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991.
Four new and seven known diterpenes have been isolated from the dichloromethane extract of the aerial parts of Calceolaria polifolia. The structures of the new compounds were established by spectroscopic evidence. 相似文献
992.
Julia Martín Carmen Mejías Juan Luis Santos Irene Aparicio Esteban Alonso 《Molecules (Basel, Switzerland)》2021,26(19)
This work evaluated the availability and sorption behaviour of four pharmaceuticals and eight of their metabolites in sewage sludge and sludge-amended soil. Digested sludge and compost were evaluated. The highest levels found in digested sludge corresponded to caffeine (up to 115 ng g−1 dm), ibuprofen (45 ng g−1 dm) and carbamazepine (9.3 ng g−1 dm). The concentrations measured in compost were even lower than in digested sludge. No compound was detected in sludge-amended soils. This fact could be due to the dilution effect after sludge application to soil. Different adsorption capacities in sludge–soil mixtures were measured for the studied compounds at the same spike concentration. In general, except for paraxanthine and 3-hydroxycarbamazepine, the metabolite concentrations measured in the mixtures were almost two-fold lower than those of their parent compounds, which can be explained by their mobility and lixiviation tendency. The log Kd ranged from −1.55 to 1.71 in sludge samples and from −0.29 to 1.18 in soil–sludge mixtures. The log Kd values calculated for compost were higher than those calculated for digested sludge. The obtained results implied that the higher organic carbon content of compost could influence soil contamination when it is applied to soil. 相似文献
993.
Osvaldo Cox Jos A. Dumas Luis A. Rivera Carmelo García Antonio E. Alegria 《Journal of heterocyclic chemistry》1999,36(4):943-947
The electrochemical reduction of the chloride or perchlorate salts of benzazolo[3,2-a]quinolinium ion and several of its analogues is reported. The compounds studied are the perchlorate salt of 3-nitrobenzothiazolo-and 3-nitro-9-methoxybenzothiazolo[3,2-a]quinolinium, and the chloride salts of 7-ethyl-, 3-nitro-7-methyl-, 3-nitro-7-ethyl-, 3-nitro-7-isopropyl-, 3-nitro-7-butyl- and 3-nitro-7-benzylbenzimidazolo[3,2-a]-quinolinium, respectively. Cyclic voltammetry of the corresponding 3-nitrobenzothiazolo[3,2-a]quinolinium derivatives in N,N-dimethylformamide shows an irreversible peak potential at -0.6 and a quasi-reversible peak at -(1.2–1.3) volts, respectively, relative to the standard calomel electrode. In contrast, the corresponding 3-nitrobenzimidazolo[3,2-a]quinolinium derivatives show, in general, reversible peaks at near -0.8 and -(1.2–1.4) volts, respectively. Upon electrolytic reduction, only the nitro-substituted derivatives produced observable electron paramagnetic resonance electron spin resonance spectra. This observation is explained in terms of the stabilization of the radicals produced by the nitro group. Theoretical MM+/AM1/UHF calculations support the idea that the larger nitrogen splitting is caused by N-12 and the minor splittings by N-7 in the benzimidazolo[3,2-a]quinolinium ion series. 相似文献
994.
Javier Negro Luis M. Nieto David J. Fernndez C. 《Czechoslovak Journal of Physics》2000,50(11):1303-1308
Irreducible second order Darboux (SUSY) transformations are applied to Lam periodic Hamiltonians in order to find physically
acceptable partner potentials with the same band structure. The main differences with the usual SUSY approach of potentials
allowing for a discrete spectrum are pointed out.
Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000.
This work has been partially supported by CONACyT (project 32086-E) Mxico, DGES (PB98-0370) from MEC (Spain), Junta de Castilla
y Len (CO2/199), and Universidad de Valladolid. 相似文献
995.
We employ the simulated annealing algorithm to optimize totally quantized Fourier diffractive elements, whose phase modulation is constrained by a symmetry similar to that of the desired diffraction pattern. Elements optimized under this restriction, show better performance than the conventionally optimized ones, for which the object phase function is randomly modified. In addition, the elements constrained by spatial symmetry are optimized with relatively low computational efforts. 相似文献
996.
Jos Luis Palacios 《International journal of quantum chemistry》2001,81(2):135-140
We find closed‐form expressions for the resistance, or Kirchhoff index, of certain connected graphs using Foster's theorems, random walks, and the superposition principle. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 135–140, 2001 相似文献
997.
998.
999.
We use equivariant bifurcation theory to show the existence of infinite sequences of isometric embeddings of tori with constant mean curvature (CMC) in Euclidean spheres that are not isometrically congruent to the CMC Clifford tori, and accumulating at some CMC Clifford torus. 相似文献
1000.
Jean-Pascal Bourgeois Luis Echegoyen Monia Fibbioli Ern Pretsch Franois Diederich 《Angewandte Chemie (International ed. in English)》1998,37(15):2118-2121
Regioselective Bingel macrocyclization of C60 with a bis-malonate containing a novel dibenzo[18] crown-6 tether provides a versatile access to trans-1 fullerene bis-adducts such as (±)- 1 . Complexation of a potassium ion by (±)- 1 has a pronounced effect on the redox properties of the carbon sphere as a result of the close proximity of the fullerene surface to the crown ether bound cation, which is enforced by the double bridging. 相似文献