Tomasz Koźlecki

Effective L-Tyrosine Hydroxylation by Native and Immobilized Tyrosinase

Hydroxylation of L-tyrosine to 3,4-dihydroxyphenylalanine (L-DOPA) by immobilized tyrosinase in the presence of ascorbic acid (AH2), which reduces DOPA-quinone to L-DOPA, is characterized by low reaction yields that are mainly caused by the suicide inactivation of tyrosinase by L-DOPA and AH2. The main aim of this work was to compare processes with native and immobilized tyrosinase to identify the conditions that limit suicide inactivation and produce substrate conversions to L-DOPA of above 50% using HPLC analysis. It was shown that immobilized tyrosinase does not suffer from partitioning and diffusion effects, allowing a direct comparison of the reactions performed with both forms of the enzyme. In typical processes, additional aeration was applied and boron ions to produce the L-DOPA and AH2 complex and hydroxylamine to close the cycle of enzyme active center transformations. It was shown that the commonly used pH 9 buffer increased enzyme stability, with concomitant reduced reactivity of 76%, and that under these conditions, the maximal substrate conversion was approximately 25 (native) to 30% (immobilized enzyme). To increase reaction yield, the pH of the reaction mixture was reduced to 8 and 7, producing L-DOPA yields of approximately 95% (native enzyme) and 70% (immobilized). A three-fold increase in the bound enzyme load achieved 95% conversion in two successive runs, but in the third one, tyrosinase lost its activity due to strong suicide inactivation caused by L-DOPA processing. In this case, the cost of the immobilized enzyme preparation is not overcome by its reuse over time, and native tyrosinase may be more economically feasible for a single use in L-DOPA production. The practical importance of the obtained results is that highly efficient hydroxylation of monophenols by tyrosinase can be obtained by selecting the proper reaction pH and is a compromise between complexation and enzyme reactivity.

Characterization of Glass Beads Surface Modified with Ionic Surfactants

Knowledge of the wetting characteristic of mineral surfaces is very important in enhancing the efficiency of separation of valuable minerals from gangue using froth flotation or oil agglomeration. In this paper a capillary rise technique was used to characterize the glass beads surface modified with cationic surfactant. The glass microspheres were used as model particles with a spherical shape and smooth surface to eliminate the roughness effect. The value of the contact angle for water was found to be 21.5 for unmodified beads, and 61.8, 89.7, 68.4 for 0.1, 1.0, 10 mg/gsolid of CTAB, and 39.8, 68.6, 87.9 for 0.1, 1.0, 10 mg/gsolid of DDAHCl, respectively. Data revealed that the adsorption of surfactant onto glass beads decreased the value of the electron donor component, γ-, which defines the hydrophobicity of the surface. Also, the property of the surface was investigated by flotation and oil agglomeration experiments. It was observed that particles with low value of contact angle for water and high for 1-bromonaphthalene and low value of γ- were floated with a recovery equal to 91.1 and 83.1% for CTAB and DDAHCl, respectively, and effectively agglomerated. This indicates that the capillary rise method can be successfully used to predict the wetting properties of solid particles in mineral processing.

Extraction of organic impurities using 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]

Extraction of organic impurities using 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] Extraction of several chloro compounds from water has been examined. As the extracting liquid the 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], which is common hydrophobic ionic liquid, was used. Additionally, extraction of selected chlorinated compounds from tert-butylmethylether (MTBE) was investigated. The obtained results show the usefulness of [BMIM][PF6] to remove the organic impurities from water, particularly at the concentration range inappropriate for biological purification plants.

Photochemical and thermal isomerization of anionic azobenzene amphiphiles in homogeneous and aggregated systems

Abstract Kinetic and thermodynamic parameters of the trans-cis photoisomerization of trans -4-(4′-alkylphenylazo)phenyl derivatives (C n AzoX; n = 4, 8; X = SO 3 , COONa) by 366 nm UV irradiation as well as the cis-trans thermal reversion of the azobenzene moiety have been determined by means of the 1 H NMR technique in homogeneous and micellar systems of C n AzoX.

Use of fly ash and fly ash agglomerates for As(III) adsorption from aqueous solution

Abstract The objective of the present study is to assess the efficiency of fly ash and fly ash agglomerates to remove arsenic(III) from aqueous solution. The maximum static uptakes were achieved to be 13.5 and 5.7 mgAs(III)/adsorbent for nonagglomerated material and agglomerated one, respectively. Isotherm studies showed good fit with the Langmuir (fly ash) and the Freundlich (fly ash agglomerates) isotherm models. Kinetic studies indicated that the sorption of arsenic on fly ash and its agglomerates follows the pseudo-second-order (PSO) chemisorption model (R2 = 0.999). Thermodynamic parameters revealed an endothermic nature of As(III) adsorption on such adsorbents. The adsorption results confirmed that fly ash and its agglomerates can be used for As(III) removal from aqueous solutions. Fly ash can adsorb more arsenic(III) than agglomerates, which are easier to use, because this material is less dusty and easier to separate from solution.

PHOTOCHEMICAL BEHAVIOR OF MICELLIZED 4-(4-ALKYLSTYRYL)PYRIDINIUM SALTS

New photochromic surfactants, 1-alkyl-4-(4′-alkylstyryl)lpyridinium halides (CnStzRX; n = 0, 4, 6, 8; R = Me, Et, CH2CH2OH, n-Bu, n-C9H19; X = Br, I), were synthesized and the photochemical behavior of their micellar aggregates in water was characterized in relation to non-micellizing 1-methyl-4-stilbazolium ions. Reversible trans-cis isomerization through a photothermal cycle was observed for the micellized CnStzRX. Furthermore, photoreactions upon prolonged irradiation of CnStzRX micelles resulted in a 3–31% formation of thermodynamically least stable syn-head-to-head and ca. 3% of anti- head-to-head dimers. These findings indicate that the self aggregation process of CnStzRX may provide some topologically organized microenvironment affecting the steric and like-charge repulsions of the aggregate components.

Influence of pH on arsenic(III) removal by fly ash

ABSTRACT The objective of this study was to compare arsenic(III) removal at natural pH (pH 10.5) with that at high alkaline (pH 12.2). Experiments were carried out using fly ash from burning brown coal and biomass from the power plant (Zgierz, Poland). Experimental data were well described by the Langmuir and the pseudo-second-order chemisorption models. The maximum adsorption capacity was 19.04 and 42.73 mg/g at pH 10.5 and 12.2, respectively. It can be explained by the fact that a phase CaAsO2OH is formed at highly alkaline pH. The value of thermodynamic parameters revealed that arsenic(III) adsorption is a spontaneous and endothermic process.

Improved Synthesis of Nanosized Silica in Water-in-Oil Microemulsions

Present contribution describes modified Stober synthesis of silica nanoparticles in oil-in-water microemulsion, formulated using heptane, 2-ethylhexanol, Tween® 85 nonionic surfactant, and tetraethyl orthosilicate (TEOS). After some specified incubation time, ammonium hydroxide was added and the reaction mixture was stirred for 24 hours at room temperature. Prior to synthesis, pseudoternary diagram was created for oil-rich area and Winsor IV region was identified. These microemulsions were used for synthesis of silica particles. Resulting particles were characterized by dynamic light scattering, electrokinetic measurements, specific surface area measurements, and powder diffraction. Particles’ diameter was ranging between ca. 130 and 500 nm; usually monodisperse distribution was obtained. The specific surface area of nanoparticles was ranging between 250 and 300 m2/g. Notably, productivity per unit volume of solution was 3 to 5 times higher than for previously reported procedures. Our method can be extended, because polymeric materials can be added to dispersed aqueous phase. In our studies, β-cyclodextrin and hydroxyethylcellulose have been used, giving particles between 170 and 422 nm, with the surface area larger than 300 m2/g.

Chapter 6 – Adsorption of Boron by Minerals, Clays, and Soils

Boron is a vital microelement, necessary for the growth of plants, albeit there is only a narrow gap between desirable and toxic concentrations. The tolerance varies among different species. For example, avocado, lemons, and wheat are sensitive, while cotton, tomato, and oat are relatively tolerant. There are many sources of possible contamination, due to anthropogenic activity and natural processes, the main source being natural weathering.

Adsorption of Silver Nanoparticles on Glass Beads Surface

Colloidal silver is widely used owing to its specific properties, which enable it to be applied in various fields. In this work, adsorption of commercially available silver nanoparticles (AgNPs; NanoSilver PVP 1000) on glass beads was investigated. The glass microspheres (70–110 μm) were used as model particles. The adsorption of AgNPs on the glass beads surface was investigated in terms of adsorbent dosage. The adsorption isotherm was determined with the adsorbent dosage of 100 g/l and the AgNPs in range 100–1000 mg/l. It was found that adsorption isotherm data best fitted the Langmuir model. Kinetics of AgNPs adsorption onto glass beads followed a pseudo-second-order model. The interaction between glass microspheres surface and polyvinylpyrrolidone (PVP)-coated AgNPs is due to hydrogen bonding with oxygen of carbonyl groups of PVP and silanol groups on the glass surface.