Phosphate bond

PhenylPhosphorothioa.te Esters. These are the most widely used OP iasecticides and iacorporate pseudoanhydride high energy phosphate bonds between phosphoric acid and phenols that are present ia the activated P=0 state. 

Dental Phosphate-Bonded Casting Investments, International Standard ISO 9694, American National Standards Institute, New York, 1988. 

Two and twelve moles of ATP are produced, respectively, per mole of glucose consumed in the glycolytic pathway and each turn of the Krebs (citrate) cycle. In fat metaboHsm, many high energy bonds are produced per mole of fatty ester oxidized. Eor example, 129 high energy phosphate bonds are produced per mole of palmitate. Oxidative phosphorylation has a remarkable 75% efficiency. Three moles of ATP are utilized per transfer of two electrons, compared to the theoretical four. The process occurs via a series of reactions involving flavoproteins, quinones such as coenzyme Q, and cytochromes. 

High Alumina Refractories. The desired alumina content, from 100% to just above 45%, is obtained by adding bauxites, synthetic aluminosihcates, and synthetic aluminas to clay and other bonding agents. These refractories are used in kilns, ladles, and furnaces that operate at temperatures or under conditions for which fireclay refractories are not suited. Phosphate-bonded alumina bricks have exceptionally high strength at low to intermediate temperatures and are employed in aluminum furnaces. High alumina and mullite are used in furnace roofs and petrochemical apphcations. 

The precerammed billets, already having appropriate tooth color, are loaded into a dedicated high temperature press and transfer-molded at 1100°C into phosphate-bonded molds. 

Model Investments. Model investments are materials used for noncasting operations in the fabrication of dental protheses. They differ from casting investments in various ways depending on the prosthetic device being constmcted. For low temperature operations, such as soldering, gypsum is used phosphate-bonded materials are employed for higher solder temperatures or for the fabrication of porcelain veneers. 

Veneering Investments. These are phosphate bonded and contain finely ground quart2, 2irconium oxide, and/or titanium oxide to produce highly refractory, low expansion dies of fine detail. The dies are formed within impressions taken of teeth that the dentist has prepared in anticipation of covering the front surface with an aesthetic ceramic veneer. Porcelain or ceramic powders are shaped to detail on the dies and these are fired at high (- 1000° C) temperatures to produce the veneers. The veneers are then cemented to the front surface of the previously prepared teeth. 

Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

The transport of each COg requires the expenditure of two high-energy phosphate bonds. The energy of these bonds is expended in the phosphorylation of pyruvate to PEP (phosphoenolpyruvate) by the plant enzyme pyruvate-Pj dikinase the products are PEP, AMP, and pyrophosphate (PPi). This represents a unique phosphotransferase reaction in that both the /3- and y-phosphates of a single ATP are used to phosphorylate the two substrates, pyruvate and Pj. The reaction mechanism involves an enzyme phosphohistidine intermediate. The y-phosphate of ATP is transferred to Pj, whereas formation of E-His-P occurs by addition of the /3-phosphate from ATP ... 

Plapp FW, Casida JE. 1958. Hydrolysis of the alkyl-phosphate bond in certain dialkyl aryl phosphorothioate insecticides by rats, cockroaches, and alkali. J Econ Entomol 51 800-803. 

Fig. 6.5 Possible interaction between the helical dinuclear Zn(ll)-peptide [33] and DNA which leads to hydrolytic cleavage of the phosphate bond. The structure of the Zn(ll)-ATANP complex is shown in the top right-hand corner...

RNA is as suitable (if not more so) than DNA as a cleavage target [37]. In contrast to DNA, RNA is substantially less prone to oxidative cleavage [38] as a consequence of the higher stability of the glycosidic bond in ribonucleotides compared to that in deoxyribonucleotides. On the basis of the properties described in the introductory sections RNA is by contrast, much less stable to hydrolytic cleavage. For this reason the hydrolysis of the phosphate bond in this system can be successfully catalyzed not only by metal ions but also by ammonium ions. 

The charging of the tRNA molecule with the aminoacyl moiety requires the hydrolysis of an ATP to an AMP, equivalent to the hydrolysis of two ATPs to two ADPs and phosphates. The entry of the aminoacyl-tRNA into the A site results in the hydrolysis of one GTP to GDP. Translocation of the newly formed pep-tidyl-tRNA in the A site into the P site by EF2 similarly results in hydrolysis of GTP to GDP and phosphate. Thus, the energy requirements for the formation of one peptide bond include the equivalent of the hydrolysis of two ATP molecules to ADP and of two GTP molecules to GDP, or the hydrolysis of four high-energy phosphate bonds. A eukaryotic ribosome can incorporate as many as six amino acids per second prokaryotic ribosomes incorporate as many as 18 per second. Thus, the process of peptide synthesis occurs with great speed and accuracy until a termination codon is reached. 

Kingery, W. D. (1950a). Fundamental study of phosphate bonding in refractories. I. Literature review. Journal of the American Ceramic Society, 33, 239 1. 

O Neill, I. K., Prosser, H. J., Richards, C. P. Wilson, A. D. (1982). NMR spectroscopy of dental materials. I. P studies on phosphate-bonded cement liquids. Journal of Biomedical Materials Research, 16, 39-49. 

The phosphate bonded cements described in this chapter are the products of the simple acid-base reaction between an aqueous solution of orthophosphoric acid and a basic oxide or silicate. Such reactions take place at room temperature. Excluded from this chapter are the cementitious substances that are formed by the heat treatment of aqueous solutions of acid metal phosphates. 

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