Publisher Summary This chapter presents the reversible hydration of carbonyl compounds. The formation of stable solid hydrates is well known for aldehydes and ketones containing several electronegative substituents and for some di- and triketones. The chapter discusses the chemical and biological reactivity of carbonyl compounds in aqueous solution, and they have proved kinetically very convenient for studying problems of homogeneous catalysis. The hydration equilibrium constants are briefly described. Later, the experimental methods and results relevant to acidity of carbonyl hydrates are discussed. The kinetics of hydration and dehydration reactions is also presented. Hydration and dehydration reactions have proved particularly convenient for studying catalysis by acids and bases over a wide range of structures and catalytic power. The absolute rate constants are relatively low even with very strong acids or bases, and diffusion-controlled rates are not approached for either the forward or reverse reactions.

The Reversible Hydration of Carbonyl Compounds

The utilization of glycerol by Candida utilis has been studied It has been found that this yeast has a permeability for glycerol and other three carbon compounds much greater than that of baker's yeast This permeability allows the entrance of glycerol in Candida cells rapidly enough to permit its efficient utilization even at low concentrations The inducibility of glycerol kinase has been established An increase in the concentration of the mitochondrial L-α-glycerophosphate oxidase when the yeast is grown on glycerol has also been observed

A model is presented for the substrate specificity pattern of glycerol kinase of C mycoderma It postulates the involvement of three hydroxyl groups in the spatial distribution corresponding to the formation of L-α-glycerophosphate from glycerol This requirement can be met by aldo-and ketotrioses in their respective hydrated forms

The pathway of glycerol formation in S cerevisiae has also been studied Evidence is shown of the existence of a NADH dependent enzymatic activity reducing triose phosphate to α-glycerophosphate which can roughly account for the glycerol production A low ionic strength seems to be required for the activity of this enzyme The α-glycerophosphatase is specific for the L from, the efficiency of α-glycerophosphatase on D-α-glycerophosphate being 1/30 of that on L-α-glycerophosphate The concentration of the α-glycerophosphatase in yeasts is higher when grown on hexoses than when grown on non-sugar carbon sources

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1968.tb00353.x

Glycerol metabolism in yeasts. Pathways of utilization and production.

The proportion of ingested anthocyanins to reach the systemic circulation is reported to be a small percentage of their ingested dose. This may be due to physiochemical degradation in vivo or following routine sample treatment. Therefore, this study aimed to quantitatively investigate the effect of anthocyanin structure on their stability under simulated (in vitro) physiological conditions and to assess their degradation and recovery following routine preanalytical sample extraction and storage. It was demonstrated that B-ring hydroxylation mediated the degradation of anthocyanins to their phenolic acid and aldehyde constituents, successful anthocyanin extraction is dependent on both sample preparation technique and anthocyanin structure, and anthocyanins are stable through multiple freeze−thaw cycles. These data indicate that significant portions of ingested anthocyanins are likely to degrade to phenolic acids and aldehyde in vivo. Consequently, these compounds should be the target of future bioavailabil...

Anthocyanin Stability and Recovery: Implications for the Analysis of Clinical and Experimental Samples

Purification and Properties of Glycerol Kinase from Escherichia coli

Publisher Summary This chapter focuses on entropies of activation and mechanisms of reactions in solution Entropy of activation is implied in the transition state theory An underlying principle of the theory is that there exists along the reaction path of any reaction a state of critical energy, the minimum energy of which must be supplied to the reactants in order to cause reaction to occur This state is termed the transition state or activated complex, and the basic Eyring proposal is that it can be treated as a normal molecule with respect to its thermodynamic properties Determination of both the energy (and enthalpy) of activation and the entropy of activation involves measurement of the temperature coefficient of the rate constant Although possessing certain inherent limitations, transition state theory seems adequate to permit the quantitative computation of kinetic parameters from first principles Practical application of the theory is impeded by incomplete information about the molecular properties of the activated complex and, for reactions in solution, the lack of a quantitative description of molecular interactions in condensed phases Because transition state theory is essentially an equilibrium theory, one basis for comparison is thermodynamic data for solution equilibria From the inception of transition state theory, entropies of activation are from the twin aspects of molecular structure and reaction mechanism in this chapter

R. P. Bell

Papers

Hydration equilibria of some aldehydes and ketones