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排序方式: 共有275条查询结果,搜索用时 46 毫秒
251.
[reaction: see text] Short oligo-U sequences containing 2'-O-acyloxymethyl or acylthiomethyl groups as biolabile 2'-O-protections of RNA have been synthesized. These modified homouridylates are deprotected upon cellular esterase activation to release the parent RNA. They exhibit exceptional resistance to nuclease degradation, and the evaluation of their pairing properties shows that the 2'-acyloxymethyl groups do not prevent the duplex dsRNA formation. These biolabile 2'-modifications overcome the first hurdle to turn oligoribonucleotides into candidates for RNA interference drugs. 相似文献
252.
A selective clean-up procedure using an immunosorbent (IS) was developed for the trace-level determination, in water and urine samples, of 3-benzo(a)pyrene-glucuronide (3-BP-G), a biomarker of exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs). First, three sorbents used for the immobilization of antibodies were evaluated for their ability to limit the risk of non-specific interactions and to provide a high bonding density. The best sorbent, i.e. sepharose, was used for the immobilization of two different monoclonal antibodies. The most specific antibody for 3-BP-G was applied to the selective extraction from urine providing a clean extract, an easy and reliable quantification by comparison with a classical SPE process. The sensitivity of the fluorescence associated with the selectivity of the IS provides a limit of detection up to 1.2 ng l(-1) in urine for 3-BP-G. 相似文献
253.
The influence of branched poly(ethyleneimine) on the phase behavior of the system sodium dodecylsulfate/toluene-pentanol (1:1)/water has been studied. The isotropic microemulsions still exist when water is replaced with aqueous solutions of PEI (up to 30% in weight), but their stability is significantly influenced. From a polymer concentration of 20 wt%, the polymer enhances the solubilization of water in oil, changes the sign of the spontaneous curvature of the surfactant film, and induces an inversion of the microemulsion type from water-in-oil (L(2)) to oil-in-water (L(1)), by the formation of a bicontinuous channel. Further investigations show that the addition of polymer in the L(2) phase changes the droplet-droplet interactions as the conductivity drops and the percolation disappears. In the bicontinuous channel, higher viscosities can be detected, as well as a weak percolation followed by a steep increase of the conductivity, which can be related to evident structural changes in the system. DSC measurements allow then to follow the changes of the water properties in the system, from interfacial-water in the L(2) phase to free-water in the sponge-like phase. Finally, all the measurements performed permit to characterize the structural transitions in the system and to understand the role of the added polymer. 相似文献
254.
A series of [AlL(H(2)O)(2)(NO(3))] complexes, with L standing for an ester substituted salophen-type ligand, has been synthesized, and the luminescence properties have been investigated. These derivatives differ by the nature of the ester-R group introduced at the C5 position of their salicylidene rings (i.e., phenyl, 7a,a'; naphthyl, 7b,b'; pentafluorophenyl, 7c,c'; and p-nitrophenyl, 7d) and by the bis-imino bridge (i.e., 1,2- phenylene, 7a-d; and 1,2-naphthalene, 7a'-c'). All the complexes are characterized by luminescence in the blue range, the chemical diversity having no effect on the emission wavelength (480-485 nm). However, the emission efficiency was found to be strongly dependent on the Schiff-base ligand with quantum yields ranging from ? = 22% to 44%, the highest values being for the salophen derivatives with the electron-withdrawing ester-R groups (7a, 34%; 7a', 23%; 7b, 31%; 7b', 22%; 7c, 40%; 7c', 29%, and 7d, 44%). Both the electrochemical data and DFT calculations show that the HOMO-LUMO band gap is modified as a function of the ester R group (from 2.92 to 3.16 eV, based on the redox potentials). The crystal structures for the N,N'-bis(5-(phenoxycarbonyl)salicylidene)-1,2-phenylenediamine and the N,N'-bis(5-(p-nitrophenoxycarbonyl)salicylidene)-1,2-phenylenediamine aluminum complexes (7a and 7d) are reported. 相似文献
255.
Iaroslav Baglai Valérie Maraval Zoia V. Voitenko Carine Duhayon Yulian M. Volovenko Remi Chauvin 《Tetrahedron》2012,68(34):6908-6913
3-Chloro-2-phenyl-isoindole-1-carbaldehyde has been prepared from N-phenylisoindolinone under Vilsmeier–Hack conditions. This electrophilic isoindole proved to be stable under the basic conditions used in the final treatment (KOH/MeOH), and for weeks under air in the solid state. Nevertheless, the C–Cl bond proved highly sensitive to any treatment with reducing or alkylating agents targeted towards the pendant carbaldehyde group, giving various phthalimide derivatives. This unique reactivity is exploited for the selective synthesis of new aminoisochromanones. 相似文献
256.
257.
Nitrone 3 analogue of 5-deoxy-l-lyxose was derived from d-ribose. Its reduction with aqueous SO2 gave the corresponding 4-amino-sugar 2, a potent α-l-fucosidase inhibitor. 1,3-Dipolar cycloaddition of 3 with alkenes allowed the synthesis of acetohydroxamic acid and ethane-phosphonate derivatives. Hydroxy-ethane derivative 15 is a nanomolar α-l-fucosidase inhibitor. 相似文献
258.
Caspar R Musatkina L Tatosyan A Amouri H Gruselle M Guyard-Duhayon C Duval R Cordier C 《Inorganic chemistry》2004,43(25):7986-7993
Herein, we report on the binding of optically pure ruthenium complexes Delta- or Lambda-[Ru(bpy)(2)(L-L)][PF(6)](2) [L-L = Hcmbpy = 4-carboxy-4'-methyl-2,2'-bipyridine (1), L-L = H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine (2)] to DNA. The binding constants of the two enantiomeric Delta-1 and Lambda-1 complexes to DNA were estimated from titration monitored by (1)H NMR spectroscopy. 2D transferred NOESY (TRNOESY) experiments support the conclusion that Delta-1 and Lambda-1 bind to DNA and that an intermediate-to-fast exchange occurs between bound and free Ru(II) complex. Further, evidence for enantioselective DNA cleavage by Delta-2 is provided by means of gel electrophoresis performed in the presence and in the absence of light; in contrast, the Lambda-2 enantiomer does not. The IR spectrum of enantiomer Delta-2 (or Lambda-2) compared to that of the racemate (rac-2) gives evidence that, in the latter form, the enantiomers are strongly associated. Moreover the X-ray structure of rac-2 was also determined and exhibits as an outstanding feature the formation of a one-dimensional supramolecular species in which the cohesion of the system is maintained by strong hydrogen bonding between carboxylic acid groups of enantiomers Delta-2 and Lambda-2 (cationic parts) with d(O...O) = 2.6 A in agreement with the infrared results. The conclusion that can be drawn from IR and X-ray spectroscopies together is that the self-association in rac-2 is strong. 相似文献
259.
Carine Note Joachim Koetz Sabine Kosmella Brigitte Tiersch 《Colloid and polymer science》2005,283(12):1334-1342
This paper is focused on the synthesis and characterization of hydrophobically modified polyelectrolytes and their use as
reducing as well as stabilizing agents for the formation of gold nanoparticles. Commercially available poly(acrylic acid)
has been hydrophobically modified with various degrees of grafting of butylamine introduced randomly along the chain. Different
analytical methods are performed, i.e., IR and 1H-NMR spectroscopy in combination with elemental analysis to determine the degree of grafting. The modified polymers can successfully
be used for the controlled single-step synthesis and stabilization of gold nanoparticles. The process of nanoparticle formation
is investigated by means of UV-vis spectroscopy. The size and shape of the particles obtained in the presence of unmodified
or modified polyelectrolytes are characterized by dynamic light scattering, zeta potential measurements and transmission electron
microscopy. The polyelectrolytes were involved in the crystallization process of the nanoparticles, and in the presence of
hydrophobic microdomains at the particle surface, a better stabilization at higher temperature can be observed. 相似文献
260.