De-aggregation

Other aspects of solvation have included the use of surfactants (SDS, CTAB, Triton X-100), sometimes in pyridine-containing solution, to solubilize and de-aggregate hemes, i.e., to dissolve them in water (see porphyrin complexes, Section 5.4.3.7.2). An example is provided by the solubilization of an iron-copper diporphyrin to permit a study of its reactions with dioxygen and with carbon monoxide in an aqueous environment. Iron complexes have provided the lipophilic and hydrophilic components in the bifunctional phase transfer catalysts [Fe(diimine)2Cl2]Cl and [EtsBzNJpeCU], respectively. 

The chiral a-cyano allylamines prepared from ( )-3-phenylpropenal, potassium cyanide and (L)-ephcdrinc [(17 ,2S )-2-methylamino-l-phenylpropanol] hydrochloride as a mixture (1 1) of C-l epimers, were deprotonated using 2 equivalents of LDA in THF to give the dilithio compound37. Alkylation at C-3 afforded regioselectively a mixture of (E)- and (Z)-enamines in variable amounts depending on reaction conditions. Diastereoselectivity varied from moderate to excellent. Addition of HMPA and especially lithium iodide improved the diastereoselectivity. De-aggregation is proposed to be the reason for the effect of these additives. 

Crotonaldehyde dimethyl acetal (7 Scheme 1) can undergo metallo-dehydrogenation or nucleophilic addition 9 for the example of n-butyllithium, the products of different experimental conditions are shown. The alternative pathways have been modelled computationally by examining the reactions of (7) with methyllithiurn and methylpotassium. The role of the potassium alkoxide in diverting the reaction towards diene is twofold it de-aggregates (RLi) , and promotes a partial cleavage of the carbon-lithium bond. 

Perhaps the most common method for preparing polymer-nanotube composites has been to mix the nanotubes and polymer in a suitable solvent before evaporating the solvent to form a composite film. One of the benefits of the solution casting method is that agitation of the nanotube powder in a solvent facilitates nanotube de-aggregation and dispersion. Almost all solution processing methods are variations on a general theme which can be summarized in three major steps ... 

In general, de-aggregation and dispersion of carbon nanotubes are provided by magnetic stirring, shear mixing, reflux, or, most commonly, ultrasonication. Sonication can be provided in... 

Kumar R, Antolino N, Wichard JE, Sutovich KJ, Chapman DM, Roberie TG, et al. Optimized de-aggregation and dispersion of high concentration slurry of nanophase alumina by chemically aided attrition milling. Working paper, 2005. 

Once the experimental heat data have been corrected to remove all contributions (e.g., heats of dilution, mixing, or de-aggregation) that do not derive from the binding process of interest, the observed heat response contains all the information on the simultaneous events happening at... 

From the above results, it could be concluded that the addition of excess amount of sodium ions into the crystallization system has apparent effect on the particulate properties of the product. At low batch alkalinity, the additional sodium ions causes de-aggregation of the final products, rendering the particles with more uniform size distributions. At high batch alkalinity, the excess amount of sodium ions triggers the surface condensation reactions on the crystalline end products. However, the crystallization rate is not enhanced by the increase of batch sodium ion content, indicating that the determining factor of crystallization of ZSM-5 zeolites in SDA-free system is concentration of low molecular weight silicate species, determined by batch alkalinity. 

Sessler, J. L. et al. Guanosine and fiiUerene derived de-aggregation of a new phthalocyanine-linked cyti-dine derivative. Tetrahedron 62, 2123-2131, 2006. 

Treatment of (7 )-cinnamaldehyde (70) with an equivalent of phenyllithium in THF yields the enol (71), as expected. However, a number of other products are formed with an excess, including dihydrochalcone (72), the result of a tandem addition )3-alkylation. Observed concentration effects and variation of product distribution with reaction conditions, together with computational results, point towards a mechanism in which dimeric PhLi attacks the aldehyde without prior de-aggregation. ... 

How about the other metals In the case of molybdenum a simultaneous irradiation with UV light is necessary to get the Mo(VI) attacked by CO [26, 27]. Even then, the average oxidation number reached was not lower than 2.7 (oxygen titration [27]). Spectroscopic evidence shows that the product contains Mo(IV) and Mo(II), formed by the reduction of octahedral and tetrahedral Mo(Vl) [28]. Vanadium(V) requires a very long time and higher temperatures (600 °C) for the reduction by CO [19, 40] (slow de-aggregation ). For iron and copper see Section 18.4.2. 

Thus, anionic polymerization of alkyl (meth)acrylates can propagate via aggregated ion pairs of lower reaaivity and nonaggregated (unimer) ion pairs of higher reactivity. The dynamics of aggregation/de-aggregation greatly influences the control of alkyl (meth)acrylate polymerization as outlined below. 

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