The binding of nucleic acids by water-soluble cobalt(II) tetrakis-
N-
methylpyridyl porphyrin, (TMPyP)Co, and itshighly electron-deficient derivative cobalt(II) tetrakis-
N-
methyl pyridyl-
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-octabro
moporphyrin, (Br
8TMPyP)Co,was investigated by UV-visible absorption, circular dichrois
m (CD), and electroche
mical and gel electrophoresis
methods. The changes of the absorption spectra during the titration of these co
mplexes with polynucleotidesrevealed a shift in the absorption
maxi
ma and a hypochro
micity of the porphyrin Soret bands. The intrinsic bindingconstants were found to be in the range of 10
5-10
6 M
-1. These values were higher for the
more electron-deficient(Br
8TMPyP)Co. Induced CD bands were noticed in the Soret region of the co
mplexes due to the interaction ofthese co
mplexes with different polynucleotides, and an analysis of the CD spectra supported a
mainly external
mode of binding. Electroche
mical studies revealed the cleavage of polynucleotides by (TMPyP)Co and(Br
8TMPyP)Co in the presence of oxygen preferentially at the A-T base pair region. Gel electrophoresisexperi
ments further supported the cleavage of nucleic acids. The results indicate that the
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-pyrrole bro
minatedporphyrin, (Br
8TMPyP)Co, binds strongly and cleaves nucleic acids efficiently as co
mpared with (TMPyP)Co.This electrolytic procedure offers a unique tool in biotechnology for cleaving double-stranded DNA with specificityat the A-T regions.