Photochemistry of Carboranylchlorin and its Complexes with DNA

The interaction of water-soluble fluorine-containing tetracarboranylchlorin (BFChl) with DNA was studied by absorption spectroscopy, fluorescence and flash photolysis techniques. The association constants of the BFChl –DNA complex were obtained: 4.2 × 104 M−1 (absorption spectroscopy data) and 4.8 × 104 M−1 (fluorescence spectroscopy data). The spectral and kinetic characteristics of BFChl excited singlet and triplet states in the presence of DNA were determined. The interaction of BFChl with DNA leads to the formation of a complex on the DNA surface by the sorption mechanism. The quenching rate constant for the BFChl triplet state by oxygen in aqueous solution corresponds to the diffusion constant (kq = 2.0 × 109 M−1 s−1). However, in presence of the DNA the quenching rate constant for the BFChl triplet state by oxygen decreases twofold (kqDNA = 1.2 × 109 M−1 s−1), which suggests the existence of dye’s weak steric shielding by the DNA molecule. The obtained data allow us to speak about the external binding of the BFChl in the major groove region of the DNA molecule.