Tendency of aggregation

A few materials are given that can be used as primary fluorescence standards in the adsorbed state, because they have high yields, show little tendency of aggregation provided the surface coverage is low, and are photochemically stable ... 

Until recently, the tendency of aggregates of cellulose molecular chains to develop what has been recognized as a right-handed helical twist has not been regarded as relevant and considered a likely artifact of methods of preparation for electron microscopic observation. It was noted, however, some two decades ago by Haigler that... 

Fig. 2.9. Heat capacity as in Fig. 2.7. At constant difference Wdd-Woo but increasing tendency of aggregation, the transformation, which is initially lambdashaped, changes into a step-like transformation...

Murakami et al. have synthesized numerous substituted [20]- and [lO.lOJparacyclo-phanes like 70 Because of low solubility and a high tendency of aggregation, a complexation with clear stoichiometry and geometry has not been achieved. Nevertheless, a remarkable acceleration of the hydrolysis of p-nitrophenol esters has been observed, which is explained in terms of the formation of inclusion complexes between host and substrate. 

The relative stabilities of P-structures were investigated by means of dilution experiments. Homooligopeptides of various residues were subjected to this approach suggesting the following order of increasing tendency of aggregation ... 

The methodology for preparation of hydrocarbon-soluble, dilithium initiators is generally based on the reaction of an aromatic divinyl precursor with two moles of butyUithium. Unfortunately, because of the tendency of organ olithium chain ends in hydrocarbon solution to associate and form electron-deficient dimeric, tetrameric, or hexameric aggregates (see Table 2) (33,38,44,67), attempts to prepare dilithium initiators in hydrocarbon media have generally resulted in the formation of insoluble, three-dimensionally associated species (34,66,68—72). These precipitates are not effective initiators because of their heterogeneous initiation reactions with monomers which tend to result in broader molecular weight distributions > 1.1)... 

Morishima etal. [29 — 31] prepared amphiphilic copolymers of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) with various hydrophobic comonomers, and studied the tendency of their self-aggregation and the nature of the hydrophobic microdomains thus formed in aqueous solution. Chart 1 shows some of these amphiphilic copolymers. Here, the value of x indicates the mol% content of hydrophobic comonomer units. 

Some ice creams contain sodium citrate to decrease the tendency of fat globules to coalesce, and to decrease protein aggregation. This results in a wetter ice cream. The citrates and phosphates are both used for this effect. Calcium and magnesium salts have the opposite effect, making a dryer ice cream. 

The perceived sensitivity of plant cells to the hydrodynamic stress associated with aeration and agitation conditions is typically attributed to the physical characteristics of the suspended cells, namely their size, the presence of a cell wall, the existence of a large vacuole, and their tendency to aggregate. Table 1 illustrates some of the differences between plant cells and other biological systems. Chalmers [19] attributed shear sensitivity in mammalian cultures at least in part to the fact that these cells occur naturally as part of a tissue, surrounded by other cells. The same is true for plant cells. The more robust microbial systems, on the other hand, exist in nature as single organisms or mycelial structures, very close to the forms they assume in submerged culture. 

Nevertheless, the shape of the isotherm in Fignre 3 is qnite similar to those of molecular films in their solid condensed state. This reflects the strong tendency of the particles to aggregate at the air-water interface. Visnal inspection dnring spreading indicates the for-... 

The frequent breaking and reforming of the labile intermolecular interactions stabilizing the reversed micelles maintain in thermodynamic equilibrium a more or less wide spectrum of aggregates differing in size and/or shape whose relative populations are controlled by some internal (nature and shape of the polar group and of the apolar molecular moiety of the amphiphile, nature of the apolar solvent) and external parameters (concentration of the amphiphile, temperature, pressure) [11], The tendency of the surfactants to form reversed micelles is, obviously, more pronounced in less polar solvents. 

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