Retention Of Activity Research Articles

Identification of HCl corrosion mechanism on Cu-based oxygen carriers in chemical looping combustion

In chemical looping combustion (CLC) of coal, HCl has been demonstrated as the primary gaseous products of the chlorine in coal. Therefore, a comprehensive characterization of Cu-based oxygen carriers (OC) by HCl corrosion was meticulously conducted, including the activity retention, composition distribution and apparent morphology. The experiment consisted of three parts: (I) evaluating of the OC performance for 100 redox cycles with 7.8 vol% CH4; (II) investigating HCl-corrosion of OC by adding 50 ppmv HCl with 7.1 vol% CH4 for the subsequent 50 cycles; (III) regenerating of OC without HCl addition during the last 50 cycles. The reactivity of OC was attenuating via the HCl addition during the 101st–150th cycles (part II) due to the competition adsorption between HCl and CH4, especially for the partly reduced OC. While, in part III, the reactivity performance of OC was partially recovered because of the abundant cracks on the surface of OC particles which ensured the sufficient gas–solid contact. It should be noted that the single particle hardness index and service life were irreversibly decreased for the HCl-treated OC. Moreover, OC particles were fragmented and the inside Al2O3 balls were exposed on the surface of the HCl-treated OC in SEM image. This work will contribute to understanding the mechanism of Cl-corrosive OC and designing the Cl-resistant OC.

Bromelain-loaded nanocomposites decrease inflammatory and cytotoxicity effects of gliadin on Caco-2 cells and peripheral blood mononuclear cells of celiac patients

Enzyme therapy can be an appropriate treatment option for celiac disease (CeD). Here, we developed Bromelain-Loaded Nanocomposites (BLNCs) to improve the stability and retention of bromelain enzyme activity. After the characterization of BLNCs, the cytotoxicity of BLNCs was determined on the Caco-2 cell line. The effect of BLNCs on gliadin degradation and the production of pro-inflammatory cytokines and anti-inflammatory molecules in peripheral blood mononuclear cells (PBMCs) obtained from celiac patients were assessed. Furthermore, the expression of CXCR3 and CCR5 genes was measured in CaCo-2 cells treated with gliadin, gliadin-digested with BLNCs, and bromelain. Our study demonstrated that the Bromelain entrapment efficiency in these nanoparticles was acceptable, and BLNCs have no toxic effect on cells. SDS-PAGE confirmed the digestion effect of bromelain released from nanocomposites. When Caco-2 cells were treated with gliadin digested by free bromelain and BLNCs, the expression of CXCR3 and CCR5 genes was significantly decreased. PBMCs of celiac patients treated with Bromelain and BLNCs decreased inflammatory cytokines (IL-1β, IL-6, TNF-α, and IFN-γ) production compared to untreated PBMCs. This treatment also increased IL-10 and CTLA-4 in PBMCs of CeD patients. According to the promising results of this study, we can hope for the therapeutic potential of BLNCs for CeD.

The doping and co-impregnation process for the synthesis of the third metal in Pt3Ni electrocatalysts

Octahedral Pt3Ni on carbon support (Pt3Ni/C) is well-known to be excellent electrocatalysts for the oxygen reduction reaction (ORR) due to its exceptional activity. However, their long-term stability is poor, since the octahedral shape is entirely shattered and Ni is simply leached out during operation. To improve activity and stability, third metals M (i.e., Ga, Ag, Cu, Rh, Co, Fe, and Mo) were added to Pt3Ni electrocatalysts by gas-phase synthesis using two distinct approaches referred to as Co-impregnation (Pt3Ni-M/C) and Metal-doping (M-Pt3Ni/C). The size distributions of octahedron and truncated octahedron were almost identical, with an average particle size of around 8–9 nm for both approaches. The Fe–Pt3Ni/C exhibited the highest pristine ORR activity in terms of both mass activity (1.64 A mgPt−1) and specific activity (65.7 A mgPt−1), which were 2.8 times greater than Pt3Ni/C and 27.3 times more than commercial Pt/C catalyst. For an accelerated durability test (ADT) of 16,000 cycles, the Cu–Pt3Ni/C exhibited the most stable catalysts with an activity retention of 69.9%, followed by Ga-Pt3Ni (61.7%) and Rh–Pt3Ni (52.2%). The Cu–Pt3Ni/C catalyst was 5.8 times more stable than the Pt3Ni/C catalyst. When the same metal was used, it was discovered that the Metal-doping (M-Pt3Ni/C) approach provided superior ORR activity and stability than the Co-impregnation (Pt3Ni-M/C) technique.

Phase engineering of Pt-Mn intermetallics for durable oxygen reduction reaction electrocatalysis

Controlling the crystal phase of intermetallic has been demonstrated as a promising strategy for enhancing oxygen reduction reaction (ORR) performance. However, the controlled synthesis of intermetallic with specific crystal phases remains a formidable challenge. Herein, structure ordered Pt-Mn intermetallics with face-centered cubic Pt3Mn (fcc-Pt3Mn/C) and face-centered tetragonal PtMn (fct-PtMn/C) are synthesized via an impregnation-reduction method. Benefiting from the rational control of crystal phase, fct-PtMn/C with optimal surface atomic arrangement and binding environment exhibits higher activity than fcc-Pt3Mn/C and Pt/C. Moreover, fct-PtMn/C exhibits a superior mass activity retention rate of 90.3 % after 50,000 potential cycles from 0.6 to 1.0 V compared to significantly lower rate of 56.0 % and 34.8 % for fcc-Pt3Mn/C and Pt/C, respectively. Structural analysis reveals that fct-PtMn/C maintains its crystal phase, particle size, and morphology exceptionally well during the durability test, demonstrating its outstanding structural stability. Theoretical calculations indicate that phase engineering can lower the reaction energy barrier, weaken the adsorption energy of reaction intermediates on fct-PtMn/C, and thus enhance the ORR performance.

Protection of antioxidant components and production of a natural food colourant powder from Ardisia compressa juice

Ardisia compressa Kunth fruit juice is rich in bioactive compounds with proven health benefits and a characteristic intense purple colour. In this investigation the effect of the wall material (using soy protein isolate (SPI) and whey protein isolate (WPI)) and type of microencapsulation (spray drying (SD) and freeze-drying techniques (FD)) on the physicochemical properties, antioxidant properties and stability in different conditions storage of the microcapsules of the juice of Ardisia compressa Kunth was evaluated. The results obtained showed that the powders developed by FD and SD exhibited differences in colour parameters, as well as physicochemical and antioxidant properties. SPI and WPI powders obtained by FD exhibited higher retention of colour, polyphenols and antioxidant activity after the drying process and during storage. Stability tests revealed that the samples obtained presented first-order degradation of polyphenols and zero-order degradation of colour, and the conditions of greatest stability were found at low water activities (0.1–0.3) at a temperature of 25 °C. The microcapsules exhibited variable morphology depending on the production technique. In conclusion, freeze-drying, using WPI and SPI as wall material, improve stability to colour, polyphenols and antioxidant activity to microcapsules produced with Ardisia compressa juice, demonstrating potential for application as a natural colourant or functional additive.

Changes in Activity of Antioxidant Systems of <i>Escherichia coli</i> under Phosphate Starvation

Changes in the activity of antioxidant systems in Escherichia coli during phosphate starvation were studied. It was shown that starvation was accompanied by a decrease in the intensity of respiration, an increase in the rate of superoxide production, and a decrease in the level of ATP. Simultaneously, there was a decrease in H2O2 in the medium and a significant increase in the expression of the katG and katE genes encoding the HPI and HPII catalases, respectively. At the same time, there was no drop in the membrane potential, which may indicate the retention of normal membrane activity in starving cells. It has been shown for the first time that the transition of E. coli to phosphate starvation is accompanied by significant changes in the status of glutathione. The most important of them are associated with a decrease in the level of glutathione reductive form (GSH) in the medium (GSHout) and with a simultaneous increase in its content in the cytoplasm (GSHin), as well as a shift in the GSHin to oxidized glutathione form (GSSGin) ratio towards reductive values, and GSHout/GSSGout towards oxidative values. Among the mutants used in the work, the double mutant gor trxB, deficient in the synthesis of glutathione reductase and thioredoxin reductase, showed the most pronounced distinctive features. Compared to the parental strain, this mutant showed a multiple higher expression of katG::lacZ, the highest level of oxidized intra- and extracellular glutathione, and, accordingly, the lowest GSH/GSSG ratio in both compartments. In general, the data obtained indicate that during phosphate starvation the interaction of the glutathione redox-system and regulons that control protection against reactive oxygen species creates conditions that allow maintaining the concentration of ROS below the toxic level. As a result, phosphate-starved E. coli cells can maintain a high viability for a long time that allows them quickly to resume growth after the addition of phosphate.

Effect of Metal Environment and Immobilization on the Catalytic Activity of a Cu Superoxide Dismutase Mimic

The Cu(II)/Cu(I) conversion involves variation in the coordination number and geometry around the metal center. Therefore, the flexibility/rigidity of the ligand plays a critical role in the design of copper superoxide dismutase (SOD) mimics. A 1,3-Bis[(pyridin-2-ylmethyl)(propargyl)amino]propane (pypapn), a flexible ligand with an N4-donor set, was used to prepare [Cu(pypapn)(ClO4)2], a trans-Cu(II) complex whose structure was determined by the X-ray diffraction. In DMF or water, perchlorate anions are exchanged with solvent molecules, affording [Cu(pypan)(solv)2]2+ that catalyzes O2•− dismutation with a second-order rate constant kMcF = 1.26 × 107 M−1 s−1, at pH 7.8. This high activity results from a combination of ligand flexibility, total charge, and labile binding sites, which places [Cu(pypapn)(solv)2]2+ above other mononuclear Cu(II) complexes with more favorable redox potentials. The covalent anchoring of the alkyne group of the complex to azide functionalized mesoporous silica through “click” chemistry resulted in the retention of the SOD activity and improved stability. A dicationic Cu(II)-N4-Schiff base complex encapsulated in mesoporous silica was also tested as an SOD mimic, displaying higher activity than the free complex, although lower than [Cu(pypapn)(solv)2]2+. The robustness of covalently attached or encapsulated doubly charged Cu(II) complexes in a mesoporous matrix appears as a suitable approach for the design of copper-based hybrid catalysts for O2•− dismutation under physiological conditions.

Cellulose nanocrystals reinforced chitosan/titanium dioxide bionanocomposite with enhanced interfacial compatibility: Fabrication, characterization, and application in fresh-cut apple slices

This research aimed to investigate the feasibility of using a bionanocomposite made of chitosan, CNC, and TiO2 nanoparticles to package freshly sliced apples. At the outset, the effect of varying concentrations of CNC (1, 5, and 10 %) and TiO2 (1, 3, and 5 %) on the mechanical, thermal, and water sensitivity characteristics of the chitosan bionanocomposite was studied. Among different combinations, the bionanocomposite containing 10 % CNC and 3 % TiO2 displayed significant enhancements compared to neat chitosan film. Notably, it exhibited a substantial increase in tensile strength (78.2 %), glass transition temperature (26.7 %), and melting temperature (30.0 %) compared to neat chitosan film. Additionally, it demonstrated reduced WVP (27.8 %), FWS (44.4 %), and SR (50.7 %). These improvements were attributed to the synergistic interactions among chitosan, CNC, and TiO2 nanoparticles through hydrogen and oxygen bonding, corroborated by spectral changes in the material. The photocatalytic degradation of ethylene and microbes by UV-A (intermittent) activated TiO2 contained in the developed bionanocomposite was confirmed by the retention of acceptable quality and radical scavenging activity (70 % retention) of fresh-cut apple slices up to 11 days. The developed bionanocomposite can thus preserve the quality of ethylene-producing horticultural produce.

Ultrasmall nickel boride nanoparticles supported on reduced graphene oxide as a high-performance catalyst for hydrazine electrooxidation

The direct hydrazine fuel cell is an attractive power generation technology for automotive applications. However, existing anode electrocatalysts generally suffer from low stability and problematic selectivity towards the non-Faradaic hydrazine (N2H4) decomposition. Herein, we report the fabrication of reduced graphene oxide (rGO)-supported nickel boride (Ni2B) nanocatalyst with a narrow size distribution around 1.5 nm by an ice-melting controlled NaBH4 reduction of Ni salt and graphene oxide. The chemical combination of Ni with B improves the intrinsic activity for N2H4 electrooxidation while suppressing the non-Faradaic N2H4 decomposition concurrently. Furthermore, Ni2B/rGO exhibits excellent stability with 91.4 % activity retention after 3000 cycles and a potential increment of only 13 mV after 50 h of constant-current measurement at 100 mA cm–2. Such stable performance is unprecedented for HzOR electrocatalysts. Our study presents the prospect of transition metal borides as high-performance HzOR electrocatalysts and may encourage further studies to explore their electrocatalytic applications.

Effect of freezing, osmodehydro-freezing, freezedrying and osmodehydro-freezedrying on the physicochemical and nutritional properties of arazá (Eugenia stipitata McVaugh)

Arazá, a berry rich in heat-sensitive bioactives (phenolics/carotenoids/flavonoids/ascorbic acid), may be suitable for preparing functional foods, however, its high perishability hinders its industrial application. Although freezing (Fr) and freezedrying (LIO) are popular methods for preserving fruits, they may cause undesirable quality changes. Adding an osmo-dehydration pretreatment (OD) before freezing (osmodehydro-freezing/OD-Fr) or freezedrying (osmodehydro-freezedrying/OD-LIO) diminishes processing time which may improve the final product quality This study analyzed the effect of Fr/LIO/OD/OD-Fr/OD-LIO on color, antioxidant content/activity, polyphenol composition and bioaccessibility (BAC) of arazá.OD pretreatment increased freezing rate (58 %) and reduced osmodehydro-frozen arazá drip-loss (40%) Osmodehydrated samples presented the highest discoloration levels (15.7), freezing/freezedrying pretreated arazá improved them 16–48 %.Fr/LIO gave the best results regarding polyphenol content (99–48 %), and activity (97–88 %) retention; whereas OD/LIO produced the highest losses (59–84 %).Results showed that in comparison with untreated fruit, freezing arazá did not affect the bioaccessible antioxidants content/activity, conversely, freezedrying reduced antioxidant activity and total-flavonoids BAC levels (14–21 %) without modifying polyphenols/carotenoids bioaccessibilities.Although osmodehydro-freezing increased total-polyphenol bioaccessibility (22 %) without affecting that corresponding to total-flavonoids, it reduced antioxidant activity retention (16–42 %). Osmodehydro-freezdrying impact was negative on all properties (13–55 %) except Ferric-Reducing-Antioxidant-Power that increased (10 %).

Impact of Processing and Preservation Methods and Storage on Total Phenolics, Flavonoids, and Antioxidant Activities of Okra (Abelmoschus esculentus L.).

Very few studies have thus far evaluated the impact of various processing and preservation techniques (blanching, frying, freezing, dehydration, and sun drying) on the levels of total phenolics, flavonoids, and antioxidant activities of okra. The primary objective of this study was to evaluate the effects of different processing and preservation methods on the levels of phenolics, flavonoids, and antioxidant activities of okra. The ethanolic extracts of each sample were analyzed before and after preservation and storage for a period of three months. The results showed a significant improvement (p < 0.05) in total phenolic content (134.1 mg GAE/100g) and DPPH (1-1-diphenyl1-2-pricrylhydrazyl) scavenging activity (IC50 value of 3.0 mg/mL) in blanched okra when compared to fresh okra (86.35 mg GAE/100g and IC50 value of 3.8 mg/mL, respectively). Fresh okra exhibited the highest flavonoid content (105.75 mg QE/100g), while sun-dried okra samples stored for three months exhibited a decrease in total phenolic content (14.45 mg GAE/100g), total flavonoid contents (13.25 mg QE/100g), reducing power activity (23.30%), and DPPH scavenging activity (IC50 value of 134.8 mg/mL). The DPPH inhibition activities of all okra treatments showed a significant and positive correlation with the okra phenolic and flavonoid content (r = 0.702 and 0.67, respectively). The reducing power activity (%) of okra treatments exhibited a strong correlation (r) with phenolic contents (r = 0.966), and the correlation with flavonoid contents was 0.459. Generally, different processing and preservation methods of okra revealed that the impact on total phenolic and flavonoid contents, as well as antioxidant activities, was slightly significant among samples preserved using the same method during storage. In addition, blanched and frozen okra resulted in the highest retention of phenolic contents and antioxidant activities.

Boronic acid functionalized silica‐coated Fe3O4 as a novel magnetically separable catalyst for the synthesis of hydrazinyl thiazoles

A novel silica‐coated magnetite supported boronic acid functionalized nanocatalyst (Fe3O4@SiO2‐Pr‐N=CH‐C6H4B[OH]2) was synthesized using a simple synthetic protocol. The catalyst was fully characterized by using Fourier transform‐infrared (FT‐IR), X‐ray diffraction (XRD), energy dispersive X‐ray (EDX), thermogravimetric analysis‐differential thermal analysis (TGA‐DTA), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM) techniques. The structural investigations revealed that the catalyst is nano‐sized (average crystallite size 13 nm), spherical, thermally stable, and magnetic in nature having a magnetic saturation of 51.26 emu/g. The catalytic activity of Fe3O4@SiO2‐Pr‐N=CH‐C6H4B(OH)2 was explored in the synthesis of hydrazinyl thiazoles via one‐pot, three‐component reaction of phenacyl halide, thiosemicarbazide and aryl aldehyde in EtOH:H2O (50:50, v/v) at room temperature and it gave above 90% yields of hydrazinyl thiazoles. The catalyst being magnetically separable can be reused six times with the retention of catalytic activity. The present approach offers the advantages of operational simplicity, shorter reaction time, ambient reaction condition, facile separation of catalyst, and higher yields of the products.

Evaluation of green chili stored at the chilling condition: Effects of thermal and ultrasound pretreatments

The research was conducted to evaluate the effect of thermal (Hot Water) and non-thermal (Ultrasound) pretreatments on the changes of physical and nutritional quality attributes, and marketability of the green chili stored at chilling condition. Freshly harvested green chili was pretreated with hot water, ultrasound and Control (Untreated) respectively and the shelf life study was performed. The experiment was designed by Completely Randomized Design with three replications. There was a significant (p < 0.05) differences observed among the treatments. It was observed that physiological weight loss, firmness, and ascorbic acid decreased significantly where pH, total soluble solids and titrable acidity increased over the storage time. The samples treated with hot water revealed the least amount of lightness in the green chili among all the treatments. The highest retention of flavonoids and antioxidant activity was found in the ultrasound treated samples. However, the total phenolic content was found to be sunstentially greater in the untreated samples after storage. The obtained results indicated that average shelf life of green chili was increased up to 16 days at chilling condition compared to untreated sample. Green chili treated with ultrasound showed the highest marketability (82%) at the end of the storage while retaining the quality attributes.

A Novel Method for γ-Aminobutyric Acid Biosynthesis Using Glutamate Decarboxylase Entrapped in Polyvinyl Alcohol-Sodium Alginate Capsules.

γ-aminobutyric acid (GABA) has essential physiological functions in the human body. A novel method using glutamate decarboxylase (GAD) entrapped in polyvinyl alcohol (PVA)-sodium alginate (SA) capsules provides a green biological strategy for GABA synthesis. In this investigation, the stability range of immobilized GAD was effectively broadened, and immobilized GAD could be repeatedly used as a batch and fixed-bed column catalyst. The immobilized enzymes were stable and retained 89% of their activity in a pH range of 4.0-5.6, while there was an approximately 50% decrease in free GAD activity in the pH range of 4.8 ± 0.4. The immobilized GAD affinity to the substrate improved, and this was evidenced by the apparent decrease in Km to 13.3 mmol/L from the 30.9 mmol/L for free GAD. The immobilized GAD retained >90.6% activity after eight cycles and a near-100% enzyme activity retention after 120 h of a continuous fixed-bed column catalyst operation. This study has thus presented an effective PVA-SA-GAD immobilization method that could be used to continuously scale-up GABA biosynthesis.

Cellulose-based fertilizers for sustainable agriculture: Effective methods for increasing crop yield and soil health

The increasing demand for sustainable agricultural practices has led to a growing need to develop novel eco-friendly fertilizers that can improve crop productivity and preserve soil quality. Research uses the distinctive characteristics of cellulose as a decomposable, and versatile biopolymer and presents an effective approach to producing fertilizers based on cellulose. This paper describes the synthesis, characterization and evaluation of fertilizers, with a specific emphasis on their ability to improve soil structure, water retention, and nutrient accessibility. Cellulose-based fertilizers are produced utilizing diverse chemical and physical procedures, incorporating nitrogen, phosphorus and potassium, along with trace elements and beneficial microorganisms. Cutting-edge analytical techniques help to rigorously investigate the properties of materials such as shape, porosity and surface chemistry. The effectiveness of cellulose-based fertilizers in terms of nutrient release, crop development and yield is evaluated in laboratory and greenhouse environments. The results indicate that cellulose fertilizers can increase crop productivity, nutrient accessibility and soil health and promote sustainable agricultural practices by influencing soil quality parameters such as organic content, microbial activity and water retention abilities. These findings help advance the corpus of knowledge on cellulose-derived products and their uses in agriculture and environmental management, laying the foundation for a more sustainable and fruitful future.

Substrate mechanical properties bias MSC paracrine activity and therapeutic potential.

Mesenchymal stromal cells (MSCs) have significant therapeutic potential due to their ability to differentiate into musculoskeletal lineages suitable for tissue-engineering, as well as the immunomodulatory and pro-regenerative effects of the paracrine factors that these cells secrete. Cues from the extracellular environment, including physical stimuli such as substrate stiffness, are strong drivers of MSC differentiation, but their effects upon MSC paracrine activity are not well understood. This study, therefore sought to determine the impact of substrate stiffness on the paracrine activity of MSCs, analysing both effects on MSC fate and their effect on T-cell and macrophage activity and angiogenesis. The data show that conditioned medium (CM) from MSCs cultured on 0.2 kPa (soft) and 100 kPa (stiff) polyacrylamide hydrogels have differing effects on MSC proliferation and differentiation, with stiff CM promoting proliferation whilst soft CM promoted differentiation. There were also differences in the effects upon macrophage phagocytosis and angiogenesis, with the most beneficial effects from soft CM. Analysis of the media composition identified differences in the levels of proteins including IL-6, OPG, and TIMP-2. Using recombinant proteins and blocking antibodies, we confirmed a role for OPG in modulating MSC proliferation with a complex combination of factors involved in the regulation of MSC differentiation. Together the data confirm that the physical microenvironment has an important influence on the MSC secretome and that this can alter the differentiation and regenerative potential of the cells. These findings can be used to tailor the culture environment for manufacturing potent MSCs for specific clinical applications or to inform the design of biomaterials that enable the retention of MSC activity after delivery into the body. STATEMENT OF SIGNIFICANCE: • MSCs cultured on 100 kPa matrices produce a secretome that boosts MSC proliferation • MSCs cultured on 0.2 kPa matrices produce a secretome that promotes MSC osteogenesis and adipogenesis, as well as angiogenesis and macrophage phagocytosis • IL-6 secretion is elevated in MSCs on 0.2 kPa substrates • OPG, TIMP-2, MCP-1, and sTNFR1 secretion are elevated in MSCs on 100 kPa substrates.

Studies on Anti-Fungal Activity of Different Macro Algal Extracts against Soil Borne Pathogen Sclerotium rolfsii Sacc.

Management of soil-borne plant pathogens is one of the single greatest challenges facing modern agriculture worldwide. Seaweeds are considered as a source of bioactive compounds as they are able to produce a great variety of secondary metabolites characterized by a broad spectrum of biological activities. The seaweeds derived compounds showing broad range of biological activities such as antiviral, antibacterial and antifungal activities. The antimicrobial activity of macro algal extracts is generally analysed using various organic solvents which always present higher efficiency in extracting bioactive compounds. Among the different the solvent extracted macro algal extracts tested, methanol extracts of Sargassum wightii recorded maximum mycelial inhibition (88.22 %) and on par with aqueous extracts recorded 85.78% of mycelial inhibition @ 10% concentration compared to other macro algal extracts.. Among the fifteen macro algal extracts, maximum inhibition of mycelial growth was recorded the Sargassum wightii (Brown algae), Ulva lactuca (Green algae) and Gracilaria salicornia (red algae) at different concentrations. In this study, we have shown that Sargassum wightii has antimicrobial potential against the S. rolfsii. Methanol extract was found to be the best solvent for retention of the antimicrobial activity

The Critical Role of Ligand Flexibility on the Activity of Free and Immobilized Mn Superoxide Dismutase Mimics

In low-molecular-weight Mn superoxide dismutase (SOD) mimics, the ligand plays a key role in tuning the reactivity of the metal center with O2•−. We used three ligands differing in their donor sites, flexibility and/or charge, to compare the redox properties and SOD activity of the resulting Mn complexes: 1,3-bis[(pyridin-2-ylmethyl)(propargyl)amino]propane (pypapn), 1,3-bis(pyridin-2-ylmethyleneamino)propane (py2pn) and 1,4-bis(salicylidenamino)butane (H2salbn). These ligands afford Mn complexes that, in aqueous solution, exist as mononuclear species [Mn(II)(pypapn)(H2O)2]2+, [Mn(II)(py2pn)(H2O)2]2+ and [Mn(III)(salbn)(H2O)2]+. The relative reactivity of these compounds with O2•− at pH 7.8, [Mn(pypapn)(H2O)2]2+ &gt; [Mn(salbn)(H2O)2]+ &gt; [Mn(py2pn)(H2O)2]2+, is independent of the redox potential but strongly depends on the ligand flexibility which becomes a critical feature when the reaction occurs through an inner-sphere electron-transfer mechanism. Immobilization was used to isolate and protect the catalyst from dissociation or dimerization during catalysis. [Mn(pypapn)(H2O)2]2+, with the alkyne group, was covalently grafted to azide functionalized mesoporous silica through click chemistry, while [Mn(py2pn)(solv)2]2+ and [Mn(salbn)(solv)2]+ were encapsulated in SBA-15 mesoporous silica through ionic exchange. The retention or enhancement of the SOD activity and the improved stability of the covalently attached catalyst and the doubly charged complex encapsulated in the silica pores, make them suitable for use in aqueous media.

Ionic liquid modulation of metal-organic framework immobilized laccase and boosted its catalytic performance for organic pollutants removal

Although Metal-organic frameworks (MOF) are a series of excellent carriers in the immobilization of laccase, excessive interaction can also lead to the denaturation and inactivation of laccase, which limited their further industrial application. In this study, ionic liquids were applied as a series of novel modifiers of metal-organic framework (ILs-NH2-MIL-101) in the immobilization of laccase. The results showed that the loading amounts and activity retention were significantly enhanced to 1.6 and 1.4 times respectively, compared with traditional laccase NH2-MIL-101. The stability and catalytic activity of the enzyme were also significantly improved. Moreover, the application of our novel-designed laccase-ILs-MIL-101 in removing organic pollutants was also examined in this study and found that the removing efficiency of 50 mg/L of 2,4-dichlorophenol, 4-chlorophenol, bisphenol A and indole, etc, can reach 95.4%, 91.4%, 90.3%, and 89.8%, respectively. The molecular dynamic simulations (MD) studies suggested that the immobilized laccase had a better rigid structure and stronger hydrogen bonding interactions with the substrate compared with free laccase, which facilitated the stability of the laccase and the degradation efficiency of the substrate. Therefore, this study proposed a simple, practical, and low-cost strategy based on ILs for the modification of various MOFs, which provides new insights into the development of high-efficiency enzyme immobilization for various industrial productions.

Rational Design and Synthesis of Novel Catalyst Support for PEMFCs

Catalysts based on metal-organic frameworks (MOFs) are promising candidates to enable fuel cells with higher performance and durability. Our recently developed PtCo catalyst on porous carbon support produced by pyrolysis of Ce-doped-ZIF (PtCo/Ce-ZIF) shows record-high outstanding performance and durability in fuel cell testing. The cell was operated under the conditions prescribed by the Million Mile Fuel Cell Truck Consortium (M2FCT) consortium (250 kPa, 85% relative humidity (RH), 90 C cell temperature, and 15% oxygen). At application-relevant operating voltages of 0.7 V and higher, the PtCo/Ce-ZIF exhibited higher performance than the commercial catalyst. The PtCo/Ce-ZIF catalyst at 0.7 V achieved a life beginning-of-life (BOL) performance level of 1.38 A/cm2; even more importantly, it showed substantially higher durability. The PtCo/Ce-ZIF catalyst provided a current density of 1.25 A/cm2 at 0.7 V after 90K accelerated stress test (AST) cycles, exceeding the M2FCT target of >1.07 A/cm2. The PtCo/Ce-ZIF also showed higher mass activity and greatly improved retention of mass activity of 0.77 A/mgPt vs. 0.54 A/mgPt, at BOL and ending of life (EOL), respectively, ~34 % mass activity loss after 90K AST cycles, exceeding the DOE target of <40% loss after 30K AST cycles. This study demonstrates that MOF-based catalysts are the leading candidates to enable fuel cell commercialization and deployment in support of the global effort to reduce greenhouse gas emissions.