フタレイン系色素とスルホンフタレン系色素の異同について

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Differences in color and molecular structure between phthalein-pigments and sulfonphthalein-pigments were investigated using X-ray crystallography and absorption spectrophotometry of their aqueous solutions. The molecular structure of sulfonefluorescein (H_2^+SF^- ) was determined as a zwitter ion, 2-(3-hydroxonio-6-hydroxy-3H-xanthen-9-yl) benzenesulfonate. The absorption spectra of H_2^+SF^- demonstrated the dissociation profile of a dibasic acid, while those of fluorescein (H_2FL) indicated a tribasic acid and further, at pH>10,SF^<2-> and FL^<2->, while at pH<0,H_2^<+>SF^- and H_3^+FL to be dominant. The spectra of H_2^+SF^- were analyzed to obtain the values of pK_1 and pK_2 together with the spectrum of HSF^- . Similarly, from the spectra of H_3^+FL the values of pK_1,pK_2 and pK_3 together with the spectra of HFL^- and H_2FL were obtained. Further by adding 1/5 of the H_3^+FL spectrum to 2/15 of HFL^- spectrum, an indicated spectrum as that of H_2FL was obtained. From these results, the features of dissociation of H_2SF^- and H_3^+FL were estimated. The molecular structure of phenolsulfonphtalein (H_2PS^-) was determined as a zwitter-ion, α-(4-hydroxonio-2,5-cyclohexadiene-1-ylidene)-α-(4-hydroxy-phenyl)-2-toluenesulfonate. The absorption spectra of H_2PS^- demonstrated that H_2PS^- , HPS^- and PS^<2-> became dominant at pH≪0,pH=4 and pH>11,respectively. On the contrary, phenolphthalein (H_2PP) displayed only one type of absorption spectrum in the visual region, the shape of which was similar to that of PS^<2-> while the molar extinction coefficient was smaller. The spectra were analyzed to obtain the valus of pK_1=9.05 and pK_2=9.5O. The spectra also demonstrated a slow addition reaction of OH^- to PP^<2->= and pK_3= 12 was obtained by measuring the absorbance after equilibration. From these results, the features of dissociation and coloration of H_2^+PS^- and H_2PP were estimated.
公益社団法人日本薬学会の論文
1997-11-01

フタレイン系色素とスルホンフタレン系色素の異同について

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