DNA-binding and physical studies of Pt(4'-NR2-trpy)CN+ systems (trpy = 2,2':6',2''-terpyridine).
This paper focuses on DNA-binding interactions exhibited by Pt(dma-T)CN(+), where dma-T denotes 4'-dimethylamino-2,2':6',2''-terpyridine, and includes complementary studies of the corresponding pyrr-T complex, where pyrr-T denotes 4'-(N-pyrrolidinyl)-2,2':6',2''-terpyridine. The chromophores are useful for understanding the interesting and rather intricate DNA-binding interactions exhibited by these and related systems. One reason is that the terpyridine ligands employed provide intense visible absorption and enhanced photoluminescence signals. Incorporating cyanide as a coligand further aids analysis by suppressing covalent binding. Physical methods utilized include X-ray crystallography for structures of the individual inorganic complexes. Viscometry as well as spectral studies of the absorbance, emission, and circular dichroism (CD) yield information about interactions with a variety of DNA hosts. Although there is no sign of covalent binding under the conditions used, most hosts exhibit two phases of uptake. Under conditions of high loading (low base-pair-to-platinum ratios), the dma-T complex preferentially binds externally and aggregates on the surface of the host, except for the comparatively rigid host [poly(dG-dC)]2. Characteristic signs of the aggregated form include a bisignate CD signal in the charge-transfer region of the spectrum and strongly bathochromically shifted emission. When excess DNA is present, however, the complex shifts to intercalative binding, preferentially next to G[triple bond]C base pairs if available. Once the complex internalizes into DNA it becomes virtually immune to quenching by O2 or solvent, and the emission lifetime extends to 11 micros when [poly(dI-dC)]2 is the host. On the other hand, the host itself becomes a potent quenching agent when G[triple bond]C base pairs are present because of the reducing strength of guanine residues.
Clark
Meaghan L
ML
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
Green
Robert L
RL
Johnson
Olivia E
OE
Fanwick
Phillip E
PE
McMillin
David R
DR
D000042:Absorption; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010165:Palladium / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
D009942:Organometallic Compounds; D011725:Pyridines; D010165:Palladium; D004247:DNA; C023666:pyridine