title: Accessibility and external versus intercalative binding to DNA as assessed by oxygen-induced quenching of the palladium(II)-containing cationic porphyrins Pd(T4) and Pd(tD4).
abstract: Studies reveal that it is possible to design a palladium(II)-containing porphyrin to bind exclusively by intercalation to double-stranded DNA while simultaneously enhancing the ability to sensitize the formation of singlet oxygen. The comparisons revolve around the cations [5,10,15,20-tetra(N-methylpyridinium-4-yl)porphyrin]palladium(II), or Pd(T4), and [5,15-di(N-methylpyridinium-4-yl)porphyrin]palladium(II), or Pd(tD4), in conjunction with A═T and G≡C rich DNA binding sequences. Methods employed include X-ray crystallography of the ligands as well as absorbance, circular dichroism, and emission spectroscopies of the adducts and the emission from singlet oxygen in solution. In the case of the bulky Pd(T4) system, external binding is almost as effective as intercalation in slowing the rate of oxygen-induced quenching of the porphyrin's triplet excited state. The fractional efficiency of quenching by oxygen nevertheless approaches 1 for intercalated forms of Pd(tD4), because of intrinsically long triplet lifetimes. The intensity of the sensitized, steady-state emission signal varies with the system and depends on many factors, but the Pd(tD4) system is impressive. Intercalated forms of Pd(tD4) produce higher sensitized emission yields than Pd(T4) is capable of in the absence of DNA.
authors.affiliation: Department of Chemistry, Purdue University , 560 Oval Drive, West Lafayette, Indiana 47907, United States.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Bork
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Gianopoulos
authors.forename: Hanyu
authors.initials: H
authors.lastname: Zhang
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Fanwick
authors.forename: Jong Hyun
authors.initials: JH
authors.lastname: Choi
authors.forename: David R
authors.initials: DR
authors.lastname: McMillin
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D007364:Intercalating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010165:Palladium; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D007364:Intercalating Agents; D011166:Porphyrins; D026082:Singlet Oxygen; D010165:Palladium; D004247:DNA; D010100:Oxygen