Experimental investigation of incipient equilibrium conditions for the formation of semi-clathrate hydrates from quaternary mixtures of (CO2 + N2 + TBAB + H2O)

The three-phase (vapour + liquid + solid) equilibrium conditions for semi-clathrates formed from three mixtures of (CO₂ + N₂), in aqueous solutions of tetra-butyl ammonium bromide (TBAB), were measured in an isochoric reactor. The experiments were conducted at temperatures between (281 and 290) K, at pressures between (1.9 and 5.9) MPa and in aqueous TBAB solutions of w_TBAB = (0.05, 0.10, and 0.20). The experimental results obtained in this study were compared with previously obtained results for gas hydrates, formed from the same three mixtures of (CO₂ + N₂) and it was observed that semi-clathrates formed at a substantially lower pressure than did gas hydrates.     

Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: comparison of experiment and theory

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe(2)O(3) nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe(2)O(3) NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe(2)O(3) core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe(2)O(3) NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average "effective" optical behavior of the Faraday medium containing magnetic nanoparticles.     

Synthesis of Iridium Oxide Nanotubes by Electrodeposition into Polycarbonate Template: Fabrication of Chromium(III) and Arsenic(III) Electrochemical Sensor

For the first time iridium oxide (IrO₂) nanotubes are synthesized by electrodeposition in a polycarbonate (PC) template. Potential cycling (90 cycles) between 0.0 and 0.9 V is used for the preparation of IrO_x nanotubes onto the PC template with a pore diameter of 100 nm. Field‐emission scanning electron microscopy (FESEM) images show, that IrO₂ nanotubes with uniform diameters of 110±10 nm and an estimated length of 1–3 µm are formed. The electrochemical properties and the electrocatalytic activity of a glassy carbon‐IrO_x nanotube modified electrode toward Cr³⁺ and As³⁺ oxidation are investigated. Finally, the modified electrode is used for micromolar detection of the proposed analytes using differential pulse voltammetry.     

Biomimetic peptide bond formation in water with aminoacyl phosphate esters

Aminoacyl phosphates, biomimetic analogues of aminoacyl adenylates, react efficiently with amino acid esters to form dipeptides with retention of stereochemical integrity. The reactions are selective and occur readily in the presence of nucleophiles other than amino groups on their side chains. Aminoacyl phosphate esters that lack an amino-protecting group are also suitable for peptide bond formation, leading to a simplified overall process.     

In vitro antioxidant activities of the methanol extract and its different solvent fractions obtained from the fruit pericarp of Terminalia bellerica

Terminalia bellerica has been used as a traditional medicine in a variety of ailments including anaemia, asthma, cancer, inflammation, rheumatism and hypertension. In this study, the free radical scavenging and antioxidant activities of methanol extract (ME) and its different solvent fractions (namely hexane (HE), ethyl acetate (EA), butanol (BL) and water (WA)) of the T. bellerica fruit pericarp were evaluated and compared with standard antioxidant compounds like gallic acid (GA), catechin and ascorbic acid. Among the different fractions tested, the EA fraction exhibited higher antioxidant and radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals than the other fractions, which may be attributed to its higher phenolic and flavonoid content, since a linear relation was observed between the phenolic content and the antioxidant parameters. The HPTLC analysis of the EA fraction revealed that it mainly contains GA and ferulic acid (FA) as major phenolics, and the higher antioxidant activities of EA fraction may be due to the presence of these compounds.     

New third and fourth order nonlinear solvers for computing multiple roots

We present a new third order method for finding multiple roots of nonlinear equations based on the scheme for simple roots developed by Kou et al. [J. Kou, Y. Li, X. Wang, A family of fourth-order methods for solving non-linear equations, Appl. Math. Comput. 188 (2007) 1031-1036]. Further investigation gives rise to new third and fourth order families of methods which do not require second derivative. The fourth order family has optimal order, since it requires three evaluations per step, namely one evaluation of function and two evaluations of first derivative. The efficacy is tested on a number of relevant numerical problems. Computational results ascertain that the present methods are competitive with other similar robust methods.     

Enzyme-free colorimetric assay of serum uric acid

A nonenzymatic method for the selective detection and quantification of serum uric acid (UA) using 2-thiouracil (2-TU) tailored Au nanoparticles is developed. The H-bonding interaction of UA with functionalized Au nanoparticles brings instantaneous visible color change and paves the way for the visible sensing of UA.     

Phase boundaries as agents of structural change in macromolecules

We model long rod-like molecules, such as DNA and coiled-coil proteins, as one-dimensional continua with a multi-well stored energy function. These molecules suffer a structural change in response to large forces, characterized by highly typical force-extension behavior. We assume that the structural change proceeds via a moving folded/unfolded interface, or phase boundary, that represents a jump in strain and is governed by the Abeyaratne–Knowles theory of phase transitions. We solve the governing equations using a finite difference method with moving nodes to represent phase boundaries. Our model can reproduce the experimental observations on the overstretching transition in DNA and coiled-coils and makes predictions for the speed at which the interface moves. We employ different types of kinetic relations to describe the mobility of the interface and show that this leads to different classes of experimentally observed force-extension curves. We make connections with several existing theories, experiments and simulation studies, thus demonstrating the effectiveness of the phase transitions-based approach in a biological setting.