An efficient multicomponent stereoselective synthesis of 1,2,4-trisubstituted 1,3-thiazetidines

The first one-pot three-component coupling reaction of O,O-diethyl hydrogen phosphorodithioate, aldehydes, and aldimines affording 1,2,4-trisubstituted 1,3-thiazetidines is reported. The product is obtained in moderate to high yields (45-94%) and has excellent diastereoselectivity (90-96%) in favour of the cis isomer. Shorter reaction times, ambient temperature, operational simplicity, and high yields are the salient features of the present procedure.     

Sintering kinetics study of mechanically alloyed nanocrystalline Mo–30 wt.% W

The paper details the results of sintering kinetics studies conducted on nanocrystalline Mo–30 wt.% W alloy powders prepared through mechanical alloying route. Both, constant rate of heating method as well as Stepwise Isothermal Dilatometry (SID) technique were used for studying the sintering kinetics. Measured step isothermal shrinkage data were analyzed by Mekipritti-Meng method. The shrinkage data was found to fit well with the rate equation proposed in this method and its validity was established for mechanically alloyed systems. Kinetic parameters were evaluated and sintering was found to occur through two major mechanisms operative successively, which are grain boundary diffusion and lattice diffusion with corresponding energies of activation as 230 kJ/mol and 480 kJ/mol, respectively. The results have been well supported by micro structural evaluation of specimens at different stages of sintering.     

Steric-effect induced alterations in streaming potential and energy transfer efficiency of non-newtonian fluids in narrow confinements

In this work, we explore the possibilities of utilizing the combined consequences of interfacial electrokinetics and rheology toward augmenting the energy transfer efficiencies in narrow fluidic confinements. In particular, we consider the exploitation of steric effects (i.e., effect of finite size of the ionic species) in non-Newtonian fluids over small scales, to report dramatic augmentations in the streaming potential, for shear-thickening fluids. We first derive an expression for the streaming potential considering strong electrical double layer interactions in the confined flow passage and the consequences of the finite conductance of the Stern layer, going beyond the Debye-Hu?ckel limit. With a detailed accounting for the excluded volume effects of the ionic species and their interaction with pertinent interfacial phenomena of special type of rheological fluids such as the power law fluids in the above-mentioned formalism, we demonstrate that a confluence of the steric interactions with the non-Newtonian transport characteristics may result in giant augmentations in the energy transfer efficiency for shear-thickening fluids under appropriate conditions.     

Methotrexate intercalated ZnAl-layered double hydroxide

The anticancerous drug methotrexate (MTX) has been intercalated into an ZnAl-layered double hydroxide (LDH) using an anion exchange technique to produce LDH-MTX hybrids having particle sizes in the range of 100-300 nm. X-ray diffraction studies revealed increases in the basal spacings of ZnAl-LDH-MTX hybrid on MTX intercalation. This was corroborated by the transmission electron micrographs, which showed an increase in average interlayer spacing from 8.9 Å in pristine LDH to 21.3 Å in LDH-MTX hybrid. Thermogravimetric analyses showed an increase in the decomposition temperature for the MTX molecule in the LDH-MTX hybrid indicating enhanced thermal stability of the drug molecule in the LDH nanovehicle. The cumulative release profile of MTX from ZnAl-LDH-MTX hybrids in phosphate buffer saline (PBS) at pH 7.4 was successfully sustained for 48 h following Rigter-Peppas model release kinetics via diffusion.     

Mechanistic studies on the oxidation of ascorbic acid and hydroquinone by a {Mn4O6}4+ core in aqueous media

Described in this work is the kinetics of oxidation of ascorbic acid and hydroquinone by a tetranuclear Mn(IV) oxidant, [Mn(4)(μ-O)(6)(bipy)(6)](4+) (1(4+), bipy =2,2(/)-bipyridine), in aqueous solution over a wide pH range 1.5-6.0. In particular, below pH 3.0, protonation on the oxo-bridge of 1(4+) results in the formation of [Mn(4)(μ-O)(5)(μ-OH)(bipy)(6)](5+) (1H(5+)) as an additional oxidant over 1(4+). Both ascorbic acid and ascorbate whereas only hydroquinone and none of its protolytic species were found to be reactive reducing agents in these reactions. Analysis of the rate data clearly established that the oxo-bridge protonated oxidant 1H(5+) is kinetically far more superior to 1(4+) in oxidizing ascorbic acid and hydroquinone. Rates of these reactions are substantially lowered in D(2)O-enriched media in comparison to that in H(2)O media. An initial one electron one proton transfer electroprotic rate step could be mechanistically conceived. DFT studies established that among the two sets of terminal and central Mn(IV) atoms in the tetranuclear oxidant, one of the two terminal Mn(IV) is reduced to Mn(III) at the rate step that we can intuitively predict considering the probable positive charge distribution on the Mn(IV) atoms.     

Intramolecularly coordinated azobenzene selenium derivatives: effect of strength of the Se···N intramolecular interaction on luminescence

A series of selenium derivatives (6-12) of 2-phenylazophenyl have been synthesized using o-lithiation route. The effect of the strength of the intramolecular Se···N interaction on the absorption spectra as well as emission spectra has been studied. The studies suggest that the secondary bonding Se···N interaction give rise to fluorescence, however, the strength of Se···N interaction cannot be directly correlated with the intensity of the fluorescence. TD-DFT calculations show that the main transition involved in the absorption spectra of the compound is the ligand based π-π* type.     

Optimal control of harvest and bifurcation of a prey-predator model with stage structure

This paper describes a prey-predator model with stage structure for prey. The adult prey and predator populations are harvested in the proposed system. The dynamic behavior of the model system is discussed. It is observed that singularity induced bifurcation phenomenon is appeared when variation of the economic interest of harvesting is taken into account. State feedback controller is incorporated to stabilize the model system in case of positive economic interest. Harvesting of prey and predator population are used as controls to develop a dynamic framework to investigate the optimal utilization of the resource, sustainability properties of the stock and the resource rent earned from the resource. The Pontryagin’s maximum principle is used to characterize the optimal controls. The optimality system is derived and then solved numerically using an iterative method with Runge-Kutta fourth order scheme. Simulation results show that the optimal control scheme can achieve sustainable ecosystem.     

Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water

This paper describes the production, characteristics, and efficacy of carbon microfibers and carbon nanofibers for the removal of phenol and Pb(2+) from water by adsorption. The first adsorbent produced in the current investigation contained the ammonia (NH(3)) functionalized micron-sized activated carbon fibers (ACF). Alternatively, the second adsorbent consisted of a multiscale web of ACF/CNF, which was prepared by growing carbon nanofibers (CNFs) on activated ACFs via catalytic chemical vapor deposition (CVD) and sonication, which was conducted to remove catalytic particles from the CNF tips and open the pores of the CNFs. The two adsorbents prepared in the present study, ACF and ACF/CNF, were characterized by several analytical techniques, including SEM-EDX and FT-IR. Moreover, the chemical composition, BET surface area, and pore-size distribution of the materials were determined. The hierarchal web of carbon microfibers and nanofibers displayed a greater adsorption capacity for Pb(2+) than ACF. Interestingly, the adsorption capacity of ammonia (NH(3)) functionalized ACFs for phenol was somewhat larger than that of the multiscale ACF/CNF web. Difference in the adsorption capacity of the adsorbents was attributed to differences in the size of the solutes and their reactivity towards ACF and ACF/CNF. The results indicated that ACF-based materials were efficient adsorbents for the removal of inorganic and organic solutes from wastewater.     

An analytical homogenization method for heterogeneous porous materials

The objective of this work is to develop an analytical homogenization method to estimate the effective mechanical properties of fluid-filled porous media with periodic microstructure. The method is based on the equivalent inclusion concept of homogenization applied earlier for solid–solid mixture. It is assumed that porous media are described by the poroelastic constitutive law developed by Biot where porosity is a material parameter. By solving the governing equations of poroelasticity in Fourier transformed domain, the relation between periodic strain and eigenstrain in porous media is established. This relation is subsequently used in an average consistency condition involving both solid and fluid phase stresses and strains. The geometry of the porous microstructure is captured in the g-integral. This homogenization method can also be applied to estimate the equivalent properties of solid–fluid mixture where a pure solid and fluid can be modeled by assuming very low and high porosity, respectively. Several examples are considered to establish this new method by comparing with other existing analytical and numerical methods of homogenization. As an application, poroelastic properties of cortical bone fibril are estimated and compared with previously computed values.