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Masaru Kihara Kouichi Yoshioka Tamboue Deffo Dwight S. Fullerton Douglas C. Rohrer 《Tetrahedron》1984,40(7):1121-1133
Earlier studies have shown that the β-D-digitoxose (2,6-dideoxy-β-D-mannopyranose) directly attached to the cardiac glycoside steroid C3 has the greatest effect on biological activity. This report describes the synthesis of eight digitoxosides (2a-9a), with widely varying cyclic and acyclic C17β-side groups, and the corresponding C3',C4'-acetonides (2b-9b). NMR analysis of conformational strain introduced by the acetonide groups is supported by crystallographic analysis of the sugars' torsion angles. 相似文献
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Hargovind Rathore Toshihiro Hashimoto Kikuo Igarashi Haruo Nukaya Dwight S. Fullerton 《Tetrahedron》1985,41(23):5427-5438
As part of a continuing study of cardiac g1ycos1des,1,2 stereoselective syntheses of the four possible glucosides of digitoxigenin were developed via the thermodynamically produced tetra-O-benzyl-D- and L-glucosyl α-trichloroacetaimidates 2α and 11α, and the kinetically produced β-trichloroacetaimidates 2β and 11β. A 58%:19% isolated yield ratio of α-D and β-D benzyl protected glycosides 6 and 3 could be obtained in 30 minutes reaction at ?10°. Halide ion catalysis with a 2:1 excess of tetra-O-benzyl-α-D-glucopyranosyl bromide for 14 days in methylene chloride at room temperature gave a 39%:11% ratio of 6 and 3, along with 43% of recovered digitoxigenin. Debenzylation of the D-glucosides required milder conditions (20% Pd/C, atmospheric pressure, 45 min-1 hr) than the L-glucosides (40% Pd/C, 2 hr) but yields were typically 80% for both groups. 相似文献
4.
Fullerton EE Robertson JL Prinsloo AR Alberts HL Bader SD 《Physical review letters》2003,91(23):237201
We have measured the antiferromagnetic spin-density-wave (SDW) order in Cr/Cr(97.5)Mn2.5(001) superlattices. The Mn doping creates a high Néel temperature layer that confines the incommensurate SDW order within the Cr layers. With temperature cycling we observe a transition from commensurate to incommensurate SDW order and discrete changes in the SDW period. We find that these transitions show significant hysteresis (up to 75 K) when the number of SDW nodes within the Cr layer changes by an odd number, while there is no hysteresis for changes of an even number of nodes. This results from the competition between maintaining the spin structure at the interfaces and introducing a spin slip at the nodes of the Cr SDW. 相似文献
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Uniaxial systems often form labyrinthine domains that exhibit short-range order but are macroscopically isotropic and would not be expected to exhibit precise symmetries. However, their underlying frustration results in a multitude of metastable configurations of comparable energy, and driving such a system externally might lead to pattern formation. We find that soft x-ray speckle diffraction patterns of the labyrinthine domains in CoPd/IrMn heterostructures reveal a diverse array of hidden rotational symmetries about the magnetization axis, thereby suggesting an unusual form of emergent order in an otherwise disordered system. These symmetries depend on applied magnetic field, magnetization history, and scattering wave vector. Maps of rotational symmetry exhibit intriguing structures that can be controlled by manipulating the applied magnetic field in concert with the exchange bias condition. 相似文献
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To help understand which tissue parameters best account for the water proton NMR relaxation times, the longitudinal relaxation time (T2), the transverse relaxation time (T2), and the water content of 16 tissues from normal adult rats were measured at 10.7 MHz and 29°C. Regression analyses between the above and other tissue parameters were performed. These other tissue parameters included: the amounts of various organic and inorganic components, protein synthetic rate, oxygen consumption rate, and morphological composition. In addition, the differences in T1, T2, and water content values between normal liver and malignant tumor (Morris #7777 a transplantable hepatoma) were studied to help understand how a disease state can be detected and characterized by NMR spectroscopy. The results of this study and information from the literature allow the following generalizations to be made about tissue T1 and T2 values: (1) Each normal tissue has rather consistent and characteristic T1 and T2 relaxation times which are always shorter than the T1 and T2 of bulk water; (2) tissues with higher water content tend to have longer T1 relaxation times; (3) tissue T2 values are not, however, as well correlated with water content as T1 values; (4) tissues with shorter T1 values have higher calculated hydration fractions, greater amounts of rough endoplasmic reticulum, and a greater rate of protein synthetic activity; (5) tissues with higher lipid content, associated with intracellular non-membrane bounded lipid droplets, tend to have longer T2 values; (6) tissues with greater overall surface area, whether in the form of cellular membranes or intracellular or extracellular fibrillar macromolecules, tend to have shorter T2 values; (7) the differences between T1 and T2 values between tumor and normal tissues correlated with differences in the volume fraction (amounts) of extracellular fluid volumes and in the amounts of membrane and fibrillar surface area in the cells. The above generalizations should be useful in predicting T1 and T2 changes associated with specific tissue pathologies. 相似文献
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A.R.E. Prinsloo H.A. Derrett O. Hellwig E.E. Fullerton H.L. Alberts N. van den Berg 《Journal of magnetism and magnetic materials》2010,322(9-12):1126-1129
Dimensionality effects on epitaxial and polycrystalline Cr1?xRux alloy thin films and in Cr/Cr–Ru heterostructures are reported. X-ray analysis on Cr0.9965Ru0.0035 epitaxial films indicates an increase in the coherence length in growth directions (1 0 0) and (1 1 0) with increasing thickness (d), in the range 20≤d≤300 nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d>50 nm, resulting in the formation of columnar structures. The Néel temperatures (TN) of the Cr0.9965Ru0.0035 films show anomalous behaviour as a function of d at thickness d≈50 nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr1?xRux thin films, with 0≤x≤0.013 and d=50 nm, give TN–x curves that correspond well with that of bulk Cr1?xRux alloys. Studies on Cr/Cr0.9965Ru0.0035 superlattices prepared on MgO(1 0 0), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr0.9965Ru0.0035 thickness constant at 10 nm, indicate a sharp decrease in TN as the Cr separation layers reaches a thickness of 30 nm; ascribed to spin density wave pinning in the Cr layers for d<30 nm by the adjacent CrRu layers. 相似文献