新たな金属蛍光試薬(3-Carboxy-2-naphthylamine-N, N-diacetic Acid)の合成とその応用

Abstract

A new metallofluorescent reagent (3-carboxy-2-naphthylamine-N, N-diacetic acid (CNDA)) was synthesized. Its possible application was discussed. CNDA was stable in 1% NaHCO3 solution. The fluorescence intensity of CNDA increased by the addition of Al, La (III) and Zn at pH 3-5 and Ca and Mg at pH 10. The acid dissociation constants (pKa) of CNDA were determined by the potentiometric method. The dissociation constants of carboxylic protons of CNDA were 2.44 for pKa1 and 3.23 for pKa2, and the pKa3 of ammonium proton was 7.67. The stability constants of CNDA Ca, Mg and Zn chelate were determined potentiometrically in accordance with the Bjerrum's method at 25± 0.2°C. The stability constants of CNDA Al and La (III) chelate were determined by spectrophotometric method at 25±0.5°C. The constitution of the CNDA chelate with each metal ion was 1 : 1, and the logarithmic stability constants of Al, Ca, La (III), Mg and Zn chelate were 11.83, 5.16, 8.25, 3.24 and 8.26, respectively. The relative quantum yields of CNDA were 0.04-0.05 at pH 5.0 or bellow and 0.09-0.10 at pH 7.0 or more. The relative quantum yields of the fluorescence of CNDA chelate were 0.06 (pH 3.0), 0.09 (pH 4.0) and 0.11 (pH 4.5) for Al, 0.08 (pH 5.0) for La (III), 0.10 (pH 4.5) for Zn, 0.18 (pH 7.0) and 0.27 (pH 10) for Ca, and 0.14 (pH 7.0) for Mg. Since CNDA can react with hard acid, such as Al, La (III) and Ca, CNDA should be a useful reagent for fluorophotometry and a metallofluorescent indicator for chelatometric titration. Using CNDA as a metallofluorescent indicator, the fluorophotometric titration of fluoride in p-fluorobenzoic acid and dexamethasone with Al by the oxygen flask method was performed. In titration, the recoveries were 99.3% or more, and the standard deviation were within 0.23%.