title: Theory of the milieu dependent isomerisation dynamics of reducing sugars applied to d-erythrose.
abstract: Quantitative (1)H selective saturation transfer NMR spectroscopy ((1)H SST qNMR) was used to fully describe the milieu dependent dynamics of the isomeric system of d-erythrose. Thermodynamic activation parameters are calculated for acidic as well as for basic catalysis combining McConnell's modified Bloch equations for the chemical exchange solved for the constraint of saturating the non-hydrated acyclic isomer, the Eyring equation and Hudson's equation for pH dependent catalysis. A detailed mathematical examination describing the milieu dependent dynamics of sugar isomerisation is provided. Thermodynamic data show evidence that photo-catalysed sugar isomerisation as well as degradation has to be considered. Approximations describing the pH and temperature dependence of thermodynamic activation parameters are derived that indicate the possibility of photo-affecting equilibrium constants. Moreover, the results show that isomerisation dynamics are closely related to degradation kinetics and that sugars' reactivities are altered by the concentration of acyclic carbonyl isomer and the sum of its ring closing rate constants. Additionally, it is concluded that sugar solutions show a limited self-stabilising behaviour.
authors.affiliation: Department of Food Chemistry and Food Analysis, Berlin Institute of Technology, Gustav-Meyer-Allee 25, TIB 4/3-1, D-13355 Berlin, Germany. Electronic address: martin.kaufmann@tu-berlin.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Kaufmann
authors.affiliation: Department of Chemistry, Humboldt University of Berlin, Brook-Taylor-Straße 2, D-12489 Berlin, Germany.
authors.forename: Clemens
authors.initials: C
authors.lastname: Mügge
authors.affiliation: Department of Food Chemistry and Food Analysis, Berlin Institute of Technology, Gustav-Meyer-Allee 25, TIB 4/3-1, D-13355 Berlin, Germany.
authors.forename: Lothar W
authors.initials: LW
authors.lastname: Kroh
mesh_terms: D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D066244:Proton Magnetic Resonance Spectroscopy; D013237:Stereoisomerism; D013780:Tetroses / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D013780:Tetroses; C073321:erythrose
keywords: Dynamic nuclear magnetic resonance; Isomeric composition; Isomerisation; Milieu dependence; Self-stabilising behaviour; d-Erythrose