[1] Bulgarian Acad Sci, Ctr Phytochem, Inst Organ Chem, Acad G Bontchev Str Bl 9, Sofia 1113, Bulgaria
[2] Sci Res Ctr Med Biophys SRCMB, Sofia 1111, Bulgaria
[3] Univ Forestry, Fac Vet Med, 10 Kl Ohridski Blvd, Sofia 1756, Bulgaria
[4] EVODROP AG, CH-8306 Bruttisellen, Switzerland
[5] Sofia Univ, Fac Phys, St Kliment Ohridski, Sofia 1000, Bulgaria
[6] Bulgarian Acad Sci, Georgi Nadjakov Inst Solid State Phys, 72 Tzarigradsko Chaussee Blvd, Sofia 1784, Bulgaria