Free energy of hydrolysis

Sodium acetate reacts with carbon dioxide in aqueous solution to produce acetic anhydride and sodium bicarbonate (49). Under suitable conditions, the sodium bicarbonate precipitates and can be removed by centrifugal separation. Presumably, the cold water solution can be extracted with an organic solvent, eg, chloroform or ethyl acetate, to furnish acetic anhydride. The half-life of aqueous acetic anhydride at 19°C is said to be no more than 1 h (2) and some other data suggests a 6 min half-life at 20°C (50). The free energy of acetic anhydride hydrolysis is given as —65.7 kJ/mol (—15.7 kcal/mol) (51) in water. In wet chloroform, an extractant for anhydride, the free energy of hydrolysis is strangely much lower, —50.0 kJ/mol (—12.0 kcal/mol) (51). Half-life of anhydride in moist chloroform maybe as much as 120 min. Ethyl acetate, chloroform, isooctane, and / -octane may have promise for extraction of acetic anhydride. Benzene extracts acetic anhydride from acetic acid—water solutions (52). 

Free Energies of Hydrolysis of Some High-Energy Compounds ... 

FIGURE 3.8 The activation energies for phosphoryl group-transfer reactions (200 to 400 kj/mol) are substantially larger than the free energy of hydrolysis of ATP ( — 30.5 kj/mol). 

For the phosphoric anhydrides, and for most of the high-energy compounds discussed here, there is an additional entropic contribution to the free energy of hydrolysis. Most of the hydrolysis reactions of Table 3.3 result in an increase in the number of molecules in solution. As shown in Figure 3.11, the hydrolysis of ATP (as pH values above 7) creates three species—ADP, inorganic phosphate (Pi), and a hydrogen ion—from only two reactants (ATP and HgO). The entropy of the solution increases because the more particles, the more disordered the system. (This effect is ionization-dependent because, at low pH, the... 

The Effect of Metal Ions on the Free Energy of Hydrolysis of ATP... 

FIGURE 3.16 The pH dependence of the free energy of hydrolysis of ATP. Because pH varies only slightly in biological environments, the effect on AG is nsnally small. 

FIGURE 3.17 The free energy of hydrolysis of ATP as a function of total ion concen-... 

The standard-state free energy of hydrolysis for acetyl phosphate is AG° = —42.3 kj/mol. 

Would you expect the free energy of hydrolysis of aceto-acetyl-coenzyme A (see diagram) to be greater than, equal to, or less than that of acetyl-coenzyme A Provide a chemical rationale for your answer. 

Based on the discussion of high-energy phosphates in this chapter, would you expect carbamoyl phosphate to possess a high free energy of hydrolysis Provide a chemical rationale for your answer. 

If the cellular free energy of hydrolysis of ATP is taken as — 50 kj/mol, the free energy available from the hydrolysis of a single ATP molecule is... 

In the kidney and in muscle tissues, fructose is readily phosphorylated by hexokinase, which, as pointed out above, can utilize several different hexose substrates. The free energy of hydrolysis of ATP drives the reaction forward ... 

The standard free energy of hydrolysis of a number of biochemically important phosphates is shown in Table 10-1. An estimate of the comparative tendency of each of the phosphate groups to transfer to a suitable acceptor may be obtained from the AG of hydrolysis at 37 °C. The value for the hydrolysis of the terminal... 

Table 10-1. Standard free energy of hydrolysis of some organophosphates of biochemical importance. ...

When ATP acts as a phosphate donor to form those compounds of lower free energy of hydrolysis (Table 10-1), the ph osphate group is invariably converted to one of low energy, eg. 

In addition, hving cells need a system of energy storage and this is provided by bond energy, strictly the free energy of hydrolysis of a diphosphate bond in the compound adenosine triphosphate (ATP). 

Based on a series of studies of the effect of organic solvent on the reaction of Ca-ATPase with Pj and ATP synthesis, De Meis et al. proposed that a different solvent structure in the phosphate microenvironment in Ej and E2 forms the basis for existence of high- and low-energy forms of the aspartyl phosphate [93]. Acyl phosphates have relatively low free energy of hydrolysis when the activity of water is reduced, due to the change of solvation energy. The covalently bound phosphate may also reside in a hydrophobic environment in E2P of Na,K-ATPase since increased partition of Pj into the site is observed in presence of organic solvent [6] in the same manner as in Ca-ATPase. 

The starting points are the free energies of hydrolysis for pNPOSOjH and pNP0P03H2. °° From these we may deduce an equation relating AGiiydroi to of HOX for... 

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