► Laccase-mediated and pH dependent synthesis of phenolic acid with chitosan. ► Coupling of phenolic o-quinone with chitosan amino groups above pH 4.5. ► Ester formation through chitosan hydroxyl ...groups below pH 4.5. ► New bi-functionalized chitosan with modulated antimicrobial and antioxidant activity.
A new strategy for the functionalization of chitosan with caffeic acid (CA) or gallic acid (GA) using laccase from Trametes versicolor is presented for the first time, yielding a product with modulated antioxidant and antimicrobial properties. UV–vis spectroscopy coupled to HPLC-SEC analysis and cyclic voltammetry kinetic studies showed that laccase catalyzes the oxidation of phenolic acids to electrophilic o-quinones, which undergo new oligomer/polymer-forming structures originated by C–C coupling between the benzene rings and C–O–C coupling involving phenolic side-chains. Furthermore, pH tunable reactions/interactions of the laccases oxidized o-quinones with nucleophilic amino groups of chitosan were determined with FTIR and 1H NMR spectroscopy's. The highest antioxidant activity was found to be for chitosan modified with phenolic acids at pH 4.5, exhibit also an increased activity against Escherichia coli and Listeria monocytogenes compared to untreated chitosan.
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•Phosphorylated nanocellulose adsorbed Ag+, Cu2+ and Fe3+ (≈100%) from water.•Ag+ reached equilibrium sorption more rapidly than Cu2+ and Fe3+.•Adsorption was efficient in model water ...as well as industrial effluent.
The potential of nanoscaled cellulose and enzymatically phosphorylated derivatives as bio-adsorbents to remove metal ions (Ag+, Cu2+ and Fe3+) from model water and industrial effluents is demonstrated. Introduction of phosphate groups onto nanocelluloses significantly improved the metal sorption velocity and sorption capacity. The removal efficiency was considered to be driven by the high surface area of these nanomaterials as well as the nature and density of functional groups on the nanocellulose surface. Generally, in the solutions containing only single types of metal ions, the metal ion selectivity was in the order Ag+>Cu2+>Fe3+, while in the case of mixtures of ions, the order changed to Ag+>Fe3+>Cu2+, irrespective of the surface functionality of the nanocellulose. In the case of industrial effluent from the mirror making industry, 99% removal of Cu2+ and Fe3+ by phosphorylated nanocellulose was observed. The study showed that phosphorylated nanocelluloses are highly efficient biomaterials for scavenging multiple metal ions, simultaneously, from industrial effluents.
Alkaline anion exchange membrane fuel cells (AAEMFC) are attracting ever-increasing attention, as they are promising electrochemical devices for energy production, presenting a viable opponent to the ...more researched proton exchange membrane fuel cells (PEMFCs). Consequently, great progress has been made in the area of designing and developing synthetic or naturally-derived anion exchange membrane (AEM), the properties of which have been discussed in this review,
i.e.
ionic conductivity, ion exchange capacity, fuel crossover, durability, stability and cell performance. Major groups of natural polymers (
e.g.
chitosan (CS)) and nanocellulose, together with modification/crosslinking routes, have been mentioned as more ecologically and economically viable raw materials for AEM processing compared to synthetic ones. Performances of fuel cells are also discussed, with different fuels used as anode feeds. Although the AEMFC technology is promising, the longevity challenges remain, originating from the still-limited long-term stability of hydroxide-conducting ionomers, particularly when operating at higher cell temperatures.
Alkaline anion exchange membrane fuel cells (AAEMFC) are attracting ever-increasing attention, as they are promising electrochemical devices for energy production, presenting a viable opponent to proton exchange membrane fuel cells (PEMFCs).
► Preparation and characterization of polyphenol-functionalized chitosans. ► Homogeneous and heterogeneous methods for functionalization using laccase as catalyst. ► Imparting remarkable antioxidant ...properties. ► Antimicrobial activities depending on the mode of functionalization and type of microorganism.
Homogeneous and heterogeneous methods for functionalization of chitosan with quercetin or tannic acid using laccase from Trametes versicolor is presented, yielding a bio-based product with synergistic antioxidant and antimicrobial properties. HPLC–SEC analysis and cyclic voltammetry kinetic studies showed that laccase catalyzes the oxidation of quercetin to electrophilic o-quinones, which undergo to an oligomer/polymer-forming structures. On the other hand, tannic acid was converted into gallic acid, its dimers, partially gallic acid esterified glucose and glucose, when exposed to laccases. ATR-FTIR spectroscopy provided evidence that quercetin o-quinones undergo coupling reactions with amino groups of chitosan via Schiff-base and Michael addition mechanisms under heterogeneous method, while oxidized tannic acid cross-linked with chitosan by hydrogen and electrostatic interactions under both methods. All polyphenols functionalized chitosans showed greatly improved ABTS+ cation radicals scavenging capacity, compared with the untreated chitosan, while antimicrobial activities significantly depended on the mode of functionalization and type of microorganism.
•Dibasic phosphate and monobasic phosphite groups are formed at C6 and C3 hydroxyls.•60-Fold higher surface charge density on NFC is created under homogenous conditions.•The phosphorylations do not ...affect the crystallinity of NC.•The weight loss is noticeably prevented during the pyrolysis process.•High hydrolytic stability to water at all pH mediums is proved.
Nano-sized cellulose ester derivatives having phosphoryl side groups were synthesised by phosphorylation of nanofibrilated cellulose (NFC) and nanocrystaline cellulose (NCC), using different heterogeneous (in water) and homogeneous (in molten urea) processes with phosphoric acid as phosphoryl donor. The phosphorylation mechanism, efficacy, stability, as well as its influence on the NC crystallinity and thermal properties, were evaluated using ATR-FTIR and 13C NMR spectroscopies, potentiometric titration, capillary electrophoresis, X-ray diffraction, colorimetry, thermogravimmetry and SEM. Phosphorylation under both processes created dibasic phosphate and monobasic tautomeric phosphite groups at C6 and C3 positioned hydroxyls of cellulose, yielded 60-fold (∼1173mmol/kg) and 2-fold (∼1038mmol/kg) higher surface charge density for p-NFC and p-NCC, respectively, under homogenous conditions. None of the phosphorylations affected neither the NC crystallinity degree nor the structure, and noticeably preventing the derivatives from weight loss during the pyrolysis process. The p-NC showed high hydrolytic stability to water at all pH mediums. Reusing of the treatment bath was examined after the heterogeneous process.
This article gives a summary of the most commonly used ecologically unfriendly processes for the reduction and oxidation of vat and sulphur dyes. It also describes the new alternatives that are in ...the development stage and could be important in the near future. Sodium dithionite as the dominant reducing agent produces large amounts of sodium sulphate, and also toxic sulphite and thiosulphate as by-products. Consequently, high amounts of hydrogen peroxide and alkali are required for the treatment of effluents, which add to the cost of the process. Attempts have been made to use organic biodegradable reducing agents, enzymes, catalytic hydrogenation, and also indirect or direct, electrochemical reductive methods that employ a redox mediator (electron-carrier). The reduction has also been carried out via the dye radical molecule or, in the case of indigo, by direct electrochemical reduction using graphite as the electrode material. Physical techniques, for example using ultrasound, magnetic fields or UV have been shown to be effective only when used to accelerate methods using classical reduction and oxidation processes. However, although these methods offer some environmental benefits, there is still no satisfactory alternative reducing and/or oxidising agent available today.
Alkali activated materials (AAMs), a potential alternative to cement-based products or ceramics, can incorporate large amounts of currently landfilled aluminosilicate rich materials such as calcined ...clay-rich river sediments collected at hydropower plant dams. Untreated fresh sediment and untreated aged sediment intended to serve as AAM precursors were calcined to increase their amorphous content, then activated by Na or K-based silicate or hydroxide solutions and cured at 60 °C for three days.
Up to 30 mass % (ma%) of fly ash (FA) or ladle slag (LS) increased the mechanical performance. The phase composition and microstructure are analyzed using X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and mercury intrusion porosimetry to gain further insight into how the additives influence the final properties of the resulting AAMs. The main crystalline components of the prepared AAMs are quartz, illite/muscovite and feldspar. The amorphous content reaches up to 52.5 ma% in the Na-activated AAMs and up to 48.8 ma% in K-activated AAMs. The acquired results confirm the suitability of the investigated sediments as sole precursors for AAMs. The mechanical properties of the AAMs can be improved by adding FA and/or LS.
•Clay-rich river sediments were calcined to increase their reactivity to be used as alkali activated (AA) precursors.•AA materials based on sediments were successfully prepared by Na- or K-based activators.•By addition of fly ash or ladle slag mechanical properties of the resulting AAMs are further improved by about 50%.•The compressive strength increase can be correlated to an increased amorphous content and solubility in alkaline media.
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•CNF/LS/CaCl2 composite membranes are formed by a dispersion casting procedure.•The addition of CaCl2 reduces the ζ potential and promotes the aggregation of CNF.•The addition of ...CaCl2 promotes LS deposition on CNFs already in dispersion phase.•Composite membranes provide excellent passive flame retardancy.•LS component contribute for up to 100 % UVA/UVB shielding capacity.
The use of biomass to produce value-adding materials is a core objective of the circular economy, which has attracted great research interest in recent decades. In this context, we present here a simple dispersion-casting process for consolidation of cellulose nanofibrils (CNF), lignosulphonate (LS)-rich bio-waste and CaCl2 in composite membranes. The addition of CaCl2 to CNF and LS dispersions reduces the ζ potential, due to an electrostatic screening, which promotes the aggregation of CNF, increases its moisture content and promotes LS deposition on CNFs already in the dispersion phase. Addition of both the LS and CaCl2 to CNF dispersion has an adverse effect on the mechanical properties of the final membranes. The effectiveness of the new composite membranes has been described in terms of their passive (charring) flame retardancy and 100 % UVA/UVB shielding capacity, both identified for membranes with the highest LS content, as well as high electronic resistance.
This study confirms the enzyme-mediated phosphorylation of cellulose nanofibers (CNF) by using hexokinase and adenosine-5′-triphosphate in the presence of Mg-ions, resulting in a phosphate group’s ...creation predominantly at C-6-O positioned hydroxyl groups of cellulose monomer rings. A proof-of-concept is provided using ¹²C CPMAS, ³¹P MAS nuclear magnetic resonance, attenuated total reflectance-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) analyzing methods. The degree of substitution (DS) is determined by elemental analysis and compared to DS estimated by XPS analysis. From the thermal degradation measurements using thermo-gravimetric analysis, the C-6-O phosphorylation was found to noticeably prevent the CNF derivatives from weight loss in the pyrolysis process, thus, providing them flame-resistance functionality. Furthermore, phosphorylation significantly enhanced adsorption capacity of Fe³⁺ ions making them interesting for fabrication of biobased filters and membranes. Finally, the biomimetic growth of Ca–P crystals (hydroxyapatite) in simulated body fluid was characterized by scanning electron microscopy and energy dispersive X-ray, showing potential application as biomedical materials.
Abstract
In some clinical situations, measurements of anticoagulant effect of apixaban may be needed. We investigated the inter- and intra-individual apixaban variability in patients with atrial ...fibrillation and correlated these results with clinical outcome. We included 62 patients receiving either 5 mg (A5, n = 32) or 2.5 mg (A2.5, n = 30) apixaban twice-daily. We collected three trough and three peak blood samples 6–8 weeks apart. Apixaban concentration was measured by liquid chromatography-tandem mass-spectrometry (LC–MS/MS) and by anti-Xa. Patients on A2.5 were older, had lower creatinine clearance, higher CHA
2
DS
2
VASc (4.7 ± 1.0 vs. 3.4 ± 1.7) and lower trough (85 ± 39 vs. 117 ± 53 ng/mL) and peak (170 ± 56 vs. 256 ± 91 ng/mL) apixaban concentrations than patients on A5 (all
p
< 0.01). In patients on A5, LC–MS/MS showed a significant difference between through levels and between peak levels (
p
< 0.01). During apixaban treatment, 21 patients suffered bleeding (2 major). There was no association between bleeding and apixaban concentrations or variability. Four patients who suffered thromboembolic event had lower peak apixaban concentrations than patients without it (159 ± 13 vs. 238 ± 88 ng/mL,
p
= 0.05). We concluded, that there was a significant intra- and inter-individual variability in apixaban trough and peak concentrations. Neither variability nor apixaban concentrations were associated with clinical outcomes.
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