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21.
The rotational dynamics of HCl in liquid Ar has been studied by means of molecular-dynamics simulations. We calculate the lifetimes of weakly bound HCl-Ar dimers induced by the anisotropic pair interaction. It is shown that, although lifetimes are small with respect to the reorientational decorrelation, the time interval between the breaking down and formation of the next dimer is negligibly small. Thus, with respect to the rotational dynamics of the probe, the effect is similar to that and eventually would cause a time-stable complex. This provokes a peculiar hindered rotation of the diatomic in the liquid which is macroscopically embodied in the infrared spectrum of the solution as a Q-branch nonexistent otherwise. 相似文献
22.
Beatriz Calvo Dr. Ramón Macías Maria Jose Artigas Dr. Fernando J. Lahoz Prof. Dr. Luis A. Oro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):3905-3912
The treatment of [1,1‐(PR3)2‐3‐(Py)‐closo‐1,2‐RhSB9H8] (PR3=PMe3 ( 2 ) or PPh3 and PMe3 ( 3 ); Py=pyridine) with triflic acid (TfOH) affords [1,3‐μ‐(H)‐1,1‐(PR3)2‐3‐(Py)‐1,2‐RhSB9H8]+ (PR3=PMe3 ( 4 ) or PMe3 and PPh3 ( 5 )). These products result from the protonation of the 11‐vertex closo‐cages along the Rh(1)? B(3) edge. These unusual cationic rhodathiaboranes are stable in solution and in the solid state and they have been fully characterized by multinuclear NMR spectroscopy. In addition, compound 5 was characterized by single‐crystal X‐ray diffraction. One remarkable feature in these structures is the presence of three {Rh(PPh3)(PMe3)}‐to‐{ηn‐SB9H8(Py)} (n=4 or 5) conformers in the unit cell, thus giving an uncommon case of conformational isomerism. [1,1‐(PPh3)2‐3‐(Py)‐closo‐1,2‐RhSB9H8] ( 1 ), that is, the bis‐PPh3‐ligated analogue of compounds 2 and 3 , is also protonated by TfOH, but, in marked contrast, the resulting cation, [1,3‐μ‐(H)‐1,1‐(PPh3)2‐3‐(Py)‐1,2‐RhSB9H8]+ ( 6 ), is attacked by a triflate anion with the release of a PPh3 ligand and the formation of [8,8‐(OTf)(PPh3)‐9‐(Py)‐nido‐8,7‐RhSB9H9] ( 9 ). The result is an equilibrium that involves cationic species 6 , neutral OTf‐ligated compound 9 , and [HPPh3]+, which is formed upon protonation of the released PPh3 ligand. The resulting ionic system reacts readily with H2 to give cationic species [8,8,8‐(H)(PPh3)2‐9‐(Py)‐nido‐8,7‐RhSB9H9]+ ( 7 ). This reactivity is markedly higher than that previously found for compound 1 and it introduces a new example of proton‐assisted H2 activation that occurs on a polyhedral boron‐containing compound. 相似文献
23.
Antonio Prez-Glvez María Visitacin Calvo Josefa Aguayo-Maldonado Javier Fontecha 《Molecules (Basel, Switzerland)》2021,26(7)
Several studies have been published regarding the effect of different factors on the digestion of milk lipids, considering their natural structural arrangement as milk fat globules and the efficiency of the digestive enzymes in the lipolysis of such complex structures. During digestion, the lipolytic products are dispersed in vesicles and micelles, which are the source for absorption of digested lipids. Therefore, it is necessary to consider the isolation of the micellar phase from the digesta to appropriately determine the amounts and classes of lipids which are bioaccessible. This study presents an integrative approach that included an isolation procedure to separate the micellar fraction from undigested and non-micellar parts, and the distribution of digested milk lipids in micelles determined directly through chromatographic techniques. Four groups of five full term mothers donated colostrum or mature milk. Two sets of samples were analyzed directly (raw), and two sets were pasteurized and then analyzed. Our data revealed that the profile of digested milk lipids is different depending on the lactation period and processing stage, while the carbon atom number distribution of the digested triacylglycerols in the micellar fraction provides a substantial information regarding the acylglycerols species that are less available for absorption. 相似文献
24.
Marcos V. Foguel Angelica M. Balcarcel Mark A. Reed Percy Calvo‐Marzal Yulia V. Gerasimova Dmitry M. Kolpashchikov Karin Y. Chumbimuni‐Torres 《Electroanalysis》2020,32(4):835-841
One major challenge in nucleic acids analysis by hybridization probes is a compromise between the probe's tight binding and sequence‐selective recognition of nucleic acid targets folded into stable secondary structures. We have been developing a four‐way junction (4WJ)‐based sensor that consists of a universal stem‐loop (USL) probe immobilized on an electrode surface and two adaptor strands (M and F). The sensor was shown to be highly selective towards single base mismatches at room temperature, able to detect multiple targets using the same USL probe, and have improved ability to detect folded nucleic acids. However, some nucleic acid targets, including natural RNA, are folded into very stable secondary and tertiary structures, which may represent a challenge even for the 4WJ sensors. This work describes a new sensor, named MVF since it uses three probe stands M, V and F, which further improves the performance of 4WJ sensors with folded targets. The MVF sensor interrogating a 16S rRNA NASBA amplicon with calculated folding energy of ?32.82 kcal/mol has demonstrated 2.5‐fold improvement in a signal‐to‐background ratio in comparison with a 4WJ sensor lacking strand V. The proposed design can be used as a general strategy in the analysis of folded nucleic acids including natural RNA. 相似文献
25.
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27.
Vega A Calvo V Spodine E Zárate A Fuenzalida V Saillard JY 《Inorganic chemistry》2002,41(13):3389-3395
The reaction of the organometallic carboxylic acid HOOCCCHCo(2)(CO)(6) with copper(II) methoxide leads to a new inorganometallic cluster; Cu(3)[mu(2)-(CCHCo(2)(CO)(6))](3). This cluster has a triangular core of copper(I) centers surrounded by three CCHCo(2)(CO)(6) fragments. The structure of the cluster has short Cu-Cu and Cu-Co distances (average 2.500 and 2.540 A, respectively). DFT calculations provide a rationalization of the peculiar bonding in this cluster. 相似文献
28.
We introduce a general Monte Carlo scheme for achieving atomistic simulations with monoelectronic Hamiltonians including the thermalization of both nuclear and electronic degrees of freedom. The kinetic Monte Carlo algorithm is used to obtain the exact occupation numbers of the electronic levels at canonical equilibrium, and comparison is made with Fermi-Dirac statistics in infinite and finite systems. The effects of a nonzero electronic temperature on the thermodynamic properties of liquid silver and sodium clusters are presented. 相似文献
29.
We investigate light beam propagation in a fast photorefractive medium placed in an alternating electric ac field to enhance the nonlinear response. It is shown that the joint action of the optical and material nonlinearities leads to formation of a narrow singularity of the light-induced space charge at the intensity maximum and to self-trapping of the light energy near the corresponding discontinuity of the index profile. Owing to the strong saturation of the material nonlinearity, the trapped beam propagates over long distances with only a weak loss of its power. 相似文献
30.
Calvo F 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):2771-2778
We present a numerical procedure for extracting Lyapunov characteristic exponents from classical molecular-dynamics simulations of molecular systems. The theoretical frame chosen to describe the orientational degrees of freedom is the quaternions scheme. We apply the method to small methane clusters. Two different model potentials are used to investigate the role of internal molecular motion on the nonlinear dynamics, and several parameters are calculated to study the thermodynamics and chaotic dynamics of these clusters. Evidence is found for a solidlike to plasticlike phase transition occurring with the release of the orientational degrees of freedom, at low temperatures below the melting point. The largest Lyapunov exponent increases significantly during this transition, but it exhibits no particular variation during melting. 相似文献