The interactions between several peptides with low molecular weight (guest, NH2 Arg Arg Trp Trp H 2; NH2 Arg Trp Arg Trp H 3; NH2 Trp Arg Arg Trp H 4; NH2 Arg Arg Trp Trp Trp Trp H 5; NH2 Trp Trp Arg Arg Trp Trp H 6; ...The interactions between several peptides with low molecular weight (guest, NH2 Arg Arg Trp Trp H 2; NH2 Arg Trp Arg Trp H 3; NH2 Trp Arg Arg Trp H 4; NH2 Arg Arg Trp Trp Trp Trp H 5; NH2 Trp Trp Arg Arg Trp Trp H 6; NH2 Arg Arg Trp Trp Trp Trp Trp Trp H 7; NH2 Arg Arg Trp Trp Trp Trp Trp Trp Trp Trp H 8) and β cyclodextrin dimer (host, 1) bridged with the derivative of (1R, 3R) 1 aminocyclobutane cis 1,3 dicar boxylic acid were investigated by using fluorescence polarization method in buffer aqueous solution (pH 7.4) at 298K. The binding constants of the cyclodextrin dimer 1 to the guests 2 8 were determined. It was shown that there was a cooperative action of the two cavities of a cyclodextrin dimer in the binding of large substrates, and that the structure and properties of amino acid in the peptides played very important roles in the synergic complexation between host and guest.展开更多
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The interactions between several peptides with low molecular weight (guest, NH2 Arg Arg Trp Trp H 2; NH2 Arg Trp Arg Trp H 3; NH2 Trp Arg Arg Trp H 4; NH2 Arg Arg Trp Trp Trp Trp H 5; NH2 Trp Trp Arg Arg Trp Trp H 6; NH2 Arg Arg Trp Trp Trp Trp Trp Trp H 7; NH2 Arg Arg Trp Trp Trp Trp Trp Trp Trp Trp H 8) and β cyclodextrin dimer (host, 1) bridged with the derivative of (1R, 3R) 1 aminocyclobutane cis 1,3 dicar boxylic acid were investigated by using fluorescence polarization method in buffer aqueous solution (pH 7.4) at 298K. The binding constants of the cyclodextrin dimer 1 to the guests 2 8 were determined. It was shown that there was a cooperative action of the two cavities of a cyclodextrin dimer in the binding of large substrates, and that the structure and properties of amino acid in the peptides played very important roles in the synergic complexation between host and guest.
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.
