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This paper describes the parallelisation of a sequential FORTRAN molecular mechanics program to run on novel hardware, where each node processor has a dedicated high speed link to the host processor, and to all of the other nodes. The host processor can broadcast code/data to the nodes over these direct links using an overhead free hardware mechanism. The broadcast hardware is supported by the COMFORT message passing subroutine library.
\n \n\n \n \nThe molecular geometry of the title compound, C15H22O, has been determined by X-ray diffraction. The double bonds in the 2,6,9,9-tetramethylcycloundeca-2,6,10-trienone ring have trans-stereochemistry. The conformation of the macrocycle differs from that found in several derivatives of humulene, C15H24, and is related to one of the low-energy conformations of cycloundecane. Force-field calculations indicate that this zerumbone conformation is of lower energy than the alternative humulene-like conformation. Crystallographic data are a = 12.619(2), b = 7.290(3), c = 23.422(3) \u00c5, \u03b2 = 98.06(1)\u00b0, 2 = 4, space group P21/c. Diffractometer intensity measurements were made with Cu-K\u03b1radiation and least-squares adjustment of the atomic parameters converged at R 0.046 for 3 222 |F0| values.
\n \n\n \n \nThe title compound has been studied by molecular mechanics calculations. There is no single, well defined global minimum energy conformation and the low energy conformations are unrelated to the conformation of the analogous alkene, trans,trans,trans-cyclodeca-1,5,9-triene. Electrostatic interactions between the amide groups are shown to be an important conformational determinant in the cyclic tripeptide. Not unexpectedly attempts to characterize a single conformation of cyclo-[\u03b2-ala]3by X-ray crystal structure analysis and2H n.m.r. were unsuccessful.
\n \n\n \n \nElucidation of the crystal structure of the title ester has established the parent alkaloid to be 4-demethylhasubanonine. In the alkaloid molecule, the five-membered ring containing the nitrogen atom has an envelope conformation with C(14) out-of-plane. The S-OC bond of the p-bromobenzenesulphonyl group is steeply inclined to the bromobenzene plane, and the conformation about the S-OC bond is gauche. The crystals are orthorhombic, space group P212121, Z = 4 in a cell of dimensions a = 8.52, b = 24.23, c = 12.60 \u00c5. The structure was solved by Patterson and Fourier methods from photographic data and refined by least-squares techniques to R 11.3% for 1783 independent reflections.
\n \n\n \n \nThe crystal structures of bromogaillardin and deacetyldihydrogaillardin p-bromobenzoate have been determined, and the results define the stereochemistry of gaillardin, a cytotoxic sesquiterpenoid lactone from Gaillardia pulchella. The atomic co-ordinates were determined by Fourier and least-squares methods, and the absolute configuration was established by the anomalous-dispersion effect. Each derivative has a cycloheptene ring in a chair conformation and a cyclopentane ring in an envelope conformation. The \u03b3-lactone ring in bromogaillardin has an exocyclic methylene group at C(11) and is notably less puckered than the \u03b3-lactone ring in the dihydro-derivative which has a methyl group at C(11).
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