Inorganic phosphate chemistry

The usual two-component diagram is plotted on rectangular coordinate graph paper. Temperature is usually the vertical axis while the relative percents of the components are plotted along the horizontal axis. The components may be molecules, salts, or ions, depending upon the system under study. In inorganic phosphate chemistry, a metal oxide is usually chosen as one component while P2O5 is chosen as a second component. 

Preoperative inorganic phosphate chemistry is not an exact science and rules remain vague, depending often as not on chance, if the systems have never been studied before. The calcium polyphosphate, Tromelite, is a mixture of calcium pentapolyphosphate and hexapolyphosphate. I am unaware of a crystallization technique to prepare directly a soluble hexapolyphosphate as a pure crystalline phase. Hopefully, a melt system will be discovered and this can be accomplished. Hexapolyphosphate can be extracted from acidic mixtures and crystallized as the acridinium salt. All phosphates ever tested by the author can be crystallized as the acridine salt (see Figure 4.1). It was first noted by Quimby that very large cations, such as acridine and guanidine, assisted in crystallizations of condensed phosphates. ... 

It is understood that inorganic phosphate chemistry is anion dominated. Once an anion such as tetrameta-, tripoly-, hexameta-, etc. has been prepared as one of its salts, there is usually very little problem converting it to another cationic species without violating the integrity of an anion. In other words, it is usually not difficult to convert a sodium salt to a potassium salt even though the potassium salt is not a member of any potassium phosphate phases and cannot be crystallized directly from a melt. This is not always true, as will be discussed in Section 6.2.5. 

Pyrite is not only one of the key compounds in Wachtershauser s theory, but could also have fulfilled an important function for phosphate chemistry in prebiotic syntheses. A group in Rio de Janeiro studied the conditions for phosphate sorption and desorption under conditions which may have been present in the primeval ocean. In particular, the question arises as to the enrichment of free, soluble inorganic phosphate (Pi), which was probably present in low concentrations similar to those of today (10 7-10 8M) (Miller and Keffe, 1995). Experiments show that acid conditions favour sorption at FeS2, while a weakly alkaline milieu works in an opposite manner. Sorption of Pi can be favoured by various factors, such as hydrophobic coating of pyrite with molecules such as acetate, which could have been formed in the vicinity of hydrothermal systems, or the neutralisation of mineral surface charges by Na+ and K+. 

Iron is an essential element, for humans and for many forms of life, but even a modest excess can be toxic as the human body does not have an effective iron excretion mechanism. It is therefore necessary to maintain an appropriate level of iron in the body, to supply iron in absorbable form if it is deficient (anemia) and to remove iron if present in excess. Inorganic coordination chemistry plays an important role in dealing with these complementary conditions of deficiency and of excess. The latter condition is much more common than often supposed, for there are a number of conditions, such as hemochromatosis and thallasemia, where the build-up of iron in essential organs is eventually lethal. Mild iron poisoning is not infrequent in children, while even iron fortification of foodstuffs can have adverse effects. Mild iron poisoning can be treated with bicarbonate or phosphate, which presumably complex and precipitate the iron. ... 

HARDEN. SIR ARTHUR (1865-1940). An English chemist who won the Nobel prize in chemistry in 1929 along with Hans von-Euler C helpin. He discovered fermentation enzy mes and demonstrated the structure of zymase, llis fermentation work proved how inorganic phosphates speeded the process. Bora in England, he received his doctorate in Germany. 

Among activated forms of amino acids, mixed anhydrides with inorganic phosphate or phosphate esters require a special discussion because they are universally involved in peptide biosynthesis through the ribosomal and non-ribosomal pathways. These mixed anhydrides have stimulated studies in prebiotic chemistry very early in the history of this field. Amino acyl adenylates 18c have been shown to polymerize in solution [159,160] and in the presence of clays [139]. However, their participation as major activated amino acid species to the prebiotic formation of peptides from amino acids is unlikely for at least two reasons. Firstly, amino acid adenylates that have a significant lifetime in aqueous solution become very unstable as soon as either CO2 or bicarbonate is present at millimolar concentration [137]. Lacey and coworkers [161] were therefore conduced to consider that CO2 was absent in the primitive atmosphere for aminoacyl adenylate to have a sufficient lifetime and then to allow for the emergence of the modern process of amino acid activation and of the translation apparatus. But this proposition is unlikely, as shown by the analysis of geological records in favor of CO2 contents in the atmosphere higher than present levels [128]. It is also in contradiction with most studies of the evolution of the atmosphere of telluric planets [30,32], Secondly, there is no prebiotic pathway available for adenylate formation and ATP proved to be inefficient in this reaction [162]. 

Weber [61,62] has developed in the context of prebiotic chemistry an original pathway for a-aminothioester synthesis [180], which can start from hydroxyaldehydes 30 intermediates in the formose reaction (a likely prebiotic pathway to carbohydrates). Obviously, thioesters themselves are not observed as products because of their fast hydrolysis in the medium, but they could be converted into peptide bonds in the presence of amino acids or peptide free amino groups, and into mixed anhydride with phosphoric acid in the presence of inorganic phosphate. The reaction involves two key-steps the condensation of ammonia and of the mercaptan on a-keto aldehyde 31... 

The appendices contain the thermodynamic data, the solubility product constants that are relevant to CBPC formation or their durability, and formulae of minerals that were discussed in the text. The thermodynamic data of phosphates is difhcult to find in the common literature. Some excellent sources such as Phosphate Minerals by Nriagu and Moore and Inorganic Phosphate Materials by Kanazawa are out of print. The most commonly used data books such as CRC Handbook of Physics and Chemistry do not contain data on most phosphate compounds. For this reason, these appendices are provided to facilitate the discussion in the text and also for the benefit of those who wish to pursue further research in CBPCs. 

At present, there are only a few comprehensive publications on phosphate chemistry, minerals, and materials. Notable ones are Inorganic Phosphate Materials by T. Kanazawa [Kodansha, Tokyo, and Elsevier, Amsterdam (1989)], Phosphate Minerals by J. Nriagu and P. Moore [Springer-Verlag, Berlin (1984)], and a chapter on CBPCs in Acid-Base Cements by A. Wilson and J. Nicholson [Cambridge Univ. Press, Cambridge (1993)]. Much of the background information on phosphate materials is derived from these and other phosphate chemistry books. 

C.E. Bamberger, in A.J. Freeman, C. Keller (Eds), Handbook on the Physics and Chemistry of the Actinides, Chapter 6, Solid Inorganic Phosphates of the Transuranium elements. Elsevier, Amsterdam, 1985, pp. 289-303. 

Nitrogen fixation, denitrification, soil weathering, phosphate fixation, clay mineral degradation, and potassium and transition metal fixation are problems for which the reaction rates are usually as, or more, important than equilibrium. Most soil chemical applications of kinetics have been in soil microbiology and soil biochemistry, where the lack of equilibrium is more obvious. The use of kinetics in inorganic soil chemistry will undoubtedly broaden in the future. It can even be argued that kinetics is basic to thermodynamics, because equilibrium is the condition where opposing reaction rates are equal. 

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