On the homo- and heteroassociation of hypericin

Abstract

Summary.Hypericin exhibits rather complicated homo-and heteroassociation behavior. Whereas in common polar solvents hypericin dissolves monomolecularly up to concentrations of 10-3 mol/1, the presence of water in these solvents leads to homoassociation. As derived by spectroscopic measurements, these homoassociates exhibit a stacking pattern similar to the one observed for the crystalline material. Tetrahydrofuran seems to be an exception, as it is the only solvent which results in 1,6-dioxo tautomer formation. Heteroassociation of hypericin involves two distinct types of behavior. In the majority of cases, hypericin forms homoassociates which then heteroassociate with the co-solvate to yield stabilized solutions of these homoassociates. Only with human serum albumin a specific heteroassociate is formed. By means of competition experiments it could be established that hypericin is binding to the active site of the IIIA subdomain of the protein.

Determination of enantiomerization barriers of hypericin and pseudohypericin by dynamic high‐performance liquid chromatography on immobilized polysaccharide‐type chiral stationary phases and off‐column racemization experiments

“…Apart from preliminary findings on (minor) enantioselective protein binding of 1 37 (discussed in Ref. 36) and a lack of enantioselectivity in steady-state spectra of 1 in different chiral environments including proteins 29 no data are available whether enantiodiscrimination is relevant for the biological fate and effect profile of this pharmacologically important class of compounds.…”

Solubilization of poorly soluble photosensitizer hypericin by polymeric micelles and polyethylene glycol

“…It means that the quantum yield of the fluorescence of Hyp incorporated in PEG-PE is similar to those for Hyp in LDL or dissolved in various polar organic solvents (e.g. DMSO), where the quantum yield of Hyp fluorescence has been determined to be ~0.2 (Falk and Meyer 1994;Hadjur et al 1996;Kascakova et al 2005).…”

“…Hyp exhibits no fluorescence in aqueous PBS. This fact is well known and is attributed to the formation of non-fluorescent Hyp aggregates in aqueous solutions (Falk and Meyer 1994;Kascakova et al 2005). The fluorescence spectra of monomeric Hyp are represented by the spectra of Hyp dissolved in DMSO and in the complex with LDL (Hyp/LDL = 10:1) (Kascakova et al 2005).…”

“…The study of Hyp distribution in human plasma has shown that Hyp molecules are predominantly associated with low-density lipoproteins (LDL) and only relatively small amounts are bound to high-density lipoproteins (HDL) and proteins (mainly serum albumin) (Chen et al 2001). In the presence of the plasma (lipo)proteins Hyp aggregates can redissociate resulting in fluorescent monomeric and biological active form of this molecule (Falk and Meyer 1994;Lavie et al 1995;Huygens et al 2005;Kascakova et al 2005). Our group has published several articles about the properties of Hyp/LDL complexes (Kascakova et al 2005;Mukherjee et al 2008;Gbur et al 2009;Huntosova et al 2010;Buriankova et al 2011).…”

“…This compound is sparingly soluble in non-polar organic solvents and oil, and in aqueous environment forms insoluble non-fluorescent aggregates (Falk and Meyer 1994;Falk 1999). The formation of aggregates significantly suppresses Hyp photodynamic activity (Falk and Meyer 1994;Kascakova et al 2005;van de Putte et al 2006).…”