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941.
942.
943.
944.
Marian Mikokajczyk Piotr Bakczewski Krzysztof Wroblewski Janina Karolak-Wojciechowska Andrzej Miller Michał W. Wieczorek Michail Y. Antipin Yurij T. Struchkov 《Tetrahedron》1984,40(23):4885-4892
1H-NMR studies and X-ray analysis indicate that 2-dimethoxyphosphoryl-1,3,5-trithiane exists both in solution and in the crystal in a chair conformation with the dimethoxyphosphoryl group at C-2 being axial. 相似文献
945.
Krzysztof Burak Zbigniew Ciunik Tadeusz Głowiak 《Journal of chemical crystallography》1994,24(8):503-506
The structures of racemic 2-hydroxy-4-hydroxyiminopinan-3-one (1) and 3-hydroxyimino-cis-pinan-4-one monohydrate (2) have been determined by X-ray diffraction. The crystals of1 are monoclinic:P21/c, a=7.838(2),b=10.776(3),c=12.025(3) Å, =105.09(1)°,Z=4, room temp.; the crystals of2 are orthorhombic;P212121,a=8.181(3),b=9.250(3),c=14.085(6)Å,Z=4, T=80K. Both structures were solved by direct methods, and refined toR=0.037 for 1920 reflections (1) and 0.032 for 1776 reflections (2). The absolute configuration of2 was not established. The hydroxyimine groups in both crystals and water molecules in2 participate in the network O–H...O of hydrogen bonds. 相似文献
946.
If L is a uniformly elliptic operator in non-divergence form,the boundary Harnack principle for the ratio of positive L-harmonicfunctions holds in Hölder domains of order if > . A counterexample shows that is sharp. For Hölder domainsof order with (0,1], the boundary Harnack principle holds providedthe domain also satisfies a strong uniform regularity condition. 相似文献
947.
Krzysztof KoŁodziejczyk 《Geometriae Dedicata》1996,61(3):271-278
Let
be the tiling of R
3 with unit cubes whose vertices belong to the fundamental lattice L
1 of points with integer coordinates. Denote by L
n
the lattice consisting of all points x in R
3 such that nx belongs to L
1. When the vertices of a polyhedron P in R
3 are restricted to lie in L
1 then there is a formula which relates the volume of P to the numbers of all points of two lattices L
1 and L
n
lying in the interior and on the boundary of P. In the simplest case of the lattices L
1 and L
2 there are 27 points in each cube from
whose relationships to the polyhedron P must be examined. In this note we present a new formula for the volume of lattice polyhedra in R
3 which involves only nine points in each cube of
: one from L
2 and eight belonging to L
4. Another virtue of our formula is that it does not employ any additional parameters, such as the Euler characteristic. 相似文献
948.
Krzysztof Stempak 《Monatshefte für Mathematik》1996,122(2):187-197
We supplement our previous paper [9] by adding a theorem that transplantsL
p
-norm maximal inequalities for Laguerre multipliers. As an immediate consequence we obtain negative results concerningL
p
-estimates of partial sum maximal operators for Laguerre expansions.Research supported in part by KBN grant No. 2 PO3A 030 09. 相似文献
949.
Abstract— N-Hydroxypyridine-2-thione, 2-S-PyrNOH, a potent antimicrobial, antifungal and anticancer agent, is photochemically active and upon UV irradiation generates free radicals. We have employed EPR and the spin-trap 5,5-dimethyl-l-pyrroline TV-oxide (DMPO) to investigate the photochemistry in aqueous solutions of 2-S-PyrNOH (used here in the form of a sodium salt, 2-S-PyrNONa). We found that upon photoactivation 2-S-PyrNONa can follow two different pathways: it can produce hydroxyl radicals and/or it can act as a photoreducing agent. The capacity of 2-S-PyrNONa to produce “OH” radicals has been demonstrated by: (1) EPR detection of the DMPO/OH adduct in UV-irradiated samples; (2) inhibition of the DMPO/OH formation by OH scavengers such as methyl alcohol, formate and DMSO and (3) by detection of EPR signals of DMPO adducts with radicals derived from reaction of OH with these inhibitors. The photoreductive capacity of 2-S-PyrNONa was deduced from the observation that the amplitude of the EPR signal of the spin adduct DMPO/OH decreased on UV irradiation in air-free pH 7.0 buffers and that the signal recovered in the dark and after aeration. The ability to generate free radicals upon UV irradiation suggests that 2-S-PyrNONa can be regarded as a potential photocytotoxic agent. This feature may be relevant to the biological action of this compound. Our findings also emphasize that caution should be used when 2-S-PyrNOH is employed as a source of OH radicals in biological or chemical systems. 相似文献
950.
Samuel J. Cole Krzysztof Szalewicz Rodney J. Bartlett 《International journal of quantum chemistry》1986,30(5):695-711
The interaction energy of several conformations of the nitromethane dimer is investigated at the SCF level. The dispersion energy and counterpoise correction are computed for certain relative orientations of the monomers. Fourth-order many body perturbation theory SDQ-MBPT(4) energies are reported for selected points. Double zeta and double zeta plus polarization basis sets were used. All calculations were done with the monomer fixed at the isolated monomer geometry. Interaction energies as large as 6 kcal/mol are found at minima of hydrogen bonding orientations. 相似文献