Pyrophosphates, formation using

Far less than the stoichiometric amount of sequestrants precipitation of insoluble salts from water hardness can be prevented by slowing down the formation of crystals and crystal growth. This process is called the threshold effect. It has long been used in the preparation of boiler feeding water, e.g., steam vessels of railroad engines. Originally sodium pyrophosphate was used for this task, but alkylphosphonic acids and derivatives thereof are superior in their effect. 

Thiamin itself (in the absence of enzyme) had previously been shown to catalyse the formation of acetoin from acetaldehyde, albeit in very poor yield (Ukai et al., 1943 Mizuhara et al., 1951 Mizuhara and Handler, 1954). The reaction parallels the formation of benzoin from benzaldehyde, catalysed by cyanide ion. The mechanism of the latter reaction had been suggested in 1903 by Arthur Lapworth, who had shown how an aldehyde, R—CHO, could be converted into the equivalent of the anion R—C=0- (Lapworth, 1903). It is this idea that Breslow carried over to thiamin pyrophosphate and used to... 

The BOP- or PyBOP-mediated SPPS of phosphinot or phosphono peptides can be carried out without protecting the phosphinic or phosphonic acid group. Indeed, phosphinic acids are activated, but the P—N bond is not formed. Phosphonic acids are also acti-vatedt and in fact an amide of methyl phenylphosphonic acid has been obtained, however, in the case of protected a-amino phosphonic acids, phosphonamides are only obtained by using AT-phthalyl protection. Side-chain unprotected phosphorylated tyrosine [Tyr(P03H2)] can be coupled by solid-phase synthesis using BOP (PyBOP), but pyrophosphate formation is also observed and some particular Tyr(P)-peptide syntheses are prone to total failure. ... 

However, the Japanese group has noted partial cleavage of the diisopropylsi-lanediyl linkage under the acidic conditions needed for the DMTr group removal [245, 247]. To circumvent this nuisance, Kobori et al. [247] have prepared a highly cross-linked polystyrene-supported phenyldiisopropylsilyl ether linker that proved to be completely stable to detritylation and used it successfully for oligonucleotide synthesis without N-protection by O-selective phosphoramidite chemistry [246] and pyrophosphate formation on solid phase [248]. The anchor can be cleaved under almost neutral conditions by 1M TBAF-AcOH in THF (90% release after 1 h) or 0.2 M triethylamine trihydrofluoride in the presence of 0.4 M triethylamine for 4h. 

Infrared spectra of hydroxyapatite (Ca,o(P04)6(OH)2), octacalcium phosphate (CagH2(P04)6-5H20X and pyrolyzed octacalcium phosphate have been studied by Fowler et al. (1966). They investigated by means of infrared techniques, weight loss of sample, and pyrophosphate analysis the conditions under which pyrophosphate formation according to either of the following two reactions would be sufficiently quantitative so that it could be used to measure the amount of octacalcium phosphate in an apatitic sample ... 

An alternative synthesis, which eliminates pyrophosphate formation, promotes cyclization by generation of a potent alkoxide nucleophile. The base used for this purpose is one of the most potent known potassium tert-butoxide in dimethyl sulfoxide. Of course, the presence of a good leaving group is also necessary ... 

Analgesic tablets are ground into a fine powder, dissolved in HCl, and analyzed for calcium by atomic absorption. A releasing agent of La + is used to prevent an interference due to the formation of calcium pyrophosphate. 

A variety of shale-protective muds are available which contain high levels of potassium ions (10). The reaction of potassium ions with clay, well known to soil scientists, results in potassium fixation and formation of a less water-sensitive clay. Potassium chloride, potassium hydroxide, potassium carbonate [584-08-7] (99), tetrapotassium pyrophosphate [7320-34-5] (100), and possibly the potassium salts of organic acids, such as potassium acetate [127-08-2] (101) and formate, have all been used as the potassium source. Potassium chloride is generally preferred because of its low cost and availabihty. 

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 ... 

Condensation of CO2, ammonia, and ATP to form carbamoyl phosphate is catalyzed by mitochondrial carbamoyl phosphate synthase I (reaction 1, Figure 29-9). A cytosolic form of this enzyme, carbamoyl phosphate synthase II, uses glutamine rather than ammonia as the nitrogen donor and functions in pyrimidine biosynthesis (see Chapter 34). Carbamoyl phosphate synthase I, the rate-hmiting enzyme of the urea cycle, is active only in the presence of its allosteric activator JV-acetylglutamate, which enhances the affinity of the synthase for ATP. Formation of carbamoyl phosphate requires 2 mol of ATP, one of which serves as a phosphate donor. Conversion of the second ATP to AMP and pyrophosphate, coupled to the hydrolysis of pyrophosphate to orthophosphate, provides the driving... 

The substrate specificity of farnesyl pyrophosphate synthetase has been studied using 3-methyl-2-aIkenyl pyrophosphates (90) as models. When (90) bears a large side-chain i.e. R = C4H9), the reaction with isopentenyl pyrophosphate ceases after the formation of (91) and this reaction has been... 

Solution pH is an important variable, as it controls solubility, the deposition potential, and precursor speciation [140], As noted, one of the advantages of using an ALE process is that very different solutions can be used for each step in the cycle. For instance, pH 4 Cd solutions have been used with pH 10 Te solutions to form CdTe. Some care must be taken rinsing between solutions, however. On the other hand, Foresti et al. have used the same pH for both the metal and chalcogenide in the formation of II-VI compounds, such as CdS and CdSe on Ag single crystals [115, 116, 123, 143], To keep the Cd from precipitating in the basic solution, they complexed it with pyrophosphate. 

For reactions that make PP (pyrophosphate), the PP, is rapidly hydrolyzed to 2 P in the cell, so we ll consider the formation of PP to use 2 high-energy-phosphate bonds. 

One of the important consequences of studying catalysis by mutant enzymes in comparison with wild-type enzymes is the possibility of identifying residues involved in catalysis that are not apparent from crystal structure determinations. This has been usefully applied (Fersht et al., 1988) to the tyrosine activation step in tyrosine tRNA synthetase (47) and (49). The residues Lys-82, Arg-86, Lys-230 and Lys-233 were replaced by alanine. Each mutation was studied in turn, and comparison with the wild-type enzyme revealed that each mutant was substantially less effective in catalysing formation of tyrosyl adenylate. Kinetic studies showed that these residues interact with the transition state for formation of tyrosyl adenylate and pyrophosphate from tyrosine and ATP and have relatively minor effects on the binding of tyrosine and tyrosyl adenylate. However, the crystal structures of the tyrosine-enzyme complex (Brick and Blow, 1987) and tyrosyl adenylate complex (Rubin and Blow, 1981) show that the residues Lys-82 and Arg-86 are on one side of the substrate-binding site and Lys-230 and Lys-233 are on the opposite side. It would be concluded from the crystal structures that not all four residues could be simultaneously involved in the catalytic process. Movement of one pair of residues close to the substrate moves the other pair of residues away. It is therefore concluded from the kinetic effects observed for the mutants that, in the wild-type enzyme, formation of the transition state for the reaction involves a conformational change to a structure which differs from the enzyme structure in the complex with tyrosine or tyrosine adenylate. The induced fit to the transition-state structure must allow interaction with all four residues simultaneously. 

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