On extension of UNIQUAC-NRF model to study the phase behavior of aqueous two phase polymer–salt systems

The UNIQUAC-NRF model for aqueous two-phase polymer–polymer systems is extended to correlate liquid–liquid equilibria of aqueous polymer–salt two-phase systems. The systems investigated are polyethylene glycol+ammonium sulfate+water and polyethylene glycol+potassium monohydrogen phosphate (K₂HPO₄)+water for five molecular weights of PEG. In this model, the nonrandom state is selected as a reference state. The model has six binary adjustable parameters that were determined by an optimization program. The Debye–Huckel equation based on Fowller–Guggenheim equation is used to calculate the long-range electrostatic interaction of the ions. The results obtained by this model are in good agreement with experimental data.     

Tetrabutylammonium bromide: an efficient media for dimethoxytritylation of the 5′-hydroxyl function of nucleosides

An efficient procedure for selective dimethoxytritylation of the 5′-hydroxyl function of nucleosides in the presence of DABCO in molten tetrabutylammonium bromide is described. The methodology is very practical, environmentally benign and produced the desired product in less than 5 min by grinding in a hot mortar. In addition, the effects of the room temperature ionic liquid (1-butyl-3-methylimidazolium chloride) and microwave irradiation on this system were also studied and the results showed that depurination of the nucleosides occurred under microwave irradiation.     

Direct preparation of primary amides from carboxylic acids and urea using imidazole under microwave irradiation

A very simple and efficient solvent-free procedure for the preparation of primary amides is described from carboxylic acids and urea using imidazole under microwave irradiation. Various aliphatic and aromatic primary amides were prepared in good yields by this direct amidation method.     

Methyl and phenyl esters and thioesters of carboxylic acids as surrogate substrates for microassay of proteinase K esterase activity

The development of a microassay for proteinase K esterase activity with carboxylic acid esters is reported using novel substrates of the general formula R-C(O)-XR. Highest rates of hydrolysis have been obtained with the O-phenyl esters CH₃(CH₂)_{n = 1 – 2}-S-(CH₂)_{n = 1 – 2} C(O)-O-phenyl and their thioester analogs in studies where R, X and R have been varied. The phenol release has been measured with 4-aminoantipyrine and potassium ferricyanide to determine the rates of O-phenyl ester hydrolyses. Thioester hydrolyses have been monitored continuously with 5,5-dithio-bis (2-nitrobenzoic acid).     

Phosphine-free conversion of alcohols into alkyl thiocyanates using trichloroisocyanuric acid/NH4SCN

A convenient and efficient phosphine-free procedure for the one-pot conversion of primary,secondary and tertiary alcohols into the corresponding alkyl thiocyanates or alkyl isothiocyanates is described using trichloroisocyanuric acid/NHUSCN.     

Magnesia-supported hydroxylamine hydrochloride in the presence of sodium carbonate as an efficient reagent for the synthesis of 1,2,4-oxadiazoles from nitriles

An efficient one-pot method has been developed for the synthesis of 1,2,4-oxadiazoles through a one-pot reaction of nitriles with hydroxylamine hydrochloride in the presence of magnesia-supported sodium carbonate followed by reaction with acyl halides under solvent-free conditions using microwave irradiation. This method is easy, rapid and good yielding.     

Modeling shear localization along granular soil–structure interfaces using elasto-plastic Cosserat continuum

The current study presents finite element simulations of shear localization along the interface between cohesionless granular soil and bounding structure under large shearing movement. Micro-polar (Cosserat) continuum approach is applied in the framework of elasto-plasticity in order to overcome the numerical problems of localization modeling seen in the conventional continuum mechanics. The effects of different micro-polar kinematic boundary conditions, along the interface, on the evolution and location of shear band are shown by the numerical results. Furthermore, shear band thickness is also investigated for its dependence on the initial void ratio, vertical pressure and mean grain size. Here, the distribution and evolution of static and kinematic quantities are the main focuses regarding infinite layer of micro-polar material during plane shearing, especially with advanced large movement of bounding structure. The influence of such movement has not been investigated yet in the literature. Based on the results obtained from this study, shear localization appears parallel to the direction of shearing. It occurs either in the middle of granular layer or near boundaries, regarding the assumed micro-polar kinematic boundary conditions at the bottom and top surfaces of granular soil layer. Narrower shear band is observed in lower rotation resistance of soil particles along the interface. It is emphasized that the displacement magnitude of bounding structure has significant effect on the distribution and evolution of state variables and polar quantities in the granular soil layer. However, continuous displacement has no meaningful effect on the thickness of shear band. Here, smooth distributions of void ratio and shear stress components are obtained within the shear band, what the other previous numerical investigations did not receive. Despite indirect linking of Lade’s model to the critical state soil mechanics, state variables tend towards asymptotical stationary condition in large shear deformation.     

Hierarchical honeycombs with tailorable properties

We investigated the mechanical behavior of two-dimensional hierarchical honeycomb structures using analytical, numerical and experimental methods. Hierarchical honeycombs were constructed by replacing every three-edge vertex of a regular hexagonal lattice with a smaller hexagon. Repeating this process builds a fractal-appearing structure. The resulting isotropic in-plane elastic properties (effective elastic modulus and Poisson’s ratio) of this structure are controlled by the dimension ratios for different hierarchical orders. Hierarchical honeycombs of first and second order can be up to 2.0 and 3.5 times stiffer than regular honeycomb at the same mass (i.e., same overall average density). The Poisson’s ratio varies from nearly 1.0 (when planar ‘bulk’ modulus is considerably greater than Young’s modulus, so the structure acts ‘incompressible’ for most loadings) to 0.28, depending on the dimension ratios. The work provides insight into the role of structural organization and hierarchy in regulating the mechanical behavior of materials, and new opportunities for developing low-weight cellular structures with tailorable properties.