Enzymes polycondensation reactions

What is the importance of this enzyme family for the biogenesis problem These enzymes form the link between the protein world and the nucleic acid world . They catalyse the reaction between amino acids and transfer RNA molecules, which includes an activation step involving ATR The formation of the peptide bond, i.e., the actual polycondensation reaction, takes place at the ribosome and involves mRNA participation and process control via codon-anticodon interaction. 

Imbalance in the stoichiometry of polycondensation reactions of AA-BB-type monomers can be overcome by changing to heterofunctional AB-type monomers. Indeed, IIMU has been subjected to bulk polycondensation using lipases as catalyst in the presence of 4 A molecular sieves. At 70 °C, CALB showed 84% monomer conversion and a low molecular weight polymer (Mn 1.1 kDa, PDI 1.9). No significant polymerization was observed with other lipases (except R cepacia lipase, 47% conversion, oligomers only) and in reference reactions with thermally deactivated CALB or in the absence of enzyme. Further optimization of the reaction conditions (60wt% CALB, II0°C, 3 days, 4 A molecular sieves) gave a polymer with Mn of 14.8 kDa (PDI 2.3) in 86% yield after precipitation [42]. 

Polycondensation reactions in oriented monolayers and bilayers proceed without catalysis, and simply occur due to the high packing density of the reactive groups and their orientation in these layers. Bulk condensation of the a-amino acid esters at higher temperatures does not lead to polypeptides but to 2,5-diketopiperazines. No diketopiperazines are found in polycondensed monolayers or liposomes. Polycondensation in monolayers and liposomes leading to oriented polyamides represents a new route for stabilizing model membranes under mild conditions. In addition, polypeptide vesicles may be cleavable by enzymes in the blood vessels. In this case, they would represent the first example of stable but biodegradable polymeric liposomes. 

The production of humic substances by microorganisms is an extracellular process, because the enzymes are secreted into the external solution that contains the phenolic compounds derived from lignin and tannic acid degradation and microbial and plant metabolites. These phenolic compounds can then be enzymatically oxidized to quinones, which can undergo further polymerization or polycondensation reactions with other biomolecules (e.g., amino acids) to form humic polymers (Stevenson, 1994 Bollag et al., 1998 Burton, 2003). 

Rodney, R.L., Allinson, B.T., Beckman, E.J., and Russell, A.). (1999) Enzyme-catalyzed polycondensation reactions for the synthesis of aromatic polycarbonates and polyesters. Biotechnol. Bioeng., 65 (4), 485-489. 

Important progress has been made on the use of immobilized enzyme catalyzed polycondensation reactions to prepare a wide range of polyesters (2,83). In this book, Hunsen et al (20) describe how an inunobilized catalyst from Humilica insolens has excellent activity for polycondensation reactions between diols and diacids. The natural role of cutinases is hydrolysis of the outer cutin polyester layer on plant leaves. Cutin is made of long chain... 

Spicule-forming cells (sclerocytes) into the growing and elongating axial canal. The experiments showed that, around a cell extension that protrudes from a sclerocyte into the axial canal of a given spicule, silicatein molecules are released into the extracellular space of the axial canal (the space between the cell membrane and the inner surface of the siliceous mantel) to catalyze biosilica deposition from the inner surface. This causes the axial canal to narrow from >1 to <0.5 pm. Intracellularly, both the enzyme and its substrate (siUca precursor) are stored in vesicles that have been termed silicasomes (MiiUer et al., 2009a,b). These vesicles are released into the axial canal to allow the enzymatic polycondensation reaction. 

Sucrose-containing linear polyesters 19 have been prepared using various enzymes from sucrose 17 and d rboxylic acid diesters 18 [41]. The polycondensation reaction proems in anhydrous pyridine. An alkaliiK protease from a Bacillus sp. catalyzes the esterification of sucrose with bis(2,2,2-trifluoro-ethyladipate) to give a sucrose-containing polyester with M = 2100. The sucrose polyester is highly water soluble and soluUe in polar organic solvents. 

In another study, lipase-catalyzed silicone polyesteramides in the bulk at 70°C under reduced pressure (10-20 mmHg) have been reported [22]. Novozym-435 was used as the enzyme under mild reaction conditions to perform the polycondensation reaction using various feed mole ratios of diethyl adipate (DBA), 1,8-octanediol (OD), and a,w-(diaminopropyl) polydimethylsiloxane (Si-NH ). The authors also synthesized poly(octamethyleneadipate), POA, and poly(a,w-(diaminopropyl) polydimethyl siloxane adipa-mide), PSiAA, using the same enzyme, and compared their properties with those of silicone polyesteramides. 

An alternative strategy to obtain silica immobilised catalysts, pioneered by Panster [23], is via the polycondensation or co-condensation of ligand functionalised alkoxysilanes. This co-condensation, later also referred to as the sol-gel process [24], appeared to be a very mild technique to immobilise catalysts and is also used for enzyme immobilisation. Several novel functional polymeric materials have been reported that enable transition metal complexation. 3-Chloropropyltrialkoxysilanes were converted into functionalised propyltrialkoxysilanes such as diphenylphosphine propyltrialkoxysilane. These compounds can be used to prepare surface modified inorganic materials. Two different routes towards these functional polymers can be envisioned (Figure 3.4). One can first prepare the metal complex and then proceed with the co-condensation reaction (route I), or one can prepare the metal complex after the... 

In Dickey s 1949 paper [24], he presented the idea that specific catalysis, analogous to that of enzymes, was a possible application for silicas imprinted against selected reactants or products. This idea does not appear to have been realised until 1962, when the group of Patrikeev demonstrated what could be regarded as an early synthetic enzyme [27]. The reaction studied was the polycondensation of amino acid esters, a reaction known to yield both linear polypeptides (4%) and cyclic peptides (diketopiperazine, 96%) (Fig. 1.7). 

A series of close-to-spherical styrene/DVB resins of varying particle size and pore diameter were employed as supports for non-covalent adsorptive attachment of CALB by hydrophobic interaction. The effect of matrix particle and pore size on CALB i) adsorption isotherms, ii) fraction of active sites, iii) distribution within supports, and iv) catalytic activity for s-CL ring-opening polymerizations and adipic acid/l,8-octanediol polycondensations is reported. Important differences in the above for CALB immobilized on methyl methacrylate and styrene/DVB resins were found. The lessons learned herein provide a basis to others that seek to design optimal immobilized enzyme catalysts for low molar mass and polymerization reactions. 

Inspired by the fmding that HiC is active for polycondensation polymerizations, studies were performed to assess HiC activity for lactone ringopening polymerizations (Scheme 2). HiC-catalyzed ROP was carried out in either bulk or toluene. To determine the relationship between reaction temperature and enzyme activity for lactone ring-opening polymerizations, e-caprolactone (1) in bulk was taken as the model system. 

In this work lipase was found to be an effective catalyst for the polycondensation of a diester with a diamine to form a polyamide. The reaction is relatively mild and can be achieved at a high yield at relatively low temperatures. The resulting polyamide is amenable to derivatization reactions, thereby generating structures that can impart additional properties to the polymer. This enzyme-catalyzed polymerization reaction is applicable to a wide range of water-soluble polyamides, including several that cannot be previously prepared via chemical methods. 

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