1H-Nuclear magnetic resonance study on imidazole–imidazole interaction in L-histidyl-L-histidine and D-histidyl-L-histidine: Analysis including microscopic dissociation series
✍ Scribed by Masaru Tanokura
- Book ID
- 102763622
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1983
- Tongue
- English
- Weight
- 662 KB
- Volume
- 22
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The 'H-nmr titration curves of chemical shifts versus pH were observed for the protons of D,L-histidyl-D,L-histidine as representative of cases with two or more ionizable groups with similar pK, values. The titration curves of L-histidyl-L-histidine and D-histidyl-L-histidine were individually analyzed according to two mathematical models: one of a macroscopic dissociation series and one of a microscopic dissociation series. Most-probable values and standard deviations were obtained for pK, values and intrinsic chemical shifts. An analysis including the microscopic dissociation series yielded an electrostatic interaction between two imidazole rings of about 0.3 pH units for L-histidyl-L-histidine and about 0.7 pH units for D-histidyl-L-histidine. The difference of the magnitude of imidazole-imidazole interactions between L-histidyl-L-histidine and D-histidyl-L-histidine was interpreted in terms of the spatial arrangement of two imidazole rings in each molecule based on the solution conformation estimated from Gd(II1)-induced relaxation enhancements.