Aggregative stability, definition

Alkyllithium compounds have solubility and stability because of their ability to associate to form aggregates of definite structure. Such aggregation confers stability but is not extensive enough to cause insolubility. Methyllithium and n-butyllithium, for instance, exist in a highly associated form, typical of electron-deficient bonding, e.g., (MeLi) and (BuLi)4. 

In aggregate stabilization we are by definition (Martin et al. 1955) concerned with both the forces and conditions that exist within the aggregate, and with those that exist on the outside. The former are so much more important that the latter are often ignored. 

Climate is often viewed as the aggregate of all of the elements of weather, with quantitative definitions being purely physical. However, because of couplings of carbon dioxide and many other atmospheric species to both physical climate and to the biosphere, the stability of the climate system depends in principle on the nature of feedbacks involving the biosphere. For example, the notion that sulfate particles originating from the oxidation of dimethylsulfide emitted by marine phytoplankton can affect the albedo (reflectivity) of clouds (Charlson et ai, 1987). At this point these feedbacks are mostly unidentified, and poorly quantified. 

On the other hand, cell immobilization on carriers definitively improves bioreactor efficiency. Cell aggregation in a biofilm structure increases process stability and tolerance to shock loadings. A proper selection of operating conditions allows... 

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. 

Pauling offered the following definition of a chemical bond ... there is a chemical bond between two atoms or groups of atoms... (if) forces acting between them are such as to lead to the formation of an aggregate with sufficient stability to make it convenient for the chemist to consider it as an independent molecular species. Chemical bonds include ionic bonds, coordinate covalent... 

Although most colloidal dispersions are not thermodynamically stable, a consequence of the small size and large surface area in colloids, and of the presence of an interfacial film on droplets, bubbles or particles, is that dispersions of these species, having reasonable kinetic stability, can be made. That is, suspended droplets or particles may not aggregate quickly nor settle or float out rapidly and droplets in an emulsion or bubbles in a foam may not coalesce quickly. Many food and personal care product emulsions and suspensions, for example, are formulated to remain stable for months to years. It is crucial that stability be understood in terms of a clearly defined process, and one must consider the degree of change and the time-scale in the definition of stability. 

This is a novel type of polymer effect due to a polymer chain shape where chemical bond stability is impaired by superimposed random shearing forces at some definite site of the molecule. A similar effect has been reported by Oster upon sonic treatment of tabacco mosaic virus where the polymer aggregates are dissociated75). 

As mentioned above, intermolecular interactions are the interactions that a stable molecule experiences in the presence of other molecules (not necessarily of the same type) [1], We consider as stable molecules any aggregate of atoms having a long enough stability and lifetime, on a chemical scale. This definition also considers as stable molecules, open-shell radicals whose chemical structure makes them long-living, like those found in molecular magnets (for instance the family of the nitronyl nitroxide radicals). 

Colloid Stability In colloid science, an indication that a specified process, such as aggregation, does not proceed at a significant rate, which is different from the definition of thermodynamic stability (4). The term colloid stability must be used with reference to a specific and clearly defined process, for example, a colloidally metastable emulsion may signify a system in which the droplets do not participate in aggregation, coalescence, or creaming at a significant rate. 

Does heat-induced aggregation involve in all cases unfolded protein molecules In Sec. II we saw that BSA and ovalbumin have a definite tendency to aggregate at room temperature this could be also the case for HSA [141] and RNase [161], since the heat stability of these proteins depends on concentration. Does this tendency increase with temperature below the temperature of incipient unfolding How could this aggregation process involving native species affect heat-induced unfolding ... 

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