Absence Of Mn2 Research Articles

Kinetic analysis of RNA cleavage by coronavirus Nsp15 endonuclease: Evidence for acid–base catalysis and substrate-dependent metal ion activation

Understanding the functional properties of severe acute respiratory syndrome coronavirus 2 nonstructural proteins is essential for defining their roles in the viral life cycle, developing improved therapeutics and diagnostics, and countering future variants. Coronavirus nonstructural protein Nsp15 is a hexameric U-specific endonuclease whose functions, substrate specificity, mechanism, and dynamics are not fully defined. Previous studies report that Nsp15 requires Mn2+ ions for optimal activity; however, the effects of divalent ions on Nsp15 reaction kinetics have not been investigated in detail. Here, we analyzed the single- and multiple-turnover kinetics for model ssRNA substrates. Our data confirm that divalent ions are dispensable for catalysis and show that Mn2+ activates Nsp15 cleavage of two different ssRNA oligonucleotide substrates but not a dinucleotide. Biphasic kinetics of ssRNA substrates demonstrates that Mn2+ stabilizes alternative enzyme states that have faster substrate cleavage on the enzyme. However, we did not detect Mn2+-induced conformational changes using CD and fluorescence spectroscopy. The pH-rate profiles in the presence and absence of Mn2+ reveal active-site ionizable groups with similar pKas of ca. 4.8 to 5.2. An Rp stereoisomer phosphorothioate modification at the scissile phosphate had minimal effect on catalysis supporting a mechanism involving an anionic transition state. However, the Sp stereoisomer is inactive because of weak binding, consistent with models that position the nonbridging phosphoryl oxygen deep in the active site. Together, these data demonstrate that Nsp15 employs a conventional acid-base catalytic mechanism passing through an anionic transition state, and that divalent ion activation is substrate dependent.

Earthworm granules: A model of non-classical biogenic calcium carbonate phase transformations.

Different non-classical crystallization mechanisms have been invoked to explain structural and compositional properties of biocrystals. The identification of precursor amorphous nanoparticle aggregation as an onset process in the formation of numerous biominerals (crystallization via particle attachment) constituted a most important breakthrough for understanding biologically mediated mineralization. A comprehensive understanding about how the attached amorphous particles transform into more stable, crystalline grains has yet to be elucidated. Here, we document structural, biogeochemical, and crystallographic aspects of the formation as well as the further phase transformations of the amorphous calcium carbonate particles formed by cultured specimens of earthworm Lumbricus terrestris. In-situ observations evidence the formation of proto-vaterite after dehydration of earthworm-produced ACC, which is subsequently followed by proto-vaterite transformation into calcite through nanoparticle attachment within the organic framework. In culture medium spiked with trace amounts of Mn2+, the cauliflower-like proto-vaterite structures become longer-lived than in the absence of Mn2+. We propose that the formation of calcite crystals takes place through a non-classical recrystallization path that involves migration of proto-vaterite nanoparticles to the crystallization site, and then, their transformation into calcite via a dissolution-recrystallization reaction. The latter is complemented by ion-by-ion crystal growth and associated with impurity release. These observations are integrated into a new model of the biocrystallization of earthworm-produced carbonate granules which highlights the sensibility of this process to environmental chemical changes, its potential impact on the bioavailability of contaminants as well as the threat that chemical pollution poses to the normal development of its early stages. STATEMENT OF SIGNIFICANCE: Understanding the mechanisms of nucleation, stabilization and aggregation of amorphous calcium carbonate (ACC) and factors controlling its further transformation into crystalline phases is fundamental for elucidation of biogenic mineralization. Some species of earthworms are natural workbench to understand the biogenic ACC, stabilization and the transformation mechanisms, because they create millimeter-sized calcareous granules from amorphous calcium carbonate, which crystallize to a more stable mineral phase (mostly calcite). This study undergoes into the mechanisms of ACC stabilization by the incorporation of trace elements, as manganese, and the ulterior precipitation of calcareous granules by a coupled process of amorphous particle attachment and ion-by-ion growth. The study points to sensibility of this process to environmental chemical changes.

A mutant R70V/E166A of short manganese peroxidase showing Mn2+-independent dye decolorization.

Il-MnP1, a short-type manganese peroxidase from Irpex lacteus F17, can oxidize some substrates in the absence of Mn2+, but the catalysis was much lower than in the presence of Mn2+. Here, we report a mutant R70V/E166A of Il-MnP1 with some unique properties, which possessed clearly higher catalysis for the decolorization of anthraquinone and azo dyes in the absence of Mn2+ than that of Il-MnP1. Importantly, the optimum pH of R70V/E166A for decolorization of anthraquinone dyes (Reactive Blue 19, RB19) was 6.5, and the mutant achieved high decolorization activities in the range of pH 4.0-7.0, whereas Il-MnP1 only showed decolorization for RB19 at pH 3.5-4.0. In addition, the optimum H2O2 concentration of R70V/E166A for RB19 decolorization was eight times that of Il-MnP1 and the H2O2 stability has improved 1.4 times compared with Il-MnP1. Furthermore, Mn2+ competitively inhibited the oxidation of RB19 by R70V/E166A, explaining the higher catalytic activity of the mutant R70V/E166A in the absence of Mn2+. Molecular docking results suggested that RB19 binds to the distal side of the heme plane in mutant R70V/E166A, which extended from the heme δ-side to the heme γ-side, and close to the mutated residues of R70V and E166A, whereas RB19 could not access the heme pocket of Il-MnP1 due to the steric hindrance of the side-chain group of Arg 70. Thus, this study constructed a useful mutant R70V/E166A and analyzed its higher Mn2+-independent activity, which is very important for better understanding the Mn2+-independent catalytic mechanism for short manganese peroxidases. KEY POINTS: • The mutant R70V/E166A of atypical MnP1 of I. lacteus F17 shows unique catalytic properties. • At pH 6.5, the R70V/E166A had a strong ability to decolorize anthraquinone dyes in the absence of Mn2+. • The binding sites of Reactive Blue 19 in mutant R70V/E166A were elucidated.

Analysis of the effect of metal ions on the ability of Xylanase to hydrolyze wheat bran by molecular dynamics simulations.

Introduction: Wheat bran is the main by-product of wheat processing, containing about 30% pentosan and 0.4%-0.7% ferulic acid. Wheat bran is the main raw material used to prepare feruloyl oligosaccharides by hydrolysis of Xylanase, we discovered that the ability of Xylanase to hydrolyze wheat bran could be affected in the presence of different metal ions. Methods: In the present study, we have probed the effects of different metal ions on the hydrolysis activity of Xylanase on wheat bran and tried to analyze the effect of Mn2+ and Xylanase by molecular dynamic (MD) simulation. Results: Our results suggested that Mn2+ had improved the Xylanase hydrolyzing wheat bran to obtain feruloyl oligosaccharides. Particularly when the concentration of Mn2+ reached 4mmol/L, the optimal product has been obtained 2.8 times higher to compare with no addition. Through the MD simulation analysis, our results reveal that Mn2+ can induce structural change in the active site, which enlarges the substrate binding pocket. The simulation results also revealed that the addition of Mn2+ resulted in a low RMSD value compared with the absence of Mn2+ and helped stabilize the complex. Conclusion: Mn2+ could increase the enzymatic activity of Xylanase in the hydrolysis of feruloyl oligosaccharides in wheat bran. The finding could have significant implications for the preparation of feruloyl oligosaccharides from wheat bran.

Structural Dynamics of the Bacillus subtilis MntR Transcription Factor Is Locked by Mn2+ Binding.

Manganese (II) ions are essential for a variety of bacterial cellular processes. The transcription factor MntR is a metallosensor that regulates Mn2+ ion homeostasis in the bacterium Bacillus subtilis. Its DNA-binding affinity is increased by Mn2+ ion binding, allowing it to act as a transcriptional repressor of manganese import systems. Although experimentally well-researched, the molecular mechanism that regulates this process is still a puzzle. Computational simulations supported by circular dichroism (CD), differential scanning calorimetry (DSC) and native gel electrophoresis (native-PAGE) experiments were employed to study MntR structural and dynamical properties in the presence and absence of Mn2+ ions. The results of molecular dynamics (MD) simulations revealed that Mn2+ ion binding reduces the structural dynamics of the MntR protein and shifts the dynamic equilibrium towards the conformations adequate for DNA binding. Results of CD and DSC measurements support the computational results showing the change in helical content and stability of the MntR protein upon Mn2+ ion binding. Further, MD simulations show that Mn2+ binding induces polarization of the protein electrostatic potential, increasing the positive electrostatic potential of the DNA-binding helices in particular. In order to provide a deeper understanding of the changes in protein structure and dynamics due to Mn2+ binding, a mutant in which Mn2+ binding is mimicked by a cysteine bridge was constructed and also studied computationally and experimentally.

Influence of polarisation time and Mn2+ on the electrochemical behaviour of different lead silver anodes

ABSTRACT The influence of polarisation time and Mn content on the electrochemical behaviour of different lead silver anodes in sulphuric acid electrolyte during decay periods has been studied. After 1, 5 and 10 h polarisation followed by one hour decay in zinc electrolyte in the presence of Mn2+, the corrosion current density of Pb-0.5% Ag was higher than that of Pb-0.6% Ag anode and even higher than that of Pb-0.7% Ag anode. It was also found that during 1 h of decay after 5 h polarisation study in the presence and the absence of Mn2+, the Pb–Ag anodes containing different silver contents have better oxide film and less corrosion current density than that of 1 and 10 h of polarisation. Electrochemical impedance results confirmed the mentioned tendency with and without Mn2+ additions. Scanning electron microscope (SEM) analysis shows that the presence of MnO2 on the anode surface provides a protective barrier against leakage of Pb2+ ions into the solution.

Mn3+ and the pink color of gem-quality euclase from northeast Brazil

Abstract Pink euclase of gem quality and centimeter size, presenting an unusual pink-orange coloration and a pink to orange pleochroism, was discovered near Livramento de Nossa Senhora, in Bahia State, Brazil. The origin of the pink coloration has been investigated using several spectroscopic techniques: UV-Vis-NIR spectroscopy, electron paramagnetic resonance (EPR), luminescence, and X-ray absorption near edge structure (XANES). The coloration is mainly due to the presence of Mn3+ substituted to octahedral Al3+ that causes an intense split band at about 18 500 and 21 000 cm−1. The crystal field splitting Dq, crystal field stabilization energy (CFSE), and Racah parameter B for Mn3+ are 2055.5 cm−1, 147 kJ/mol, and 886 cm−1, respectively. The Mn3+ molar extinction coefficient varies as a function of polarization, between 23 and 55 L.mol−1·cm−1. An additional absorption band, near 24 000 cm−1, together with the rising background toward the UV, tentatively assigned to the O → Fe3+ OMCT, contributes to the pink-orange hue. The in-situ UV-Vis-NIR spectra on heating up to 500 °C show a color change toward an intense, stable pink color. CIE colorimetric parameters demonstrate that the color of the investigated euclase remains in the pink domain before and after heat treatment. In the absence of Mn2+, shown by EPR and luminescence, the presence of Mn3+ evidences oxidative formation conditions due to contamination of the hydrothermal fluids by the surrounding host rock.

In silico Prediction of Protein-Protein Interaction Network Induced by Manganese II in Meyerozyma guilliermondii.

Recently, there has been an increasing interest in the use of yeast to produce biosorbent materials, because yeast is economical to use, adaptable to a variety of conditions, and amenable to morphological manipulations to yield better raw biomaterials. Previous studies from our laboratory have shown that Meyerozyma guilliermondii, a non-pathogenic haploid yeast (ascomycete), exhibits excellent biosorption capacity for Mn2+, as demonstrated by kinetic analyses. Shotgun/bottom-up analyses of soluble fractions revealed a total of 1257 identified molecules, with 117 proteins expressed in the absence of Mn2+ and 69 expressed only in the presence of Mn2+. In this article, we describe the first in silico prediction and screening of protein–protein interactions (PPIs) in M. guilliermondii using experimental data from shotgun/bottom-up analyses. We also present the categorization of biological processes (BPs), molecular functions (MFs), and metabolic pathways of 71 proteins upregulated in the M. guilliermondii proteome in response to stress caused by an excess of Mn2+ ions. Most of the annotated proteins were related to oxidation–reduction processes, metabolism, and response to oxidative stress. We identified seven functional enrichments and 42 metabolic pathways; most proteins belonged to pathways related to metabolic pathways (19 proteins) followed by the biosynthesis of secondary metabolites (10 proteins) in the presence of Mn2+. Using our data, it is possible to infer that defense mechanisms minimize the impact of Mn2+ via the expression of antioxidant proteins, thus allowing adjustment during the defense response. Previous studies have not considered protein interactions in this genus in a manner that permits comparisons. Consequently, the findings of the current study are innovative, highly relevant, and provide a description of interactive complexes and networks that yield insight into the cellular processes of M. guilliermondii. Collectively, our data will allow researchers to explore the biotechnological potential of M. guilliermondii in future bioremediation processes.

Manganese-oxidizing bacteria isolated from natural and technical systems remove cylindrospermopsin

The cyanotoxin cylindrospermopsin was discovered during a drinking water-related outbreak of human poisoning in 1979. Knowledge about the degradation of cylindrospermopsin in waterbodies is limited. So far, only few cylindrospermopsin-removing bacteria have been described. Manganese-oxidizing bacteria remove a variety of organic compounds. However, this has not been assessed for cyanotoxins yet. We investigated cylindrospermopsin removal by manganese-oxidizing bacteria, isolated from natural and technical systems. Cylindrospermopsin removal was evaluated under different conditions. We analysed the correlation between the amount of oxidized manganese and the cylindrospermopsin removal, as well as the removal of cylindrospermopsin by sterile biogenic oxides. Removal rates in the range of 0.4–37.0 μg L−1 day−1 were observed. When MnCO3 was in the media Pseudomonas sp. OF001 removed ∼100% of cylindrospermopsin in 3 days, Comamonadaceae bacterium A210 removed ∼100% within 14 days, and Ideonella sp. A288 and A226 removed 65% and 80% within 28 days, respectively. In the absence of Mn2+, strain A288 did not remove cylindrospermopsin, while the other strains removed 5–16%. The amount of manganese oxidized by the strains during the experiment did not correlate with the amount of cylindrospermopsin removed. However, the mere oxidation of Mn2+ was indispensable for cylindrospermopsin removal. Cylindrospermopsin removal ranging from 0 to 24% by sterile biogenic oxides was observed. Considering the efficient removal of cylindrospermopsin by the tested strains, manganese-oxidizing bacteria might play an important role in cylindrospermopsin removal in the environment. Besides, manganese-oxidizing bacteria could be promising candidates for biotechnological applications for cylindrospermopsin removal in water treatment plants.

Catalytic properties of a short manganese peroxidase from Irpex lacteus F17 and the role of Glu166 in the Mn2+-independent activity

Il-MnP1 (GenBank: AGO86670.2) has been confirmed by sequence analysis as a short manganese peroxidase (MnP) from Irpex lacteus F17 (CCTCC AF 2014020). To investigate the catalytic properties, the oxidation of typical aromatic substrates and the pathways of guaiacol oxidation by Il-MnP1, both in the presence and absence of Mn2+ at either pH 4.0 or pH 7.4, were analyzed. Results showed that Il-MnP1 exhibited higher oxidative activity in the presence of Mn2+ than in the absence of Mn2+ toward the majority of the selected substrates at pH 4.0. Additionally, the similar product compositions suggested that the oxidation of guaiacol mainly belongs to a series of polymeric reactions of radicals initiated by Il-MnP1, whether they were in the presence and absence of Mn2+ at either pH 4.0 or 7.4. Furthermore, two variants (E166G, E166Q) were found using site-directed mutagenesis, to improve the Mn2+-independent oxidative activity significantly. The catalytic efficiency (Kcat/Km) of E166G and E166Q in 2, 6-dimethoxyphenol oxidation was higher than Il-MnP1 by 170 and 34 times, respectively. The study revealed certain differences in catalytic properties between Mn2+ dependent and independent oxidation by Il-MnP1. More importantly, a residue (E166) was related to the Mn2+-independent activity of a short MnP.

Template-free synthesis of mesoporous Mn3O4-Al2O3 catalyst for low temperature selective catalytic reduction of NO with NH3

Abstract Mesoporous Mn3O4-Al2O3 catalyst with highly dispersed Mn3O4 and a high surface area is prepared using a one-pot synthesis technique without any templates. The synthesis procedure is environmentally friendly due to the low concentration of residual metal ions in the filtered solution, which allows for its direct release without further processing. The results show that the presence of Mn2+ ions stabilizes the Al(OH)3 crystal phase during hydrothermal treatment and prevents the formation of the AlOOH phase otherwise observed in the absence of Mn2+ ions. Because of the high stability of the resulted Mn3O4-Al(OH)3 nanoplatelets, a mesoporous Mn3O4-Al2O3 structure was formed via the dehydration of the Al(OH)3 after high-temperature calcination. The catalytic efficiencies of the Mn3O4-Al2O3 catalysts in the low-temperature selective catalytic reduction of NO with NH3 are examined under various reaction temperatures in the range of 80–200 °C. The results show that the NO conversion reaches as much as 94% at a reaction temperature of 80 °C. The proposed synthesis method thus holds considerable promise for the green, low-cost and scalable production of highly mesoporous Al2O3-based catalysts.

Symbiosis mechanism of iron and manganese oxides in oxic aqueous systems

Iron and manganese oxides are ubiquitous in soils and sediments, and their formation and conversion processes affect the migration and transformation of heavy metals and organic pollutants. Mn2+ was found to affect the formation of iron oxides from Fe2+ oxidation. However, little attention has been paid to the oxidation process at the initial stage and generation of manganese oxides in the reaction system of Fe2+aq and Mn2+aq. This work investigated the formation process and mechanism of iron and manganese oxides in a mixed solution system of Fe2+aq and Mn2+aq under oxic condition. The effect of pH (5.0–9.0) on the reaction process and products was further studied. The results indicated that Fe2+aq was oxidized to goethite and lepidocrocite, and Mn2+ adsorbed on the surface of iron oxides was catalytically oxidized to poorly crystalline manganese oxides by dissolved O2 in a mixed solution of Fe2+aq and Mn2+aq. Compared with the absence of Mn2+aq, the presence of Mn2+aq caused no obvious changes in the species of iron oxides, but significantly increased the oxidation rate of Fe2+aq. Formation of manganese oxides on the surface decreased the crystallinity of the iron oxides. The increase of pH enhanced the oxidation of Fe2+aq and Mn2+aq and formation of lepidocrocite. This work expands our understanding of the interactions and geochemical processes of Fe2+aq and Mn2+aq.

Fixed-Bed Catalytic Oxidative Removal of Dissolved Iron by Manganese Oxide-Coated Clinoptilolite: Enhanced Activity in the Presence of Aqueous Mn2+ Cations

The kinetics for the fixed-bed catalytic oxidative removal of Fe2+ from aqueous feeds with and without the presence of Mn2+ cations by manganese oxide-coated clinoptilolite zeolite granules has been investigated for the first time. The feed flow rate under study were 40, 60 and 80 cm3 min−1. The initial Fe2+ or Mn2+ concentrations were 50 ppm. The continuous operation system exhibited two peculiarities: (1) In the absence of Mn2+ cations, the catalyst undergoes gradual and continuous deactivation but assumes a finite value of activity at long times (steady-state activity); (2) In the presence of Mn2+ in the liquid phase, the deactivation rate increases substantially while the final activity of the catalyst increases significantly. The gradual deactivation in the absence of Mn2+ is mainly due to the blinding of the active sites by Fe(III) species precipitates. In the presence of Mn2+ cations, the deactivation rate is highly enhanced due to the physical adsorption of these ions on the catalyst exposed surface. The increase in the permanent activity in the presence of Mn2+ cations in the liquid phase has been attributed to the creation of new active sites, mediated by the presence of the precipitated iron (III) species on the composite catalyst surface. The deductions are supported by Raman, XPS and XRD analysis of the catalysts.

Metal-dependent SpoIIE oligomerization stabilizes FtsZ during asymmetric division in Bacillus subtilis.

SpoIIE is a bifunctional protein involved in asymmetric septum formation and in activation of the forespore compartment-specific transcription factor σF through dephosphorylation of SpoIIAA-P. The phosphatase activity of SpoIIE requires Mn2+ as a metal cofactor. Here, we show that the presence of a metal cofactor also influences SpoIIE oligomerization and asymmetric septum formation. Absence of Mn2+ from sporulation medium results in a delay of the formation of polar FtsZ-rings, similar to a spoIIE null mutant. We purified the entire cytoplasmic part of the SpoIIE protein, and show that the protein copurifies with bound metals. Metal binding both stimulates SpoIIE oligomerization, and results in the formation of larger oligomeric structures. The presence of SpoIIE oligomers reduces FtsZ GTP hydrolysis activity and stabilizes FtsZ polymers in a light scattering assay. Combined, these results indicate that metal binding is not just required for SpoIIE phosphatase activity but also is important for SpoIIE's role in asymmetric septum formation.

An ultrasensitive chemiluminescence sensor for sub-nanomolar detection of manganese(II) ions in mineral water using modified gold nanoparticles

A simple, rapid, facile and ultrasensitive chemiluminescence (CL) sensor was developed for detection of Mn2+ in mineral water samples. The developed CL sensor was based on the enhancement effect of manganese ion (Mn2+) on the CL between luminol-modified AuNPs and AgNO3 system. In the absence of Mn2+, the CL intensity from the luminol-modified AuNPs and AgNO3 was relative weak owing to the bad stability of superoxide anion radical (O2−) which was the key intermediate for the CL reaction. However, the addition of Mn2+ to this CL system would generate hydrogen peroxide (H2O2) according to the specific reaction of Mn2+ and O2−. The produced H2O2 had a better stability and reaction activity, thereby enhancing the CL emission. This phenomenon allowed to selective and highly sensitive detection of Mn2+. Under the optimal sensing conditions, the developed CL sensor showed a wide linear range for Mn2+ detection in the range of 1–600nM, with a detection limit of 0.3nM at a signal-to-noise of 3. This sensitivity was about 2–3 orders of magnitude higher than that reported techniques based on metal nanoparticles-based optical sensors. In addition, the developed CL sensor exhibited excellent selectivity toward Mn2+ over other metal ions, and it had a good stability and reproducibility.

The impact of manganese on biofilm development of Bacillus subtilis.

Bacterial biofilms are dynamic and structurally complex communities, involving cell-to-cell interactions. In recent years, various environmental signals that induce the complex biofilm development of the Gram-positive bacterium Bacillus subtilis have been identified. These signalling molecules are often media components or molecules produced by the cells themselves, as well as those of other interacting species. The responses can also be due to depletion of certain molecules in the vicinity of the cells. Extracellular manganese (Mn2+) is essential for proper biofilm development of B. subtilis. Mn2+ is also a component of practically all laboratory biofilm-promoting media used for B. subtilis. Comparison of complex colony biofilms in the presence or absence of supplemented Mn2+ using microarray analyses revealed that genes involved in biofilm formation are indeed downregulated in the absence of Mn2+. In addition, Mn2+ also affects the transcription of several other genes involved in distinct differentiation pathways of various cellular processes. The effects of Mn2+ on other biofilm-related traits like motility, antimicrobial production, stress and sporulation were followed using fluorescent reporter strains. The global transcriptome and morphology studies highlight the importance of Mn2+ during biofilm development and provide an overview on the expressional changes in colony biofilms in B. subtilis.

Limits of Versatility of Versatile Peroxidase.

Although Mn(2+) is the most abundant substrate of versatile peroxidases (VPs), repression of Pleurotus ostreatus vp1 expression occurred in Mn(2+)-sufficient medium. This seems to be a biological contradiction. The aim of this study was to explore the mechanism of direct oxidation by VP1 under Mn(2+)-deficient conditions, as it was found to be the predominant enzyme during fungal growth in the presence of synthetic and natural substrates. The native VP1 was purified and characterized using three substrates, Mn(2+), Orange II (OII), and Reactive Black 5 (RB5), each oxidized by a different active site in the enzyme. While the pH optimum for Mn(2+) oxidation is 5, the optimum pH for direct oxidation of both dyes was found to be 3. Indeed, effective in vivo decolorization occurred in media without addition of Mn(2+) only under acidic conditions. We have determined that Mn(2+) inhibits in vitro the direct oxidation of both OII and RB5 while RB5 stabilizes both Mn(2+) and OII oxidation. Furthermore, OII was found to inhibit the oxidation of both Mn(2+) and RB5. In addition, we could demonstrate that VP1 can cleave OII in two different modes. Under Mn(2+)-mediated oxidation conditions, VP1 was able to cleave the azo bond only in asymmetric mode, while under the optimum conditions for direct oxidation (absence of Mn(2+) at pH 3) both symmetric and asymmetric cleavages occurred. We concluded that the oxidation mechanism of aromatic compounds by VP1 is controlled by Mn(2+) and pH levels both in the growth medium and in the reaction mixture. VP1 is a member of the ligninolytic heme peroxidase gene family of the white rot fungus Pleurotus ostreatus and plays a fundamental role in biodegradation. This enzyme exhibits a versatile nature, as it can oxidize different substrates under altered environmental conditions. VPs are highly interesting enzymes due to the fact that they contain unique active sites that are responsible for direct oxidation of various aromatic compounds, including lignin, in addition to the well-known Mn(2+) binding active site. This study demonstrates the limits of versatility of P. ostreatus VP1, which harbors multiple active sites, exhibiting a broad range of enzymatic activities, but they perform differently under distinct conditions. The versatility of P. ostreatus and its enzymes is an advantageous factor in the fungal ability to adapt to changing environments. This trait expands the possibilities for the potential utilization of P. ostreatus and other white rot fungi.

Mn2+-mediated homogeneous Fenton-like reaction of Fe(III)-NTA complex for efficient degradation of organic contaminants under neutral conditions

In this work, we report a novel Mn2+-mediated Fenton-like process based on Fe(III)-NTA complex that is super-efficient at circumneutral pH range. Kinetics experiments showed that the presence of Mn2+ significantly enhanced the effectiveness of Fe(III)-NTA complex catalyzed Fenton-like reaction. The degradation rate constant of crotamiton (CRMT), a model compound, by the Fe(III)- NTA_Mn2+ Fenton-like process was at least 1.6 orders of magnitude larger than that in the absence of Mn2+. Other metal ions such as Ca2+, Mg2+, Co2+ and Cu2+ had no impacts or little inhibitory effect on the Fe(III)-NTA complex catalyzed Fenton-like reaction. The generation of hydroxyl radical (HO) and superoxide radical anion (O2−) in the Fe(III)-NTA_Mn2+ Fenton-like process were suggested by radicals scavenging experiments. The degradation efficiency of CRMT was inhibited significantly (approximately 92%) by the addition of HO scavenger 2-propanol, while the addition of O2− scavenger chloroform resulted in 68% inhibition. Moreover, the results showed that other chelating agents such as EDTA- and s,s-EDDS-Fe(III) catalyzed Fenton-like reactions were also enhanced significantly by the presence of Mn2+. The mechanism involves an enhanced generation of O2− from the reactions of Mn2+-chelates with H2O2, indirectly promoting the generation of HO by accelerating the reduction rate of Fe(III)-chelates to Fe(II)- chelates.

Luminescence and energy transfer properties of Sr3Y(PO4)3:Ce3+, Mn2+ phosphors

A series of highly efficient Sr3−yY1−x(PO4)3:xCe3+,yMn2+(SYP:xCe3+, Mn2+) phosphors have been prepared via a solid state reaction. The XRD (X-ray diffraction) data, PL (photoluminescence) and PLE (photoluminescence excitation) properties and ET (energy transfer) mechanism of obtained phosphors were discussed. When prepared in air, the self-reducing process of turning Ce4+ into Ce3+ can be found in SYP:xCe3+ phosphor. A bright red light emission was presented in the Ce3+ and Mn2+ co-doping samples via the efficient ET from the sensitizer Ce3+ to Mn2+, which is ascribed to electric multipolar interaction between these two kinds of ions. The critical concentration of Ce3+ in SrY1−x(PO4)3:xCe3+ and Mn2+ in Sr3−yY1−x(PO4)3:xCe3+, yMn2+ are x=0.07 and y=0.15, respectively. In addition, the ET efficiency reach 51.6% when the luminescence intensity of Ce3+ is half of that in the absence of Mn2+ and the concentration of Mn2+ is 0.15. The emission color of the phosphors were also clarify by CIE coordinate briefly.

Removal of chloride from simulated zinc sulfate electrolyte by ozone oxidation

The removal of chloride from simulated zinc sulfate electrolyte by ozone oxidation was investigated. The effects of various process factors including the O2 flow, bubbling time, reaction temperature, H2SO4 and ZnSO4 concentration, and existence of Mn2+ were systematically studied. The results showed that with increasing O2 flow, the chloride removal increased first and then decreased. Increasing both the bubbling time and reaction temperature was beneficial to dechlorination while an increase in the ZnSO4 concentration had an adverse effect. With increasing sulfuric acid concentration, the dechlorination rapidly rose due to the increasing hydrogen ion concentration in electrolyte. Optimum dechlorination process conditions in the absence of Mn2+ were obtained as follows: O2 flow 0.4L·min−1, H2SO4 concentration 160g·L−1, Zn2+concentration 40g·L−1, reaction temperature 70°C, and reaction time 120min. Under these conditions, the concentration of Cl− was reduced from 300 to 5mg·L−1. The existence of Mn2+ can further accelerate the reaction of ozone with chloride, which was probably through charge-transfer and coordination catalysis mechanism.