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91.
Pereira AS Timóteo CG Guilherme M Folgosa F Naik SG Duarte AG Huynh BH Tavares P 《Journal of the American Chemical Society》2012,134(26):10822-10832
Ferritins are ubiquitous and can be found in practically all organisms that utilize Fe. They are composed of 24 subunits forming a hollow sphere with an inner cavity of ~80 ? in diameter. The main function of ferritin is to oxidize the cytotoxic Fe(2+) ions and store the oxidized Fe in the inner cavity. It has been established that the initial step of rapid oxidation of Fe(2+) (ferroxidation) by H-type ferritins, found in vertebrates, occurs at a diiron binding center, termed the ferroxidase center. In bacterial ferritins, however, X-ray crystallographic evidence and amino acid sequence analysis revealed a trinuclear Fe binding center comprising a binuclear Fe binding center (sites A and B), homologous to the ferroxidase center of H-type ferritin, and an adjacent mononuclear Fe binding site (site C). In an effort to obtain further evidence supporting the presence of a trinuclear Fe binding center in bacterial ferritins and to gain information on the states of the iron bound to the trinuclear center, bacterial ferritin from Desulfovibrio vulgaris (DvFtn) and its E130A variant was loaded with substoichiometric amounts of Fe(2+), and the products were characterized by M?ssbauer and EPR spectroscopy. Four distinct Fe species were identified: a paramagnetic diferrous species, a diamagnetic diferrous species, a mixed valence Fe(2+)Fe(3+) species, and a mononuclear Fe(2+) species. The latter three species were detected in the wild-type DvFtn, while the paramagnetic diferrous species was detected in the E130A variant. These observations can be rationally explained by the presence of a trinuclear Fe binding center, and the four Fe species can be properly assigned to the three Fe binding sites. Further, our spectroscopic data suggest that (1) the fully occupied trinuclear center supports an all ferrous state, (2) sites B and C are bridged by a μ-OH group forming a diiron subcenter within the trinuclear center, and (3) this subcenter can afford both a mixed valence Fe(2+)Fe(3+) state and a diferrous state. Mechanistic insights provided by these new findings are discussed and a minimal mechanistic scheme involving O-O bond cleavage is proposed. 相似文献
92.
93.
Mustafa Zengin Hayriye GencTuna Demirci Mustafa ArslanMustafa Kucukislamoglu 《Tetrahedron letters》2011,52(18):2333-2335
An efficient, easy, cheap, convenient, and safe procedure for the reduction of various alkenes to the corresponding alkanes is developed by using scrap automobile catalyst as an efficient hydrogenation catalyst. This procedure not only gives high yields, but also allows recycling of automobile wastes as a catalyst in organic reactions and is representative of green chemistry. 相似文献
94.
Reducible Dimeric Conjugates of Small Internally Segment Interfering RNA for Efficient Gene Silencing 下载免费PDF全文
The condensation of nucleic acids into compact nanoparticles with cationic carriers is a powerful tool for translocating exogenous nucleic acids into cells. To date, most efforts have been focused on the development of novel gene carriers for safe and efficient gene delivery. However, small interfering RNA (siRNA) is generally not strongly associated with cationic carriers due to its stiff structure and low spatial charge density. To overcome this limitation, this work introduces a well‐defined dimeric conjugate of small internally segment interfering RNA (sisiRNA) linked via a disulfide bond for enhanced cellular uptake and gene silencing. Dimeric sisiRNA is synthesized through oxidizing two monomeric sisiRNA molecules, each of which consists of a sense strand carrying a nick and an antisense strand modified with a thiol group at the 3′‐end. The nick in the sense strand enables the dimeric sisiRNA to be more effectively condensed into nanosized complexes due to the increased structural flexibility, which results in a higher gene silencing efficiency compared with the dimeric siRNA containing the intact sense strands. The results indicate that the discontinuity of the sense strands is a simple method of adding more flexibility to various siRNA‐based nanostructures for enhanced gene silencing.
95.
Whei Oh Lin José Américo de Azeredo Figueira Helmut G. Alt 《Monatshefte für Chemie / Chemical Monthly》1985,116(2):217-221
The syntheses of acyclic compounds featuring ether-amide groups and different terminal substituents are presented. Three series of new multidentate potential ligands were obtained.
Neue mehrzähnige potentielle Ionophore des Ether-Amid-Typs
Zusammenfassung Es wird die Synthese acyclischer Verbindungen mit Ether-Amid-Gruppen und verschiedenen endständigen Substituenten beschrieben. Es wurden drei Verbindungsreihen erhalten, die neue potentielle mehrzähnige Liganden repräsentieren.相似文献
96.
Santos MA Gil M Marques S Gano L Chaves S 《Analytical and bioanalytical chemistry》2005,381(2):413-419
A study of a series of bifunctional 3-hydroxy-4-pyridinone derivatives, containing side-chains with various alkyl-aryl-amine-amides as extra-functional groups, was conducted to assess the relevance of those groups to the Al-chelating affinity, the lipo–hydrophilic balance of the compounds, and 67Ga biodistribution in mice, in view of their potential use as Al-decorporating agents; the results were compared with those for the drug Deferriprone. Their acid–base properties and Al-chelating affinity in aqueous solution were studied by potentiometric techniques. These ligands form very stable tris-chelated Al complexes and the non-chelating extra-groups are only responsible for small differences in the complex stability (pAl1.2). At physiological pH the major ligand/complex species have different charges, because of the different extent of protonation of the ligands. The introduction of the different groups induces a well-balanced stepwise-like lipo–hydrophilic character (–0.2<log Doct./water<+1.1). The effect of each ligand on the biodistribution of 67Ga in overloaded mice is rapid blood clearance for all of them, but with different biodistribution patterns, namely excretion pathways and brain uptake/clearance, thus suggesting potential different clinical use. 相似文献
97.
Rauter AP Fernandes AC Czernecki S Valery JM 《The Journal of organic chemistry》1996,61(11):3594-3598
A five-step synthesis from 3 leading to a partially protected amipurimycin sugar moiety 14 in an overall yield of 47% is described and includes deoxygenation at C-4 and regio- and stereoselective construction of the branched chain. Deoxygenation at C-4 of 3 was possible by three different methods. Radical reduction with tri-n-butyltin hydride of the appropriate phenoxythiocarbonyl derivative afforded the desired deoxysugar 5 in 47% overall yield together with the secondary products 6 and 7 due to depivaloylation at C-2 and elimination of methanol. The most adequate deoxygenation procedure used the system Ph(3)P/I(2)/imidazole which led to the preparation of 5 in one step in 61% yield. When the system Ph(3)PBr(2)/Ph(3)P was tried, only 8 was formed due to elimination of methanol. The synthesis of 5 was then accomplished by reaction of 8 with methanol in the presence of triphenylphosphine hydrobromide in 37% overall yield. Branched-chain construction was accomplished by Wittig reaction of 5 with [(ethoxycarbonyl)methylene]triphenylphosphorane, followed by osmilation and reduction with lithium aluminum hydride. Isopropylidenation of 14 afforded 16 with a free hydroxy group at C-6 for chain elongation and further synthesis of amipurimycin. 相似文献
98.
We report the synthesis of new prochiral imines by the reaction of nonsymmetric benzophenone derivates, bencylamines, and anilines in good yields. All the products were characterized by 1H and 13C NMR as an isomeric E/Z mixture. Also, the molecular structures for five derivatives determined by single-crystal x-ray experiments are presented. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
99.
Amédée Debiard 《Journal of Functional Analysis》1981,40(2):185-265
Growth of harmonic functions and boundary values in a Sobolev space; comparison between the Hp space associated to Calderón Lusin's area integral and the Hp space associated to the maximal admissible function; study of Littlewood-Paley functions for the harmonic functions for the invariant laplacian of the hermitian hyperbolic space; relation between a Littlewood-Paley function and the bounded mean oscillation functions; study of H1 and H1 B.M.O. duality. 相似文献
100.
[reaction: see text] A base-induced ring opening/imine isomerization/diastereoselective organometallic addition sequence on 4-substituted 2-perfluoroalkyl-1,3-oxazolidines has been developed for the asymmetric synthesis of aryl alpha-perfluoroalkylamine derivatives. This practical method provides chiral amino alcohols in 60-95% yield with uniformely high diastereoselectivities ranging from 35:1 to >100:1. 相似文献