SUPRAMOLECULAR CHEMISTRY .50. DNA INTERACTIONS WITH PORPHYRINS BEARING AMMONIUM SIDE-CHAINS

Eleven new porphyrins bearing either tertiary amine or ammonium groups with different spacers in the meso position have been synthesized. Fi ve of them were water-soluble enough for DNA binding studies. UV/vis m easurements of some derivatives as a function of pH quantifies the por phyrin core protonation postulated recently by Marzilli et al. with an uptake of two protons and pK values of 6.0 or 6.4, respectively. The porphyrins as well as their Cu(II) or Zn(II) derivatives decrease the viscosity of ds(CT) DNA slightly and increase the melting point of DNA by only up to 1.7 degrees C at DNA base pair/ligand ratios of 40. DNA causes either a red shift (less than or equal to 6 nm) or a blue shif t (greater than or equal to-7 nm) of the Soret bands. These results as well as the observed small hypochromicities show that all new porphyr ins interact with DNA without intercalation. However, their affinity i n comparison with other macrocycles bearing four positive charges is, based on ethidium bromide assays with C-50 values of 7 x 10(-8) to 2 x 10(-7) M relatively high and points to groove binding contributions b y other than electrostatic forces.