Biopolymers and cell. 2001; 17 (5): 363 - 373

H NMR structural and thermodynamical analysis of complexation of propidium iodide with deoxytetranucleotide 5'-d(TpGpCpA) in aqueous solution

D. A. Veselkov, P. O. Bolotin, V. O. Sigaev, L. N. Djimant, D. B. Davies, A. N. Veselkov

The interaction of phenantridine dye propidium iodide with self-complementary deoxytetraribonucleoside triphosphate 5'-d(TpGp-CpA) in aqueous salt solu.tj.on has been studied by one- and two-dimensional 500 MHz H NMR spectroscopy. The concen¬tration and temperature dependences of proton chemical shifts of the interacting molecules have been measured. Different schemes of complexation of propidium with the tetranucleotide have been analysed and the equilibrium constants, free energy AG, enthalpies A//, entropies AS of different reactions leading to the formation of 1:1, 1:2, 2:1, 2:2 complexes have been determined. The specific features of the dynamic equilibrium of different complexes as a function of the drug-tetranucleotide ratio and temperature have been examined. It is concluded that propidium intercalates preferentially to pyrimidine-purine d(T-G)- and d(C-A)-sites of the tetranuc¬leotide sequence. The most favourable structures of 1:2 and 2:2 propidium-tetranucleotide complexes have been constructed using the calculated values of induced chemical shift of dye protons and 2D-NOE spectra. A comparative analysis of the complexation of phenantridine dyes, propidium iodide, ethidium bromide, and acridine dye proflavine with deoxytetranucleotide d(TGCA) under the same experimental conditions, has been made.