Muzafera Paljevac

Ionic liquids as (co)solvents for enzymatic reactions

Ionic liquids are low melting point salts that represent an exciting new class of reaction solvents. Many reactions show advantages when carried out in ionic liquids, either with regard to enhanced reaction rates, improved selectivity, or easier reuse of catalysts. To ascertain the influence of ionic liquids on the enzyme activity, three different ionic liquids 1-butyl-3-methylimidazolium chloride ([bmim] [CI]) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF6]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) were synthesized and investigated as potential media for the hydrolysis of carboxymethyl cellulose, catalyzed by non-immobilized cellulase from Humicola insolens (Celluzyme 0,7T) and for ester synthesis, catalyzed by immobilized lipase from Rhizomucor miehei (Lipozyme RM IM). Enzyme-catalyzed reactions were performed in a batch stirred reactor at atmospheric pressure. Celluzyme 0,7T showed better activity in hydrophobic ionic liquid ([bmim] [PF6]), as compared to hydrophilic ionic liquid ([bmim] [BF4]). In the case of Lipozyme RM IM, the synthetic activity of the enzyme was strongly reduced by incubating the enzyme in ionic liquids.

Microcellular open porous polyester membranes from thiol-ene polymerisations of high internal phase emulsions

Abstract A high internal phase emulsion templating procedure is applied for the preparation of membranes which exhibit an open porous morphology with interconnected macro pores and open porous surfaces. A doctor blading procedure is used to cast the high internal phase emulsion onto glass substrates. Continuous phase of the emulsions contain divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) which are photopolymerised using the thiol-ene click chemistry to yield polyester type polymer network. The resulting polymer morphology features primary pores as a result of emulsion’s droplet phase, with diameters between 7 and 14 µm and interconnecting pores as a result of polymerisation shrinkage, with diameters between 1.6 and 2.2 µm. The highly porous and interconnected morphology mirrors the precursor emulsion structure with a dense packing of internal (aqueous) phase droplets. Doctor blades with different slit dimensions are used for casting thus producing membranes with different thicknesses while in all cases typical polyHIPE morphology is observed. Mechanical tests show a dependence of tensile modulus and tensile strength on the membrane thickness and also on pore size distribution.

Multiple-Level Porous Polymer Monoliths with Interconnected Cellular Topology Prepared by Combining Hard Sphere and Emulsion Templating for Use in Bone Tissue Engineering

A combination of hard sphere and high internal phase emulsion templating gives a platform for synthesizing hierarchically porous polymers with a unique topology exhibiting interconnected spherical features on multiple levels. Polymeric spheres are fused by thermal sintering to create a 3D monolithic structure while an emulsion with a high proportion of internal phase and monomers in the continuous phase is added to the voids of the previously constructed monolith. Following polymerization of the emulsion and dissolution of the templating structure, a down-replicating topology is created with a primary level of pores as a result of fused spheres of the 3D monolithic structure, a secondary level of pores resulting from the emulsions internal phase, and a tertiary level of interconnecting channels. Thiol-ene chemistry with divinyladipate and pentaerythritol tetrakis(3-mercaptopropionate) is used to demonstrate the preparation of a crosslinked polyester with overall porosity close to 90%. Due to multilevel porosity, such materials are interesting for applications in bone tissue engineering, possibly simulating the native sponge like bone structure. Their potential to promote ossteointegration is tested using human bone derived osteoblasts. Material-cell interactions are evaluated and they reveal growth and proliferation of osteoblasts both on surface and in the bulk of the scaffold.

Enzyme-catalyzed reactions in different types of high-pressure enzymatic reactors

The enzyme-catalyzed hydrolysis of carboxy-methyl cellulose (CMC) was performed in three different types of reactors; in a batch stirred-tank reactor (BSTR) operating at atmospheric pressure, in a high-pressure batch stirred-tank reactor (HP BSTR) and in a high-pressure continuous tubular-membrane reactor (HP CTMR). In the high-pressure reactors aqueous SC CO2 was used as the reaction medium. The aim of our research was optimization of the reaction parameters for reaction performance. All the reactions were catalyzed by cellulase from Humicola insolens. Glucose production in the high-pressure batch stirred-tank reactor was faster than in the BSTR at atmospheric pressure. The optimal temperature for the reaction performed in the BSTR at atmospheric pressure was 30°C, while the optimal temperature for the reaction performed in SC CO2 was 32°C. The influence of the application of tubular ceramic membranes in the high-pressure reaction system was studied on the model reaction of CMC hydrolysis at atmospheric pressure and in SC CO2. The reaction was catalyzed by cellulase from Humicola insolens covalently linked to the surface of the ceramic membrane. The hydrolysis of CMC in SC CO2 and at atmospheric pressure was performed for a long time period. The reaction carried out in SC CO2 was more productive than the reaction performed at atmospheric pressure.