P-linkage

Cellulose and amylose are comprised of the same glucose subunits as the cyclodexttins. In the case of cellulose, the glucose units are attached through 1,4-P-linkages resulting ia a linear polymer. In the case of amylose, the 1,4-a-linkages, as are found ia the cyclodexttins, are thought to confer heUcity to the polymeric chain. 

Condensed phosphates are derived by dehydration of acid orthophosphates. The resulting polymeric stmctures are based on a backbone of P—O—P linkages where PO tetrahedra are joined by shared oxygen atoms. The range of materials within this classification is extremely broad, extending from the simple diphosphate, also known as pyrophosphate, to indefinitely long-chain polyphosphates and ultraphosphates (see Table 1). Both weU-defined crystalline and amorphous materials occur among the condensed phosphates. 

Pyrophosphates. The simplest linear condensed phosphates are pyrophosphates, which can be considered as the dehydration product of two orthophosphate groups. A water molecule is eliniinated to form a P—O—P linkage in a reversible reaction. 

Hydrolysis. Condensed phosphates all exhibit hydrolytic instabiUty of the P—O—P linkages and, under the appropriate conditions, can all be... 

Like P—O—C linkages, P—O—P linkages are susceptible to hydrolytic degradation. Scrambling or interchange usually occurs for phosphoms oxyesters at temperatures and acidities lower than those required for the carbon esters but greater than those for the sulfur esters. 

The alkah metal phosphides of formula M P and the alkaline-earth phosphides of formula M2P2 contain the P anion. Calcium diphosphide [81103-86-8] CaP2, contains P reaction with water Hberates diphosphine and maintains the P—P linkage. 

Cellulase The enzyme that cuts the linear chain of cellulose, a glucose polymer at 1-4-p-linkages into cellodextrins and glucose. 

Ta 1.5 X 10 2, K3 2.1 X 10 and 2.4 x and the corresponding negative logarithms are pA" 1.0, pA"2 1.8, pA"3 6.57 and pA"4 9.62. The P—O—P linkage is kinetically stable towards hydrolysis in dilute neutral solutions at room temperature and the reaction half-life can be of the order of years. Such hydrolytic breakdown of polyphosphate is of considerable importance in certain biological systems and has been much studied. Some factors which affect the rate of degradation of polyphosphates are shown in Table 12.10. 

Successful strategies for generating complexes of the di(terf-butyl)phosphate ligand primarily focus on the use of H0P(0)(0 Bu)2 as a reagent. As with the related siloxide species, all synthetic manipulations must be performed under inert conditions to avoid hydrolysis of the M - O - P linkages. Complexes of the - 02P(0 Bu)2 ligand are useful precursors to M/P/0 oxide materials. 

The most important of these are the refractory cements formed by the heat treatment of aluminium acid phosphate solutions. This subject has been well reviewed by Kingery (1950a), Morris et al. (1977), Cassidy (1977) and O Hara, Duga Sheets (1972). The chemistry of these binders is extremely complex as the action of heat on acid phosphates gives rise to polymeric phosphates, with P-O-P linkages, and these are very complex systems (Ray, 1979). 

A process using a microbially gelled biopolymer was developed and used to modify the permeability in coreflood experiments [128]. Curdlan is a microbial carbohydrate with 1,3-P-linkages. Alkaline-soluble curdlan biopolymer was... 

Figure 17-5. Amylose, cellulose. Amylose consists of a water-soluble portion, a linear polymer of glucose, the amylose and a water-insoluble portion, the amylopectin. The difference between amylose and cellulose is the way in which the glucose units are linked. In amylose, a-linkages are present, whereas in cellulose, p-linkages are present. Because of this difference, amylose is soluble in water and cellulose is not. Chemical modification allows cellulose to become water soluble.

Bisphosphonic acids and their salts are analogs of pyrophosphate where the P-O-P linkage of the latter has been replaced by P-C-P. Bisphosphonates are known to inhibit bone resorption, and have attracted much attention as potential therapeutic agents. Bisphosphonates do not absorb or fluoresce, and sample matrix interferences can make detection difficult, especially in biological samples. Successful applications of IEC to bisphosphonate analysis have been described.173174... 

Figure 2 Schematic representations of the Olin polymers 2 (with —P—O—P— linkages), 3 and 4 (DEXSIL carborane polymers), and 5 (carborane polymers with tin bridges). (Adapted from ref. 7.)...

A structural compromise between these two types of compound can also give products with sequestering properties, although they are phosphonates rather than phosphates, since they contain C-P rather than C-O-P linkages. Examples of these aminopolyphosphonates are ... 

The generation of aromatic C-P linkages can be accomplished by the reaction of dialkyl phosphites with quinones in the presence of catalytic amounts of acetic acid.449 Excellent yield of the mono-phosphorus product is reported using benzene as the solvent. 

In this chapter, we consider two aspects of carbon-phosphorus bond formation as they relate to pentacoordinated phosphorus species. The first aspect is the preparation of stable phosphorane species — compounds bearing five bonds to phosphorus with at least one of them being a C-P linkage. At present, this is an area of rather specialized interest, but one that has potential for broader applications. 

The earliest developments in transition metal-assisted formation of aromatic C-P linkages were the result of the efforts of Tavs28 that were concerned with the use of Ni(II) halide salts for the reaction of aryl halides with trialkyl phosphites. These reactions involved conditions reminiscent of the Michaelis-Arbuzov reaction (heating at an elevated temperature) and produced arylphosphonate products in reasonable yield (Figure 6.8). 

Figure 6.12 Friedel-Crafts approach toward formation of an aryl C-P linkage.

Figure 6.26 Phosphorus acid in formation of a vinylic C-P linkage.

Some interatomic distances in the two forms of the molecule are compared in Table 1. Fc and Fc represent the haem groups in the two p-chains, Fog and Fe the haem groups in the two a-chains and Hg, and Hgg the heavy atom positions near to the reactive sulphhydryl groups of the 3-cliains. These distances are identical, within experimental error, except for Fcj - Fcg and Fcj —Fe, which represent the p—p linkage and one of the a--p linkages. It is interesting to note that the second a--p... 

The structural and chemical diversity of compounds containing the Si-N-P linkage is a result of both the variety of coordination numbers which phosphorus may assume and the reactivity of the Si-N bond. The combination of these features gives Si-N-P compounds very promising synthetic utility, particularly in the area of inorganic polymer synthesis. 

The simple definition of chitinase activity, EC 3.2.1.14, "hydrolysis of iV-acetyl-D-glucosaminide (l-4)-P-linkages in chitin and chitodextrins", belies the complexity and diversity of this group of enzymes. When chitinolytic organisms are investigated in detail, they are found to produce a range of chitinase activities. Usually these can be separated readily by chromatography or electrophoresis. However, it is more difficult to define their precise activities, chiefly because of the uncertain nature of the available assays for chitinases, with non-linear time courses... 

Endo-chitinases randomly catalyse hydrolysis of iV-acetylglucosaminide (l-4)-P-linkages of chitin chains. 

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