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231.
Aprahamian I Bodwell GJ Fleming JJ Manning GP Mannion MR Sheradsky T Vermeij RJ Rabinovitz M 《Journal of the American Chemical Society》2003,125(7):1720-1721
The two-electron reduction of strained pyrenes ([7](2,7)pyrenophanes) with lithium metal leads to the formation of a new sigma-bond as a means to "escape" strained antiaromaticity. 相似文献
232.
Hallinan EA Kramer SW Houdek SC Moore WM Jerome GM Spangler DP Stevens AM Shieh HS Manning PT Pitzele BS 《Organic & biomolecular chemistry》2003,1(20):3527-3534
In the literature, the introduction of fluorine into bioactive molecules has been known to enhance the biological activity relative to the parent molecule. Described in this article is the synthesis of 4R-fluoro-L-NIL (12) and 4,4-difluoro-L-NIL (23) as part of our iNOS program. Both 12 and 23 were found to be selective iNOS inhibitors as shown in Table 2 below. Secondarily, methodology to synthesize orthogonally protected 4-fluoro-L-lysine and 4,4-difluoro-L-lysine has been developed. 相似文献
233.
We describe a novel all-optical regenerative memory comprising two nonlinear optical switching gates coupled by an optical fibre storage loop. Binary pulse patterns were stored in the memory circuit for periods of several hours. This long term storage corresponds to > 10 billion circulations around the fibre storage loop. 相似文献
234.
Hilbert and Cohn-Vossen [2, p. 221] incorrectly suggested a flexible knitting needle, constrained to conform to a surface, as one model for a geodesic on a surface. This model actually gives a relaxed elastic line on the surface, and is not generally a geodesic unless the surface lies in a plane or on a sphere.In this paper we derive the intrinsic equations for a relaxed elastic line on an oriented surface. This formulation should give a more direct and more geometric approach to questions concerning relaxed elastic lines on a surface. We apply this formulation to give alternate proofs of some results of [3] found by the less direct method of Lagrange multipliers and to give additional results about relaxed elastic lines on various surfaces. For further considerations of a relaxed elastic line on a surface as a model of the DNA molecule, see [3].Partially supported by NIH grant GM 36284-01. 相似文献
235.
The reactions of [Co(η-C5H5)(CO)(PR3)] or [Co(η-C5GH5)(CO)2]/R3P mixtures (R = alkyl or aryl) with CS2 in refluxing CS2 or CS2/toluene gives rise to [Co(η-C5H5)(PR3)(CS)], [Co(η-C5H5)(PR3)(CS2)], [Co(η-C5H5)(PR3)(CS3)], and [Co3(η-C5H5)3 (CS)(S)] in reasonable yields. The corresponding reactions using PhNCS give [Co(η-C5H5)(PPh3)(PhNCS)] and a polymeric species which appears to be [Co4(η-C5H5)4 (PhNCS)]. Similar products are obtained with [Co(η-C5H5)(CO)(CNR)] or [Co(η0C5H5)(CO)2]/RNC mixtures. 相似文献
236.
237.
Ronald G. Manning Edward R. Grant Jerald C. Merrill Norris J. Parks John W. Root 《国际化学动力学杂志》1975,7(1):39-44
Modified nuclear recoil techniques have been used to obtain accurate relative bimolecular rate coefficients for thermally induced hydrogen abstraction reactions by atomic fluorine. New results are reported for 12 hydrocarbons and partially fluorinated hydrocarbons studied at 303°K. 相似文献
238.
239.
Wang TS Manning SA Walker S Kahne D 《Journal of the American Chemical Society》2008,130(43):14068-14069
Peptidoglycan is an essential component of bacterial cell wall. The glycan strands of peptidoglycan are synthesized by enzymes called peptidoglycan glycosyltransferases (PGTs). Using a high-resolution SDS-PAGE assay, we compared the glycan strand lengths of four different PGTs from three different organisms (Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus). We report that each enzyme makes a polymer having an intrinsic characteristic length that is independent of the enzyme:substrate ratio. The glycan strand lengths vary considerably, depending on the enzyme. These results indicate that each enzyme must have some mechanism, as yet unknown, for controlling product length. The observation that different PGTs produce different length glycan chains may have implications for their cellular roles and for the three-dimensional structure of bacterial peptidoglycan. 相似文献
240.
Lopez-Capel E Krull ES Bol R Manning DA 《Rapid communications in mass spectrometry : RCM》2008,22(11):1751-1758
The effect of a recent vegetation change (<100 years) from C(4) grassland to C(3) woodland in central Queensland, Australia, on soil organic matter (SOM) composition and SOM dynamics has been investigated using a novel coupled thermogravimetry-differential scanning calorimetry-quadrupole.mass spectrometry-isotope ratio mass spectrometry (TG-DSC-QMS-IRMS) system. TG-DSC-QMS-IRMS distinguishes the C isotope composition of discrete SOM pools, showing changes in labile, recalcitrant and refractory carbon in the bulk soil and particle size fractions which track the vegetation changes. Analysis of evolved gases (by QMS) from thermal decomposition, rather than observed weight loss, proved essential in determining the temperature at which SOM decomposes, because smectite and kaolinite clays contribute to observed weight losses. The delta(13)C analyses of the CO(2) evolved at different temperatures for bulk soil and particle size-separates showed that most of the labile SOM under the more recent woody vegetation was C(3)-derived carbon whereas the delta(13)C values in the recalcitrant SOM showed greater C(4) contributions. This indicated a shift from grass (C(4))- to tree (C(3))-derived carbon in the woodland, which was also supported by the two-phase (13)C enrichment with depth, i.e. C(3) vegetation dominated the top soil (0-10 cm), but the C(4) contribution increased with depth (more gradual). This is perturbed by the inclusion of charcoal from forest fires ((14)C age incursions) and by the deep incorporation of C(3) carbon due to root penetration. 相似文献