title: Acid-base characterization of 5-hydroxypyrazine-2-carboxylic acid and the role of ionic equilibria in the optimization of some process conditions for its biocatalytic production.
abstract: This paper describes the use of potentiometric titration to determine the relevant acid-base properties of 5-hydroxypyrazine-2-carboxylic acid (5OH-PYCA), an important intermediate in the production of tuberculostatics. The data obtained were used for calculation of the dissociation constants of 5OH-PYCA. It was found that 5OH-PYCA dissociates in two steps, with the corresponding dissociation constants pK (a1)=3.42 and pK (a2)=7.96, designating 5OH-PYCA as a medium weak acid (1st step). The distribution diagram of dissociated species and the buffer-strength diagram of 5OH-PYCA provide useful information about its behaviour at different pH. The ionic equilibria data obtained can be used for selection of the optimum pH for biotransformation of pyrazine-2-carboxylic acid (PYCA) and for prediction of pH changes during the biotransformation. These data can also be used for selection of the optimum pH for precipitating 5OH-PYCA in downstream processing. All computations have been optimized by mathematical modelling using Solver.
authors.affiliation: Department of Chemistry, University Josip Juraj Strossmayer in Osijek, F. Kuhaca 18, 31000 Osijek, Croatia. milan.sak-bosnar@ptfos.hr
authors.forename: M
authors.initials: M
authors.lastname: Sak-Bosnar
authors.forename: K
authors.initials: K
authors.lastname: Kovar