1. Technical University of Sofia, Department of Thermal and Nuclear Power Engineering, 8 Kl. Ohridsky Blvd, 1000 Sofia, Bulgaria
2. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria
3. Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 9, 1113, Sofia, Bulgaria