The 125Te Chemical Shift of Diphenyl Ditelluride: Chasing Conformers over a Flat Energy Surface

The interest in diphenyl ditelluride (Ph2Te2) is related to its strict analogy to diphenyl diselenide (Ph2Se2), whose capacity to reduce organic peroxides is largely exploited in catalysis and green chemistry. Since the latter is also a promising candidate as an antioxidant drug and mimic of the ubiquitous enzyme glutathione peroxidase (GPx), the use of organotellurides in medicinal chemistry is gaining importance, despite the fact that tellurium has no recognized biological role and its toxicity must be cautiously pondered. Both Ph2Se2 and Ph2Te2 exhibit significant conformational freedom due to the softness of the inter-chalcogen and carbon\u2013chalcogen bonds, preventing the existence of a unique structure in solution. Therefore, the accurate calculation of the NMR chemical shifts of these flexible molecules is not trivial. In this study, a detailed structural analysis of Ph2Te2 is carried out using a computational approach combining classical molecular dynamics and relativistic density functional theory methods. The goal is to establish how structural changes affect the electronic structure of diphenyl ditelluride, particularly the 125Te chemical shift

Ionic Liquid Crystals

In this book we have collected a series of state-of-the art papers written by specialists in the field of ionic liquid crystals (ILCs) to address key questions concerning the synthesis, properties, and applications of ILCs. New compounds exhibiting ionic liquid crystalline phases are presented, both of calamitic as well as discotic type. Their dynamic and structural properties have been investigated with a series of experimental techniques including differential scanning calorimetry, polarized optical spectroscopy, X-ray scattering, and nuclear magnetic resonance, impedance spectroscopy to mention but a few. Moreover, computer simulations using both fully atomistic and highly coarse-grained force fields have been presented, offering an invaluable microscopic view of the structure and dynamics of these fascinating materials

Computational NMR spectroscopy of ionic liquids: [C4C1Im]Cl/water mixtures

none1noIn this work, I have analyzed the structure of binary mixtures of 1‐butyl‐3-methylimidazolium chloride ionic liquid, [C4C1im]Cl, and water, using computational NMR spectroscopy. The structure of the complex fluid phase, where the ionic and hydrophobic nature of ionic liquids is further complicated by the addition of water, is first generated by classical Molecular Dynamics (MD) and then validated by calculating the NMR properties with DFT at the ONIOM(B3LYP/cc‐pVTZ//B3LYP/3‐21G) on clusters extracted during the MD trajectories. Three ionic liquid/water mixtures have been considered with the [C4C1im]Cl mole fraction of 1.00, 0.50, and 0.01, that is the pure ionic liquid [C4C1im]Cl, the equimolar [C4C1im]Cl/water mixture, and a diluted solution of [C4C1im]Cl in water. A good agreement is obtained with published experimental data that, at the same time, validates the structural features obtained from the MD and the force field used, and provides an example of the power of NMR spectroscopy applied to complex fluid phases.noneSaielli G.Saielli, G

Special Issue Editorial: Ionic Liquid Crystals

The term “Ionic Liquid Crystals” (ILCs) clearly results from the blending of the well-known “Ionic Liquids” (ILs) and “Liquid Crystals” (LCs) names of the corresponding materials [...

Distribution and Dynamic Properties of Xenon Dissolved in the Ionic Smectic Phase of [C16mim][NO3]: MD Simulation and Theoretical Model

We have investigated the structural and dynamic properties of Xe dissolved in the ionic liquid crystal (ILC) phase of 1-hexadecyl-3-methylimidazolium nitrate using classical molecular dynamics (MD) simulations. Xe is found to be preferentially dissolved within the hydrophobic environment of the alkyl chains rather than in the ionic layers of the smectic phase. The structural parameters and the estimated local diffusion coefficients concerning the short-time motion of Xe are used to parametrize a theoretical model based on the Smoluchowski equation for the macroscopic dynamics across the smectic layers, a feature which cannot be directly obtained from the relatively short MD simulations. This protocol represents an efficient combination of computational and theoretical tools to obtain information on slow processes concerning the permeability and diffusivity of the xenon in smectic ILCs

A pairwise additive potential for the elastic interaction energy of a chiral nematic

We have developed a pairwise additive potential model to describe the macroscopic elastic interactions of a chiral nematic liquid crystal. The potential is obtained from the expression for the elastic free energy density discretized onto a cubic lattice and mapped onto a suitable expansion in scalar invariants. ne value of the pair potential is explored by means of a Monte Carlo lattice computer simulation. It allows, in a simple and efficient way, the simulation of liquid crystal devices and samples in confined geometries, taking into account the effect of the temperature of the sample and of the thermal fluctuations in the director distribution, as well as the elastic interactions

Aggregation Behavior of Octyl Viologen Di[bis(trifluoromethanesulfonyl)amide] in Nonpolar Solvents

The aggregation behavior in nonpolar solvents of the octyl viologen (OV) salt with the hydrophobic anion bis(trifluoromethanesulfonyl)amide (Tf2N 12) has been investigated. 1H and 19F NMR, ESI-MS and DFT calculations suggest that large aggregates are formed in toluene, benzene and chloroform, where the salt is highly soluble. The lifetime of the aggregates is long enough to be detected as independent species by 1H and 19F NMR spectroscopy, together with the smaller neutral OV(Tf2N)2 cluster. This behavior is quite at variance with usual NMR detected equilibria where only average signals are generally observed. Large aggregates are also observed in ESI-MS spectra of toluene and chloroform solutions despite the well-known low-coordinating ability of Tf2N 12. It is suggested that the structure of the large aggregates mimics the thermotropic smectic phase that this system exhibits near room temperature

Comparison of the Mesomorphic Behaviour of 1:1 and 1:2 Mixtures of Charged Gay-Berne GB(4.4,20.0,1,1) and Lennard-Jones Particles

We present a Molecular Dynamics study of mixtures of charged Gay-Berne (GB) ellipsoids and spherical Lennard-Jones (LJ) particles as models of ionic liquids and ionic liquid crystals. The GB system is highly anisotropic (GB(4.4,20.0,1,1)) and we observe a rich mesomorphism, with ionic nematic and smectic phases in addition to the isotropic mixed phase and crystalline phases with honeycomb structure. The systems have been investigated by analyzing the orientational and translational order parameters, as well as radial distribution functions. We have directly compared 1:1 mixtures, where the GB and LJ particles have a charge equal in magnitude and opposite in sign, and 1:2 mixtures where the number of LJ particles is twice as large compared to the GB and their charge half in magnitude. The results highlight the role of the long-range isotropic electrostatic interaction compared to the short-range van der Waals anisotropic contribution, and the effect of the stoichiometry on the stability of ionic mesophases

The structuring effect of the alkyl domains on the polar network of ionic liquid mixtures: a molecular dynamics study

By using molecular dynamics simulations, we investigate the structural and dynamic properties of mixtures of 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [C(1)C(1)im][Tf2N] and 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C(12)C(1)im][Tf2N] (also C-1 and C-12 in short). Such mixtures feature an imidazolium bistriflimide salt with a very short alkyl chain, not giving rise to any nano-segregation as a pure component, with another one with a longer alkyl chain that exhibits a substantial nano-segregation as a pure liquid. As the mole fraction of the long-chain component C-12 is increased, the so-called pre-peak of the structure factor S(q), occurring in the region 1-3 nm(-1), shows a shift to higher values of the wavevector q, mirroring a decrease of the corresponding correlation length. Moreover, the intensity of the pre-peak strongly increases with the C-12 concentration. These results are in very good agreement with experimental X-ray scattering data in the literature. On the other hand, the diffusion of the ions is found to exhibit a simple behaviour consistent with the increased viscosity of the mixture, and these results are also in good agreement with NMR experimental data from the literature. The simulation results are rationalized as caused by a structuring effect, similar to the hydrophobic effect, of the alkyl domains of the C-12 component dissolved in the "solvent" represented by the C-1 cation, the Tf2N- anion and the C-12 cation head. In short, the exclusion of the alkyl chains from the polar network, a process mostly governed by electrostatic interactions, favours the formation of hydrophobic domains, which in turn exert a structuring effect on the ions of the polar domains, favouring a stronger ionic interaction. This is finally reflected in a shorter correlation length and a higher intensity of the pre-peak of the structure factor S(q) as the C-12 mole fraction is increased. At variance with the microscopic structure, the diffusion of all three types of ions is not strongly influenced by the nano-segregation and is essentially dependent on the viscosity of the mixture

Spectroscopic signatures of the carbon buckyonions C60@C180 and C60@C240: a dispersion-corrected DFT study

We have investigated, by dispersion corrected DFT methods, the structure and the spectroscopic properties of carbon buckyonions C60@C180 and C60@C240. C60, C180 and C240 showed a noticeable variation of their geometries in C60@C180 and C60@C240, upon encapsulation. Inclusion of the dispersion correction term in the calculations has a significant effect on the geometry. C60@C180 has a large positive interaction energy, while for C60@C240 a negative value is found indicating that only C240 can easily accommodate C60. In both cases dispersion interactions strongly contribute to the stabilization of the complexes. Vibrational frequencies, electronic transitions and NMR properties have been computed. The results show that encapsulation leads to appreciable variation in the characteristic resonances thus offering a useful tool for a spectroscopic identification of these species