The Simple Method of Preparation of Highly Carboxylated Bacterial Cellulose with Ni- and Mg-Ferrite-Based Versatile Magnetic Carrier for Enzyme Immobilization

The bacterial cellulose (BC) is a versatile biopolymer of microbial origin characterized by high purity and unusual water and material properties. However, the native BC contains a low number of functional groups, which significantly limits its further application. The main goal of its effective modification is to use methods that allow the unusual properties of BC to be retained and the desired functional group to be efficiently introduced. In the present study, the new magnetic carrier based on functionalized citric acid (CA) bacterial cellulose was developed and tested to support critical industrial enzymes such as lipase B from Candida antarctica and phospholipase A from Aspergillus oryzae. The applied method allowed BC to be effectively modified by citric acid and a sufficient number of carboxylic groups to be introduced, up to 3.6 mmol of COOH per gram of dry mass of the prepared carrier. The DSC and TGA analyses revealed carrier stability at operational temperatures in the range of 20 °C to 100 °C and substantially influenced the amount of the introduced carboxyl groups on carrier properties. Both enzymes’ immobilization significantly improves their thermal stability at 60 °C without a significant thermal and pH optima effect. The analyzed enzymes showed good operational stability with a significant residual activity after ten cycles of repeated uses. The new magnetic carrier based on highly carboxylated bacterial cellulose has a high application capability as matrix for immobilization the various enzymes of industrial interest.     

Differences in electrophysical and gas sensing properties of flame spray synthesized Fe2O3(gamma-Fe2O3 and alpha-Fe2O3)

Nanoscaled Fe2O3 powders as candidates for gas sensing material for hydrogen detection were synthesized by the high temperature flame spray assisted combustion of ferrocene dissolved in benzene. X-ray diffraction (XRD) and selected area electron diffraction (SAED) show that the as prepared nanopowder consists of maghemite (gamma-Fe2O3) with low crystallinity. Thermal post-treatment causes a phase transformation towards hematite (alpha-Fe2O3) accompanied by an increase in the crystallinity. Upon exposure to air and hydrogen at elevated temperatures, both phases show a significant variation of conductivity and activation energy-as evidenced by impedance spectra-and thus a favorable sensor response, surpassing even that of flame-synthesized nanocrystalline tin dioxide. The conductivity has been identified as of electronic origin, affected by trap states located in the region adjacent to grain boundaries. Quantitative analysis of the impedance spectra with equivalent circuits shows that the conductivity is thermally activated and affected by the interaction of hydrogen with the sensor material. The calculated Debye screening length of gamma-Fe2O3 and alpha-Fe2O3 is about 27 nm and 16 nm, respectively, what contributes significantly to the sensitivity of the material. Gamma-Fe2O3 and alpha-Fe2O3 exhibit high sensor response towards hydrogen in a wide concentration range. Gamma-Fe2O3 shows n-type semiconducting behavior up to 573 K. Alpha-Fe2O3 shows p-type semiconducting behavior, as reflected in the dynamic changes of the resistivity. For both sensor materials, 523 K was the optimal operating temperature.     

The Role of pH in the Mechanism of .OH Radical Induced Oxidation of Nicotine

The ^.OH radical induced oxidation of nicotine was studied using pulse radiolysis techniques from pH 1 to 13.6. Theoretical calculations were used to help interpret the experimental results. The bond dissociation enthalpies of all of the C H bonds of nicotine were determined using DFT calculations, coupled with the isodesmic reaction. From time-dependent density functional response theory, estimates were obtained of the location of the dominant transient absorption bands (λ_max), their intensities (electronic oscillator strength, f), and the electronic composition of these transitions. OH radicals as well as other potent oxidants reacted with free nicotine through separated, concerted electron proton transfer, leading mostly to the formation of an alpha-aminoalkyl radical located on the C_2′ carbon of the aliphatic ring ( A_2′ ). Protonated nicotine underwent hydrogen atom abstraction at the C_2′ and N_1′ positions, resulting in the formation of the conjugate acid of A_2′ ( A_2′H⁺ ) and the alkylamine radical cation ( N⁺ ), respectively. Doubly protonated nicotine underwent the same reaction pathways, leading to two corresponding conjugate acid species, protonated at the aromatic nitrogen position: PyrH⁺A_2′H⁺ and PyrH⁺N⁺ _. All these radicals interconverted between each other through hydrolytic reactions. The radical A_2′ and its conjugate acid PyrH⁺A_2′ absorbed 10 times stronger than the N⁺ species, based on calculations of f. From the growth of the transient absorption of A_2′ (λ_max=330 nm, ε=8080 M ⁻¹ cm⁻¹), second-order rate constants were determined: k_(OH+Nic)=6.7×10⁹ M ⁻¹ s ⁻¹, k_(OH+NicH)=1.0×10⁹ M ⁻¹ s⁻¹. The alpha-aminoalkyl radicals decayed by disproportionation to form iminium cations 1 – 5 , which contributed to an increase in the specific conductivity of the basic solutions of nicotine following electron pulse irradiation.     

Modeling of thermally induced damage in the processing of Cr–Al2O3 composites

Thermal stresses induced during the cooling of Cr–Al₂O₃ (MMC) processed by sintering are modeled numerically using the FEA. The composite microstructure is modeled as (i) random distribution of ceramic particles (voxels) in the metal matrix, and (ii) using micro-CT scans of the real microstructure transformed into a FE mesh. Numerical simulations of the thermal residual stresses are compared with the test data measured by X-ray diffraction. A simple numerical model is then proposed to predict the overall elastic properties of the composite with account of the porosity and damage induced by the thermal stresses. Comparison of the model predictions with the measured data for Young’s modulus is presented.     

Conjugated polymers as robust carriers for controlled delivery of anti-inflammatory drugs

Conjugated polymers due to their reversible transition between the redox states are potentially able to immobilise and release ionic species. In this study, we have successfully developed a conducting polymer system based on poly(3,4-ethylenedioxythiophene) (PEDOT) for electrically triggered, local delivery of an ionic form of ibuprofen (IBU), a non-steroidal anti-inflammatory, and analgesic drug. It was shown that by changing the electropolymerisation conditions, the polymer matrix of specified IBU content can be synthesised. The electrochemical synthesis has been optimised to obtain the conducting matrix with the highest possible drug content. The process of electrically stimulated drug release has been extensively studied in terms of the dynamics of the controlled IBU release under varying conditions. The maximum concentration of the released IBU, 0.66 (±0.10) mM, was observed at the applied potential E = ?0.5 V (vs. Ag/AgCl). It was demonstrated that the immobilisation-release procedure can be repeated several times making the PEDOT matrix promising materials for controlled drug release systems applied e.g. in neuroprosthetics.     

Mullitization process of andalusite concentrates – Role of natural inclusions

In the article the results of investigations into the mullitization process of two andalusite concentrates are presented. XRD, XRF and ICP investigations revealed nearly identical phase and chemical composition of both concentrates. However, the andalusites considerably differ in the rate of the mullitization process. XPS and LM investigations revealed that the factors responsible for mullitization include not only the content of mineral inclusions and grain size distribution but also impurities dispersion and the content of naturally occurring carbon in andalusite grains.     

Modified Densified Waste of Expanded Polystyrene and Its Blends With Polyamide 6

The regularities of expanded polystyrene (EPS) waste modified by polyvinylpyrrolidone (PVP) with the simultaneous gas release in various solvents were revealed. The upper sorption limit depends on the nature of the solvent, the concentration and molecular mass of the PVP, the temperature of the process, and the apparent density of the EPS. It was established that the sorption limit of PVP increases with increasing of its concentration in the system and decreases with molecular mass increasing. Based on XRD and FTIR analyses, it was determined that materials based on polyamide 6 and EPS modified by PVP have an increased crystallinity degree by 10–15%, a smaller average crystallite size and higher technological compatibility. The addition of PVP-modified EPS contributes to the increase of the yield strength of polyamide 6 by about 5%–10%. The increase of the Vicat softening point by 5–8 K and the surface hardness by 25–30 MPa of materials based on polyamide 6 and modified polystyrene was investigated. It is caused by the redistribution of intermolecular bonds between the components of the blend under by the effect of a uniformly distributed PVP in the EPS resulting in increased compatibility between the components and the compacted structure. POLYM. ENG. SCI., 60:935–943, 2020. © 2020 Society of Plastics Engineers