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961.
Michel M Arntz Y Fleith G Toquant J Haikel Y Voegel JC Schaaf P Ball V 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2358-2364
The development of chemical reactions in nanospaces is of paramount importance for the development of active nanodevices, particularly in nanofluidics. It has been shown in a previous paper that phospholipid vesicles can be incorporated without spontaneous bilayer rupture into poly-L-glutamic acid/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films. The aim of the present study was to use such a system as an "embedded submicronic reactor" able to trigger precipitation of calcium phosphates within closed spaces through an enzymatic reaction, the enzyme also being encapsulated in the vesicle interior. To this aim, large unilamellar vesicles (LUVs) were produced containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. After stabilization by adding a layer of poly-(D-lysine), these vesicles were embedded in a (PGA-PAH)n film. A paranitrophenyl phosphate containing solution was then put in contact with this film. It is shown by means of infrared spectroscopy in the attenuated total reflection mode that, consecutively to this contact, calcium phosphates are growing inside the embedded vesicles. By using scanning near-field fluorescence microscopy, it is demonstrated that the alkaline phosphatase enzymes are most probably located inside the vesicles after their embedding. In addition, atomic force microscopy was used to show, after chemical removal of the organic top layer of the film, that the inorganic platelets produced after the precipitation reaction are localized in volumes of similar size and shape as that of the vesicles into which the phosphate ester hydrolysis and subsequent precipitation reaction did occur. 相似文献
962.
Wang Y Holmes MC Leaver MS Fogden A 《Langmuir : the ACS journal of surfaces and colloids》2006,22(26):10951-10957
The binary system of hexaethylene glycol n-hexadecyl ether (C16EO6) and water (2H2O) has a complex, temperature-dependent lyotropic phase sequence, in the concentration region of 48-62 wt %. On cooling it shows the sequence lamellar phase, L(alpha), random mesh phase Mh1(0), rhombohedral mesh phase, Mh1(R(-)3m), bicontinuous cubic phase, V1(Ia(-)3d), and a two-phase hexagonal region, H1+Lbeta. On heating from the latter two-phase region the phase sequence is V1(Ia(-)3d), ,Mh1(0), and Lalpha. Polarizing optical microscopy, 2H nuclear magnetic resonance, and small-angle X-ray scattering have been used to study the stability of these phases, their sequence, and their physical parameters with the addition of the oils, 1-hexene, decane, and octadecane. The oils are located within the alkyl chain regions of the mesophase structures. Depending on whether the added oil is "penetrating" or "swelling", it may reside in the region between the C16 alkyl chains of the surfactant or at the center of the bilayer and affect phase stability. Oils affect both the volume of the alkyl chain region (at fixed surfactant water mole ratio) and the rigidity of the interfacial region. Both effects can influence the phase structures and their ranges of stability. Adding different types of oil to the mesh phases gives an opportunity to understand the factors that are important in their formation. The transition from the Mh1(R(-)3m) phase to Mh1(0) phase is triggered by the hydrocarbon region swelling to a critical volume fraction of 0.32, a surfactant rod radius of approximately 1.75 nm, and a critical water layer thickness of approximately 2.5 nm. The latter is most likely responsible for a weakening of the interlayer headgroup overlap interaction and the loss of correlation between the layers. The lamellar phase becomes the only stable phase at high oil content. 相似文献
963.
Martin D Kehrli S d'Augustin M Clavier H Mauduit M Alexakis A 《Journal of the American Chemical Society》2006,128(26):8416-8417
The copper-catalyzed asymmetric conjugate addition of Grignard reagents to trisubstituted cyclic enones affords enantioenriched all-carbon quaternary centers with up to 96% ee. The chiral ligand is a diaminocarbene, directly generated in situ. The combination of Grignard reagent and diaminocarbene is unprecedented in conjugate addition, and the additon of the phenyl group, on such enones, cannot be done by other conjugate addition methods. 相似文献
964.
Imoto S Patro JN Jiang YL Oka N Greenberg MM 《Journal of the American Chemical Society》2006,128(45):14606-14611
The nucleoside triphosphates of N6-(2-deoxy-alpha,beta-d-erythro-pentofuranosyl)-2,6-diamino-4-hydroxy-5-formamidopyrimidine (Fapy.dGTP) and its C-nucleoside analogue (beta-C-Fapy.dGTP) were synthesized. The lability of the formamide group required that nucleoside triphosphate formation be carried out using an umpolung strategy in which pyrophosphate was activated toward nucleophilic attack. The Klenow fragment of DNA polymerase I from Escherichia coli accepted Fapy.dGTP and beta-C-Fapy.dGTP as substrates much less efficiently than it did dGTP. Subsequent extension of a primer containing either modified nucleotide was less affected compared to when the native nucleotide is present at the 3'-terminus. The specificity constants are sufficiently large that nucleoside triphosphate incorporation could account for the level of Fapy.dG observed in cells if 1% of the dGTP pool is converted to Fapy.dGTP. Similarly, polymerase-mediated introduction of beta-C-Fapy.dG could be useful for incorporating useful amounts of this nonhydrolyzable analogue for use as an inhibitor of base excision repair. The kinetic viability of these processes is enhanced by inefficient hydrolysis of Fapy.dGTP and beta-C-Fapy.dGTP by MutT, the E. coli enzyme that releases pyrophosphate and the corresponding nucleoside monophosphate upon reaction with structurally related nucleoside triphosphates. 相似文献
965.
Spijksma GI Bouwmeester HJ Blank DH Fischer A Henry M Kessler VG 《Inorganic chemistry》2006,45(13):4938-4950
The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr(OnPr)3(thd)](2), [Zr(OnPr)(OiPr)2(thd)]2, Zr(OiPr)(thd)3, [Hf(OnPr)3(thd)]2, and Hf(OiPr)(thd)3 were isolated and characterized. The structure of the n-propoxide analogue of Zr(OiPr)(thd)3 could not be refined, but its existence was clearly demonstrated by XRD and 1H NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be "Zr(OiPr)2(thd)2" and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)(OiPr)(thd)2]2, which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)4 or Hf(thd)4) The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of MIV(thd)4 has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds. 相似文献
966.
The syntheses of two isoprostanyl phospholipids are described. A newly established route to 15-F(2t)-isoprostane and ent-15-epi-F(2t)-isoprostane has allowed for the selective preparation of 15-F(2t)-isoprostanyl phosphatidylethanolamine and ent-15-epi-F(2t)-isoprostanyl phosphatidylcholine. The nature of the headgroups dictates the coupling strategy used to attach the appropriately protected isoprostanes to the corresponding lysophospholipids. Preliminary 1H NMR and 31P NMR studies indicate that these isoprostanyl phospholipids aggregate in apolar solvents. 相似文献
967.
Peters R Althaus M Diolez C Rolland A Manginot E Veyrat M 《The Journal of organic chemistry》2006,71(20):7583-7595
Two practical, efficient, and scalable asymmetric routes to DE ring fragment 7, a key building block in the synthesis of the homocamptothecin derivative diflomotecan 4, are described. The "acetal route" starts from 2-chloro-4-cyanopyridine 8 and represents an enantioselective and optimized modification of the original racemic discovery chemistry synthesis. The inefficient optical resolution procedure was replaced by an efficient asymmetric acetate aldol addition (dr 87:13) to a ketone substrate as the key step generating the (R)-configured quaternary stereocenter with high stereoselectivity. 7 was finally obtained in 8.9% overall yield (er 99.95:0.05) over nine steps, avoiding chromatographic purifications and comparing favorably with the initial procedure. In the related "amide route" starting from 2-chloroisonicotinic acid 41, a secondary amide directing group was used to facilitate the ortho lithiation of the pyridine 3-position. The key step of this protocol again consists of a practical asymmetric acetate aldol addition (dr = 87:13). The DE ring building block 7 was thus obtained in 11.1% overall yield (er > 99.95:0.05) over nine steps requiring only one chromatographic purification. 相似文献
968.
The pressure-induced redox reaction within the system Cs2[Pd2+I4].I2/Cs2[Pd4+I6] was investigated by means of powder X-ray diffraction. Analogous high-pressure X-ray diffraction experiments were performed on the isostructural compounds Cs2[PdX4].I2 (X = Cl, Br). Additionally, the phase transition of Cs2[PdBr4].I2 to Cs2[PdBr4I2] was characterized by means of Raman scattering experiments as well as theoretical calculations based on density functional theory. On the basis of experimentally determined crystal structure data, a pathway for the topology of the redox reactions was developed and outlined. 相似文献
969.
Identification of small-molecule targets remains an important challenge for chemical genetics. We report an approach for target identification and protein discovery based on functional suppression of chemical inhibition in vitro. We discovered pirl1, an inhibitor of actin assembly, in a screen conducted with cytoplasmic extracts. Pirl1 was used to partially inhibit actin assembly in the same assay, and concentrated biochemical fractions of cytoplasmic extracts were added to find activities that suppressed pirl1 inhibition. Two activities were detected, separately purified, and identified as Arp2/3 complex and Cdc42/RhoGDI complex, both known regulators of actin assembly. We show that pirl1 directly inhibits activation of Cdc42/RhoGDI, but that Arp2/3 complex represents a downstream suppressor. This work introduces a general method for using low-micromolar chemical inhibitors to identify both inhibitor targets and other components of a signaling pathway. 相似文献
970.
Nicolas Lebouvier Typhanie Corbin Guillaume Le Baut Marc Le Borgne 《Tetrahedron letters》2006,47(36):6479-6483
New conazole antifungals, in the series of triazole alcohols 23a-d and 24a-e incorporating an indole moiety substituted at 5-position by halogens, a cyano or 4-methoxyphenyl group, have been synthesized by ring opening of corresponding oxiranes 15 and 16. These dihalogeno intermediates and their congeneers could be prepared in high yields by Corey-Chaykovsky reaction under microwave irradiation. 相似文献