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Hydrolysis (; ) is any chemical reaction in which a molecule of breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and reactions in which water is the .

Biological hydrolysis is the cleavage of where a water molecule is consumed to effect the separation of a larger molecule into component parts. When a is broken into its component sugar molecules by hydrolysis (e.g., being broken down into and ), this is recognized as .

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.


Types
Usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both the substance and water molecule to split into two parts. In such reactions, one fragment of the target molecule (or parent molecule) gains a . It breaks a chemical bond in the compound.


Salts
A common kind of hydrolysis occurs when a salt of a or (or both) is dissolved in water. Water spontaneously ionizes into and . The salt also dissociates into its constituent anions and cations. For example, dissociates in water into and ions. Sodium ions react very little with the hydroxide ions whereas the acetate ions combine with hydronium ions to produce . In this case the net result is a relative excess of hydroxide ions, yielding a basic solution.

also undergo hydrolysis. For example, dissolving () in water is accompanied by hydrolysis to give and , the sulfuric acid's . For a more technical discussion of what occurs during such a hydrolysis, see Brønsted–Lowry acid–base theory.


Esters and amides
Acid–base-catalysed hydrolyses are very common; one example is the hydrolysis of or . Their hydrolysis occurs when the (a nucleus-seeking agent, e.g., water or hydroxyl ion) attacks the carbon of the of the or . In an aqueous base, hydroxyl ions are better nucleophiles than polar molecules such as water. In acids, the carbonyl group becomes protonated, and this leads to a much easier nucleophilic attack. The products for both hydrolyses are compounds with groups.

Perhaps the oldest commercially practiced example of ester hydrolysis is (formation of soap). It is the hydrolysis of a (fat) with an aqueous base such as (NaOH). During the process, 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 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 converts into a and an or (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 gives .

Many polymers such as nylon 6,6 hydrolyze in the presence of strong acids. The process leads to . 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.


ATP
Hydrolysis is related to energy metabolism and storage. All living cells require a continual supply of energy for two main purposes: the of micro and macromolecules, and the active transport of ions and molecules across cell membranes. The energy derived from the of nutrients is not used directly but, by means of a complex and long sequence of reactions, it is channeled into a special energy-storage molecule, adenosine triphosphate (ATP). The ATP molecule contains linkages (bonds formed when two phosphate units are combined) that release energy when needed. ATP can undergo hydrolysis in two ways: Firstly, the removal of terminal phosphate to form adenosine diphosphate (ADP) and inorganic phosphate, with the reaction:

ATP + H2O -> ADP + P_{i}

Secondly, the removal of a terminal diphosphate to yield adenosine monophosphate (AMP) and . 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.


Polysaccharides
can be linked together by , which can be cleaved by hydrolysis. Two, three, several or many monosaccharides thus linked form , , , or , respectively. Enzymes that hydrolyze glycosidic bonds are called "glycoside hydrolases" or "glycosidases".

The best-known disaccharide is (table sugar). Hydrolysis of sucrose yields and . is a used industrially for the hydrolysis of sucrose to so-called . is essential for digestive hydrolysis of 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 . Malt made from is used as a source of β-amylase to break down into the disaccharide , which can be used by yeast to . Other enzymes may convert starch to glucose or to oligosaccharides. is first hydrolyzed to by and then cellobiose is further hydrolyzed to by . such as cows are able to hydrolyze cellulose into cellobiose and then glucose because of bacteria that produce cellulases.


DNA
Hydrolysis of 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 bases turn over every day due to hydrolytic depurination, and that this is largely counteracted by specific rapid processes. Hydrolytic DNA damages that fail to be accurately repaired may contribute to and .


Metal aqua ions
Metal ions are , and in they form metal aquo complexes of the general formula .
(1978). 9780853120278, Ellis Horwood.
(1997). 9780471970583, Wiley.
The aqua ions undergo hydrolysis, to a greater or lesser extent. The first hydrolysis step is given generically as

M(H2O)_\mathit{n}^{\mathit{m}+}{} + H2O <=> M(H2O)_{\mathit{n}-1}(OH)^{(\mathit{m}-1){}+}{} + H3O+

Thus the aqua behave as acids in terms of Brønsted–Lowry acid–base theory. This effect is easily explained by considering the 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.

(1976). 9780471039853, Wiley.
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 . Solutions of salts such as or in water are noticeably ; the hydrolysis can be suppressed by adding an acid such as , making the solution more acidic.

Hydrolysis may proceed beyond the first step, often with the formation of polynuclear species via the process of . 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 , 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.


Mechanism strategies
, , and can be converted back into by treatment with excess water under acid-catalyzed conditions: ; ; .
(2024). 9780471756149, Wiley.


Catalysis

Acidic hydrolysis
can be applied to hydrolyses.
(2016). 9780128006689 .
in
(2024). 9780128044926
For example, in the conversion of or to .
(1983). 9781475708356
Carboxylic acids can be produced from acid hydrolysis of esters.

Acids catalyze hydrolysis of 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.

(2024). 9780081001356, Woodhead Publishing.

Acid hydrolysis can be utilized in the pretreatment of cellulosic material, so as to cut the interchain linkages in hemicellulose and cellulose.

(2024). 9780123850997, Academic press.


Alkaline hydrolysis
Alkaline hydrolysis usually refers to types of nucleophilic substitution reactions in which the attacking is a . The best known type is : cleaving into salts and alcohols. In , the hydroxide ion nucleophile attacks the carbon. This mechanism is supported by experiments. For example, when with an oxygen-18 labeled ethoxy group is treated with (NaOH), the oxygen-18 is completely absent from the sodium propionate product and is found exclusively in the formed.
(1996). 9780534238322, Brooks/Cole Publishing Company. .

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.


See also
  • Adenosine triphosphate
  • Alkaline hydrolysis (body disposal)
  • Condensation reaction
  • Dehydration reaction
  • Hydrolysis constant
  • Inhibitor protein
  • Polymer degradation
  • Sol–gel polymerisation
  • Thermal hydrolysis

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