Abstract
AbstractXanthene dyes, such as fluorescein and rhodamine, have played crucial rules in biological sciences especially covalent attachment of these organic compounds to biomolecules. 3‐O‐methylfluorescein and 3,6‐O‐dimethylfluorescein were synthesized and purified using a facile procedure. 3,6‐O‐dimethylfluorescein, which lacks fluorescence, was treated with sodium hydroxide and sulfuric acid solutions, giving rise to yellow and green fluorescent compounds, respectively. In both basic and acidic conditions, donor‐acceptor structures were formed. The reaction of 3,6‐O‐dimethylfluorescein with acids, in a reversible manner, emitted green fluorescence, whereas its reaction with hydroxide ion, irreversibly shifted the fluorescence to the yellow region. Using MS spectrometry, the product identity was determined as a xanthylium ion derivative. Stokes shift and quantum yield for xanthylium ion were measured. Various nucleophiles were examined for studying the mechanism of the xanthylium ion in aqueous solutions; the results confirmed that hydroxide ion was mediatory for the emission of the fluorescence. In addition, 3‐O‐methyl‐5(6)‐carboxyfluorescein and 3,6‐O‐dimethyl‐5(6)‐carboxyfluorescein were synthesized that can potentially be used in bioorthogonal reactions for labeling proteins. The synthesized products were used in covalent attachment to bovine serum albumin (BSA) and their unique fluorescences were detected.
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