Binding of the Mn(III) complex of meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin to DNA.: Effect of ionic strength

Interactions of the water-soluble Mn(III) complex of meso-tetrakis( 4-N-methyl-pyridiniumyl)porphyrin (Mn(III) TMPyP) with DNA in aqueous solutions at low (0.01 M) and high (0.2 M) ionic strengths have been studied by optical absorption, resonance light scattering (RLS) and H-1 NMR spectroscopies. Optical absorption and RLS measurements have demonstrated that in DNA solutions at low ionic strength the Mn(III)TMPyP forms aggregates, which are decomposed at DNA excess. At high ionic strength the aggregation was not observed. We explain this effect by assuming that, upon increase in ionic strength, Mn(III)TMPyP dislocates from the DNA sites, which produces better conditions for the porphyrin aggregation, to sites where the aggregation is hindered. The H-1 NMR data demonstrated that the aggregation observed at low ionic strength reduces the paramagnetism of Mn(III)TMPyP. This phenomenon was not observed at the high ionic strength in the absence of aggregation. (C) 1999 Elsevier Science Inc. All rights reserved.