Hydrolytic Degradation Hydrolysis

Hydrolytic degradation of polyphosphates is the main theme of this book. Not only is it of ultimate importance (Focal Points 8, 9, 12, and 13) in phosphate chemistry, but also in biochemistry and most other biological sciences. It is the hydrolytic degradation of ATP that has been discussed over and over as an example of the types of reactions expected from phosphate fibers. 

It was noted in Chapter 2 that hydrolytic degradation may be represented as  

Again X may represent one equivalent of almost anything cationic. 

Two classes of studies have been published. Most have dealt with the kinetics of degradation, while a few have attempted to define the products of these reactions. 

More than 100 articles have been published dealing with hydrolytic degradation. Several quality reviews will be cited rather than repeating the entire list.  

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Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

The hexahydrate is formed by the addition of anhydrous STP to water or by the hydrolysis of sodium trimetaphosphate [7785-84-4] (STMP), (NaP02)3, in alkaline media. The hexahydrate is stable at room temperature but undergoes rapid hydrolytic degradation to pyro- and orthophosphate upon drying. 

Hydrolytically degradable plastic is a degradable plastic in which the degradation results from hydrolysis. 

It has also been found that there can be interactions between hydrolytic degradation and photochemical degradation. Especially in the case of melamine-formaldehyde cross-linked systems, photochemical effects on hydrolysis have been observed. 

Poly(L-malate) decomposes spontaneously to L-ma-late by ester hydrolysis [2,4,5]. Hydrolytic degradation of the polymer sodium salt at pH 7.0 and 37°C results in a random cleavage of the polymer, the molecular mass decreasing by 50% after a period of 10 h [2]. The rate of hydrolysis is accelerated in acidic and alkaline solutions. This was first noted by changes in the activity of the polymer to inhibit DNA polymerase a of P. polycephalum [4]. The explanation of this phenomenon was that the degradation was slowest between pH 5-9 (Fig. 2) as would be expected if it were acid/base-catalyzed. In choosing a buffer, one should be aware of specific buffer catalysis. We found that the polymer was more stable in phosphate buffer than in Tris/HCl-buffer. 

Endosulfan undergoes hydrolysis to endosulfan diol in surface water and groundwater. The rate of hydrolysis is influenced by pH. Half-life values reported in the literature vary somewhat. The chemical degradation of a- and P-endosulfan was studied under both anaerobic and aerobic environments. Under aerobic conditions, both hydrolysis and oxidation of endosulfan can occur, while under anaerobic conditions, only hydrolysis can occur. The hydrolytic half-lives for a- and P-endosulfan under anaerobic conditions at pH 7 were 35 and 37 days, respectively (Greve and Wit 1971). At pH 5.5 the half-lives were 151 and 187 days, respectively. Under aerobic conditions, the half-lives decreased. At pH 7, the half-lives of the chemical degradation (hydrolysis and oxidation) of both a- and P-endosulfan were 23 and 25 days, respectively, while at pH 5, the half-lives were 54 and 51 days, respectively. At T=20 and pHs of 5.5 and 8.0, the half-lives of a-endosulfan in distilled water were 11.3 and 5.3 days. 

Hammer and coworkers prepared PEG-h-PCL polymersomes entrapping DXR (Fig. 11a). The release of DXR from the polymersomes was in a sustained manner over 14 days at 37 °C in PBS via drug permeation through the PCL membrane, and hydrolytic degradation of the PCL membrane [228]. The release rate of encapsulated molecules from polymersomes can be tuned by blending with another type of block copolymer [229]. Indeed, the release rate of encapsulated DXR from polymersomes prepared from mixtures of PEG- -PLA with PEG- -PBD copolymers increased linearly with the molar ratio of PEG- -PLA in acidic media (Fig. lib). Under acidic conditions, the PLA first underwent hydrolysis and, hours later, pores formed in the membrane followed by final membrane... 

The potential sites of cleavage in the hydrolytic degradation of the trisiloxane surfactant, M2D-C3-0-(E0)n-CH3 (1) are illustrated in Fig. 5.5.3. The Si-0 bond (c) is a likely site of cleavage according to the chemistry of silicones and the relative instability of this bond to hydrolysis [23]. 

One may, therefore, assume that the lactam metabolites formed are rather resistant to hydrolytic degradation and do not contribute significantly to the formation of the co-amino acid derivatives. This is in line with the observation that substituted pyrrolidin-2-ones are generally resistant to metabolic hydrolysis (see Sect. 5.3). 

Loos MA (1975) Phenoxyalkanoic acids. In Kemey PC, Kaufman DD (eds) Herbicides chemistry, degradation and mode of action, vol 1. Marcel Dekker New York, pp 1-128 Lovley DR (1993) Dissimilatory metal reduction. Annual Review of Microbiology 47 263-290 Macalady DL, Wolfe NL (1983) New perspectives on the hydrolytic degradation of the organo-phosphorothionate insecticide chloropyrifos. J Agric Food Chem 31 1139-1147 Macalady DL, Wolfe NL (1985) Effects of sediment sorption and abiotic hydrolysis. J Agric Food Chem 33 167-173... 

Until recently, no efforts to measure the rates of hydrolytic degradation of sorbed pesticides have been reported. Indeed, it has been widely assumed that hydrolytic reactions are important only in the aqueous phase and that hydrolysis of sorbed pesticides proceeds at an insignificant rate (. ... 

Hydrolytic degradation is especially important in polymers with hydrolyzable links between the CRUs. Thus, polyesters can be saponified to yield the starting materials from which they were formed. Acetal links in synthetic polymers such as polyoxymethylene, or in natural polymers such as cellulose, can be hydrolyzed with acids. However, the resistance to hydrolysis depends very much on the structure of the polymer for example, polyesters of terephthalic acid are very difficult to hydrolyze while aliphatic polyesters are generally easily hydro-... 

Hydrolytic Degradation of Cellulose and Separation of the Hydrolysis Products by Chromatography... 

These values reveal that the rate of hydrolysis in the alkaline range up to pH < 9 is very small and practically constant, but that it then rises rapidly with decreasing pH. It is also evident that the stability of oligophosphates to hydrolytic degradation decreases in the order diphosphate > triphosphate > tetraphosphate. Degradation experiments with small quantities of oligophosphates with chain lengths n = 4-8 show (858) that stability decreases further up to the octaphosphate (see Fig. 7). (The... 

In any quantitative work on protein hydrolysis, it is necessary to have a measure of the extent of the hydrolytic degradation. The measurement of the number of peptide bonds cleaved during a hydrolytic process is related to the activity of proteinolytic enzymes and the extent of hydrolysis. Various techniques that evaluate the progress of hydrolysis have been reported, such as the trichloroacetic acid (TCA) solubility index, which evaluates the percentage of nitrogen soluble in TCA after partial hydrolysis of the protein. 

A common feature of vapor-phase thermohydrolysis, liquid-phase acid hydrolysis, and enzymatic hydrolysis of cellulose is a significant influence of lateral order on the rate of chain cleavage, the DP finally reached, and weight loss. But with regard to this influence of the physical structure of cellulose, there also exist remarkable differences between these three modes of hydrolytic degradation. 

Polymer-based systems. Pulsatile release of medicaments can be obtained from polymer-based delivery systems. Based on the mechanism of drug release from the polymer, these systems can be divided into various classes and subclasses. Broadly, they can be classified into three classes delivery by hydrolysis of polymers, delivery by osmotic pressure, and delivery by both hydrolytic degradation and osmotic effects. 

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