45 research outputs found
Spectroscopic on-line monitoring and stopped-flow kinetic analysis of dye degradation by laccase/mediator systems
The laccase catalyzed transformation of the acid dye Indigo Carmine (CI Acid Blue 74) was studied using various redox mediators: violuric acid (VIO), 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), 1-hydroxybenzotriazole (HOBT), and 2,2-azinobis-(3-ethylbenzothiazoline-6-disulfonic acid diammonium salt (ABTS). Inline UV/Vis and IR spectroscopy was employed to monitor the decolorization in real-time during batch decolorization. ABTS was the most effective mediator follwed by TEMPO. Stopped flow kinetics was employed to study the initial phase of dye degradation in more detail.
While the batch decolorization experiments suggested zero-order rate laws for dye
transformation at an early stage, the more accurate stopped-flow kinetic experiments revealed that the rate laws for the initial phase were actually more complicated.
Different pH optima for dye decolorization were found for the laccase catalyzed
reaction (pH 3.5) and for the oxidation brought about by the isolated ABTS radical cation (pH 6.7)
Indigo degradation with purified laccases from Trametes hirsuta and Sclerotium rolfsii
The degradation of the textile dye indigo with purified laccases from the fungi Trametes hirsuta (THL1 and THL2) and Sclerotium rolfsii (SRL1) was studied. All laccases were able to oxidize indigo yielding isatin (indole-2,3-dione), which was further decomposed to anthranilic acid (2-aminobenzoic acid). Based on the oxygen consumption rate of the laccases during indigo degradation, a potential mechanism for the oxidation of indigo involving the step-wise abstraction of four electrons from indigo by the enzyme was suggested. Comparing the effect of the known redox-mediators acetosyringone, 1-hydroxybenzotriazole (HOBT) and 4-hydroxybenzenesulfonic acid (PHBS) on laccase-catalyzed degradation of indigo, we found a maximum of about 30% increase in the oxidation rate of indigo with SRL1 and acetosyringone. The particle size of indigo agglomerates after laccase treatment was influenced by the origin of the laccase preparation and by the incubation time. Diameter distributions were found to have one maximum and compared to the indigo particle size distribution of the control, for all laccases, the indigo agglomerates seemed to have shifted to smaller diameters. Bleaching of fabrics by the laccases (based on K/S values) correlated with the release of indigo degradation products. (C) 2001 Elsevier Science BY. All rights reserved
Specificities of a chemically modified laccase from trametes hirsuta on soluble and cellulose-bound substrates
Laccases could prevent fabrics and
garments from re-deposition of dyes during
washing and finishing processes by degrading the solubilized dye. However, laccase action must be restricted to solubilized dye molecules thereby
avoiding decolorization of fabrics. Chemical
modification of enzymes can provide a powerful tool to change the adsorption behaviour of enzymes on water insoluble polymers. Polyethylene glycol (PEG) was covalently attached onto a laccase from Trametes hirsuta. Different molecular
weights of the synthetic polymer were tested
in terms of adsorption behaviour and retained
laccase activity. Covalent attachment of PEG
onto the laccase resulted in enhanced enzyme
stability while with increasing molecular weight of attached PEG the substrate affinity for the laccase conjugate decreased. The activity of the modified laccases on fibre bound dye was drastically reduced decreasing the adsorption of the enzyme on various fabrics. Compared to the 5 kDa PEG laccase conjugate (K/S value 47.60
Restricting detergent protease action to surface of protein fibres by chemical modification
Due to their excellent properties, such as
thermostability, activity over a broad range of pH and
efficient stain removal, proteases from Bacillus sp. are
commonly used in the textile industry including industrial
processes and laundry and represent one of the most
important groups of enzymes. However, due to the action
of proteases, severe damage on natural protein fibres such
as silk and wool result after washing with detergents
containing proteases. To include the benefits of proteases in
a wool fibre friendly detergent formulation, the soluble
polymer polyethylene glycol (PEG) was covalently
attached to a protease from Bacillus licheniformis. In
contrast to activation of PEG with cyanuric chloride (50%)
activation with 1,1′-carbonyldiimidazole (CDI) lead to
activity recovery above 90%. With these modified
enzymes, hydrolytic attack on wool fibres could be
successfully prevented up to 95% compared to the native
enzymes. Colour difference (ΔE) measured in the three dimensional colour space showed good stain removal
properties for the modified enzymes. Furthermore, half-life
of the modified enzymes in buffers and commercial
detergents solutions was nearly twice as high as those of
the non-modified enzymes with values of up to 63 min. Out
of the different modified proteases especially the B.
licheniformis protease with the 2.0-kDa polymer attached
both retained stain removal properties and did not
hydrolyse/damage wool fibres
Allyls
This chapter addresses the importance and usage of the commercially low volume thermoset plastics group known as allyls. The three significant sub-elements of this group are poly(diallylphthalates), poly(diallylisophthalates), and poly(allyldiglycol carbonate). Chemistry, processing, and properties are also described. Allyl polymers are synthesized by radical polymerizations of allyl monomers that usually do not produce high-molecular-mass macromolecules. Therefore, only a few specific monomers can produce thermosetting materials. Diallyldiglycolcarbonate (CR-39) and diallylphthalates are the most significant examples that have considerably improved our everyday life
Monodisperse Porous Silica/Polymer Nanocomposite Microspheres with Tunable Silica Loading, Morphology and Porosity
Hybrid organic/inorganic nanocomposites combine the distinct properties of the organic polymer and the inorganic filler, resulting in overall improved system properties. Monodisperse porous hybrid beads consisting of tetraethylene pentamine functionalized poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) particles and silica nanoparticles (SNPs) were synthesized under Stoeber sol-gel process conditions. A wide range of hybrid organic/silica nanocomposite materials with different material properties was generated. The effects of n(H2O)/n(TEOS) and c(NH3) on the hybrid bead properties particle size, SiO2 content, median pore size, specific surface area, pore volume and size of the SNPs were studied. Quantitative models with a high robustness and predictive power were established using a statistical and systematic approach based on response surface methodology. It was shown that the material properties depend in a complex way on the process factor settings and exhibit non-linear behaviors as well as partly synergistic interactions between the process factors. Thus, the silica content, median pore size, specific surface area, pore volume and size of the SNPs are non-linearly dependent on the water-to-precursor ratio. This is attributed to the effect of the water-to-precursor ratio on the hydrolysis and condensation rates of TEOS. A possible mechanism of SNP incorporation into the porous polymer network is discussed