Vanja Kokol

Nanocelluloses and their phosphorylated derivatives for selective adsorption of Ag+, Cu2+ and Fe3+ from industrial effluents

The potential of nanoscaled cellulose and enzymatically phosphorylated derivatives as bio-adsorbents to remove metal ions (Ag(+), Cu(2+) and Fe(3+)) from model water and industrial effluents is demonstrated. Introduction of phosphate groups onto nanocelluloses significantly improved the metal sorption velocity and sorption capacity. The removal efficiency was considered to be driven by the high surface area of these nanomaterials as well as the nature and density of functional groups on the nanocellulose surface. Generally, in the solutions containing only single types of metal ions, the metal ion selectivity was in the order Ag(+)>Cu(2+)>Fe(3+), while in the case of mixtures of ions, the order changed to Ag(+)>Fe(3+)>Cu(2+), irrespective of the surface functionality of the nanocellulose. In the case of industrial effluent from the mirror making industry, 99% removal of Cu(2+) and Fe(3+) by phosphorylated nanocellulose was observed. The study showed that phosphorylated nanocelluloses are highly efficient biomaterials for scavenging multiple metal ions, simultaneously, from industrial effluents.

Homogeneous and heterogeneous methods for laccase-mediated functionalization of chitosan by tannic acid and quercetin

Homogeneous and heterogeneous methods for functionalization of chitosan with quercetin or tannic acid using laccase from Trametes versicolor is presented, yielding a bio-based product with synergistic antioxidant and antimicrobial properties. HPLC-SEC analysis and cyclic voltammetry kinetic studies showed that laccase catalyzes the oxidation of quercetin to electrophilic o-quinones, which undergo to an oligomer/polymer-forming structures. On the other hand, tannic acid was converted into gallic acid, its dimers, partially gallic acid esterified glucose and glucose, when exposed to laccases. ATR-FTIR spectroscopy provided evidence that quercetin o-quinones undergo coupling reactions with amino groups of chitosan via Schiff-base and Michael addition mechanisms under heterogeneous method, while oxidized tannic acid cross-linked with chitosan by hydrogen and electrostatic interactions under both methods. All polyphenols functionalized chitosans showed greatly improved ABTS(+) cation radicals scavenging capacity, compared with the untreated chitosan, while antimicrobial activities significantly depended on the mode of functionalization and type of microorganism.

The effect of the cellulose-binding domain from Clostridium cellulovorans on the supramolecular structure of cellulose fibers.

The cellulose-binding domain (CBD) is the second important and the most wide-spread element of cellulase structure involved in cellulose transformation with a great structural diversity and a range of adsorption behavior toward different types of cellulosic materials. The effect of the CBD from Clostridium cellulovorans on the supramolecular structure of three different sources of cellulose (cotton cellulose, spruce dissolving pulp, and cellulose linters) was studied. Fourier-transform infrared spectroscopy (FTIR) was used to record amides I and II absorption bands of cotton cellulose treated with CBD. Structural changes as weakening and splitting of the hydrogen bonds within the cellulose chains after CBD adsorption were observed. The decrease of relative crystallinity index of the treated celluloses was confirmed by FTIR spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the binding of the CBD on the cellulose surface and the changing of the cellulose morphology.

Collagen- vs. Gelatine-Based Biomaterials and Their Biocompatibility: Review and Perspectives

Selection of a starting material, which will somehow mimic a naturally-existing one, is one of the most important points and crucial elements in biomaterials development. Material biomimetism is one of those approaches, where restoration of an organ’s function is assumed to be obtained if the tissues themselves are imitated (Barrere et al., 2008). However, some of the biopolymers as e.g collagen can be selected from within a group of biomimetic materials, since they already exist, and have particular functions in the human body. Collagen is one of the key structural proteins found in the extracellular matrices of many connective tissues in mammals, making up about 25% to 35% of the whole-body protein content (Friess, 2000; Muyonga et al., 2004). Collagen is mostly found in fibrous tissues such as tendons, ligaments and skin (about one half of total body collagen), and is also abundant in corneas, cartilages, bones, blood vessels, the gut, and intervertebral discs (Brinckmann et al., 2005). It constitutes 1% to 2% of muscle tissue, and accounts for 6% of strong, tendinous muscle-weight. Collagen is synthesized by fibroblasts, which originate from pluripotential adventitial cells or reticulum cells. Up to date 29 collagen types have been identified and described. Over 90% of the collagen in the body is of type I and is found in bones, skins, tendons, vascular, ligatures, and organs. However, in the human formation of scar tissue, as a result of age or injury, there is an alteration in the abundance of types I and III collagen, as well as their proportion to one another (Cheng et al., 2011). Collagen is readily isolated and purified in large quantities, it has well-documented structural, physical, chemical and immunological properties, is biodegradable, biocompatible, non-cytotoxic, with an ability to support cellular growth, and can be processed into a variety of forms including cross-linked films, steps, sheets, beads, meshes, fibres, and sponges (Sinha & Trehan, 2003). Hence, collagen has already found considerable usage in clinical medicine over the past few years, such as injectable collagen for the augmentation of tissue defects, haemostasis, burn and wound dressings, hernia repair, bioprostetic heart valves, vascular grafts, a drug –delivery system, ocular surfaces, and nerve regeneration (Lee et al., 2001). However, certain properties of collagen have adversely influenced some of its usage: poor dimensional stability due to swelling in vivo; poor in vivo mechanical strength and low elasticity, the possibility of an antigenic response (Lynn et

Effects of low-density static magnetic fields on the growth and activities of wastewater bacteria Escherichia coli and Pseudomonas putida

The aim of this study was to explore the influence of a moderate static magnetic field (SMF) of different densities on Escherichia coli and Pseudomonas putida that are commonly found in wastewater treatment plants. In line with literature reports that SMF increases the efficiency of wastewater treatment the findings of this study indicated that SMF negatively influenced the growth but positively influenced the enzymatic activities and ATP levels of the two model bacteria. The inhibitory effect of SMF on growth of E. coli and P. putida was most pronounced at their optimal growth temperature (37°C and 28°C respectively) and was reversible shortly after the SMF had been terminated. Finally, the results suggested that the induced energy metabolism reflected in higher dehydrogenase activities and ATP levels may be more important for survival, and adaptation to SMF induced stress than the increase in the expression of the rpoS gene.

Antimicrobial and antioxidant properties of chitosan-based viscose fibres enzymatically functionalized with flavonoids

The main purpose of this research was to qualitatively and quantitatively identify chitosan-based viscose fibre functional group surfaces as modified by two chemically-similar phenolics, namely fisetin and quercetin. Potentiometric titration was used to determine fibre-dissociable weak acids as a consequence of the presence of chitosan and deposited flavonoids. In addition, a conventional spectrophotometric method using C.I. Acid Orange 7 dye was used for determining the amino groups only. Finally, the antioxidant and antimicrobial properties of the fibres were evaluated, respectively. It has been clearly shown that the introduction of flavonoid onto the fibres introduces a significant amount of anionic phenolic hydroxyl groups, leading to fibre antioxidant activity and a decrease in fibre antimicrobial efficiency.

Introduction of aldehyde vs. carboxylic groups to cellulose nanofibers using laccase/TEMPO mediated oxidation.

The chemo-enzymatic modification of cellulose nanofibers (CNFs) using laccase as biocatalysts and TEMPO or 4-Amino-TEMPO as mediators under mild aqueous conditions (pH 5, 30 °C) has been investigated to introduce surface active aldehyde groups. 4-Amino TEMPO turned out to be kinetically 0.5-times (50%) more active mediator, resulting to oxoammonium cation intermediacy generated and its in situ regeneration during the modification of CNFs. Accordingly, beside of around 750 mmol/kg terminally-located aldehydes, originated during CNFs isolation, the reaction resulted to about 140% increase of C6-located aldehydes at optimal conditions, without reducing CNFs crystallinity. While only the C6-aldehydes were wholly transformed into the carboxyls after additional post-treatment using NaOH according to the Cannizzaro reaction, the post-oxidation with air-oxygen in EtOH/water medium or NaClO2 resulted to no- or very small amounts of carboxyls created, respectively, at a simultaneous loss of all C6- and some terminal-aldehydes in the latter due to the formation of highly-resistant hemiacetal covalent linkages with available cellulose hydroxyls. The results indicated a new way of preparing and stabilizing highly reactive C6-aldehydes on cellulose, and their exploitation in the development of new nanocellulose-based materials.

Enzymatic phosphorylation of cellulose nanofibers to new highly-ions adsorbing, flame-retardant and hydroxyapatite-growth induced natural nanoparticles

Abstract This study confirms the enzyme-mediated phosphorylation of cellulose nanofibers (CNF) by using hexokinase and adenosine-5′-triphosphate in the presence of Mg-ions, resulting in a phosphate group’s creation predominantly at C-6-O positioned hydroxyl groups of cellulose monomer rings. A proof-of-concept is provided using 12C CPMAS, 31P MAS nuclear magnetic resonance, attenuated total reflectance-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) analyzing methods. The degree of substitution (DS) is determined by elemental analysis and compared to DS estimated by XPS analysis. From the thermal degradation measurements using thermo-gravimetric analysis, the C-6-O phosphorylation was found to noticeably prevent the CNF derivatives from weight loss in the pyrolysis process, thus, providing them flame-resistance functionality. Furthermore, phosphorylation significantly enhanced adsorption capacity of Fe3+ ions making them interesting for fabrication of biobased filters and membranes. Finally, the biomimetic growth of Ca–P crystals (hydroxyapatite) in simulated body fluid was characterized by scanning electron microscopy and energy dispersive X-ray, showing potential application as biomedical materials.

Tyrosinase-Catalysed Coating of Wool Fibres With Different Protein-Based Biomaterials

The potential of tyrosinases to activate tyrosine residues of wool protein fibres for cross-linking with different materials like collagen, elastin and gelatine was assessed. Natural fibres like wool offer an excellent environment for the growth of micro-organisms when the conditions like moisture, oxygen and temperature are appropriate. Coating with collagen, a very useful biomaterial with bactericidal and fungicidal properties, could be used to improve the properties of wool-based materials, especially when applied in hygienically sensitive applications like in hospitals. Tyrosinases were shown to catalyse the oxidation of tyrosine residues in wool and wool hydrolysates as model substrates, as determined by UV-Vis spectroscopy. Structural differences of the surface were evident from the increase of the intensity in the NH bending and stretching regions in the spectra of NIR FT Raman analysis of the enzyme treated and grafted wool fibres. The durability of the coating was also shown by using FITC-labelled collagen that was bound to the wool fibres, even after severe washing. Additionally, antimicrobial properties were successfully imparted due to the collagen grafted on the wool fibres. The functional and mechanical properties of the treated wool fibres showed no significant changes.

Enzymatic reduction of complex redox dyes using NADH-dependent reductase from Bacillus subtilis coupled with cofactor regeneration

Conventional vat dyeing involves chemical reduction of dyes into their water-soluble leuco form generating considerable amounts of toxic chemicals in effluents. In the present study, a new β-nicotinamide adenine dinucleotide disodium salt (NADH)-dependent reductase isolated from Bacillus subtilis was used to reduce the redox dyes CI Acid Blue 74, CI Natural Orange 6, and CI Vat Blue 1 into their water-soluble leuco form. Enzymatic reduction was optimized in relation to pH and temperature conditions. The reductase was able to reduce Acid Blue 74 and Natural Orange 6 in the presence of the stoichiometrically consumed cofactor NADH; meanwhile, Vat Blue 1 required the presence of mediator 1,8-dihydroxyanthraquinone. Oxygen from air was used to reoxidize the dyes into their initial forms. The enzymatic reduction of the dyes was studied and the kinetic constants determined, and these were compared to the chemically-reduced leuco form. The enzyme responsible for the reduction showed homology to a NADH-dependent reductase from B. subtilis based on results from the MS/MS peptide mass mapping of the tryptically digested protein. Additionally, the reduction of Acid Blue 74 to its leuco form by reductase from B. subtilis was confirmed using NADH regenerated by the oxidation of formic acid with formate dehydrogenase from Candida boidinii in the same solution.