L. Van Puyvelde

Investigation of the antimutagenic effects of selected South African medicinal plant extracts

Dichloromethane extracts from different parts of Rhamnus prinoides, Ornithogalum longibracteatum, Gardenia volkensii, Spirostachys africana, Diospyros whyteana, Syzigium cordatum and Prunus africana were investigated for mutagenic and antimutagenic effects in Salmonella/microsome and micronucleus tests. None of the extracts tested in the Ames test were found to induce mutations or to modify the effect of the mutagen 4-nitroquinoline-oxide (4NQO). In the micronucleus test, extracts from twigs/bark of R. prinoides, twigs of D. whyteana, P. africana and S. cordatum significantly lowered the effect of the mutagen mitomycin C (MMC). Extracts from twigs/bark of G. volkensii and S. africana were genotoxic in the micronucleus test, while extracts of O. longibracteatum leaves potentiated the genotoxicity of MMC. This preliminary investigation shows that plant extracts used in traditional medicine may have particular effects with regard to mutagenicity and antimutagenicity indicating careful use in some instances and the need to isolate their active principles for further research.

Study of Rwandese medicinal plants used in the treatment of diarrhoea I

A series of 20 medicinal plants used in the Rwandese traditional medicine to treat diarrhoeal diseases has been screened for antibacterial activity against several Salmonella and Shigella and for antidiarrhoeal activity on mice. Fifty percent of the plants tested showed antibacterial activity against one or more microorganisms and 65% showed antidiarrhoeal activity.

Study of Rwandese medicinal plants used in the treatment of scabies

A series of 15 medicinal plants used in the Rwandese traditional medicine to treat scabies has been screened for anti-scabies activity against the mite Psoroptes cuniculi. Four of the plants tested showed anti-scabies activity.

The hepatoprotective principle of Hypoestes triflora leaves

Hypoestes triflora is frequently used in Rwandese native medicine to treat hepatic diseases. Premedication with a water extract of the leaves prevented the prolongation of the barbiturate sleeping time associated with carbon tetrachloride-induced liver damage in mice. The compound responsible for this protective activity was benzoic acid. Mice previously treated with benzoic acid also showed a significant diminution of the increased GOT and GPT levels seen after carbon tetrachloride administration.

Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study

Sb doping of Cu(In,Ga)Se2 (CIGS) solar cells has been reported to exhibit a positive effect on the morphology of the absorber layer, offering a possibility to lower manufacturing cost by lowering the annealing temperatures during the CIGS deposition. In this work electron microscopy, energy-dispersive x-ray spectroscopy and photoluminescence experiments have been performed on cells deposited on soda-lime glass substrates, adding a thin Sb layer onto the Mo back contact prior to the CIGS absorber deposition. The defect structure of CIGS solar cells doped with Sb in this way has been investigated and is compared with that of undoped reference cells. The influence of substrate temperature during absorber growth has also been evaluated. For all samples the photoluminescence results can be explained by considering three donor–acceptor pair recombination processes involving the same defect pairs.

Electronic defect study on low temperature processed Cu(In,Ga)Se2 thin-film solar cells and the influence of an Sb layer

A way to lower the manufacturing cost of Cu(In,Ga)Se2 (CIGS) thin-film solar cells is to use flexible polymer substrates instead of rigid glass. Because such substrates require lower temperature during absorber deposition, the grain growth of the absorber layer can be hindered which leads to a lower cell performance. Partial compensation of this efficiency loss might be accomplished by growing the absorber in the presence of Sb, which is reported to promote grain growth. In this work CIGS solar cells, deposited on glass substrates, at a reduced substrate temperature with a thin Sb layer (7, 12 nm) on top of the Mo contact are investigated. The diffusion profile of Sb is measured with plasma profiling time of flight mass spectrometry. The beneficial effect of Sb on efficiency and grain size is shown in quantum efficiency measurements and with scanning electron microscopy, respectively. Electric spectroscopy is used to explore the possible effects on the defect structure, more in particular on the dominant shallow acceptor. Admittance spectra exhibit a capacitance step to the geometric capacitance plateau at low temperature (5–60 K). Analyzing this capacitance step, we obtained a good estimate of the activation energy of the intrinsic defects that provide the p-type conductivity of the CIGS absorber. The measurements did not show a change in the nature of the dominant acceptor upon Sb treatment.