Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluores...Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.展开更多
A series of affinity media were synthesized by using the oligohistines, His Gly, (His) 3 Gly and (His) 5 Gly as the ligands and the home made monosized, non porous copolymer(CL PGMA) beads containing active epoxide gr...A series of affinity media were synthesized by using the oligohistines, His Gly, (His) 3 Gly and (His) 5 Gly as the ligands and the home made monosized, non porous copolymer(CL PGMA) beads containing active epoxide groups as the support. The affinity chromatographic behavior between IgG and the oligohistines was investigated at pH 3 0, 4 5, 7 0 and 10 0. It showed the specific interaction at pH 4 5. The dissociation constants of IgG and oligohistine media(1H, 3H, 5H) were 3 037×10 -6 , 2 459×10 -6 and 1 905×10 -6 L/mol, respectively. The dissociation constants decreased with increasing the number of histine residue in oligopeptide chains. [WT5HZ]展开更多
基金supported by the National Natural Science Foundation of China(Nos.41173084,41521003,41573130,41630645,41703115 and 41503104)the Beijing Natural Science Foundation(No.8162044)the Canada Research Chair program,Einstein Professor Program of the Chinese Academy of Sciences,and the High Level Foreign Experts Program(#GDT20143200016)
文摘Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.
文摘A series of affinity media were synthesized by using the oligohistines, His Gly, (His) 3 Gly and (His) 5 Gly as the ligands and the home made monosized, non porous copolymer(CL PGMA) beads containing active epoxide groups as the support. The affinity chromatographic behavior between IgG and the oligohistines was investigated at pH 3 0, 4 5, 7 0 and 10 0. It showed the specific interaction at pH 4 5. The dissociation constants of IgG and oligohistine media(1H, 3H, 5H) were 3 037×10 -6 , 2 459×10 -6 and 1 905×10 -6 L/mol, respectively. The dissociation constants decreased with increasing the number of histine residue in oligopeptide chains. [WT5HZ]
