1. Department of Chemistry, P.M.B.1515, University of Ilorin, Ilorin, Kwara State, Nigeria
2. Department of Chemistry, University of South Africa, South Africa
3. Department of Chemistry and Biochemistry, University of Mississippi, P.O. Box 1848, MS 38677-1448, USA
4. Department of Chemistry, Nelson Mandela University, PO Box 77000, Port Elizabeth 6031, South Africa