Large magnetoresistances and non-Ohmic conductivity in EuWO[1+x]N[2-x]

The magnetic field and voltage dependent electronic transport properties of EuWO[1+x]N[2-x] ceramics are reported. Large negative magnetoresistances are observed at low temperatures, up to 70% in the least doped (x=0.09) material. Non-Ohmic conduction emerges below the 12 K Curie transition. This is attributed to a microstructure of ferromagnetic conducting and antiferromagnetic insulating regions resulting from small spatial fluctuations in the chemical doping

A Network of Conformational Transitions Revealed by Molecular Dynamics Simulations of the Binary Complex of <i>Escherichia coli</i> 6‑Hydroxymethyl-7,8-dihydropterin Pyrophosphokinase with MgATP

6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the first reaction in the folate biosynthetic pathway. Comparison of its X-ray and nuclear magnetic resonance structures suggests that the enzyme undergoes significant conformational change upon binding to its substrates, especially in three catalytic loops. Experimental research has shown that, in its binary form, even bound by analogues of MgATP, loops 2 and 3 remain rather flexible; this raises questions about the putative large-scale induced-fit conformational change of the HPPK–MgATP binary complex. In this work, long-time all-atomic molecular dynamics simulations were conducted to investigate the loop dynamics in this complex. Our simulations show that, with loop 3 closed, multiple conformations of loop 2, including the open, semiopen, and closed forms, are all accessible to the binary complex. These results provide valuable structural insights into the details of conformational changes upon 6-hydroxymethyl-7,8-dihydropterin (HP) binding and biological activities of HPPK. Conformational network analysis and principal component analysis related to the loops are also discussed

Programmed Synthesis of Sn₃N₄ Nanoparticles via a Soft Chemistry Approach with Urea: Application for Ethanol Vapor Sensing

Metal nitrides are a significant class of multifunctional materials that have attracted a huge and ever-increasing interest for their new structural and redox chemical, as well as physical, characteristics. In this work, we present a designed synthesis of Sn₃N₄ nanoparticles through a soft urea route for the first time. The strategy includes the synthesis of gel-like tin–urea precursor and subsequent transformation to Sn₃N₄ nanoparticles via thermal treatment of the as-prepared precursor under NH₃ flow. Various techniques were employed to characterize the structure and morphology of the as-prepared Sn₃N₄ samples. When innovatively utilized as sensing material for a gas sensor, Sn₃N₄ nanoparticles exhibited high sensitivity, excellent cyclability, and long-term stability to ethanol at the operating temperature of 120 °C, which is lower than those of metal oxide-based ethanol sensors. This research work provides an efficient method for preparing Sn₃N₄nanoparticles that are promising sensing materials for ethanol gas sensors

Mesoporous Ti_0.5Cr_0.5N Supported PdAg Nanoalloy as Highly Active and Stable Catalysts for the Electro-oxidation of Formic Acid and Methanol

We report a robust noncarbon Ti_0.5Cr_0.5N support synthesized by an efficient solid–solid phase separation method. This ternary nitride exhibits highly porous, sintered, and random network structure with a crystallite size of 20–40 nm, resulting in a high specific surface area. It is not only kinetically stable in both acid and alkaline media, but also electrochemically stable in the potential range of fuel cell operation. Two typical anode reactions, formic acid oxidation in acid media and methanol oxidation in alkaline media, are employed to investigate the possibility of Ti_0.5Cr_0.5N as an alternative to carbon. Bimetallic PdAg nanoparticles (∼4 nm) act as anode catalysts for the two anode reactions. PdAg/Ti_0.5Cr_0.5N exhibits much higher mass activity and durability for the two reactions than PdAg/C and Pd/C catalyst, suggesting that mesoporous Ti_0.5Cr_0.5N is a very promising support in both acid and alkaline media

Convenient Size Analysis of Nanoplastics on a Microelectrode

Chemical recycling is a promising approach to reduce plastic pollution. Timely and accurate size analysis of produced nanoplastics is necessary to monitor the process and assess the quality of chemical recycling. In this work, a sandwich-type microelectrode sensor was developed for the size assessment of nanoplastics. β-Mercaptoethylamine was modified on the microelectrode to enhance its surface positive charge density. Polystyrene (PS) nanoplastics were captured on the sensor through electrostatic interactions. Ferrocene was used as an electrochemical beacon and attached to PS via hydrophobic interactions. The results show a nonlinear dependence of the sensor’s current response on the PS particle size. The size resolving ability of the microelectrode is mainly attributed to the small size of the electrode and the resulting attenuation of the electric field strength. For mixed samples with different particle sizes, this method can provide accurate average particle sizes. Through an effective pretreatment process, the method can be applied to PS nanoplastics with different surface properties, ensuring its application in evaluating different chemical recycling methods

Electrochemical Biosensing Platform Using Hydrogel Prepared from Ferrocene Modified Amino Acid as Highly Efficient Immobilization Matrix

To increase the loading of glucose oxidase (GOx) and simplify glucose biosensor fabrication, hydrogel prepared from ferrocene (Fc) modified amino acid phenylalanine (Phe, F) was utilized for the incorporation of GOx. The synthesized hydrogel displays good biocompatibility and contains a significant number of Fc moieties, which can be considered as an ideal matrix to immobilize enzymes for the preparation of mediator-based biosensors. The hydrogel was studied by scanning electron microscopy, which indicated that it was composed of nanofibers with a diameter of around 50–100 nm and length extended to 1 mm. With the addition of GOx into the hydrogel and by directly dropping the resulting biocomposite onto the electrode surface, a glucose biosensor, that displays good performance due to improved enzyme loading and efficient electron transfer, can be simply constructed. The favorable network structure and good biocompatibility of the hydrogel could effectively avoid enzyme leakage and maintain the bioactivity of the enzymes, which resulted in good stability of the biosensor. The biosensor was utilized for the detection of glucose in blood samples with results comparable to those obtained from the hospital. The hydrogel as a functional component of an amperometric biosensor has implications for future development of biosensors and for clinical applications

Molecular Dynamics Simulations of the <i>Escherichia coli</i> HPPK Apo-enzyme Reveal a Network of Conformational Transitions

6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the first reaction in the folate biosynthetic pathway. Comparison of its X-ray and nuclear magnetic resonance structures suggests that the enzyme undergoes significant conformational change upon binding to its substrates, especially in three catalytic loops. Experimental research has shown that even when confined by crystal contacts, loops 2 and 3 remain rather flexible when the enzyme is in its apo form, raising questions about the putative large-scale induced-fit conformational change of HPPK. To investigate the loop dynamics in a crystal-free environment, we performed conventional molecular dynamics simulations of the apo-enzyme at two different temperatures (300 and 350 K). Our simulations show that the crystallographic <i>B</i>-factors considerably underestimate the loop dynamics; multiple conformations of loops 2 and 3, including the open, semi-open, and closed conformations that an enzyme must adopt throughout its catalytic cycle, are all accessible to the apo-enzyme. These results revise our previous view of the functional mechanism of conformational change upon MgATP binding and offer valuable structural insights into the workings of HPPK. In this paper, conformational network analysis and principal component analysis related to the loops are discussed to support the presented conclusions

Silver Nanoclusters-Based Fluorescence Assay of Protein Kinase Activity and Inhibition

A simple and sensitive fluorescence method for monitoring the activity and inhibition of protein kinase (PKA) has been developed using polycytosine oligonucleotide (dC₁₂)-templated silver nanoclusters (Ag NCs). Adenosine-5′-triphosphate (ATP) was found to enhance the fluorescence of Ag NCs, while the hydrolysis of ATP to adenosine diphosphate (ADP) by PKA decreased the fluorescence of Ag NCs. Compared to the existing methods for kinase activity assay, the developed method does not involve phosphorylation of the substrate peptides, which significantly simplifies the detection procedures. The method exhibits high sensitivity, good selectivity, and wide linear range toward PKA detection. The inhibition effect of kinase inhibitor H-89 on the activity of PKA was also studied. The sensing protocol was also applied to the assay of drug-stimulated activation of PKA in HeLa cell lysates

Electronic tuning of two metals and colossal magnetoresistances in EuWO1+ xN2- x perovskites

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN 2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN 2-x perovskites that show a wide range of compositions -0.16 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. © 2010 American Chemical Society

Quasiclassical Trajectory Studies of the O(³P) + CX₄(<i>v</i>_<i>k</i> = 0, 1) → OX(<i>v</i>) + CX₃(<i>n</i>₁<i>n</i>₂<i>n</i>₃<i>n</i>₄) [X = H and D] Reactions on an Ab Initio Potential Energy Surface

We report quasiclassical trajectory calculations of the integral and differential cross sections and the mode-specific product state distributions for the “central-barrier” O­(³P) + CH₄/CD₄(<i>v</i>_<i>k</i> = 0, 1) [<i>k</i> = 1, 2, 3, 4] reactions using a full-dimensional ab initio potential energy surface. The mode-specific vibrational distributions for the polyatomic methyl products are obtained by doing a normal-mode analysis in the Eckart frame, followed by standard histogram binning (HB) and energy-based Gaussian binning (1GB). The reactant bending excitations slightly enhance the reactivity, whereas stretching excitations activate the reaction more efficiently. None of the reactant vibrational excitations is as efficient as an equivalent amount of translational energy to promote the reactions. The excitation functions without product zero-point energy (ZPE) constraint are in good agreement with previous 8-dimensional quantum mechanical (QM) results for the ground-state and stretching-excited O + CH₄ reactions, whereas for the bending-excited reactions the soft ZPE constraint, which is applied to the sum of the product vibrational energies, provides better agreement with the QM cross sections. All angular distributions show the dominance of backward scattering indicating a direct rebound mechanism, in agreement with experiment. The title reactions produce mainly OH/OD­(<i>v</i> = 0) products for all the initial states. HB significantly overestimates the populations of OH/OD­(<i>v</i> = 1), especially in the energetic threshold regions, whereas 1GB provides physically correct results. The CH₃/CD₃ vibrational distributions show dominant populations for ground (<i>v</i> = 0), umbrella-excited (<i>v</i>₂ = 1, 2), in-plane-bending-excited (<i>v</i>₄ = 1), and <i>v</i>₂ + <i>v</i>₄ methyl product states. Neither translational energy nor reactant vibrational excitation transfers significantly into product vibrations