Chain phosphates

Maddrell salt, NaP03. A long chain phosphate obtained by heating Na2H2P407 to 230 300 C. 

The only tme metaphosphate (ring stmcture) of significant commercial interest is sodium trimetaphosphate (STMP), Na P O. Because of the strain inherent in the small ring stmcture, STMP is more reactive toward nucleophiles than chain phosphates. In the presence of NaOH, for example, STMP forms sodium tripolyphosphate. 

Phosphorus(V) oxide is very hygroscopic and the bottle must be closed except when an addition is made. The reactor is cooled with ice water so that the reaction temperature is maintained at 5-10°. Methanol (125 mL)is added drop-wise to the stirred solution to precipitate the crude ammonium tetrametaphos-phate, which is collected by suction filtration, washed with methanol, and dried in vacuum over anhydrous CaS04. The product weighs 33 g and contains about 65% of its phosphorus as tetrametaphosphate. The remainder is a mixture of ortho-, trimeta- and short-chain phosphates. Any lumps are crushed and the crude ammonium tetrametaphosphate is spread in a no. 1 porcelain evaporating dish and heated for 2 hours at 240° in a slow stream,of anhydrous ammonia (about 100 mL/min or 3-5 g/hr). Care is taken to avoid absorption of moisture before or during heating, as this adversely affects the formation of the product. 

ATP + myosin light chain = ADP + myosin hght chain phosphate... 

P ADP -I- smooth muscle myosin light chain phosphate... 

Cheeseman et al. reported in 1972 the purification and properties of a fluorescent compound from Methanobacterium. Owing to the first visible absorption at 420 nm the unknown compound was called Factor-420. It was not until 1978 till it became clear that the compound is a flavin-like molecule By different physical techniques it could be shown that the molecule is a 5-deaza-FMN derivative (Scheme 2, (70)) where at position 8 the methyl group is replaced by a hydroxy group. In addition, the side chain phosphate group is esterified by a lactyl group which, in turn, is linked to a diglutamyl moiety via a peptide bond. Factor-420 functions as... 

It would be interesting to test the reversal of the 7r-A isotherms with monolayers of long-chain phosphates, but the only data available to our knowledge are for octadecyl phosphates and phosphoric acids over... 

Figure 10. Models of complexes between long-chain phosphate esters (sodium salts of the monoesters) and insulin based on Raman spectroscopy. Shorter chains (e.g. C10) have a protein environment whereas lipid regions with disordered chains are formed when chains are longer (>CJ.

The role of organic sulfur species (other than those in thiophosphate form) in the tribochemical process is to react immediately with the nascent iron surfaces and ZnO to form metal sulfides (FeS, ZnS) embedded in the short chain phosphate matrix. 

The tribochemical reactions based on the hard and soft acids and bases (HSAB) principle linked to the friction coefficient (p) are summarized above. The effect of tribological processes consists of the formation of mixed short-chain phosphate glasses containing sulfide precipitates. 

The thermal film made of long-chain zinc polyphosphates is formed on the surface. When friction increases, the process of transformation of phosphorus compounds into short-chain phosphate glasses is observed and iron sulfide abrasive particles are eliminated by tribochemical acid-base reactions. Under very severe wear conditions (nascent metal surface creation), an iron sulfide is formed, which will be mixed with the phosphate glasses tribofilm. 

If less ZDDP is adsorbed on the surface, a greater percent is transformed as a short chain phosphate tribofilm. 

The tribofilms formed from a ZDDP were composed of long chain phosphates with zinc as a cation but with a mixture of a ZDDP + detergent and ZDDP + dispersant, only short-chain phosphates with zinc and calcium as cations are formed in the presence of a sulfide (Barcroft and Park, 1986 Willermet et al., 1995a). 

The tribofilms consist of amorphous, short-chain phosphates (ortho- and metaphosphates), with some evidence of sulfur incorporated into the phosphate chain structure. Tribofilm structure depends not only on the lubricant composition of the substrate material, but also on the severity of the rubbing contact. The ZDDP typically forms phosphates under antiwear conditions, whereas sulfides and sulfates are typically formed under severe or very severe conditions, li > 0.8 (Willermet et al., 1997). 

The engine oil containing ZDDP and carbonate-detergents RMs formed orthophosphate and pyrophosphate tribofilms. In the presence of detergent and dispersant only short-chain phosphates were observed (Willermet et al., 1991, 1992 and 1997 Yin et al., 1997b). 

The tribochemical and thermally generated films contained mostly a mixture of short-and long-chain phosphates. The sulfur in tribofilms is always present as sulfide (Canning et al., 1999 Fuller et al., 1997 Yin et al., 1997a). 

A Cameron-Plint friction machine generated tribofilms with two-layer structure a zinc polyphosphate thermal film overlying a mixed short-chain phosphate glass, containing iron sulfide precipitates. A tribochemical reaction between the zinc polyphosphate and the iron oxides species is proposed on the basis of the hard and soft acid and base HSAB principle (Martin, 1999 Martin et al., 2001). 

A recent XANES experiment showed that the ZDDP tribofilm generally has a two-layer structure a short-chain phosphate layer covered by a thin, long-chain polyphosphate layer. XANES spectra analysis of tribofilms did not show a substantial difference between neutral and basic ZDDPs (Fuller et al., 1997 Martin, 1999 Martin at al., 2001 Varlot et al., 2000 Willermet et al., 1991 and 1992 Yamaguchi et al., 1993 and 1996). 

The tribofilm composition On the basis of Table 4.1, what analytical surface techniques were used to evaluate the tribofilm composition after ZDDP degradation The tribofilm conditions include the following (a) the tribofilm consists of Zn, P, S, O and Fe and (b) the tribofilm contains mostly of a mixture of short-and long-chain phosphates and sulfur is present as zinc sulfide. What analytical technique has the ability to identify elements and their chemical state, e.g., Fe° or Fe2+, in case (a), and compounds in case (b) More about analytical techniques for evaluation of the metal surfaces can be found in chapter 4.3. 

Physical parameters By using Table 4.3. The effect of physical parameters such as adsorption, rubbing, temperature, concentration, load, surface roughness on antiwear performance of ZDDPs , which term is described by the physical parameter (a) the tribofilm accumulated on the surface becomes thicker with adsorption time (b) long-chain phosphates are formed on the topmost surface, but short-chain phosphates were present in the bulk (c) sulfur and phosphorus ratio changes with rubbing time and (d) when load increased the concentration of (S) and decreased that of (P) ... 

FIGURE 8. Linear chain phosphate, [CnWfaNZntHPQdz] (12), which transforms to a tubular layered phosphate, [C10N4l-y [Zn3(P04)2-(HP04)1 (13). The features of the linear chain can be delineated in the tubular structure of 13. 

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