1,721,039 research outputs found
CAGE: Software for a critical analysis of H-2 spin-lattice relaxation in liquid crystals
No full textA software package of Mathematica, aimed at the analysis of 2H NMR Zeeman (T1Z) and quadrupolar (T1Q) spin-lattice relaxation times in liquid crystals in terms of diffusional models, is presented. The models most commonly used to describe internal, overall, and collective motions in liquid-crystalline phases are considered, and dynamic parameters are obtained by means of either single point or global target approaches using simulation or fitting procedures. The use of the software as a tool for highlighting the problems encountered in this kind of analysis as well as for dealing with such problems following suitable strategies is illustrated by means of applications to experimental 2H relaxation times of three different calamitic liquid crystals
Molecular rotation and conformational transitions studied by H-2 NMR in a smectogen
No full textWe present a quantitative analysis of the spectral density data from the core and chain deuterons in the liquid crystal p-hexyloxybenzylidene-pX-fluoroaniline. The unusually small J1Žv.rJ2Ž2v. ratio for the methylene deuterons near the core in the highly ordered smectic B phase is reproduced using a decoupled model for correlated internal bond rotations in the chain
Reactivity of Bis(į6-Arene) Derivatives of Titanium, Vanadium and Niobium with Fulvenes bearing Electron-Withdrawing Substituents
No full textThe reaction of M(ƒØ6-arene)2 (M = Ti, arene = MeC6H5; M = V, Nb, arene = 1,3,5-Me3C6H3) with ¡§pentacarbomethoxycyclopentadiene¡ ̈ (pcmcpH), 1-benzoyl-6-hydroxy-6-phenyl fulvene (dbcpH), and 1-benzoyl-3-nitro-6-hydroxy-6-phenyl fulvene (dbncpH) proceeds with evolution of dihydrogen and oxidation of the metal to coordination compounds containing O,O¡¦-coordinated cyclopentadienyl anions, i.e., [pcmcp]ƒ{, [dbcp]ƒ{, and [dbncp]ƒ{, respectively. Complexes of general formula M(O,O¡¦-anion)3, where the metal is in the +III oxidation state, have been isolated for titanium and niobium. In the case of vanadium, different compounds have been obtained depending on the fulvene and the reaction conditions. In particular, solvated derivatives of vanadium(II) of general formula V(O,O¡¦-anion)2(THF)2 have been prepared in THF whereas V(O,O¡¦-anion)2 complexes have been isolated in toluene even in the presence of excess fulvene
Reactivity of Tris(1-pyrazolyl)methane Towards Ru0 Complexes
No full textBy treating tris(1-pyrazolyl)methane (tpm) with suitably activated [Ru(cod)(cot)] and [Ru(cod)(nap)] (cod = η4-cycloocta-1,5-diene, cot = η6-cycloocta-1,3,5-triene, nap = η6-naphthalene) the (hydrido)RuII species [Ru(N2,N2',C5''-tpm)(cod)H] with cyclometalated tpm was obtained. This complex reacted with chloroform at room temperature to give
[Ru(N2,N2',C5''-tpm)(cod)Cl] and dichloromethane. The coordination and symmetry of the novel complexes were elucidated by 1H and 13C NMR spectroscopy
Dynamics of liquid crystals by means of H-2-NMR: a comparison between 4,4 '-bis(hexyloxy)azoxybenzene and the derivative Pd(II) complex AZPAC
No full textμ-1,2,4,5-Tetrazine-N1:N4-bis(pentaammineruthenium) Tetracation: Synthesis and X-ray Structure
No full textThe 2:1 reaction of [Ru(H2O)2(NH3)5]2+ with 1,2,4,5-tetrazine (tz) gives rise to the formation of the dinuclear complex ion [{Ru(NH3)5}2(μ-tz-N1:N4)]4+. Its tetraphenylborate and hexafluoro-phosphate salts have been fully characterized; the X-ray structure of the former has also been determined
Collective and molecular motions of fluorinated liquid crystals by means of 19F Fast Field-Cycling NMR relaxometry
No full text19F Fast Field-Cycling (FFC) NMR relaxometry was applied for the first time for the investigation of the dynamics of a liquid crystal. Longitudinal 19F relaxation rates were measured at different temperatures in the nematic phase of 4DBF2 in the frequency range between about 9.5 kHz and 33 MHz. The observed relaxation dispersions could be well reproduced using a simple model in which contributions due to order director fluctuations and molecular rotational diffusion motions were considered. The obtained results indicate 19F FFC NMR relaxometry as a valuable method for the investigation of molecular and col- lective motions of fluorinated liquid crystals
C-13 and H-1 solid state NMR investigation of hydration effects on gluten dynamics
No full textThe effect of hydration on the molecular dynamics of soft wheat gluten was investigated by solid state NMR. For this purpose, we recorded static and MAS 1H spectra and SPE, CP, and other selective 13C spectra under MAS and dipolar decoupling conditions on samples of dry and H2O and D2O hydrated gluten. Measurements of carbon-proton CP times and several relaxation times (proton T1, T1 and T2, and carbon T1) were also performed. The combination of these techniques allowed both site-specific and domain-averaged motional information to be obtained in different characteristic frequency ranges. Domains with different structural and dynamic behaviour were identified and the changes induced by hydration on the dynamics of different domains could be monitored. The proton spin diffusion process was exploited to get information on the degree of mixing among different gluten domains. The results are consistent with the “loop and train” model proposed for hydrated gluten
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