[1] Univ Cape Town, Dept Chem, ZA-7700 Cape Town, South Africa
[2] Obafemi Awolowo Univ, Fac Sci, Dept Chem, Ile Ile 220005, Nigeria
[3] Stellenbosch Univ, Dept Chem & Polymer Sci, Private Bag X1, ZA-7602 Stellenbosch, South Africa
[4] Rhodes Univ, Dept Biochem & Microbiol, Biomed Biotechnol Res Unit BioBRU, ZA-6139 Makanda, South Africa