SPECTRAL AND ELECTROCHEMICAL-BEHAVIOR OF COPPER(II)-PHENANTHROLINES BOUND TO CALF THYMUS DNA - [(5,6-DIMETHYL-OP)(2)CU](2-DIMETHYL-OP = 5,6-DIMETHYL-1,10-PHENANTHROLINE) INDUCES A CONFORMATIONAL TRANSITION FROM B-DNA TO Z-DNA() (5,6)
S. Mahadevan et M. Palaniandavar, SPECTRAL AND ELECTROCHEMICAL-BEHAVIOR OF COPPER(II)-PHENANTHROLINES BOUND TO CALF THYMUS DNA - [(5,6-DIMETHYL-OP)(2)CU](2-DIMETHYL-OP = 5,6-DIMETHYL-1,10-PHENANTHROLINE) INDUCES A CONFORMATIONAL TRANSITION FROM B-DNA TO Z-DNA() (5,6), Inorganic chemistry, 37(16), 1998, pp. 3927-3934
The interaction of 1:2 copper(II) complexes of 1,10-phenanthroline (OP
) and variously methyl-substituted phenanthrolines with calf thymus DN
A has been investigated by viscometry and spectral and electrochemical
techniques. Viscometry and competitive, ethidium bromide (EthBr) emis
sion studies reveal that substitutions at 4- and 4,7-positions confer
the complex a reduced affinity for DNA via partial intercalative inter
action of the middle ring of OP between the base pairs of DNA, while s
ubstitutions at 5- and 5,6-positions confer a weak affinity toward DNA
. The tetramethyl substitution at 3,4,7,8-positions lead to an interme
diate behavior for the complex. Circular dichroism spectral studies of
the interaction disclose for the first time that, of all the complexe
s, the 5,6-dimethyl-OP complex is a unique and remarkable reagent in t
hat it reversibly binds to DNA and effects the important conversion of
right-handed B DNA to left-handed Z DNA even in the presence of EthBr
, an allosteric effector of the B conformation of DNA. This novel conf
ormational transition is unexpected of the low GC content of natural D
NA. The ratios of the binding constants (K+/K2+) for DNA binding of th
e Cu(I) and Cu(II) forms of the redox active OP complexes rather than
the Cu(II)/Cu(I) redox potentials (0.023 to -0.098 V vs SCE) are good
measures of the substituent dependent DNA cleavage efficiency and rate
. They also reveal that the Cu(I) form of OP and 4-methyl- and 5,6-dim
ethyl-substituted OP complexes displays enhanced affinity to bind but
noncovalently to the minor groove of DNA. Attempts have been made to i
llustrate the cleavage rate and efficiency of nucleolytic reactions in
the light of the relative binding constants of Cu(I) and Cu(II) forms
of the OP complexes.