Chemical Properties of Expanded Porphyrins and their Application to Analytical Chemistry

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An Expanded Porphyrin, 2,23-diethyl-8,17-bis (2-ethoxycarbonylethyl) -3,7,12,13,18,22,22-hexamethylsapphyrin (H_3sap), was synthesized by condensation of tripyrrane derivative with bipyrrole and highly selective methods for the determination of anions and metal ions were developed.The sapphyrin reacts with fluoride to give out an enhanced fluorescence intensity at 680 nm on excitation at 450 nm in the presence of fluoride ion as small as parts per billion level via the ion-pair complex, [H_5sap F]^+ formation. Since the present method is based on a direct reaction of the fluoride ion with the sappyrin, a 200-fold amount of the aluminum (III) ion and 2000-fold amount of the iron (III) ion over the fluoride ion did not interfere with determination of the fluoride. The method was applied to determination of the fluoride ion in various water samples.The detailed reaction mechanism was studied by using stopped-flow method. The rate constants and activation energies for the formation and dis … More sociation reactions of[H<@D25@>D2sap F]<@D1+@>D1 were found to be k<@D2f@>D2=(1.53 0.03)x10<@D17@>D1 mol<@D1-1@>D1 dm<@D13@>D1 s<@D1-1@>D1(25ﾟC), DELTAH<@D1*@>D1=24.1(]SY.+-.[) 0.3 kJ mol<@D1-1@>D1, DELTAS<@D1*@>D1=-26.6(]SY.+-.[)1.0J mol<@D1-1@>D1 K<@D1-1@>D1, and k<@D2d@>D2=(4.08(]SY.+-.[)0.08)x10<@D15@>D1(25ﾟC), DELTAH<@D1(]SY.Thermod.[)@>D1=4.79(]SY.+-.[)0.10 kJ mol<@D1-1@>D1, DELTAS<@D1(]SY.Thermod.[)@>D1=4.79(]SY.+-.[)0.10 J mol<@D1-1@>D1 K<@D1-1@>D1. The rate constant is 10000 times smaller than that of the protanation of fluoride ion. The results suggest existence of a pre-equilibrium of a deformed sapphyrin structure to accept the fluoride ion. The rate constants for the formation and dissociation of zinc (II) complex were k<@D2f@>D2=(11.8(]SY.+-.[)0.2)x10<@D14@>D1(25ﾟC)mol<@D1-1@>D1 dm<@D13@>D1 s<@D1-1@>D1, DELTAH<@D1(]SY.Thermod.[)@>D1=82.0(]SY.+-.[)0.8 kJ mol<@D1-1@>D1, DELTAS<@D1(]SY.Thermod.[)@>D1=127(]SY.+-.[)3J mol<@D1-1@>D1 K<@D1-1@>D1, and k<@D2b@>D2=7.66(]SY.+-.[)0.71(25ﾟC), DELTAH<@D1(]SY.Thermod.[)@>D1=82.9(]SY.+-.[)6.5kJ mol<@D1-1@>D1, DELTAS<@D1(]SY.Thermod.[)@>D1=126(]SY.+-.[)22 J mol<@D1-1@>D1 K<@D1-1@>D1. The formation rate of zinc (II) complex is 1000 times as reactive as the zinc (II) porphyrin formation rate but is still smaller 100 times than the water dissociation from aqua zinc (II) ion.The fluoride ion-pair complex was extracted into chloroform and the chemical species is[H_4sap F^-]which also shows tfluoresence. Less