Phosphates, inhibitors

In nitrogenous fertiliser solutions of the NH4NOJ—NHj —HjO type corrosion of steel can be prevented by 500 p.p.m. of sulphur-containing inhibitors, e.g. mercaptobenzothiazole, thiourea and ammonium thiocyanate. However, these inhibitors are not so effective where most of the NHj is replaced by urea. For these solutions phosphate inhibitors such as (NH4>2HP04 and polyphosphates were more effective... 

SS/MA is an excellent calcium phosphate inhibitor when soluble iron is absent and can perform better than AA/HPA or AA/AMPS. However, the rankings change a little when soluble iron is present. 

In general, SS/MA and the other calcium phosphate inhibitors are not as good at inhibiting calcium carbonate scale as PMA or HEDP or as good at inhibiting calcium sulfate scale as PMA and 2000 MW PAA. 

Lead-based inhibitors and zinc phosphate inhibitors are thought to plug up the discontinuities in the natural oxide layer and hence offer protection. This is akin to the repair of an imperfect oxide film of iron by chromates, molybdates or tungstates. 

This concept has been extended. Thus the trione (696) rapidly and irreversibly inactivates human erythrocyte nucleoside phosphorylase (PNPase), which catalyzes the reversible phosphorylation of inosine and guanosine to the respective bases and ribose 1-phosphate. Inhibitors of this enzyme have several potential medical applications, for example, in the prevention of foreign tissue rejection, in the treatment of gout and malaria, and for the potentiation of antineoplastic nucleosides. Mechanistically the 5,8-dione (quinone) (696) enters the enzyme active site. An active-site nucleophilic residue subsequently converts the quinone moiety to a hydroquinone by reductive addition (701). The resulting hydroquinone affords an alkylating quinone methide species by elimination of HCl (702) and then traps a second nucleophilic enzyme residue by a Michael type reaction (703). Cross-linking of the active site rationalizes the observed potency <91B8480>. 

The C-1 phosphate has been drawn in a position hydrogen-bonded with an arginine residue. The iminium ion is sufficiently exposed to solvent so that borohydride, cyanide or tetranitromethane [58] reactions with the bound substrate are possible. A thiol group has been drawn in a position where the enone phosphate inhibitor could react with it. 

Table 8.21 Calcium Phosphate Inhibitor Dosage Optimization Example...

Phosphate retards corrosion by promoting the growth of protective iron oxide films and by healing the defects in protective films. The effectiveness of phosphate inhibitor is reduced by chloride ions which damage the protective film formed by phosphate. 

Figure 2 Protection of papaya fruits in the field from Colletotri chum gioeosporioides by a cutinase inhibitor. Chlorpyrifos, an organic phosphate inhibitor of cutinase, a fungicide (Mancozeb) or water was sprayed on the growing fruits on a biweekly interval and after the fruits reached maturity, the lesions observed were recorded (W. Nishijima,...

Sodium-zinc molecularly dehydrated glassy phosphate inhibitor is used... 

Figure 14.21 shows SVET maps and optical micrographs over the cut edge with and without phosphate addition as a function of time. The maps reveal that the cathodes (attributed to O2 reduction) are located on the steel, whereas the anodes (attributed to Zn oxidation) are located on the Zn. With phosphate inhibitor, the Zn dissolution was more localized, the lifetime of the local anodes was shorter (note the anodes change position with time), and the peak currents were approximately half to one-third those observed in the absence of phosphate (note differences in current scale). The repassivation of local anodes in the presence of phosphate was attributed to the precipitation of... 

Uses Calcium phosphate inhibitor, zinc stabilizer, iron inhibitor, dispersant for detergents (auto dish, hard surf.), textiles (scours, dyebaths)... 

Uses Deposit control additve, dispersant, crystal modifier, antiscalanL sludge preventive in boilers and rxxrling towers caldum phosphate inhibitor iron oxide dispersant iron control aid on-line cleaner Features High pressure and thermally stable Regulatory SARA nonreportable... 

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