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31.
Ángeles G. De la Torre Antonio J. M. Cuberos Gema Álvarez‐Pinazo Ana Cuesta Miguel A. G. Aranda 《Journal of synchrotron radiation》2011,18(3):506-514
Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared with ordinary Portland cement fabrication. However, their formation mechanism has not been studied in detail so far. Here, an in situ high‐temperature high‐resolution synchrotron X‐ray powder diffraction study is reported. Two types of BSA clinkers have been characterized, both containing 50–60 wt% C2S and 20–30 wt% C4A3 as main phases. One type is iron‐rich and a second type (with different phase assemblage) is aluminium‐rich. Furthermore, the C2S phase reacts slowly with water, thus activation of this compound is desirable in order to enhance the mechanical strength development of the resulting cements. To do so, iron‐rich BSA clinkers have been doped with minor amounts of B2O3 and Na2O to promote stabilization of α‐forms of C2S, which are more reactive with water. The decarbonated raw materials were loaded into Pt tubes and heated to between 973 K and 1673 K, and patterns were collected using a high‐energy synchrotron beam of wavelength λ = 0.30 Å. The thermal stability of Klein's salt in these clinkers has been clarified. Several reactions have been followed: formation and decomposition of Klein's salt, melting of aluminates and ferrite, and polymorphic transformations of dicalcium silicate: ‐C2S →α‐C2S. Changes in mineralogical phase assemblages at a given temperature owing to the addition of minor amounts of selected elements have also been determined. 相似文献
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Kristian B. ?rns? Juan M. Garcia-Lastra Gema De La Torre F. J. Himpsel Angel Rubio Kristian S. Thygesen 《Chemical science》2015,6(5):3018-3025
An extensive database of spectroscopic properties of molecules from ab initio calculations is used to design molecular complexes for use in tandem solar cells that convert two photons into a single electron–hole pair, thereby increasing the output voltage while covering a wider spectral range. Three different architectures are considered: the first two involve a complex consisting of two dye molecules with appropriately matched frontier orbitals, connected by a molecular diode. Optimized combinations of dye molecules are determined by taking advantage of our computational database of the structural and energetic properties of several thousand porphyrin dyes. The third design is a molecular analogy of the intermediate band solar cell, and involves a single dye molecule with strong intersystem crossing to ensure a long lifetime of the intermediate state. Based on the calculated energy levels and molecular orbitals, energy diagrams are presented for the individual steps in the operation of such tandem solar cells. We find that theoretical open circuit voltages of up to 1.8 V can be achieved using these tandem designs. Questions about the practical implementation of prototypical devices, such as the synthesis of the tandem molecules and potential loss mechanisms, are addressed. 相似文献
33.
Bartelmess J Ballesteros B de la Torre G Kiessling D Campidelli S Prato M Torres T Guldi DM 《Journal of the American Chemical Society》2010,132(45):16202-16211
In the present work, a new family of pyrene (Py)-substituted phthalocyanines (Pcs), i.e., ZnPc-Py and H(2)Pc-Py, were designed, synthesized, and probed in light of their spectroscopic properties as well as their interactions with single-wall carbon nanotubes (SWNTs). The pyrene units provide the means for non-covalent functionalization of SWNTs via π-π interactions. Such a versatile approach ensures that the electronic properties of SWNTs are not impacted by the chemical modification of the carbon skeleton. The characterization of ZnPc-Py/SWNT and H(2)Pc-Py/SWNT has been performed in suspension and in thin films by means of different spectroscopic and photoelectrochemical techniques. Transient absorption experiments reveal photoinduced electron transfer between the photoactive components. ZnPc-Py/SWNT and H(2)Pc-Py/SWNT have been integrated into photoactive electrodes, revealing stable and reproducible photocurrents with monochromatic internal photoconversion efficiency values for H(2)Pc-Py/SWNT as large as 15 and 23% without and with an applied bias of +0.1 V. 相似文献
34.
Rosillo M Domínguez G Casarrubios L Amador U Pérez-Castells J 《The Journal of organic chemistry》2004,69(6):2084-2093
Enynes connected through aromatic rings are used as substrates for metathesis reactions. The reactivity of three ruthenium carbene complexes is compared. The resulting 1,3-dienes are suitable precursors of polycyclic structures via a Diels-Alder process. Some domino RCM-Diels-Alder reactions are performed, suggesting a possible beneficial effect of the ruthenium catalyst in the cycloaddition process. Other examples require Lewis acid cocatalyst. When applied to aromatic ynamines or enamines, a new synthesis of vinylindoles is achieved. Monitorization of several metathesis reactions with NMR shows the different behavior for ruthenium catalysts. New carbenic species are detected in some reactions with an important dependence on the solvent used. 相似文献
35.
V. Mickevicius R. Vaickelioniene G. Mikulskiene N. Sewald 《Chemistry of Heterocyclic Compounds》2005,41(6):754-760
A series of 1-aryl-1,4,5,6-tetrahydro-4(1H)-pyridones having substituents in 2,3- and 2,3,5-positions was prepared from N-aryl-β-alanines
and ethyl acetoacetate or 2,4-pentanedione. Twelve tentative biologically active compounds were identified by the combination
of 1H, 13C and 1H/13C NMR spectroscopy. The extensive interest has been focused on the influence of substituents as well as on the number, attachment
position, and the nature of the substituents. The unknown shielding of the heterocyclic ring on the aromatic carbon atoms
was determined and the averaged chemical shift increments were successfully used for the assignment of the aromatic moiety
of the studied compounds. The presence of two chiral elements in compounds 16, 17, 20–21 resulted in the mixture of diastereomers and double sets of the resonances in NMR spectra.
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Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 874–881, June 2005. 相似文献
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A series of condensation products of 1-aryl-4-hydrazinecarbonyl-2-pyrrolidinones with acetone, 2,4-pentanedione, and aromatic
aldehydes was obtained and identified by the combination of IR, mass and 1H, 13C NMR spectroscopy. The results of their structural studies by NMR spectroscopy are provided. It was ascertained that the
presence of the NH group determines the existence of the mixtures of the Z/E-isomers of compounds under study. The availability
of Z-isomer as a sterically favorable one was also verified by computer molecular modeling.
Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1336–1345, September, 2006. 相似文献
40.
Gracia Patricia Blanch Gema Flores Maria del Mar Caja Maria Luisa Ruiz del Castillo 《Journal of separation science》2009,32(2):180-184
A method based on the use of HPLC for the enantioselective resolution of the four stereoisomers of methyl jasmonate (MJ) with no need for the previous formation of the diastereoisomers is developed. To that end, a Nucleodex‐β‐PM column as well as an optimization process considering different flow rates and mobile phase compositions were required. As a result, 0.8 mL/min and 55:45 methanol/water composition were the conditions selected to carry out the separation of the stereoisomers. Isolation of pure (–)‐ and (+)‐MJ was accomplished by collecting the HPLC fractions corresponding to their elution time. SPE was subsequently used to concentrate and change the solvent of the HPLC fractions collected. Chiral GC and polarimetry were additionally employed to evaluate the purity and optical rotation, respectively, of the enantiomers separated. The results found in this study are particularly relevant considering that MJ stereoisomers are not commercially available. 相似文献