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341.
Ranaweera RA Sankaranarayanan J Casey L Ault BS Gudmundsdottir AD 《The Journal of organic chemistry》2011,76(20):8177-8188
Photolysis of 1 in chloroform yielded 2 as the major product and a small quantity of 3. Laser flash photolysis demonstrated that upon irradiation, the first excited triplet state of the ketone (T(1K)) of 1 is formed and decayed to form radical 4, which has a λ(max) at 380 nm (τ = 2 μs). Radical 4 expelled a nitrogen molecule to yield imine radical 5 (λ(max) at 300 nm). Density functional theory (DFT) calculations showed that the transition state barrier for the formation of 5 is approximately 4 kcal/mol. In comparison, photolysis of 1 in argon matrices resulted in triplet nitrene 6, which was further characterized with (15)N and D isotope labeling and DFT calculations. Prolonged irradiation of 6 yields triplet imine nitrene 7. 相似文献
342.
Numerical simulations have been carried out in the framework of waveguide theory to model collection mode scanning near-field
optical microscopy (SNOM). The theoretical model includes the optical fiber end and describes the metal coated aperture on
the probe tip. The developed formalism goes beyond the existing Bethe-Bouwkamp theories for electromagnetic transmission of
subwavelength apertures. The finite coating and optical fiber end are now taken into account. The new features enable us to
simulate the near-field probes that are widely used in the collection mode SNOM. The emphases of the numerical analyses have
been mainly on the resolution mechanism of the microscopy. Influence on the resolution from important parameters of the probe
tips, such as the size of the apertures and the probe-sample distance, is extensively studied. The resolution dependence has
been analyzed in the light of the near-field coupling efficiency of the probe tip. An optimum tip size has been found which
is balanced between the significant signal transmission and the resolution of the device. 相似文献
343.
A mixture of 2-(di-tert-butylphosphino)biphenyl and dicarbonylacetonato rhodium(I) provides an effective catalyst system for the addition of alkynes to aldehydes and activated ketones. In contrast to the more common zinc-catalyzed processes, enolizable 1,2-dicarbonyls are excellent substrates for these rhodium-catalyzed additions. This reaction allows for the formation of propargylic alcohols under mild conditions, tolerating many functional groups (such as carboxylic acids) that are incompatible with other methods. Little selectivity was observed in cases of unsymmetrical 1,2-diketones. Addition of alkynes to aldehydes with an adjacent chirality center usually provides the Felkin addition product with excellent selectivity in some cases. Studies on the catalyst structure show that both the beta-diketonate and a carbon monoxide ligand appear to be bound to the active catalyst. The use of chiral phosphines to induce asymmetry in the propargyl alcohol products provided low enantioselectivity, which may be due to the phosphine having a distal relationship to the reacting centers. Modification of other ligands, such as the beta-diketonate, appears to be a more promising avenue for the development of an enantioselective variant. 相似文献
344.
Synthesis of an epoxy functionalized spiroorthocarbonate used as low shrinkage additive in cationic UV curing of an epoxy resin 总被引:1,自引:0,他引:1
Marco Sangermano Ricardo Acosta Ortiz Lydia Berlanga Duarte Ramiro Guerrero Santos 《European Polymer Journal》2008,44(4):1046-1052
The synthesis of an epoxy functionalized spiroorthocarbonate (SOC) is reported. The obtained monomer has been used a slow shrinkable additive in cationic UV curing of a commercially available dicycloepoxy resin. A polymer network flexibilization was evidenced by increasing the SOC content in the photocurable formulation. It has been demonstrated that SOC acts as shrinkage reduction additive reaching expansion on volume after polymerization in the presence of 10 wt% of the functionalized spiroorthocarbonate. 相似文献
345.
The relative affinity of the cationic triangular metallaprism, [(pCH(3)C(6)H(4)Pr(i))(6)Ru(6)(tpt)(2)(dhbq)(3)](6+) ([1](6+)), for various amino acids, ascorbic acid, and glutathione (GSH) has been studied at 37 °C in aqueous solutions at pD 7, using NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The metallaprism [1](6+), which is constituted of six (pCH(3)C(6)H(4)Pr(i))Ru corners bridged by three 1,4-benzoquinonato (dhbq) ligands and connected by two 2,4,6tri(pyridin4yl)1,3,5-triazine (tpt) triangular panels, disassembled in the presence of Arg, His, and Lys, while it remains intact with Met. Coordination to the imidazole nitrogen atom in His or to the basic NH/NH(2) groups in Arg and Lys displaces the dhbq and tpt ligands from the (p-cymene)Ru units, and subsequent coordination to the amino and carboxylato groups forms stable N,N,O metallacycles. The binding to amino acids proceeds rapidly, as determined by NMR spectroscopy. Interestingly, solutions of [1](6+) are able to catalyze oxidation of the thiol group of Cys and GSH to give the corresponding disulfides and of ascorbic acid to give the corresponding dehydroascorbic acid. Competition experiments with Arg, Cys, His, and Lys show the simultaneous formation of one single adduct, the (p-cymene)Ru-His complex, and oxidation of Cys to cystine. Furthermore, the (p-cymene)Ru-His complex formed upon the addition of His to [1][CF(3)SO(3)](6) is able to oxidize Cys to cystine much more efficiently than [1](6+). These results provide evidence against interaction with proteins as process in the release of encapsulated guest molecules. Oxidation of Cys and GSH to give the corresponding disulfides may explain the in vitro anticancer activity of [1](6+). 相似文献
346.
Cyclohexyl radicals have been produced by λ-irradiation of cyclohexane incorporated in an adamantane matrix. ESR spectra of both rigid and inverting radicals have been observed. 相似文献
347.
The paper presents some approximate and exact tests for testing variance components in general unbalanced mixed linear model. It extends the results presented by Seifert (1992) with emphasis on the computational aspects of the problem. 相似文献
348.
349.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
350.