Numerical investigation of serrated fins on natural convection from concentric and eccentric annuli with different cross sections

Journal of Thermal Analysis and Calorimetry - In this paper, the effect of internal serrated fins and eccentricity on natural convection heat transfer between annular spaces with the equivalent...     

Conversion of organic halides to disulfanes using KCN and CS2

A sulfur transfer reagent was produced in situ upon stirring a mixture of KCN and CS₂ in DMF at r.t. for 15 min, which after heating with an alkyl halide or aryl halide and CuI gave the corresponding symmetric dialkyl or diaryl disulfide, respectively, in high to excellent yields.     

Morphologies of branched-chain pyrogallol[4]arenes in the solid state

A suite of branched-chain pyrogallol[4]arene (Pg) macrocycles, most of which show activity in bilayer membranes, has been prepared and studied by X-ray crystallography. The little-known branched side-chain Pgs include 2-propyl, 2-butyl, 2-pentyl, 3-pentyl, 3-heptyl, 4-heptyl, 5-nonyl and cyclohexyl. The Pgs form self-assembled structures having bilayer, capsule or, in one case, a nanotube morphology. The nanotube structure observed for C-(di-n-ethyl)pyrogallol[4]arene was confirmed by X-ray structure analysis and by transmission and scanning electron microscopies.     

Tungsten hexachloride nanoparticles loaded on montmorillonite K-10: a novel solid acid catalyst in the synthesis of symmetrical and unsymmetrical azines

In the present investigation, we have developed a novel technique to prepare azines using nano-WCl₆ loaded on Montmorillonite K10 clay as a highly active catalyst. A variety of aldehydes and ketones were efficiently converted to the corresponding azines using catalytic amounts of nanosized WCl₆/Mont. K10 under mild conditions. The nanostructures of WCl₆ loaded on Mont. K10 as solid acid catalyst have been prepared by solid dispersion method. The advantages of this catalyst are rapid completion of the reactions, simplicity of performance, lack of pollution and mild and green reaction conditions. The morphologies, structure, and chemical components of parent and modified clay were successfully characterized using SEM, FT-IR, CV, XRD and EDX measurements.     

Cyproterone Synthesis, Recognition and Controlled Release by Molecularly Imprinted Nanoparticle

In this study, we used novel synthetic conditions of precipitation polymerization to obtain nanosized cyproterone molecularly imprinted polymers for application in the design of new drug delivery systems. The scanning electron microscopy images and Brunauer?CEmmett?CTeller analysis showed that molecularly imprinted polymer (MIP) prepared by acetonitrile exhibited particles at the nanoscale with a high degree of monodispersity, specific surface area of 246?m²?g^?1, and pore volume of 1.24?cm³?g^?1. In addition, drug release, binding properties, and dynamic light scattering of molecularly imprinted polymers were studied. Selectivity of MIPs was evaluated by comparing several substances with similar molecular structures to that of cyproterone. Controlled release of cyproterone from nanoparticles was investigated through in vitro dissolution tests and by measuring the absorbance by HPLC-UV. The pH dissolution media employed in controlled release studies were 1.0 at 37?°C for 5?h and then at pH 6.8 using the pH change method. Results show that MIPs have a better ability to control the cyproterone release in a physiological medium compared to the non molecularly imprinted polymers (NMIPs).     

Characterization and evaluation of the photocatalytic properties of wormhole-like mesoporous silica incorporating TiO2, prepared using different hydrothermal and calcination temperatures

TiO₂?CSiO₂ mesoporous materials were synthesised by deposition of TiO₂ nanoparticles prepared by the sol?Cgel method on to the internal pore surface of wormhole-like mesoporous silica. In this work we synthesised wormhole-like mesoporous silica of different surface area by changing the hydrothermal temperature (70, 100, or 130?°C). Subsequent to this, titania solution was deposited on to the inner surface of the pores and this was followed by calcination at different temperatures (400, 600, or 800?°C). The effect of different hydrothermal and calcination temperature on the photocatalytic properties was evaluated. The samples were characterized by N₂-sorption, X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The effect of different hydrothermal and calcination temperatures on the photocatalytic properties was evaluated by measuring the degradation of methylene blue in aqueous solution under UV light irradiation (mercury lamp, 125?W). The results indicated that appropriate surface area and degree of crystallinity are two important factors for obtaining high photocatalytic efficiency. Samples prepared at a hydrothermal temperature of 100?°C and calcined at 800?°C had the best photocatalytic performance, because of the highest surface area and high crystallinity.     

New voltammetric strategy for simultaneous determination of norepinephrine, acetaminophen, and folic acid using a 5-amino-3′,4′-dimethoxy-biphenyl-2-ol/carbon nanotube paste electrode

A carbon paste electrode modified with 5-amino-3??,4??-dimethoxy-biphenyl-2-ol and carbon nanotubes was used for the sensitive voltammetric determination of norepinephrine (NE). The electrochemical response characteristics of the modified electrode toward NE, acetaminophen (AC), and folic acid (FA) were investigated by cyclic and square wave voltammetry (SWV). The results show an efficient catalytic activity of the electrode for the electrooxidation of NE, which leads to lowering its overpotential more than 160?mV. The modified electrode exhibits an efficient electron-mediating behavior together with well-separated oxidation peaks for NE, AC, and FA. Under the optimum pH of 7.0 in 0.1?M phosphate buffer solution, the SWV anodic peak current showed a linear relation vs. NE concentration in the range of 15.0 to 1,000.0???M with a detection limit of 8.0???M.     

Highly efficient and chemoselective acetalization of carbonyl compounds catalyzed by new and reusable zirconyl triflate,ZrO(OTf)2

Various types of aromatic aldehydes were efficiently converted to their corresponding 1,3‐dioxanes and 1,3‐dioxolane with 1,3‐propanediol and ethylene glycol, respectively, in the presence of catalytic amount of ZrO(OTf)₂ in acetonitrile at room temperature. The catalyst can be reused several times without loss of its catalytic activity. Very short reaction times, selective acetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones, very mild reaction conditions, reusability of the catalyst, and easy workup are noteworthy advantages of this method. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:131–135, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20523     

Acetylcholinesterase Immobilization on Polyacrylamide/Functionalized Multi-walled Carbon Nanotube Nanocomposite Nanofibrous Membrane

In this work, polyacrylamide/multi-walled carbon nanotubes (MWCNT) solution is electrospun to nanocomposite nanofibrous membranes for acetylcholinesterase enzyme immobilization. A new method for enzyme immobilization is proposed, and the results of analysis show successful covalent bonding of enzymes on electrospun membrane surface besides their non-covalent entrapment. Fourier transform infrared spectroscopy, mechanical and thermal investigations of nanofibrous membrane approve successful cross-linking and enzyme immobilization. The enzyme relative activity and kinetic on both pure and nanocomposite membranes is investigated, and the results show proper performance of designed membrane to even improve the enzyme activity followed by immobilization compared to free enzyme. Scanning electron microscopy images show nanofibrous web of 3D structure with a low shrinkage and hydrogel structure followed by enzyme immobilization and cross-linking. Moreover, the important role of functionalized carbon nanotubes on final nanofibrous membrane functionality as a media for enzyme immobilization is investigated. The results show that MWCNT could act effectively for enzyme immobilization improvement via both physical (enhanced fibers’ morphology and conductivity) and chemical (enzyme entrapment) methods.