The determination of protonation constants of some amino acids and their esters by potentiometry in different media

Canel E., Gultepe A., Dogan A., Kilic E.

JOURNAL OF SOLUTION CHEMISTRY, cilt.35, sa.1, ss.5-19, 2006 (SCI-Expanded) identifier identifier

  • 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
  • Gazi 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 degrees C and the ionic strength of the medium was maintained at 0.10 mol center dot 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.