Chemistry

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Browsing Chemistry by Author "Lewu, F.B."

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    Chemical composition and biological potential of the volatile and non-volatile constituents of tarchonanthus camphoratus and tarchonanthus trilobus var galpinni of KwaZulu–Natal province.
    (University of Zululand, 2013) Nanyonga, Sarah Kiwanuka; Oyedeji, O.A.; Opoku, A.R.; Lewu, F.B.
    The chemical composition and the biological activities of the volatile extracts (essential oils) and non-volatile (solvent extracts) of the aerial parts Tarchonanthus camphoratus and Tarchonanthus trilobus var galpinni collected from Sangoyana and Ubombo respectively, in the Kwa-Zulu Natal province were investigated in this study. The essential oils were separately extracted from the fresh leaves, dry leaves and dry stem by hydro-distillation and their chemical constituents determined by Gas chromatography/mass spectrometry (GC/MS). The essential oils investigated were of the dry leaf of T. camphoratus harvested in 2009 and of the fresh leaf, dry leaf and dry stem of both T. camphoratus leaf and T. trilobus var galpinni harvested in 2010 and 2011. The compounds present in all the essential oils were categorised as monoterpene hydrocarbons, sesquiterpene hydrocarbons, oxygenated monoterpenes, oxygenated sesquiterpenes and others but they differed in the type and percentage composition. Sesquiterpene hydrocarbons dominated all the essential oils with β–caryophyllene and allo-aromadendrene present in all the essential oils either as minor or major compounds. The oxygenated monoterpene 1,8-cineole, which is suspected to be responsible for the camphor smell of T. camphoratus, was present in all the essential oils of the leaves and stem of T. camphoratus. δ-Cadinene, a sesquiterpene hydrocarbon, featured in all the essential oils except of the fresh and dry leaf of T. camphoratus harvested in 2011. The chemical constituents in the non volatile extracts were determined by Pyrolysis-Gas chromatography/mass spectrometry (Py-GC/MS). A variety of compounds categorised as hydrocarbons, tetraterpenes, triterpenoids, phenols, fatty acids, fatty alcohols, steroids and sterols among others were identified in the extracts. Phenols were identified in the aqueous, methanol, dichloromethane leaf extracts and the methanol bark extract of T. camphoratus and in the dichloromethane leaf and ethyl acetate leaf extracts of T. trilobus var galpinni. Steroids were identified in the bark extracts of T. camphoratus and in the methanol leaf extract of T. trilobus var galpinni. Hydrocarbons were identified in all the solvent/non volatile extracts but were more dominant in the dichloromethane bark extracts of both T. camphoratus and T. trilobus var galpinni. Triterpenoids were identified in the dichloromethane leaf extracts, ethyl acetate bark extracts of both species, in the methanol leaf of T. trilobus var galpinni and in the methanol bark extract of T. camphoratus. The preliminary phytochemical screening of the extracts also revealed the presence of phenols, flavonoids, saponins and tannins in some of the extracts. The volatile and non volatile extracts were screened for their antibacterial activity, antioxidant activity and cytotoxic activities and the volatile extracts were further screened for their insecticidal activities. The extracts were screened for antibacterial activity against 4 Gram positive and 5 Gram negative bacteria. The zones of inhibition of the fresh leaves, dry leaves and dry stem essential oils of T. camphoratus ranged from 7.3 – 14.0, 7.3 – 16.7 and 13.5 – 20.4 mm respectively and the zones of inhibition of the fresh leaf oil of T. trilobus var galpinni ranged from 8.2 – 21.8 mm. The volatile extracts exhibited higher percent inhibition than the non volatile extracts and the dry stem essential oil of T. camphoratus showed the highest antibacterial activity of all the extracts. The non volatile extracts exhibited significant antioxidant potential when tested by DPPH and ABTS•+ radical scavenging assays plus reducing power assay but showed poor nitric oxide inhibition and iron chelating ability. The volatile extracts generally showed poor antioxidant activity in all the antioxidant assays. The essential oils of both the dry leaf of T. camphoratus and fresh leaf of T. trilobus var galpinni showed the highest larval mortality of 100% which was observed at a concentration of 300 ppm after 24h whereas the lowest mortality after 24h was 20% at 25 ppm for T. camphoratus and 20% at 50 ppm for T. trilobus var galpinni. Insecticidal activity of the volatile extracts against stored product pests, S. zeamais and S. oryzae revealed a lack of contact and fumigation toxicity by essential oils of both plant species. The essential oil of the dry leaf of T. camphoratus, however, showed repellent activity of over 50% after 24h at all the concentrations used on both S. zeamais and S. oryzae. Cytotoxic investigation of the volatile and non volatile extracts revealed that the extracts generally had low toxicity. This study is the first to provide the chemical profiles and biological activities of the volatile and non volatile extracts of T. camphoratus and T. trilobus var galpinni from Kwa-Zulu Natal. The volatile extracts could be considered as potential alternatives, whether alone or in combination, to synthetic antibiotics, larvicides and repellents. The non volatile extracts on the other hand, could be potential sources of antioxidants that could have great importance as therapeutic agents.
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    Essential oil composition and some biological activities of tetradenia riparia
    (University of Zululand, 2011) Khuzwayo, Joyce Khethiwe; Oyedeji, A.O.; Opoku, A.R.; Lewu, F.B.
    This dissertation has a brief historical overview of medicinal plants, T. riparia and their traditional uses. The choice of the medicinal plant studied was based on the evidence in literature that oils of the species contain phenolic compounds and the herbs belonging to the family Lamiaceae was implicated in the management of chronic and infectious diseases. The study was designed to determine the secondary metabolites present in the plant through phytochemical screening of the plant material, establish the chemical profile of the isolated oils using GC-MS and evaluate the biological potential of both the crude extracts and the isolated oils which included; antioxidant, antibacterial and anti-ulcer activities. The essential oils were extracted from the dry stem and fresh leaves of T. riparia. Farnesol, caryophyllene oxide, -fenchyl acetate, and guaiol (12.3 - 7.1%) were the most prominent compounds identified in the dry stem oil collected from the botanic garden, Botany Department, University of Zululand (UZ). The analysis of the fresh leaf oil from the botanic garden collection had hexane as the major compound (60.9%), while -fenchyl acetate (6.7%), caryophyllene oxide (4.1%) and farnesol (2.5%) were other prominent components present in the oil. The dry stem oil from Maphumulo had farnesol (27.4%), humulene oxide (11.5%), -eudesmol (8.9%), caryophyllene oxide (3.8%) and terpinene-4-ol (3.35) as the main components, while the fresh leaf oil composition from Maphumulo was similar to that of botanic garden with hexane accounting for over 50% of the oil composition. Other prominent compounds identified in the GC-MS analysis of the fresh leaf oil were farnesol (6.3%) and a-thujone (3.6%). The chemical profiles of the T. riparia plant samples collected from two difference location within the KwaZulu-Natal suggest two distinct chemotypes of the plant species. Nonetheless, farnesol was found to be the major constituents of all the oils parts isolated. To the best of my literature knowledge and search, this is the first time that the chemical composition of the essential oils isolated from the leaf and stem of T. riparia is been reported. The phytochemical screening of the plant reveals saponins (23.3%), flavoinoids (3.7-4.9%) and tannins (4.1%) to be prominent secondary metabolites presence. These compounds are known to exhibit anti-ulcer activities. Indeed, a 65% inhibition of indomethacin-induced gastric ulceration was observed for the plants essential oil. The antibacterial activity studies indicated that the oil had moderate inhibitory effect on most of the bacteria. Zones of inhibition, from the disc diffusion assay of the essential oil, ranged from 6.3- 19.3 mm. The minimum inhibitory concentration (MIC) value of 0.157 mg/ml was recorded for the dry stem oil extracts from Maphumulo. The results from the biological assays showed that there is good correlation with the traditional usage of T. riparia. The results are explained fully in the body of the dissertation. The limitation for this work is that the isolation of essential oil compounds using Preparative GC was not possible as the equipment though available was not functional due to some technical unresolved issues.
University of Zululand