Copper scavenger

EDTA (Ki 1.6 X 10 M) (Rae et al., 1999). The primary conclusion derived from these studies is that in the presence of copper scavengers, Cu(I)yCCS activates ySODl hut Cu(l)GSH and CUSO4 cannot. Importantly, the copper insertion event likely occurs with direct transfer of the metal ion from yCCS to the ySODl, as copper ions that might possibly dissociate from the yCCS or GSH donor molecules are rapidly sequestered by the BCS competitor molecule, which is present in 20-fold excess over the copper donor molecules under these assay conditions. This in turn suggests that specific protein-protein interactions are involved in the recognition of ySODl by yCCS (Rae et al., 1999). 

DNPD is used as an effective, reiatively nonstaining AO and a copper scavenger to proiong the service iife of many rubber compounds based on a wide range of different raw eiastomers. 

Copper(l)-Catalyzed Azide—Alkyne Cycloaddition with Integrated Copper Scavenging Unit [61]... 

Figure 11.18 Microfluidic setup for copper(l)-catalyzed azide—alkyne cycloaddition with integrated copper scavenging unit...

Textiles. Sorbitol sequesters iron and copper ions in strongly alkaline textile bleaching or scouring solutions (see Textiles). In compositions for conferring permanent wash-and-wear properties on cotton fabrics, sorbitol is a scavenger for unreacted formaldehyde (252) and a plasticizer in sod-resistant and sod-release finishes (253). 

Metal or metal oxides may be added to perform specific functions. Brass chips and copper powder are frequently used in heavy-duty organics where these metaUics act as scavengers to break up undesirable surface films. Zinc chips used in Class A organics contribute significantly to recovery of normal performance following fade. Aluminum is also used. Most of these inorganic materials tend to detract from antinoise properties and mating surface compatibihty. 

When the ore contains a large amount of clay minerals, these form difficult to separate slimes, which hinder the recovery of the minerals (see Clays). The tailing from the scavenger cells can be cycloned to remove the slimes before the coarse material is floated in a tailings retreatment plant. The flotation product from the rougher cells of this plant can be reground and cleaned. This additional treatment of the tailings from the main copper flotation plant may improve the recovery of metal values by 1—3%. 

Catalysis plays an important part in the hydrazine/oxygen reaction. Copper salts were formerly added for this purpose, but in recent years certain organic substances, e.g. quinhydrone, have been employed and a number of proprietary activated hydrazines have been available. These are useful at low temperatures above 150°C scavenging rates with normal hydrazine are such that no great benefit is achieved by their use. 

NOTE Probably the most important junction of oxygen scavengers is, in reality, the ability to passivate boiler steel. In recognition of this, today most novel oxygen scavenger trials try to identify, not merely comparative oxygen reaction rates, but more importantly, the reduction in iron and copper transport rates through the boiler system. In other words, they seek to optimize the passivation of boiler surfaces and other system components. 

Similarly, when catalyzed the reaction rate decreases significantly as a function of pH level. The optimum reaction pH level is approximately 9.5 to 10.5. Iron, and especially copper, in the boiler may act as adventitious catalysts. However, as metal transport polymers are frequently employed, iron, copper, or cobalt may be transported away from contact with sulfite, and thus are not available for catalysis. (This may be a serious problem in high-pressure units employing combinations of organic oxygen scavengers and metal ion catalysts.)... 

In its catalyzed form [catalyzed with hydroquinone (HQ), benzo-quinone, or copper], DEHA has a very fast reaction rate, almost as fast as catalyzed sulfite. Hydroquinone is the most popular catalyst for DEHA, and it is likely that the rapid reaction rate is, in part at least, due to the catalyst simply acting as an oxygen scavenger in its own right. 

Where copper corrosion occurs, the problem usually can be traced back to an excess feed of hydrazine, DEHA, or similar product, coupled with inadequate post-boiler oxygen scavenging. 

Erythorbates are safe products and there are no harmful breakdown products, although when early formulations utilized ammonia as a PH buffer (and neutralizer for part of the carbon dioxide), copper corrosion problems resulted. However, erythorbates are not steam-volatile,and consequently there is no post-boiler oxygen scavenging potential available. Thus, in the event of complete breakdown of the product at high pressure, oxygen-induced, ammonia corrosion of copper may continue unchecked. 

MEKO is a very volatile scavenger with a distribution ratio between that of DEAE and cyclohexylamine, which enables it to provide postboiler oxygen scavenging protection in larger steam-condensate lines. It is fast-reacting, although in the boiler this reaction does not always proceed to completion, even in the presence of copper (perhaps only 60-70% complete). 

Whether ammonia arises from its use as a FW pH level adjuster or from adventitious provision as a result of DO scavenger breakdown, it should be recognized that any excess ammonia will clearly end up in the steam-condensate system. Although the benefit of carbon dioxide neutralization may be legitimately claimed, unfortunately, excess ammonia also may permit the corrosion of copper and its alloys, especially if some oxygen persists. 

The potency of a chain-breaking antioxidant, which scavenges peroxyl radicals, will decrease as the concentration of lipid peroxides in the LDL particle increases (Scheme 2.2). This is illustrated in the experiment shown in Fig. 2.3 in which the antioxidant potency of a peroxyl radical scavenger (BHT) decreases as a function of added exogenous hpid hydroperoxide. If the endogenous lipid peroxide content of LDL were to vary between individuals, this could explain the observed diferences in the effectiveness of a-tocopherol in suppressing lipid peroxidation promoted by copper. 

Lovstad, R.A. (1984). Catecholamine stimulation of copper-dependent haemolysis protective action of superoxide dismutase, catalase, hydroxyl radical scavengers and scrum proteins (ceruloplasmin, albumin and apotransferrin). Acta Pharmacol. Toxicol. 54, 340-345. 

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