Self-association of hypericin analyzed by light absorption and fluorescence spectroscopy and molecular dynamics simulations

Self-association of hypericin was investigated with absorption and fluorescence spectroscopy methods. Constants of hypericin association in a 50% aqueous solution of DMSO were determined in the function of temperature, and absorption spectra of the monomer and molecules participating in the complex were examined. Changes in enthalpy ΔHθ and entropy ΔSθ in the process of hypericin association accounted for −46 kJ mol−1 and −55 J mol−1 K−1, respectively. Molecular dynamics simulations methods were applied to determine conformations of the hypericin complex, and ‘head-to-head’ and ‘head-to-tail’ models of interaction were proposed. The ‘head-to-head’ conformation turned out to be the most stable one.