1. Chemistry
Department, University of Dschang, P.O. Box 96, Dschang, Cameroon
2. Chemistry
Department, Higher Teacher Training College, University of Yaoundé I, P.O.
Box 47, Yaoundé, Cameroon
3. CRM2, CNRS Université de Lorraine, Vandoeuvre-lès-Nancy CEDEX BP
70239, France