1. University of Plovdiv; Faculty of Chemistry, Department of Analytical Chemistry and Computer Chemistry; 24, Tzar Assen Street Plovdiv 4000 Bulgaria
2. Bulgarian Academy of Sciences, Institute of Organic Chemistry; Acad. Georgi Bonchev Street Sofia 1113 Bulgaria
3. Konstantin Preslavski Shumen University; Natural Sciences Faculty, Department of General Chemistry; 115 Universitetska Street 9712 Shumen Bulgaria