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91.
Weak Intermolecular Hydrogen Bonds with Fluorine: Detection and Implications for Enzymatic/Chemical Reactions,Chemical Properties,and Ligand/Protein Fluorine NMR Screening 下载免费PDF全文
Dr. Claudio Dalvit Dr. Anna Vulpetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7592-7601
It is known that strong hydrogen‐bonding interactions play an important role in many chemical and biological systems. However, weak or very weak hydrogen bonds, which are often difficult to detect and characterize, may also be relevant in many recognition and reaction processes. Fluorine serving as a hydrogen‐bond acceptor has been the subject of many controversial discussions and there are different opinions about it. It now appears that there is compelling experimental evidence for the involvement of fluorine in weak intramolecular or intermolecular hydrogen bonds. Using established NMR methods, we have previously characterized and measured the strengths of intermolecular hydrogen‐bond complexes involving the fluorine moieties CH2F, CHF2, and CF3, and have compared them with the well‐known hydrogen‐bond complex formed between acetophenone and the strong hydrogen‐bond donor p‐fluorophenol. We now report evidence for the formation of hydrogen bonds involving fluorine with significantly weaker donors, namely 5‐fluoroindole and water. A simple NMR method is proposed for the simultaneous measurement of the strengths of hydrogen bonds between an acceptor and a donor or water. Important implications of these results for enzymatic/chemical reactions involving fluorine, for chemical and physical properties, and for ligand/protein 19F NMR screening are analyzed through experiments and theoretical simulations. 相似文献
92.
The main objective of the study is the accurate modeling of the bubble pressure and of the vapor phase concentration in associating hydrocarbon + alcohol mixtures and the correct comparison with results from the literature. A relatively simple equation of state is used and comparison is done considering various factors that affect the accuracy of the results, so fair and correct conclusions can be drawn. The mathematical complexity of the model, the type and amount of basic properties and the number of adjustable parameters used by the model, among other factors are discussed. The Peng-Robinson equation of state including the Wong-Sandler mixing rules was used. This combination of equations of state and mixing rules have not yet been applied in a systematic way to alcohol + hydrocarbon mixtures at low and moderate pressure, as done in this work, although other complex equation of state models have been used for some selected systems. It is concluded that simple and well-founded models can correlate equilibrium data in these complex mixtures with similar accuracy than other more sophisticated models. 相似文献
93.
Francesco Gasparrini Francesco Maggio Claudio Villani Alberto Brandi Stefano Cicchi K Michał Pietrusiewicz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract High-performance liquid chromatography utilizing chiral stationary phases (CSPs) is well established as a very simple and efficient method for obtaining discrete amounts of optically active compounds with high e.e., as well as for determining their enantiomeric composition We wish to demonstrate in the present work that a totally synthetic brush-type π-acidic CSP based on a bis(N,N′-3,5-dinitrobenzoyl) derivative of (R,R)- or (S,S)-trans-1,2-diaminocyclohexane as selector can be used successfully to resolve variety of chiral organophosphorus compounds containing stereogenic centers at phosphorus 相似文献
94.
Claudio C. Silveira Samuel R. Mendes Guilherme M. Martins 《Tetrahedron letters》2012,53(13):1567-1570
Ce(OTf)3 was successfully employed as catalyst for the activation of the hydroxyl group in the Friedel–Crafts reaction of aromatic compounds with propargylic alcohols in nitromethane. The products were obtained in good to excellent yields. 相似文献
95.
Development of a syn‐Selective Mannich Reaction of Aldehydes with Propargylic Imines by Dual Catalysis: Asymmetric Synthesis of Functionalized Propargylic Amines 下载免费PDF全文
Irati Lapuerta Dr. Silvia Vera Prof. Mikel Oiarbide Prof. Claudio Palomo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7229-7237
Direct coupling of enolizable aldehydes with C‐alkynyl imines is realized affording the corresponding propargylic Mannich adducts of syn configuration, thus complementing previous methods that gave access to the anti‐isomers. The combination of proline and a urea Brønsted base cocatalyst is key for the reactions to proceed under very mild conditions (3–10 mol % catalyst loading, dichloromethane as solvent, ?20 °C, 1.2 molar equivalents of aldehyde) and with virtually total stereocontrol (syn/anti ratio up to 99:1; ee up to 99 %). Some possibilities of further chemical elaboration of adducts are also briefly illustrated. 相似文献
96.
Francesco Carlà Giulio Campo Claudio Sangregorio Andrea Caneschi César de Julián Fernández Lourdes I. Cabrera 《Journal of nanoparticle research》2013,15(8):1-16
Quantum dots (QDs) have received considerable attention due to their unique optical and electrical properties. Although substantial research has focused on the potential applications and toxicological impacts of QDs, far less effort has been directed toward understanding their fate and transport in the environment. In this work, the effect of four coatings, polyethylene glycol functionalized polymer (PEGP), carboxyl derivatized polymer (COOHP), linoleic acid (LA), and polyacrylic acid-octylamine (PAA-OA), on the transport and retention of QDs in porous media were evaluated under environmentally relevant conditions. Aqueous QD suspensions (ca. 10 nM) were introduced into water-saturated columns packed with 40–50 mesh Ottawa sand at a pore-water velocity of 7.6 m/day. At an ionic strength (IS) of 3 mM and pH of 7, PEGP-coated QDs were completely retained within the column, while more than 60 % of COOHP-coated QDs were transported through a column run under identical conditions. When PAA-OA and LA were used as coatings, effluent QD recoveries increased to more than 65 and 89 % of the injected mass, respectively. Additionally, a decrease in pH from 9.5 to 5.0, or an increase of IS from 0 to 30 mM reduced the eluted mass of PAA-OA-coated QDs by more than 2 and 15 times, respectively. The relative mobility of coated QDs (LA > PAA-OA > COOHP > PEGP) was consistent with total interaction energy profiles between QDs and sand surfaces calculated based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. At an IS of 3 mM (NaCl) and pH 7, a linear correlation was obtained between the fraction of eluted QDs and the magnitude of the primary interaction energy barrier. These findings demonstrate the strong dependence of QD transport on coating type and indicate that interaction energies based on DLVO theory can be used to predict the relative mobility of QDs in porous media. 相似文献
97.
Anaí Duarte Wilson Cunico Claudio M.P. Pereira Alex F.C. Flores Rogério A. Freitag Geonir M. Siqueira 《Ultrasonics sonochemistry》2010,17(2):281-283
An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields. 相似文献
98.
99.
100.
Claudio L. Donnici Elaine Henriques Teixeira Pereira Júlio C. Dias Lopes Liliana Marzorati Blanka Wladislaw 《合成通讯》2013,43(3):342-350
The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu3N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO2 and CO2R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu3N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate. 相似文献