponding 3-substituted-4-hydroxy-1-methyl-2(1H)-quinolinones (5) in good yields. The reaction of the lithium enolate of 5-methyl-4-hexenoic acid ethyl ester ( 14 ) with various nuclear substituted isatoic anhydrides gives 4-hydroxyl-methyl-3-prenyl-2(1H)-quinolinones 8, 9 , and 18 which are highly desirable intermediates in the synthesis of a variety of quinoline alkaloids. Treatment of 18 with DDQ furnishes oricine in 73% yield.