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101.
We present a quantum-mechanical investigation of the LiH depletion reaction LiH+H-->Li+H2 and of the H exchange reaction LiH+H'-->LiH'+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The 1H2 nuclear-spin statistics and progressions of vib-rotational states (v',j') rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j' preferred with respect to even j'. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results. 相似文献
102.
Rodríguez-Calvillo Pablo Ferrer Nuria Cabrera José-María 《Journal of Thermal Analysis and Calorimetry》2021,146(3):1393-1403
Journal of Thermal Analysis and Calorimetry - The thermal behavior of two copper alloys, with 0.2 and 0.5 mass % of Mg, was analyzed after severe plastic deformation processing by Equal Channel... 相似文献
103.
Juan Francisco Palacios-Espinosa Pablo No Núez-Aragn Erika Gomez-Chang Edelmira Linares Robert Bye Irma Romero 《Molecules (Basel, Switzerland)》2021,26(12)
Artemisia ludoviciana subsp. mexicana has been traditionally used for the treatment of digestive ailments such as gastritis, whose main etiological agent is Helicobacter pylori. In a previous screening study, the aqueous extract exhibited a good in vitro anti-H. pylori activity. With the aim of determining the efficacy of this species as a treatment for H. pylori related diseases and finding bioactive compounds, its aqueous extract was subjected to solvent partitioning and the fractions obtained were tested for their in vitro anti-H. pylori effect, as well as for their in vivo gastroprotective and anti-inflammatory activities. The aqueous extract showed a MIC = 250 µg/mL. No acute toxicity was induced in mice. A gastroprotection of 69.8 ± 3.8%, as well as anti-inflammatory effects of 47.6 ± 12.4% and 38.8 ± 10.2% (by oral and topical administration, respectively), were attained. Estafiatin and eupatilin were isolated and exhibited anti-H. pylori activity with MBCs of 15.6 and 31.2 µg/mL, respectively. The finding that A. ludoviciana aqueous extract has significant anti-H. pylori, gastroprotective and anti-inflammatory activities is a relevant contribution to the ethnopharmacological knowledge of this species. This work is the first report about the in vivo gastroprotective activity of A. ludoviciana and the anti-H. pylori activity of eupatilin and estafiatin. 相似文献
104.
105.
Anne Techen Sylvia Czapla Kristian Möllnitz Dennis Budach Pablo Wessig Michael U. Kumke 《Helvetica chimica acta》2013,96(11):2046-2067
Fluorescence probes consisting of well‐established fluorophores in combination with rigid molecular rods based on spirane‐type structures were investigated with respect to their fluorescence properties under different solvent conditions. The attachment of the dyes was accomplished by 1,3‐dipolar cycloaddition between alkynes and azides (‘click’ reaction) and is a prime example for a novel class of sensor constructs. Especially, the attachment of two (different) fluorophores on opposite sides of the molecular rods paves the way to new sensor systems with less bulky (compared to the conventional DNA‐ or protein‐based concepts), nevertheless rigid spacer constructs, e.g., for FRET‐based sensing applications. A detailed photophysical characterization was performed in MeOH (and in basic H2O/MeOH mixtures) for i) rod constructs containing carboxyfluorescein, ii) rod constructs containing carboxyrhodamine, iii) rod constructs containing both carboxyfluorescein and carboxyrhodamine, and iv) rod constructs containing both pyrene and perylene parts. For each dye (pair), two rod lengths with different numbers of spirane units were synthesized and investigated. The rod constructs were characterized in ensemble as well as single‐molecule fluorescence experiments with respect to i) specific rod? dye and ii) dye? dye interactions. In addition to MeOH and MeOH/NaOH, the rod constructs were also investigated in micellar systems, which were chosen as a simplified model for membranes. 相似文献
106.
Dr. Camino Bartolomé Dr. Fernando Villafañe Dr. Jose M. Martín‐Alvarez Dr. Jesús M. Martínez‐Ilarduya Prof. Dr. Pablo Espinet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(11):3702-3709
The X‐ray structure of the title compound [Pd(Fmes)2(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF3 groups of the Fmes ligand. The 19F NMR spectra in CD2Cl2 at very low temperature (157 K) detect restricted rotation for the two ortho‐CF3 groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol?1) to account for the rotational barrier observed (ΔH≠=26.8 kJ mol?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA. 相似文献
107.
Prof. Javier A. Cabeza Dr. Pablo García‐Álvarez Dr. Enrique Pérez‐Carreño Dr. Vanessa Pruneda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3426-3436
The methylation of the uncoordinated nitrogen atom of the cyclometalated triruthenium cluster complexes [Ru3(μ‐H)(μ‐κ2N1,C6‐2‐Mepyr)(CO)10] ( 1 ; 2‐MepyrH=2‐methylpyrimidine) and [Ru3(μ‐H)(μ‐κ2N1,C6‐4‐Mepyr)(CO)10] ( 9 ; 4‐MepyrH=4‐methylpyrimidine) gives two similar cationic complexes, [Ru3(μ‐H)(μ‐κ2N1,C6‐2,3‐Me2pyr)(CO)10]+( 2 +) and [Ru3(μ‐H)(μ‐κ2N1,C6‐3,4‐Me2pyr)(CO)10]+ ( 9 +), respectively, whose heterocyclic ligands belong to a novel type of N‐heterocyclic carbenes (NHCs) that have the Ccarbene atom in 6‐position of a pyrimidine framework. The position of the C‐methyl group in the ligands of complexes 2 + (on C2) and 9 + (on C4) is of key importance for the outcome of their reactions with K[N(SiMe3)2], K‐selectride, and cobaltocene. Although these reagents react with 2 + to give [Ru3(μ‐H)(μ‐κ2N1,C6‐2‐CH2‐3‐Mepyr)(CO)10] ( 3 ; deprotonation of the C2‐Me group), [Ru3(μ‐H)(μ3‐κ3N1,C5,C6‐4‐H‐2,3‐Me2pyr)(CO)9] ( 4 ; hydride addition at C4), and [Ru6(μ‐H)2{μ6‐κ6N1,N1′,C5,C5′,C6,C6′‐4,4′‐bis(2,3‐Me2pyr)}(CO)18] ( 5 ; reductive dimerization at C4), respectively, similar reactions with 9 + have only allowed the isolation of [Ru3(μ‐H)(μ3‐κ2N1,C6‐2‐H‐3,4‐Me2pyr)(CO)9] ( 11 ; hydride addition at C2). Compounds 3 and 11 also contain novel six‐membered ring NHC ligands. Theoretical studies have established that the deprotonation of 2 + and 9 + (that have ligand‐based LUMOs) are charge‐controlled processes and that both the composition of the LUMOs of these cationic complexes and the steric protection of their ligand ring atoms govern the regioselectivity of their nucleophilic addition and reduction reactions. 相似文献
108.
Joaquin Barbera Mercedes Marcos Ana Omenat Jose-Luis Serrano Jesus I. Martinez Pablo J. Alonso 《Liquid crystals》2013,40(2):255-262
The synthesis and liquid crystalline behaviour of the first and second generations of a dendrimeric structure based on poly(propyleneimine)(DAB-dendr(NH2)x) are reported. 4-(4-n-Alkoxybenzoyloxy)salicylaldehydes are used as mesogenic moieties attached at the peripheral amino groups of the dendrimers giving rise to dendromesogens with four and eight mesogenic branches. From these dendromesogens, considered as organic ligands, were prepared six metal-containing dendrimers which incorporate two or four copper atoms in their structures. All the dendrimeric ligands and three of the metal-containing dendrimers exhibit liquid crystalline properties which were studied by optical microscopy, DSC, X-ray diffraction and EPR spectroscopy. 相似文献
109.
Jaime Pacheco-Arjona Pablo Rodriguez-Gonzalez Manuel Valiente David Barclay 《International journal of environmental analytical chemistry》2013,93(13):923-932
A new self-tuning single-mode-focused microwave technology has been evaluated in this work to perform the quantitative routine extraction of organometallic species from solid matrices of environmental interest. Species-specific isotope dilution analysis has been employed to better investigate the real influence of the microwave-assisted extractions on the final results. The advantages of such methodology in comparison with other established microwave units for the routine speciation analysis of organomercury and organotin compounds are discussed (such as the capability of using disposable glass vials, a self-tuning mode to provide an accurate control of the temperature and pressure inside of the vials, and the possibility of performing automated sequence of extractions with low sample size). The results obtained in this work demonstrated that such technology provides a fast and reliable quantitative extraction of the organometallic species in a wide range of extraction conditions even when the multi-elemental (Sn and Hg) species-specific determination is carried out. 相似文献
110.
Valeria Verdinelli Bruno Vuano Pablo C. Schulz 《Journal of Dispersion Science and Technology》2013,34(10):1538-1544
The emulsifier properties of n-alkane phosphonic acids (C10H21PO3H2; C12H25PO3H2 and C13H27PO3H2) and their mono- and di-sodic salts were studied, with emphasis on the morphological and dynamical inversion properties as a function of their neutralization degree. Maximum stabilization properties were appreciated for C10PO3H2 and C12PO3H2 while not for C13PO3H2. Such fact is associated to their odd number of carbon atoms chain, which is the origin of the intrachain constraints on the tail-chain flexibility. 相似文献