Core, react

Complex (860)2085 containing a (/i-aqua)bis(/i-carboxylato) core reacts with urea to provide the first example of urea coordination to a dinickel(II) site.2067 In the resulting (861), the urea molecule binds through its carbonyl-O to one of the Ni11 ions, which is the most commonly observed coordination mode. 

Figure 3-6 shows the damaged areas of the core as now known from the available information (OECD, 1994). It can be calculated that about 50 per cent of the zirconium present in the TMI-2 core reacted with water to produce hydrogen and that practically all the volatile fission products were released by the core into the primary circuit and hence, through the stuck open relief valve, into the containment building. Forty-five per cent (62 t) of the fuel melted and about 20 t migrated from their original position and collected on the vessel bottom head. 

Nonetheless, one observation is accounted for by a simple empirical extension of the above theory, the undamped propagation of a high-density polymer pulse as illustrated in Figure 9.5. In this experiment, the whole cylinder is initially in the swollen F state. An acid perturbation is made at the bottom end of the cylinder. This induces a transition to the collapse state of the gel, which starts to invade the swollen upper part. Yet, after some time, the collapsed part of the cylinder slowly reswells and relaxes back to the stable swollen state. The phenomenon can be explained by a chemomechanical version of the propagation of an excitability wave [13]. After the initial acid perturbation, the core of the cylindrical OSFR switches to the acid-core reacted state. The acid core contaminates the neighboring unreacted swollen part by diffusion, which, in turn, shrinks, following the acid wave. But the collapse of the gel undershoots the critical size Rinf below which the reacted acid state is stable. Diffusion from the boundary overtakes the reaction, the composition... 

Reoxidation occurs when the metallic iron in hot DRI reacts with oxygen in the air to form either Ee O or Ee202. The reaction continues as long as the DRI remains hot and sufficient oxygen is avadable. Because reoxidation reactions are exothermic and DRI is a good insulator, it is possible that once reoxidation begins inside a pde, the DRI temperature increases and accelerates the reoxidation rate. Although the inner core of the pde may reach temperatures up to the fusion point of iron, the maximum temperature of the outer parts of the pde will be much lower because of heat dissipation. 

Figure 4a represents interfacial polymerisation encapsulation processes in which shell formation occurs at the core material—continuous phase interface due to reactants in each phase diffusing and rapidly reacting there to produce a capsule shell (10,11). The continuous phase normally contains a dispersing agent in order to faciUtate formation of the dispersion. The dispersed core phase encapsulated can be water, or a water-immiscible solvent. The reactant(s) and coreactant(s) in such processes generally are various multihmctional acid chlorides, isocyanates, amines, and alcohols. For water-immiscible core materials, a multihmctional acid chloride, isocyanate or a combination of these reactants, is dissolved in the core and a multihmctional amine(s) or alcohol(s) is dissolved in the aqueous phase used to disperse the core material. For water or water-miscible core materials, the multihmctional amine(s) or alcohol(s) is dissolved in the core and a multihmctional acid chloride(s) or isocyanate(s) is dissolved in the continuous phase. Both cases have been used to produce capsules. 

A key feature of encapsulation processes (Figs. 4a and 5) is that the reagents for the interfacial polymerisation reaction responsible for shell formation are present in two mutually immiscible Hquids. They must diffuse to the interface in order to react. Once reaction is initiated, the capsule shell that forms becomes a barrier to diffusion and ultimately begins to limit the rate of the interfacial polymerisation reaction. This, in turn, influences morphology and uniformity of thickness of the capsule shell. Kinetic analyses of the process have been pubHshed (12). A drawback to the technology for some apphcations is that aggressive or highly reactive molecules must be dissolved in the core material in order to produce microcapsules. Such molecules can react with sensitive core materials. 

Figure 4b represents the case where a reactant dissolved in the dispersed phase reacts with the continuous phase to produce a co-reactant. The co-reactant and any remaining unreacted original reactant left in the dispersed phase then proceed to react with each other at the dispersed phase side of the interface and produce a capsule shell. Capsule shell formation occurs entirely because of reaction of reactants present in the droplets of dispersed phase. No reactant is added to the aqueous phase. As in the case of the process described by Figure 4a, a reactive species must be dissolved in the core material in order to produce a capsule shell. 

A specific example of the process represented by Figure 4b occurs when a multihmctional isocyanate is dissolved in a Hquid, water-immiscible core material and the mixture produced is dispersed in an aqueous phase that contains a dispersing agent. The aqueous phase reacts with some of the isocyanate groups to produce primary amine functionaHties. These amino groups react with unreacted isocyanate groups to produce a polyurea capsule shell (13). 

Barium carbonate of finely controlled particle size reacts in the soHd state when heated with iron oxide to form barium ferrites. Magnetically aligned barium ferrite [11138-11-7] powder can be pressed and sintered into a hard-core permanent magnet which is used in many types of small motors. Alternatively, ground up magnetic powder can be compounded into plastic strips which are used in a variety of appHances as part of the closure mechanism. 

Carbon dioxide is widely used in the hardening of sand cores and molds in foundries. Sand is mixed with a sodium siHcate binder to form the core or mold after which it is contacted with gaseous carbon dioxide. Carbon dioxide reacts with the sodium siHcate to produce sodium carbonate and bicarbonate, plus siHcic acid, resulting in hardening of the core or mold without baking. 

CORCON initially assumes that the molten core debris is stratified as a dense oxidic layer on the bottom and a less dense metallic layer on the top. Later, when molten concrete slag dilutes the heavy oxide layer, the lighter oxide layer than the metal layer rises to the top. Each layci is assumed to be isothermal and heat is exchanged between (1) the melt and the concrete, (2) layers of the melt, and (3) the top surface of the melt and the atmosphere above it. When the concrete heats up to about 2500 F, CORCON predicts the release of steam and COj from concrete decomposition. Tile lieat of reaction of the gases reacting with the materials of the melt are calculated. 

A surpnsing feature of the reactions of hexafluoroacetone, trifluoropyruvates, and their acyl imines is the C-hydroxyalkylation or C-amidoalkylaOon of activated aromatic hydrocarbons or heterocycles even in the presence of unprotected ammo or hydroxyl functions directly attached to the aromatic core Normally, aromatic amines first react reversibly to give N-alkylated products that rearrange thermally to yield C-alkylated products. With aromatic heterocycles, the reaction usually takes place at the site of the maximum n electron density [55] (equaUon 5). 

Other addition reactions are shown in the scheme. Thus, Ceo reacts as an olefin towards [Pt (PPh3)2] to give the t adduct [Pt(>j -C6o)(PPh3)2]. Indeed six centres can simultaneously be coordinated by a single fullerene cluster to give [C6o M(PEt3)2 6], (M = Ni, Pd, Pt), with the 6M arranged octahedrally about the core. Likewise, reaction... 

Copper metal is comparatively inactive, but it reacts with concentrated nitric acid. The brown fumes are I l02(g), a reduction product of HN03. The copper is oxidized to Cuz+ ions, which impart their color to the solution. (The penny is an old one made of solid copper. Newer pennies have a coating of copper over a zinc core.)... 

Tannic acid is a strong inhibitor of virus particles in vitro. It inactivated both TMV and TMV-RNA by forming noninfectious complexes (1). TMV-RNA was much more sensitive to inactivation than was whole TMV. It would thus appear that tannic acid could possibly inactivate TMV by reacting with either the protein coat or the RNA core. 

The authors have also elaborated a microwave-enhanced one-pot procedure [90] for the Huisgen 1,3-dipolar cycloaddition reaction. In a typical procedure, a pyrazinone with a triple bond connected to the core via C - O linkage, was reacted with a suitable benzylic bromide and NaNs in presence of the Cu(I) catalyst in a t Bu0H/H20 system under microwave irradiation (Scheme 26). The cycloaddition was found to proceed cleanly and with full regioselectivity. As the azide is generated in situ, this procedure avoids the isolation and purification of hazardous azides, which is especially important when handling the ahphatic ones, which are known to be toxic and explosive in nature. 

Hasegawa s group has also demonstrated that when T8[OSiMe2H]8 reacts with MeOH or Fl20, the silicate core is retained while a cleavage of the SiO-SiMe2H bond occurs. This does not happen for TslOSiMesls indicating that the reactivity... 

The first true dendrimers were the polyamidoamines (PAMAMs). They are also known as starburst dendrimers, and the term starburst is a trademark of the Dow Chemical Company, who have commercialized these materials for a range of applications. These dendrimers use ammonia as the core molecule, and this is reacted with methyl acrylate in the presence of methanol, after which ethylenediamine is added. This is shown in Scheme 9.2. 

Electrochemical studies performed in the 7 x Cys-Aspl4 D. afri-canus Fdlll indicate that the reduced [3Fe-4S] center can react rapidly with Fe to form a [4Fe-4S] core that must include noncysteinyl coordination (101). The carboxylate side chain of Asp 14 was proposed as the most likely candidate, since this amino acid occupies the cysteine position in the typical sequence of a 8Fe protein as indicated before. The novel [4Fe-4S] cluster with mixed S and O coordination has a midpoint redox potential of 400 mV (88). This novel coordinated state with an oxygen coordination to the iron-sulfur core is a plausible model for a [4Fe-4S] core showing unusual spin states present in complex proteins (113, 114). 

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