Phosphate esters phosphoric anhydride

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. 

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). 

The concepts of destabilization of reactants and stabilization of products described for pyrophosphate also apply for ATP and other phosphoric anhydrides (Figure 3.11). ATP and ADP are destabilized relative to the hydrolysis products by electrostatic repulsion, competing resonance, and entropy. AMP, on the other hand, is a phosphate ester (not an anhydride) possessing only a single phosphoryl group and is not markedly different from the product inorganic phosphate in terms of electrostatic repulsion and resonance stabilization. Thus, the AG° for hydrolysis of AMP is much smaller than the corresponding values for ATP and ADP. 

Phosphoric anhydride will also convert a neutral phosphate ester into the metaphosphate ester 2... 

Problem 13.15 Supply equations for the formation from phosphoric acid of (o) alkyl phosphate esters by reactions with an alcohol, in which each acidic H is replaced and H O is eliminated (6) phosphoric anhydrides on heating to eliminate H,0. 4... 

Also, phosphoric acid forms an extensive series of anhydrides (with P—O—P bonds), which further diversify the number and kind of phosphate esters. The most important phosphate esters are derivatives of mono-, di-, and triphosphoric acid (sometimes classified as ortho-, pyro-, and meta-phos-... 

Derivatives of phosphoric acid, pyrophosphoric acid, and related compounds are very important in biological systems. Pyrophosphoric acid is an anhydride of phosphoric acid. Adenosine triphosphate, an energy carrier that is universally found in living organisms, has a phosphorus dianhydride connected to an adenosine group by a phosphate ester linkage. Phosphorus ester bonds are used to form the polymeric backbone of DNA (see Chapter 27). 

The thiol ester intermediate resulting from oxidation of glyceraldehyde 3-phosphate next reacts with phosphate ion in a nucleophilic acyl substitution step (Section 21.2) to yield 3-phosphoglyceroyl phosphate, a mixed anhydride between a carboxylic acid and phosphoric acid. 

C-O bond and forming a carboxylic ester (Section 21.5), phosphoric anhydrides react with alcohols by breaking a P-O bond and forming a phosphate ester, ROPO ". Note that phosphorylation reactions with ATP generally require the presence of a divalent metal cation in the enzyme, usually Mg ", to form a Lewis acid/base complex with the phosphate oxygen atoms and neutralize some negative charge. 

ATP consists of a nitrogenous base (adenine) and a phosphate ester of the five-carbon sugar ribose (Figure 15.5). The triphosphate group attached to libose is made up of three phosphate groups bonded to one another by phosphoric anhydride bonds. When two phosphate groups react with one another, a water molecule is lost. Because water is lost, the resulting bond is called a phosphoric anhydride, or phosphoanhydride, bond. 

An alcohol can react with phosphoric acid to produce a phosphate ester iphosphoester). When two phosphate groups are joined, the resulting bond is a phosphoric anhydride bond. These two functional groups are important to the structure and fimction o( adenosine triphosphate (ATP), the universal energy currency of all cells. Cellular enzymes can carry out a reaction between a thiol and a carboxylic acid to produce a thioester. This reaction is essential for the activation of acyl groups in carbohydrate and fatty acid metabolism. Coenz)une A is the most important thiol involved in these pathways. 

Isooctyl alcohol phosphate, potassium salt EINECS 271-944-0 Isooctyl alcohol phosphate, potassium salt Isooctyl alcohol, phosphoric anhydride condensation product, potassium salt Isooctyl phosphate, potassium salt. Phosphoric acid, isooctyl ester, potassium salt... 

As noted in the introduction, the effects of multiple modes of catalysis are often multiplicative rather than simply additive. Consequently, it is not surprising that a number of hydrolytic metalloenzymes have evolved that utilize a constellation of three metal ions in catalysis. Perhaps not coincidentally, all well-characterized examples of this class catalyze the hydrolytic cleavage of phosphate ester or phosphoric acid anhydride bonds, which represent a difficult and long-standing chemical problem. In every case but one, the metal ions in the trimetal centers are all zinc. As we shall see, alkaline phosphatase utilizes a Zn2Mg trinuclear center. It should be pointed out that in the older literature many of the enzymes discussed in this section have been described as containing dinuclear metal centers. Only in the last few years has it become clear that three metal ions are present and participate in catalysis by these systems. 

Trimellitates are the esters of trimellitic anhydride (1,2,4-benzenetricarboxy-lic acid anhydride) and are noted for their low volatility. The most frequently used are trioctyl trimellitate (TOTM) and tri-isononyl trimellitate (TINTM). They are included in plastics which have to function at high temperatures for long periods and for PVC cable insulation in combination with phthalates. Phosphorous oxychloride reacts with various aliphatic and aromatic alcohols and phenols (triphenylphosphate) to produce triesters. Tricresyl phosphate was patented as a plasticizer for PVC in 1933, but was later found to be highly toxic and replaced. In addition to their role as plasticizers, phosphate esters, particularly triphenyl phosphate, function as flame retardants. 

As we study key compounds in the storage and transfer of chemical energy in living systems (Chapter 12), we will encounter phosphate esters in which two or three phosphate groups are linked. These phosphoric anhydrides are referred to as diphosphates and triphosphates. 

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