Ionic liquid nanotribology: stiction suppression and surface induced shear thinning

The friction and adhesion between pairs of materials (silica, alumina, and polytetrafluoroethylene) have been studied and interpreted in terms of the long-ranged interactions present. In ambient laboratory air, the interactions are dominated by van der Waals attraction and strong adhesion leading to significant frictional forces. In the presence of the ionic liquid (IL) ethylammonium nitrate (EAN) the van der Waals interaction is suppressed and the attractive/adhesive interactions which lead to "stiction" are removed, resulting in an at least a 10-fold reduction in the friction force at large applied loads. The friction coefficient for each system was determined; coefficients obtained in air were significantly larger than those obtained in the presence of EAN (which ranged between 0.1 and 0.25), and variation in the friction coefficients between systems was correlated with changes in surface roughness. As the viscosity of ILs can be relatively high, which has implications for the lubricating properties, the hydrodynamic forces between the surfaces have therefore also been studied. The linear increase in repulsive force with speed, expected from hydrodynamic interactions, is clearly observed, and these forces further inhibit the potential for stiction. Remarkably, the viscosity extracted from the data is dramatically reduced compared to the bulk value, indicative of a surface ordering effect which significantly reduces viscous losses.     

Thermomolecular orientation of nonpolar fluids

We investigate the response of molecular fluids to temperature gradients. Using nonequilibrium molecular dynamics computer simulations we show that nonpolar diatomic fluids adopt a preferred orientation as a response to a temperature gradient. We find that the magnitude of this thermomolecular orientation effect is proportional to the strength of the temperature gradient and the degree of molecular anisotropy, as defined by the different size or mass of the molecular atomic sites. We show that the preferred orientation of the molecules follows the same trends observed in the Soret effect of binary mixtures. We argue this is a general effect that should be observed in a wide range of length scales.     

Synthesis of azanucleosides through regioselective ring-opening of epoxides catalyzed by sulphated zirconia under microwave and solvent-free conditions

New azanucleosides were obtained using sulphated zirconia (ZS) as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl) pyrimidine-2,4(1H,3H)-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl)-pyrimidine-2,4(1H,3H)-dione, with (S)-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.     

Diethyl 2-[cyano(toluene-4-sulfinyl)methylene]propanedioate and its Diels–Alder adduct with cyclopentadiene

The thermal Diels–Alder cyclo­additon reaction of diethyl 2-­[cyano­(toluene-4-sulfinyl)­methyl­ene]­propane­dioate, C₁₆H₁₇­NO₅S, with cyclo­penta­diene gave the pure racemates of two of the four possible diastereomers, with a complete π-facial selectivity and a high (80:20) endo/exo-sulfinyl selectivity. X-ray diffraction studies of diethyl 2-[cyano­(toluene-4-sulfinyl)­methyl­ene]­propane­dioate and the major isomer of the cyclo­addition product, namely diethyl 3-cyano-3-(toluene-4-sulfinyl)­bi­cyclo­[2.2.1]­hepta-5-ene-2,2-di­carboxyl­ate, C₂₁H₂₃­NO₅S, reveal that the conformation of the substituents on the acrylo­nitrile moiety produces both steric and electronic effects, which affect the stereoselectivity of the reaction.     

Weierstrass weight of the hyperosculating points of generalized Fermat curves

Let $(S,H)$ be a generalized Fermat pair of the type $(k,n)$. If $F?S$ is the set of fixed points of the non-trivial elements of the group H, then F is exactly the set of hyperosculating points of the standard embedding $S?{\mathbb{P}}^n$. We provide an optimal lower bound (this being sharp in a dense open set of the moduli space of the generalized Fermat curves) for the Weierstrass weight of these points.     

Magnetic resonance studies of copper (II) sorbitol complex,in solution,reveal a supramolecular structure compatible to the crystal structure

Although the Cu²⁺-sorbitol complex [Cu²⁺-Sorb] structure in crystalline state has been determined by X rays, it is not known in solution, where most studies of this complex are performed. Therefore, the goal of this work was to obtain information about the structure of this complex in aqueous solution using nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The magnetic resonance results indicate that the complex is formed at approximately pH 12. In this pH the sorbitol ¹H relaxation times were so short (broad line) that was not possible to use standard nuclear magnetic resonance parameters (nuclear Overhauser effect and spin–spin coupling constants values) to solve the three-dimensional structure. However, valuable structural information about the complex in solution was obtained. The relaxation results indicate that the Cu²⁺ ions are buried in the structure and not accessible to solvent; the ¹H and ¹³C spectra shows strong paramagnetic shift effect indicating short distance between these nuclei and Cu²⁺ in the structure. No electron paramagnetic resonance signal was observed in pH 12 indicating strong Cu²⁺- Cu²⁺ dipolar interaction, compatible to Cu²⁺-Cu²⁺ distances measured in crystal, from 1.148 to 1.393 Angstroms. The complex self-diffusion coefficient (D) of 1.58 × 10⁻¹⁰ m²/s value, determined by Diffusion-Ordered Spectroscopy, is compatible to a molecular weight of 3–6 KDa. Therefore, these results corroborate that the [Cu²⁺-Sorb] complex is assembled in solution, at pH 12, with several structural parameters compatible to the toroidal hexadecacuprate supramolecular structure determined in solid state.     

Tables of Fourier, Laplace and Hankel Transforms of (u,n)-Dimensional Generalized Functions

The present note contains the Tables of Fourier, Laplace and Hankel transforms of several dimensional generalized functions. They are, mainly, based on the Laplace transform of retarded, Lorentz-invariant functions and the Fourier transforms of causal distributions.     

When Fluorescent Proteins Meet White Light‐Emitting Diodes

Over the last decades, fluorescent proteins (FPs) have been extensively employed for imaging and tracing in cell biology and medicine. However, their application for lighting devices like light‐emitting diodes (LEDs) and lasers has recently started. The interest of FPs is the result of their good photoluminescence features (high emission efficiency with a narrow spectrum and a high photon‐flux saturation), good photostability, sustainable production by bacteria, and eco‐friendly recycling. Their low stability at high temperatures as well as the need for an aqueous environment have, however, strongly limited their use in optoelectronics. This has recently been circumvented with new coating systems that are paving the way for the entrance of FPs into the LED field. In this Minireview, we summarize the first steps taken by a few groups towards the development of bio‐hybrid white LEDs (Bio‐HWLEDs) with a focus on using FPs as color down‐converters, highlighting the state of the art and challenges associated with this emerging field.