Hypericin (Hyp) is a natural photosensitizing pigment with a possible application in the photodynamic therapy of cancer. Hyp is readily dissolved in dimethylsulfoxide (DMSO) but forms nonsoluble aggregates in an aqueous environment. Fluorescence spectroscopy and diffusion coefficient measurements are used to investigate the self-association of Hyp molecules in DMSO/water mixtures. Fluorescence measurements reveal that Hyp remains in its monomeric form in DMSO/water mixtures containing up to ∼20-30 wt % water. At higher water concentration, Hyp starts to form nonfluorescent aggregates. To determine the size of the aggregates, the diffusion coefficient of Hyp is determined for different DMSO/water mixtures both experimentally and theoretically. Our data indicate that the size of the aggregates increases as more water is added into DMSO. At 50 wt % water content, the effective diffusion coefficient is about 30% smaller than the calculated value for the stacked Hyp tetramer. The results indicate that in an aqueous environment, Hyp presumably produces large molecular weight stacked H-aggregates. We have also confirmed that in an aqueous environment at alkaline pH, molecules of Hyp remain in the monomeric state.

ABSTRACT:In this article, we deal with the 80th birthday of Prof. Jozef Vodrážka, M.V.D., D.Sc., and also with 52-year history of the Department of Pharmacology, since the establishment of the University of Veterinary Medicine in Košice, Slovak Republic, in the academic year 1949/1950. Our goal is to provide the basic information about the history of the Department of Pharmacology. We also describe the activity of its full-time staff as well as some other people (undergraduate and postgraduate home students, and some foreign visiting teachers and scientists) in a summary form. In conclusion we can say that the history of this department and its people has been very rich and highly productive, not only in their scientific and publishing activities but also in the pedagogical and intellectual orientation of the section. We hope that this tendency will remain not only in the nearest but also in more distant future to enhance the reputation of the University of Veterinary Medicine, Košice.

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