Entangled polymer solutions, protein

One tool for working toward this objective is molecular mechanics. In this approach, the bonds in a molecule are treated as classical objects, with continuous interaction potentials (sometimes called force fields) that can be developed empirically or calculated by quantum theory. This is a powerful method that allows the application of predictive theory to much larger systems if sufficiently accurate and robust force fields can be developed. Predicting the structures of proteins and polymers is an important objective, but at present this often requires prohibitively large calculations. Molecular mechanics with classical interaction potentials has been the principal tool in the development of molecular models of polymer dynamics. The ability to model isolated polymer molecules (in dilute solution) is well developed, but fundamental molecular mechanics models of dense systems of entangled polymers remains an important goal. 

D. Blankschtein, and T. A. Hatton, Protein partitioning in two-phase aqueous polymer systems. 4. Proteins in solutions of entangled polymers, Macromolecules 1992c, 25, 5192-5200. 

Because the partitioning behavior of proteins in two-phase aqueous polymer systems reflects the relative interactions between the proteins and the two coexisting polymer solution phases, and because the independent control of the polymer concentration in only one of the two coexisting phases is not possible, we have explored an alternative experimental technique, namely, the measurement of the partitioning of proteins between an entangled PEO solution phase and an aqueous (polymer-free) phase using a diffusion cell (24). 

It can be seen that the addition of com steep liquor to a xanthan solution led to a drastic decrease in the viscosity in conjunction with an increase of the Huggins constant (Fig.l). This decrease of the macromolecule dimension, due to an entanglement of the polymer chains, and the prevalence of polymer-polymer interactions to solvent interactions, indicate that the polysaccharide molecules are aggregated. A possible explanation of this phenomenon is that proteins from com steep liquor can induce interactions between xanthan chains, forming xanthan-protein complexes. 

Chemically, rubber is dr-l,4-polyisoprene, a linear polymer, having a molecular weight of a few tens of thousands to almost four million, and a wide molecular-weight distribution. The material collected fi om the rubber tree is a latex containing 30-40% of submicron rubber particles suspended in an aqueous protein solution, and the rubber is separated by coagulation caused by the addition of acid. At room temperature, natural rubber is really an extremely viscous liquid because it has a Tg of —70°C and a crystalline melting point of about —5°C. It is the presence of polymer chain entanglements that prevents flow over short time scales. 

---