The Extent of Hydrolysis

Disinfection. The disinfection efficiency of /V-ha1amines is related to the extent of hydrolysis to hypohalous acid. For example, NH2CI (Kf 10 ) is a poor bactericide compared to HOCl (5). By contrast, monochloroisocyanurate 10 ) exhibits good bactericidal properties (6). 

Although pH determines the ratio of hypohalous acid to hypohaUte ion, the fraction of the total available halogen present as HOX is dependent on of the halamine as well as the concentration of excess amine. In the case of chloroisocyanurates, which are the most widely used /V-ch1oramine disinfectants in swimming pools and spas, the extent of hydrolysis at 1 ppm av CI2 (as monochloroisocyanurate) is - 34% but only - 1% when 25 ppm cyanuric acid is added (4). Nevertheless, effective disinfection can stiU occur with chloroisocyanurates if a sufficient FAC is maintained, eg, 1—3 ppm. The observed reduction in disinfection rate because of cyanuric acid (6) has been shown to be direcdy related to the concentration of HOCl formed by hydrolysis of chloroisocyanurates (10). 

The extent of hydrolysis of (MY)(n 4)+ depends upon the characteristics of the metal ion, and is largely controlled by the solubility product of the metallic hydroxide and, of course, the stability constant of the complex. Thus iron(III) is precipitated as hydroxide (Ksal = 1 x 10 36) in basic solution, but nickel(II), for which the relevant solubility product is 6.5 x 10 l8, remains complexed. Clearly the use of excess EDTA will tend to reduce the effect of hydrolysis in basic solutions. It follows that for each metal ion there exists an optimum pH which will give rise to a maximum value for the apparent stability constant. 

Transport in the polymeric system is assumed to be by Fickian diffusion, although the diffusivity of the various species depends on the extent of hydrolysis of the polymeric linkages. 

The coupling of solute transport in the GI lumen with solute lumenal metabolism (homogeneous reaction) and membrane metabolism (heterogeneous reaction) has been discussed by Sinko et al. [54] and is more generally treated in Cussler s text [55], At the cellular level, solute metabolism can occur at the mucosal membrane, in the enterocyte cytosol, and in the endoplasmic reticulum (or microsomal compartment). For peptide drugs, the extent of hydrolysis by lumenal and membrane-bound peptidases reduces drug availability for intestinal absorption [56], Preferential hydrolysis (metabolic specificity) has been targeted for reconversion... 

Hydrolysis of amide groups to carboxylate is a major cause of instability in acrylamide-based polymers, especially at alkaline pH and high temperatures. The performance of oil-recovery polymers may be adversely affected by excessive hydrolysis, which can promote precipitation from sea water solution. This work has studied the effects of the sodium salts of acrylic acid and AMPS, 2-acrylamido-2-methylpropanesulfonic acid, as comonomers, on the rate of hydrolysis of polyacrylamides in alkaline solution at high temperatures. Copolymers were prepared containing from 0-53 mole % of the anionic comonomers, and hydrolyzed in aqueous solution at pH 8.5 at 90°C, 108°C and 120°C. The extent of hydrolysis was measured by a conductometric method, analyzing for the total carboxylate content. 

The hydrolysis of polyacrylamide and acrylamide/sodium acrylate copolymers has been extensively studied [1,2,3,5,6,7,8,-9,10], in relatively strongly alkaline conditions, above pH 12. These studies demonstrated that the hydrolysis of the amide groups is hydroxide-catalyzed and that neighboring ionized carboxyl groups in the polymer inhibit the hydrolysis by electrostatic repulsion of the hydroxide ions. Senju et al. [6] showed that at temperatures up to 100°C, there is an apparent limit to the extent of hydrolysis of polacrylamide when approximately 60% of the amide groups are hydrolyzed. 

The extent of hydrolysis of the copolymers was determined by conductometric titration. The increase in carboxylate content was determined by difference, before and after hydrolysis. (The AMPS content of the polymers, where measured, was determined by colloid titration with poly [diallyl dimethyl ammonium chloride].)... 

It is time to introduce a few new words. We say carbonic acid forms by hydrolysis, i.e. by splitting a molecule of water. We describe the extent of hydrolysis in Equation (6.5) by the following equilibrium constant ... 

The compounds are, in general, stable and fairly resistant to hydrolysis in spite of the >POF grouping. We showed, for example, that diphenylphosphorodiamidic fluoride could be recrystallized from aqueous alcohol. Tetramethylphosphoro-diamidic fluoride was not affected to any extent by contact with water at 18° for 6 hr. The reaction between n/2 aqueous sodium hydroxide solution and the compound was studied. The extent of hydrolysis (removal of fluorine) after 30 min. was about 8-9 per cent, and even after 500 hr. it was only 29-9 per cent. The compound is also affected by acid. 

The first systematic study of the metabolic hydrolysis of primary aliphatic amides was carried out by Bray et al. in 1950 [1]. The substrates were incubated in rabbit liver preparations for 5 h at 37°. In Fig. 4.2, the effect of chain length on the degree of hydrolysis of amides containing 1 to 18 C-atoms (4.1) is shown. The extent of hydrolysis was very small for the first three homo-... 

The in vivo metabolism of a homologous series of alkyl carbamates (7.2, Fig. 7.3) has yielded some informative results [13]. The hydrolysis of these esters liberates carbamic acid (7.3, Fig. 7.3), which breaks down spontaneously to C02 and NH3, allowing the extent of hydrolysis to be determined conveniently and specifically by monitoring C02 production. When such substrates were administered to rats, there was an inverse relationship between side-chain hydroxylation and ester-bond hydrolysis. Thus, for compounds 12 the contribution of hydrolysis to total metabolism (90 - 95% of dose) decreased in the series R=Et (ca. 85-90%), Bu (ca. 60-65%), hexyl (ca. 45 - 50%), and octyl (ca. 30%). Ethyl carbamate (urethane) is of particular toxicological interest, being a well-established carcinogen in experimental animals. In vitro studies of adduct formation have confirmed the competition between oxidative toxification mediated by CYP2E1 and hydrolytic detoxification mediated by carboxylesterases [14]. 

The conversion of parathion is affected by soil constituents in the order kaolinite > smectite > organic matter and is related inversely to the adsorption affinity of these materials for this contaminant (Mingelgrin and Saltzman 1977). Although the extent of hydrolysis differs among soils, it is apparent that soil-surface degradation of parathion is caused by hydrolysis of the phosphate ester bond. The presence of water in the soil-parathion system led to a decrease in the surface-induced degradation of the organic molecule and diminished the effect of natural soil properties on its persistence. 

The most promising new approaches to using enzymes in the pulp and paper industry, however, are based either on the idea of selected hydrolysis of certain components or limited hydrolysis of several components in the fibre. This concept is apparently in accord with both the technical and economic demands of a feasible process. By limiting the extent of hydrolysis... 

Esters such as PVAc may be hydrolyzed producing alcohols such as PVA (16.1), which will have the same DP as the ester. In fact, PVAc does not totally hydrolyze, but with reasonable effort the extent of hydrolysis is greater than 90%. Since PVAc is not water-soluble, but PVA, the extent of water solubility is dependent on the extent of hydrolysis. 

In this section we first describe the results of measurements made on fresh and aged solutions. Potentlometric, pH, measurements, which Indicate the extent of hydrolysis of the aluminum Ions, were made on all solutions during the aging process. Next, we report surface areas of pillared clays made from the aged solutions. Finally, we will discuss the cracking activities of some selected pillared clay samples. 

The specificity of a xylanase preparation may be determined from the isolation and characterization of oligosaccharides formed from xylan hydrolysis. While the oligosaccharides released were mainly dependent on the specificity of the xylanase, the complex structure of the heteroxylan also determines the extent of hydrolysis and the site of cleavage. Two types of xylooligosaccharides are usually produced acidic (from glucuronoxylans) and neutral (from arabino- and arabinoglucurono-xylans). The specificity of the action of several purified xylanases on various heteroxylans is shown below ... 

Wolfrom and coworkers studied the changes that occurred in cellulose in strong hydrochloric acid under conditions that gave an ethyl mercaptan derivative of the hydroljrtic product. n-Glucose diethyl mercaptal derivatives did not appear until the hydrolysis was two-thirds complete. The extent of hydrolysis was determined by the number of sulfur groups introduced. 

Presently, FAB-MS spectra are routinely used to characterize synthetic tyrosine O-sulfate peptides.152,57,63-671 Since partial hydrolysis of the sulfate ester occurs in the gas phase, quantification of the tyrosine O-sulfate residue by mass spectrometry is not possible, but combined with one-peak assignment in HPLC, FAB-MS represents a powerful analytical tool. On the other hand, partial hydrolysis in the gas phase excludes the presence of sul-fonated species which should be perfectly stable. In early studies the presence of such species were excluded by quantitative recovery of tyrosine upon acid hydrolysis or upon hydrolysis with arylsulfatase.1361 Recently, even MALDI-TOF-MS spectra of CCK-peptides1441 and of conotoxins a-PnIA and a-PnlB 138 were reported which show that in the positive-ion mode the [M + H-S03]+ ions represent the base peaks, while in the negative-ion mode, [M-H]-ions consistently correspond to the base peaks. In the CCK peptides intramolecular salt bridging of the sulfate hemi-ester with proximal positive charges of arginine or lysine side chains was found to reduce the extent of hydrolysis in the gas phase significantly.144,1491... 

In dilute solutions, these reactions produce a series of M(OH) (n = 1-4) hydrolysis species with populations that depend on solution pH (17). Hydrolysis chemistry is fundamental to the behavior of trivalent metal ions in water as the extent of hydrolysis governs the polymerization of metal ions into extended structures that eventually crystallize into secondary oxide and oxyhydroxide minerals and clays. When building a general capability to simulation geochemical reaction mechanisms, hydrolysis is the place to begin. If the hydrolysis equilibria of... 

Adler-Nissen and Olsen (40) studied the influence of peptide chain length on the taste anT functional properties of enzymatically modified soy protein. The emulsifying capacity of modified proteins could be improved significantly compared to unmodified control samples by controlling the extent of hydrolysis. 

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