Fructose catalytic oxidation

Bioelectrocatalytic properties were obtained for FDH at carbon and gold and platinum electrodes [111,113]. The catalytic oxidation current of FDH-modified carbon paste electrodes approached a maximum value at 4-0.5 V vs. Ag/AgCl. At this potential and under optimum conditions, i.e., pH 4.5, fi uctose can be measured between 0.2 and 20 mM in fi uit juices. Most importantly the fructose sensor was insensitive to ambient oxygen. 

Dianhydro-D-fructose (26), a viscous sirup, was obtained during the catalytic oxidation of l,4 3,6-dianhydro-D-mannitol (25) to the corresponding diketone (27). A reaction time of 20 hours at room temper-... 

The catalytic oxidation of sucrose is described in several patents. This oxidation ought to lead to a uronic acid derivative from which D-glu-curonic acid could be obtained by hydrolysis. This acid has, indeed, been obtained in this manner but, according to our experience," the catalytic oxidation of sucrose does not proceed uniformly. All three susceptible primary hydroxyl groups, on C-1 and C-6 of the D-fructose residue and at C-6 of the D-glucose residue, are oxidized at a similar rate and, therefore, a reaction product is obtained which contains all of the expected mono- and di-carboxylic acids, and which presents a difficult problem in separation. 

D-fructose (13) undergoes photochemically induced catalytic oxidation by 0 to D-erythrose (14) and other fragments in the presence... 

The catalytic oxidation of the carbohydrates in the presence of Cu(II) for the detection of sucrose, galactose, and fructose was exploited using a Teflon-coated platinum wire plated with copper as the working electrode. Therefore, the addition of copper ions in the run buffer increased the sensitivity to an order of magnitude compared to run buffer without copper. Detection limits were 1 pmol 1 ... 

The breakthrough came already in 1996, one year after Curd s prediction, when Yang and coworkers reported the C2-symmetric binaphthalene-derived ketone catalyst 6, with which ee values of up to 87% were achieved. A few months later, Shi and coworkers reported the fructose-derived ketone 7, which is to date still one of the best and most widely employed chiral ketone catalysts for the asymmetric epoxidation of nonactivated alkenes. Routinely, epoxide products with ee values of over 90% may be obtained for trans- and trisubstituted alkenes. Later on, a catalytic version of this oxygen-transfer reaction was developed by increasing the pH value of the buffer. The shortcoming of such fructose-based dioxirane precursors is that they are prone to undergo oxidative decomposition, which curtails their catalytic activity. 

Fructose 1,6-bisphosphatase is inhibited by AMP—a compound that activates phosphofructokinase Elevated AMP thus stimulates path ways that oxidize nutrients to provide energy for the cell. [Note ATP and NADH, produced in large quantities during fasts by catalytic path ways, such as fatty acid oxidation, are required for gluconeogenesis.]... 

A reversible covalent modification that plants use extensively is the reduction of cystine disulfide bridges to sulf-hydryls. Many of the enzymes of photosynthetic carbohydrate synthesis are activated in this way (table 9.3). Some of the enzymes of carbohydrate breakdown are inactivated by the same mechanism. The reductant is a small protein called thioredoxin, which undergoes a complementary oxidation of cysteine residues to cystine (fig. 9.5). Thioredoxin itself is reduced by electron-transfer reactions driven by sunlight, which serves as a signal to switch carbohydrate metabolism from carbohydrate breakdown to synthesis. In one of the regulated enzymes, phosphoribulokinase, one of the freed cysteines probably forms part of the catalytic active site. In nicotinamide-adenine dinucleotide phosphate (NADP)-malate dehydrogenase and fructose-1,6-bis-... 

The oxidation of D-fructose with cerium(IV) in sulfuric acid medium is inhibited by an increase in the acidity. A cationic surfactant, CTAB, catalyses the reaction, whereas SDS has no effect. The catalytic role of CTAB has been explained using the pseudophase model of Menger and Portnoy. A mechanism involving the formation of an intermediate complex between /3-D-fructopyranose and Ce(S04)32- has been proposed.61 The oxidation of cycloalkanones with cerium(IV) in sulfuric acid medium showed a negligible effect of acidity. Formation of an intermediate complex, which decomposes in the rate-determining step, has been suggested.62... 

Although several methods have been reported in recent literature concerning the preparation of 5-hydroxymethylfurfural by dehydration of fructose, we have shown that microporous catalyts in their protonic form, for instance, Mordenites, Beta, Y-faujasites and ZSM-5 zeolites constituted a convenient alternative route to the catalysts used up to now, namely mineral acids, oxides or ion-exchange resins/27,281... 

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