Conformational dimorphism in o‐nitrobenzoic acid: alternative ways to avoid the O…O clash

Polymorphism is a challenging phenomenon and the competitive packing alternatives which are characteristic for polymorphs may be encountered for essentially rigid molecules. A second crystal form of the well known compound o‐nitrobenzoic acid, C₇H₅NO₄, an important intermediate in the production of dyes, pharmaceuticals and agrochemicals, is described. Although obtained serendipitously, its intra‐ and intermolecular features match expectations from database searches and theoretical calculations. O—H…O hydrogen‐bonded carboxylic acid dimers represent the building blocks in both polymorphs. For steric reasons and in agreement with a calculated potential energy surface, the carboxylic acid and nitro groups cannot simultaneously be coplanar with the benzene ring but have to tilt. In the well established crystal form, this out‐of‐plane torsion is more pronounced for the nitro substituent. In contrast, the new polymorph is characterized by a major tilt of the carboxylic acid group. The molecules in both alternative crystal forms achieve a similar compromise with respect to acceptable intramolecular O…O contacts.     

Optimization of Formulation and Process Variables for the Preparation of Novel Doxorubicin-Loaded Sonosensitive Nanodroplets

In the present study the effect of process (homogenization speed) and formulation (polymer concentration, surfactant concentration, drug amount, perfluorohexane volume fraction and co-surfactant inclusion) variables on particle size, entrapment efficiency, and drug release kinetics of doxorubicin-loaded alginate stabilized perfluorohexane nanodroplets were evaluated. Particle size and doxorubicin entrapment efficiency were highly affected by formulation and process variables. In vitro release profile of doxorubicin from all formulations was an apparently biphasic release process and 7–13 % of drug released from nanodroplets after 24 h incubation in PBS, pH 7.4, depending on the nanodroplets composition but ultrasound exposure for 10 min resulted in triggered release of 85.95 % of doxorubicin fromoptimal formulation (G). The inclusion of Span 60 (0.15 %), Poloxamer 188 (0.15 %) as co-surfactants reduced the particle size of nanodroplets from 51.8 to 42.3 and 35.6 nm, respectively. The entrapment efficiency decreased for span 60, while it did not changed in the case of Poloxamer 188. Comparison of drug release kinetics demonstrated that drug release was delayed for both Span 60 and Poloxamer 188. Thus, it was concluded that the particle size, entrapment efficiency and the doxorubicin release kinetics could easily be adjusted by taking advantage of process and formulation variables.     

A novel correlation approach for prediction of natural gas compressibility factor

Gas compressibility factor (z-Factor) is one of the most important parameters in upstream and downstream calculations of petroleum industries. The importance of z-Factor cannot be overemphasized in oil and gas engineering calculations. The experimental measurements, Equations of State (EoS) and empirical correlations are the most common sources of z-Factor calculations. There are more than twenty correlations available with two variables for calculating the z-Factor from fitting in an EoS or just through fitting techniques. However, these correlations are too complex, which require initial value and more complicated and longer computations or have magnitude error. The purpose of this study is to develop a new accurate correlation to rapidly estimate z-Factor. Result of this correlation is compared with large scale of database and experimental data also. Proposed correlation has 1.660 of Absolute Percent Relative Error (E_(ABS)) versus Standing and Katz chart and has also 3.221 of E_(ABS) versus experimental data. The output of this correlation can be directly assumed or be used as an initial value of other implicit correlations. This correlation is valid for gas coefficient of isothermal compressibility (c_g) calculations also.     

Topology optimization based on the finite cell method

We present an extension of the Finite Cell Method (FCM) to topology optimization utilizing the Fully Stressed Design (FSD) approach. The proposed method is briefly explained in 2D and its potential is demonstrated by means of a linear elastic 3D problem. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of cyanide using a chemiluminescence system composed of permanganate,rhodamine B,and gold nanoparticles

We describe a new chemiluminescence (CL) system based on the oxidation of rhodamine B (RhoB) with alkaline potassium permanganate in the presence of gold nanoparticles (Au-NPs) and anionic detergent sodium dodecyl sulfate. Free RhoB is weakly chemiluminescent when oxidized with permanganate at alkaline pH values. However, a remarkably strong enhancement of CL is observed in the presence of Au-NPs, probably due to a strong interaction between RhoB and the NPs. The possible mechanism was studied via recording the CL emission. It is also found that the intensity of CL gradually decreases in the presence of cyanide due to its interaction with the Au-NPs. The relation between the decreased CL intensity and cyanide concentration was exploited to develop a method for the determination of cyanide in the 0.01–0.5 μM concentration range, with a detection limit of 2.8 nM. The method was used to determine cyanide in spiked water, urine, and serum. Figure

Alkaline permanganate-rhodamine B-SDS CL reaction is dramatically enhanced by gold nanoparticles. Based on the inhibiting effect of cyanide on this system, a sensitive CL method was developed for its determination     

Application of crude extract of kohlrabi (Brassica oleracea gongylodes) as a rich source of peroxidase in the spectrofluorometric determination of hydrogen peroxide in honey samples.

Crude extract of kohlrabi (Brassica oleracea gongylodes) was prepared by a simple procedure and its enzymatic activity and total protein concentration were determined. It was found that this crude extract is a rich source of peroxidase (POx) and has high specific activity. Cross-linked polyvinylpyrrolidone was used as a stabilizer in the preparation of the crude extract. The POx activity of kohlrabi crude extract did not vary for at least 2 months when deoxygenated and stored at 4 degrees C. This extract was applied for the spectrofluorometric determination of hydrogen peroxide using homovanillic acid as a fluorogenic substrate. POx catalyzes the hydrogen peroxide oxidation of homovanillic acid to produce a dimer which shows strong fluorescence at 420 nm with excitation at 312 nm. In the optimum conditions, the calibration graph for hydrogen peroxide was linear up to 190 ng mL(-1), with a detection limit of 4.4 ng mL(-1). The relative standard deviation (RSD) was 1.48% for 50 ng mL(-1) hydrogen peroxide. The proposed method was successfully applied to the determination of hydrogen peroxide in honey. The concentration-time profile of H2O2 produced upon dilution of honey was studied and H2O2 contents of some different honeys from various areas of Iran were determined.     

Simplified cloud point extraction for the preconcentration of ultra-trace amounts of gold prior to determination by electrothermal atomic absorption spectrometry

A simple and sensitive cloud point extraction method has been developed for the preconcentration of ultra-trace amounts of gold as a prior step to its determination by electrothermal atomic absorption spectrometry. It is based on the extraction of gold in hydrochloric acid medium using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding a chelating agent. The preconcentration of a 50 mL sample solution was thus enhanced by a factor of 200. The resulting calibration graph was linear in the range of 10–200 ng L⁻¹ with a correlation coefficient of 0.9993. The limit of detection (3s) obtained under optimal conditions was 2.0 ng L⁻¹. The relative standard deviation for 10 replicate determinations at a 100 ng L⁻¹ Au level was 3.6%. The method was applied to the ultra-trace determination of gold in water and copper samples.     

The variation of heat transfer in a two‐sided lid‐driven differentially heated square cavity with nanofluids containing carbon nanotubes for physical properties of fluid dependent on temperature

The behavior of nanofluids containing cylindrical nanoparticles are investigated numerically inside a two‐sided lid‐driven differentially heated square cavity to gain insight into the convective recirculation and flow processes induced by a nanofluid. The physical properties of the base fluid such as viscosity, thermal conductivity and thermal expansion coefficient are, respectively, assumed to be temperature independent (taking the mean temperature of the left and right walls) and temperature dependent. A model is developed to analyze the behavior of nanofluids taking into account the nanoparticle volume fraction whereas the transport equations are solved numerically with finite volume approach using SIMPLEC algorithm. The left and right moving walls are maintained at different constant temperatures while the upper and bottom walls are thermally insulated. The directions of the moving walls were considered in a way that the force and natural convections aid each other. The governing parameter Richardson number was 0.1<Ri<50.0 but due to space constraints only the results for 0.1<Ri<10.0 from fluid flow are presented. It was found that the temperature dependency of physical properties at different Richardson numbers and nanoparticle volume fractions affects the fluid flow and heat transfer in the cavities. Finally, comparisons between the behaviors of the average Nusselt number at the left wall for two cases are presented. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of multi-wall carbon nanotubes by copper vapor laser

Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is reported. The operating parameters of this laser, i.e. a high fluence at the focal point and an extremely high frequency of 10 kHz, distinguished it from common laser sources in the synthesis of CNTs. Therefore, the unexpected experimental findings, the formation of MWNTs instead of the generally reported SWNTs, would be verified by these two notable parameters. Electron microscopy beside Raman spectroscopy illustrates the presence of multi-wall carbon nanotubes in the resulting product.     

Cooling performance of a microchannel heat sink with nanofluids containing cylindrical nanoparticles (carbon nanotubes)

In this paper, we present the numerical method for explaining the cooling performance of a microchannel heat sink with carbon nanotubes (CNTs)-fluid suspensions. Here we will show that with increase of nanolayer thickness of multiwalled carbon nanotubes (MWCNTs) the microchannel heat sink temperature gradient will be decreased. By using a theoretical model for explaining the enhancement in the effective thermal conductivity of nanotubes (cylindrical shape particles) for use in nanotube-in-fluid suspension, we investigate the temperature contours and thermal resistance of a microchannel heat sink with MWCNTs (with ~25 nm diameter) dispersed in water.