Polyethylene alanine

A solution to this problem is the enzyme membrane reactor (Figure 10.8). This is a kind of CSTR (continuous stirred tank reactor), with retains the enzyme and the cofactor using an ultrafiltration membrane. This membrane has a cut-off of about 10000. Enzymes usually have a molecular mass of 25000-250000, but the molecular mass of NAD(H) is much too low for retention. Therefore it is first derivatized with polyethylene glycol (PEG 20000). The reactivity of NAD(H) is hardly affected by the derivatization with this soluble polymer. Alanine can now be produced continuously by high concentrations of both enzymes and of NAD (H) in this reactor. 

Similar results were obtained when polyethylene was modified by grafting acrylamide and cholesterol ester of N-methacryloyl-[3-alanine to get 0.3 + 0.1 mg UChD/ cm2. The efficiency of UChD bound to polymer was close to that of UChD immobilized in a polyacrylamide gel the graft copolymers sorbed from the plasma solution the amount of 0.9 mg heparin/mg of immobilized UChD. The clotting time of blood contacting the modified (but not heparinized) polyethylene was 6 min, whereas on its heparinization the time increased to 30 minutes. The latter figure was actually unaltered after sixfold repetition of the heparin sorption, subsequent washing heparin off the polymer and its repeated sorption. 

Fig. 7.3. Alanine production with cofactor regeneration. The black and gray dumbbell shapes are the reduced and oxidized forms of the NAD cofactor bound to polyethylene glycol.

ZAGORSKI, Z.P., RAFALSKI, A., A thin alanine-polyethylene film dosimetry system with diffuse reflection spectrophotometric evaluation J.Radioanal.Nucl.Chem., Articles, 196(1995) 97-105. 

In addition to the equipment properties and selected operating conditions, the process performance depends to a large extent on the state of the active solvent component(s). Commonly nsed solvents include physical solvents like methanol (Rectisol) and the dimethyl ethers of polyethylene glycol (Selexol), chemical solvents like aqneous solutions of carbonates such as K2CO3 and Na2C03, of amino acid salts such as mixtures of potassium hydroxide and alanine or tanrine, and especially of alkanolamines such as mono-ethanolamine (MEA), di-ethanolamine (DEA), (activate) methyl-di-ethanolamine (MDEA), di-isopropanolamine (DIPA), di-glycolamine (DGA), 2-amino-2-methyl-l-propanol (AMP), and piperazine (PZ) (1). 

As can be seen from Table 3 all of these accordion-like modes lie in the range 5—70 cm . Until recently there was scant hope of observing such low frequencies in the Raman. However, this is now possitde. While no one has yet been able to find these modes in poIy-L-alanine they have been seen in polyethylene and these experiments will be discussed below. 

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