Polyethylene glycol model systems

Wiesmet V, Weidner E, Behme S et al (2000) Measurement and modelling of high-pressure phase equilibria in the systems polyethylene glycol (PEG)-propane, PEG-nitrogen and PEG-carbon dioxide. J Supercrit Fluids 17(1) 1-12... 

Apparently, no colloids are formed when polyethylene glycol is added to rhodium trichloride hydrate to obtain a water-soluble rhodium polyethylene glycolate highly active in the hydroformylation of heavy alkenes such as dodec-l-ene [75]. Such a system does not require the presence of other ligands and works efficiently at 70-120 bar. Besides a hypothesis in which it is envisioned a migration of the catalyst into the organic phase, a model where the reaction takes place in the interphase, due to the presence of polyethylene glycol, is favored. 

The activity of some polyethylene glycols bonded with macroporous copolymers of glycidylmethacrylate during the interfacial catalysis of the model reaction of sodium phenolate with n-BuBr, were investigated [79]. Rate constants of phenol alkylation in the aqueous system NaOPh-n-BuBr (in toluene)-PEG were measured at 60°C as a function of the molecular weight of PEG and its concentration. The obtained results were compared with the data on the kinetics of the reaction occurring in the presence of soluble PEG. Upon the insertion of immobilized and soluble PEG, alkylation rates increased 168 and 139 fold, respectively. The increase of the catalytic activity of immobilized PEG, which corresponded to a rise in the molecular weight of the polymer, was caused by an increase in the PEG ability to sorb alkali metal cations. 

DAL Dallora, N.L.P., Klemz, J.G.D., and Filho, P. de A.P., Partitioning of model proteins in aqueous two-phase systems containing polyethylene glycol and ammonium carbamate, Biochem. Eng. J., 34, 92, 2007. 

The stretching and rupture of a polyethylene glycol (PEG) fragment was examined in water to determine the impact of solvent molecules on the rupture process. The model system included water molecules in the simulation supercell and the molecule was stretched at constant velocity in the maimer described above. Two simulations were completed at 250 K and 320 K. The findings determined that both the presence of water influenced the rupture mechanism, and that the reactivity of the PEG molecule was affected by the elongation. Two reaction mechanisms were observed at 250 K and 320 K but both pathways were similar in their overall form (Fig. 12). 

The interfacial tension between CO2 and various condensed phases including water [63], styrene oligomers[64] and polyethylene glycol[8] has been measured with a tandem variable-volume tensiometer and modeled with gradient theory. Also surfactants were added to these systems to lower the interfacial tension and to determine the surfactant adsorption. A critical micelle concentration was observed for... 

Molecular dynamics (MD) is a method in which Newton s equations of motion are solved for a molecular system obeying a differentiable potential function. A few efforts at modeling proteins at interfaces using MD have appeared (183-187). Obviously, these studies provide dynamic as well as thermodynamic information on biomolecules at interfaces. Systems studied have included lysozyme and myoglobin on polyethylene glycol (183), cytochrome c on hydrophilic and hydrophobic self-assembled monolayers (184), leucine enkephalin near a crystalline polyethylene surface (185), thermal hysteresis proteins on ice (186), and lysozyme on polyvinylimidazole (187). 

A number of studies have been made into the use of SLMs for CO2 separation and the most recent works have investigated amine based carrier systems. Meldon et al. (1986) used mono-, di- and tri-ethanolamine in polyethylene glycol solution whilst Davis and Sandall (1993) compare the performance of diethanolamine (DEA) and diisoproponal-amine as CO2 carriers. Guha et al. (1990) and Teramoto et al. (1996) also investigated the use of aqueous DEA in SLMs for CO2 separation and published models for predicting the flux of CO2 through flat-sheet membranes. Both models were derived in the same way but different solution methods were used. 

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