Zinc, stability

Typically, soHd stabilizers utilize natural saturated fatty acid ligands with chain lengths of Cg—C g. Ziac stearate [557-05-1/, ziac neodecanoate [27253-29-8] calcium stearate [1592-23-0] barium stearate [6865-35-6] and cadmium laurate [2605-44-9] are some examples. To complete the package, the soHd products also contain other soHd additives such as polyols, antioxidants, and lubricants. Liquid stabilizers can make use of metal soaps of oleic acid, tall oil acids, 2-ethyl-hexanoic acid, octylphenol, and nonylphenol. Barium bis(nonylphenate) [41157-58-8] ziac 2-ethyIhexanoate [136-53-8], cadmium 2-ethyIhexanoate [2420-98-6], and overbased barium tallate [68855-79-8] are normally used ia the Hquid formulations along with solubilizers such as plasticizers, phosphites, and/or epoxidized oils. The majority of the Hquid barium—cadmium formulations rely on barium nonylphenate as the source of that metal. There are even some mixed metal stabilizers suppHed as pastes. The U.S. FDA approved calcium—zinc stabilizers are good examples because they contain a mixture of calcium stearate and ziac stearate suspended ia epoxidized soya oil. Table 4 shows examples of typical mixed metal stabilizers. 

Antimony tris(isooctylthioglycolate) has found use in pipe formulations at low levels. Its disadvantage is that it cross-stains with sulfide-based tin stabilizers (122). Barium—zinc stabilizers have found use in plasticized compounds, replacing barium—cadmium stabilizers. These are used in mol dings, profiles, and wire coatings. Cadmium use has decreased because of environmental concerns surrounding certain heavy metals. 

Calcium—zinc stabilizers are used in both plasticized PVC and rigid PVC for food contact where it is desired to minimize taste and odor characteristics. AppHcations include meat wrap, water botdes, and medical uses. 

Many stabilizers require costabilizers. Several organic costabilizers are quite useful with barium—zinc and calcium—zinc stabilizers, eg, P-diketones, epoxies, organophosphites, hindered phenols, and polyols (122). 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials May be corrosive to aluminum, magnesium and zinc Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Klier and coworkers—Role of ZnO in stabilizing Cu in Cu+ oxidation state, proposed to be the active site. Klier and coworkers235 241 provided a different explanation for the role of zinc in promoting the activity of Cu/ZnO catalysts. They suggested that zinc stabilizes the Cu in the Cu1 + oxidation state, and that it is the Cu ions in the 1 + oxidation state that serve as the active sites. 

Figure 7-17 The structure of insulin. (A) The amino acid sequence of the A and B chains linked by disulfide bridges. (B) Sketch showing the backbone structure of the insulin molecule as revealed by X-ray analysis. The A and B chains have been labeled. Positions and orientations of aromatic side chains are also shown. (C) View of the paired N-terminal ends of the B chains in the insulin dimer. View is approximately down the pseudo-twofold axis toward the center of the hexamer. (D) Schematic drawing showing packing of six insulin molecules in the zinc-stabilized hexamer.

The addition of small amounts of various stabilizers to untreated or polybutadiene-grafted PVC decreased the rate of hydrogen chloride evolution. Thus, as shown in Figure 1, 0.15 phr which is less than 10% of the recommended amounts of a mixture of non-toxic calcium-zinc stabilizers, increased the time for 0.1 mole % dehydrochlorination of suspension polymerized PVC from 28 to 36 minutes and of Type M PVC prepared from the suspension polymer from 41 to 47 minutes. Type P PVC prepared from the same polymer required 49 minutes for the same extent of dehydrochlorination. 

In low pH cooling waters (pH 6.0 to 7.4), when treating with zinc programs, levels of 3 to 5 ppm of soluble zinc can often be obtained, which tends to provide good corrosion protection to carbon steel. Its solubility rapidly decreases as the pH rises it may only be 0.2 to 0.3 ppm or less in high pH cooling water (say pH 8.3 and above), giving rise to the risk of zinc precipitation in the bulk water. This is partly overcome by the incorporation of zinc stabilizers ( zinc dispersants or zinc enhancers ) in the formulation. 

NOTE Some researchers claim that the zinc stabilizer should not be too efficient as this may prevent the ultimate precipitation of zinc at the cathodic site. Whether this is true or not is debatable. 

The 1990s has seen the entry of terpolymers with basic calcium carbonate control, but with designer functional groups to provide various additional properties such as excellent high-stress dispersion, iron control, phosphate control, zinc stabilization, and silica control, all on the same polymeric molecule ... 

Certain acrylic acid copolymers are often used as DCAs for CajfPO, as zinc stabilizers, as dispersants for iron oxides, and as antiprecipitants for BaSOi (an example is acrylic acid/sulfonic acid, or AA/SA). 

PBTC is a good zinc stabilizer and can sequester the zinc and transport it to the metal surface under high pH conditions (where it precipitates at the localized high pH and acts to swamp the cathodic area). 

PCA 4 acts as a good zinc stabilizer in high alkalinity, high pH operating conditions. Typically, 2.5 ppm zinc reserve may require 2.5 ppm of PCA 4 for zinc stabilization alone, but 5 to 15 ppm of PCA 4 for complete corrosion control (as actives). 

Zinc stabilizer and building block corrosion inhibitor, esp. in soft water AEC Alkyl epoxy carboxylate example Continuum AEC... 

Improved deposit control agents and phosphate/zinc stabilizers have permitted these programs to operate with high levels of calcium (up to 1200 ppm) and high pH (up to 9.0). 

Fertilizer plant, main C/S Zinc + stabilized PO4 + acid pH 6.9-7.3... 

Any proposal for a future chemical inhibitor program needs to employ an alkaline zinc/stabilized phosphate base, similar to that currently used, as required by the customer. However, as noted previously, the inhibitor needs improved deposit control agent (DCA) performance. This is especially important, as a new program would not start with a properly cleaned cooling system (an on-line clean will be recommended, but is likely to have only limited effect). Thus the inhibitor would include better/more polymers. 

The development and testing of a suitable inhibitor program of alkaline zinc/stabilized phosphate combination was undertaken in the United States. The conditions for the trial unfortunately required the product to be similar to the existing vendor s program (a me-too" product). In addition, the formulation had to be fairly simple, as the raw material blending was to take place within the region by relatively inexperienced people (which saved on the cost of effectively importing water). 

Fig. 11 Three-dimensional structures of epothilones determined in different environments (O red, S yellow, N dark blue). Top structures of free EpoA determined by X-ray crystallography from dichloromethane/petroleum ether (top left [9 8] (a)) and from methanol/water (top right [143](b)). Bottom structures of EpoA bound to tubulin determined by solution NMR in aqueous medium (bottom left [96]) and by electron crystallography from zinc-stabilized tubulin sheets (bottom right [26]).(a) The crystal structure data have been available from the author to interested research groups since October 1995.(b) H.-J. Hecht, G. Hofle, unpublished results CCDC 241333 and CCDC 241334 contain the crystallographic data of this structure. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retiieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK fax (+ 44) 1223-336-033 or deposit cede. cam. ac. uk)...

Fig. 24 Laulimalide stabilizes microtubules, but destabilizes zinc sheets. This multipart figure illustrates the effect of addition of laulimalide upon the polymerization of tubulin. Tubulin polymers, as sheets or microtubules, are inherently unstable and disassemble rapidly at low temperatures. Addition of paclitaxel (or epothilone, not shown) protect sheets from disassembly, a Control zinc sheets stabilized with PTX after 20 minutes in a bath of ice and water, b The effect of laulimalide under the same ice bath conditions as a. After 20 minutes, sheets exposed to laulimalide have significantly disassembled and reformed into microtubules, c Microtubules formed at room temperature from addition of laulimalide to zinc-stabilized sheets and incubated overnight. Almost all sheets have converted to microtubules (enlarged microtubules shown inset). By comparison, paclitaxel and epothilone-stabilized sheets remain intact under the same conditions, d Magnified microtubules seen in b. Figure provided by Huilin Li...

The inclusion of heat stabilizers is essential to protect the system against thermal decomposition at elevated temperatures during processing. For this purpose, tin carboxylate esters or liquid calcium-zinc stabilizers are preferred. Thio-tin compounds are very effective as heat stabilizers but must be regarded with caution, bearing in mind that they can lead to unpleasant and unacceptable residual odours. Secondary stabilizers that can be used include epox-idized soya bean oil. 

The system containing barium-cadmium-zinc stabilizer significantly outperformed the corresponding system based on tin mercaptide. The addition of the phosphite did not alter relative performance in Ba-Cd-Zn systems (Table VII). 

Although copper binds tighter than zinc to aU forms of the enzyme tested, zinc stabilizes the protein fold better as judged by solvent-induced denaturation experiments. In addition the dissociation rate constant for zinc is about 100 times slower than copper suggesting the zinc is kinetically trapped once folding has occurred. This may thus be a physiological means by which metal ion specificity is achieved. ... 

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