Immobilization and Stabilization of Xylanase by Multipoint Covalent Attachment on Agarose and on Chitosan Supports

Xylanases have important applications in industry. Immobilization and stabilization of enzymes may allow their reuse in many cycles of the reaction, decreasing the process costs. This work proposes the use of a rational approach to obtain immobilized commercial xylanase biocatalysts with optimized features. Xylanase NS50014 from Novozymes was characterized and immobilized on glyoxyl-agarose, agarose-glutaraldehyde, and agarose-amino-epoxy support and on differently activated chitosan supports: glutaraldehyde-chitosan, glyoxyl-chitosan, and epoxy-chitosan. Two different chitosan matrices were tested. The best chitosan derivative was epoxy-chitosan-xylanase, which presented 100% of immobilization yield and 64% of recovered activity. No significant increase on the thermal stability was observed for all the chitosan-enzyme derivatives. Immobilization on glyoxyl-agarose showed low yield immobilization and stabilization degrees of the obtained derivative. The low concentration of lysine groups in the enzyme molecule could explain these poor results. The protein was then chemically modified with ethylenediamine and immobilized on glyoxyl-agarose. The new enzyme derivatives were 40-fold more stable than the soluble, aminated, and dialyzed enzyme (70 °C, pH 7), with 100% of immobilization yield. Therefore, the increase of the number of amine groups in the enzyme surface was confirmed to be a good strategy to improve the properties of immobilized xylanase.     

Electrochemical sensing of trypanosome- and flavivirus-related neglected tropical diseases

Virus infections and parasitic diseases that are often found in tropical countries represent a large burden on societies in those regions but are unfortunately rarely studied by electrochemistry. These neglected tropical diseases (NTDs) are a concerning issue, especially in developing nations because a challenged healthcare system often negatively affects the economy. Besides the exploration of new treatment strategies, the development of early diagnostic methods is crucial to attenuate negative impacts related to NTDs. This review highlights the most recent developments of electrochemical biosensing efforts for five NTDs, Chagas disease, leishmaniasis, sleeping sickness, dengue fever and Zika virus infection, which affect a number of Latin American, African, and Asian countries. Special focus is placed on the design and fabrication of genosensors and immunosensors, designed as innovative and promising diagnostic tools with the potential of being integrated into portable systems to advance the development of point-of-care devices.     

Analytical tools for urocanic acid determination in human samples: A review

Urocanic acid is a chromophore found in the skin that has been identified as an important immunosuppressant and carcinogenesis mediator through its photoisomerization from trans to cis form induced by ultraviolet radiation. Research on analytical methods that explore urocanic acid isomerization is indispensable to fully understand the deleterious effects mediated by this biomarker. In this context, the current relevant analytical methods for determination of these isomers in human samples are summarized in this review. The methods presented here are applicable to human samples collected by noninvasive methods (or minimally invasive), encompassing an array of analytical techniques, including high‐performance capillary electrophoresis, confocal Raman spectroscopy, gas chromatography, high‐performance liquid chromatography, and mass spectrometry, among others. Developed high‐performance liquid chromatography methods have proven to be advantageous, allowing noninvasive collections for in vivo analysis and the confocal Raman, specially, for real‐time analysis. Among all these methods, high‐performance liquid chromatography is the most investigated one with mass spectrometry or ultraviolet detector, and the mass spectrometry detector being the most studied in the last years, demonstrating high sensitivity, very low detection limits, and accurate identification, especially for clinical investigations.     

Characterization of βN-Octadecanoyl-5-hydroxytryptamide Anti-Inflammatory Effect

Background: N-octadecanoyl-5-hydroxytryptamide (C₁₈-5HT) is an amide that can be obtained by the coupling of serotonin and octadecanoic acid. This study aims to characterize the in vivo and in vitro anti-inflammatory activity of C₁₈-5HT. Methods: A subcutaneous air pouch model (SAP) was used. The exudates were collected from SAP after carrageenan injection to assess cell migration and inflammatory mediators production. RAW 264.7 cells were used for in vitro assays. Results: C₁₈-5HT significantly inhibited leukocyte migration into the SAP as well as nitric oxide (NO) and cytokines production and protein extravasation. We also observed an reduction in some cytokines and an increase in IL-10 production. Assays conducted with RAW 264.7 cells indicated that C₁₈-5HT inhibited NO and cytokine produced. Conclusions: Taken together, our data suggest that C₁₈-5HT presents a significant effect in different cell types (leukocytes collected from exudate, mainly polumorphonuclear leukocytes and cell culture macrophages) and is a promising compound for further studies for the development of a new anti-inflammatory drug.     

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P₂O₅/SiO₂ and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al₂O₃:1.0 P₂O₅:1.2 DPA:0.3 SiO₂:120 H₂O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P₂O₅/SiO₂ molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m²/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.     

Activated Copper Cathodes as Sensors for Nitrite Analysis

The increased surface area of copper electrodes upon applying a suitable potential protocol was characterized by atomic force microscopy images. Scanning electrochemical microscopy was used to demonstrate the enhanced reactivity of the generated surface. The modified electrode showed excellent catalytic activity towards nitrite reduction in acidic medium (pH 2). This new platform was used in the development of a fast and simple voltammetric method for nitrite determination. Commercial and rainwater spiked samples were analyzed and the data showed an excellent agreement with those obtained with a reference spectrophotometric method (Griess reaction) at a confidence level of 95 % (Student’s t‐test).     

A Three-Scale Model of pH-Dependent Flows and Ion Transport with Equilibrium Adsorption in Kaolinite Clays: I. Homogenization Analysis

A new three-scale model to describe the coupling between pH-dependent flows and transient ion transport including sorption phenomena in kaolinite clays is proposed. The kaolinite is characterized by three separate nano-micro and macroscopic length scales. The (micro)-scale consists of micro-pores saturated by an aqueous solution containing four monovalent ionic species (Na⁺, H⁺, Cl^?, OH^?) and charged solid particles surrounded by thin electrical double layers. The movement of the ions is governed by the Nernst-Planck equations and the influence of the double layers upon the flow is dictated by the Helmholtz–Smoluchowski slip boundary condition in the tangential velocity. In addition, sorption interface conditions for ion transport are postulated in the sense of Auriault and Lewandowska (Eur. J. Mech. A 15:681–704, 1996) to capture the immobilization of the ions in the electrical double layer and on particle surface due to protonation/deprotonation reactions. The intensity of sorption relative to diffusion effects is quantified by the Damköhler number, whose order of magnitude is estimated by invoking the nanoscopic modeling of the thin EDL based on Poisson–Boltzmann problem for the local electric potential coupled with a non-linear surface charge density with constitutive law dictated by the protonation/deprotonation reactions. The two-scale nano/micro model including sorption and slip boundary condition is homogenized to the core scale leading to a derivation of macroscopic governing equations.     

Influence of the network former on the properties of magnesium spinels

Undoped and/or doped with 1 mol% of Co²⁺ Mg₂TiO₄ andMg₂SnO₄ powders were synthesized by the polymeric precursor method. The influence of the network former (Sn⁴⁺ or Ti⁴⁺) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg₂TiO₄ crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg₂SnO₄ has.     

NMR assignments of unusual flavonoids from the kino of Eucalyptus citriodora

Two unusual flavonoids, 3,5,4',5'-tetrahydroxy-7-methoxy-6-[1-(p-hydroxy-phenyl)ethyl]flavanone (1) and 3,5,7,4',5'-pentahydroxy-6-[1-(p-hydroxy-phenyl)ethyl] flavanone (2), were isolated from the kino of Eucalyptus citriodora. Structural elucidation of the new compounds were established on the basis of spectral data, particularly by the use of 1D NMR and several 2D shift-correlated NMR pulse sequences ((1)H, (1)H-COSY, HMQC, HMBC).     

Finite volume solution of the modified Poisson-Boltzmann equation for two colloidal particles

The double layer forces between spherical colloidal particles, according to the Poisson-Boltzmann (PB) equation, have been accurately calculated in the literature. The classical PB equation takes into account only the electrostatic interactions, which play a significant role in colloid science. However, there are at, and above, biological salt concentrations other non-electrostatic ion specific forces acting that are ignored in such modelling. In this paper, the electrostatic potential profile and the concentration profile of co-ions and counterions near charged surfaces are calculated. These results are obtained by solving the classical PB equation and a modified PB equation in bispherical coordinates, taking into account the van der Waals dispersion interactions between the ions and both surfaces. Once the electrostatic potential is known we calculate the double layer force between two charged spheres. This is the first paper that solves the modified PB equation in bispherical coordinates. It is also the first time that the finite volume method is used to solve the PB equation in bispherical coordinates. This method divides the calculation domain into a certain number of sub-domains, where the physical law of conservation is valid, and can be readily implemented. The finite volume method is implemented for several geometries and when it is applied to solve PB equations presents low computational cost. The proposed method was validated by comparing the numerical results for the classical PB calculations with previous results reported in the literature. New numerical results using the modified PB equation successfully predicted the ion specificity commonly observed experimentally.