Active Metal Ions Research Articles

Metal Ions (Li, Mg, Zn, Ce) Doped into La2O3 Nanorod for Boosting Catalytic Oxidative Coupling of Methane

A series of La2O3 nanorod catalysts with doping of active metal ions (Li, Mg, Zn and Ce) were synthesized successfully by the hydrothermal method. The La2O3 nanorods show a uniform size with the length of 50–200 nm and the width of 5–20 nm, and the {110} crystal facet is a preferentially exposed surface. The active metal ions (Li, Mg, Zn and Ce) doped into the lattice of La2O3 nanorods enhance the selectivity of the desired products during oxidative coupling of methane (OCM) and decrease the reaction temperature. Among these catalysts, the Mg-La2O3 catalyst exhibits the best catalytic performance during the OCM reaction, i.e., its selectivity and yield of C2 products at 780 °C is 73% and 21%, respectively. The effect of doped metal ions on catalytic activity for OCM was systematically investigated. Insight into the fabrication strategy and promoting factors of the OCM reaction indicates the potential to further design a high-efficient catalyst in the future.

Metal Ion Binding in Wild-Type and Mutated Frataxin: A Stability Study.

This work studies the stability of wild-type frataxin and some of its variants found in cancer tissues upon Co2+ binding. Although the physiologically involved metal ion in the frataxin enzymatic activity is Fe2+, as it is customarily done, Co2+ is most often used in experiments because Fe2+ is extremely unstable owing to the fast oxidation reaction Fe2+ → Fe3+. Protein stability is monitored following the conformational changes induced by Co2+ binding as measured by circular dichroism, fluorescence spectroscopy, and melting temperature measurements. The stability ranking among the wild-type frataxin and its variants obtained in this way is confirmed by a detailed comparative analysis of the XAS spectra of the metal-protein complex at the Co K-edge. In particular, a fit to the EXAFS region of the spectrum allows positively identifying the frataxin acidic ridge as the most likely location of the metal-binding sites. Furthermore, we can explain the surprising feature emerging from a detailed analysis of the XANES region of the spectrum, showing that the longer 81-210 frataxin fragment has a smaller propensity for Co2+ binding than the shorter 90-210 one. This fact is explained by the peculiar role of the N-terminal disordered tail in modulating the protein ability to interact with the metal.

Review on Green Synthesis of Nanoparticles using Various Strong Electrolytic Metal Solutions Mediated by Various Plant Parts

The present review targets the comparative biogenic synthesis and mechanisms of nanoparticles using various plant-parts extracts and various solutions of strong electrolytic metal salts. The metal salts are AgNO3, Zn(OAc)2, Zn(NO3)2, ZnSO4, CuSO4.5H2O, Cu(NO3)2, Cu(OAc)2, CuCl2, HAuCl4.3H2O, Mg(NO3)2, Mg(OAc)2, TiO(OH)2, Fe(NO3)2.6H2O, FeCl3.6H2O, FeCl2.4H2O, Al(NO3)2, BaCl2·2H2O, Bi(NO3)2, PdCl2, H2PtCl6.6H2O, NaHSeO3, Na2SeO3, Ca(NO3)2.4H2O, ZrOCl2.4H2O, Zr(OAc)4, NiCl2, NiSO4.6H2O, Ni(NO3)2, VCl2, Co(NO3)2 6H2O, CoCl2, Hg(OAc)2, Mn(OAc)2, (NH4)6Mo7O24, Sr(NO3)2, SnCl2.2H2O, Na2S2O3.5H2O, K2Cr2O7, Cr(NO)3.9H2O and Pb(NO3)2. These salts are soluble to produce to highly active positive metal ions in deionised water. These ions are effectively nucleated in the plant constituents. The plant acts akin to a huge ‘‘bio-laboratory” comprising of leaves, seeds, steam, root, sprout, fruits, latex, parks, fruits peel, fruits, juices. etc… which are composed of biomolecules and phytoconstituents. These naturally happening biomolecules and phytoconstituents have been recognized to play an energetic role in the formation of nanoparticles with discrete shapes and sizes thus acting as a pouring force for the manipulative of greener, safe and environmentally benign protocols for the synthesis of nanoparticles.

Visualization of mutagenic nucleotide processing by Escherichia coli MutT, a Nudix hydrolase

Escherichia coli MutT prevents mutations by hydrolyzing mutagenic 8-oxo-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) in the presence of Mg2+ or Mn2+ ions. MutT is one of the most studied enzymes in the nucleoside diphosphate-linked moiety X (Nudix) hydrolase superfamily, which is widely distributed in living organisms. However, the catalytic mechanisms of most Nudix hydrolases, including two- or three-metal-ion mechanisms, are still unclear because these mechanisms are proposed using the structures mimicking the reaction states, such as substrate analog complexes. Here, we visualized the hydrolytic reaction process of MutT by time-resolved X-ray crystallography using a biological substrate, 8-oxo-dGTP, and an active metal ion, Mn2+. The reaction was initiated by soaking MutT crystals in a MnCl2 solution and stopped by freezing the crystals at various time points. In total, five types of intermediate structures were refined by investigating the time course of the electron densities in the active site as well as the anomalous signal intensities of Mn2+ ions. The structures and electron densities show that three Mn2+ ions bind to the Nudix motif of MutT and align the substrate 8-oxo-dGTP for catalysis. Accompanied by the coordination of the three Mn2+ ions, a water molecule, bound to a catalytic base, forms a binuclear Mn2+ center for nucleophilic substitution at the β-phosphorus of 8-oxo-dGTP. The reaction condition using Mg2+ also captured a structure in complex with three Mg2+ ions. This study provides the structural details essential for understanding the three-metal-ion mechanism of Nudix hydrolases and proposes that some of the Nudix hydrolases share this mechanism.

Nostoc muscorum is a novel source of microalgal lectins with potent antiviral activity against herpes simplex type-1

In our survey for a new antiviral agent, two types of lectin were purified from Nostoc muscorum using both ion-exchange and affinity columns chromatography. Nostoc muscorum lectins (NMLs) are categorized based on their carbohydrate preference. Nostoc muscorum lectin-1(NML-1) exhibited a strict binding specificity for complex glycoproteins without linked carbohydrates, and the other displayed specificity for α- glycosides mannose polymers (NML-2) and was classified as a glycoprotein with 16.8% linked carbohydrates. NML-1 displayed a single band of 166 kDa on native-PAGE and two bands of 81 kDa and 85 kDa on SDS-PAGE, which confirmed the heterodimeric nature of this lectin. While NML-2 is a 50 kDa glycoprotein composed of 25 kDa subunits. Physical characterization of NML-1 displayed its stability at a higher temperature of 90 °C for 5 min and over a wide pH range (4–9), while MNL-2 displayed stability up to a temperature of 80 °C for 25 min and a pH range of 5–8. NML-1 didn't require metal ions for agglutination activity, while the activity of NML-2 was doubled by manganese ions. The antiviral activity of two lectins was assessed against herpes simplex type-1 (HSV-1) using a plaque assay which revealed that NML-1 inhibited HSV-1 infection at an early stage in contrast to NML-2 which exerted its antiviral effect at the late stage of infection. These results suggest that Nostoc muscorum is a unique lead for antiviral drug discovery as it is a novel source for antiviral lectins with different modes of action.

Controlled Synthesis of Perforated Oxide Nanosheets with High Density Nanopores Showing Superior Water Purification Performance.

A method for creating genuine nanopores in high area density on monolayer two-dimensional (2D) metallic oxides has been developed. By use of the strong reduction capability of hydroiodic acid, active metal ions, such as FeIII and CoIII, in 2D oxide nanosheets can be reduced to a divalent charge state (2+). The selective removal of FeO2 and CoO2 metal oxide units from the framework can be tuned to produce pores in a range of 1-4 nm. By monitoring of the redox reaction kinetics, the pore area density can be also tuned from ∼0.9 × 104 to ∼3.3 × 105 μm-2. The universality of this method to produce much smaller pores and higher area density than the previously reported ones has been proven in different oxide nanosheets. To demonstrate their potential applications, ultrasmall metal organic framework particles were grown inside the pores of perforated titania oxide nanosheets. The optimized hybrid film showed ∼100% rejection of methylene blue (MB) from the water. Its water permeance reached 4260 L m-2 h-1 bar-1, which is 1-3 orders of that for reported 2D membranes with good MB rejections.

A polysaccharide-based bioflocculant BP50-2 from banana peel waste: Purification, structure and flocculation performance.

In this study, the purification and characterization of a polysaccharide-based bioflocculant BP50-2 of banana peel waste were investigated. BP50-2 was purified and identified through HPLC, XPS, TG, SEM, AFM, etc. The results showed that BP50-2 was a heteropolysaccharide composed of Mannose, Rhamnose, Glucuronic acid, Galacturonic acid, Glucose, Galactose, and Fucose at a molar ratio of 8.97:5.36:1.92:1.00:32.52:8.30:2.64, respectively. The MW of BP50-2 was 1.47×10 3 KDa. BP50-2 had high pH stability that maintained flocculation activity on kaolin suspension for a pH range from 3 to 11, and high-temperature stability ranged from room temperature to 90°C. BP50-2 was non-sensitive to cation and affected by HCl, EDTA, little affected by urea, which showed that the BP50-2 was non-cation dependent and its main binding mode with kaolin was ionic bond and contained a small amount of hydrogen bond. And flocculation mechanisms were discussed, which indicated that adsorption bridging was the main mechanism of the flocculation process of BP50-2-Kaolin or BP50-2-Mg2+-Kaolin. Moreover, BP50-2 had decolorization activity on RhB and removal activity of heavy metal ion, of which removal rate of Pb2+ was the highest. In brief, BP50-2 showed good performance on the removal of pigment, adsorption of heavy metals, and flocculation of particles.

Magnetic Interplay between π-Electrons of Open-Shell Porphyrins and d-Electrons of Their Central Transition Metal Ions.

Magnetism is typically associated with d‐ or f‐block elements, but can also appear in organic molecules with unpaired π‐electrons. This has considerably boosted the interest in such organic materials with large potential for spintronics and quantum applications. While several materials showing either d/f or π‐electron magnetism have been synthesized, the combination of both features within the same structure has only scarcely been reported. Open‐shell porphyrins (Pors) incorporating d‐block transition metal ions represent an ideal platform for the realization of such architectures. Herein, the preparation of a series of open‐shell, π‐extended Pors that contain magnetically active metal ions (i.e., CuII, CoII, and FeII) through a combination of in‐solution and on‐surface synthesis is reported. A detailed study of the magnetic interplay between π‐ and d‐electrons in these metalloPors has been performed by scanning probe methods and density functional theory calculations. For the Cu and FePors, ferromagnetically coupled π‐electrons are determined to be delocalized over the Por edges. For the CoPor, the authors find a Kondo resonance resulting from the singly occupied CoII d z 2 orbital to dominate the magnetic fingerprint. The Fe derivative exhibits the highest magnetization of 3.67 μB (S≈2) and an exchange coupling of 16 meV between the π‐electrons and the Fe d‐states.

Development of quantitative ion physic chemistry properties-activity relationship (QIPAR) and docking simulation for sars-covid-2 protein

Currently, many drugs are being studied and potentially used in the treatment of SARS-CoV-2. Compounds studied are mostly organic substances. This work investigates the ability to inhibit SARS-CoV-2 of various 20 metal ions based on their ability to inhibit several biological systems; the physicochemical properties of metal ions were calculated by quantum chemistry DFT (B3LYP/ LanL2DZ) were used to develop the QIPAR hybrid models. Hybrid models QIPARGA-MLR (k = 4) and QIPARGA-ANN with architecture I(4)-HL(9)-O(1) were developed to predict the biological activity of metal ions. Metal ions were also investigated for their inhibitory potential for the protein SARS-CoV-2 (PDB6LU7) by docking simulation techniques. We predicted the binding sites of metal ions to the active sites of the SARS-CoV-2 protein (PDB6LU7). These studies are consistent with their activities against different biological systems. This research will also contribute to the development of metal oxide nanomaterials.

Modification Strategies of Layered Double Hydroxides for Superior Supercapacitors

Layered double hydroxides (LDHs), as classic 2D materials, have received worldwide attention in electrochemical energy storage devices due to its superior ion insertion rate and ultrahigh specific capacitance. However, the poor conductivity, severe aggregation limited capacitance, and unsatisfied internal stability have become the main factors hinder its further development as the electrode of supercapacitor. In recent years, various strategies on the modification of the LDHs’ structure, composition, properties, and fabrication have been demonstrated to effectively improve their electrochemical performance, and fruitful achievements have been made. However, there is a lack of systematic summary on the functional mechanisms and effects of various modification strategies. Herein, this review gives a comprehensive introduction of the modification strategies based on LDHs for superior supercapacitor, including active metal ions adjustment, intercalated ions adjustment, morphology optimization, conductivity enhancement and internal stability enhancement. Particularly, an in‐depth and fundamental understanding on the effects and mechanisms of modification on LDHs’ electrochemical properties and performance. Furthermore, the general performance metrics of above strategies, the potential directions and perspectives for further research are proposed.

Deracemisation and stereoinversion by a nanoconfined bidirectional enzyme cascade: dual control by electrochemistry and selective metal ion activation.

The unique ability of the 'electrochemical leaf' (e-Leaf) to drive and control nanoconfined enzyme cascades bidirectionally, while directly monitoring their rate in real-time as electrical current, is exploited to achieve deracemisation and stereoinversion of secondary alcohols using a single electrode in one pot. Two alcohol dehydrogenase enzymes with opposing enantioselectivities, from Thermoanaerobacter ethanolicus (selective for S) and Lactobacillus kefir (selective for R) are driven bidirectionally via coupling to the fast and quasi-reversible interconversion of NADP+/NADPH catalysed by ferredoxin NADP+ reductase - all enzymes being co-entrapped in a nanoporous indium tin oxide electrode. Activity of the Lactobacillus kefir enzyme depends on the binding of a non-catalytic Mg2+, allowing it to be switched off after an oxidative half-cycle, by adding EDTA - the S-selective enzyme, with a tightly-bound Zn2+, remaining fully active. Racemate → S or R → S conversions are thus achieved in high yield with unprecedented ease.

An exsolution constructed FeNi/NiFe2O4 composite: preferential breaking of octahedral metal-oxygen bonds in a spinel oxide.

Exsolution is an ingenious strategy for the in situ construction of metal- or alloy-decorated oxides and, due to its promising energy related catalysis applications, has advanced from use in perovskites to use in spinels. Despite its great importance for designing target composites, the ability to identify whether active metal ions at octahedral or tetrahedral sites will preferentially exsolve in a spinel remains unexplored. Here, an inverse spinel NiFe2O4 (NFO) was employed as a prototype and FeNi/NFO composites were successfully constructed via exsolution. The preferential breaking of octahedral metal–oxygen bonds in the spinel oxide was directly observed using Mössbauer and X-ray absorption spectroscopy. This was further verified from the negative segregation energies calculated based on density-functional theory. One exsolved FeNi/NFO composite exhibits enhanced electrochemical activity with an overpotential of 283 mV at 10 mA cm−2 and a long stability time for the oxygen evolution reaction. This work offers a unique insight into spinel exsolution based on the preferential breaking of chemical bonds and may be an effective guide for the design of new composite catalysts where the desired metal ions are deliberately introduced to octahedral and/or tetrahedral sites.

Oxygen reduction activity of Fe/Co/Ni doped MnOx @ graphene nanohybrid: A comparative study

• Fe, Co, and Ni doped MnO x was grown on NG. • Doped catalysts show better ORR activity than the undoped one. • Doping can tune the Mn valence. • Enhanced activity for doped MnO x owing to increase in Mn valence on doping. We report the electrochemical activity of transition metal ion (Fe, Co and Ni) doped MnO x @ N -graphene (MnO x @NG) hybrid catalysts towards oxygen reduction reaction (ORR). The doped catalysts displayed significantly enhanced electrochemical performance than the undoped one. The Fe doped MnO x @NG exhibited highest positive shift in onset potential (0.93 V vs. RHE), highest electron transfer number (n) (3.87) and lowest peroxide yield (6.35 %) in 0.1 M KOH solution. The Co doped catalyst showed highest current density, which is comparable to that of benchmark 20 wt% Pt/C. The XRD analysis showed that the catalyst samples are poorly crystalline and the doping of either Fe or Co or Ni cation induces formation of Mn 2 O 3 , whereas the undoped catalyst consists of both Mn 2 O 3 and MnOOH. The STEM (scanning transmission electron microscope) micrographs revealed that in all the samples the MnO x nanostructures are well dispersed on NG and the elemental mapping of the doped catalysts showed uniform distribution of dopants. The X-ray photoelectron spectroscopy (XPS) studies revealed that doping of either cation results an increase in the average Mn valency of the host MnO x . The change in crystal structure and corresponding ORR activity has also been investigated with increase in dopant amount for Fe doped samples.

Salicylate metal-binding isosteres as fragments for metalloenzyme inhibition.

Metalloenzyme inhibitors typically share a common need to possess a metal-binding pharmacophore (MBP) for binding the active site metal ions. However, MBPs can suffer from physicochemical liabilities, impeding the pharmacological properties and drug-likeliness of inhibitors. To circumvent this, problematic features of the MBP can be identified and exchanged with isosteric replacements. Herein, the carboxylic and hydroxyl group of the salicylic acid MBP were replaced and a total of 27 salicylate metal-binding isosteres (MBIs) synthesized. Of these 27 MBIs, at least 12 represent previously unreported compounds, and the metal-binding abilities of >20 of the MBIs have not been previously reported. These salicylate MBIs were examined for their metal-binding features in model complexes, physicochemical properties, and biological activity. It was observed that salicylate MBIs can demonstrate a range of attractive physicochemical properties and bind to the metal in a variety of expected and unexpected binding modes. The biological activity of these novel MBIs was evaluated by measuring inhibition against two Zn2+-dependent metalloenzymes, human glyoxalase 1 (GLO1) and matrix metalloproteinase 3 (MMP-3), as well as a dinuclear Mn2+-dependent metalloenzyme, influenza H1N1 N-terminal endonuclease (PAN). It was observed that salicylate MBIs could maintain or improve enzyme inhibition and selectivity. To probe salicylate MBIs as fragments for fragment-based drug discovery (FBDD), an MBI that showed good inhibitory activity against GLO1 was derivatized and a rudimentary structure–activity relationship was developed. The resulting elaborated fragments showed GLO1 inhibition with low micromolar activity.

Cadmium thiosulfate complexes can be assimilated by a green alga via a sulfate transporter but do not increase Cd toxicity

Environmental context Thiosulfate is present in natural waters, especially those influenced by sulfide oxidation, and it has a marked affinity for metals such as cadmium. Normally the binding of cadmium by thiosulfate would be expected to reduce the metal’s bioavailability. However, here we demonstrate that algal uptake of cadmium is enhanced in the presence of thiosulfate, indicating that Cd can enter the alga via a novel route as an intact Cd-thiosulfate complex. Rationale For a given free metal ion activity in the exposure solution, the Biotic Ligand Model assumes that metal uptake will be independent of the various ligands present in solution that are buffering [Mz+]. In this context, we have evaluated cadmium bioavailability in the absence or presence of thiosulfate, using Chlamydomonas reinhardtii as the test alga. Methodology Short-term exposures (≤41 min) were run with a fixed concentration of the free Cd2+ ion (3.0 ± 0.1 nM), buffered with either nitrilotriacetate or thiosulfate, to determine Cd uptake. Subsequent long-term exposures (72 h) over a range of free Cd2+ concentrations were used to determine the effects of Cd on algal growth. Results Contrary to Biotic Ligand Model predictions, Cd uptake was enhanced when Cd2+ was buffered with thiosulfate. Removal of sulfate from this exposure medium increased Cd uptake; conversely, if [SO42−] was increased, Cd uptake decreased. In the absence of thiosulfate, Cd uptake was unaffected by changes in [SO42−]. In the long-term exposures, the cellular Cd quota needed to reduce algal growth by 50% was significantly higher in the presence of thiosulfate than in its absence. Discussion In the presence of thiosulfate, Cd can enter the algal cell not only by cation transport but also by transport of the intact Cd-thiosulfate complex via the anion transporter responsible for sulfate uptake. We speculate that some of the Cd taken up by anion transport remains in complexed form and is less bioavailable than the Cd that enters the cell via cation transport.

Study of the critical angle of channeling of active metal ions through thin aluminum films

The spatial distributions of ions (K+, Na+) passed through thin polycrystalline and single-crystalline Al films with the thickness from 180 to 600 Angstrem and critical channeling angles have been studied. The ion energies have been varied within the range E0=10-30 keV. It has been shown that an increase in the energy of the primary ion beam leads to a decrease in the width of the maxima of the angular distribution, which is associated with a decrease in the critical channeling angle psicr. It has been found that the value psicr does not exceed 4-50 for axial channeling and 9-100 for planar channeling Keywords: critical angle, passage of ions, angular distribution, channeling, spatial distribution.

Inhibition Molecular Mechanism of the Novel Fungicidal N-(Naphthalen-1-yl) phenazine-1-carboxamide against Rhizoctonia solani

To explore the molecular mechanism through which the novel fungicide N-(naphthalen-1-yl) phenazine-1-carboxamide (NNPCN) inhibits Rhizoctonia solani, we clarified the target and mode of action, explored lead compounds, and developed novel fungicides. Methods: Growth observation, scanning electron microscopy, transmission electron microscopy, transcriptome sequencing technology, quantitative real-time PCR (qRT-PCR), physiological and biochemical determination, and reverse molecular docking technology were used to study the effects of this compound on the microscopic morphology of R. solani. The differentially expressed genes (DEGs), functions, and metabolic pathways were analyzed. The genes displaying significant differences were randomly selected for qRT-PCR verification and confirmed by physiological and biochemical determination to construct their binding mode with key targets. The results showed that the mycelium treated with NNPCN produced a red secretion and exhibited progressive creeping growth. Under a scanning electron microscope, hyphal swelling, uneven thickness, fractures, deformities, and hyphal surface warts increased. Under a transmission electron microscope, the cell wall was separated, the subcellular organelles were disintegrated, and the septum disappeared. Furthermore, there were 6838 DEGs under NNPCN treatment, including 291 significant DEGs, of which 143 were upregulated and 148 downregulated. Ten DEGs were randomly selected for qRT-PCR verification, and the gene expression trend was consistent with the transcriptome sequencing results. Gene Ontology enrichment analysis showed that the DEGs were significantly enriched in cell wall glucan decomposition and metabolism, cell membrane synthesis, metabolism, composition, organic hydroxyl compounds, oxidoreductase activity, and transition metal ion binding. Metabolic pathway enrichment analysis showed that there were 16 significant metabolic pathways, such as steroid biosynthesis and ABC transporters. Further study found that genes, such as the glycosyl hydrolase family 10 domain-containing protein, which is related to glucan catabolic process function as tied to the cell wall, were downregulated. Lipid oxidation, modification, and other genes related to the cell membrane were also downregulated. Secondly, genes related to lipid modification, lipid metabolism processes, integral components of the membrane, and other ABC transporters were downregulated. Fatty-acid oxidation and carbohydrate metabolic processes, which are related to antioxidant and metabolic functions, displayed significant differences in their target genes. Nitrite reductase [NADH] activity and mitochondrial organization gene expression were downregulated. These results revealed that target genes may involved in the cell wall, cell membrane, antioxidant and metabolism, nitrogen metabolism, and mitochondria. The results of the physiological and biochemical tests showed that NNPCN decreased the β-1,3-glucanase, malondialdehyde, and ATPase activities and nucleic acid leakage but increased the activity of nitrate reductase. The results of the reverse molecular docking showed that NNPCN could freely bind to target proteins such as β-1,3-glucanase, ABC transporter, and NADPH nitrate reductase, whereby NNPCN could bind to glucanase via van der Waals and electrostatic forces and to ABC transporter and NADPH nitrate reductase via hydrogen bonding. Conclusion: The mechanism via which NNPCN inhibits R. solani may be related to the cell wall structure, cell membrane damage, antioxidant activity, and metabolism.

The impact of partial oil substitution and trace metal ions on the evolution of peroxidation products in thermally stressed culinary oils

Suppressing toxic aldehydic lipid oxidation product (LOP) generation in culinary oils is now considered vital, since the deleterious effects arising from their ingestion are implicated in a wide range of disease conditions. Partial substitution involves the replenishment of thermally-stressed culinary oils with corresponding unheated ones. This technique was tested by employing 10%, 25%, 50%, and 75% (v/v) partial substitutions of coconut, olive, rapeseed, and sunflower oils at 180℃ for a 300 min continuous thermo-oxidation duration. Oil samples were analysed by proton nuclear magnetic resonance (1H NMR) spectroscopy. Trace metal levels, including oxidation–reduction (redox)-active metal ions credited with enhancing cooking oil oxidation were also analysed using inductively coupled plasma-optical emission spectroscopy (ICP-OES). As expected, the degree of oil unsaturation, and the % partial substitutions significantly influenced their susceptibility to thermo-oxidation. In view of the very low polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of coconut oil, both the class and concentrations of evolved LOPs were found to be least affected by this partial substitution process. Aldehydic LOPs were greatly suppressed in partially-substituted rapeseed oil. The % suppression activity of LOPs evaluated for the partially substituted oils were generally high making partial oil substitutions an effective chemical-free method in suppressing LOPs at both industrial and commercial levels. In general, the % partial oil substitutions were directly related to the dilution effect observed for LOPs quantified in the oils. Furthermore, trace metal ion concentrations measured in the culinary oils did not influence the evolution of LOPs in the oils.

PH-dependent concatenation of an inorganic complex results in solid state helix formation

Growth of the library of tetraaza macrocyclic pyridinophane ligands is a result of the potential to treat neurodegenerative diseases by binding unregulated redox active metal-ions, scavenging radicals, and reducing oxidative stress. As part of this work, the copper complex of OHPyN3Cu (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-trien-13-ol) was previously identified as a discrete molecule in the solid state when isolated at lower pH values. However, here we report that OHPyN3Cu forms a helical structure upon crystallization around pH 6.5. Several properties of the ligand and complex were evaluated to understand the driving forces that led to the concatenation and formation of this solid-state helix. DFT studies along with a comparison of keto/enol tautomerization stability and bond lengths were used to determine the keto-character of the CO within each subunit. This pH-dependent keto-enol tautomerization is responsible for the solid state intermolecular CO···Cu bonds observed in this metallohelix (Cu1H) when produced around pH 6.5. Perchlorate templating that occurs through hydrogen bonding between perchlorate counter ions and each Cu1H unit is the primary driving factor for the twist that leads to the helix structure. Cu1H does not exhibit the typical factors that stabilize the formation of helices, such as intra-strand hydrogen bonding or π-stacking. The helix structure further highlights the diversity of inorganic metallohelices and demonstrates the importance of tautomerization and pH that occurs with the pyridinophane ligand used in this study. To our knowledge and although these phenomena have been observed individually, this is the first example of a pH-dependent keto-enol tautomerization in an azamacrocycle being the driving force for the formation of a metallohelix solid state structure and is a particularly unique observation for pyridinophane complexes.

Metal Exchange of ZIF-8 and ZIF-67 Nanoparticles with Fe(II) for Enhanced Photocatalytic Performance.

Zeolitic imidazolate frameworks (ZIFs), such as ZIF-8 and ZIF-67, were found to be efficient catalysts. However, ZIFs are not used much in photocatalysis due to their low photocatalytic activity for most reactions. The photocatalytic activity can be improved by modifying the framework by exchanging the Zn(II) ions (ZIF-8) and Co(II) ions (ZIF-67) with a more photocatalytically active metal(II) ion to form an efficient bimetallic ZIF photocatalyst. Redox-active iron (Fe)-based materials are known to be highly potent photocatalysts. Thus, incorporating iron into ZIFs could significantly enhance their photocatalytic performance. In this study, we modified nanosized ZIF-8(Zn) and ZIF-67(Co) via metal (Fe2+) exchange to produce bimetallic frameworks that are photocatalytically more active than their parent ZIFs. Nanosized ZIF-8 and ZIF-67 were synthesized isothermally in either water or methanol under ambient conditions. From these, Fe-containing bimetallic ZIF-8 and ZIF-67 nanoparticles were synthesized via the metal exchange, and their performance on the photocatalytic degradation of dye was evaluated. The morphology and crystal structures of the pristine ZIF-8 and ZIF-67 nanoparticles were retained to a large extent during the iron exchange. Their Brunauer–Emmett–Teller (BET) surface areas decreased by less than 15% for nZIF-8 and less than 12% for nZIF-67. The binding energy values on X-ray photoelectron spectroscopy (XPS) confirmed the preservation of the oxidation state of Fe(II) during the exchange process. A remarkably higher catalytic activity was observed for the photocatalytic degradation of dye by the Fe-exchanged nZIF-8 and nZIF-67 compared to their parent ZIFs. This proved that the incorporation of Fe(II) centers into the ZIF framework enhanced the photocatalytic activity of the framework dramatically. In addition, these catalysts can be regenerated and reused without an appreciable loss in activity.