Phosphate esters defined

Series of various mono,- bi-, and poly-(thio)urea-functionalized (poly)saccha-rides have already been synthesized and studied for molecular recognition of, e.g., dimethyl and phenylphosphate as model compounds for monoanionic and polyanionic phosphate esters, respechvely [111]. Thiourea derivatives such as 195-197 were analyhcally identified to provide double hydrogen bonding mediated host-guest complexes of well-defined dimension and orientations and were also reported to serve as phosphate binders even in the hydrogen bonding environment of water (Figure 6.57) [111]. 

With the existence of this new cyclodextrin lock, it was again important to select a key to fit it and to serve as substrate. For this we wanted a cyclic phosphate ester that this cyclodextrin bisimidazole could hydrolyze. The enzyme ribonuclease hydrolyzes cyclic phosphates as the second step in the hydrolysis of RNA, and cyclic phosphates are used as assay substrates for the enzyme. The advantage to us of such a substrate was that the geometry of the transition state would be relatively well-defined, so that it should be possible to design congruence between the catalyst and the transition state. Molecular model building indicated that a possible substrate was the cyclic phosphate derived from 4-f-butylcatechol (VIII). Indeed, the cyclodextrin bisimidazole (VII) is a catalyst for the cleavage of cyclic phosphate (VIII) (14). 

Traditionally the phosphate ester moiety is often overlooked and viewed as a passive element of nucleic acid structure. Base pairing and other nucleic acid base oriented structural features have been assumed to control nucleic acid structure and conformation. More recently (and as discussed in this paper) we have begun to appreciate the important role played by the phosphate ester (Figure 1) in defining the structure and dynamics of nucleic acids as well as nucleic acid-drug or protein complexes. 

Metal ions have been known for many years to promote the hydrolysis of polyphosphates and phosphate esters [12]. A major problem with these systems is that die divalent metal ions are substitutionally labile and form a variety of complexes, many of which are in rapid equilibrium. As a result it has been quite difficult to define any... 

From my laboratory and the laboratories of Ef Racker, Frank Dickens and Melvin Calvin, the years that followed witnessed a series of parallel and often highly synergistic discoveries on the nature of the pentose phosphate pathway and the path of carbon in photosynthesis. Andrew Benson and others in Calvin s laboratory, had shown that phosphate esters of ribulose and sedoheptulose were early products of CO2 fixation in photosynthesis,and the immediate precursor of phosphoglyceric acid, and therefore the primary CO2 acceptor, appeared to be ribulose diphosphate. The major problems became (1) to find the enzyme or enzymes that catalyzed the formation of phosphoglyceric acid from ribulose diphosphate and (2) to define the reactions leading to the synthesis of ribulose diphosphate from triose and hexose phosphates. 

Of this family of products, triaryl phosphates (TAP) and alkyl diaryl phosphates (ADP) are the two important categories of FR plasticizers for PVC. Trialkyl phosphates are considered too volatile for most vinyl processes, and are more commonly found in other applications, such as leveling agents or antifoam additives. In vinyl, TAP and ADP plasticizers are used to flame-retard thin films and laminates for articles such as wall covering, tarpaulins (transportation), and vinyl-coated furniture fabric. Another major application area is in vinyl for electrical insulation in wire and cable. In addition to these applications, phosphate esters are used as functional fluids for hydraulic equipment (metal industries, power generation, and aircraft hydraulic systems) and as additives in formulated lubricant systems. As flexible vinyl composites are usually defined by their additives, when formulated correctly, phosphate esters can help produce a very cost-efficient vinyl composite capable of very low smoke and flammabihty. In nearly all markets, phosphate esters are valued primarily for their FR properties, and the distinction from function and plasticization is sometimes obscured. 

There are some means for synthesis of defined primary or secondary esters. Monoester salts of phosphoric acid, for instance, are prepared by addition of alcohol or ethoxylated alcohol, alkali fluoride, and pyrophosphoryl chloride (C12P0)20 in a molar ratio of 0.9-1.5 0.05-1 1.0 at -50 to +10°C and hydrolysis of the Cl-containing intermediates with base. Thus, 32.3 g (C12P0)20 was treated at -50°C with 23.9 g lauryl alcohol in the presence of 0.7 g KF and the mixture was slowly warmed to room temperature and hydrolyzed with H20 and 40% NaOH to give 83% sodium monolauryl phosphate. The monoester salts showed comparable or better washing and foaming efficiency than a commercial product [12]. 

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