Ali H. Al-Marzouqi

Physicochemical properties of antifungal drug–cyclodextrin complexes prepared by supercritical carbon dioxide and by conventional techniques

Antifungal drugs are the most common systemic drugs used for the treatment of oropharyngeal candidiasis, which is the first symptom of HIV infection. However, the efficacy and bioavailability of these drugs have been limited by their poor aqueous solubility and dissolution rate. Therefore, the aim of this study was to investigate the effect of different preparation methods (i.e. kneading, coevaporation, sealed-heating, and a solid inclusion technique using supercritical carbon dioxide carrier (SC CO(2)-inclusion)) for obtaining solid inclusion complexes between beta-cyclodextrin and three antifungal drugs (itraconazole, econazole, and fluconazole). The physicochemical properties of the different products were characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffractometry (PXRD). For the complexes prepared by the SC CO(2)-inclusion method, the effects of temperature and pressure have also been investigated. Results suggested the possibility of complex formation between beta-cyclodextrin and the three antifungal agents, and indicated that inclusion formation was influenced by the preparation technique. SC CO(2)-inclusion method proved to be an effective technique for preparing solid-state inclusion complexes between beta-cyclodextrin and antifungal drugs, avoiding the use of organic solvents. Moreover, temperature of the SC CO(2) played a major role in promoting drug-carrier interactions, whereas pressure had limited effects.

A Review of Enzymatic Transesterification of Microalgal Oil-Based Biodiesel Using Supercritical Technology

Biodiesel is considered a promising replacement to petroleum-derived diesel. Using oils extracted from agricultural crops competes with their use as food and cannot realistically satisfy the global demand of diesel-fuel requirements. On the other hand, microalgae, which have a much higher oil yield per hectare, compared to oil crops, appear to be a source that has the potential to completely replace fossil diesel. Microalgae oil extraction is a major step in the overall biodiesel production process. Recently, supercritical carbon dioxide (SC-CO2) has been proposed to replace conventional solvent extraction techniques because it is nontoxic, nonhazardous, chemically stable, and inexpensive. It uses environmentally acceptable solvent, which can easily be separated from the products. In addition, the use of SC-CO2 as a reaction media has also been proposed to eliminate the inhibition limitations that encounter biodiesel production reaction using immobilized enzyme as a catalyst. Furthermore, using SC-CO2 allows easy separation of the product. In this paper, conventional biodiesel production with first generation feedstock, using chemical catalysts and solvent-extraction, is compared to new technologies with an emphasis on using microalgae, immobilized lipase, and SC-CO2 as an extraction solvent and reaction media.

Comparative evaluation of SFE and solvent extraction methods on the yield and composition of black seeds ( Nigella Sativa )

Abstract Supercritical Fluid Extraction (SFE) conditions (temperature, pressure, and volume of CO2) were optimized to obtain high quality black seed oil rich in antioxidants. The highest extraction yield (31.7%) was obtained under the SFE condition (50°C, 400 bar, and 100 mL), whereas SFE condition (50°C, 100 bar, 200 mL) gave a low yield (0.84%) as lipids were not extracted. HPLC characterization of compounds in the SFE extracts indicates the presence of a large number of compounds in high concentrations in the extract with a low yield. The yield and composition of SFE extracts were compared with the extracts obtained by the soxhlet extraction method and the SFE extract with low yield was found to be superior. Selected SFE extracts were also subjected to GSH recovery tests, and maximum recovery (84.6%) was obtained for the extract with low yield confirming the presence of antioxidant compounds.

Comparative Evaluation of SFE and Steam Distillation Methods on the Yield and Composition of Essential Oil Extracted from Spearmint (Mentha spicata)

Abstract A supercritical fluid extraction (SFE) process was optimized to obtain high quality mint oil. The effect of oven and freeze drying techniques on the quality of mint oil was investigated. The flavor principles in the SFE extract were compared with those obtained by a conventional steam distillation method. Then highest extraction yield was obtained at SFE conditions (50°C and 350 bar), however, high quality oil was obtained at 30°C and 150 bar. The compositional quality of SFE extract was found to be superior as compared to that of a steam distillation process. The extraction yield and compositional quality of oil from mint samples obtained from different regions of UAE and other countries were reported.

Review of Dynamic Electric Circuit Models for PEM Fuel Cells

Many studies have been conducted to understand the phenomena underlying the operation of fuel cells in order to enhance both the efficiency and the durability of these systems, by optimizing the cell’s operating conditions, structure and materials used in their manufacturing. Different characterization techniques have been exploited in order to establish comprehensive models that describe the complex electrochemical and thermodynamic behavior of the fuel cell. Since the output resulting from these chemical and physical processes is electric power, an equivalent circuit model is preferred in order to describe the electrical interaction of the fuel cell with the load and to facilitate the development of adequate power converter designs. Moreover, these models present a useful method for interpreting the characterizations results and provide sensible evaluation of the effects of the operating and the environmental conditions on the fuel cell performance. This paper presents the recent research efforts related to the modeling of the dynamic electric behavior of Proton Exchange Membrane (PEM) fuel cells using equivalent electric circuits. It also highlights the studies that use these circuit models to evaluate the effects of low and high current harmonics on the fuel cell’s efficiency and durability.

Electrical circuit modeling of a PEM fuel cell including compressor effect

This study aims to investigate the development of an Electrical Circuit Model (ECM) that represents the behavior of a PEM fuel cell system. The ECM parameters are identified based on sets of impedance data obtained by using a characterization process known as Electrochemical Impedance Spectroscopy (EIS). The measured impedance is fitted to an ECM using a nonlinear least-square fitting method. The proposed ECM is able to represent the effect of the compressor. The proposed model is validated using a commercial fuel cell power module. In general, such model representation is useful for analyzing the effects of the operating conditions on the fuel cell performance, efficiency and durability.

Effectiveness of Enzymatic Biodiesel Production from Microalga Oil in Supercritical Carbon Dioxide

Biodiesel production from microalgae lipids showed to be the promise approach for alternative fuels. However, this is not yet commercialized. In the present study, the efficient production of biodiesel from Nannochlorpsis sp. grown locally was confirmed. Novozyme®435 and supercritical carbon dioxide were used as reaction catalyst and reaction medium, respectively, and the results were compared to lamb fat. In addition, the microalgae biomass production was studied extensively. It was found that Nannochlorpsis sp. can accumulate lipids by nitrogen starvation reaching 29 % with 21.06 mg L-1d-1 lipid productivity when grown in nitrogen sufficient medium. The enzymatic production in supercritical carbon dioxide was efficient with 55 % ester yield higher than lamb meat fat.