Enzyme activated monomer

Acyl-enzyme intermediate (enzyme-activated monomer, EM)... 

The enzymatic polymerization of lactones is explained by considering the following reactions as the principal reaction course (Fig. 9) [83,85,95,96]. The key step is the reaction of the lactone with lipase involving the ring-opening of the lactone to give the acyl-enzyme intermediate (enzyme-activated monomer,... 

It is generally accepted that the eROP of CL is initiated by a nucleophilic attack of a hydroxy compound on the enzyme activated monomer (8-10). Various hydroxy-fimctionalized (macro)initiators have been reported in the past for the enzymatic synthesis of functionalized polymers and block copolymers, respectively (8-11). As outlined above, only a high initiation efficiency of the dual initiator in the eROP leads to high block copolymer yield. This efficiency mainly depends on two factors side reactions caused by competitive water initiation and the initiator design. We achieved the reduction of the water initiation by developing a thorough drying protocol prior to the enzymatic reaction (12). In order to study the influence of the initiator structure, several dual... 

The reaction of TMC with lipase to form the lipase-TMC enzyme-activated monomer (EAM) complex. 

Dimer of trimethylene carbonate Ethylene-acrylic acid Enzyme-activated monomer European Gommission European Ghemicals Agency... 

These findings led to elucidation of the mechanistic aspects of Upase (Novozym 435) catalysis enantioselection is operated by the deacylation step as shown in Fig. 3 [53], where only dimer formation is shown for simphcity. It is well accepted that at first the monomer (substrate) is activated by enzyme with formatimi of an (/ )-acyl-enzyme intermediate (enzyme-activated monomer, EM) [ acylation of lipase step (a) in Fig. 3]. Onto the activated carlxMiyl carbon of EM, the OH group of the D-lactate nucleophUically attacks to form an ester bond, liberating Upase enzyme and giving rise to D,D-dimer [ deacylation of Upase step (b) in Fig. 3]. 

To date, many investigations have been conducted on the (non)-substituted-four-membered lactone polymerizations using enzymes as catalysts. The ratedetermining step in the overall polymerization scheme corresponds to the formation of the enzyme-activated monomer (EAM), which itself is obtained by reaction of the monomer with the catalytic site of the lipase (serine residue), followed by ring-opening cleavage [80]. 

The mechanism of enzyme-catalyzed ROP was first proposed by Uyama et al. [54]. Here, the catalyhc site of lipase is the serine residue, which forms a complex with the lactone, leading to the formation of an enzyme-monomer complex (EMC). The rate-determining step in the overall polymerization was believed to be the formation of EMC (also known as an enzyme-activated monomer ). 

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