Single component and binary diffusion of n-heptane and toluene in SBA-15 materials

In this work, the diffusion properties of single component n-heptane and toluene as well as their binary mixtures in two SBA-15 samples with different structural characteristics were studied by the standard Zero Length Column (ZLC) technique under three different concentration levels. A theoretical ZLC desorption model considering the Generalized Maxwell-Stefan (GMS) formulation was developed. Using the independently measured single component equilibrium and kinetic parameters, the model was able to reasonably predict experimental binary ZLC desorption curve for countercurrent diffusion of toluene in the presence of n-heptane. However, there was a significant deviation between model prediction results and experimental data for countercurrent desorption of n-heptane in the presence of toluene. The diffusion of n-heptane is reduced by the presence of toluene, regardless of the relative content of micropores in the intrawall pores, while that of toluene is virtually unaffected by the counter-diffusion of n-heptane. The observed phenomena cannot be addressed by the simple model considering the cross term diffusion effect. The structural property of material and the molecular characteristics of probe molecules were used to account for the difference in the behavior between n-heptane and toluene.     

Development and validation of an HPLC stability-indicating method for identification and assay of elemental iron(II) in pharmaceutical drug products using reversed-phase HPLC

Ferrous sulfate tablets are a supplementary iron source for people who suffer from iron deficiency anemia. A simple, fast, and QC-friendly HPLC method was developed and validated to determine elemental iron in ferrous sulfate drug products. A TSK-GEL Super octadecylsilyl column (50 x 4.6 mm id, 2 microm particle size) with a mobile phase consisting of 0.06 M methanesulfonic acid in water-acetonitrile (40 + 60, v/v) and UV detection at 282 nm were used for this method. Separation of the elemental iron peak from the matrix was achieved within 5 min. This method was successfully validated according to International Conference on Harmonization guidelines, and shown to be stability-indicating for the shelf-life samples of ferrous sulfate tablets, as well as selective for the analyte of interest.     

Chemical constituents of Jordanian propolis

Seventeen compounds, including a new lanostane triterpenoid, 24(Z)-1β-3β-dihydroxyeupha-7,24-dien-26-oic acid, have been isolated from the methanolic extracts of two samples of Jordanian propolis collected from two different places with different dominant flora. The structures of the isolated compounds were elucidated by spectral methods including IR, UV, MS and 1- and 2-D NMR.     

Synthesis,Antioxidant, Antituomer Activities of Some New Thiazolopyrimidines,Pyrrolothiazolopyrimidines and Triazolopyrrolothiazolopyrimidines Derivatives

Reaction of 6‐amino‐2‐thiouracil 1 with ethyl bromoacetate yielded ethyl 2‐(7‐amino‐2,5‐dioxo‐3,5‐dihydro‐2H‐thiazolo[3,2‐a]pyrimidin‐6‐yl)acetate 2 . Reaction of 2 with sodium ethoxide afforded the pyrrolothiazolopyrimidine derivative 3 . Compound 2 reacted with hydrazine hydrate to give 7‐amino‐thiazolopyrimidine‐carbohydrazide 4 . The latter compound 4 reacted with carbon disulphide to form 7‐amino‐6‐(oxadiazolylmethyl) thiazolopyrimidine 5 . Compound 5 was heated in methanol to yield 9‐thioxotriazolopyrrolothiazolopyrimidine 6 . Also, the reaction of 3 with aromatic aldehydes afforded the diarylmethylenepyrrolothiazolopyrimidine derivatives 7a‐c . The latter compounds 7a‐c underwent cyclocondensation with hydroxylamine to give diaryldioxazolopyrrolothiazolopyrimidine derivatives 8a‐c . The new prepared compounds were subjected for antioxidant and antituomer studies, some of these compounds exhibited promising activity.     

Floating and sustained-release characteristics of effervescent tablets prepared with a mixed matrix of Eudragit L-100-55 and Eudragit E PO

The aim of this study was to evaluate the influence of Na-bicarbonate as an effervescent agent on the floating and sustained-release characteristics in 0.1 M HCl of tablets made of Eudragit E PO (EE) and/or Eudragit L-100-55 (EL) as matrix formers at different EE:EL weight ratios: 0:100, 25:75, 50:50, 75:25, and 100:0. The tablets were made by direct compression utilizing metronidazole as a model drug. Effervescent tablets with 50EE/50EL (w/w) showed the best floating and sustained drug release properties in the dissolution medium. The corresponding noneffervescent tablets were nonfloating and showed significantly faster drug release. Effervescent tablets with single polymers showed an immediate drug release pattern. These results were explained by Fourier-transform infrared spectroscopy and elemental analysis, which showed strong evidence of interpolyelectrolyte complexation between EE and EL when they were exposed to 0.1 M HCl as an effervescent hybrid matrix, but not as a noneffervescent hybrid matrix. The role of Na-bicarbonate in allowing EE-EL complexation during dissolution was explained as due to raising the pH around EL particles for sufficient polymer ionization and ionic-interaction with the ionized EE.     

The use of umbelliferone in the synthesis of new heterocyclic compounds

New coumarin derivatives, namely 7-[(5-amino-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one, 5-[(2-oxo-2H-chromen-7-yloxy)methyl]-1,3,4-thiadiazol-2(3H)-one, 2-[2-(2-oxo-2H-chromen-7-yloxy)acetyl]-N-phenylhydrazinecarbothioamide, 7-[(5-(phenylamino)-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one and 7-[(5-mercapto-4-phenyl-4H-1,2,4-triazol-3-yl)methoxy]-2H-chromen-2-one were prepared starting from the natural compound umbelliferone. The newly synthesized compounds were characterized by elemental analysis and spectral studies (IR, 1H-NMR and 13C-NMR).     

Interactions of the N3 dye with the iodide redox shuttle: quantum chemical mechanistic studies of the dye regeneration in the dye-sensitized solar cell

The iodide/triiodide redox couple plays a unique role in the dye-sensitized solar cell (DSSC). It is a necessary and unique part of every highly efficient DSSC published to date; alternative redox couples do not perform nearly as well. Hence, a detailed molecular-level understanding of its function is desirable. A density-functional theory (DFT) study has been carried out on the kinetic and thermodynamic aspects of the dye regeneration mechanism involving the iodide/triiodide redox couple and the prototypical N3 dye in the DSSC. The intermediate complexes between the oxidized dye and iodide have been identified. These are outer-sphere complexes of the general formula [dye(+)···I(-)]. Solvent effects are seen to play a critical role in the thermodynamics, whereas relativistic spin-orbit effects are less important. Both the kinetic and thermodynamic data reveal that the formation of complexes between [dye(+)···I(-)] and I(-) is the rate limiting step for the overall dye regeneration process. The regeneration of the neutral dye proceeds with the liberation of I; processes involving atomic iodine or I(-) are inferior, both from thermodynamic and kinetic considerations. The overall dye regeneration reaction is an exothermic process.     

Design of fiber Bragg grating-based Fabry–Perot sensor for simultaneous measurement of humidity and temperature

A new sensor for simultaneous measurement of humidity and temperature is proposed. The sensor consists of Fabry–Perot cavity formed by two identical uniform fiber Bragg gratings. To make the cavity serves as humidity sensor, moisture sensitive polymer, which is polyimide, is coated on the FBG and on the cavity with different thickness. When the sensor is exposed to the relative humidity change, the polyimide will expand and stretch the fiber and induces strain on the FBG and on the cavity. The induced strain alters the grating period, cavity length and effective refractive index of fiber. The simulation results show that the humidity sensitivity and thermal sensitivity are 1.92 pm/%RH and 8.87 pm/°C, respectively, for polyimide coating thickness of 10 μm on the FBG and 15 μm on the cavity.     

On the interplay between inertial and viscoelastic effects for the flow in weakly modulated channels

The flow inside a spatially modulated channel is examined for viscoelastic fluids of the Oldroyd‐B type. The lower wall is flat and the upper wall is sinusoidally modulated. The modulation amplitude is assumed to be small. Thus, a regular perturbation expansion of the flow field coupled to a variable‐step finite‐difference scheme is used to solve the problem. Convergence and accuracy assessment against earlier experimental results indicate that there is a significant range of validity of the perturbation approach. The influences of wall geometry, inertia and viscoelasticity on the flow kinematics and stresses are investigated systematically. In particular, the interplay between the flow and fluid parameters effects on the conditions for the onset of backflow, number of vortices, their size and location is revealed. The distance between the flow separation and reattachment locations identifies the vortex size. Non‐monotonic dependence of the vortex size on elasticity is reported. The critical conditions for the onset of negative elasticity effects on vortex size are identified. The critical Reynolds number for the onset of backflow initially decreases then levels off or even increases as elasticity increases. For highly elastic fluid and large enough Reynolds number, more than one vortex appear near the lower wall. Copyright © 2005 John Wiley & Sons, Ltd.     

Spectral Properties of Bifunctional Schiff Bases, [Bis (X-Phenyl)-Ethane Diimine]

Electronic spectra of five (Bis(X-phenyl)-Ethane diimine] compounds I-V, have been investigated in various organic solvents and aqueous buffer solutions of varying pH's. The observed visible band is assigned to intramolecular CT transition. Furthermore, it is deduced that structure of the o-hydroxy derivative is not entirely planar. The acid dissociation constant values of the hydroxy derivatives have been determined and are discussed.