Green synthesis of silica-coated magnetic nanocarriers for simultaneous purification-immobilization of ß-1,3-xylanase.

Tailoring magnetic nanocarriers with tunable properties is of great significance for the development of multifunctional candidate materials in numerous fields. Herein, we report a one-pot biomimetic silicification-based method for the synthesis of silica-coated magnetic nanoparticles. The synthesis process was mild, low cost, and highly efficient, which took only about 21 min compared with 4.5-120 h in other literature. Then, the carriers had been characterized by VSM, SEM, TEM, XRD, FT-IR, and EDS to confirm their function. To evaluate the usefulness of the carriers, they were adopted to couple the purification and immobilization of ß-1,3-xylanase from the cell lysate in a single step with high immobilization yield (92.8 %) and high activity recovery (82.4 %). The immobilized enzyme also retained 58.4 % of the initial activity after 10 cycles and displayed good storage properties, and improved thermal stability, which would be promising in algae biomass bioconversion as well as other diverse applications.

Evaporative silicification in floating microbial mats: patterns of oxygen production and preservation potential in silica-undersaturated streams, El Tatio, Chile.

Microbial mats floating within multiple hydrothermally sourced streams in El Tatio, Chile, frequently exhibit brittle siliceous crusts (~1 mm thick) above the air-water interface. The partially silicified mats contain a diverse assemblage of microbial clades and metabolisms, including cyanobacteria performing oxygenic photosynthesis. Surficial crusts are composed of several amorphous silica layers containing well-preserved filaments (most likely cyanobacteria) and other cellular textures overlying EPS-rich unsilicified mats. Environmental logs, silica crust distribution, and microbial preservation patterns provide evidence for crust formation via repeated cycles of evaporation and silica precipitation. Within the mats, in situ microelectrode profiling reveals that daytime oxygen concentrations and pH values are diminished beneath silica crusts compared with adjacent unencrusted communities, indicating localized inhibition of oxygenic photosynthesis due to light attenuation. As a result, aqueous conditions under encrusted mats have a higher saturation state with regard to amorphous silica compared with adjacent, more active mats where high pH increases silica solubility, likely forming a modest feedback loop between diminished photosynthesis and crust precipitation. However, no fully lithified sinters are associated with floating encrusted mats in El Tatio streams, as both subaqueous and subaerial silica precipitation are limited by undersaturated, low-SiO2 (<150 ppm) stream waters. By contrast, well-cemented sinters can form by evaporation in silica-undersaturated solutions above 200 ppm SiO2 . Floating mats in El Tatio therefore represent a specific sinter preservation window, where evaporation in silica-undersaturated microbial mats produces crusts, which preserve cells and affect mat chemistry, but low-silica concentrations prevent the formation of lasting sinter deposits. Patterns of silica precipitation in El Tatio microbial communities show that the preservation potential of silicifying mats in the rock record is strongly dependent on aqueous silica concentrations.

Intrafibrillar silicified collagen scaffold promotes in-situ bone regeneration by activating the monocyte p38 signaling pathway.

Intrafibrillar silicified collagen scaffold (SCS) is a promising biomaterial for bone regeneration because it promotes cell homing and angiogenesis in bone defects via monocyte modulation. In the present study, a rat femoral defect model was used to examine the contribution of monocyte signaling pathways to SCS modulation. Activation of the monocyte p38 signaling pathway by SCS resulted in monocyte differentiation into TRAP-positive mononuclear cells. These cells demonstrated increased secretion of SDF-1α, VEGFa and PDGF-BB, which, in turn, promoted homing of bone marrow stromal cells (BMSCs) and endothelial progenitor cells (EPCs), as well as local vascularization. Monocyte differentiation and secretion were blocked after inhibition of the p38 pathway, which resulted in reduction in cell homing and angiogenesis. Taken together, these novel findings indicate that the p38 signaling pathway is crucial in SCS-modulated monocyte differentiation and secretion, which has a direct impact on SCS-induced bone regeneration. STATEMENT OF SIGNIFICANCE: Intrafibrillar silicified collagen scaffold (SCS) is a promising biomaterial for bone regeneration. The present work demonstrates that SCS possesses favorable bone regeneration potential in a rat femoral defect model. The degrading scaffold modulates monocyte differentiation and release of certain cytokines to recruit MSCs and EPCs, as well as enhances local vascularization by activating the p38 MAPK signaling pathway. These findings indicate that SCS contributes to bone defect regeneration by stimulating host cell homing and promoting local angiogenesis and osteogenesis without the need for loading cytokines or xenogenous stem cells.

Spectroscopic analysis and X-ray diffraction of trunk fossils from the Parnaíba Basin, Northeast Brazil.

The Parnaiba Sedimentary Basin is of the Paleozoic age and is located in Northeast Brazil, covering the states of Piauí, Maranhão and Tocantins and a small part of Ceará and Pará. In this work we applied several chemical analytical techniques to characterize trunk fossils found in the Parnaíba Sedimentary Basin, collected from four different sites, and discuss their fossilization process. We performed a study of the trunk fossils through X-ray diffraction, energy dispersive spectroscopy, infrared and Raman spectroscopy. The analysis allow us to identify the different compositions which are present in the trunk fossils: kaolinite (Al2Si2O5(OH)4), hematite (Fe2O3) and quartz (SiO2). Based in these results we were able to identify that the main fossilization mechanism of the trunk fossil was silicification. Furthermore, through Raman spectroscopy, we have observed the presence of carbonaceous materials in the Permian fossils, as evidenced by the D and G Raman bands. The relative intensities and bandwidths of the D and G bands indicated that the carbon has a low crystallinity. Thus, most of trunk fossils analyzed were permineralized and not petrified, because there is the presence of carbon that characterizes the partial decomposition of the organic matter in some trunks.

Effect of silicification on the water sorption properties of microcrystalline cellulose II

The aim of this study was to investigate the water sorption behavior of cellulose II:SiO2 composites and to determine the influence of silicification on this property. These composites were prepared by spray-drying at a cellulose II:SiO2 ratio of 98:2, 95:5, 90:10 and 80:20. The nonlinear models of Guggenheim-Anderson-de Boer (GAB), Generalized D'Arcy and Watt (GDW) and Hailwood & Horrobin (HH), were used for the characterization and analysis of the isotherms. The infrared and powder X-rays characterization showed no signs of chemical modification or change in the polymorphic form of cellulose II by SiO2. The parameters derived from these models indicated that only a 20 percent level of silicification was able to hinder the water sorption properties of cellulose. Silicon dioxide was the most hydrophobic material since it had a lower ability to form hydrogen bonds with water than cellulose II. This finding was reflected in a delayed compact disintegration time when high levels of silicification (20 percent) and compression pressures higher than 120 MPa were used.

O objetivo deste estudo é investigar o comportamento de sorção de água a partir de misturas de celulose II e SiO2 e determinar a influência da silicificação nesse processo. Estas misturas foram preparadas por nebulização (spray-drying) usando misturas de celulose II e SiO2 nas proporções de 98:2, 95:5, 90:10 e 80:20. Os modelos não-lineares de Guggenheim-Anderson-de Boer (GAB), "Generalized" D'Arcy e Watt (GDW) e Hailwood & Horrobin (HH) foram utilizados para caracterização e análise das isotermas. As misturas foram caracterizadas por infravermelho e raio-X e os resultados não mostraram indicativo de modificação química ou polimórfica da celulose II em combinação com SiO2. Os parâmetros derivados desses modelos indicaram que as propriedades de sorção de água da celulose foram prejudicadas apenas quando empregado um nível de silicificação de 20 por cento. O dióxido de silício foi o material mais hidrofóbico, provavelmente por possuir uma menor capacidade de formar pontes de hidrogênio com a água quando comparado com a celulose II. Este resultado foi refletido em redução no tempo de desintegração, especialmente quando altos níveis de silicificação (20 por cento) e força de compressão (acima de 120 Mpa) foram utilizados.