Thermodynamics of the conversion of aqueous xylose to xylulose.

The thermodynamics of the conversion of aqueous xylose to xylulose has been investigated using high-pressure liquid chromatography (HPLC) and microcalorimetry. The reaction was carried out in aqueous phosphate buffer over the pH range 6.8-7.4 using solubilized glucose isomerase with MgSO(4) as a cofactor. The temperature range over which this reaction was investigated was 298.15-342.15 K. A combined analysis of both the HPLC and microcalorimetric data leads to the following results at 298.15 K for the conversion process: DeltaG degrees = 4389 +/- 31 J mol(-1), DeltaH degrees = 16090 +/- 670 J mol(-1), and DeltaC(p) degrees = 40 +/- 23 J mol(-1) K(-1). The temperature dependence of the equilibrium constant for the reaction is expressed as R ln K = -4389/298.15 +16090[(1/298.15)-(1/T)]+40[(298.15/T)-1 + ln(T/298.15)]. Comparisons are made with literature data.

[1]  R. Goldberg,et al.  A scanning microcalorimeter for thermally induced transitions in solution , 1974 .

[2]  E. S. Domalski.  Selected Values of Heats of Combustion and Heats of Formation of Organic Compounds Containing the Elements C, H, N, O, P, and S. , 1972 .

[3]  R. Jasra,et al.  Enthalpies of solution, partial molal heat capacities and apparent molal volumes of sugars and polyols in water , 1982, Journal of Solution Chemistry.

[4]  H. Uedaira,et al.  Activity Coefficients of Aqueous Xylose and Maltose Solutions , 1969 .

[5]  L. Piché,et al.  THE THERMODYNAMICS OF MUTAROTATION OF SOME SUGARS: I. MEASUREMENT OF THE HEAT OF MUTAROTATION BY MICROCALORIMETRY , 1958 .

[6]  L. Hansen,et al.  Thermodynamics of proton dissociation in dilute aqueous solution. V. An entropy titration study of adenosine, pentoses, hexoses, and related compounds. , 1966, Journal of the American Chemical Society.

[7]  E. Clarke,et al.  Evaluation of thermodynamic functions from equilibrium constants , 1966 .

[8]  Robert Schaal.  Nouvellles méthodes cryométriques et potentiométriques de mesure des très faibles constantes d'ionisation , 1955 .

[9]  R. Goldberg,et al.  Thermodynamics of the conversion of aqueous glucose to fructose , 1984 .

[10]  H. Hsiao,et al.  Effects of borate on isomerization and yeast fermentation of high xylulose solution and acid hydrolysate of hemicellulose , 1982 .

[11]  T. Benzinger.  EQUATIONS TO OBTAIN, FOR EQUILIBRIUM REACTIONS, FREE-ENERGY, HEAT, AND ENTROPY CHANGES FROM TWO CALORIMETRIC MEASUREMENTS. , 1956, Proceedings of the National Academy of Sciences of the United States of America.