Abstract
AbstractThionine (7‐amino‐3‐imino‐3‐H‐phenothiazine) undergoes reversible photobleaching when exposed to visible light in the presence of ethylenediaminetetraacetic acid (EDTA) with the associated development of an electromotive force (emf). This photocreation between EDTA and thionine is inhibited in the presence of excess Mg+ +. Polyanions like DNA, RNA and polystyrenesulfonate also protect the dye from the EDTA induced photoreduction; this protective power of the polyanions depends on their nature and increases with their concentration. DNA, thought a weak chromotrope to form a metachromatic compound with thionine, protects the dye from photobleaching efficiently, presumbly due to the intercalation of the dye cations between base pairs of DNA; denatured DNA is relatively poorer in its ability to protect the dye and resembles RNA and polystyrenesulfonate in this respect. The results indicate that EDTA and thionine form a transient complex or are at least associated before electron transfer from EDTA to thionine in the excited‐triplet state takes place.
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