Phosphate esters conclusion

The half-life of Fe2(OH)2" at room temperature is a few seconds. An improved model for the kinetics of dissociation of this dinuclear cation recognizes significan articipation by Fe2(OH)3 + at higher pHs, thus clearing up earlier slight anomalies in this area. Phosphate ester hydrolysis at the di-iron center of uteroferrin has now been shown to involve nucleophilic attack by bridging hydroxide (as proposed but not conclusively demonstrated for several M—OH—M-containing catalytic species) rather than by hydroxide bonded to just one Fe. ... 

In conclusion, alkaline phosphatase, pyrophosphatase, and a calcium ATPase appear to be the same enzyme. The enzyme has three separate functions (1) breaking down ATP, (2) hydrolysing inorganic pyrophosphate and possibly other phosphate esters, and (3) opening of C—0-P bonds. In this capacity it has a profound impact on transport and regulation of phosphates and calcium, and is involved in biomineralization processes171 173. ... 

Lehn and Wipff (72) and Gorenstein and co-workers (73-80) have proposed on the basis of molecular orbital calculations that stereoelectronic effects similar to those observed in esters and amides play also an important role in the hydrolysis of phosphate esters. For instance, calculations suggest that the axial P — OR bond in the trigonal bipyramid conformation 120 is weaker than that in the conformation 121 because in the former, the oxygen atom of the equatorial OR group has an electron pair anti peri planar to the axial P — OR bond. Experimental results tend to support this interesting proposal but additional experiments are needed before unambiguous conclusions can be reached (81). 

The slow, post-irradiation decrease in viscosity ( after-effect ) was investigated by Daniels, Scholes, Weiss, and Wheeler, who relate this phenomenon to the labilization of phosphate bonds by the intermediate formation of labile phosphate esters. Leading to this conclusion is the observation that about fifteen times as much inorganic phosphate can be obtained by acid hydrolysis of irradiated, aqueous solutions of nucleic acid as is formed directly by the radiation. It is, therefore, thought that, after the labile phosphate esters have been formed, they undergo slow acid hydrolysis, and that this mild hydrolysis occurring at the diester phosphate groups, even... 

For tricresyl phosphate to be effective, oxygen, water and other polar impurities are important for the formation of reaction films. The beneficial influence of water and oxygen indicates that the formation of the reaction film is preceded by the hydrolysis of ester and the release of phosphoric acid which Anally reacts with the surface oxide film. The importance of the polar impurities present in TCP has been demonstrated [26] the probable identity of the important impurity is lauryl acid phosphate, found to be 20 times as effective at wear protection compared to pure tricresyl phosphate. A conclusion is that the ester function of phosphoric acid is necessary only to ensure solubility of the product in oil. TCP can also give rise to anti-rust protection by hydrolysis to phosphoric acid. 

Zinc complexes of the cyclen ([12]aneN4 = 1,4,7,10-tetraazacyclododecane) ligand have been extensively studied in terms of phosphate ester hydrolysis reactivity. For example, a proposed binuclear Zn(II) hydroxide complex of cyclen was reported to enhance the rate of hydrolysis of ethyl(2,4-dinitrophenyl)-methylphosphonate and diethyl(2,4-dinitrophenyl) phosphate.223,224 It should be noted that the nuclearity of the zinc-cyclen complex in solution was not conclusively identified in this work. 

The orders of nucleophilic reactivity for alkylation and acylation were found to be quite different (13, 14) and in subsequent work (15) this finding was related to the extent of bond formation in the transition state as given empirically by the Brpnsted coefficient, (3. Previously, this difference was used to predict the position of bond fission in the alkaline hydrolysis of phosphinate, phosphonate, and phosphate esters (12). Jencks and Carriuolo (16) came to similar conclusions around the same time in outstanding work on the acylation of p-nitrophenyl acetate. 

Much has been reported in recent years about phosphate ester for use as a deflocculant/dispersant for tape casting slips. Phosphate ester is a very powerful dispersant for many oxide powders, including BaTiOg, AI2O3, and TiOg. Phosphate ester is soluble in either water or a number of organic solvents and is described as an anionic surfactant in polar liquids.Overall conclusions about this additive are that it functions both as an ionic repulsion and steric hindrance deflocculant. 

The data and mechanistic conclusions summarized above come from work with aryl phosphomonoesters as predicted by the steep jSlg value, alkyl ester dianions react at very slow rates. A recent study of methyl phosphate found the rate of the dianion hydrolysis to be below the threshold of detectability, with an estimated rate constant of 2 x 10 20 s 1 at 25 °C.3 Since this value is close to the rate predicted from an extrapolation of the Bronsted plot of aryl phosphomonoester dianions, a similar mechanism is likely to be followed for alkyl and aryl esters. 

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