title: On the diffusion of hypericin in dimethylsulfoxide/water mixtures-the effect of aggregation.
abstract: 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.
authors.affiliation: Department of Biophysics, P. J. Šafárik University, Košice, Slovakia.
authors.forename: Gregor
authors.initials: G
authors.lastname: Bánó
authors.forename: Jana
authors.initials: J
authors.lastname: Staničová
authors.forename: Daniel
authors.initials: D
authors.lastname: Jancura
authors.forename: Jozef
authors.initials: J
authors.lastname: Marek
authors.forename: Mikuláš
authors.initials: M
authors.lastname: Bánó
authors.forename: Jozef
authors.initials: J
authors.lastname: Uličný
authors.forename: Alena
authors.initials: A
authors.lastname: Strejčková
authors.forename: Pavol
authors.initials: P
authors.lastname: Miškovský
mesh_terms: D000042:Absorption; D000873:Anthracenes; D004058:Diffusion; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010569:Perylene / Q000031:analogs & derivatives* / Q000737:chemistry; D017319:Photosensitizing Agents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: D000873:Anthracenes; D017319:Photosensitizing Agents; D014867:Water; D010569:Perylene; C004965:hypericin; D004121:Dimethyl Sulfoxide