pH titration of the fluorescence of N-(1-naphthyl)aminoacetic acid(NAA) was performed in aqueous solution over pH range of 1 5—12 5. Despite no shift in the fluorescence maximum wavelength, the titration curve showed...pH titration of the fluorescence of N-(1-naphthyl)aminoacetic acid(NAA) was performed in aqueous solution over pH range of 1 5—12 5. Despite no shift in the fluorescence maximum wavelength, the titration curve showed an Ω-shaped profile with increasing pH with two inflection points at pH 4 1 and pH 11 5, respectively. These values correspond to the excited-state pK *_a s of carboxylic group and ammonium cation, respectively, which are both higher than those of the corresponding ground-state pK_as of 2 64 and 11 83, of which the former changes more. The substantial weakening of the proton dissociation of carboxylic group in the excited state should be indicative of the decrease in the inductive +I-effect of the ammonium cation at the β-position due to the excited-state intramolecular charge transfer from naphthalene moiety to ammonium. The latter was also confirmed by the slight increase in the exited-state pK *_ a2. The fact that the increase in pK *_ a1 is larger than that in pK *_ a2 suggests that the effect of the intramolecular charge transfer on the involved moiety be weaker than that on a remote moiety in the same species. This could be taken into consideration for designing means of tuning the structures and properties of peptide and protein via photo-excitation. It was identified that the NAA zwitterion(Ⅱ) was the emissive species. The fluorescence quenching at high pH was assumed to be due to the photo-induced intramolecular electron transfer between carboxylate anion and the excited naphthalene moiety. The present case represents an example in which both intramolecular charge transfer and electron transfer occur to shape the pH titration profile.展开更多
文摘以三乙醇胺和氯化亚砜为原料,在N,N-二甲基甲酰胺(DMF)溶剂中经氯代反应合成中间体三(2-氯乙基)胺盐酸盐,然后与过量的氨水在乙醇溶剂中经氨解反应,得N,N-二(2-氨乙基)-1,2-乙二胺.优化实验得出N,N-二(2-氨乙基)-1,2-乙二胺合成反应原料氨水与中间体三(2-氯乙基)胺盐酸盐的最佳摩尔比为30,最佳反应温度为65℃,最优反应时间不低于12 h.
文摘pH titration of the fluorescence of N-(1-naphthyl)aminoacetic acid(NAA) was performed in aqueous solution over pH range of 1 5—12 5. Despite no shift in the fluorescence maximum wavelength, the titration curve showed an Ω-shaped profile with increasing pH with two inflection points at pH 4 1 and pH 11 5, respectively. These values correspond to the excited-state pK *_a s of carboxylic group and ammonium cation, respectively, which are both higher than those of the corresponding ground-state pK_as of 2 64 and 11 83, of which the former changes more. The substantial weakening of the proton dissociation of carboxylic group in the excited state should be indicative of the decrease in the inductive +I-effect of the ammonium cation at the β-position due to the excited-state intramolecular charge transfer from naphthalene moiety to ammonium. The latter was also confirmed by the slight increase in the exited-state pK *_ a2. The fact that the increase in pK *_ a1 is larger than that in pK *_ a2 suggests that the effect of the intramolecular charge transfer on the involved moiety be weaker than that on a remote moiety in the same species. This could be taken into consideration for designing means of tuning the structures and properties of peptide and protein via photo-excitation. It was identified that the NAA zwitterion(Ⅱ) was the emissive species. The fluorescence quenching at high pH was assumed to be due to the photo-induced intramolecular electron transfer between carboxylate anion and the excited naphthalene moiety. The present case represents an example in which both intramolecular charge transfer and electron transfer occur to shape the pH titration profile.
