Intracellular signal triggered by cholera toxin in Saccharomyces boulardii and Saccharomyces cerevisiae

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Selective Catalytic Transfer Hydrogenation of Lignin to Alkyl Guaiacols Over NiMo/Al-MCM-41

Efficient deoxygenation of lignin-derived bio-oils is central to their adoption as precursors to sustainable liquid fuels in place of current fossil resources. In-situ catalytic transfer hydrogenation (CTH), using isopropanol and formic acid as solvent and in-situ hydrogen sources, was demonstrated over metal-doped and promoted MCM-41 for the depolymerization of oxygen-rich (35.85 wt%) lignin from Chinese fir sawdust (termed O-lignin). A NiMo/Al-MCM-41 catalyst conferred an optimal lignin-derived oil yield of 61.6 wt% with a comparatively low molecular weight (M_w =542 g mol^-1 , M_n =290 g mol^-1 ) and H/C ratio of 1.39. High selectivity to alkyl guaiacols was attributed to efficient in-situ hydrogen transfer from isopropanol/formic acid donors, and a synergy between surface acid sites in the Al-doped MCM-41 support and reducible Ni/Mo species, which improved the chemical stability and quality of the resulting lignin-derived bio-oils.

Phosphate Enrichment of Niobium-Based Catalytic Surfaces in Relation to Reactions of Carbohydrate Biomass Conversion: The Case Studies of Inulin Hydrolysis and Fructose Dehydration

In this work, some physical mixtures of Nb2O5·nH2O and NbOPO4 were prepared to study the role of phosphate groups in the total acidity of samples and in two reactions involving carbohydrate biomass: hydrolysis of polyfructane and dehydration of fructose/glucose to 5-hydroxymethylfurfural (HMF). The acid and catalytic properties of the mixtures were dominated by the phosphate group enrichment. Lewis and Brønsted acid sites were detected by FT-IR experiments with pyridine adsorption/desorption under dry and wet conditions. Lewis acidity decreased with NbP in the composition, while total acidity of the samples, measured by titrations with phenylethylamine in cyclohexane (~3.5 μeq m−2) and water (~2.7 μeq m−2), maintained almost the same values. Inulin conversion took advantage of the presence of surfaces rich in Brønsted sites, and NbOPO4 showed the best hydrolysis activity with glucose/fructose formation. The catalyst with a more phosphated surface showed less deactivation during the dehydration of fructose/glucose into HMF.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Heparin Immobilized on Multiwalled Carbon Nanotubes for Catalytic Conversion of Fructose in Water with High Yield and Selectivity

Being a member of the glycosaminoglycan family of carbohydrates, native heparin is a highly sulfated polysaccharide. Herein, heparin was grafted onto polydopamine (PDA)- and poly(ethylene imine) (PEI)-coated multiwalled carbon nanotubes (MWCNTs) (heparin-PEI@PDA@MWCNT). The immobilized heparin consists of a sulfated repeating disaccharide unit, conferring a unique microenvironment when catalyzing fructose dehydration into 5-hydroxymethylfurfural (HMF). The hydrogen bonding interactions naturally occur between the disaccharide unit of heparin and the monosaccharide fructose, and the adjacent sulfonic acid groups catalyze the fructose dehydration. The reactions were performed in water, and heparin-PEI@PDA@MWCNT achieved an HMF yield of 46.2% and an HMF selectivity of 82.2%. For the dehydration of fructose in water, heparin-PEI@PDA@MWCNT exhibits advantages over published heterogeneous catalysts on the basis of HMF yield and HMF selectivity. Three aspects contribute to the environmentally benign processing: (1) the catalyst heparin is a natural sulfated polysaccharide; (2) the catalysis is carried out in water and not in organic solvents; and (3) fructose can be produced from a biomass resource.

Furfural Hydrogenation on Modified Niobia

In this study, niobia-based materials have been used as supports for Pt nanoparticles and used in the hydrogenation of furfural. The incorporation of dopants (W6+ and Ti4+) in the Nb2O5 structure induced modifications in the surface acidity of the support; in particular, the addition of W6+ increased the amount of Lewis acid sites, while the addition of Ti4+ decreased the number of Lewis acid sites. As a result, the catalytic activity towards the hydrogenation of furfural was affected; high surface acidity resulted in high catalytic activity. The selectivity of the reaction changed with the support acidity as well, with higher amount of furfuryl alcohol produced decreasing the Lewis acid sites.

Diversity of Saccharomyces boulardii CNCM I-745 mechanisms of action against intestinal infections

The yeast Saccharomyces boulardii CNCM I-745 is one of the probiotics recommended for the prevention of antibiotic-associated diarrhea. Studies conducted in vivo and in vitro demonstrated that in the case of infectious diseases there are two potential sites of action of Saccharomyces boulardii CNCM I-745: (1) An action on enteropathogenic microorganisms (adhesion of bacteria and their elimination or an effect on their virulence factors: Toxins, lipopolysaccharide, etc.); and (2) a direct action on the intestinal mucosa (trophic effects, effects on epithelial reconstitution, anti-secretory effects, anti-inflammatory, immunomodulators). Oral administration of Saccharomyces boulardii CNCM I-745 to healthy subjects does not alter their microbiota. However, in the case of diseases associated with the use of antibiotics or chronic diarrhea, Saccharomyces boulardii CNCM I-745 can restore the intestinal microbiota faster. The interaction of Saccharomyces boulardii CNCM I-745 with the innate immune system have been recently demonstrated thus opening up a new therapeutic potential of this yeast in the case of diseases associated with intestinal infections but also other pathologies associated with dysbiosis such as inflammatory diseases.

Dehydration of fructose over thiol- and sulfonic- modified alumina in a continuous reactor for 5-HMF production: Study of catalyst stability by NMR

In the present study, the synthesis of an organic group-modified alumina by the sol-gel method is proposed. This material has shown to have an enhanced catalytic performance with grafted organic groups and showed an improved stability. The prepared material has shown to have several O - H groups and an enhanced surface acidity. The alumina acidity was improved by incorporating thiol groups by grafting method, which promotes the tautomerization of fructose to its furanose form. Furthermore, the grafting of sulfonic groups catalyzes its dehydration. The modified alumina was thermally treated up to 200 °C to improve the functional groups stability. After, this modified material was packed into a continuous reactor system, designed and built by this group, to obtain 5-hydroxymethylfurfural (5-HMF) from fructose dissolved in a single-phase solution of tetrahydrofuran (THF) and H2O (4:1 w/w). The catalytic activity of this material was evaluated by the reaction of fructose dehydration at different reaction temperatures (60, 70, 80 and 90 °C). Fructose conversion and selectivity toward 5-HMF were determined by high performance liquid chromatography (HPLC), obtaining 95% and 73% respectively for the highest temperature. The catalyst showed an efficient stability after 24 hours in continuous flow at 70 °C. The loss of sulfur content was 15%, but the fructose conversion yield and the selectivity to 5-HMF after 24 hours of continuous reaction did not undergo significant changes (less than 5%). The nuclear magnetic resonance (NMR) tests confirmed the presence of the thiol and sulfonic groups before and after 24 hours of reaction, as well as the conservation of the same structure, demonstrating the efficient catalytic performance of the material. The catalysts were characterized by nitrogen adsorption/desorption, X-ray diffraction and infrared (IR) spectroscopy. Also, before and after use by utilizing elemental analysis and  1 H - 13 C cross-polarization magic-angle spinning (CPMAS) and dynamic-nuclear polarization (DNP)-enhanced  1 H - 13 C and  1 H - 29 Si CPMAS as well as directly excited  29 Si magic-angle spinning (MAS) NMR methods in solid-state.

Metal-Support Cooperative Effects in Au/VPO for the Aerobic Oxidation of Benzyl Alcohol to Benzyl Benzoate

This paper studies the cooperative effect of Au nanoparticles deposited on vanadyl pyrophosphate oxide (VPO) in the liquid phase oxidation of benzyl alcohol. VPO was prepared using the classical method by thermally treating VOHPO₄·0.5H₂O precursor in reacting atmosphere at 420 °C for a period of 72 h. Au nanoparticles were deposited by incipient wetness method. The catalysts were characterized by means of XRD, TEM, XPS and Raman. The bulk VPO catalyst contains vanadyl pyrophosphate phase ((VO)₂P₂O₇), and a small amount of VOPO₄. The catalytic system exhibits a high activity in the base-free liquid phase oxidation of alcohols compared to Au on activated carbon, classic catalyst used for this type of reaction. Au/VPO showed a high peculiar selectivity to benzyl benzoate (76%), an important product used in the pharmaceutical and perfume industries. This behavior might be ascribed to the presence of strong acid sites of VPO, as determined by liquid phase titration. Stability tests performed on Au/VPO showed a deactivation of 10% after the first run, but a constant conversion along the following five cycles. This phenomenon can be attributed to the increase of mean Au particle size (from 19.1 to 23.4 nm) after recycling tests as well as the partial leaching of Au and V in the reaction media. Moreover, XRD evidenced a modification in the VPO structure with the partial formation of VOHPO₄·0.5H₂O phase.

Niobic acid nanoparticle catalysts for the aqueous phase transformation of glucose and fructose to 5-hydroxymethylfurfural

The first catalytic application of a nanoparticulate niobia solid acid prepared from a high area peroxo niobic acid sol, and its SBA-15 supported analogue, is demonstrated for the heterogeneously catalysed aqueous phase conversion of glucose and fructose to 5-HMF.

Hydrolysis of oligosaccharides over solid acid catalysts: a review

Mild fractionation/pretreatment processes are becoming the most preferred choices for biomass processing within the biorefinery framework. To further explore their advantages, new developments are needed, especially to increase the extent of the hydrolysis of poly- and oligosaccharides. A possible way forward is the use of solid acid catalysts that may overcome many current drawbacks of other common methods. In this Review, the advantages and limitations of the use of heterogeneous catalysis for the main groups of solid acid catalysts (zeolites, resins, carbon materials, clays, silicas, and other oxides) and their relation to the hydrolysis of model soluble disaccharides and soluble poly- and oligosaccharides are presented and discussed. Special attention is given to the hydrolysis of hemicelluloses and hemicellulose-derived saccharides into monosaccharides, the impact on process performance of potential catalyst poisons originating from biomass and biomass hydrolysates (e.g., proteins, mineral ions, etc.). The data clearly point out the need for studying hemicelluloses in natura rather than in model compound solutions that do not retain the relevant factors influencing process performance. Furthermore, the desirable traits that solid acid catalysts must possess for the efficient hemicellulose hydrolysis are also presented and discussed with regard to the design of new catalysts.