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21.
Scott JP Mullens PR Brewer SE Brands KM Chilenski JR Davies AJ Gibb AD Lieberman DR Oliver SF Dolling UH 《Organic & biomolecular chemistry》2006,4(9):1806-1810
Intramolecular nitrile oxide-olefin cycloaddition to form hexahydrobenzisoxazole 14, which engenders a phenylsulfonyl, 2,5-difluorophenyl geminally substituted carbon substructure, proceeds with up to 99% ds. A rationalization of the high level of substrate-based stereo-induction observed in this and related ketone and acrylonitrile metallohydride reductions, supported by single crystal X-ray crystallography, is presented. 相似文献
22.
Tang H de Oliveira CS Sonntag G Gibb CL Gibb BC Bohne C 《Journal of the American Chemical Society》2012,134(12):5544-5547
Water-soluble octaacid cavitands (OAs) form dimeric capsules suitable for guest incorporation. Our studies reveal that the mechanism of pyrene (Py) binding involves the rapid (<1 ms) formation of the Py·OA complex followed by slower binding with the second OA. The dissociation of the capsular OA·Py·OA complex occurs with a lifetime of 2.7 s, which is 5 orders of magnitude slower than the microsecond opening/closing ("breathing") previously observed to provide access of small molecules to the encapsulated guest. These different dynamics of the capsules have a potential impact on how the chemistry of included guests could be altered. 相似文献
23.
Philip J. Cox Stephen M. MacManus Bruce C. Gibb Ian W. Nowell Alan B. Turner R. Alan Howie 《Journal of chemical crystallography》1990,20(5):415-418
The crystal and molecular structure of 3,5-cycloandrostan-6-ol-17-one has been determined by X-ray analysis,13C-NMR,1H-NMR, IR and elemental analyses. The compound was obtained from dehydroepiandrosterone (DHEA) via the 3-tosyl derivative by refluxing in a butan-2-one/water mixture. The X-ray analysis shows that the planar cyclopropane ring is predominantly orientated and the formation of the C(3)-C(5) bond enables the A ring to adopt a distorted boat conformation. Spectroscopic evidence for the presence of the cyclopropane ring and the 6-hydroxy group are presented. 相似文献
24.
The dynamic mobility spectra of several colloidal systems having a ratio of particle radius to double-layer thickness between 1 and 20 have been measured using the technique of electroacoustics. Good agreement is found between the experimental mobility spectra and the theoretical spectra generated by the computer program of Manglesdorf and White for spherical monodisperse suspensions with sizes in the neighborhood of 0.1 μm. Smaller and larger particles show some minor discrepancies which are more likely to be due to limitations of the model systems being used for the test than to any basic limitation of the theoretical analysis. Copyright 2000 Academic Press. 相似文献
25.
L. Corner J.S. Gibb G. Hancock A. Hutchinson V.L. Kasyutich R. Peverall G.A.D. Ritchie 《Applied physics. B, Lasers and optics》2002,74(4-5):441-444
We have used a violet diode laser at 404 nm and a distributed feedback diode laser at 1320 nm to produce 0.8 nW of radiation
at 309 nm by sum frequency generation in beta-barium borate. The UV radiation was tuned mode-hop-free over 30 GHz and used
to detect OH radicals produced in a microwave discharge. By chopping the UV light at 500 Hz, we observed a concentration of
2×1012 cm-3 with a signal to noise ratio of 30:1.
Received: 16 November 2001 / Revised version: 23 January 2002 / Published online: 14 March 2002 相似文献
26.
Fabrication of electrospun fibrous scaffolds as future medical devices is being widely researched, with particular emphasis given to their material properties and effect on cell response and differentiation. However, the vast majority of these scaffolds are sterilized via nonmedically approved methods, including submersion in ethanol and exposure to UV light. Although these techniques are adequate for laboratory‐based research, they are not sufficient for human implantation. In this case, regulatory approved, medical grade sterilization is required. In this study, we report the effects of gamma irradiation, a regulatory approved technique, on electrospun poly(ε‐caprolactone) fibers. Fabricated fibers were separately subjected to different dosages of irradiation ranging from 0 to 45 kGy and then assessed for their physicochemical properties. Gamma irradiation affected fiber properties irrespective of dosage. A dose‐dependent decrease in polymer molecular weight was observed and an increase in melting point and crystallinity reported. Similarly, irradiation had a significant effect on mechanical properties with greatest decrease in tensile strength (68%) for fibers exposed to 40 kGy. The method of sterilization had no effect on cell response. Seeded tenocytes attached to all fibers and elongated parallel to the underlying fiber direction. The results demonstrate the importance of incorporating medical grade sterilization procedures early in the research projects time line to assist translation from bench to clinic. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
27.
The concentration of residual tetrahydrofuran in cast poly(vinyl chloride) films has been varied. It is shown that the amount of tetrahydrofuran present does not affect the extent of degradation but that it does affect the relative concentration of the conjugated polyenes produced. A shift towards shorter polyenes is observed with increasing concentration of residual solvent; this effect is attributed to its ability to act as a plasticizer. 相似文献
28.
Davies AJ Scott JP Bishop BC Brands KM Brewer SE Dasilva JO Dormer PG Dolling UH Gibb AD Hammond DC Lieberman DR Palucki M Payack JF 《The Journal of organic chemistry》2007,72(13):4864-4871
This paper describes a remarkably efficient process for the preparation of gamma-secretase inhibitor 1. The target is synthesized in only five steps with an overall yield of 58%. The key operation is a highly selective and practical, crystallization-driven transformation for the conversion of a mixture of tertiary benzylic alcohols into the desired sulfide diastereomer with 94:6 dr. This unprecedented process is based upon a reversible carbon-sulfur bond formation under acidic conditions. 相似文献
29.
The water soluble capsule formed by a deep cavity cavitand with eight carboxylic acid groups controls product distribution during photo-Fries rearrangement of naphthyl esters in water by restricting the mobility of primary singlet radical pair. 相似文献
30.
T.C. Gibb 《Chemical physics letters》1975,30(1):137-139
The orientation of the electric field gradient tensor at the iron nucleus in a single crystal of Na2[Fe(CN)5(NO)]·2H2O has been determined using a polarized Mössbauer source of 57Co in iron metal. 相似文献