ISSN:
1572-8927
Keywords:
Lysine
;
ornithine
;
2,4-diaminobutyric acid
;
2,3-diaminopropionic acid
;
microscopic ionization
;
mixed solvents
;
nuclear magnetic resonance
;
water-dioxane
;
acid-base-chemistry amino acids
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The macroscopic and microscopic acid-base chemistry of a series of α,ω-diaminocarboxylic acids, H2N(CH2)nCH(NH2)COOH [n=4, lysine (LYS);n=3, ornithine (ORN);n=2, 2,4-diaminobutyric acid (DAB);n=1, 2,3-diaminopropionic acid (DAP)], was determined in water and its binary mixtures with dioxane (20.5, 40.7, 60.7, and 80.5 mass % dioxane) using carbon-13 nuclear magnetic resonance spectroscopy. The macroscopic acid dissociation constants for the titration of the two ammonium groups decrease uniformly with increasing dioxane composition. The microscopic constants, however, which characterize the relative concentrations of the two tautomers of singly protonated amino acid (I and II) $$\begin{gathered} H_3 \mathop N\limits^ + (CH_2 )_n CHCOO^ - H_2 N(CH_2 )_n CHCOO^ - \hfill \\ || \hfill \\ NH_2 \mathop N\limits_ + H_3 \hfill \\ III \hfill \\ \end{gathered}$$ reveal that while tautomer I is favored in aqueous solution, tautomer II becomes more important with increasing dioxane composition for LYS and ORN. The relative concentrations of I and II remain unchanged with solvent composition for DAP. These results are explained in terms solute-solvent and solvent-solvent interactions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00716000
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