Synthesis, characterization, DNA binding and DNA photocleavage of two new dipyrromethenes and their ruthenium (II) and N-methylated analogs

Date of Award


Degree Name

M.S. in Chemistry


Department of Chemistry


Advisor: Shawn Swavey


Two new bridging ligands have been synthesized by solvent-free reactions of substituted benzaldehydes, 3-methoxy-4-hydroxy benzaldehyde and flurobenzaldehyde, with isoquino[5,6-c]pyrrole resulting in two new organic chromophores with two peripheral nitrogen coordination sites capable of metal interaction. The ligands have been characterized by 1HNMR, mass spectroscopy, elemental analysis, UV/Vis spectroscopy, and cyclic voltammetry. Both ligands display low energy π-π* transitions above 500 nm with modest molar absorptivities. To make chromophores water soluble, N-methylated dipyrromethenes were synthesized and show bathochromic shifts compared to the neutral dipyrromethenes, which suggests that localized positive charge on the peripheral nitrogen of N-methylated compounds stabilize the π* orbitals. When coordinated to two ruthenium (II) bis(bipyridyl) groups, the new bimetallic complexes generated give an overall 2+ charge. The electronic transition of the bimetallic ruthenium (II) complexes display typical bipyridyl intraligand π-π* transitions at 295 nm and metal-to-ligand charge-transfer transitions above 500 nm with molar absorptivities greater than 40000 M-1cm-1. Oxidation of the ruthenium (II) metal centers to ruthenium (III) occurs at potentials above 0.80 V versus the Ag/ AgCl reference electrode. Binding studies with calf thymus DNA (ctDNA) show intrinsic binding constants as high as 105 M-1 (106 M-1 for Ru2-IsoQvan, complex III) indicating very strong interactions of N-methylated and ruthenium compounds with DNA. In this study, the N-methylated and ruthenium compounds are water-soluble and show the ability to photonick plasmid DNA when irradiated with low-energy light above 550 nm for brief periods of time. In addition, one of the complexes, Ru2-IsoQvan (complex III), shows the ability to initiate double-strand breaks of plasmid DNA by gel electrophoresis. Studies indicate that the photoinduced mechanism of Ru2-IsoQvan (complex III) is quite complex and both type I and type II pathways are involved resulting in both the formation of singlet oxygen and radicals. In addition, singlet oxygen is responsible for DNA double-strand breaking.


Ligands (Biochemistry) Synthesis, Ligands (Biochemistry) Properties, Photosensitizing compounds, Chemistry

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