Deaggregation

A retained its compact capsule shape no matter what the initial pH of the dissolution medium. Moreover, the dissolution rate of phenytoin from preparation A was pH-independent. Preparation B, however, broke down into fine particles. When the initial pH was neutral, these particles rapidly dissolved. As the initial pH was lowered, these fine particles precipitated. Since these precipitated particles then dissolved very slowly, it would appear that the precipitate was not the freely soluble sodium phenytoin, but the poorly soluble acid form of phenytoin. Since capsule A did not disintegrate or deaggregate, most of the sodium phenytoin was not exposed to the lower pH media and, as a result, was not converted to its very slowly dissolving acid form. 

Fig. 11 Cartoons of tum-on mechanisms. The target (in red) may (a) remove a quencher, (b) deaggregate chains, or (c) twist the backbone, leading to increases in emission...

A general procedure has been reported by Killian et al. for the incorporation of hydro-phobic peptides into micelles [75]. Therein, the peptides were first dissolved in TFA for deaggregation, dried under nitrogen and redissolved as 5 mM (clear) solutions in TFE or HFIP. The solution is subsequently diluted 1 1 by addition of an aqueous solution containing a varying SDS concentration (typically 500 mM, depending on the protein concentration). Water is then added to yield a 16 1 ratio of water to TFE (HFIP) by volume. Upon addition of excess water the peptide loses its solubility, but at the same time the... 

Sessler JL, Jayawickramarajah J, Gouloumis A et al. (2006) Guanosine and fullerene derived deaggregation of a new phthalocyanine-linked cytidine derivative. Tetrahedron. 62 2123-2131. 

Since Lewis base additives and basic solvents such as tetrahydrofuran are known to deaggregate polymeric organolithium compounds, (21,23,26) it was postulated that ketone formation would be minimized in the presence of sufficient tetrahydrofuran to effect dissociation of the aggregates. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium (eq. 9), poly(isoprenyl)-lithium, and poly(styrene-b-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the carboxylic acid chain ends (8 ). 

By provoking the complete deaggregation of the growing chains as initiated by R2AIOR. This is the case of secondary amines, the addition of which increases the overall rate of polymerization [55]. 

The LIC-KOR reagent consisting of stoichiometrically equal amounts of butyllithium ( LIC ) and potassium feri-butoxide ( KOR ) was conceived in Heidelberg and optimized in a trial-and-error effort . The fundamental idea was simple. To activate butyllithium optimally by deaggregation and carbon-metal bond polarization, a ligand was required that would surpass as an electron donor any crown ether but not suffer from the drawback of the latter, i.e. its proneness to /3-elimination. Whereas pinacolates and other v/c-diolates proved too labile to be generally useful, potassium terf-butoxide or any other bulky, hence relatively soluble, potassium or cesium alkoxide was found to serve the purpose. ... 

Detailed NMR and theoretical studies have identified and characterized a number of the complexes along the proposed reaction pathways for anisole, 1,2-dimethoxybenzene and Al,Al-dimethylaniline ° . For example, anisole deaggregates the BuLi hexamer to form a tetrameric BuLi-anisole complex 4. Adding TMEDA displaces the anisole from the tetramer and breaks it down further to give a BuLi-TMEDA dimer 5, which deprotonates anisole at >0°C yielding 6 (Scheme 4). 

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