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961.
962.
Mattea Carmen Castrovilli Paola Bolognesi Antonella Cartoni Daniele Catone Patrick O’Keeffe Anna Rita Casavola Stefano Turchini Nicola Zema Lorenzo Avaldi 《Journal of the American Society for Mass Spectrometry》2014,25(3):351-367
In the present work, we studied the photoinduced ion chemistry of the halogenated pyrimidines, a class of prototype radiosensitizing molecules, in the energy region 9–15 eV. The work was stimulated by previous studies on inner shell site-selective fragmentation of the pyrimidine molecule, which have shown that the fragmentation is governed by the population/formation of specific ionic states with a hole in valence orbitals, which in turn correlate to accessible dissociation limits. The combined experimental and theoretical study of the appearance energies of the main fragments provides information on the geometric structure of the products and on the role played by the specific halogen atom and the site of halogenation in the dissociation process. This information can be used to gain new insights on the elementary mechanisms that could possibly explain the enhanced radiation damage to the DNA bases or to the medium in which the bases are embedded, thereby contributing to their radiosensitizing effect. Figure
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963.
Ventrella Andrea Verrone Raffaella Cosma Pinalysa Fini Paola Longobardi Francesco Lippolis Vincenzo Pascale Michelangelo Catucci Lucia 《Journal of solution chemistry》2014,43(8):1436-1447
Journal of Solution Chemistry - The interaction of ochratoxin A (OTA) with heptakis-2,6-di-O-methyl-β-cyclodextrin (DIMEB) in aqueous solutions at two different pHs (3.5 and 9.5) was studied... 相似文献
964.
Anna Barattucci Paola Bonaccorsi Teresa Papalia Nadia Manganaro Giuseppe Gattuso 《Tetrahedron letters》2014
meso-(R,S)-Dithia[3.3]-paracyclophane S,S′-dioxide is formed with complete stereoselection by the thermolysis of 3,3′-[1,4-phenylene-bis(methylenesulfinyl)]-dipropanoate—that generates in situ two transient sulfenic acid functions—in the presence of p-diethynylbenzene. By employing an improved procedure that we have recently optimized, the title compound has been prepared in a 70% yield as a single diastereoisomer. A density functional B3LYP/6-311+G(d,p) study demonstrates that the final syn-addition cyclization step takes place under kinetic control, through a five-membered transition state that defines the stereochemistry of the resulting cyclophane. 相似文献
965.
Aura Tintaru Christophe Chendo Qi Wang Stéphane Viel Gilles Quéléver Ling Peng Paola Posocco Sabrina Pricl Laurence Charles 《Analytica chimica acta》2014
Tandem mass spectrometry and ion mobility spectrometry experiments were performed on multiply charged molecules formed upon conjugation of a poly(amidoamine) (PAMAM) dendrimer with a poly(ethylene oxide) (PEO) linear polymer to evidence any conformational modification as a function of their charge state (2+ to 4+) and of the adducted cation (H+vs Li+). Experimental findings were rationalized by molecular dynamics simulations. The G0 PAMAM head-group could accommodate up to three protons, with protonated terminal amine group enclosed in a pseudo 18-crown-6 ring formed by the PEO segment. This particular conformation enabled a hydrogen bond network which allowed long-range proton transfer to occur during collisionally activated dissociation. In contrast, lithium adduction was found to mainly occur onto oxygen atoms of the polyether, each Li+ cation being coordinated by a 12-crown-4 pseudo structure. As a result, for the studied polymeric segment (Mn = 1500 g mol−1), PEO-PAMAM hybrid molecules exhibited a more expanded shape when adducted to lithium as compared to proton. 相似文献
966.
Cezar A. Bizzi Joaquim A. Nóbrega Juliano S. Barin Jussiane S.S. Oliveira Lucas Schmidt Paola A. Mello Erico M.M. Flores 《Analytica chimica acta》2014
The present work evaluates the influence of vessel cooling simultaneously to microwave-assisted digestion performed in a closed system with diluted HNO3 under O2 pressure. The effect of outside air flow-rates (60–190 m3 h−1) used for cooling of digestion vessels was evaluated. An improvement in digestion efficiency caused by the reduction of HNO3 partial pressure was observed when using higher air flow-rate (190 m3 h−1), decreasing the residual carbon content for whole milk powder from 21.7 to 9.3% (lowest and highest air flow-rate, respectively). The use of high air flow-rate outside the digestion vessel resulted in a higher temperature gradient between liquid and gas phases inside the digestion vessel and improved the efficiency of sample digestion. Since a more pronounced temperature gradient was obtained, it contributed for increasing the condensation rate and thus allowed a reduction in the HNO3 partial pressure of the digestion vessel, which improved the regeneration of HNO3. An air flow-rate of 190 m3 h−1 was selected for digestion of animal fat, bovine liver, ground soybean, non fat milk powder, oregano leaves, potato starch and whole milk powder samples, and a standard reference material of apple leaves (NIST 1515), bovine liver (NIST 1577) and whole milk powder (NIST 8435) for further metals determination by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results were in agreement with certified values and no interferences caused by matrix effects during the determination step were observed. 相似文献
967.
Carmen A. Mak Sara Ranjbar Paola Riente Carles Rodríguez-Escrich Miquel A. Pericàs 《Tetrahedron》2014
Two hybrid magnetic materials have been prepared from κ-carrageenan and Fe3O4 nanoparticles and tested as catalysts for the Michael addition of aldehydes to nitroalkenes. Remarkably, the material prepared from unmodified κ-carrageenan showed catalytic activity in the reaction of choice, while the individual components were inactive. This points out to a synergistic effect between the MNPs and κ-carrageenan. The second catalyst, bearing a diphenylprolinol silyl ether moiety, was also shown to promote the reaction, giving rise to the corresponding adducts in excellent ees. After the reaction is complete, the catalysts can be conveniently retrieved by simple magnetic decantation. 相似文献
968.
Synthesis and Electronic Properties of 1,2‐Hemisquarimines and Their Encapsulation in a Cucurbit[7]uril Host 下载免费PDF全文
Christian C. De Filippo Dr. Hao Tang Luca Ravotto Dr. Giacomo Bergamini Dr. Patrizio Salice Dr. Miriam Mba Prof. Paola Ceroni Prof. Elena Galoppini Prof. Michele Maggini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(21):6412-6420
The synthesis of a new class of robust squaraine dyes, colloquially named 1,2‐hemisquarimines (1,2‐HSQiMs), through the microwave‐assisted condensation of aniline derivatives with the 1,2‐squaraine core is reported. In CH3CN, 1,2‐HSQiMs show a broad absorption band with a high extinction coefficient and a maximum at around λ=530 nm, as well as an emission band centered at about λ=574 nm, that are pH dependent. Protonation of the imine nitrogen causes a redshift of both absorption and emission maxima, with a concomitant increase in the lifetime of the emitting excited state. Encapsulation of the chromophore into a cucurbit[7]uril host revealed fluorescence enhancement and increased photostability in water. The redox characteristics of 1,2‐HSQiMs indicate that charge injection into TiO2 is possible; this opens up promising perspectives for their use as photosensitizers for solar energy conversion. 相似文献
969.
Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes 下载免费PDF全文
Luca Biasiolo Marina Trinchillo Prof. Paola Belanzoni Dr. Leonardo Belpassi Prof. Dr. Vincenzo Busico Dr. Gianluca Ciancaleoni Dr. Angela D'Amora Prof. Alceo Macchioni Prof. Francesco Tarantelli Dr. Daniele Zuccaccia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14594-14598
The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N‐heterocyclic carbene‐based gold catalyst, [(NHC)AuX] (X=BARF?, BF4?, OTf?, OTs?, TFA?, or OAc?) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs? anion provides the best compromise to achieve efficient catalysis. 相似文献
970.
Dr. Paola Riente Alba Matas Adams Dr. Josep Albero Prof. Emilio Palomares Prof. Miquel A. Pericàs 《Angewandte Chemie (International ed. in English)》2014,53(36):9613-9616
The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α‐alkylation of aldehydes with α‐bromocarbonyl compounds can be successfully achieved by combining bismuth‐based materials as low‐band‐gap photocatalysts with the second‐generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low‐cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain. 相似文献