Organization processes of a pyropheophorbide–spermidine conjugate in the presence or absence of DNA

Abstract

The spectroscopic properties of a pyropheophorbide–spermidine conjugate, a new chemical photonuclease, are described in the absence and in the presence of DNA. The strong variations in the absorption, emission and circular dichroism spectra of this pyropheophorbide, induced by changing the solvent ethanol for phosphate buffer, indicate the occurrence of an aggregation process in aqueous solution. Addition of calf thymus (CT) DNA to a phosphate buffer solution of dye promotes biphasic variations on both the UV absorption and fluorescence spectra. These data are accounted for by an increase in the pyropheophorbide organization due to a template effect at low DNA concentrations (Dye/DNA > 1) and a redistribution of the dye on the DNA backbone at high DNA concentrations (Dye/DNA < 1). A model of the reorganization of the pyropheophorbide in the presence of DNA is proposed on the basis of a mathematical framework.