Glucose thermodynamic equilibrium

The two main fields of application in the CFF group in Lyngby are saccharides and coordination compounds. Here we shall mention only the saccharide work. The first attempts to calculate saccharide equilibrium structures were made by use of two PEFs developed by trial-and-error, PEF300 (7-8 without and PEF400 (9-10) with charges. In spite of this, good results were obtained, both for structures of glucose and for the thermodynamic equilibrium between the anomers. 

The input of four additional high-phosphoryl-transfer-potential molecules in gluconeogenesis changes the equilibrium constant by a factor of 10, which makes the conversion of pyruvate into glucose thermodynamically feasible. Without this energetic input, gluconeogenesis would not take place. 

In the case of two flavoenzyme oxidase systems (glucose oxidase (18) and thiamine oxidase s where both oxidation-reduction potential and semiquinone quantitation values are available, semiquinone formation is viewed to be kinetically rather than thermodynamically stabilized. The respective one-electron redox couples (PFl/PFl- and PFI7PFIH2) are similar in value (from essential equality to a 50 mV differential) which would predict only very low levels of semiquinone (32% when both couples are identical) at equilibrium. However, near quantitative yields (90%) of semiquinone are observed either by photochemical reduction or by titration with dithionite which demonstrates a kinetic barrier for the reduction of the semiquinone to the hydroquinone form. The addition of a low potential one-electron oxidoreductant such as methyl viologen generally acts to circumvent this kinetic barrier and facilitate the rapid reduction of the semiquinone to the hydroquinone form. 

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