Mechanism, dual

Precipita.tingInhibitors. As discussed earlier, the localized pH at the cathode of the corrosion cell is elevated due to the generation of hydroxide ions. Precipitating inhibitors form complexes that are insoluble at this high pH (1—2 pH units above bulk water), but whose deposition can be controlled at the bulk water pH (typically 7—9 pH). A good example is zinc, which can precipitate as hydroxide, carbonate, or phosphate. Calcium carbonate and calcium orthophosphate are also precipitating inhibitors. Orthophosphate thus exhibits a dual mechanism, acting as both an anodic passivator and a cathodic precipitator. 

First, one pump running in a parallel system tends to suffer from cavitation because operation to the right of the BF.P indicates that the NPSHr of the pump rises drastically. To survive this condition, you should use dual mechanical seals on these pumps. Dual or double mechanical seals can withstand cavitation better than a single seal. There is a discussion on this in the mechanical seal chapter of this book. Many engineers perceive that parallel pumps are problematic becau.se they appear to suffer a lot of premature seal failure. Parallel pumps deserve double seals even if it s only a cold water system. 

The real world of Sn reactions is not quite as simple as the discussion has so far suggested. The preceding treatment in terms of two clearly distinct mechanisms, SnI and Sn2, implies that all substitution reactions will follow one or the other of these mechanisms. This is an oversimplification. The strength of the dual mechanism hypothesis and its limitations are revealed by these relative rates of solvolysis of alkyl bromides in 80% ethanol methyl bromide, 2.51 ethyl bromide, 1.00 isopropyl bromide, 1.70 /er/-butyl bromide, 8600. Addition of lyate ions increases the rate for the methyl, ethyl, and isopropyl bromides, whereas the tert-butyl bromide solvolysis rate is unchanged. The reaction with lyate ions is overall second-order for methyl and ethyl, first-order for tert-butyl, and first- or second-order for the isopropyl member, depending upon the concentrations. Similar results are found in other solvents. These data show that the methyl and ethyl bromides solvolyze by the Sn2 mechanism, and tert-butyl bromide by the SnI mech-... 

Tedder400 proposed that dual mechanisms, analogous to those proposed for alkylation, may apply to acylation also. Thus substitution may occur via a free... 

Bolton TB, Large WA 1986 Are junction potentials essential Dual mechanism of smooth muscle cell activation by transmitter released from autonomic nerves. Q J Exp Physiol 71 1-28... 

Beilby MJ, Cherry C, Shepherd VA. Dual mechanisms of turgor regulation in Lam-prothamnium papulosum. Plant Cell Environ 1999 22 347-361. 

HY-10275 (no structure reported), having such a dual mechanism, has been recently reported to meet the primary and secondary endpoints in the initial phase II trial at doses of 1 and 3 mg in adults with transient insomnia [93]. 

The laser flash photolysis of aromatic diisocyanate based polyurethanes in solution provides evidence for a dual mechanism for photodegradation. One of the processes, an N-C bond cleavage, is common to both TDI (toluene diisocyanate) and MDI (methylene 4,4 -diphenyldiisocyanate) based polyurethanes. The second process, exclusive to MDI based polyurethanes, involves formation of a substituted diphenylmethyl radical. The diphenylmethyl radical, which readily reacts with oxygen, is generated either by direct excitation (248 nm) or indirectly by reaction with a tert-butoxy radical produced upon excitation of tert-butyl peroxide at 351 nm. 

CRX 026 Dual mechanism — PRLl inhibitor and kinesin inhibitor... 

Thut, C., J. Goodrich, and R. Tjian, Repression of p53-mediated transcription by Mdm2 a dual mechanism. Genes Dev, 1997, 11(15), 1974-86. 

The Taft plot for the oxidation of substituted alkynes, as illustrated in Figure 2c, is also concave upward (17). Consequently, it appears as if this reaction may also have a dual mechanism. One possibility has been summarized in Equations 8 and 9. 

The standard unpressurized dual mechaiucal seal (previously referred to as a tandem mechanical seal) shall be a balanced seal (with two flexible elements and two mating rings in series). Unpressurized dual mechanical seals shall be designed to withstand pressurization of the bnffer flnid to 275 kPa (40 psig). 

The standard pressurized dual mechanical seal (previously referred to as a double mechanical seal) shall be... 

Alloy 20 or Monel pump material and dual mechanical seals should be used with a pressurized seal oil system. 

Russell and Danen (1968) studied the sonication effect on the reaction between the lithium salt of 2-nitropropane and 4-nitrobenzyl bromide. A dual mechanism, ionic and ion-radical, characterizes this reaction. The ionic mechanism leads to the 0-alkylation product and, eventually, to 4-nitrobenzaldehyde ... 

Pharmacology Brimonidine is an alpha-2 adrenergic receptor agonist. It has a peak ocular hypotensive effect occurring at 2 hours postdose. Brimonidine has a dual mechanism of action it reduces aqueous humor production and increases uveoscleral outflow. 

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