1. Department of Chemistry, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa
2. Department of Chemistry, University of Kabianga, Kericho 2030, Kenya
3. Department of Chemistry, University of Pretoria, Private Bag X20, Pretoria 0001, South Africa
4. Biosciences, Council for Scientific and Industrial Research, Pretoria 0001, South Africa
5. Science Department, Royal Botanic Gardens, Kew TW9 3DS, UK
6. Department of Pharmaceutical Sciences, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa