An investigation of the equilibria between aqueous ribose, ribulose, and arabinose
1985; Elsevier BV; Volume: 22; Issue: 3 Linguagem: Inglês
10.1016/0301-4622(85)80043-0
ISSN1873-4200
AutoresYadu B. Tewari, Robert N. Goldberg,
Tópico(s)Chemical and Physical Properties in Aqueous Solutions
ResumoThe thermodynamics of the equilibria between aqueous ribose, ribulose, and arabinose were investigated using high-pressure liquid chromatography and microcalorimetry. The reactions were carried out in aqueous phosphate buffer over the pH range 6.8–7.4 and over the temperature range 313.15–343.75 K using solubilized glucose isomerase with either Mg(NO3)2 or MgSO4 as cofactors. The equilibrium constants (K) and the standard state Gibbs energy (ΔG°) and enthalpy (ΔH°) changes at 298.15 K for the three equilibria investigated were found to be: ribose(aq) = ribulose(aq) K = 0.317, ΔG° = 2.85 ± 0.14 kJ mol−1, ΔH° = 11.0 ± 1.5 kJ mol−1; li] ribose(aq) = arabinose(aq) K = 4.00, ΔG° = − 3.44 ± 0.30 kJ mol−1, ΔH° = − 9.8 ± 3.0 kJ mol−1; ribulose (aq) = arabinose(aq) K = 12.6, ΔG° = − 6.29 ± 0.34 kJ mol−1, ΔH° = − 20.75 ± 3.4 kJ mol−1. Information on rates of the above reactions was also obtained. The temperature dependencies of the equilibrium constants are conveniently expressed as R ln K = − ΔG° 298.15/298.15 + ΔH°298.15[(1/298.15)-(1/T)] where R is the gas constant (8.31441 J mol−1K−) and T the thermodynamic temperature.
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