Polyethylene glycol ligands

Water-soluble polymers and polyelectrolytes (e.g., polyethylene glycol, polyethylene imine polyacrylic acid) have been used success-hilly in protein precipitations, and there has been some success in affinity precipitations wherein appropriate ligands attached to polymers can couple with the target proteins to enhance their aggregation. Protein precipitation can also be achieved using pH adjustment, since proteins generally exhibit their lowest solubility at their isoelectric point. Temperature variations at constant salt concentration allow for frac tional precipitation of proteins. 

The simplest way to prepare a biocatalyst for use in organic solvents and, at the same time, to adjust key parameters, such as pH, is its lyophilization or precipitation from aqueous solutions. These preparations, however, can undergo substrate diffusion limitations or prevent enzyme-substrate interaction because of protein-protein stacking. Enzyme lyophilization in the presence of lyoprotectants (polyethylene glycol, various sugars), ligands, and salts have often yielded preparations that are markedly more active than those obtained in the absence of additives [19]. Besides that, the addition of these ligands can also affect enzyme selectivity as follows. 

The development of catalysts for the efficient oxidation of catechol and its derivatives in water is topic of ongoing work in this laboratory. Towards this end, polyethylene glycol side-chains were incorporated in a pentadentate salen ligand to enhance the water solubility of the complexes derived thereof. A dinuclear copper(II) complex is found to catalyze the oxidation of 3,5-di-tert.-butylcatechol into 3,5-di-tert-butyl-o-benzoquinone more than twice as fast in aqueous organic solution as in purely organic solvents (ly,at/knon= 140,000). Preliminary data are discussed. 

In our ongoing efforts to develop oxidation catalysts that are functional in water as environmentally berrign solvent, we synthesized a water-soluble pentadentate salen ligand with polyethylene glycol side chairts (8). After coordination of copper(II) ions to the salen ligand, a dinuclear copper(II) complex is obtained that is soluble in water, methanol and mixtures of both solvents. The aerobic oxidation of 3,5-di-tert.-butylcatechol (DTBC) into 3,5-di-terr.-butylqitinone (DTBQ) was used as a model reaction to determine the catalytically active species and initial data on its catalytic activity in 80% methanol. 

Chiral bisoxazolines (box) ligands have been attached to a polyethylene glycol (PEG) matrix 25.24 The supported ligands were tested on a variety of reactions for their enantioselectivity. The carbonyl-ene reaction between a-methyl styrene or methylene cyclohexane (26, Equation (15)) and ethylglyoxalate 12 afforded the corresponding ene adduct 27 in 96% and 91% yield and 95% and 85% ee, respectively. 

To avoid difficulties with the low solubility of Pd/TPPTS the monosul-fonated triphenylphosphine (TPPMS) was used as the ligand, which is less polar than the trisulfonated TPPTS. With the following solvents s3 a homogeneous phase is obtained DMF, DMSO, PEG 400 and isopropyl alcohol. A smaller amount of the mediator is required if TPPMS is used than with TPPTS as the hgand. hi further experiments the use of polyethylene glycol... 

PEG)-modified ligands [e.g. polyethylene glycol triphenylphosphine oxide (PETPPO) and methyl polyethylene glycol diphenylphosphine (MDPP)— Pig. 5] was investigated. 

Keywords Immobilization Thermoregulated catalysis Thermomorphic ligands Hydroformylation Polyethylene glycol modified phosphites... 

Efforts should be made to stabilize an enzyme s activity. Certain agents (such as glycerol, ammonium ions, boric acid, polyethylene glycol, and even talcum powder or bentonite clay) have proven widely to be effective enzyme stabilizers. For multisubstrate enzymes, inclusion of one particular substrate with the enzyme (in the absence of other substrates or cofactors) often stabilizes an enzyme s catalytic activity. Such a substrate may also assist in unlocking the enzyme from a particularly inactive conformational form. In addition to substrates, other ligands and effectors (including reaction products. 

All but the polyurethane are characterized by methylene backbones with ligands that are sufficiently polar to make them water soluble. Thus, upon dissolution in water, the polarity of the water molecule associates with the polarity of the acrylic or acrylamide groups to form a shell. We discussed hydrophilic polyurethanes that are typically cross-linked and are not (but could be) considered effective thickeners. Nevertheless they too have hydration shells developed due to the influence of the polyethylene glycol backbone. The extent of that shell is determined by the hydro-philicity of the ligand the acrylic > acrylamide > alcohol > polyurethane. The volume... 

Shanbhag, V.P. and Johansson, G. 1974. Specific extraction of human albumin by partition in aqueous biphasic containing polyethylene glycol) bound ligand. Biochem. Biophys. Res. Com-mun. 61 1141-1146. 

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