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991.
Valerie Huemer Gernot A. Eller Wolfgang Holzer 《Magnetic resonance in chemistry : MRC》2010,48(6):476-482
Various [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐thiones were synthesized in high yields by treatment of the corresponding [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐ones with Lawesson's reagent. Detailed NMR spectroscopic studies were undertaken of the title compounds. Complete and unambiguous assignment of chemical shifts (1H, 13C, 15N) and coupling constants (1H,1H; 13C,1H) was achieved by the combined application of various one‐ and two‐dimensional (1D and 2D) NMR spectroscopic techniques. Unequivocal mapping of most 13C,1H spin coupling constants is accomplished by 2D (δ, J) long‐range INEPT spectra with selective excitation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
992.
A blue light-inducible phosphodiesterase (PDE) activity, specific for the hydrolysis of cyclic di-GMP (c-di-GMP), has been identified in a recombinant protein from Synechococcus elongatus. Blue light (BL) activation is accomplished by a light, oxygen, voltage (LOV) domain, found in plant phototropins and bacterial BL photoreceptors. The genome of S. elongatus contains two genes coding for proteins with LOV domains fused to EAL domains (SL1 and SL2). In both cases, a GGDEF motif is placed in between the LOV and the EAL motifs. Such arrangement is frequently found with diguanylate-cyclase (DGC) functions that form c-di-GMP. Cyclic di-GMP acts as a second messenger molecule regulating biofilm formation in many microbial species. Both enzyme activities modulate the intracellular level of this second messenger, although in most proteins only one of the two enzyme functions is active. Both S. elongatus LOV-GGDEF-EAL proteins were expressed in full length or as truncated proteins. Only the SL2 protein, expressed as a LOV-GGDEF-EAL construct, showed an increase of PDE activity upon BL irradiation, demonstrating this activity for the first time in a LOV-domain protein. Addition of GTP or c-di-GMP did not affect the observed enzymatic activity. In none of the full-length or truncated proteins was a DGC activity detected. 相似文献
993.
J. C. Gómez-Larrañaga F. González-Acuña Wolfgang Heil 《Mathematische Zeitschrift》2010,266(4):783-788
A closed topological n-manifold M
n
is of S
1-category 2 if it can be covered by two open subsets W
1, W
2 such that the inclusions W
i
→ M
n
factor homotopically through maps W
i
→ S
1. We show that for n > 3 the fundamental group of such an n-manifold is either trivial or infinite cyclic. 相似文献
994.
Hempel and McMillan showed that a closed 3-manifold that can be covered by three open balls is a connected sum of S3- and S2-bundles over S1. In this paper we obtain a classification of all closed 3-manifolds that can be covered by two open balls and one open solid torus or by one open ball and two open solid tori. 相似文献
995.
996.
997.
998.
Richard E. Wendt III Wolfgang Nitz Joel D. Morrisett Thomas D. Hedrick 《Magnetic resonance imaging》1990,8(6):723-728
A two-dimensional, flow-enhanced gradient echo pulse sequence for nuclear magnetic resonance angiography is described. It employs interleaved, presaturated slices to acquire data efficiently on imagers which favor interleaved acquisition over sequential acquisition for multislice imaging. It is useful on any imager when the effective TR is extended to enhance the sensitivity to slow flow. The technique was applied to the region from aortic bifurcation to the iliac bifurcations of three normal volunteers. The right and left common iliac arteries and veins, the separation of the external and internal iliac arteries, and secondary branches were clearly depicted. 相似文献
999.
1000.