Polyethyleneglycol immobilization

Formate dehydrogenase in conjunction with polyethyleneglycol-immobilized nicotinamide adenine dinudeotide has been used to good effect as a cofactor recycle system (39). The alcohol dehydrogenase from Thermoanaerobium hrockii catalyzed the reduction of ketones independently when driven by the cooxidation of isopropanol (40,41). 

Triphase catalysis is applicable not only to liquid-liquid-solid (L, L, S) systems, but also to liquid-solid-solid (L, S, S) systems. For instance, McKenzie and Sherrington (1978) studied the substitution of phenoxide for bromide in 1-bromobutane using immobilized polyethyleneglycol monoethers such as [131] as triphase catalyst they found (Table 38) that under L, L, S... 

A number of chemical modifications and spacers for the covalent immobilization of PNAs onto surfaces are already available [26]. The spacer at the terminus of PNA strands has an additional function. Due to their uncharged backbone, solubility of PNAs in water is sometimes a problem and therefore hydrophylic spacers (like polyethyleneglycol derivatives) are introduced into the PNA structure not only for steric reasons, but also to avoid solubility problems. 

Figure 6.22. The immobilization of polyoxometalate POM catalyst within a polyethyleneglycol layer.

Further improvement of this process can be reached by immobilization of the enzymes in an EMR. The coenzyme can be enlarged chemically by binding it to polyethyleneglycol (PEG) in order to prevent leakage of the coenzyme through the membrane. This LeuDH catalyzed synthesis of enantiomerically pure L-Tle runs now routinely on a multiton scale at Degussa [154]. 

Figure 5 Starting from natural mRNA, a cDNA library (A blue) is produced and like ribosomal display, the cDNA is transcribed into mRNA (B) with no stop codons. The 3 -end of each mRNA molecule is ligated to a short synthetic DNA linker (C) and sometimes a polyethyleneglycol spacer, which terminates with a puramycin molecule (small red sphere). The ligation is stabilized by the addition of psoralen (green clamp), which is photoactivated to covalently join both strands. Addition of crude polysomes or purified ribosomes (D) results in translation of the mRNA into protein, but the ribosome stalls at the mRNA-DNA junction. Since there are no stop codons, release factors cannot function and instead the puromycin enters the A-site of the ribosome (A). Because puramycin is an analog of tyrosyl-tRNA, the peptidyl transferase subunit catalyzes amide bond formation between the puromycin amine and the peptide carboxyl terminus, but is unable to hydrolyze the amide link (which should be an ester in tyrosyl-tRNA) to release the dimethyladenosine. The ribosome is dissociated to release the mRNA-protein fusion (E), which is protected with complementary cDNA using RT-PCR (F). The mRNA library can then be selected against an immobilized natural product probe (G), nonbinding library members washed away and the bound mRNA (H) released with SDS. PCR amplification of the cDNA provides a sublibrary (A) for another round of selection or for analysis/ sequencing.

For soluble reactants and products, enzymes are preferentially immobilized in an enzyme-membrane reactor (EMR). To prevent the cofactor from penetrating through the membrane, it can be enlarged with polyethyleneglycol (PEG) 163l... 

Fig. 10 Typical time coiu se of frequency changes of the dsDNA 1-immobilized QCM, responding to the addition of ATP-dependent DNase and ATP at arrows. Curve a DNase was added at first, and then ATP was excessively added after the enzyme bound. Curve b DNase was added in the presence of excess ATP. Conditions 66.7 mM Glycine-NaOH buffer, pH 9.4, 30 mM MgCl2, 8.4 mM 2-mercaptoethanol, 0.1% Nonidet P-40 (ethylphenyl polyethyleneglycol), 30 °C, [DNase] = 138 nM, [ATP] = 0.5 mM...

Mixtures of polyethyleneglycols (and ethylene oxide-propylene oxide copolymers), a base and a peroxide (or other radical initiators) allow the preparation of several reagents which, suitably formulated according to their different use, are able to degrade the chemically stable chlorinated aromatics. Such a method, called CDP-Process, is active on TCDD and can be applied in different ways as an example, the reagent, when immobilized on a solid bed, allows the continuous-flow decontamination of mineral oils containing PCB this is useful for the decontamination of an electrical transformer during operation. Another reported example is the decontamination of surfaces contaminated by PCB or PCB fires (where PCDF and PCDD are also present). 

In contrast to earlier polymer-supported complex catalysts in which complexes were immobilized through electrostatic interaction, covalent bonds, or coordinative bonds, in this case the complex is captured in Ihe elastomer network by occlusion in a dense polymer in Ihe absence of any supplementary chemical bonding and only as result of steric restrictions. In the hydrogenation of methyl acetoacetate by this catalyst an ee of 70% was obtained in polyethyleneglycol solution at 60 °C. Afer regeneration of the catalyst and reuse, its activity and enantioselectivity were almost unchanged. 

Arthrobacter simplex cells coprecipitated with calcium alginate gel have been used for the production of prednisolone from cortisol.The conversion of hydrocortisone into prednisolone has been czxned out ismg Arthrobacter simplex cells entrapped in a polypropylene glycol-polyethyleneglycol copolymer,in a maleic polybutadiene gel, or in urethane prepolymers.Mass-transfer effects on the rate of isomerization of D-glucose into D-fructose catalysed by commercially available immobilized Arthrobacter cells have been investigated and a theoretical treatment proposed. 

In 2000, Reiser [96] reported the first immobilization of aza-bis(oxazolines). Aza-bis(oxazoline) 74b has been easily grafted to a soluble polymeric support ((methoxy(polyethyleneglycol) MeOPEG 5000) in order to form soluble catalysts which could be recovered by precipitation. This polymer (100 Scheme 47) was obtained successfully (55% yield) if a benzylidene spacer linked to the PEG was employed. Complexed with Cu(II), this ligand was able to promote asymmetric cyclopropanation of styrene (Scheme 36 Ri = Ph, R2 = H, R3 = Me, R4 = H) and 1,1-diphenylethene (scheme 36 ... 

There is a quest for more integrated systems in which not only the enzyme but also the mediator is immobilized on the electrode surface. Two approaches have been followed for this purpose. One uses antigen-antibody immobilization of the enzyme, while the second rehes on the avidin-biotin interaction. In both cases, the cosubstrate is linked to one end of a long polyethyleneglycol chain attached to the structure by its other end. 

To achieve high covalent-immobilization efficiency, several important factors must be optimized including protein load, pH, ionic strength, temperature, mass volume ratio, and agitation rate [70,71]. Moreover, it is sometimes necessary to add protective molecules such as carbohydrates and polyethyleneglycol to avoid enzyme denaturation and/or inactivation during conjugations. 

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