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1.
2.
Illumination of a p-type semiconductor—NH3 interface (or heterojunction) with photons of energy greater than the semiconductor band gap causes electrons to be injected into the NH3. There is no hole injection at a n-type electrode. Suggestions are made for the required energy levels in the liquid. 相似文献
3.
A thermodynamic equilibrium model has been developed to describe amino acid adsorption on microporous materials. The model addresses electrostatic, hydrophobic and steric interactions. A procedure for fitting the model's parameters is presented and should be applicable to the majority of the common 20 amino acids. The approach is demonstrated using experimental measurements of L-phenylalanine and L-arginine on zeolite beta. Between the adsorption mechanisms of ion exchange and physisorption, the first can contribute as much as two-thirds of the phenylalanine adsorbed at saturation. For the materials tested, ion exchange is maximized when the zeolite's silicon-to-aluminum ratio is 12. When this atom ratio is raised to 100, ion exchange no longer plays a significant role, but the amount physisorbed increases by 30%. 相似文献
4.
Six known metabolites, two new isocoumarins 4 and 8, and one new highly substituted benzoic acid derivative 9 were isolated from the ethyl acetate culture extract of a fungal endophyte, Scytalidium sp. In addition, another new benzoic acid 10 with an unusual 1,2-dicarbonyl side chain was indirectly identified from its methylated derivatives 10a-10d. 相似文献
5.
Treatment of the 1,6‐anhydrosugar epoxide 5 with a cyano‐Gilman cuprate [(CuCN (6 eq.), MeLi (12 eq.)] surprisingly led to the open chain rearranged (2S,3R)‐1,2‐dihydroxy‐3,6‐dimethylheptan‐4‐one (7), structurally confirmed by conversion to the corresponding diacetate 8. Another unusual reaction was found by hydrogenation of the 2‐tosyl‐1‐bromosugar 11, leading in one operation to the twofold deoxygenated chiral pyran derivative 14. This procedure might prove to be useful in the rapid deoxygenation of sugar derivatives. 相似文献
6.
In the course of our investigations on the synthesis of enantiomerically pure anthracycline antibiotics by incorporation of chiral building blocks we prepared the O-methyl 3-deoxy-2-C-ethylribopyranoside 1.1 The further synthetic plan required the conversion of 1 to the dithioacetal 2 followed by glycol cleavage to a partially protected 1,4-dialdehyde for coupling experiments to leucoquinizarine in a Marschalk reaction. However, the reaction sequence failed1 and optically active rhodomycinone had to be synthezised in a different way.2 A reinvestigation of the synthesis revealed that the thioacetalization of 1 using the acidic conditions recommended by Corey et al.3 did not yield the usual open chain dithioacetal 2 but rather three new unexpected products. The less polar fraction was identified by 1H and 13C NMR as tetrahydrofuran derivative 3a with the dithiane ring in a ß-orientation. The solid polar fraction (12%) consisted of a nonseparable 1:2.2 mixture of the epimeric deoxygenation products 4/5. 相似文献
7.
The synthesis of the aliphatic subunit 9 of the macrolide LL‐Z1640‐2 (I), starting from a 4‐deoxy‐D‐mannose derivative 2a, is described. The procedure includes the first successful application of a Vasella ring opening reaction for a 4‐deoxypyranoside. Nucleophilic addition of an alkynyllithium reagent to the aldehyde 4 led to the propargylic alcohol 7, which was converted to the advanced building block 9 in two further steps. 相似文献
8.
Karsten Krohn 《Tetrahedron letters》1980,21(37):3557-3560
Naturally occurring quinones such as 7-methyljuglone, chrysophanol, emodin, helminthosporin, phomarin and physcion were prepared via Diels-Alder reaction and PCC-oxidation of the allylic alkohols obtained from the adducts. 相似文献
9.
H.W. Galbraith C.W. Patterson B.J. Krohn W.G. Harter 《Journal of Molecular Spectroscopy》1978,73(3):475-493
For states of high angular momentum we obtain expressions for the transition frequencies in the triply degenerate fundamental of a “heavy” spherical top, that are accurate to spectroscopic resolution, without tedious calculation of octahedral (or tetrahedral) vector coupling coefficients or diagonalization of matrices. Our calculations are based upon the physical assumption that as the molecule rotates with larger angular momentum it behaves like a symmetric top with the coupled pure rotational angular momentum quantized along either the four- or threefold body-fixed axes. We find that the approximate calculation which involves only 3-J symbols quite accurately reproduces the result of a complete diagonalization of the Hamiltonian, so that for all but the most accurate saturated absorption spectra theoretical analysis may be carried out without reference to the octahedral (or tetrahedral) subgroup of the rotation group. 相似文献
10.