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91.
Trevor R. Simmons Christopher J. Pickett Joseph A. Wright 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(1):o1-o5
A new synthetic route to 2,2‐bis(sulfanylmethyl)propane‐1,3‐diol, (II), is described starting from the commercially available 2,2‐bis(hydroxymethyl)propane‐1,3‐diol. The structures of two intermediates on this route are described. 5,5‐Dimethenyl‐2,2‐dimethyl‐1,3‐dioxane bis(thiocyanate) (systematic name: {[5‐(cyanosulfanyl)‐2,2‐dimethyl‐1,3‐dioxan‐5‐yl]sulfanyl}formonitrile), C10H14N2O2S2, (X), crystallizes in the space group P21/c with no symmetry relationship between the two thiocyanate groups. There is a short intramolecular N...S contact for one thiocyanate group, while the second group is positioned such that this type of interaction is not possible. 1,3‐(Hydroxymethyl)propane‐1,3‐diyl bis(thiocyanate), C7H10N2O2S2, (XI), also features a single short N...S contact in the solid state. Hydrogen bonding between two molecules of compound (XI) results in the formation of dimers in the crystal, which are then linked together by a second hydrogen‐bond interaction between the dimers. In addition, the structures of two intermediates from an unsuccessful alternative synthesis of (II) are reported. 2,2‐Bis(chloromethyl)propane‐1,3‐diol, C5H10Cl2O2, (VI), crystallized as an inversion twin with a minor twin fraction of 0.43 (6). It forms a zigzag structure as a result of intermolecular hydrogen bonding. The structure of 9,9‐dimethyl‐2,4,8,10‐tetraoxa‐3λ4‐thiaspiro[5.5]undecan‐3‐one, C8H14O5S, (VII), shows evidence for a weak S...O contact with a distance of 3.2529 (11) Å. 相似文献
92.
Using a two-dimensional self-consistent field calculation, we determine the equilibrium morphology of thin films of ABC triblock copolymers confined between hard, smooth plates. The B segment is chosen to be the central block and all the blocks are incompatible. The chains microphase-segregate into a lamellar phase, with the stripes either perpendicular or parallel to the walls. When all the monomer-surface interactions are identical, the perpendicular orientation has the lowest free energy. When a repulsion is introduced between the surface and the A and C monomers. The surface interactions further stabilize the perpendicular orientation. At strong surface interactions, the morphology of the perpendicular structure is controlled by the overall thickness of the molten layer. In comparing diblocks to triblocks as candidates for forming laterally patterned films, our work indicates that triblocks possess distinct advantages over diblocks. First, no special effort needs to be taken to establish neutral surfaces. Second, the film does not have to be confined between two substrates. Thus, triblocks can be used to fabricate patterned polymer surfaces, which can be used for novel optical or electronic applications. 相似文献
93.
S G Revoile L Kozma-Spytek L Holden-Pitt J M Pickett J Droge 《The Journal of the Acoustical Society of America》1991,89(1):457-460
Moderately to profoundly hearing-impaired (n = 30) and normal-hearing (n = 6) listeners identified [p, k, t, f, theta, s] in [symbol; see text], and [symbol; see text]s tokens extracted from spoken sentences. The [symbol; see text]s were also identified in the sentences. The hearing-impaired group distinguished stop/fricative manner more poorly for [symbol; see text] in sentences than when extracted. Further, the group's performance for extracted [symbol; see text] was poorer than for extracted [symbol; see text] and [symbol; see text]. For the normal-hearing group, consonant identification was similar among the syllable and sentence contexts. 相似文献
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97.
The reversible reduction protons to dihydrogen: 2H+ + 2e [symbol: see text] H2 is deceptively the simplest of reactions but one that requires multistep catalysis to proceed at practical rates. How the metal-sulfur clusters of the hydrogenases catalyse this interconversion is currently the subject of extensive structural, spectroscopic and mechanistic studies of the enzymes, of synthetic assemblies and of in silico models. This is driven both by curiosity and by the view that an understanding of the underlying chemistry may inform the design of new electrocatalytic systems for hydrogen production or uptake, pertinent to energy transduction technology in an 'Hydrogen Economy'. Can chemists design materials that replace the expensive platinum metal catalysts of fuel cells with metal-sulfur cluster assemblies utilising abundant Ni, Fe and S as in the natural systems? Here we review the state of the art. 相似文献
98.
Chehade KA Kiegiel K Isaacs RJ Pickett JS Bowers KE Fierke CA Andres DA Spielmann HP 《Journal of the American Chemical Society》2002,124(28):8206-8219
Farnesylation is a posttranslational lipid modification in which a 15-carbon farnesyl isoprenoid is linked via a thioether bond to specific cysteine residues of proteins in a reaction catalyzed by protein farnesyltransferase (FTase). We synthesized analogues (3-6) of farnesyl pyrophosphate (FPP) to probe the range of modifications possible to the FPP skeleton which allow for efficient transfer by FTase. Photoaffinity analogues of FPP (5, 6) were prepared by substituting perfluorophenyl azide functional groups for the omega-terminal isoprene of FPP. Substituted anilines replace the omega-terminal isoprene in analogues 3 and 4. Compounds 3-5 were prepared by reductive amination of the appropriate anilines with 8-oxo-geranyl acetate, followed by ester hydrolysis, chlorination, and pyrophosphorylation. Additional substitution of three methylenes for the beta-isoprene of FPP gave photoprobe 6 in nine steps. Preparation of the analogues required TiCl(4)-mediated imine formation prior to NaBH(OAc)(3) reduction for anilines with a pK(a) < 1. The azide moiety was not affected by Ph(3)PCl(2) conversion of allylic alcohols 13-16 into corresponding chlorides 17-20. Analogues 3-6 are efficiently transferred to target N-dansyl-GCVLS peptide substrate by mammalian FTase. Comparison of analogue structures and kinetics of transfer to those of FPP reveals that ring fluorination and para substituents have little effect on the affinity of the analogue pyrophosphate for FTase and its transfer efficiency. These results are also supported with models of the analogue binding modes in the active site of FTase. The transferable azide photoprobe 5 photoinactivates FTase. Transferable analogues 5 and 6 allow the formation of appropriately posttranslationally modified photoreactive peptide probes of isoprene function. 相似文献
99.
The rates of radiative recombination to form HD+ and HeH+ along the ground electronic state potential surface have been calculated from known potentials. These exact quantum calculations are compared with a classical model. For the formation HD+, the classical model predicts the rate in the range of 100–1000 K. Below 100 K, the rate is dominated by the effect of low energy shape resonances. For the formation of HeH+, the classical model predicts the correct temperature dependence. 相似文献
100.