Georgi Chernev

Silica-carrageenan hybrids used for cell immobilization realizing high-temperature degradation of nitrile substrates

In this work the application of hybrid materials, containing TEOS as source of SiO2 and k-carrageenan in different percentage, synthesized by the sol-gel method at room temperature was studied. They were used as matrices for entrapment of whole Bacillus sp. UG-5B cells, producers of thermostable nitrilase. The effect of the surface area and size and quantity of pores in the synthesized materials on the enzyme activity was evaluated. The process of biodegradation of different concentrations of toxic, potentially carcinogenic and mutagenic substrates by the obtained biocatalysts was investigated. The enzyme reaction takes place by the nitrilase pathway, catalysing nitrile hydrolysis directly to the corresponding carboxylic acid, forming ammonia. At batch experiments the influence of the substrate concentration of different nitriles was tested and 20 mM concentration was found most suitable. A two-step biodegradation process in a laboratory-scale column bioreactor of o-, m- and p-tolunitrile as a mixture was followed. After operation of the system for nine hours for the mixture of substrates at a flow rate of 45 mL h−1 and at 60°C, the overall conversion realized was above 90%, showing a good efficiency of the investigated process.

Silica hybrid biomaterials containing gelatin synthesized by sol-gel method.

This work reports the sol-gel synthesis of silica hybrids. We determined the effect of the type and quantity of silica precursors and organic compounds on the resulting structure, surface area, nanostructure design and size, and potential applications. The structure of the synthesized hybrids was analyzed using FT-IR, XRD, BET-Analysis, SEM, and AFM. We demonstrate the immovilization of whole living thermophilic bacterial cells with cyanocompound degradation activity in the synthesized silica hybrid biomaterials by entrapment, chemical binding, and adsorption.

IMMOBILIZATION IN NANOMATRICES OF HUMICOLA LUTEA MYCELIUM FOR ALPHA-GALACTOSIDASE BIOSYNTHESIS IN LABORATORY AIR-LIFT BIOREACTOR

ABSTRACT The sol-gel synthesis of both hybrid nanomatrices containing tetraethylortosilicate (TEOS) as an inorganic precursor and lactic acid, or sepharose as an organic component was made. Crystal as well as surface morphology of the hybrids were investigated using different methods: X-ray diffraction, infrared spectra, BET-analysis and atomic force microscopy (AFM). The obtained nanomatrices were applicated for immobilization of the α-galactosidase producing fungal strain Humicola lutea 120–5. The semicontinuous cultivation was carried out in laboratory air-lift bioreactor. Maximal level of enzyme activity (1050–1130 U/l) that was reached in the third to fourth fermentation cycle using TEOS+40% lactic acid was higher than that obtained in the samples with TEOS+20% sepharose (660–770 U/l). The correlation between enzyme productivity and fungal development in the pore structure of the carriers was examined using scanning electron microscopy observation.

Silica hybrid nanocomposites

In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m2/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles.

Phenol biodegradation by fungal cells immobilized in sol-gel hybrids.

The capability of cells of the fungus Aspergillus awamori, either free or immobilized in hybrid sol-gel material cells, for phenol biodegradation was demonstrated. Phenol was present in the reaction mixture as the sole carbon and energy source, and its decomposition was followed in repeated batch degradation experiments. Atomic force microscopy provided information on the development of self-organizing structures in the materials synthesized by the sol-gel method. Phenol biodegradation was mediated only by the fungal cells, and no absorption by the hybrid matrix was observed. Ten cycles of phenol biodegradation using the immobilized cells system were conducted during which up to 2000 mg l-1 phenol was completely decomposed. Immobilized cells degraded phenol at 8.33 mg h-1, twice as fast as free cells. The good performance of the immobilized fungal cell system is promising for the development of an efficient technology for treating phenol-containing waste waters

SOL-GEL NANOMATERIALS WITH ALGAL HETEROPOLYSACCHARIDE FOR IMMOBILIZATION OF MICROBIAL CELLS, PRODUCING α-GALACTOSIDASE AND NITRILASE

ABSTRACT The main purpose of the present work is the sol-gel synthesis and structure of the hybrid nanomaterials as matrices for two types of cells, producing hydrolytic enzymes. The effect of different percent of algal polysaccharide included in them on the hydrolytic activity of fungal and bacterial cells was investigated. The hybrid sol-gel nanomaterials were synthesized from tetraethylortosilicate (TEOS) as a silicon precursor and heteropolysaccharide (AHPS) from the red microalga Dixonella grisea as an organic part. The structure of these matrices was investigated using different methods: FT-IR, XRD, BET-Analysis, EDS, SEM and AFM. The sol-gel hybrids were used for the immobilization of fungal (Humicola lutea) and bacterial (Bacillus sp.) cells, producing α-galactosidase and nitrilase, respectively. It was established the effect of the quantity of the heteropolysaccharide in the matrices on the activity of these hydrolytic enzymes. Using 20% AHPS in the hybrid nanomaterials the α-galactosidase yield exceeded over two-fold the enzyme titre of the free cells in the third cycle of repeated batch shake flask cultivation. These results correlated with a dense growth of immobilized mycelium observed with scanning electron microscopy (SEM). The increase of the percentage of organic part in the sol-gel matrix up to 20% led to an increase in the nitrilase activity. The addition of 40% AHPS did not significantly affect the decrease of the nitrile biodegradation.

Structure and properties of innovative silica hybrid materials synthesized for environmental applications

Today, environmental protection is one of the main goals in the strive to preserve the human existence. Development in this area requires invention of new materials, which can reduce the levels of pollution. Hybrid materials are suitable for this purpose, because they combine different desirable properties existing in separate sources into one unique and accessible structure. Most of the commonly used materials for the degradation of different kind of pollutants are based on titanium dioxide, because of its photocatalytic activity under UV irradiation. Innovative silica hybrid materials, containing an organic component (chitosan) and titanium nanoparticles, were successfully synthesized via the sol–gel method and tetraethyl orthosilicate was used as a silica source and network former. Interaction between the chitosan and titanium units, and their influence on the structure of final material, were observed and discussed. A homogeneous structure with an even distribution of titanium and chitosan particles was visible from scanning electron microscopy (SEM) micrographs and the particle size varied between 50 and 150 nm. The formed silica network, characteristic peaks of chitosan and titanium groups and possible interactions between them are observed from Fourier transform infrared (FTIR) spectroscopy spectra and nuclear magnetic resonance (NMR) spectroscopy results. The behaviour of the synthesized silica hybrids after thermal treatment was investigated via differential thermal/thermo-gravimetric analysis (DTA/TG) analysis and the sorption and degradation activities of the obtained hybrid materials were investigated using a solution of methyl orange as model pollutant. The structure and properties of the synthesized silica hybrid materials assert their potential application in environmental remediation due to their photocatalytic degradation and sorption activities against pollutants.

New Approach for n-Hexadecane Biodegradation by Sol-Gel Entrapped Bacterial Cells

Abstract In this study sol-gel hybrid materials in the system SiO2-chitosan (CS) - polyethylene glycol (PEG), as novel structures with potential application in bioremediation were investigated. The organic components - CS and PEG were used as structural modifiers for functionality improvement. The catabolic activity to n-hexadecane of Pseudomonas aeruginosa BN10 free and immobilized cells was estimated. The cell immobilization technique was employed to evaluate its efficiency on biodegradation and protective effect from high levels of hydrocarbons. The characteristics of obtained hybrid materials were investigated via X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Atomic-force microscopy (AFM) analyses. The obtained results revealed that the organic part in the synthesized hybrids is important for microstructure and defined properties creation. The rate of n-hexadecane mineralization by the bacterial strain was influenced by variation in cell densities applied in the immobilization procedures. Semi-continuous processes with multiple xenobiotic supplies were carried out. The synthesized by the sol-gel method hybrid matrices proved to be suitable carriers for realizing an effective biodegradation process of n-hexadecane by Pseudomonas aeruginosa BN10. Biodegradation of 50 kg/m3 of n-hexadecane was realized by free cells. Significantly greater quantity (150 kg/m3) was mineralized for 15 active cycles by entrapped bacterial cells. Biodegradation process with gradual increase of xenobiotic concentration reaching 30 kg/m3 for 120 h was also accomplished.

Synthesis and Selected Properties of Silicate Hybrids Containing Sepharose

The main purpose of the present work is the sol-gel synthesis, structure and application of hybrid inorganic–organic hybrids based on different silica precursors and addition of the organic compound sepharose (SP). The structural evolution of the hybrid materials containing different amounts of SP is examined. Formation of silica nanocomposites by self-assembling processes was studied by AFM and roughness analysis. The average size of nanoparticles on the sample surface is about 7 to 14 nm and the formation of their self-organized structures is observed. The hybrids are used for immobilization of bacterial cells, producers of thermostable nitrilase. The biocatalysts show good operational stability for a long period-18 days, as well as high thermostability. The degradation capability is greater for the encapsulated cells in the hybrid matrix with 5% SP.

Examination of Humicola lutea Immobilized in Sol-Gel Matrices: Effective Source of α-Galactosidase

Abstract α-Galactosidase production by the fungus Humicola lutea 120-5 immobilized in a hybrid sol-gel matrix, consisting of tetraethylorthosilicate (TEOS) as a precursor and a mixture of polyethyleneglycol (PEG) and polyvinylalcohol (PVA), was investigated under semicontinuous shake flask cultivation and compared to the enzyme secretion by free cells. The influence of the carrier weight on the α-galactosidase biosynthesis in repeated batch experiments was followed. Best results were obtained with 2 g of the sol-gel particles per culture flask using 144-h runs. The growth behaviour of the immobilized mycelium during both the growth and productive phases was observed by scanning electron microscopy. The presence of abundant mycelial growth of intact hyphae correlated with a 2-fold higher enzyme activity compared to free cells. The obtained biocatalyst retained a high level of enzyme titer exceeding the activity of free cells during four cycles of operation (24 days). This result is confirmed by the micrographs showing the retained viability of the growing vegetative cells due to the protective role of the carrier.