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Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis is the cleavage of Biomolecule where a water molecule is consumed to effect the separation of a larger molecule into component parts. When a carbohydrate is broken into its component sugar molecules by hydrolysis (e.g., sucrose being broken down into glucose and fructose), this is recognized as saccharification.
Hydrolysis reactions can be the reverse of a condensation reaction in which two molecules join into a larger one and eject a water molecule. Thus hydrolysis adds water to break down, whereas condensation builds up by removing water.
Strong acids also undergo hydrolysis. For example, dissolving sulfuric acid () in water is accompanied by hydrolysis to give hydronium and bisulfate, the sulfuric acid's conjugate acid. For a more technical discussion of what occurs during such a hydrolysis, see Brønsted–Lowry acid–base theory.
Perhaps the oldest commercially practiced example of ester hydrolysis is saponification (formation of soap). It is the hydrolysis of a triglyceride (fat) with an aqueous base such as sodium hydroxide (NaOH). During the process, glycerol is formed, and the react with the base, converting them to salts. These salts are called soaps, commonly used in households.
In addition, in living systems, most biochemical reactions (including ATP hydrolysis) take place during the catalysis of . The catalytic action of enzymes allows the hydrolysis of , fats, oils, and . As an example, one may consider (enzymes that aid digestion by causing hydrolysis of in ). They catalyze the hydrolysis of interior peptide bonds in peptide chains, as opposed to (another class of enzymes, that catalyze the hydrolysis of terminal peptide bonds, liberating one free amino acid at a time).
However, proteases do not catalyze the hydrolysis of all kinds of proteins. Their action is stereo-selective: Only proteins with a certain tertiary structure are targeted as some kind of orienting force is needed to place the amide group in the proper position for catalysis. The necessary contacts between an enzyme and its substrates (proteins) are created because the enzyme folds in such a way as to form a crevice into which the substrate fits; the crevice also contains the catalytic groups. Therefore, proteins that do not fit into the crevice will not undergo hydrolysis. This specificity preserves the integrity of other proteins such as , and therefore the biological system continues to function normally.
Upon hydrolysis, an amide converts into a carboxylic acid and an amine or ammonia (which in the presence of acid are immediately converted to ammonium salts). One of the two oxygen groups on the carboxylic acid are derived from a water molecule and the amine (or ammonia) gains the hydrogen ion. The hydrolysis of peptide bond gives .
Many polyamide polymers such as nylon 6,6 hydrolyze in the presence of strong acids. The process leads to depolymerization. For this reason nylon products fail by fracturing when exposed to small amounts of acidic water. Polyesters are also susceptible to similar polymer degradation reactions. The problem is known as environmental stress cracking.
Secondly, the removal of a terminal diphosphate to yield adenosine monophosphate (AMP) and pyrophosphate. The latter usually undergoes further cleavage into its two constituent phosphates. This results in biosynthesis reactions, which usually occur in chains, that can be driven in the direction of synthesis when the phosphate bonds have undergone hydrolysis.
The best-known disaccharide is sucrose (table sugar). Hydrolysis of sucrose yields glucose and fructose. Invertase is a sucrase used industrially for the hydrolysis of sucrose to so-called invert sugar. Lactase is essential for digestive hydrolysis of lactose in milk; many adult humans do not produce lactase and cannot digest the lactose in milk.
The hydrolysis of polysaccharides to soluble sugars can be recognized as saccharification. Malt made from barley is used as a source of β-amylase to break down starch into the disaccharide maltose, which can be used by yeast to brewing. Other amylase enzymes may convert starch to glucose or to oligosaccharides. Cellulose is first hydrolyzed to cellobiose by cellulase and then cellobiose is further hydrolyzed to glucose by beta-glucosidase. Ruminants such as cows are able to hydrolyze cellulose into cellobiose and then glucose because of symbiosis bacteria that produce cellulases.
Thus the aqua behave as acids in terms of Brønsted–Lowry acid–base theory. This effect is easily explained by considering the inductive effect of the positively charged metal ion, which weakens the bond of an attached water molecule, making the liberation of a proton relatively easy.
The dissociation constant, pKa, for this reaction is more or less linearly related to the charge-to-size ratio of the metal ion.
Hydrolysis may proceed beyond the first step, often with the formation of polynuclear species via the process of olation. Some "exotic" species such as are well characterized. Hydrolysis tends to proceed as pH rises leading, in many cases, to the precipitation of a hydroxide such as or . These substances, major constituents of bauxite, are known as and are formed by leaching from rocks of most of the ions other than aluminium and iron and subsequent hydrolysis of the remaining aluminium and iron.
Acids catalyze hydrolysis of nitriles to amides. Acid hydrolysis does not usually refer to the acid catalyzed addition of the elements of water to double or triple bonds by electrophilic addition as may originate from a hydration reaction. Acid hydrolysis is used to prepare monosaccharide with the help of but formic acid and trifluoroacetic acid have been used.
Acid hydrolysis can be utilized in the pretreatment of cellulosic material, so as to cut the interchain linkages in hemicellulose and cellulose.
The reaction is often used to solubilize solid organic matter. Chemical drain cleaners take advantage of this method to dissolve hair and fat in pipes. The reaction is also used to dispose of human and other animal remains as an alternative to traditional burial or cremation.
DNA
Hydrolysis of DNA occurs at a significant rate in vivo.Lindahl T. Instability and decay of the primary structure of DNA. Nature. 1993 Apr 22;362(6422):709-15. doi: 10.1038/362709a0. PMID 8469282 For example, it is estimated that in each human cell 2,000 to 10,000 DNA purine bases turn over every day due to hydrolytic depurination, and that this is largely counteracted by specific rapid DNA repair processes. Hydrolytic DNA damages that fail to be accurately repaired may contribute to carcinogenesis and ageing.
Metal aqua ions
Metal ions are , and in aqueous solution they form metal aquo complexes of the general formula . (1978). 9780853120278, Ellis Horwood. ISBN 9780853120278 The aqua ions undergo hydrolysis, to a greater or lesser extent. The first hydrolysis step is given generically as
(1976). 9780471039853, Wiley. ISBN 9780471039853 Ions with low charges, such as are very weak acids with almost imperceptible hydrolysis. Large divalent ions such as , , and have a pKa of 6 or more and would not normally be classed as acids, but small divalent ions such as undergo extensive hydrolysis. Trivalent ions like and are weak acids whose pKa is comparable to that of acetic acid. Solutions of salts such as or in water are noticeably acidic; the hydrolysis can be suppressed by adding an acid such as nitric acid, making the solution more acidic.
Mechanism strategies
, , and can be converted back into by treatment with excess water under acid-catalyzed conditions: ; ; .
Catalysis
Acidic hydrolysis
Acid catalysis can be applied to hydrolyses. in (2024). 9780128044926 ISBN 9780128044926 For example, in the conversion of cellulose or starch to glucose. (1983). 9781475708356 ISBN 9781475708356 Carboxylic acids can be produced from acid hydrolysis of esters.
(2024). 9780123850997, Academic press. ISBN 9780123850997
Alkaline hydrolysis
Alkaline hydrolysis usually refers to types of nucleophilic substitution reactions in which the attacking nucleophile is a hydroxide ion. The best known type is saponification: cleaving into carboxylate salts and alcohols. In ester hydrolysis, the hydroxide ion nucleophile attacks the carbonyl carbon. This mechanism is supported by isotope labeling experiments. For example, when ethyl propionate with an oxygen-18 labeled ethoxy group is treated with sodium hydroxide (NaOH), the oxygen-18 is completely absent from the sodium propionate product and is found exclusively in the ethanol formed.
See also
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