Long-Range Fluorescence Quenching Of Ethidium Ion By Cationic Porphyrins In The Presence Of DNA
Journal Of The American Chemical Society
Binding of ethidium to DNA increases the fluorescence efficiency of the molecular ion by about 1 order of magnitude. Quenching of the fluorescence of such an ethidium.DNA complex by tetrakis(4-N-methylpyridyl)porphine (H2T4), and its nickel(II) and zinc(II) derivatives (NiT4 and ZnT4), was investigated in the present study. Results of absorbance and fluorescence measurements obtained for these systems are consistent with a mechanism for quenching that does not involve appreciable displacement of ethidium from the nucleic acid. Sten-Volmer-type plots are nonlinear and can be fit satisfactorily by an equation of the form[GRAPHICS]in which [Q] is the concentration of the porphyrin quencher and sigma is the minimum number of base pairs between ethidium (E+) and the porphyrin required to permit the excited fluorophore to emit a photon. It can be concluded from these studies that, in the presence of DNA, porphyrins are capable of efficiently quenching the fluorescence of an excited ethidium ion at a distance of 25-30 angstrom.
Robert F. Pasternack; Melissa Caccam , '89; Bartholomew Patrick Keogh , '88; Thomas Alex Stephenson; A. P. Williams; and E. J. Gibbs.
"Long-Range Fluorescence Quenching Of Ethidium Ion By Cationic Porphyrins In The Presence Of DNA".
Journal Of The American Chemical Society.
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