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71.
[Structure: see text] Gronert (J. Org. Chem. 2006, 71, 1209) has challenged the importance of hyperconjugation in determining C-H bond dissociation enthalpies (BDEs) in alkanes. Electron paramaganetic resonance spectra of H3CCH2*, (H3C)2CH*, and (H3C)3C* show significant positive spin on their beta-H3C groups' hydrogens. A 55%/45% partitioning of these spins between hyperconjugation and spin polarization mechanisms linearly correlates with the C-H BDEs in methane, ethane, propane, isobutane and propene. Hyperconjugation is an important factor determining alkane C-H BDEs. 相似文献
72.
An existence result of multiple solutions for a fourth-order Sturm-Liouville boundary value problem with variable parameters is established. As a consequence, three solutions for a boundary value problem with a fourth-order equation in a complete form are obtained. Our approach is based on variational methods. 相似文献
73.
Chiara Lavarello Sebastiano Barco Martina Bartolucci Isabella Panfoli Emanuele Magi Gino Tripodi Andrea Petretto Giuliana Cangemi 《Molecules (Basel, Switzerland)》2021,26(14)
Liquid-chromatography coupled to high resolution mass spectrometry (LC-HRMS) is currently the method of choice for untargeted metabolomic analysis. The availability of established protocols to achieve a high confidence identification of metabolites is crucial. The aim of this work is to describe the workflow that we have applied to build an Accurate Mass Retention Time (AMRT) database using a commercial metabolite library of standards. LC-HRMS analysis was carried out using a Vanquish Horizon UHPLC system coupled to a Q-Exactive Plus Hybrid Quadrupole-Orbitrap Mass Spectrometer (Thermo Fisher Scientific, Milan, Italy). The fragmentation spectra, obtained with 12 collision energies, were acquired for each metabolite, in both polarities, through flow injection analysis. Several chromatographic conditions were tested to obtain a protocol that yielded stable retention times. The adopted chromatographic protocol included a gradient separation using a reversed phase (Waters Acquity BEH C18) and a HILIC (Waters Acquity BEH Amide) column. An AMRT database of 518 compounds was obtained and tested on real plasma and urine samples analyzed in data-dependent acquisition mode. Our AMRT library allowed a level 1 identification, according to the Metabolomics Standards Initiative, of 132 and 124 metabolites in human pediatric plasma and urine samples, respectively. This library represents a starting point for future metabolomic studies in pediatric settings. 相似文献
74.
Kapusta Dmitry P. Firsov Denis A. Khrenova Maria G. Grigorenko Bella L. Nemukhin Alexander V. 《Structural chemistry》2019,30(2):481-488
Structural Chemistry - In this work, we focus on some structural aspects of enzyme catalysis by modeling effects of the electrostatic potential created by the solvation water shells on properties... 相似文献
75.
Aurora Modica Marco Di Bella Maria Francesca Alberghina Maria Brai Dorotea Fontana 《Natural product research》2019,33(7):987-996
AbstractThe subject of this present work is a group of nine historical pictures shot in Palermo by the Sicilian photographer E. Interguglielmi in 1912. They are nine matte-collodion prints mounted on the original cardboard supports and all of them show foxing stains affecting the paper surface. In order to characterise the chemical composition of the supports and investigate foxing spots, non-destructive and micro-destructive analysis were carried out. X-rays fluorescence (XRF) analysis was used to characterise the elemental composition of all the mounting boards, allowing a comparison between the foxing spots and non-affected areas. Laser-Induced Breakdown Spectroscopy was used to investigate the presence of lower atomic number elements, not detectable by XRF, while SEM imaging allowed the investigation of surface appearance and nature of original paper samples from the cardboards. 相似文献
76.
Stephen J. Mihailov Dan Grobnic Robert B. Walker Christopher W. Smelser Gino Cuglietta Tom Graver Alexis Mendez 《Optics Communications》2008,281(21):5344-5348
Bragg gratings are written with ultrafast 800 nm radiation and a phase mask through the polyimide polymer coatings of commercially available high NA fibres that are both unloaded and loaded with high pressure hydrogen gas. For polyimide coated fibres with very high germanium core concentrations, index modulations greater than 1 × 10−4 are induced. Stable core index modulations 60% of their original value were present after 115 h at 500 °C. 相似文献
77.
78.
Dr. Mojtaba Alidoost Anna Mangini Dr. Fabrizio Caldera Dr. Anastasia Anceschi Dr. Julia Amici Dr. Daniele Versaci Dr. Lucia Fagiolari Prof. Francesco Trotta Prof. Carlotta Francia Prof. Federico Bella Prof. Silvia Bodoardo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(6):e202104201
Manufactured globally on industrial scale, cyclodextrins (CD) are cyclic oligosaccharides produced by enzymatic conversion of starch. Their typical structure of truncated cone can host a wide variety of guest molecules to create inclusion complexes; indeed, we daily use CD as unseen components of food, cosmetics, textiles and pharmaceutical excipients. The synthesis of active material composites from CD resources can enable or enlarge the effective utilization of these products in the battery industry with some economical as well as environmental benefits. New and simple strategies are here presented for the synthesis of nanostructured silicon and sulfur composite materials with carbonized hyper cross-linked CD (nanosponges) that show satisfactory performance as high-capacity electrodes. For the sulfur cathode, the mesoporous carbon host limits polysulfide dissolution and shuttle effects and guarantees stable cycling performance. The embedding of silicon nanoparticles into the carbonized nanosponge allows to achieve high capacity and excellent cycling performance. Moreover, due to the high surface area of the silicon composite, the characteristics at the electrode/electrolyte interface dominate the overall electrochemical reversibility, opening a detailed analysis on the behavior of the material in different electrolytes. We show that the use of commercial LP30 electrolyte causes a larger capacity fade, and this is associated with different solid electrolyte interface layer formation and it is also demonstrated that fluoroethylene carbonate addition can significantly increase the capacity retention and the overall performance of our nanostructured Si/C composite in both ether-based and LP30 electrolytes. As a result, an integration of the Si/C and S/C composites is proposed to achieve a complete lithiated Si−S cell. 相似文献
79.
80.
G. Bombieri F. Demartin D. Braghiroli M. Di Bella 《Journal of chemical crystallography》1990,20(5):403-406
The crystal structure of taurocyamine has been determined by single-crystal diffraction methods. The compound crystallizes in the monoclinic space groupCc witha=5.418(4),b=13.403(9),c=9.533(7) Å,=91.26(4)° andZ=4. The structure was solved by direct methods, and refined by least-squares procedures toR=0.027 (R
w
=0.034). The molecule is characterized by statistical distribution of the SO3H group proton as well of the C=NH proton, suggesting the presence either of different isomers or, in some percentage, of zwitterions in the crystal. An extensive hydrogen-bond system dominates the structure in the crystal state. 相似文献