Lactate esters can be used in food industry for preservation and flavouring purpose, as well as in the pharmaceutical and cosmetic industries. Direct esterification of n-butanol and lactic acid (LA), catalyzed by immobilized lipase B from Candida antarctica (Novozyme 435), was performed in supercritical carbon dioxide (SC CO2) with or without co-solvent. Process conditions (pressure and temperature) were optimized performing experiments in a high-pressure batch-stirred tank reactor. Experiments were carried out in the operative pressure range from 7.5 to 40 MPa and at temperatures 35 ◦C and 55 ◦C. The highest conversion of LA after 26 h of reaction performance was obtained in SC CO2 with n-hexane serving as a co-solvent, at 40 MPa and 55 ◦C. The optimal temperature and pressure for butyl lactate synthesis in SC CO2 medium was determined at 55 ◦C and 30 MPa. Phase behavior for LA/nbutanol/ SC CO2 system and LA/n-butanol/n-hexane/ SC CO2 system at different pressures and temperatures was also studied.
COBISS.SI-ID: 15598102
A systematic approach towards the fabrication of highly functionalized silica shell magnetic nanoparticles, presently used for enzyme immobilization, is herein fully presented. The synthesis of bare maghemite (y-Fe2O3) nanoparticles was accomplished by thermal co-precipitation of iron ions in ammonia alkaline solution at harsh reaction conditions, respectively. Primary surface engineering of maghemite nanoparticles was successfully performed by the proper deposition of silica onto nanoparticles surface under strictly regulated reaction conditions. Next, the secondary surface functionalization of the particles was achieved by coating the particles with organosilane followed by glutaraldehyde activation in order to enhance protein immobilization. Covalent immobilization of cholesterol oxidase was attempted afterwards. The structural and magnetic properties of magnetic silica nanocomposites were characterized by TEM and vibrating sample magnetometer (VSM) instruments. X-ray diffraction measurements confirmed the spinel structure and average size of uncoated maghemite nanoparticles to be around 20nm in diameter. SEM-EDS spectra indicated a strong signal for Si, implying the coating procedure of silica onto the particles surface to be successfully accomplished. Fourier transform infrared (FT-IR) spectra analysis confirmed the binding of amino silane molecules onto the surface of the maghemite nanoparticles mediated Si-O-Si chemical bonds. Compared to the free enzyme, the covalently bound cholesterol oxidase retained 50% of its activity. Binding of enzyme onto chemically modified magnetic nanoparticles via glutaraldehyde activation is a promising method for developing biosensing components in biomedicine.
COBISS.SI-ID: 13418262
Herein we report the successful preparation of catalytically active crosslinked enzyme aggregates (CLEAsr) of peroxidase (HRP, EC 1.11.1.7) from horseradish roots (Armoracia rusticana or Cochlearia armoracia) using various aggregation agents, followed by crosslinking with glutaraldehyde. The percent activity recovery of the HRP-CLEAs was 83% of that of the native enzyme. The CLEAs were prepared in the presence of egg albumin (37 mg/mL) and pentaethylenehexamine (PEHA; 10 mM). The albumin played a significant role in stabilizing the CLEA particles, and the PEHA was necessary to obtain fully crosslinked HRP aggregates. Because HRP possesses only six Lys (lysine) residues, the addition of PEHA increases the number of free amino groups (-NH2) on the outer surface of the enzyme, thus facilitating the crosslinking.A potential application of HRP aggregates is envisaged for coupled oxidation reactions with cholesterol oxidase in the biosensor field.
COBISS.SI-ID: 14712598
Recent researches have demonstrated the possibility to carry out integral green biocatalytic processes by combining SC CO2 and ILs with enzymes, because their different miscibilities produce the twophase systems that show an exceptional ability to carry out both the biotransformation and the products extraction steps simultaneously. In our studies, ILs were used as reaction media for lipase catalyzed kinetic resolution of (R,S)1-phenylethanol with vinyl acetate. Transesterification of chiral substrate, (R,S)1-phenylethanol with vinyl acetate was performed in different ILs at atmospheric pressure and in SC CO2/IL biphasic system. Influence of different parameters such as concentration of IL, type of IL on conversion or reaction rate of transesterification were studied. Next, stability of immobilized CALB in selected IL was tested. According to a recent review work on biocatalysis in ILs, factors such as polarity and nucleophilicity of the anion, pH, purity of the IL and water content, have a major effect on the activity, the stability and the solubility of enzymes in these nonconventional media. The influence of IL concentration on the CALB activity was found to be a determining factor for the performance of the (R,S)1-phenylethanol kinetic resolution at atmospheric pressure, as well as in SC CO2/[bmim][BF4] system. Biocatalysis with CALB, which is an excellent chiral biocatalyst for the stereoselective acylation of racemic alcohols, gave very high kinetic resolution (R)enantiomer yields and selectivity.
COBISS.SI-ID: 14858262
In this study, supercritical carbon dioxide (SC CO2) was used to obtain proteins and enzymes from yeast Saccharomyces cerevisiae. The changes in viability and cell morphology, the release of the cellular proteins and the activity alteration of the enzyme alcohol dehydrogenase (ADH) from S. cerevisiae resulting from the exposure to SC CO2 were investigated. The suspension of the S. cerevisiae culture was incubated in SC CO2 at different pressures (7.5, 15 and 30 MPa) for different treatment times (30–300 min) and at constant temperature (35 °C). The influences of these parameters on total protein concentration, ADH activity and changes in absorbance of nucleic acids in the suspension of S. cerevisiae during SC CO2 treatment were studied. The use of SC CO2 is a suitable option to achieve cell death and consequently the secretion of proteins and ADH from cells of S. cerevisiae.
COBISS.SI-ID: 15901462