Magnetic field effects on bioelectrocatalytic reactions of surface-confined enzyme systems: enhanced performance of biofuel cells

The effect of a constant magnetic field on bioelectrocatalytic transformations of three different enzyme assemblies linked to electrodes is examined and correlated with a theoretical magnetohydrodynamic model. The systems consist of surface-reconstituted glucose oxidase (GOx), an integrated lactate dehydrogenase/nicotinamide/pyrroloquinoline quinone assembly (LDH/NAD+ -PQQ), and a cytochrome c/cytochrome oxidase system (Cyt c/COx) linked to the electrodes. Pronounced effects of a constant magnetic field applied parallel to the electrode surface are observed for the bioelectrocatalyzed oxidation of glucose and lactate by the GOx-electrode and LDH/NAD+ -PQQ-electrode, respectively. The enhancement of the bioelectrocatalytic processes correlates nicely with the magnetohydrodynamic model, and the limiting current densities (iL) relate to B1/3 (B = magnetic flux density) and to C4/3 (C* = bulk concentration of the substrate). A small magnetic field effect is observed for the Cyt c/COx-electrode, and its origin is still questionable. The effect of the constant magnetic field on the performance of biofuel cells with different configurations is examined. For the biofuel cell consisting of LDH/NAD+ -PQQ anode and Cyt c/COx cathode, a 3-fold increase in the power output was observed at an applied magnetic field of B = 0.92 T and external load of 1.2 kOhms.     

Magnetization-induced double-layer capacitance enhancement in active carbon/Fe_3O_4 nanocomposites

The effects of magnetic fields on electrochemical processes have made a great impact on both theoretical and practical significances in improving capacitor performance. In this study, active carbon/Fe3O4-NPs nanocomposites(AC/Fe3O4-NPs) were synthesized using a facile hydrothermal method and ultrasonic technique. Transmission electron micrographs(TEM) showed that Fe3O4nanoparticles(Fe3O4-NPs) grew along the edge of AC. AC/Fe3O4-NPs nanocomposites were further used as an electrochemical electrode, and its electrochemical performance was tested under magnetization and non-magnetization conditions, respectively, in a three-electrode electrochemical device. Micro-magnetic field could improve the electric double-layer capacitance, reduce the charge transfer resistance, and enhance the discharge performance. The capacitance enhancement of magnetized electrode was increased by 33.1% at the current density of 1 A/g, and the energy density was improved to 15.97 Wh/kg, due to the addition of magnetic particles.     

Magnetization-induced double-layer capacitance enhancement in active carbon/Fe3O4 nanocomposites

The effects of magnetic fields on electrochemical processes have made a great impact on both theoretical and practical significances in im-proving capacitor performance. In this study, active carbon/Fe...     

(La0.67Ca0.33MnO3)x/(ZrO2)1-x复合体系的磁性和传输特性

将用溶胶-凝胶法得到的La0.67Ca0.33MnO3(LCMO)微粉与ZrO2的颗粒进行复合,制备了(LCMO)x/(ZrO2)1-x渗流复合体系.当LCMO的体积分数为40%时,复合体系达到渗流阈值,此时材料在低温下的磁电阻得到显著增强.77 K时在10 mT的磁场下,(LCMO)0.4/(ZrO2)0.6的磁电阻比为7.8%,相对于LCMO增加了712%.低场磁电阻(LFMR)的增强是由于载流子在二者界面处发生的自旋相关隧穿效应.由于界面反应,不可避免地产生了Zr离子对Mn离子的B位替代,从而引起材料磁性M和居里温度Tc的下降.在x＜60%时,Tc保持在220 K附近基本不变,说明该B位替代是有限的.     

Magnetic control of electrocatalytic and bioelectrocatalytic processes

Bioelectronics is a rapidly progressing interdisciplinary research field that has important implications for the development of biosensors, biofuel cells, biomaterial-based computers, and bioelectronic devices. Magneto-controlled molecular electronics and bioelectronics are new topics that examine the effect of an external magnetic field on electrocatalytic and bioelectrocatalytic processes of functionalized magnetic particles associated with electrodes. In this article we describe the progress in the developments of magneto-switchable electrocatalytic and bioelectrocatalytic transformations, and the effects of the rotation of the magnetic particles on the electrocatalytic and bioelectrocatalytic processes are discussed. Finally, the implications of the results on the development of biosensors, amplified immunosensors, and DNA sensors are described.     

Main group bimetallic partnerships for cooperative catalysis

Over the past decade s-block metal catalysis has undergone a transformation from being an esoteric curiosity to a well-established and consolidated field towards sustainable synthesis. Earth-abundant metals such as Ca, Mg, and Al have shown eye-opening catalytic performances in key catalytic processes such as hydrosilylation, hydroamination or alkene polymerization. In parallel to these studies, s-block mixed-metal reagents have also been attracting widespread interest from scientists. These bimetallic reagents effect many cornerstone organic transformations, often providing enhanced reactivities and better chemo- and regioselectivities than conventional monometallic reagents. Despite a significant number of synthetic advances to date, most efforts have focused primarily on stoichiometric transformations. Merging these two exciting areas of research, this Perspective Article provides an overview on the emerging concept of s/p-block cooperative catalysis. Showcasing recent contributions from several research groups across the world, the untapped potential that these systems can offer in catalytic transformations is discussed with special emphasis placed on how synergistic effects can operate and the special roles played by each metal in these transformations. Advancing the understanding of the ground rules of s-block cooperative catalysis, the application of these bimetalic systems in a critical selection of catalytic transformations encompassing hydroamination, cyclisation, hydroboration to C–C bond forming processes are presented as well as their uses in important polymerization reactions.

Exporting cooperative effects in main group heterobimetallic reagents to catalytic regimes, this Perspective showcases key advances in their applications for hydroelementation, cyclisation, C–C bond formation and polymerization processes.     

Redox‐Active NOx Ligands in Palladium‐Mediated Processes

This Minireview highlights the redox and non‐innocent behavior of NO_x ligands (x=1, 2, or 3) in selected Pd‐mediated processes, for example, alkene and aromatic oxidation processes. A focus is placed on mechanistic understanding and linking recent transformations, such as C? H bond activation/functionalization and Wacker oxidation, with previous work on the functionalization of aromatics and alkenes by Pd^II salts.     

Solid-solid phase transitions: interface controlled reactivity and formation of intermediate structures

Finding new pathways to novel materials is an open challenge in modern solid-state chemistry. Among the reasons that still prevent a rational planning of synthetic routes is the lack of an atomistic understanding at the moment of phase formation. Metastable phases are, in this respect, powerful points of access to new materials. For the synthetic efforts to fully take advantage of such peculiar intermediates, a precise atomistic understanding of critical processes in the solid state in its many facets, that is, nucleation patterns, formation and propagation of interfaces, intermediate structures, and phase growth, is mandatory. Recently we have started a systematic theoretical study of phase transitions, especially of processes with first-order thermodynamics, to reach a firm understanding of the atomistic mechanisms governing polymorphism in the solid state. A clear picture is emerging of the interplay between nucleation patterns, the evolution of domain interfaces and final material morphology. Therein intermediate metastable structural motifs with distinct atomic patterns are identified, which become exciting targets for chemical synthesis. Accordingly, a new way of implementing simulation strategies as a powerful support to the chemical intuition is emerging. Simulations of real materials under conditions corresponding to the experiments are shedding light onto yet elusive aspects of solid-solid transformations. Particularly, sharp insights into local nucleation and growth events allow the formulation of new concepts for rationalizing interfaces formed during phase nucleation and growth. Structurally different and confined in space, metastable interfaces occurring during polymorph transformations bring about distinct diffusion behavior of the chemical species involved. More generally, stable structures emerge as a result of the concurrence of the transformation mechanism and of chemical reactions within the phase-growth fronts.     

Can an external magnetic field affect the thermal reaction of pentafluorobenzyl chloride with n-butyllithium in hexane?

The magnetic field effects reported in 1973 for the thermal reaction of pentafluorobenzyl chloride with n-butyllithium in hexane were re-examined at 23±3°C with modern techniques. Using a new reaction apparatus, which has an electromagnet (up to 14.9 kG) in a glove box under argon atmosphere (H₂O and O₂<1 ppm), we studied the magnetic field effects on the yields of final products of pentafluorophenylpentane and decafluorodiphenylethane in the absence and presence of an external magnetic field of 14.9 kG. No significant magnetic field effect was observed upon the yields of pentafluorophenylpentane and decafluorodiphenylethane under well-controlled conditions with sufficient repetitions.     

Magneto-optical enhancement by plasmon excitations in nanoparticle/metal structures

Coupling magnetic materials to plasmonic structures provides a pathway to dramatically increase the magneto-optical response of the resulting composite architecture. Although such optical enhancement has been demonstrated in a variety of systems, some basic aspects are scarcely known. In particular, reflectance/transmission modulations and electromagnetic field intensification, both triggered by plasmon excitations, can contribute to the magneto-optical enhancement. However, a quantitative evaluation of the impact of both factors on the magneto-optical response is lacking. To address this issue, we have measured magneto-optical Kerr spectra on corrugated gold/dielectric interfaces with magnetic (nickel and iron oxide) nanoparticles. We find that the magneto-optical activity is enhanced by up to an order of magnitude for wavelengths that are correlated to the excitation of propagating or localized surface plasmons. Our work sheds light on the fundamental principles for the observed optical response and demonstrates that the outstanding magneto-optical performance is originated by the increase of the polarization conversion efficiency, whereas the contribution of reflectance modulations is negligible.     

Ultrafast Auger Spectroscopy of Quantum Well Excitons in Strong Magnetic Fields

We study theoretically the ultrafast nonlinear optical response of quantum well excitons in a perpendicular magnetic field. We address the role of many-body correlations originating from the electron scattering between Landau levels (LL). In the linear optical response, the processes involving inter-LL transitions are suppressed provided that the magnetic field is sufficiently strong. However, in the nonlinear response, the Auger processes involving inter-LL scattering of two photoexcited electrons remain unsuppressed. We show that Auger scattering plays a dominant role in the coherent exciton dynamics in strong magnetic fields. We perform numerical calculations for the third-order four-wave-mixing (FWM) polarization, which incorporate the Auger processes nonperturbatively. We find that inter-LL scattering leads to a strong enhancement of FWM signal and to oscillations at negative time delays. These oscillations represent quantum beats between optically inactive two-exciton states related to each other via Auger processes.     

磁场对铁卟啉仿生催化性能的影响

在生命体中,细胞色素P－450单充氧酶辅基是具有铁Df琳结构的血红素．用金属叶琳作为细胞色素P－450单充氧酶的模型化合物探讨和研究人类生命现象一直是国内外化学仿生催化领域极为感兴趣的研究内容之一［’1．我们曾用p一氧代双铁叶琳作为细胞色素P－450单充氧酶的模型化合物,发现改变金属叶琳结构和金属原子电子自旋态将会引起金属叶琳磁性改变,而金属叶琳磁性改变会进一步导致金属叶琳仿生催化性能发生改变D”‘．我们认为,这一现象与人类和地球构成的生物圈可能有某些关联．为了考察地球磁场对人类生命现象的影响,我们进一步建立…     

Energy‐level alignment at metal–organic and organic–organic interfaces

This article reports on the electronic structure at interfaces found in organic semiconductor devices. The studied organic materials are C₆₀ and poly (para‐phenylenevinylene) (PPV)‐like oligomers, and the metals are polycrystalline Au and Ag. To measure the energy levels at these interfaces, ultraviolet photoelectron spectroscopy has been used. It is shown how the energy levels at interfaces deviate from the bulk. Furthermore, it is demonstrated that the vacuum levels do not align at the studied interfaces. The misalignment is caused by an electric field at the interface. Several effects are presented that influence the energy alignment at interfaces, such as screening effects, dipole layer formation, charge transfer, and chemical interaction. The combination of interfaces investigated here is similar to interfaces found in polymer light‐emitting diodes and organic bulk heterojunction photovoltaic devices. The result, the misalignment of the vacuum levels, is expected to influence charge‐transfer processes across these interfaces, possibly affecting the electrical characteristics of organic semiconductor devices that contain similar interfaces. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2549–2560, 2003     

The ion–lipid battle for hydration water and interfacial sites at soft-matter interfaces

At charged surfaces “bound” ions reduce the repulsive electrostatic forces, while dissociated ions control the osmotic pressure in colloidal systems. For systems charged through ionic adsorption on the other hand, the adsorbed ions determine the charging boundary condition and colloidal interactions. Soft-matter interfaces have considerable flexibility and compressibility, hence ionic adsorption at such interfaces may generate new phenomena when (a) the ions compete with the lipid or polymeric components for water of hydration, or (b) position themselves at the polar–nonpolar interface and modify its structure. We review some recent advances on the understanding of specific ion effects from this perspective, and provide some unpublished illustrative examples involving soft flexible interfaces. We propose an extension of the chaotropic series to include disruptors of soft matter, which may act as cosurfactants or even as hydrotropes. We also examine the effects of coordinating ligands on specific ion adsorption at soft interfaces, using lanthanides as test cations, and discuss how such effects may be used to change the affinities between ions and interfaces in controlled ways.     

A joint study based on the electron localization function and catastrophe theory of the chameleonic and centauric models for the Cope rearrangement of 1,5-hexadiene and its cyano derivatives

A novel interpretation of the chameleonic and centauric models for the Cope rearrangements of 1,5-hexadiene (A) and different cyano derivatives (B: 2,5-dicyano, C: 1,3,4,6-tetracyano, and D: 1,3,5-tricyano) is presented by using the topological analysis of the electron localization function (ELF) and Thom's catastrophe theory (CT) on the reaction paths calculated at the B3LYP/6-31G(d,p) level. The progress of the reaction is monitorized by the changes of the ELF structural stability domains (SSD), each being change controlled by a turning point derived from CT. The reaction mechanism of the parent reaction A is characterized by nine ELF SSDs. All processes occur in the vicinity of the transition structure and corresponding to a concerted formation/breaking of C(1)-C(6) and C(3)-C(4) bonds, respectively, together with an accumulation of charge density onto C(2) and C(5) atoms. Reaction B presents the same number of ELF SSDs as A, but a different order appears; the presence of 2,5-dicyano substituents favors the formation of C(1)-C(6) bonds over the breaking of C(3)-C(4) bond process, changing the reaction mechanism from a concerted towards a stepwise, via a cyclohexane biradical intermediate. On the other side, reaction C presents the same type of turning points but two ELF SSD less than A or B; there is an enhancement of the C(3)-C(4) bond breaking process at an earlier stage of the reaction by delocalizing the electrons from the C(3)-C(4) bond among the cyano groups. In the case of competitive effects of cyano subsituents on each moiety, as it is for reaction D, seven different ELF SSDs have been identified separated by eight turning points (two of them occur simultaneously). Both processes, formation/breaking of C(1)-C(6) and C(3)-C(4) bonds, are slightly favored with respect to the parent reaction (A), and the TS presents mixed electronic features of both B and C. The employed methodology provides theoretical support for the centauric nature (half-allyl, half-radical) for the TS of D.     

Magnetic water treatment for a less tenacious scale

This paper discusses the mechanism for magnetic water treatment, which has been used practically for over a century but is still not completely understood. Modified crystallization and agglomeration, which produce a less tenacious scale, retain this property for hours following treatment. It is considered to be a result of magnetically modified hydration and Lorentz force effects of magnetic devices. In treated water, as a complex solution/dispersion system, they affect the kinetics of processes at solution/solid interfaces. Which effect prevails depends on the treatment regime and water composition.     

Magneto‐switchable Electrodes and Electrochemical Systems

This article is an overview of extensive research efforts in many laboratories in the last two decades in the area of magneto‐switchable electrochemical systems. Electrochemical reactions, including electrocatalytic and bioelectrocatalytic processes, have been reversibly activated and inhibited upon physical translocation and reorientation of different magnetic micro/nano‐species on electrode surfaces, particularly using magnetic micro/nanoparticles, adaptive nanowires and hybrid‐graphene sheets. These processes were triggered by repositioning an external magnet, thus resulting in changes in magnetic field at the electrode interfaces. Coupling of the magneto‐activated electrochemical systems with enzymatic reactions of various complexity allowed sophisticated bioelectronic devices for tunable biosensing, on‐demand power production, unconventional computing and other novel bioelectronic applications.