An anion induced multisignaling probe for Hg2+ and its application for fish kidney and liver tissue imaging studies

Abstract

3′,6′-Bis(diethylamino)-2-(pyridin-2-ylmethyl)spiro[isoindoline-1,9′-xanthen]-3-one (L) was synthesized for the selective fluorescence and colorimetric recognition of Hg²⁺ at pH 6.0. In addition, L was useful for imaging Hg²⁺ in fish kidney and liver tissues using a fluorescence microscope. Spirolactam ring opening of L for Hg²⁺ recognition is strongly influenced by the nature of the mercury salt and found to be NO₃⁻-induced. Other mercury salts such as HgCl₂, Hg(CH₃COO)₂ and Hg(ClO₄)₂ failed to induce fluorescence and colorimetric response of L under the same experimental conditions. For instance, the former salt does not exhibit spirolactam ring opening but forms a new ionic compound (H₃L)₂[Hg₆Cl₁₈]·2H₂O (1), whose structure has been elucidated by single crystal X-ray diffraction. This might be explained by (1) the higher covalent nature of Hg²⁺ and, hence, the lower acidity of the metal center and its inability to induce the ring opening reaction, and (2) the bulky anion, in the case of Hg(ClO₄)₂, which is also ionic, faces steric hindrance to accommodate within the N(Et)₂ group upon spirolactam ring opening.