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41.
Villorbina G Roura L Camps F Joglar J Fabriàs G 《The Journal of organic chemistry》2003,68(7):2820-2829
The formation of methylenecyclopropanes by enzymatic desaturation of 11-cyclopropylundecanoic acid (1) and its disubstituted derivatives cis- and trans-3-5 has been investigated using the Delta(11) desaturase of Spodoptera littoralis as model enzyme. Gas chromatography coupled to mass spectrometry analyses of methanolyzed lipidic extracts from tissues incubated with each probe revealed that all the cyclopropyl fatty acids were transformed into the corresponding 11-cyclopropylidene acids, except for compound trans-5 (5b), which was not desaturated at C11. The formation of methylenecyclopropane 9 as the only reaction product from 1 indicates that a potential radical intermediate is too short-lived to allow rearrangement reactions. Information on the Delta(11) desaturase substrate binding domain is provided considering the cyclopropyl probes 3-5 as conformationally restricted analogues of the straight-chain substrates. 相似文献
42.
The relative importance of local and long range interactions in the characteristics of the protein folding process has long been a matter of controversy. Computer simulations based on Gō-type models have been widely used to study this topic, but without much agreement on which type of interactions is more relevant for the foldability of a protein. In this work, the authors also employ a topology-based potential and simulation model to analyze the influence of local and long range interactions on the thermodynamics of the folding transition. The former are mainly used to control the degree of flexibility (or stiffness) of the chain, mostly appreciable in the unfolded (noncompact) state. Our results show the different effects that local and nonlocal interactions have on the entropy and the energy of the system. This implies that a balance between both types of interactions is required, so that a free energy barrier exists between the native and the denatured states. The variations in the contribution of both types of interactions have also a direct effect on the stability of the chain conformations, including the possible appearance of thermodynamic folding intermediates. 相似文献
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Lidia Jasinska Cor E. Koning 《Journal of polymer science. Part A, Polymer chemistry》2010,48(13):2885-2895
Biobased, unsaturated polyesters derived from isosorbide, maleic anhydride, and succinic acid were synthesized and characterized. The presence of maleic anhydride units in the structure of the polyesters allowed converting them into cured coatings by radical copolymerization with crosslinking agents such as 2‐hydroxyethyl methacrylate, N‐vinyl‐2‐pyrrolidinone, acrylic acid or methacrylamide. The investigated polyesters were obtained via bulk polycondensation, catalyzed by titanium(IV) n‐butoxide. 2D NMR and MALDI‐Tof‐MS spectroscopy proved that this polymerization resulted in isomerization of maleic acid units into fumaric ones and in the formation of slightly branched structures by the reaction of isosorbide (end) groups with main chain unsaturated bonds. Moreover, some double bonds proved to have reacted with the condensation by‐product water. The resulting polyesters displayed the expected correlation between variables such as molecular weight and content of unsaturated bonds and their Tg values. Since the thermal properties of the obtained polyesters were appropriate for coating applications, the polymers were crosslinked with unsaturated monomers by radical copolymerization. The crosslinking process was studied using FTIR spectroscopy and by measurements of the soluble part of the cured coatings. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2885–2895, 2010 相似文献
46.
Asymmetric Synthesis of Fluorinated Isoindolinones through Palladium‐Catalyzed Carbonylative Amination of Enantioenriched Benzylic Carbamates 下载免费PDF全文
Dr. Pablo Barrio Ignacio Ibáñez Lidia Herrera Dr. Raquel Román Dr. Silvia Catalán Prof. Dr. Santos Fustero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11579-11584
The asymmetric synthesis of fluorinated isoindolinones has been achieved by a palladium‐catalyzed aminocarbonylation reaction of the corresponding α‐fluoroalkyl o‐iodobenzylamines. A base‐mediated anti β‐hydride elimination process was suggested to explain the partial erosion of the optical purity observed in some cases. This mechanistic rationale enabled the minimization of this partial racemization by fine‐tuning the pKa of the base. 相似文献
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Agnieszka Chojnacka Marcin Molenda Dorota Majda Piotr Natkański Roman Dziembaj 《Journal of Thermal Analysis and Calorimetry》2017,127(1):47-53
Electrode materials consisted of tin nanograins encapsulated in different origin carbon buffer matrix (starch or water soluble polymer) were obtained in a simple and inexpensive process. The tin precursor was synthesized using modified reverse nanoemulsion technique (w/o) and then coated by a source of carbon. The composites precursors were pyrolysed, affording formation of C/Sn anode materials. The resulting samples were investigated by powder X-ray diffraction studies in order to verify the structure and calculate crystallites sizes. The morphology of the nanocomposites was characterized by low-temperature nitrogen adsorption method (N2-BET). Thermal analysis measurements (EGA-TG/DTG/DTA and DSC) allowed determining optimal conditions of preparation process and estimating carbon content in the obtained anode materials. Thermogravimetric studies also proved to be highly useful in establishing the leak behaviour of C/Sn nanocomposites. The electrochemical performance of the nanopowders was examined by charge–discharge tests in R2032-type coin cell. The thermal analysis results as well as low-temperature nitrogen adsorption data indicated that the origin of carbon precursor has major impact on morphology and leak behaviour of the obtained carbon buffer matrix. The electrochemical tests showed that better tightness of carbon–tin nanocomposites resulted in higher gravimetric capacity and better cell performance. 相似文献
49.
Lidia Zapa?a 《Journal of solution chemistry》2011,40(2):198-210
In this paper, the flufenamic acid equilibria in aqueous solution and in two-phase organic solvent + aqueous solution are described and presented. The dissociation constants K a1 and K a2 were determined in MDM + water mixtures. The Yashuda-Shedlovsky extrapolation procedure has been used to obtain the values of K a1 and K a2 in aqueous solutions. The distribution ratio D was measured in the toluene + water system over a wide range of pH by the shaking flask method. Based on the results of potentiometric titrations in two-phase organic solvent (benzene, ethylbenzene, toluene, carbon tetrachloride, chloroform, chlorobenzene, and bromobenzene) + aqueous systems, and using models of single and multistep equilibria, the values of distribution constants K D and dimerization constants K dim were calculated. The influences of polarity of the applied solvents and pH of the aqueous phase, on the speciation of the particular forms of flufenamic acid in both phases, were demonstrated. 相似文献
50.
Gabrieli L. ParrilhaAuthor VitaeRafael P. VieiraAuthor Vitae Anayive P. RebolledoAuthor VitaeIsolda C. MendesAuthor Vitae Lidia M. LimaAuthor VitaeEliezer J. BarreiroAuthor Vitae Oscar E. PiroAuthor VitaeEduardo E. CastellanoAuthor Vitae Heloisa BeraldoAuthor Vitae 《Polyhedron》2011,30(11):1891-1898
Complexes [Zn2(HL1)2(CH3COO)2] (1) and [Zn2(L2)2] (2) were synthesized with salicylaldehyde semicarbazone (H2L1) and salicylaldehyde-4-chlorobenzoyl hydrazone (H2LASSBio-1064, H2L2), respectively. The crystal structure of (1) was determined. Upon recrystallization of previously prepared [Zn2(HL2)2(Cl)2] (3) in 1:9 DMSO:acetone crystals of [Zn2(L2)2(H2O)2]·[Zn2(L2)2(DMSO)4] (3a) were obtained. The crystal structure of 3a was also determined. All crystal structures revealed the presence of phenoxo-bridged binuclear zinc(II) complexes. 相似文献