Nigist Asfaw

Remote-controlled experiments with cloud chemistry

Developing cleaner chemical processes often involves sophisticated flow-chemistry equipment that is not available in many economically developing countries. For reactions where it is the data that are important rather than the physical product, the networking of chemists across the internet to allow remote experimentation offers a viable solution to this problem.

Moringa stenopetala seed oil as a potential feedstock for biodiesel production in Ethiopia

Moringa stenopetala seed oil was evaluated as a potential sustainable feedstock for biodiesel production in Ethiopia. Base catalyzed transesterification of M. stenopetala seed oil was carried out with methanol, ethanol and a mixture of methanol and ethanol (1:1 molar ratios) with an alcohol to oil molar ratio of 6:1. The physiochemical characteristics of the esters were assessed to evaluate their suitability for use in standard diesel engines. The study indicated that M. stenopetala seeds yield 45% w/w of oil. The oil contains 78% mono-unsaturated fatty acid and 22% saturated fatty acid. Oleic is the dominant fatty acid, about 76%. When mixtures of alcohols were used, the amount of ethyl ester formed was 30% that of methyl ester. The physicochemical properties of M. stenopetala oil methyl ester and mixture of esters (methyl and ethyl) were found to comply with both the American ASTM D6751 and the European standard EN 14214. Overall, the physicochemical properties of the ester mixture of M. stenopetala oil were better than that of methyl ester. The recommended way to use the oil as a fuel is as a mixture of esters. The study indicates that compared to biodiesel fuels derived from other vegetable oils, M. stenopetala has a number of advantages. Furthermore, the use of M. stenopetala seed oil for the production of biodiesel will not compete with food as neither the seeds nor the oil are used for food in Ethiopia.

Green Chemistry in Ethiopia: the cleaner extraction of essential oils from Artemisia afra: a comparison of clean technology with conventional methodology

One of the principal aims of Green Chemistry is to bring the benefits of modern chemical manufacture to developing countries without imposing the environmental burden that has plagued the industrialised world. In this paper we present early results from a comparative study of greener extraction methods (microwaves, ultrasound, supercritical fluids) on Artemisia afra, a plant traditionally employed as a fragrance, insect repellent and as a treatment for heart troubles and coughs. We show that lower temperature extraction methods give a qualitatively larger range of extracts than traditional hydrodistillation and therefore may have some promise for use in developing countries.

Constituents of the Essential Oils from Wild and Cultivated Lippia adoensis Hochst. ex Walp.

ABSTRACT The essential oils of wild and cultivated forms of Lippia adoensis Hochst. ex Walp. collected in Ethiopia were examined by GC and GC/MS. The oils from both forms were found to differ in their physical characteristics and chemical composition. Fourteen compounds representing 88–95% of the oil from the cultivated plants and sixteen compounds constituting 68–86% of the oil from the wild plants were identified. Linalool, which was absent in the oil of the wild form, is the major component (68.06–82.57%) in the oil of the cultivated form. Also limonene (3.44–32.73%), perillaldehyde (0.04–26.90%) and piperitenone (0.15–44.48%) are found in oils from the wild plants but not in oils from the cultivated plants. The uncommon monoterpene ketone, 2-methyl-6-methylene-2, 7-octadien-4-one (ipsdienone), was found in the oils of the cultivated plants (0.06–0.81%) and the wild plants (0.81–14.89%).

Chemical composition, antimicrobial and antioxidant activities of the essential oil of Lippia javanica leaves from Ethiopia

Abstract The leaves of Lippia javanica are used for the treatment of several skin diseases in Ethiopia. Forty-two components were identified and quantified, by GC–MS and GC–FID, comprising 98.9% of the total oil with cis-sabinene hydrate (20.3%) and limonene (13.9%) as major components. cis-Sabinene hydrate is reported here for the first time as a constituent of L. javanica leaf oil (Ethiopia). The essential oil and its two fractions were assessed for their possible antimicrobial activities against two bacterial strains (Bacillus cereus and Klebsiella pneumoniae) and one fungal pathogen (Cryptococcus neoformans) using the disc diffusion method. K. pneumoniae was found to be the most susceptible bacteria to the oxygenated fraction (MIC < 5 g/mL). The antioxidant property of the oil was assessed by free radical scavenging (DPPH) assay, with IC50 = 16.6 L/mL. These findings may support the traditional uses of the plant for the treatment of skin diseases.