Structure and Properties of Nanocomposites Based on SBS Block Copolymer and Alumina

The addition of inorganic filler into commodity plastics has a long history. Today, polymer composites based on nanosized filler are popular among polymer scientists from academia and industries due to their ability to enhance a number of physical properties. In this work, we investigate the dispersion and reinforcing effect of alumina nanoparticles using a polystyrene-polybutadiene based block copolymer (SBS) and organically modified alumina nanofiller. With the aid of solution casting procedures, polymer composites with good dispersion of nanoparticles could be produced. It has been demonstrated that with suitably coated nanoparticles, polymer composites with optimum dispersion of nanofiller ensuring marked reinforcement effect can be achieved.     

Preparation of calix[4]arene methylene crosslinked resins with 2-pyridyl pendant group and their adsorption behavior towards silver ion

Three different resins namely 1:5 MC-resin, 1:3 MC-resin and 1:1 MC-resin have been synthesized by methylene crosslinking of 2-pyridylcalix[4]arene. Adsorption behavior of these resins towards the metal ions existing in photographic waste was investigated. The resins show absolute efficiency for adsorption of silver ion with no affinity for other coexisting ions. First two resins form 1:1 complex whereas the third one forms 2:1 complex with silver ion. Maximum loading capacity of silver ion on the present resins was found to be 1.15, 1.29 and 0.69 mol kg^?1, respectively. Column chromatographic separation of silver ion in presence of excess of sodium ions was also carried out with 1:5 MC-resin. Selective adsorption of silver ions over excess of sodium ions was achieved.     

Chemical ordering and thermodynamic properties of HgNa liquid alloys

We have studied the thermodynamic properties and microscopic structures of HgNa liquid alloy at 673 K on the basis of regular associated solution model. The concentrations of ApB type complex in a regular associated solution of Hg and Na have been determined. We have then used the concentration of complex to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit S_CC(0) and the Warren-Cowley short-range parameter α₁. The analysis suggests that heterocoordination leading to the formation of complex Hg₄Na is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Hg-rich region.     

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.     

A Temperature and Salt-Tolerant <Emphasis Type="SmallCaps">l</Emphasis>-Glutaminase from Gangotri Region of Uttarakhand Himalaya: Enzyme Purification and Characterization

Purification and characterization of halotolerant, thermostable alkaline l-glutaminase from a Bacillus sp. LKG-01 (MTCC 10401), isolated from Gangotri region of Uttarakhand Himalaya, is being reported in this paper. Enzyme has been purified 49-fold from cell-free extract with 25% recovery (specific activity 584.2 U/mg protein) by (NH₄)₂SO₄ precipitation followed by anion exchange chromatography and gel filtration. Enzyme has a molecular weight of 66 kDa. l-Glutaminase is most active at pH 11.0 and stable in the pH range 8.0–11.0. Temperature optimum is 70 °C and is completely stable after 3 h pre-incubation at 50 °C. Enzyme reflects more enhanced activity with 1–20% (w/v) NaCl, which is further reduced to 80% when NaCl concentration was increased up to 25%. l-Glutaminase is almost active with K⁺, Zn²⁺, and Ni²⁺ ions and K _m and V _max values of 240 μM and 277.77 ± 1.1 U/mg proteins, respectively. Higher specific activity, purification fold, better halo-tolerance, and thermostability would make this enzyme more attractive for food fermentation with respect to other soil microbe derived l-glutaminase reported so far.     

Retention of nisin activity at elevated pH in an organic acid complex and gold nanoparticle composite

Biocompatible organic acids and citrate-stabilized gold nanoparticles were interacted with nisin to generate robust antimicrobial agents, which display archetypical nisin activity even at elevated pH.     

Eigenvalue density of linear stochastic dynamical systems: A random matrix approach

Eigenvalue problems play an important role in the dynamic analysis of engineering systems modeled using the theory of linear structural mechanics. When uncertainties are considered, the eigenvalue problem becomes a random eigenvalue problem. In this paper the density of the eigenvalues of a discretized continuous system with uncertainty is discussed by considering the model where the system matrices are the Wishart random matrices. An analytical expression involving the Stieltjes transform is derived for the density of the eigenvalues when the dimension of the corresponding random matrix becomes asymptotically large. The mean matrices and the dispersion parameters associated with the mass and stiffness matrices are necessary to obtain the density of the eigenvalues in the frameworks of the proposed approach. The applicability of a simple eigenvalue density function, known as the Marenko–Pastur (MP) density, is investigated. The analytical results are demonstrated by numerical examples involving a plate and the tail boom of a helicopter with uncertain properties. The new results are validated using an experiment on a vibrating plate with randomly attached spring–mass oscillators where 100 nominally identical samples are physically created and individually tested within a laboratory framework.