Phosphate esters specifications

ANTARA anionics are complex phosphate esters specifically developed for use as extreme pressure additives for metal working fluids. 

The largest volume of hydrauHc fluids are mineral oils containing additives to meet specific requirements. These fluids comprise over 80% of the world demand (ca 3.6 x 10 L (944 x 10 gal))- In contrast world demand for fire-resistant fluids is only about 5% of the total industrial fluid market. Fire-resistant fluids are classified as high water-base fluids, water-in-oil emulsions, glycols, and phosphate esters. Polyolesters having shear-stable mist suppressant also meet some fire-resistant tests. 

Dialkylphosphorochloridates, (R0)2P(=0)C1, react with trialkyl phosphate esters to give organic pyrophosphates. Organopyrophosphates are anticholinesterase agents and should be handled with great caution (16). Atropine sulfate is a specific antidote. 

Three types of synthases catalyze the addition of phosphoenolpyruvate (PEP) to aldoses or the corresponding terminal phosphate esters. By concurrent release of inorganic phosphate from the preformed enolate nucleophile, the additions are essentially irreversible. None of the enzymes are yet commercially available and little data are available oil the individual specificities for the aldehydic substrates. A bacterial NeuAc synthase (EC 4.1.3.19) has been used for the microscale synthesis of A -acetylncuraminic acid from Af-acetyl-D-mannosamine31 and its 9-azido analog from 2-acetamido-6-azido-2,6-dideoxy-D-mannose32. 

The contractile apparatus may be thought of as the sum of those intracellular components which constitute the machinery of chemomechanical transduction. It is the set of proteins which convert the chemical energy of the terminal phosphate ester bond of ATP into mechanical work. The structure of the contractile apparatus is determined by the connections between the various protein molecules via specific binding sites or, in a minority of cases, via labile covalent linkages. The kinetics of the contractile machinery are determined by the regulation of changes in these connections. 

Furthermore, the GPO procedure can also be used for a preparative synthesis of the corresponding phosphorothioate (37), phosphoramidate (38), and methylene phosphonate (39) analogs of (25) (Figure 10.20) from suitable diol precursors [106] to be used as aldolase substrates [102]. In fact, such isosteric replacements of the phosphate ester oxygen were found to be tolerable by a number of class I and class II aldolases, and only some specific enzymes failed to accept the less polar phosphonate (39) [107]. Thus, sugar phosphonates (e.g. (71)/(72)) that mimic metabolic intermediates but are hydrolytically stable to phosphatase degradation can be rapidly synthesized (Figure 10.28). 

The first commercial trialkyl phosphate esters (TAP) were tricresyl phosphate (TCP) and trixylenyl phosphate (TXP), referred to as "natural" phosphate esters because the cresols and xylenols used as raw materials are derived from petroleum oil or coal tar (Marino and Placek 1994). These products are not commercially significant at present however, at waste disposal sites, contaminants from older product formulations may be encountered, particularly those containing the neurotoxic tri-o/T/io-cresyl phosphate isomer. "Synthetic" phosphate esters are derived from synthetic feedstocks. Specific synthetic reactions have been developed to produce triaryl, trialkyl, and alkyl Aryl esters. The triaryl phosphates are currently... 

Enzymes that react with a specific type of ester linkage are known as general hydrolysing enzymes. Thus lipases hydrolyse a wide range of organic esters. Generally, phosphatases will break down phosphate esters into phosphoric acid and an alcohol. 

Collectors from the PM series were specifically developed for beneficiation of niobium ores that contain nepheline/cyanite as the major gangue minerals. The collector is composed of a mixture of phosphate ester collector (SM15, Clariant) and phosphonic acid treated with octanol. From an ore that assays 0.5% Nb20s, a concentrate grade of 49% Nb205 at a recovery of 73% was achieved. 

Identification of the energy source for muscle contraction and determination of the order in which the phosphate esters were metabolized was helped by the use of inhibitors. These inhibitors blocked different stages in glycolysis and caused preceding substrates to accumulate in quantities which could greatly exceed those normally present. The compounds were then isolated, identified, and used as specific substrates to identify the enzymes involved in their metabolism. Iodoacetic acid (IAc) was one of the most important inhibitors used to analyze glycolysis. 

A different application of visible microscopy was pioneered by Gomori. In 1941 he showed that alkaline phosphatase could be specifically located by its hydrolysis of soluble phosphate esters (initially glycerophosphate). If calcium ions were present in the medium in which the sections were incubated, insoluble calcium phosphate precipitated as a result of the action of the hydrolase. The site of the precipitate could be visualized if cobalt or lead salts were subsequently added to replace calcium and the sections exposed to hydrogen sulfide. In principle many hydrolases and other enzymes could be studied using the appropriate substrates and precipitants. It was important to ensure that the products of the enzyme reactions did not diffuse from the sites where the enzymes were located. It was also essential that the reagents could reach the enzyme site. 

Fig. 2.10. Change in charge state of proteins via phosphorylation. The phosphorylation of Ser residues is catalyzed by a Ser/Thr-specific kinase that utilizes ATP as the phosphate group donor. The product of the reaction is a Ser-phosphate ester which carries a net charge of -2 at physiological pH.

The phosphate ester of Ser, Thr, or Tyr residues are quite stable at room temperature and neutral pH the rate of spontaneous hydrolysis is very low. Therefore, to remove the phosphate residue the cell utilizes specific enzymes termed phosphatases. Based on substrate specificity, these can be classified as Ser-, Thr- or Tyr-specific phosphatases (see chapter 8). 

Tyr-specific protein kinases create a phosphate ester with the phenolic OH group of Tyr residues. 

Under physiological conditions, phosphate esters of Ser and Thr residues are stable and only show a low rate of spontaneous hydrolysis. Thus, the cell requires its own tools for regulated cleavage of phosphate residues, to terminate and damp signals mediated by protein phosphorylation. This role is performed by specific protein phosphatases. 

Milk acid phosphatase has been purified to homogeneity by various forms of chromaotgraphy, including affinity chromatography purification up to 40 000-fold has been claimed. The enzyme shows broad specificity on phosphate esters, including the phosphoseryl residues of casein. It has a molecular mass of about 42 kDa and an isoelectric point of 7.9. Many forms of inorganic phosphate are competitive inhibitors, while fluoride is a powerful non-competitive inhibitor. The enzyme is a glycoprotein and its amino acid composition is known. Milk acid phosphatase shows some similarity to the phosphoprotein phosphatase of spleen but differs from it in a number of characteristics. 

One of the most studied examples of signaling with membrane lipids is provided by the phospho-inositide cascade, which is pictured in Fig. 11-9. Six or more phosphate esters of phosphatidylinositol (PI) are generated by the action of kinases.219 220 More than 100 extracellular signaling molecules activate specific isozyme forms of phospholipase C,221-224 releasing 20 or more different inositol phosphates from these... 

The preceding experiments prove that there is an intermediate on the reaction pathway in each case, the measured rate constants for the formation and decay of the intermediate are at least as high as the value of kcat for the hydrolysis of the ester in the steady state. They do not, however, prove what the intermediate is. The evidence for covalent modification of Ser-195 of the enzyme stems from the early experiments on the irreversible inhibition of the enzyme by organo-phosphates such as diisopropyl fluorophosphate the inhibited protein was subjected to partial hydrolysis, and the peptide containing the phosphate ester was isolated and shown to be esterified on Ser-195.1516 The ultimate characterization of acylenzymes has come from x-ray diffraction studies of nonspecific acylenzymes at low pH, where they are stable (e.g., indolylacryloyl-chymotrypsin),17 and of specific acylenzymes at subzero temperatures and at low pH.18 When stable solutions of acylenzymes are restored to conditions under which they are unstable, they are found to react at the required rate. These experiments thus prove that the acylenzyme does occur on the reaction pathway. They do not rule out, however, the possibility that there are further intermediates. For example, they do not rule out an initial acylation on His-57 followed by rapid intramolecular transfer. Evidence concerning this and any other hypothetical intermediates must come from additional kinetic experiments and examination of the crystal structure of the enzyme. 

The activity of the enzyme from the various organisms for a variety of phosphate esters is given in Table I. The enzyme is highly specific... 

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