Phosphoric Acid Anhydride

The largest-volume phosphoms compounds are the phosphoric acids and phosphates (qv), ie, the oxide derivatives of phosphoms ia the + 5 oxidation state. With the exception of the phosphoric acid anhydride, P O q, and the phosphate esters, these materials are discussed elsewhere (see Phosphoric acids and phosphates). An overview of phosphoms compounds other than the phosphoric acids and phosphates is given herein. These compounds constitute a large variety of phosphoms compounds that are either nonoxide derivatives or derivatives of phosphoms ia oxidation states lower than + 5. These phosphoms compounds are manufactured only from elemental phosphoms (qv) obtained by reduction of naturally occurring phosphate rock (calcium phosphate). 

Phosphorsaure, /. phosphoric acid, -anhydrid, n. phosphoric anhydride (phosphorus pentoxide). -losimg, /. phosphoric acid solution, -salz, n. phosphate. 

ADP and ATP are both phosphoric acid anhydrides, which contain 0 0 0 0... 

Phosphoric acid anhydride (Section 29.1) A substance that contains P02P0 link, analogous to the C02CO link in carboxylic acid anhydrides. 

Phosphine(s), chirality of, 314 Phosphite, DNA synthesis and, 1115 oxidation of, 1116 Phospholipid, 1066-1067 classification of, 1066 Phosphopantetheine, coenzyme A from. 817 structure of, 1127 Phosphoramidite, DNA synthesis and, 1115 Phosphoranc, 720 Phosphoric acid, pKa of, 51 Phosphoric acid anhydride, 1127 Phosphorus, hybridization of, 20 Phosphorus oxychloride, alcohol dehydration with. 620-622 Phosphorus tribromide, reaction with alcohols. 344. 618 Photochemical reaction, 1181 Photolithography, 505-506 resists for, 505-506 Photon, 419 energy- of. 420 Photosynthesis, 973-974 Phthalic acid, structure of, 753 Phthalimide, Gabriel amine synthesis and, 929... 

Attention has been drawn to the potential of phosphoric acid anhydrides of nucleoside 5 -carboxylic acids (14) as specific reagents for investigating the binding sites of enzymes. For example, (14 B = adenosine) inactivates adenylosuccinate lyase from E. coli almost completely, but has little effect on rabbit muscle AMP deaminase. The rate of hydrolysis of (14) is considerably faster than that of acetyl phosphate, suggesting intramolecular assistance by the 3 -hydroxyl group or the 3-nitrogen atom. 

The only element that was discovered in body fluids (urine). This is plausible, as P plays a main role in all life processes. It is one of the five elements that make up DNA (besides C, H, N, and 0 evolution did not require anything else to code all life). The P-O-P bond, phosphoric acid anhydride, is the universal energy currency in cells. The skeletons of mammals consists of Ca phosphate (hydroxylapatite). The element is encountered in several allotropic modifications white phosphorus (soft, pyrophoric P4, very toxic), red phosphorus (nontoxic, used to make the striking surface of matchboxes), black phosphorus (formed under high pressures). Phosphates are indispensable as fertilizer, but less desirable in washing agents as the waste water is too concentrated with this substance (eutrophication). It has a rich chemistry, is the basis for powerful insecticides, but also for warfare agents. A versatile element. 

When two phosphate residues bond, they do not form an ester, but an energy-rich phosphoric acid anhydride bond, as... 

Phosphoric acid molecules can form acid-anhydride bonds with each other. It is therefore possible for two nucleotides to be linked via the phosphate residues. This gives rise to dinucleotides with a phosphoric acid-anhydride structure. This group includes the coenzymes NAD(P) " and CoA, as well as the flavin derivative FAD (1 see p. 104). 

Acyl residues are usually activated by transfer to coenzyme A (2). In coenzyme A (see p. 12), pantetheine is linked to 3 -phos-pho-ADP by a phosphoric acid anhydride bond. Pantetheine consists of three components connected by amide bonds—pantoic acid, alanine, and cysteamine. The latter two components are biogenic amines formed by the decarboxylation of aspartate and cysteine, respectively. The compound formed from pantoic acid and p-alanine (pantothenic acid) has vitamin-like characteristics for humans (see p. 368). Reactions between the thiol group of the cysteamine residue and carboxylic acids give rise to thioesters, such as acetyl CoA. This reaction is strongly endergonic, and it is therefore coupled to exergonic processes. Thioesters represent the activated form of carboxylic adds, because acyl residues of this type have a high chemical potential and are easily transferred to other molecules. This property is often exploited in metabolism. 

In standard conditions, the change in free enthalpy AG° (see p. 18) that occurs in the hydrolysis of phosphoric acid anhydride bonds amounts to -30 to -35 kj mol at pH 7. The particular anhydride bond of ATP that is cleaved only has a minor influence on AG° (1-2). Even the hydrolysis of diphosphate (also known as pyrophosphate 4) still yields more than -30 kJ mol . By contrast, cleavage of the ester bond between ribose and phosphate only provides -9 kJ mol (3). 

The subsequent cleavage of the thio-ester succinylCoA into succinate and coenzyme A by succinic acid-CoA ligase (succinyl CoA synthetase, succinic thiokinase) is strongly exergonic and is used to synthesize a phosphoric acid anhydride bond ( substrate level phosphorylation , see p. 124). However, it is not ATP that is produced here as is otherwise usually the case, but instead guanosine triphosphate (CTP). However, GTP can be converted into ATP by a nucleoside diphosphate kinase (not shown). 

Energy requirements in protein synthesis are high. Four energy-rich phosphoric acid anhydride bonds are hydrolyzed for each amino acid residue. Amino acid activation uses up two energy-rich bonds per amino acid (ATP AMP + PP see p. 248), and two GTPs are consumed per elongation cycle. In addition, initiation and termination each require one GTP per chain. 

Metal ions have been shown to catalyze the hydrolysis of phosphate esters, phosphoric and phosphonic acid halides, and various phosphoric acid anhydrides including acyl phosphates, pyrophosphate derivatives, and ATP. 

ATP, a phosphoric acid anhydride, is the storehouse for biochemical energy. 

Look at ATP. In the figure the bolded region is the "recognition" part of the molecule, while the polyphosphate is the chemically active portion. Each of the phosphoric acid anhydride bonds is unstable. That is hydrolyzing either will release a lot of energy. 

So why ATP First, we want a compound with intermediate hydrolysis energy so it can pick up energy from some reactions and deliver to others. Second we want a kinetically stable molecule which is thermodynamically unstable. Thus acetic acid anhydride would not work it is thermodynamically unstable to hydrolysis, but it is also kinetically unstable, with the carbonyl carbons wide open to water attack. Phosphoric acid anhydride is equally unstable, but is is sterically protected from water attack - in order to react quickly we need a catalyst -perfect. 

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