Abstract

The ability of Rh(III) tetrakis-N-methylpyridyl porphyrin, Rh^III(TMPyP)⁵⁺, to interact with and cleave DNA was, investigated by UV-visible, luminescence, circular dichroism (CD), electron spin resonance (ESR) and gel electrophoresis methods in the presence or absence of ascorbic acid. UV-absorption data showed that Rh^III(TMPyP)⁵⁺ is capable of interacting with DNA, as indicated by the appearance of a red shift and hypochromicity of the Soret band. The CD data revealed that Rh^III(TMPyP)⁵⁺ was capable of binding to DNA via an external binding mode. The Rh^III(TMPyP)⁵⁺ showed fluorescence and phosphorescence at room temperature. The phosphorescence increased in the presence of DNA and this could be attributed to the shielding of the metal-porphyrin by DNA. Gel electrophoresis studies revealed that Rh^III(TMPyP)⁵⁺ was only able to cleave DNA in the presence of the reducing agent  ascorbic acid. ESR data indicated the formation of Rh^II(TMPyP)⁵⁺ by reduction of Rh^III(TMPyP)⁵⁺ with ascorbic acid. The involvement of Rh(III)/Rh(II) species in catalytic DNA cleavage and a possible DNA cleavage mechanism is discussed.

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