水溶性ポルフィリンの酸解離平衡の測定とその分光特性

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タイトル別名
  • Determination of acid-base dissociation constants of porphyrins and their spectroscopic behavior.
  • スイヨウセイ ポルフィリン ノ サン カイリ ヘイコウ ノ ソクテイ ト ソノ

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The acid-base equilibria of four water soluble porphyrins {α, β, γ, δ-tetrakis(4-N-methylpyridil) porphine: TMPyP, α, β, γ, δ-tetrakis(4-N-trimethylaminophenyl) porphine : TTMAPP, α, β, γ, δ-tetraphenylporphine trisulfonic acid : TPPS3, α, β, γ, δ-tetrakis(4-sulfophenyl) porphine : TPPS4} were investigated spectroscopically. They showed remarkable variation in their Q-band spectra (500700 nm) at various pH solutions, and pK values could be determined by an acid-base titration method (Hildebrand plot) at (20±1)°C. The pK values of the methylpyridyl groups or the trimethylamino groups at α, β, γ, δ-positions on the porphyrins were as follows. (TMPyP : pK4=1.17, pK3=2.10, pK2=5.99, pK1=11.27; TTMAPP : pK4=0.97, pK3=3.00, pK2=7.64, pK1=9.45). The pK values of TPPS3 and TPPS4 which have sulfonic groups at the meso-positions are different from that of TMPyP and TTMAPP, and are shifted to the narrow acidic range by effect of the acidic-sulfonic groups. The difference in the number of sulfonic groups gave different pK values between TPPS3 and TPPS4. They were pK4(3.57), pK3(4.88), pK2(5.15) and pK1(8.31) for TPPS3, and pK4(1.16), pK1(5.20) for TPPS4. The fluorescence lifetimes (τf) of five protopic species of the water soluble porphyrins (TMPyP, TTMAPP, TPPS3, TPPS4) showed remarkable variation among them. The lifetime of the species of TMPyP were 6 ns for the di-cationic species (PH42+) and the di-anionic species(P2-). The other three species mono-catonic species (PH3+), neutral species (PH2) and mono-anionic species (PH-) have long fluorescence lifetime which are twice the former. The long fluorescence lifetime (11.113.2 ns, mean : 12 ns) suggests that protoropic resonance in the pyrrol rings was retained.

収録刊行物

  • 分析化学

    分析化学 37 (6), 284-291, 1988

    公益社団法人 日本分析化学会

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