Ka. Meadows et al., SPECTROSCOPIC AND PHOTOPHYSICAL STUDIES OF THE BINDING INTERACTIONS BETWEEN COPPER PHENANTHROLINE COMPLEXES AND RNA, Inorganic chemistry, 32(13), 1993, pp. 2919-2923
The interactions of two Cu(I) phenanthroline complexes, Cu(bcp)2+ and
Cu(dMP)2+, where bcp and dmp denote 2,9-dimethyl-4,7-diphenyl-1,10-phe
nanthroline and 2,9-dimethyl-1,10-phenanthroline, respectively, with s
everal different types of RNA have been investigated by means of spect
roscopic, photophysical, and viscometric methods. Surface association
occurs between Cu(dMP)2+ and RNA, but binding of CU(bcP)2+ with RNA st
rongly perturbs the spectral properties of the metal complex in ways t
hat depend on the nucleotide-to-copper ratio. Thus, at low ratios, an
aggregated form of Cu(bcp)2+ binds to RNA. At higher ratios, the aggre
gates break up, but the Cu(bcP)2+ remains bound to RNA since solvent-i
nduced quenching of the charge-transfer emission from the copper compl
ex continues to be suppressed. Furthermore, a circular dichroism signa
l can be observed from Cu(bcP)2+ in the presence of high levels of pol
y(C).poly(I). An intimate association with the biopolymer must occur,
but viscometric measurements indicate that Cu(bcP)2+ is not intercalat
ed into the RNA. One possibility is that the local RNA structure melts
out to allow internalization of the Cu(bcp)2+ ion into the macromolec
ule. Another possibility is that CU(bcP)2+ may be sandwiched between s
eparate runs of double-helical RNA structure in solution.