STUDIES ON THE INTERACTION BETWEEN NUCLEI C-ACIDS AND CATIONIC PORPHYRINS .2.

The interaction of a tetracationic porphyrin is[4[(3-trimethylaminopro pyl)oxy]-phenyl]porphine, TTHETAOPP, and Calf Thymus DNA can lead to t he formation of a DNA-bound protonated porphyrin species. Protonation of the bound TTHETAOPP is promoted both by lower pH and larger DNA exc ess. This species can be formed even at pH 7 under optimal conditions. At pH 6, in large nucleic acid excess, this protonated species is dom inant and exhibits a single positive CD signal. The formation of the g reen colored protonated species is unfavored in solution at low DNA ex cess both at pH 7 and pH 6; the CD shows exciton curves. The presence of PIPES (pH 7) favors porphyrin stacking and prevents porphyrin proto nation.