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Julian R. Koe Douglas R. Powell Jarrod J. Buffy Shuzi Hayase Robert West 《Angewandte Chemie (International ed. in English)》1998,37(10):1441-1442
The silicon backbone is all- trans in the crystal structure of perchloropolysilane [SiCl2]n (see structure on the right). The Cl atoms can be substituted by nucleophiles to form polymers such as peralkoxy- and peraminopolysilanes. 相似文献
13.
E. Kengne R. Vaillancourt 《Communications in Nonlinear Science & Numerical Simulation》2009,14(11):3804-3810
A class of dissipative complex Ginzburg–Landau (DCGL) equations that govern the wave propagation in dissipative nonlinear transmission lines is solved exactly by means of the Hirota bilinear method. Two-soliton solutions of the DCGL equations, from which the one-soliton solutions are deduced, are obtained in analytical form. The modified Hirota method imposes some restrictions on the coefficients equations. Namely, the second-order dispersion must be real. The physical requirement of the solutions imposes complementary conditions on the combination of the dispersion and nonlinear gain/loss terms of the equation, as well as on the coefficient of the Kerr nonlinearity. The analytical solutions for one-solitary pulses are tested in direct simulations. 相似文献
14.
Galonić DP Vaillancourt FH Walsh CT 《Journal of the American Chemical Society》2006,128(12):3900-3901
The in vitro reconstitution of leucine halogenation during barbamide biosynthesis has been accomplished. It has been demonstrated that the triple chlorination of the unactivated pro-R methyl group of the peptidyl carrier protein-tethered l-Leu substrate is carried out by the tandem action of two nonheme iron(II)-dependent halogenases, BarB1 and BarB2. Investigation of the substrate specificities of each of the halogenating enzymes revealed their complementary roles in the generation of trichloroleucine. 相似文献
15.
The human mouth is home to a rich assortment of native and transient microorganisms. One of the commonly encountered bacterial species, Streptococcus mutans, was shown to generate the novel hybrid polyketide-nonribosomal peptide metabolite mutanobactin A (1). We have characterized three new analogues, mutanobactins B-D (2-4), and subjected these compounds to further biomedical evaluation. Metabolites 1, 2, and 4 were found to inhibit biofilm formation by the fungal oral-pathogen Candida albicans. Compound 4 was the most potent metabolite with an IC(50) value of 5.3 ± 0.9 μM. Using a combination of Marfey's analysis, proton spin-spin coupling, and (1)H-(1)H NOESY data, we proposed absolute configuration assignments in toto for 1-3 and a partial assignment for 4. In addition, feeding studies with isotopically labeled precursor metabolites (acetate and amino acids) have helped to determine the biosynthetic origins of this unique natural product family. 相似文献
16.
Gerea AL Branscum KM King JB You J Powell DR Miller AN Spear JR Cichewicz RH 《Tetrahedron letters》2012,53(32):4202-4205
A collection of fungal isolates was obtained from a complex microbial mat, which occupied an iron-rich freshwater spring that feeds into Clear Creek, Golden, Colorado, USA. Two of the fungal isolates, a Glomeromycete (possibly Entrophospora sp.) and a Dothideomycete (possibly Phaeosphaeria sp.), were investigated for bioactive secondary metabolites. In total, six new compounds consisting of clearanols A-E (5, 6, 10-12) and disulochrin (7) were purified and their structures were determined. Disulochrin exhibited modest antibacterial activity against methicillin-resistant Staphylococcus aureus, whereas clearanol C showed weak inhibitory activity against Candida albicans biofilm formation. 相似文献
17.
William T. A. Harrison Jarrod H. Buttery 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):274-275
Hydrothermally prepared Ba3V2(HPO4)6 contains a three‐dimensional network of VIIIO6 octahedra [dav(V—O) = 2.014 (2) Å] and HPO4 [dav(P—O) = 1.537 (3) Å] tetrahedra, sharing vertices. 12‐coordinate Ba2+ cations [dav(Ba—O) = 2.944 (4) Å] complete the structure. 相似文献
18.
Nonlinear interface elements are currently used to represent nonbonded interfaces such as bone/implant and turbine blade/disk interfaces in finite-element analyses. The accuracy of the two-dimensional interface element of ANSYS was verified by comparing the finite-element solution of a problem involving a nonbonded interface with the analytical solution. Then, photoelastic tests were conducted in order to validate the finite-element solutions in problems similar in geometry to a specific bone/dental implant system. It was concluded that the two-dimensional interface element of ANSYS can be used with confidence. 相似文献
19.
3,5-Dihydroxyphenylglycine is a crucial amino acid monomer in the nonribosomal glycopeptide antibiotic vancomycin. This nonproteinogenic amino acid is constructed from malonyl-CoA by a set of four enzymes, DpgA-D, in the biosynthetic cluster. DpgC is an unusual metal-free, cofactor-free enzyme that consumes O(2) during the conversion of 3,5-dihydroxyphenylacetyl-CoA (DPA-CoA) to the penultimate intermediate 3,5-dihydroxyphenylglyoxylate (DPGx). We show that in anaerobic incubations, DpgC catalyzes the exchange of the C(2)-methylene hydrogens of DPA-CoA at unequal rates, consistent with enzyme-mediated formation of the substrate-derived C(2)-carbanion as an early intermediate. Incubations with (18)O(2) reveal that DpgC transfers both atoms of an O(2) molecule to DPGx product. This establishes DpgC as a 1,2-dioxygenase that mediates thioester cleavage by the oxygen transfer process. These results are consistent with a DPA-CoA C(2)-peroxy intermediate, followed by enzyme-directed alpha-peroxylactone formation and collapse by O-O bond cleavage. 相似文献
20.
Abdulrahman Karouma Truong Nguyen-Ba Thierry Giordano Rémi Vaillancourt 《Numerical Algorithms》2018,79(1):251-280
A family of one-step, explicit, contractivity preserving, multi-stage, multi-derivative, Hermite–Birkhoff–Taylor methods of order p =?5,6,…,14, that we denote by CPHBTRK4(d,s,p), with nonnegative coefficients are constructed by casting s-stage Runge–Kutta methods of order 4 with Taylor methods of order d. The constructed CPHBTRK4 methods are implemented using efficient variable step control and are compared to other well-known methods on a variety of initial value problems. A selected method: CP 6-stages 9-derivative HBT method of order 12, denoted by CPHBTRK412, has larger region of absolute stability than Dormand–Prince DP(8,7)13M and Taylor method T(12) of order 12. It is superior to DP(8,7)13M and T(12) methods on the basis the number of steps, CPU time, and maximum global error on several problems often used to test higher-order ODE solvers. Also, we show that the contractivity preserving property of CPHBTRK412is very efficient in suppressing the effect of the propagation of discretization errors and the new method compares positively with explicit 17 stages Runge-Kutta-Nyström pair of order 12 by Sharp et al. on a long-term integration of a standard N-body problem. The selected CPHBTRK412is listed in the Appendix. 相似文献