Radim Hrdina

Studies on the biotransformation of novel disazo dyes by laccase

Abstract Four novel disazo dyes were synthesized with a hydroxyl group in the para position of the phenolic ring in relation to the disazo bond, whereas the other substituents on the phenolic ring varied. The decolorization of the dyes was studied using a purified fungal laccase. Dyes I to III were not substrates for the phenoloxidase laccase regardless of whether or not redox mediators were added. In contrast, rapid and total decolorization of dye IV was obtained. Laccase oxidation of dye IV was described using Michaelis–Menten kinetics, giving an apparent affinity constant of 0.5 mM and a V max of 2.76 mM min −1 . N -hydroxybenzotriazole had no effect on the laccase catalysis whereas violuric acid inhibited the decolorization of disazo dye IV. A hypothetical mechanism is proposed for the biotransformation of this dye by laccase.

Green synthesis of hyaluronan fibers with silver nanoparticles

The application of green chemistry in the nano-science and technology is very important in the area of the preparation of various materials. In this work, an eco-friendly chemical method was successfully used for the preparation of hyaluronan fibers containing silver nanoparticles (AgNPs). Thus, hyaluronic acid (HA) was dissolved in an aqueous solution of sodium hydroxide to prepare a transparent solution, which was used for the preparation of fibers by a wet-spinning technique. Consequently, silver nanoparticles inside the fiber were prepared. Different parameters affecting the preparation of final product, such as concentration of silver nitrate, hyaluronan fiber concentration, time and temperature of the reaction, pH of the reaction mixture, were studied. AgNPs were confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD), two-dimensional X-ray scattering (2D SWAXS), UV/Vis spectroscopy, inductively coupled plasma optical emission spectrometry (ICP OES) and scan electron microscopy (SEM). Mechanical properties of prepared fibers were also measured.

Antibacterial activity and cell viability of hyaluronan fiber with silver nanoparticles

Silver has been used since time immemorial in different chemical form to treat burns, wounds and several different infections caused by pathogenic bacteria, advancement of biological process of nanoparticles synthesis is evolving into a key area of nanotechnology. The current study deals with the green synthesis, characterization, and evaluation of the biological activity and cell viability of hyaluronan fibers with incorporated silver nanoparticles (HA-Ag NPs). Hyaluronan fiber was prepared by the dissolving of sodium hyaluronate (HA) in aqueous alkaline solution to prepare a transparent solution, which was used for the preparation of fibers by a wet-spinning technique. Consequently, hyaluronan fiber was used as capping and stabilizing agent for the preparation of fibers with silver nanoparticles. HA-Ag NPs were confirmed by transmission electron microscopy, dynamic light scattering, UV/VIS spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermal analysis, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. HA-Ag NPs showed high antibacterial activity of against Staphylococcus aureus and Escherichia coli. Cell viability tests indicated that hyaluronan, hyaluronan fibers and hyaluronan fibers with silver nanoparticles were non-toxic on the cell growth. Two different particles size of Ag NPs (10, 40 nm) had not any toxicity till the concentration limit. These tests were performed using mouse fibroblast cell line 3T3.

Antibacterial cotton fabrics treated with core-shell nanoparticles.

Multifinishing treatment of cotton fabrics was carried out using core-shell nanoparticles that consists of silver nanoparticles (Ag(0)) as core and chitosan-O-methoxy polyethylene glycol (CTS-O-MPEG) as shell. The synthesized (Ag(0)-CTS-O-MPEG) core-shell nanoparticle was applied to cotton fabrics using the conventional pad-dry-cure method. The finished fabrics were examined for their morphological features and surface characteristics by making use of scanning electron microscope (SEM-EDX), which reveals the well dispersion of (Ag(0)-CTS-O-MPEG) core-shell nanoparticles on cotton fabrics. Factors affecting the treatment such as core shell nanoparticles, citric acid (CA) concentration as well as curing temperature were studied. The treated fabrics, at optimum condition of 1% core shell nanoparticles, 5% citric acid, drying at 80°C, curing at 160°C for 2 min, showed excellent antibacterial activity against Gram-negative Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus), even after 20 washing cycles in addition to an enhancement in crease recovery angles (CRA) along with a slight improvement in tensile strength (TS).

Biomedical Textiles Through Multifunctioalization of Cotton Fabrics Using Innovative Methoxypolyethylene Glycol-N-Chitosan Graft Copolymer

Multifunctioalization of cotton fabrics was developed by a novel finishing formulation. The method is based on chitosan-N-polyethylene glycol graft copolymer along with citric acid and sodium hypophosphite (SHP) as catalysts. Treatment of the cotton fabric resulted in the chemical attachment of the copolymer to the cotton fabric via bridging-based esterification where the latter involves reaction of one molecule of the polycarboxylic acid (citric acid) with both the amino group of the copolymer and the hydroxyl groups of cotton. Inclusion of the copolymer in the crosslinked structure of cotton as well as by hydrogen bonding and van der Waals forces are additionally possible. Synthesis of the copolymer was raised out by the reaction of chitosan with methoxy polyethylene glycol (MPEG) aldehyde followed by the reduction with sodium borohydride. MPEG was prepared by oxidation of PEG with acetic anhydride in dimethyl sulphoxide at room temperature. Methoxypolyethylene glycol-N-chitosan graft copolymer (MPEG-N-CTS) structure was confirmed by IR, NMR, X-RD and TGA techniques. The copolymer is soluble in water. The pad dry-cure method was used for the cotton fabrics treatment with aqueous solution of prepared copolymer along with citric acid and SHP. The so treated fabrics were monitored for copolymer content (expressed as N%), crease recovery, tensile strength, elongation at break, air permeability, water permeability, roughness, bursting strength and antibacterial activity. Fabric performances based on the outputs of these measurements advocate these multifunctionalized fabrics for use as medical textile.

Chitin and chitosan from Brazilian Atlantic Coast: Isolation, characterization and antibacterial activity

Chitin and chitosan were obtained by chemical treatments of shrimp shells. Different particle sizes (50-1000 μm) of the raw material were used to study their effect on size distribution, demineralization, deproteinization and deacetylation of chitin and chitosan isolation process. The particle size in the range of 800-1000 μm was selected to isolate chitin, which was achieved by measuring nitrogen, protein, ash, and yield %. Hydrochloric acid (5%, v/v) was optimized in demineralization step to remove the minerals from the starting material. Aqueous solution of sodium hydroxide (5%, w/v) at 90 °C for (20 h) was used in deproteinization step to remove the protein. Pure chitin was consequently impregnated into high concentration of sodium hydroxide (50%) for 3.5 h at 90 °C to remove the acetyl groups in order to form high pure chitosan. The degree of deacetylation (DDA) of chitosan was controlled and evaluated by different analytical tools. The chemical structure of chitin and chitosan was confirmed by elemental analysis, ATR-FTIR, H/C NMR, XRD, SEM, UV-Vis spectroscopy, TGA, and acid-base titration. The isolated chitin and chitosan from shrimp shell showed excellent antibacterial activity against Gram (-ve) bacteria (Escherichia coli) comparing with commercial biopolymers.

Specificity of phenolic disazo dyes in relation to transformation by laccase

Four novel disazo dyes were synthesized and characterized using FTIR and NMR spectroscopy. These water-soluble dyes had a hydroxyl group in the para position of the phenolic ring in relation to the azo bond, whereas the other substituents on the phenolic ring and/or between the two azo bonds varied. The transformation of the dyes was studied using purified fungal laccase. The rank order in which the dyes were transformed was IV > III ≫ I. Dye II was not a laccase substrate. As both dye I and II had a carboxylic substituent on the phenolic ring but the ring structures between the two azo linkages were different, we suggest that the latter also influenced laccase catalysis. Both of the redox mediators tested, violuric acid and N-hydroxybenzotriazole, enhanced the laccase reaction with violuric acid, being generally more effective. The results show that the chemical structure of both the phenolic ring as well as the ring distal to the phenolic moiety affect the reaction kinetics.

Electronic excited states of azo compounds: Strong ππ* fluorescence of bis-4,4′-diethylaminoazobenzene

Abstract The low-temperature absorption and luminescence spectra of bis-4,4′-diethylaminoazobenzene (BDAAB) in 2-methyltetrahydrofurane (MTHF) have been measured. On the basis of the spectral characteristics, this luminescence is interpreted as the fluorescence from the first excited singlet state (ππ*). A comparison of the spectral and photophysical properties of BDAAB with those of other para-substituted trans-azobenzenes enables us to draw some conclusions concerning the structure and fluorescence of these systems.

Excited states of azo compounds. II: Vibrational structure of the electronic absorption spectra of 4,4'-di-substituted azobenzene derivatives

Abstract The electronic absorption spectra of azobenzene and its fourteen symmetrical and non-symmetrical derivatives substituted in both para positions by electron-donating substituents were studied in 2-methyl-tetrahydrofuran solvent at room (293 K) and low (103 K) temperatures. The main effect destroying the vibronic structure of the absorption spectra of the azobenzene derivatives was found-the ground state non-planarity caused by torsions around the NPh bond. The central azo bond stretching was interpreted as the dominant vibrational mode in absorption spectrum. It has been shown that increasing electron-donating ability of azobenzene substituents in para positions increases the planarity of the molecules in the ground state and decreases the difference between equilibrium azo bond lengths in the ground and first excited singlet ππ * states.

Structure and properties of fluorescent reactive dyes : Electronic structure and spectra of some benzanthrone derivatives

Absorption and fluorescence spectra of N-(disubstituted-1,3,5-triazinyl)-3-aminobenzanthrones, 3-acetylaminobenzanthrone and 3-methoxybenzanthrone have been investigated. Excitation energies and the character of the first absorption band have been calculated by the PPP-MO method. Some data on substituent and solvent effects on fluorescence spectral position and quantum yields are reported. The connection between electron density distribution in the electronic ground and excited state, and spectroscopic properties of those compounds, is explained.