Macromolecular stabilizers

Laederach, A., Shcherbakova, I., et al. (2007). Distinct contribution of electrostatics, initial conformational ensemble, and macromolecular stability in RNA folding. Proc. Natl. Acad. Sci. USA. ... 

The proton, the smallest solute in the cellular water, illustrates particularly well the critical role of the aqueous milieu of the cell in governing macromolecular stability and function under both stable and variable thermal conditions. One of the ubiquitous features of cellular regulatory processes involves control of pH. No type of cell allows the proton activity within its cytoplasm to equilibrate with that of the external medium, whether the medium in question is the external environment or the extracellular fluids. Organelles, too, may maintain a steep proton gradient between the intra-organellar fluids, for instance, the mitochondrial matrix, and the cytoplasm. 

Exploitation of Pendant Reactive Groups. Pendant and linkage forming stabilizing moieties can be created in this way. Macromolecular stabilizers thus formed have general structures B, C, and E (Scheme 1) and are formally structurally related to stabilizers prepared by other polyreactions. The distribution mode of stabilizing moieties and the presence of foreign structures and mentioned above represent the main difference between stabilizers prepared via different synthetic approaches. 

It has been generally accepted that macromolecular stabilizers protect polymers by the same physical or chemical mechanism as conventional stabilizers containing a comparable functional moiety. (For details dealing with activity mechanisms of macromolecular stabilizers see Sect. 4.2.) Some differences must be however taken into consideration due to the macromolecular character of polymeric stabilizers. 

Improvement of physical persistence was the main aim of the development of the latter. The problem of stabilizer volatilization was solved practically by the application of HMW stabilizers. The extraction problem remains however open even with the macromolecular stabilizers. Oligomeric stabilizers are slowly lost. 

Due to the above-mentioned physical facts, some differences in mechanistic details in the effectivity between conventional and macromolecular stabilizers should be expected. 

Macromolecular stabilizers are immobile in the polymer matrix [284], This is unfavourable for applications where surface concentration of stabilizers in thick-walled products should remain high. It was reported [34] that rubber-bound derivatives of PD provide only very poor antiozonant protection. Their antioxidant efficiency was only comparable with that of conventional HMW PD. This indicates that application of polymer-bound amines in rubbers has the prospect of exclusive long-term use in extracting media. 

Most papers analysing properties of functionalized macromolecular stabilizers deal with HAS. The rating conditions and the host material may cause some discrepancies in results. 

Like all polymers, proteins and DNA are composed of a sequence of repeating units that interact at various levels to produce the active structure. Although the primary structure of DNA does largely determine its physical and biological properties, that of proteins is of minimal use in determining the desired active structure. This section is not intended to replace a biochemistry textbook, but it provides the basic information necessary to understand how the molecular structure of proteins and plasmid DNA differ, and how this impacts macromolecular stability in a general sense. 

Several other examples may be found in the literature, in which a correlation between the interfacial viscosity of macromolecular stabilized films with droplet stability was found. However, there are also a number of cases where stable emulsions could be prepared without any significant interfacial viscosity or elasticity. It can be concluded, therefore, that one should be careful in using interfacial rheology as a predictive test for emulsion stability. Other factors, such as film drainage and thickness, may be more important. In spite of these limitations, interfacial rheology offers a powerful tool for understanding the properties of surfactant and macromolecular films at the liquid/liquid interface. In cases where a correlation between the interfacial viscosity and/or elasticity and emulsion stability is found, one could use these measurements to screen various other components that have a marked effect on these parameters. 

Typical emulsion polymerizations utilize oil-soluble monomers dispersed in an aqueous media with a water-soluble initiator, whereas inverse emulsions employ water-soluble monomers dispersed in an organic medium containing an oil-soluble initiator. The insoluble polymer particles that result from these reactions are stabilized as colloids in solution by repulsive forces imparted by a small molecule ionic surfactant and/or an amphiphilic macromolecular stabilizer (56,57). These reactions produce high molecular weight, spherical polymer particles with sizes typically smaller than 1 fj,m. Since most common monomers are highly soluble in CO2, there are very few examples of C02-based emulsion poljnnerizations. However, acrylamide is a rare example of a vinyl monomer that has a low solubility in CO2 at moderate temperatures and pressures. The AIBN-initiated water-in-oil or inverse emulsion polymerization of acrylamide has been attempted at 65°C in 35.2 MPa (352 bar) CO2 (41,58) (eq. (3)). 

Several other examples may be found in the literature [65], in which a correlation between the interfacial viscosity of macromolecular stabilized films with droplet stability was found. However, there are also several cases where stable emulsions could be prepared without any significant interfacial viscosity or elasticity. There-... 

The main contribution to the stability of macromolecular-stabilized emulsions is related to droplets reaching a distance where compression due to polymer... 

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