1. Chemistry Department, Faculty
of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
2. Chemistry Department, Faculty
of Science, University of Khartoum, P.O. Box
321, Khartoum 11111, Sudan
3. School of Chemistry and Molecular
Sciences, University of Sussex, Brighton BN1 9QJ, United Kingdom