Activity In Acidic Environment Research Articles

Optimizing ultrasonic extraction of polysaccharides from Spirulina platensis and evaluating their antioxidant and antibacterial activities in acidic environments.

In this study, the response surface method was used to optimize the ultrasonic extraction of polysaccharide from Spirulina platensis. The optimal extraction conditions were ultrasonic time 50 min, solid-liquid ratio 1: 40, ultrasonic power 265 w, and the predicted extraction rate was 6.861 ± 0.116 %. The FT-IR and NMR confirmed that polysaccharide from S. platensis would protonate to form β-glucoside bond in acidic environment, and the original carbonyl group would be converted to carboxyl group and then esterified to form acyl group donor. In the acidic pH range (7.0, 6.0, 5.0 and 4.0), the antioxidant, nitrite scavenging and bacteriostatic activities of the extracted polysaccharide from S. platensis were measured in vitro. The results showed that polysaccharide of S. platensis had better antioxidant activity in acidic environment and better performance in low pH condition. In addition, it has the best inhibitory effect on Salmonella enteritidis (14.3-17.15 mm) in acidic environment, and the inhibitory effect on Staphylococcus aureus (11.95-12.87 mm) is stronger than that in neutral environment (10.48-12.08 mm). To sum up, the structure of polysaccharide from S. platensis will change in acidic environment, and it has good antioxidant and antibacterial properties.

Efficient spermidine production using a multi-enzyme cascade system utilizing methionine adenosyltransferase from Lactobacillus fermentum with Reduced Product Inhibition and Acidic pH Preference.

Methionine adenosyltransferases (MATs; EC 2.5.1.6) are key enzymes that catalyze a crucial step in the spermidine biosynthesis pathway. Due to MAT's significant product inhibition, S-adenosylmethionine (SAM) and spermidine production faces challenges. We evaluated MATs from 20 lactic acid bacteria (LAB) to identify enzymes with acidic preference and lower susceptibility to product inhibition. Lactobacillus fermentum's MAT (LfMAT) emerged as a candidate with desirable characteristics. LfMAT exhibited strong activity in acidic environments, maintaining over 85 % activity between pH 6.0-8.5 for 60 min, with peak efficacy at pH 7.0. LfMAT produced 4.2 mM SAM from 5 mM substrate, indicating reduced product inhibition. Ultimately, using an in vitro multi-enzyme cascade system containing LfMAT, S-adenosylmethionine decarboxylase, and spermidine synthase, we successfully produced 12.9 g·L-1 of spermidine. This study establishes a cascade reaction platform, offering a novel approach for the efficient synthesis of spermidine and other polyamines.

Bond engineering: weakening Ru–O covalency for efficient and stable water oxidation in acidic solutions

The persistent stability of ruthenium dioxide (RuO2) in acidic oxygen evolution reactions (OER) is compromised by the involvement of lattice oxygen (LO) and metal dissolution during the OER process. Heteroatom doping has been recognized as a viable strategy to foster the stability of RuO2 for acidic OER applications. This study presented an ion that does not readily gain or lose electrons, Ba2+, into RuO2 (Ba–RuO2) nanosheet (NS) catalyst that increased the number of exposed active sites, achieving a current density of 10 mA/cm2 with an overpotential of only 229 mV and sustaining this output for over 250 h. According to density functional theory (DFT) and X-ray absorption spectroscopy, Ba doping resulted in a longer Ru–O bond length, which in turn diminished the covalency of the bond. This alteration curtailed the involvement of LO and the dissolution of ruthenium (Ru), thereby markedly improving the durability of the catalyst over extended periods. Additionally, attenuated total reflectance-surface enhanced infrared absorption spectroscopy analysis substantiated that the OER mechanism shifted from a LO-mediated pathway to an adsorbate evolution pathway due to Ba doping, thereby circumventing Ru over-oxidation and further enhancing the stability of RuO2. Furthermore, DFT findings uncovered that Ba doping optimizes the adsorption energy of intermediates, thus enhancing the OER activity in acidic environments. This study offers a potent strategy to guide future developments on Ru-based oxide catalysts’ stability in an acidic environment.

Facet Engineering of Cobalt Manganese Oxide for Highly Stable Acidic Oxygen Evolution Reaction

AbstractDeveloping cost‐effective, robust, and durable catalysts for water oxidation in acidic conditions remains a significant challenge for the practical application of proton exchange membrane electrolyzers. Cobalt‐based spinel catalysts, known for their effective oxygen evolution reaction (OER) activity in acidic environments, are promising alternatives to the costly iridium‐based catalysts. However, their application is often limited by poor stability under corrosive acidic conditions and oxidative potential. Here it is demonstrated that doping Co2MnO4 with Ni effectively regulates the structural and electronic properties of the catalysts, enabling stable operation for over 285 h at 100 mA cm−2 in 0.5 m H2SO4. This stability enhancement is primarily due to the increased exposure of the (400) facet, a result supported by theoretical studies. The proton exchange membrane water electrolysis (PEMWE) performance of Ni(5%)Co2MnO4 further demonstrates its potential, achieving 1 A cm−2 at a cell voltage of 2.3 V, with minimal degradation over 100 h at 500 mA cm−2. This study not only provides insights into the design of advanced OER catalysts through the doping of heteroatoms but also offers a pathway to enhance the sustainability and economic viability of acidic OER applications.

Progress of Metal Chalcogenides as Catalysts for Efficient Electrosynthesis of Hydrogen Peroxide.

Hydrogen peroxide (H2O2) is a high-demand chemical, valued as a powerful and eco-friendly oxidant for various industrial applications. The traditional industrial method for producing H2O2, known as the anthraquinone process, is both costly and environmentally problematic. Electrochemical synthesis, which produces H2O2 using electricity, offers a sustainable alternative, particularly suited for small-scale, continuous on-site H2O2 generation due to the portability of electrocatalytic devices. For efficient H2O2 electrosynthesis, electrocatalysts must exhibit high selectivity, activity, and stability for the two-electron pathway-oxygen reduction reaction (2e- ORR). Transition-metal chalcogenide (TMC)-based materials have emerged as promising candidates for effective 2e- ORR due to their high activity in acidic environments and the abundance of their constituent elements. This review examines the potential of TMC-based catalysts in H2O2 electrosynthesis, categorizing them into noble-metal and non-noble-metal chalcogenides. It underscores the importance of achieving high selectivity, activity, and stability in 2e- ORR. By reviewing recent advancements and identifying key challenges, this review provides valuable insights into the development of TMC-based electrocatalysts for sustainable H2O2 production.

A novel lytic phage infecting MDR Salmonella enterica and its application as effective food biocontrol.

Salmonella enterica is a foodborne pathogen associated with both typhoid and non-typhoid illness in humans and animals. This problem is further exacerbated by the emergence of antibiotic-resistant strains of Salmonella enterica. Therefore, to meet public health and safety, there is a need for an alternative strategy to tackle antibiotic-resistant bacteria. Bacteriophages or (bacterial viruses), due to their specificity, self-dosing, and antibiofilm activity, serve as a better approach to fighting against drug-resistant bacteria. In the current study, a broad-host range lytic phage phiSalP219 was isolated against multidrug-resistant Salmonella enterica serotypes Paratyphi from a pond water sample. Salmonella phage phiSalP219 was able to lyse 28/30 tested strains of Salmonella enterica. Salmonella phage phiSalP219 exhibits activity in acidic environments (pH3) and high temperatures (70°C). Electron microscopy and genome analysis revealed that phage phiSalP219 is a member of class Caudoviricetes. The genome of Salmonella phage phiSalP219 is 146Kb in size with 44.5% GC content. A total of 250 Coding Sequence (CDS) and 25 tRNAs were predicted in its genome. Predicted open reading frames (ORFs) were divided into five groups based on their annotation results: (1) nucleotide metabolism, (2) DNA replication and transcription, (3) structural proteins, (4) lysis protein, and (5) other proteins. The absence of lysogeny-related genes in their genome indicates that Salmonella phage phiSalP219 is lytic in nature. Phage phiSalP219 was also found to be microbiologically safe (due to the absence of toxin or virulence-related genes) in the control of Salmonella enterica serovar Typhimurium infections in the ready-to-eat meat and also able to eradicate biofilm formed by the same bacterium on the borosilicate glass surface.

Lactic acid bacteria with weak post-acidification potential applied for low-salt paocai fermentation: A perspective from screening to molecular mechanism

Reducing post-acidification is crucial for extending the shelf-life and facilitating industrial-scale production of low-salt paocai. This study aimed to screen and identify a lactic acid bacteria strain with weak post-acidification potential from 39 commonly used strains in vegetable fermentation. We employed transcriptomic and metabolite analysis to investigate the mechanisms underlying the weak post-acidification traits of the selected strain. Notably, W. cibaria SC5R3 had a minimum survival rate at pH 4.5 by 39.02% and survival rate to pH 4.0 was only 1.82%. The incorporation of W. cibaria SC5R3 in low-salt paocai showed a low content of total titratable acidity and stable viable count during 8 days of storage at 25 °C, which also exhibited good sensory quality. Furthermore, W. cibaria SC5R3 exhibited significant down-regulation of genes associated with the hetero-fermentation pathway during late-stage fermentation, contributing to its weak acid-producing characteristic. The strain SC5R3 displayed deficiencies in the glutamate decarboxylase system, histidine synthesis, and aspartate metabolism, along with reduced H⁺-ATPase activity in acidic environments, making it sensitive to acid. This research provides valuable insights into optimizing low-salt paocai fermentation processes and improving product quality by minimizing acidity changes during shelf-life storage.

Investigation on the Corrosion Resistance of 3003 Aluminum Alloy in Acidic Salt Spray under Different Processing States

3003 aluminum alloy exhibits commendable corrosion resistance, ease of processing, and good formability, rendering it extensively utilized across many industrial sectors. In this study, the corrosion behavior of 3003 aluminum alloy in a homogenized state and after hot extrusion deformation in an acidic salt spray environment for different times was studied. The microstructure of the 3003 aluminum alloy in the homogenized state and after hot extrusion was characterized using scanning electron microscopy (SEM), optical microscope (OM), laser scanning confocal microscope (LSCM) etc., while electrochemical methods were employed to study the difference in corrosion resistance between these two states. The results show that corrosion pits on the surface of the homogenized 3003 aluminum alloy increase with time, and corrosion extends along the second phase arrangement, while the hot extruded 3003 aluminum alloy mainly exhibits corrosion pit extension. The grain size of the homogenized 3003 aluminum alloy is larger than that of the hot extruded state, and the second phase is distributed in a reticular pattern. Hot extrusion deformation ensures not only a uniform distribution of the second phase in the 3003 aluminum alloy but also a reduced grain size, an increased grain boundary density, a heightened electrochemical activity in acidic environments, and an augmented pitting density. Compared with the homogenized 3003 aluminum alloy, the pitting density, maximum pitting depth, and weight loss of the hot extruded state are increased.

Bimetallic oxide Cu–Fe3O4 nanoclusters with multiple enzymatic activities for wound infection treatment and wound healing

Infections and oxidative stress complicate wound healing. In recent years, nanomaterials with natural enzymatic activities have enabled the development of new antibacterial pathways. In this study, Cu–Fe3O4 nanoclusters with multienzyme properties were synthesized. Interestingly, they exhibited activity similar to that of horseradish peroxidase (POD) in acidic environments but their functions resembled superoxide dismutase and catalase in neutral or weakly alkaline environments. In vitro studies have demonstrated the good free-radical scavenging activity of Cu–Fe3O4 nanoclusters in a neutral environment. Under acidic conditions, Cu–Fe3O4 nanoclusters combined with H2O2 demonstrated good antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). The combination of Cu–Fe3O4 and H2O2 was found to be effective in preventing MRSA infections and promoting wound healing in animal models. RNA sequencing (RNA-seq) technology revealed that chemodynamic therapy (CDT) using nanoparticles can interfere with metabolic processes such as galactose metabolism in MRSA bacteria, destroy the transport system on the surface of MRSA, and affect quorum sensing to hinder the formation of biofilms, thus achieving effective antibacterial efficacy. The use of Cu–Fe3O4 nanoclusters as a novel class of multi-catalytically active nanozymes in the anti-infection of disease-causing pathogens and wound healing has significant potential. Statement of significanceCu–Fe3O4 nanoclusters with multienzyme properties were successfully prepared by a solvothermal method. Cu–Fe3O4 nanoclusters exhibited horseradish peroxidase (POD)-like activity in acidic environments and also showed synergistic effects similar to superoxide dismutase peroxidase in neutral or weakly basic environments. More importantly, these Cu–Fe3O4 nanoclusters showed high biosafety with no apparent in vivo toxicity. Chemodynamic therapy (CDT) using Cu–Fe3O4 nanoclusters was revealed by RNA sequencing (RNA-Seq) technology to interfere with the metabolic processes of MRSA bacteria, such as galactose metabolism, disrupt the MRSA surface transport system, and impede biofilm formation, resulting in effective antibacterial efficacy. The use of Cu–Fe3O4 nanoclusters for anti-infection and wound healing of pathogenic pathogens has significant potential as a novel class of multi-catalytic active nanoclusters.

Thoracic limb activity of Simocephalus vetulus and its descendants is shaped by the combination of delafloxacin and calcium

Due to its robust antibacterial activity in acidic environments and effectiveness against old fluoroquinolone-resistant bacterial strains, the use of delafloxacin (DFX) is projected to increase in the coming years. Here, we investigated the effect on the thoracic limb rate (TLR) of the water flea Simocephalus vetulus under the combined exposure of DFX (0, 100, 200, and 400 µg L−1) and calcium (Ca) (26 and 78 mg L−1) using Bayesian statistics-based linear models. The findings showed unexpected increases and decreases in the TLR of maternal S. vetulus exposed to DFX in the 26 mg Ca L−1. In the 78 mg Ca L−1 condition, we found a clearer decrease in TLR during DFX treatments. In addition, in the 26 mg Ca L−1, elusive changes in the TLR of neonatal S. vetulus whose mothers were exposed to DFX were observed, whereas the reduced TLR of the neonate, whose mother was exposed to 400 µg DFX L−1, was apparent in the higher Ca condition. While the elevated Ca content did not appear to have a clear effect on organisms’ TLR, it acted as a synergist in conjunction with DFX, leading to a reduction in TLR, the underlying mechanism of which remains poorly understood. The results of our study indicate that DFX may pose an ecological risk as a xenobiotic; therefore, taking into account the abundance of Ca in specific aquatic environments, a comprehensive ecological risk assessment should be conducted. Moreover, the inclusion of Bayesian statistics in ecotoxicological studies is highly recommended to improve data analysis and interpretation.

Theoretical prediction of LaNxC4-x-doped graphene as potential bifunctional and acidic-alkaline omnipotent electrocatalysts for oxygen electrode reaction

The oxygen reduction/evolution reaction (ORR/OER) on oxygen electrode are the definitive reactions in charge/discharge process of fuel cells and metal air batteries. The research of bifunctional and acidic-alkaline omnipotent electrocatalysts for the oxygen electrode reaction is of great significance for the development and application of electrochemical storage and conversion technologies. In this paper, the catalytic performance of the rare earth LaNxC4-x-doped graphene (LaNxC4-x-Gra) catalysts has been discussed extensively. The results demonstrate that in the alkaline environment, LaN2C2hex-Gra exhibits potential bifunctional activity with the original ηOER is 0.68 V, and the ηORR is 0.56 V accompanied by OH ligands modified. Impressive, LaN2C2hex-Gra also shows excellent OER activity in acidic environment with the η of 0.68 V. Finally, the catalytic activity can be rapidly evaluated by scale relationship with the introduced band center, which will provide guidance for the development of efficient rare earth single atomic catalysts.

PMo12 induced MoP as hydrogen evolution electrocatalysts

In recent years, electrolytic water has become the mainstream method of producing hydrogen energy, in which the development of efficient electrocatalysts is particularly important. Herein, MoP@C was synthesized by simple hydrothermal following one-step calcination process. MoP@C shows excellent catalytic activity in acidic environment, requiring only a small overpotential (196 mV) at the current density of 10 mA cm-2 and exhibiting a small Tafel slope (91 mV dec-1). Meanwhile, MoP@C displays good stability within 24 hours. This work has a positive effect for the subsequent large-scale preparation of phosphides electrocatalysts.

Synthesis of a Pt/Carbon-Sphere Catalyst and Evaluation of Its Oxygen Reduction Reaction Activity in Acidic Environments

Synthesis of a Pt/Carbon-Sphere Catalyst and Evaluation of Its Oxygen Reduction Reaction Activity in Acidic Environments

Solvent Dependency of Sorghum Bran Phytochemicals Acting as Potential Antioxidants and Antibacterial Agents.

SUMMARYResearch backgroundSorghum bran, although considered as an agricultural waste, is an abundant source of various bioactive compounds. These bioactive compounds require specific extraction with particular solvents and therefore ionic liquid and three different conventional solvents, viz. anhydrous methanol, acidified methanol and water were used in this work.Experimental approachTo evaluate the phytochemicals in the different sorghum bran extracts, total phenol content, flavonoids, condensed tannins and anthocyanins were determined as per standard protocols. Liquid chromatography with tandem mass spectrometryanalysis of extracts was also performed for their phenolic profiling. The antioxidant activity of the extracts was estimated via three assays: 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolourization assay and Cu2+ reducing antioxidant capacity (CUPRAC) method. The antibacterial activity against two most opportunistic foodborne pathogens: Escherichia coli and Staphylococcus aureus was measured by agar well diffusion assay and minimum inhibitory concentration (MIC) was determined by serial dilution method.Results and conclusionsIonic liquid extract of sorghum bran gave the highest yield ((14.9±0.7) %), which indicated that various possible interactions like Van der Waals forces, H-bonding, hydrophobic and cation-π bonding can occur when ionic liquid is used as an extractant compared to other conventional solvents, although total phenol mass fraction expressed as gallic acid equivalents on dry mass basis was only (7.4±0.7) mg/g. The hydrophobicity of the ionic liquid also helped in efficient extraction of condensed tannins ((63.2±2.1) mg/g expressed on dry mass basis), which resulted in significant antioxidant activity of the ionic liquid extract ((85.2±1.2) µmol/g in DPPH assay, (100.8±0.9) µmol/g in ABTS assay and (63.2±1.9) µmol/g in CUPRAC). An interesting revelation reported in this work is the inability of DPPH assay to evaluate the antioxidant activity in acidic environment. The anhydrous methanolic extract of sorghum bran displayed pH sensitivity, making the extract beneficial for certain applications. Qualitative analysis of extracts revealed greater number of phenolic compounds to be present in methanol and distilled water extracts. Moreover, various derivatives of apigenin and luteolin were also observed in all four extracts. In addition, the acidified methanol extract of the sorghum bran exhibited antimicrobial property at a concentration of 12 mg/mL. A larger inhibition zone was observed against Escherichia coli than Staphylococcus aureus, while the MIC against these two bacteria was 2.2 and 1.1 mg/mL, respectively.Novelty and scientific contributionThis paper presents the first information on the application of ionic liquids as extracting phase for sorghum bran polyphenols and the quantification of such extracts. As evident from the study, each solvent has its own role in the extraction of bioactive compounds. This work also proves that sorghum bran imparts antibacterial activity against foodborne pathogens.

Legumain Induces Oral Cancer Pain by Biased Agonism of Protease-Activated Receptor-2.

Oral squamous cell carcinoma (OSCC) is one of the most painful cancers, which interferes with orofacial function including talking and eating. We report that legumain (Lgmn) cleaves protease-activated receptor-2 (PAR2) in the acidic OSCC microenvironment to cause pain. Lgmn is a cysteine protease of late endosomes and lysosomes that can be secreted; it exhibits maximal activity in acidic environments. The role of Lgmn in PAR2-dependent cancer pain is unknown. We studied Lgmn activation in human oral cancers and oral cancer mouse models. Lgmn was activated in OSCC patient tumors, compared with matched normal oral tissue. After intraplantar, facial or lingual injection, Lgmn evoked nociception in wild-type (WT) female mice but not in female mice lacking PAR2 in NaV1.8-positive neurons (Par2Nav1.8), nor in female mice treated with a Lgmn inhibitor, LI-1. Inoculation of an OSCC cell line caused mechanical and thermal hyperalgesia that was reversed by LI-1. Par2Nav1.8 and Lgmn deletion attenuated mechanical allodynia in female mice with carcinogen-induced OSCC. Lgmn caused PAR2-dependent hyperexcitability of trigeminal neurons from WT female mice. Par2 deletion, LI-1, and inhibitors of adenylyl cyclase or protein kinase A (PKA) prevented the effects of Lgmn. Under acidified conditions, Lgmn cleaved within the extracellular N terminus of PAR2 at Asn30↓Arg31, proximal to the canonical trypsin activation site. Lgmn activated PAR2 by biased mechanisms in HEK293 cells to induce Ca2+ mobilization, cAMP formation, and PKA/protein kinase D (PKD) activation, but not β-arrestin recruitment or PAR2 endocytosis. Thus, in the acidified OSCC microenvironment, Lgmn activates PAR2 by biased mechanisms that evoke cancer pain.SIGNIFICANCE STATEMENT Oral squamous cell carcinoma (OSCC) is one of the most painful cancers. We report that legumain (Lgmn), which exhibits maximal activity in acidic environments, cleaves protease-activated receptor-2 (PAR2) on neurons to produce OSCC pain. Active Lgmn was elevated in OSCC patient tumors, compared with matched normal oral tissue. Lgmn evokes pain-like behavior through PAR2 Exposure of pain-sensing neurons to Lgmn decreased the current required to generate an action potential through PAR2 Inhibitors of adenylyl cyclase and protein kinase A (PKA) prevented the effects of Lgmn. Lgmn activated PAR2 to induce calcium mobilization, cAMP formation, and activation of protein kinase D (PKD) and PKA, but not β-arrestin recruitment or PAR2 endocytosis. Thus, Lgmn is a biased agonist of PAR2 that evokes cancer pain.

Chitosan microparticles as entrapment system for trans- cinnamaldehyde: Synthesis, drug loading, and in vitro cytotoxicity evaluation

The ionic gelation method was used to study the effect of the crosslinking agent, sodium tripolyphosphate on average particle size (Dp) and zeta potential (ζp) of chitosan microparticles (CSMP) unloaded and loaded with trans-cinnamaldehyde (TCIN). The obtained values of Dp and ζp trend as 117.6 ± 0.4 ≤ Dp ≤ 478.5 ± 3.5 nm and +27.8 ± 1.3 ≤ ζp ≤ +103.5 ± 4.2 mV, respectively. The entrapment efficiency of TCIN in CSMP was 9.1 ± 2.0% and 71.5 ± 2.9% was released after 360 min (pH = 6.5) which reveals a potential anti-cancer activity in acidic environment. Cytotoxicity of TCIN in DMSO (0–50 μM) was evaluated on MDCK and HeLa cell lines and exhibited low effect at either 24 or 48 h of exposure; whereas TCIN-loaded CSMP (0–50 μM) showed, after 24 h of exposure, 67.6 ± 7.0 and 64.5 ± 3.9% cytotoxicity for MDCK and HeLa cell lines, respectively. At 48 h of exposure, TCIN-loaded CSMP achieved 81.1 ± 0.26 and 77.9 ± 4.2% cytotoxicity for MDCK and HeLa cell lines, respectively.

A metal-free nanozyme-activated prodrug strategy for targeted tumor catalytic therapy

Abstract Enzyme-mediated activation of prodrug in tumor cells is an attractive strategy for targeted cancer therapy. Of note, natural peroxidase and indole-3-acetic acid (IAA) have been shown as a promising enzyme-prodrug combination. However, insufficient endogenous peroxidase activity and the difficulty in selectively expressing exogenous peroxidase in tumor cells have severely limited its antitumor efficiency. The discovery of nanomaterials with peroxidase-like activity (nanozyme), particularly the metal-free nanozymes that possesses high stability and good biocompatibility, bring a new opportunity to overcome these challenges. Here, under the guidance of theoretical calculations, we developed a metal-free phosphorous and nitrogen dual-doped porous hollow carbon sphere nanozyme (PNCNzyme) with robust peroxidase-like activity in acidic environment. Based on this metal-free nanozyme, we developed a nanozyme-IAA activation strategy that activated IAA to produce abundant ROS and trigger tumor cell apoptosis. We also introduced folate (FA) onto the nanozyme to enhance its tumor targeting and endocytosis efficacy by tumor cells. Upon administrated to mice, the FA-PNCNzymes@IAA effectively accumulated in the xenografts derived from cervical cancer cells, catalyzed the production of ROS, and induced apoptosis. Taken together, these data demonstrate that the nanozyme-IAA combination is an effective enzyme-prodrug activation strategy for tumor targeted catalytic therapy.

Durability screening of Pt ternary alloy (111) surfaces for oxygen reduction reaction using Density Functional Theory

Degradation of Oxygen Reduction Reaction (ORR) catalytic activity in acidic environments is one of the biggest challenges in developing cost-effective Proton Exchange Membrane Fuel Cells (PEMFCs). In this work, we screened the durability of 138 Pt ternary alloy (111) surfaces by calculating the surface Pt vacancy formation energy, and surface segregation energy using a Density Functional Theory (DFT). Specifically, we investigated Pt ternary systems showing improved durability over corresponding Pt binary systems. Our results identify Pt-Cu-Pd as the most promising candidate. We analyzed the reason for the improved durability using a Density Derived Electrostatic and Chemical (DDEC) method. The improved durability is attributed to the strong resistance to oxygen-induced surface segregation of Cu and Pd, attractive interactions between corresponding bonds (Pt-Cu, Pt-Pd, Cu-Pd). We also show that the ORR activity of the Pt-Cu-Pd(111) is higher than that of Pt(111). We studied the effect of Pd on the ORR activity, and we found that the subsurface Pd slightly strengthen the bonding between surface Pt and adsorbates but its effect is negligible when the overall Pt content is 75 at%, while the effect is noticeable when Pt content is ~50 at%. Although Pt-Cu-Pd catalysts were previously synthesized and tested, our comprehensive screening of Pt ternary alloy (111) surfaces provides an explanation of why Pt-Cu-Pd is the most durable ORR catalysts in an acidic environment.

Ru@Pt/C core-shell catalyst for SO2 electrocatalytic oxidation in electrochemical Bunsen reaction

Although SO2 is a highly toxic industrial pollutant, it can be used as a potential source of hydrogen and H2SO4 in the presence of water. This characteristic of SO2 is widely applied in desulfurization of industrial flue gas, hybrid-sulfur cycle and sulfur-iodine cycle. The main way to advance this technology is to develop a suitable electrocatalyst. So far researches on electrocatalysts for liquid phase oxidation of SO2 mainly focus on noble metal, which have excellent corrosion resistance and catalytic activity in acidic environment. In order to improve the performance of Pt-catalysts in SO2 electrocatalytic oxidation and reduce the use of Pt, a series of Ru@Pt/C core-shell catalysts with different Ru/Pt molar ratios were synthesized by microwave-assisted alcohol reduction. Reduction in the size of Pt shell is beneficial to increase the catalytic activity brought by the electronic effect. The bi-functional effect of Ru and Pt is more pronounced in the case of low Pt coverage. Ru only plays an auxiliary role and does not have the property of direct catalytic oxidation of SO2. The results showed that the optimal mass activity was achieved when Ru/Pt was 1:1. While when Ru/Pt was 3:1, the unit mass activity of Pt was the highest, which was 3.97 times of Pt/C.

Enhanced photo-assistant electrocatalysis of anodization TiO 2 nanotubes via surrounded surface decoration with MoS 2 for hydrogen evolution reaction

Abstract A highly ordered TiO2 nanotube array covered with MoS2 is fabricated through a facile anodization of a metallic Ti followed by electrochemical deposition approach. The morphologies characterization of v-TiO2@MoS2 indicate that a whole scale of 1D TiO2nanotube uniformly covered with the MoS2 layer inside and outside, and the pathway inside the TiO2nanotube is kept flow-through. The as-synthesized v-TiO2@MoS2 hybrid exhibits higher efficient and stable visible light activities than that of either pure TiO2 nanotubes or nv-TiO2@MoS2 nanostructures. By electrochemical measurements such as linear sweep voltammetry(LSV) and electrochemical impedance spectroscope (EIS) under light illumination or in dark, we find that the v-TiO2@MoS2hybrid shows markedly enhanced photoelectrochemical performance. Furthermore, we compare the electrocatalytic behavior of v-TiO2@MoS2under illumination in H2SO4/Lactic acid within Na2S/NaSO3 solution. The results show that the photo-assistant electrocatalytic activity in acidic environment is much better than in alkaline environment. The highly directional and orthogonal separation of charge carriers between TiO2 nanotubes and MoS2 layer, together with maximally exposed MoS2 edges, light harvesting and junctions formed between TiO2 and MoS2 is supposed to be mainly responsible for the enhanced photo-assistant electrocatalytic activity of v-TiO2@MoS2.