The determination of protonation constants of some amino acids and their esters by potentiometry in different media
Journal of Solution Chemistry, cilt.35, sa.1, ss.5-19, 2006 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 35 Sayı: 1
- Basım Tarihi: 2006
- Doi Numarası: 10.1007/s10953-006-8934-3
- Dergi Adı: Journal of Solution Chemistry
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
- Sayfa Sayıları: ss.5-19
- Anahtar Kelimeler: protonation constants, amino acids, amino acid esters, potentiometric method, ETHANOL-WATER MIXTURES, ORGANIC-SOLVENT MIXTURES, DISSOCIATION-CONSTANTS, IONIZATION-CONSTANTS, AUTOPROTOLYSIS CONSTANTS, SOLVATION, SPECIATION, COMPLEXES, GLYCINE
- Ankara Üniversitesi Adresli: Evet
Özet
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and their methyl and ethyl esters in water and ethanol-water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25°C and the ionic strength of the medium was maintained at 0.10 mol·L -1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition on the protonation constants is discussed. The log 10 K 2 values of esters generally decreased with increasing ethanol content. However, the log 10 K 1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content in contrast those of L-lysine and L-histidine esters. © 2006 Springer Science+Business Media, Inc.