Phosphate compounds, coordinative

Phosphate esters, particularly AMP, ADP and ATP, have vital biological functions and this fact has generated intense interest in their reaction mechanisms. Subtle stereochemical experiments, such as the use of isotopically chiral compounds, have been important and, since all biological phosphorylation reactions appear to involve metal ion catalysis, the stereochemistry of phosphate ion coordination has also been subject to much attention.229,230 Apart from its biological significance, this work has revealed some interesting contrasts with the stereochemistry of ligand systems in which saturated carbon units link the donor atoms. 

Other compounds such as phosphate esters, pyrophosphates, and amides of phosphoric acid, are hydrolyzed in similar reactions. Coordination may be through only one oxygen of these phosphate compounds, but the overall effect is similar. 

Monodentate phosphate compounds. The monodentate phosphate compounds are stronger Lewis bases and have a higher coordinating ability than ethers. Their basicity is in the order phosphate <... 

Although the log values for first complexations of lns(l,4,5)P3 with (5,5)-and [(R,R)-35f were nearly identical, the differences in thermodynamic parameters (enthalpy and entropy changes) suggest different binding modes for the two combinations. These results provide important information about the design and synthesis of chemical receptors, sensors, and inhibitors for lns(l,4,5)P3 and related compounds such as Ptdlns(4,5)P2, and for the design of supramolecular complexes using phosphate-metal coordination bonds. 

Only the phosphate polyanion has been considered here. For completeness, we can also mention a pyrophosphate, Li2CoP20g, considered as a 4.9 V cathode [218]. This pyrophosphate crystallizes in the monoclinic structure (P2 lc S.G.), in which Li occupies five sites two are tetrahedraUy coordinated, one forms bipyra-midal sites, and two Li share them occupancy with Co bipyramids. The material synthesized using a two-step solid-state method delivered a discharge capacity of ca. 80 mAh g at C/20 rate, which illustrates the superiority of the phosphate compounds as active cathode elements. The fluoro-polyanionic compoxmds, however, deserve a special attention, and the next chapter is devoted to them. 

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). 

Sohd uranium—phosphate complexes have been reported for the IV and VI oxidation states, as well as for compounds containing mixed oxidation states of U(IV) and U(VI). Only a few sohd state stmctures of U(IV) phosphates have been reported, including the metaphosphate U(P03)4, the pyrophosphate U(P202), and the orthophosphate, CaU(PO4)2. The crystal stmcture of orthorhombic CaU(POis similar to anhydrite (194). Compounds of the general formula MU2(PO4)3 have been reported for M = Li, Na, and K, but could not be obtained with the larger Rb and Cs ions (195). In the sohd state, uranium(IV) forms the triclinic metaphosphate, U(P03)4. Each uranium atom is eight-coordinate with square antiprismatic UOg units bridged by... 

For microporous compounds with special compositions, calcination effects are even more severe. As compared with zeolites, these compounds have lower thermal stability. Strictly speaking, most of them are nonporous since removal of the occluded guest molecules by calcination usually results in collapse. This is due to strong H-bonds with the framework, coordination bonds, and sometimes the templating molecule is shared with the inorganic polyhedra. Relevant examples of low-stability microporous compounds with interesting structural features are zeolitic open-framework phosphates made of Ga [178], In [179], Zn [180], Fe [181],... 

Zinc phosphates and phosphonates can form highly interesting coordination networks, some in the presence of additional ligands. A number of compounds that have useful properties for the formation of zinc phosphate materials will also be discussed. 

The study of [4.4.0] ring systems has resulted primarily from the study of various other aspects of phosphorus chemistry. An investigation into the effect of nitrogen donor action on the increase in coordination at phosphorus in a series of oxyphosphoranes led Holmes and co-workers <1998IC4945> to compounds 24 and 25. The compounds were fully characterized by NMR spectroscopy and X-ray diffraction. Compound 24 was heated for 30 min at 140°C in an NMR tube. The reaction was followed by 31P NMR spectroscopy which indicated that conversion to a phosphorane 26 and a small amount of phosphate had taken place (Equation 4). The pentaoxyphosphorane 25 was successfully produced via an oxidative addition reaction between the diol 27 and triphenyl phosphate in the presence... 

Pavan Kumar et al. <2006NJC717> investigated the reaction of diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) with cyclic phosphates or phosphoramides in order to determine the structural preferences in spirocyclic penta- and hexacoordinate aminophosphoranes. They found that sulfur would coordinate to phosphorus to form the [3.3.0] bicyclic compounds 94-96. 

An early example of a combinatorial approach to a reaction catalyzed by transition metal coordination compounds concerns phosphatase mimics, specifically in the hydrolysis of bis(/ -nitrophenyl)phosphate (1)—>(2) (Equation (l)) 29... 

The nature of the target to be attacked by any drug obviously depends on the specific application. Many cytotoxic metal complexes target DNA because of its importance in replication and cell viability. Coordination compounds offer many binding modes to polynucleotides, including outer-sphere noncovalent binding, metal coordination to nucleobase and phosphate backbone... 

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