Patty K.-L. Fu

Photoinduced DNA Cleavage and Cellular Damage in Human Dermal Fibroblasts by 2,3-Diaminophenazine {

Aromatic amines, such as o‐phenylenediamine (OPD), have been used extensively in commercial hair dyes and in the synthesis of agricultural pesticides. Air oxidation of OPD results in the formation of 2,3‐diaminophenazine (DAP). Although the mutagenic toxicity of DAP has been shown in both prokaryotic and eukaryotic systems, its phototoxicity remains largely unexplored. This study focuses on the pH‐dependent photophysical properties of DAP and demonstrates its ability to photoinduce DNA damage to pUC19 plasmid in vitro. The photocytotoxicity of DAP toward human skin fibroblasts was also measured. DAP exhibits weak intercalative binding to double‐stranded DNA with a binding constant Kb= 3.5 × 103M−1. Furthermore, upon irradiation with visible light, DAP is able to nick plasmid DNA in the presence of oxygen. The concentration of DAP that resulted in 50% cell death was 172 ± 9 μM in the dark and 13 ± 1 μM after irradiation of the DAP‐treated cell cultures with visible light (400–700 nm, 30 min, 5 J/cm2). The 13‐fold increase in toxicity upon exposure to visible light shows the need for further study of the photocytotoxicity of contaminants such as DAP.

Excited State Properties of Rh2(O2CCH3)4: Solution Photochemistry and Photoinitiated DNA Cleavage

Abstract The photophysical properties of Rh2(O2CCH3)4(L)2 (L = CH3OH, THF = tetra-hydrofuran, PPh3 = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. All the complexes exhibit a long-lived transient absorption signal (τ = 3.5–5.0 μs) assigned as an electronic excited state of each molecule. An optical transition at −760 nm is observed in the spectra of the transients, whose position is relatively independent of axial ligand. No emission from the Rh2(O2CCH3)4(L)2 (L = CH3OH, THF, PPh3, py) systems was observed at room temperature or at 77 K, but energy transfer from excited Rh2(O2CCH3)4(PPh3)2 to tetracene and perylene takes place to form the 3ππ* excited state of each acceptor. Electron transfer from *Rh2(O2CCH3)4(PPh3)2 to dimethyl viologen (MV2+) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (kq) of 8.0 × 106 M−1s−1 and 1.2 × 106 M−1s−1 in methanol, respectively. A kq value of 2 × 108 M−1s−1 was measured for the quenching of the excited state of Rh2(O2CCH3)4(PPh3)2 by O2 in methanol. The results of the energy and electron transfer experiments are consistent with the production of an excited state of Rh2(O2CCH3)4(PPh3)2 with energy, E00, between 1.34 eV and 1.77 eV. The excited state of Rh2(O2CCH3)4 is not able to undergo hydrogen abstraction chemistry. However, the photoproduced one-electron oxidized complex, Rh2(O2CCH3)4 +, is able to convert isopropanol to acetone and to efficiently cleave DNA with λirr≥ 610 nm.

Transcription inhibition by Rh(phi)2(phen)3

Rh(phi)2(phen)3+ (phi = 9,10-phenanthrenequinone diimine, phen = 1,10-phenanthroline) increases the melting temperature (ΔTm) of a 15-mer duplex DNA by 21 °C and it is able to inhibit transcription in vitro; the concentration ratio of Rh(phi)2(phen)3+ relative to DNA bases of the template required to inhibit the RNA transcribed by 50%, Rinh50, was found to be 0.13; in contrast, Rh(phen)2(phi)3+, which also possesses the intercalating phi ligand, exhibits only a +7 °C shift in Tm and Rinh50 = 4.5; Rh(phen)33+, RhCl3, and ethidium bromide result in negligible or small ΔTm and exhibit Rinh50 values that range from 4.8 to 12.5; these results suggest that the intercalation of the phi ligand between the DNA bases and electrostatic binding are not the only means of duplex stabilization by these complexes.