Zusammenfassung
From the data of vapor pressure osmometry the activity of water, osmotic coeffs., and the values of activity coeffs. of two derivs. of histidine: N-Boc-L-histidine (Boc-His-OH, m = 0.005-0.14 mol/kg-1) and N-Boc-L-histidine-Me ether (Boc-His-OMe, m = 0.005-0.05 mol/kg-1) are obtained in aq. solns. at 310.15 K. From the comparison of water activity and osmotic coeff. values it follows that ...
Zusammenfassung
From the data of vapor pressure osmometry the activity of water, osmotic coeffs., and the values of activity coeffs. of two derivs. of histidine: N-Boc-L-histidine (Boc-His-OH, m = 0.005-0.14 mol/kg-1) and N-Boc-L-histidine-Me ether (Boc-His-OMe, m = 0.005-0.05 mol/kg-1) are obtained in aq. solns. at 310.15 K. From the comparison of water activity and osmotic coeff. values it follows that Boc-His-OMe shows a more pronounced deviation from ideality than Boc-His-OH. Both components exhibit a stronger non-ideality than histidine and a weaker one than His/HCl. By means of potentiometric titrn. the acid-base properties of Boc-His-OMe are investigated and the ionization const. at 298.15 K is detd. The pK value related to the acid-base equil. of the nitrogen atom in the imido group of the imidazole ring is higher (6.47) than the corresponding value of histidine (6.00).
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