1. Molecular Sciences Institute; School of Chemistry; University of the Witwatersrand; P/Bag X3, Wits 2050 Johannesburg South Africa
2. Institute of Organic Chemistry; School of Chemistry; Johannes Gutenberg University; Duesbergweg 10-14 55128 Mainz Germany
3. Chemistry Department; School of Chemistry; University of Dar es Salaam; P.O. Box 35061 Dar es Salaam Tanzania