Dioxides, reactions Disodium phosphate

The presence of carbon dioxide in the atmosphere is a crucial factor in the pH measurement of some air-sensitive solutions, which should not be underestimated. Sodium carbonate, bicarbonate and disodium phosphate are all sensitive to the presence of COj. The presence of carbon dioxide, which may enter a reaction with the ionic species in these solntions, may result in the formation of carbonic acid. In addition, these solutions may act as buffers, and therefore resist dilution. This may be prevented by the introdnction into the system of an inert gas such as N, which prevents COj from entering any reaction in the system. The quality of water used may also be an influential factor. 

Macerate (grind) one-half cake of yeast or half an envelope of dry yeast in 50 mL of water in a beaker, add 0.35 g of disodium hydrogen phosphate, and transfer this slurry to a 500-mL round-bottomed flask. Add a solution of 51.5 g of sucrose in 150 mL of water, and shake to ensure complete mixing. Fit the flask with a one-hole rubber stopper containing a bent glass tube that dips below the surface of a saturated aqueous solution of calcium hydroxide (limewater) in a 6-in. test tube (Fig. 1). The tube in limewater will act as a seal to prevent air and unwanted enzymes from entering the flask, but will allow gas to escape. Place the assembly in a warm spot in your desk (the optimum temperature for the reaction is 35°C) for one week, at which time the evolution of carbon dioxide will have ceased. What is the precipitate in the limewater ... 

Randolph s tests with alkaline phosphatase were carried out in a stirred autoclave. An amount of the disodium salt and some water, which is required for the enzyme catalyzed hydrolysis, were placed in the autoclave along with a sealed glass ampule containing the enzyme. In this case water is necessary not just to render the enzyme active, as Klibanov found, but also to serve as a reactant in the hydrolysis. Carbon dioxide was admitted, the temperature and pressure adjusted to the level desired, and the sealed ampule shattered to expose the enzyme and to mark the zero point of the reaction sequence. In their studies they investigated the effects of changing the relative amount of enzyme on the rate of conversion of the disodium salt of p-nitrophenyl phosphoric acid to p-nitrophenol. They measured the amount of conversion by UV analysis of the solution removed from the autoclave at the end of a reaction test. The results are shown in Figure 11.1 based upon these results and other experimental results, the authors concluded that the rate-determining step of the enzyme-catalyzed reaction was the dissolution of disodium p-nitrophenyl phosphate in supercritical carbon dioxide. 

The earliest reported demonstration of enzymatic activity in a supercritical fluid was for the reaction of disodium p-nitrophenyl phosphate to p-nitro-phenol, catalysed by alkaline phosphatase. Randolph et aL [26] detected the product in yields of up to 71% in carbon dioxide at 35°C and 100 atm, in the presence of 0.1% v/v water. Hammond et al. [33] found tyrosinase, a polyphenol oxidase, to be catalytically active for the oxidation of 4-methyl phenol in both supercritical carbon dioxide at (36 2)°C and supercritical trifluoro-methane at (34 2)°C, with oxygen, at a total pressure of 345 bar. Use of a flow reactor permitted isolation of greater quantities of the catecholic product (1,2-dihydroxy, 4-methylbenzene). Oxidative activity for 4-chlorophenol substrate was appreciably lower. 

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