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991.
Camilla?Terenzi Cinzia?CasieriEmail author Francesco?De?Luca Raimondo?Quaresima Giovanni?Quarta Valentina?Tudisca 《Applied magnetic resonance》2015,46(10):1159-1178
This study deals with the application of two-dimensional proton nuclear magnetic resonance relaxometry (2D 1H NMR-R) to the characterization of porous ceramics nearly free of magnetic compounds. Different microstructural properties were obtained by firing a diamagnetic mixture of kaolin, calcium, and magnesium carbonate over a wide range of maximum temperatures (600–1100 °C) and firing times at the maximum temperature (soaking times) (0–10 h). The 2D 1H NMR-R method relies on the correlated measurement of 1H longitudinal (T 1) and transverse (T 2) relaxation times of pore-filling water by which the properties of the interconnected pore space may be investigated. In the absence of significant magnetic susceptibility effect due to para- and ferro-magnetic compounds, the 2D 1H NMR-R maps allow studying the conjoint effects on pore size distribution and inter-pore coupling due to the variations in both time and temperature of firing. The NMR experiments were performed with a low-field 1H NMR sensor, which allows non-destructive and in situ analysis. For ceramic specimens fired at 600 and 700 °C, the fraction of smallest pores increases with firing time at the expenses of those with intermediate size. The pore shrinkage occurring at this stage, and likely associated with the transformation of kaolinite in metakaolinite, is affected in a similar way by soaking time and firing temperature, in line with the concept of equivalent firing temperature. At temperatures from 800 to 1100 °C, the structural modifications involving interconnectivity and average pore size are driven primarily by firing temperature and, secondarily, by soaking time. The 2D 1H NMR-R results are confirmed by more traditional, but destructive, mineralogical, and structural analyses like X-ray powder diffraction, helium pycnometry, mercury intrusion porosimetry, and nitrogen adsorption/desorption method. 相似文献
992.
993.
Annali di Matematica Pura ed Applicata (1923 -) - We obtain convolution inequalities in Lebesgue and Lorentz spaces with power weights when the functions involved are assumed to be radially... 相似文献
994.
Denis Morsa Valérie Gabelica Edwin De Pauw 《Journal of the American Society for Mass Spectrometry》2014,25(8):1384-1393
During their travel inside a traveling wave ion mobility cell (TW IMS), ions are susceptible to heating because of the presence of high intensity electric fields. Here, we report effective temperatures T eff,vib obtained at the injection and inside the mobility cell of a SYNAPT G2 HDMS spectrometer for different probe ions: benzylpyridinium ions and leucine enkephalin. Using standard parameter sets, we obtained a temperature of ~800 K at injection and 728?±?2 K into the IMS cell for p-methoxybenzylpyridinium. We found that T eff,vib inside the cell was dependent on the separation parameters and on the nature of the analyte. While the mean energy of the Boltzmann distributions increases with ion size, the corresponding temperature decreases because of increasing numbers of vibrational normal modes. We also investigated conformational rearrangements of 7+ ions of cytochrome c and reveal isomerization of the most compact structure, therefore highlighting the effects of weak heating on the gas-phase structure of biologically relevant ions. Figure
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995.
Riccardo Flamini Mirko De Rosso Annarita Panighel Antonio Dalla Vedova Fabiola De Marchi Luigi Bavaresco 《Journal of mass spectrometry : JMS》2014,49(12):1214-1222
A ‘suspect screening analysis’ method for grape metabolomics by ultra‐high performance‐liquid chromatography (UHPLC) and high‐resolution quadrupole‐time of flight (QTOF) mass spectrometry was recently developed. This method was applied to study grape monoterpene glycosides, the main grape aroma precursors. Since standard compounds were not available, they were tentatively identified by overlapping various analytical approaches, in agreement with the indications recommended in mass spectrometry (MS)‐based metabolomics. Accurate mass and isotopic pattern, MS/MS fragmentation, correlation between fragments observed and putative structures and between liquid chromatography coupled with mass spectrometry (LC/MS) and gas chromatography/mass spectrometry signals were studied. Seventeen monoterpene glycosides were identified without performing the hydrolytic artifacts commonly used to study these compounds which may affect sample profile. This is the first time that a detailed study of these aroma precursors has been carried out by direct LC/MS analysis. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
996.
A Phosphine‐Catalyzed Novel Asymmetric [3+2] Cycloaddition of C,N‐Cyclic Azomethine Imines with δ‐Substituted Allenoates 下载免费PDF全文
Dr. De Wang Yu Lei Dr. Yin Wei Prof. Dr. Min Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15325-15329
Catalytic asymmetric [3+2] cycloadditions of C,N‐cyclic azomethine imines with δ‐substituted allenoates have been developed in the presence of (S)‐Me‐f‐KetalPhos, affording functionalized tetrahydroquinoline frameworks in good yields with high diastereo‐ and good enantioselectivities under mild condition. The substrate scope has been also examined. This is the first time that δ‐substituted allenoates have been applied as a δ,γ‐C?C bond participated C2 synthon in asymmetric synthesis. 相似文献
997.
Tian Wen Prof. Dr. Xiao‐Ping Zhou De‐Xiang Zhang Prof. Dr. Dan Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):644-648
Three 2D luminescent isomeric porous coordination polymers are synthesized and characterized. Their luminescence properties can be modified by grinding and they can act as mechanochromic materials and their properties are probably related to the weak interactions of cuprophilicity and π–π interactions. 相似文献
998.
Qing He Dr. Yuchun Han Prof. Yilin Wang Prof. Zhi‐Tang Huang Prof. De‐Xian Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7486-7491
Taking tetraoxacalix[2]arene[2]triazine as a functionalization platform, a series of new amphiphilic molecules were synthesized in 18 to 53 % yields by using a fragment coupling protocol. These amphiphilic molecules self‐assembled into stable vesicles in a mixture of THF and water, with the surface of the vesicles engineered by electron‐deficient cavities. Various anions are able to selectively influence the size of self‐assembled vesicles, following the order of F?<ClO4?<SCN?<BF4?<Br?<Cl?<NO3?, as revealed by DLS measurements. Such a sequence was independent with the hydration cost and in agreement with the binding strength of anions with tetraoxacalix[2]arene[2]triazine host molecule, indicating that the anion–π interaction most probably competed over other possible weak interactions and accounted for this interesting selectivity. In addition, the chloride permeation process across the membrane of the vesicles was also preliminarily studied by means of fluorescent experiments. This study, in addition to providing the potentiality of heteracalixaromatics as new models to construct functional vesicles, opens a new avenue to study the anion–π interactions in aqueous and also potentially in living systems. 相似文献
999.
Denise T. B. De Salvi Hernane S. Barud Agnieszka Pawlicka Ritamara I. Mattos Ellen Raphael Younés Messaddeq Sidney J. L. Ribeiro 《Cellulose (London, England)》2014,21(3):1975-1985
New bacterial cellulose (BC)–triethanolamine (TEA) ion-conducting membranes have been prepared and characterized. The samples were obtained by soaking BC membranes in triethanolamine aqueous solutions and drying. The scanning electron microscopy pictures revealed that the incorporation of TEA in BC membranes covers the cellulose microfibrils. Raman spectra exhibited BC and TEA characteristic group frequencies and thermal analysis evidenced an influence of TEA content on the sample thermal stability. The ion-conductivity as a function of the temperature showed an Arrhenius behavior increasing from 1.8 × 10?5 S/cm at room temperature to 7.0 × 10?4 S/cm at 80 °C for the BC–TEA 1 M sample. 相似文献
1000.
Functionalization of a Ruthenium–Diacetylide Organometallic Complex as a Next‐Generation Push–Pull Chromophore 下载免费PDF全文
Samuel De Sousa Dr. Laurent Ducasse Dr. Brice Kauffmann Prof. Thierry Toupance Dr. Céline Olivier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7017-7024
The design and preparation of an asymmetric ruthenium–diacetylide organometallic complex was successfully achieved to provide an original donor–π–[M]–π–acceptor architecture, in which [M] corresponds to the [Ru(dppe)2] (dppe: bisdiphenylphosphinoethane) metal fragment. The charge‐transfer processes occurring upon photoexcitation of the push–pull metal–dialkynyl σ complex were investigated by combining experimental and theoretical data. The novel push–pull complex, appropriately end capped with an anchoring carboxylic acid function, was further adsorbed onto a semiconducting metal oxide porous thin film to serve as a photosensitizer in hybrid solar cells. The resulting photoactive material, when embedded in dye‐sensitized solar cell devices, showed a good spectral response with a broad incident photon‐to‐current conversion efficiency profile and a power conversion efficiency that reached 7.3 %. Thus, this material paves the way to a new generation of organometallic chromophores for photovoltaic applications. 相似文献