Aleksandra B. Nastasović

Immobilization of biocatalysts for enzymatic polymerizations: Possibilities, advantages, applications

Biotechnology also holds tremendous opportunities for realizing functional polymeric materials. Biocatalytic pathways to polymeric materials are an emerging research area with not only enormous scientific and technological promise, but also a tremendous impact on environmental issues. Many of the enzymatic polymerizations reported proceed in organic solvents. However, enzymes mostly show none of their profound characteristics in organic solvents and can easily denature under industrial conditions. Therefore, natural enzymes seldom have the features adequate to be used as industrial catalysts in organic synthesis. The productivity of enzymatic processes is often low due to substrate and/or product inhibition. An important route to improving enzyme performance in non-natural environments is to immobilize them. In this review we will first summarize some of the most prominent examples of enzymatic polymerizations and will subsequently review the most important immobilization routes that are used for the immobilization of biocatalysts relevant to the field of enzymatic polymerizations.

Equilibrium and kinetics study on hexavalent chromium adsorption onto diethylene triamine grafted glycidyl methacrylate based copolymers.

Two porous and one non-porous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) [abbreviated PGME] were prepared by suspension copolymerization and functionalized with diethylene triamine [abbreviated PGME-deta]. Samples were characterized by elemental analysis, mercury porosimetry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Kinetics of Cr(VI) sorption by PGME-deta were investigated in batch static experiments, in the temperature range 25-70°C. Sorption was rapid, with the uptake capacity higher than 80% after 30 min. Sorption behavior and rate-controlling mechanisms were analyzed using five kinetic models (pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion and Bangham model). Kinetic studies showed that Cr(VI) adsorption adhered to the pseudo-second-order model, with definite influence of pore diffusion. Equilibrium data was tested with Langmuir, Freundlich and Tempkin adsorption isotherm models. Langmuir model was the most suitable indicating homogeneous distribution of active sites on PGME-deta and monolayer sorption. The maximum adsorption capacity from the Langmuir model, Q(max), at pH 1.8 and 25°C was 143 mg g(-1) for PGME2-deta (sample with the highest amino group concentration) while at 70°C Q(max) reached the high value of 198 mg g(-1). Thermodynamic parameters revealed spontaneous and endothermic nature of Cr(VI) adsorption onto PGME-deta.

Kinetics of hexavalent chromium sorption on amino-functionalized macroporous glycidyl methacrylate copolymer

Two samples of macroporous crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), poly(GMA-co-EGDMA), with different porosity parameters were synthesized by suspension copolymerization and functionalized with ethylene diamine and diethylene triamine. The kinetics of Cr(VI) sorption by amino-functionalized poly(GMA-co-EGDMA) was investigated under non-competitive conditions. Competitive kinetics was studied from following multicomponent solutions: Cu(II) and Cr(VI); Cu(II), Co(II), Cd(II) and Ni(II); Cr(VI), Cu(II), Co(II) and Cd(II) solutions. Two kinetic models (the pseudo-first and pseudo-second-order) were used to determine the best-fit equation for the metals sorption by poly(GMA-co-EGDMA)-en and poly(GMA-co-EGDMA)-deta.

Determination of glass temperature of polymers by inverse gas chromatography

Inverse gas chromatography (IGC) is an attractive technique for polymer characterization due to possible simultaneous determination of various physicochemical properties of polymer systems merely from retention times of selected sorbates. The technique is especially advantageous to polymers that cannot be characterized by conventional methods. In this review, the utilization of the method for glass transition determination of homopolymers, copolymers and polymer blends is described. Advantages and drawbacks of the IGC method over traditionally used methods for glass transition temperature determination is discussed, along with the most important parameters that influence the precision and accuracy of the glass transition temperature (T(g)) measurements.

Effect of Candida antarctica Lipase B Immobilization on the Porous Structure of the Carrier

A series of poly(GMA-co-EGDMA) resins with identical composition but varying particle sizes, pore radii, specific surface areas and specific volumes are studied to assess how Candida antarctica lipase B immobilization affects the porosity of the copolymer particles. Mercury porosimetry reveals a significant change in the average pore size (up to 6.1-fold), the specific surface area (up to 3.2-fold) and the specific volume (up to 2.1-fold) of the epoxy resin. A similar behaviour is observed for glutaraldehyde-modified epoxy resins. The influences of the resin porosity properties on the loading of Candida antarctica lipase B during immobilization and on the hydrolytic activity (hydrolysis of p-nitrophenyl acetate) of the immobilized lipase are studied.

Textural properties of poly(glycidyl methacrylate): acid-modified bentonite nanocomposites

The aim of this study was to obtain enhanced textural properties of macroporous crosslinked copolymer poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) by synthesizing nanocomposites with acid-modified bentonite. Nanocomposites were obtained by introducing various amounts of acid-modified bentonite (BA) into the reaction system. All samples were characterized by attenuated total reflectance infrared spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), mercury intrusion porosimetry, and low temperature physisorption of nitrogen. The FTIR and TEM analysis confirmed incorporation of BA into the copolymer structure and the successful formation of nanocomposites. TEM images confirmed formation of nanocomposites having both intercalated and exfoliated acid-modified bentonite in copolymer matrix. A significant increase of specific surface area, pore volume, and porosity of the nanocomposites in comparison to the copolymer were obtained. The difference between textural properties of nanocomposites with different amounts of incorporated acid-modified bentonite was less prominent.

Novel negatively-charged membrane adsorbers made using combination of photopolymerization and immersion precipitation

A novel method combining a traditional immersion precipitation process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution was used to prepare asymmetric polyethersulfone membranes with submicron particles incorporating glycidyl methacrylate copolymer. In order to introduce sulfonic groups epoxide rings of glycidyl methacrylate were opened using two methods. The first method was functionalization with sodium sulfite, and the second method was functionalization with sulfuric acid and then grafting with 2-acrylamido-2-methylpropane sulfonic acid. Obtained membranes were characterized using infrared spectroscopy, conductometric titration and water permeability measurements. Scanning electron microscopy and atomic force microscopy were used to investigate the surface morphology and topology of membrane. Dynamic adsorption of Rhodamine B as a model dye was used to demonstrate suitability of these novel membranes for membrane adsorption since the adsorption capacity for dye cations was much better for both functionalized membrane with sodium sulfite and grafted membrane with 2-acrylamido-2-methylpropane sulfonic acid compared to the nonfunctionalized membrane.

Porous glycidyl methacrylate-bentonite composite

Crosslinked macroporous copolymer of glycidyl methacrylate and ethylene glycol dimethacrylate (CP) and copolymer composite with acid modified clay (CP-SA) were prepared by radical suspension copolymerization and functionalized by ring-opening reaction of the pendant epoxy groups with diethylene triamine (CP-deta and CP-SA-deta). Both SAmples were characterized by mercury porosimetry. The influence of pH, sorption time and initial 4-nitrophenol (4-NP) concentration on sorption efficiency of CP-deta and CP-SA-deta was studied in order to evaluate this material as wastewater sorbent. The isotherm data were best fitted with Langmuir model, while the sorption dynamics obeyed the pseudo-second-order kinetic model.

A novel macroporous polymer–inorganic nanocomposite as a sorbent for pertechnetate ions

A novel magnetic macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (mPGME) was prepared by suspension copolymerization and functionalized with diethylenetriamine (mPGME-deta). The samples were characterized by Fourier transform infrared spectroscopy (FTIR) analysis, mercury porosimetry, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), atomic force microscopy (AFM) and SQUID magnetometry. The sorption behavior of mPGME-deta toward pertechnetate ions (TcO4−) from aqueous solution was studied. Experimental results indicated relatively fast TcO4− sorption kinetics that depends on pH and ionic strength, with a high removal efficiency of 99% within 180 min in the pH range 3.0–5.0. The pseudo-second-order model yielded the best fit for the kinetic data.

Polymer-Based Monolithic Porous Composite

Porous monolithic glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) copolymer [PGME] and three composite samples with alumina (PGME/alumina) were synthesized by radical copolymerization in a cast and functionalized by reaction of diethylene triamine (deta) with epoxy groups in GMA. All the samples were characterized using FTIR-ATR spectroscopy, SEM, AFM, solid state NMR, thermogravimetry and mercury porosimetry. Additionally, amino functionalized PGME/alumina with the highest alumina content (PGME/alumina50-deta) was loaded with chromium [Cr(VI)] ions. Kinetics of Cr(VI) sorption was investigated in batch static experiments, at 298 K and pH = 2, for various initial concentrations (C i = 0.5, 1.5 and 2.5 mM) and analyzed using three kinetic models. Cr(VI) sorption by PGME/alumina50-deta obeys the PSO kinetic model, while IPD model suggests some degree of intraparticle pore diffusion control.