Biological hydrolysis is the cleavage ofbiomolecules where a water molecule is consumed to effect the separation of a larger molecule into component parts. When acarbohydrate is broken into its component sugar molecules by hydrolysis (e.g.,sucrose being broken down intoglucose andfructose), this is recognized assaccharification.[2]
Hydrolysis reactions can be the reverse of acondensation 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.[3]
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 ahydrogen ion. It breaks a chemical bond in the compound.
A common kind of hydrolysis occurs when asalt of aweak acid orweak base (or both) is dissolved in water.Water spontaneously ionizes intohydroxide anions andhydronium cations. The salt also dissociates into its constituent anions and cations. For example,sodium acetate dissociates in water intosodium andacetate ions. Sodium ions react very little with the hydroxide ions whereas the acetate ions combine with hydronium ions to produceacetic acid. In this case the net result is a relative excess of hydroxide ions, yielding a basicsolution.
Acid–base-catalysed hydrolyses are very common; one example is the hydrolysis ofamides oresters. Their hydrolysis occurs when thenucleophile (a nucleus-seeking agent, e.g., water or hydroxyl ion) attacks the carbon of thecarbonyl group of theester oramide. 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 withcarboxylic acid groups.
Perhaps the oldest commercially practiced example of ester hydrolysis issaponification (formation of soap). It is the hydrolysis of atriglyceride (fat) with an aqueous base such assodium hydroxide (NaOH). During the process,glycerol is formed, and thefatty acids 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 ofenzymes. The catalytic action of enzymes allows the hydrolysis ofproteins, fats, oils, andcarbohydrates. As an example, one may considerproteases (enzymes that aiddigestion by causing hydrolysis ofpeptide bonds inproteins). They catalyze the hydrolysis of interior peptide bonds in peptide chains, as opposed toexopeptidases (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 ashormones, and therefore the biological system continues to function normally.
Mechanism for acid-catalyzed hydrolysis of an amide.
Upon hydrolysis, anamide converts into acarboxylic acid and anamine orammonia (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 ofpeptides givesamino acids.
Manypolyamide polymers such asnylon 6,6 hydrolyze in the presence of strong acids. The process leads todepolymerization. For this reason nylon products fail by fracturing when exposed to small amounts of acidic water. Polyesters are also susceptible to similarpolymer degradation reactions. The problem is known asenvironmental stress cracking.
Hydrolysis is related toenergy metabolism and storage. All living cells require a continual supply of energy for two main purposes: thebiosynthesis of micro and macromolecules, and the active transport of ions and molecules across cell membranes. The energy derived from theoxidation 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 containspyrophosphate 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 formadenosine diphosphate (ADP) and inorganic phosphate, with the reaction:
ATP + H2O → ADP + Pi
Secondly, the removal of a terminal diphosphate to yieldadenosine monophosphate (AMP) andpyrophosphate. 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 hydrolysis of polysaccharides to soluble sugars can be recognized assaccharification.[2] Malt made frombarley is used as a source of β-amylase to break downstarch into the disaccharidemaltose, which can be used by yeast toproduce beer. Otheramylase enzymes may convert starch to glucose or to oligosaccharides.Cellulose is first hydrolyzed tocellobiose bycellulase and then cellobiose is further hydrolyzed toglucose bybeta-glucosidase.Ruminants such as cows are able to hydrolyze cellulose into cellobiose and then glucose because ofsymbiotic bacteria that produce cellulases.
Hydrolysis ofDNA occurs at a significant rate in vivo.[4] For example, it is estimated that in each human cell 2,000 to 10,000 DNApurine bases turn over every day due to hydrolytic depurination, and that this is largely counteracted by specific rapidDNA repair processes.[4] Hydrolytic DNA damages that fail to be accurately repaired may contribute tocarcinogenesis andageing.[4]
Metal ions areLewis acids, and inaqueous solution they formmetal aquo complexes of the general formulaM(H2O)nm+.[5][6] The aqua ions undergo hydrolysis, to a greater or lesser extent. The first hydrolysis step is given generically as
M(H2O)nm+ + H2O ⇌ M(H2O)n−1(OH)(m−1)+ + H3O+
Thus the aquacations behave as acids in terms ofBrønsted–Lowry acid–base theory. This effect is easily explained by considering theinductive effect of the positively charged metal ion, which weakens theO−H bond of an attached water molecule, making the liberation of a proton relatively easy.
Thedissociation constant, pKa, for this reaction is more or less linearly related to the charge-to-size ratio of the metal ion.[7] Ions with low charges, such asNa+ are very weak acids with almost imperceptible hydrolysis. Large divalent ions such asCa2+,Zn2+,Sn2+ andPb2+ have a pKa of 6 or more and would not normally be classed as acids, but small divalent ions such asBe2+ undergo extensive hydrolysis. Trivalent ions likeAl3+ andFe3+ are weak acids whose pKa is comparable to that ofacetic acid. Solutions of salts such asBeCl2 orAl(NO3)3 in water are noticeablyacidic; the hydrolysis can besuppressed by adding an acid such asnitric acid, making the solution more acidic.
Hydrolysis may proceed beyond the first step, often with the formation of polynuclear species via the process ofolation.[7] Some "exotic" species such asSn3(OH)2+4[8] are well characterized. Hydrolysis tends to proceed aspH rises leading, in many cases, to the precipitation of a hydroxide such asAl(OH)3 orAlO(OH). These substances, major constituents ofbauxite, are known aslaterites 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.
Acetals,imines, andenamines can be converted back intoketones by treatment with excess water under acid-catalyzed conditions:RO·OR−H3O−O;NR·H3O−O;RNR−H3O−O.[9]
Acids catalyze hydrolysis ofnitriles to amides. Acid hydrolysisdoes not usually refer to the acid catalyzed addition of the elements of water to double or triple bonds byelectrophilic addition as may originate from ahydration reaction. Acid hydrolysis is used to prepare monosaccharide with the help ofmineral acids but formic acid andtrifluoroacetic acid have been used.[15]
Acid hydrolysis can be utilized in the pretreatment of cellulosic material, so as to cut the interchain linkages in hemicellulose and cellulose.[16]
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 todispose of human and other animal remains as an alternative to traditional burial or cremation.
^abcLindahl T. Instability and decay of the primary structure of DNA. Nature. 1993 Apr 22;362(6422):709-15. doi: 10.1038/362709a0. PMID 8469282
^Burgess, John (1978).Metal Ions in Solution. Chichester: Ellis Horwood.ISBN978-0853120278.
^Richens, D. T. (1997).The Chemistry of Aqua Ions: Synthesis, Structure, and Reactivity: A Tour through the Periodic Table of the Elements. Wiley.ISBN0-471-97058-1.
^abBaes, Charles F.; Mesmer, Robert E. (1976).The Hydrolysis of Cations. New York: Wiley.ISBN9780471039853.
^US 5726046, Farone, William A. & Cuzens, John E., "Method of producing sugars using strong acid hydrolysis", published 1998-03-10, assigned to Arkenol Inc.
^Vaughn, H. L.; Robbins, M. D. (April 1975). "Rapid procedure for the hydrolysis of amides to acids".The Journal of Organic Chemistry.40 (8):1187–1189.doi:10.1021/jo00896a050.
