Effect of Anesthesia Gases on the Oxygen Reduction Reaction

Anaesthetics disrupt complex I-linked respiration and reverse the ATP synthase

The mechanism of volatile general anaesthetics has long been a mystery. Anaesthetics have no structural motifs in common, beyond lipid solubility, yet all exert a similar effect. The fact that the inert gas xenon is an anaesthetic suggests their common mechanism might relate to physical rather than chemical properties. Electron transfer through chiral proteins can induce spin polarization. Recent work suggests that anaesthetics dissipate spin polarization during electron transfer to oxygen, slowing respiration. Here we show that the volatile anaesthetics isoflurane and sevoflurane specifically disrupt complex I-linked respiration in the thoraces of Drosophila melanogaster, with less effect on maximal respiration. Suppression of complex I-linked respiration was greatest with isoflurane. Using high-resolution tissue fluorespirometry, we show that these anaesthetics simultaneously increase mitochondrial membrane potential, implying reversal of the ATP synthase. Inhibition of ATP synthase with oligomycin prevented respiration and increased membrane potential back to the maximal (LEAK state) potential. Magnesium-green fluorescence predicted a collapse in ATP availability following a single anaesthetic dose, consistent with ATP hydrolysis through reversal of the ATP synthase. Raised membrane potential corresponded to a rise in ROS flux, especially with isoflurane. Anaesthetic doses causing respiratory suppression were in the same range as those that induce anaesthesia, although we could not establish tissue concentrations. Our findings show that anaesthetics suppress complex I-linked respiration with concerted downstream effects. But we cannot explain why only mutations in complex I, and not elsewhere in the electron-transfer system, confer hypersensitivity to anaesthetics.

Influence of intrinsic spin ordering in La0.6Sr0.4Co0.8Fe0.2O3-δ and Ba0.6Sr0.4Co0.8Fe0.2O3-δ towards electrocatalysis of oxygen redox reaction in solid oxide cell

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O2 is associated with singlet oxygen in H2O/OH-), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction). We suggest that, presence of inherent spin polarization within La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF6482) (15.86 emu g-1) and Ba0.6Sr0.4Co0.8Fe0.2O3-δ (BSCF6482) (3.64 emu g-1) accounts for the excellent selective electrocatalysis towards ORR and OER. QSEI forms the atomic level basis for OER/ORR which is directly proportional to spin ordering (non-zero magnetization) of the active electrocatalyst. LSCF6482 exhibits (21.5 kJ mol-1@0.8 V for ORR compared to 61 kJ mol-1@0.8 V for OER) improved ORR kinetics whereas BSCF6482 (18.79 kJ mol-1@0.8 V for OER compared to 32.19 kJ mol-1 for ORR@-0.8 V) is best suited for OER under the present stoichiometry. The findings establish the presence of inherent spin polarization of catalyst to be an effective descriptor for OER and ORR kinetics in solid oxide cell (SOC).

Magnetic Monopole-Like Behavior in Superparamagnetic Nanoparticle Coated With Chiral Molecules

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted wide attention due to their promising applications in biomedicine, chemical catalysis, and magnetic memory devices. In this work, the force is measured between a single SPION coated with chiral molecules and a ferromagnetic substrate by atomic force microscopy (AFM), with the substrate magnetized either toward or away from the approaching AFM tip. The force between the coated SPION and the magnetic substrate depends on the handedness of the molecules adsorbed on the SPION and on the direction of the magnetization of the substrate. By inserting nm-scale spacing layers between the coated SPION and the magnetic substrate it is shown that the SPION has a short-range magnetic monopole-like magnetic field. A theoretical framework for the nature of this field is provided.

Current Induced Spin-Polarization in Chiral Molecules

The inverse spin-galvanic effect or current-induced spin-polarization is mainly associated with interfaces between different layers in semiconducting heterostructures, surfaces of metals, and bulk semiconducting materials. Here, we theoretically predict that the inverse spin-galvanic effect should also be present in chiral molecules, as a result of the chiral induced spin selectivity effect. As proof-of-principle, we calculate the nonequilibrium properties of a model system that previously has been successfully used to explain a multitude of aspects related to the chiral induced spin selectivity effect. Here we show that current driven spin-polarization in a chiral molecule gives rise to a magnetic moment that is sensitive to external magnet field. The chiral molecule then behaves like a soft ferromagnet. This, in turn, suggests that magnetic permeability measurement in otherwise nonmagnetic systems may be used noninvasively to detect the presence of spin-polarized currents.

Electron Spin-Dependent Electrocatalysis for the Oxygen Reduction Reaction in a Chiro-Self-Assembled Iron Phthalocyanine Device

The chiral-induced spin selectivity effect (CISS) is a breakthrough phenomenon that has revolutionized the field of electrocatalysis. We report the first study on the electron spin-dependent electrocatalysis for the oxygen reduction reaction, ORR, using iron phthalocyanine, FePc, a well-known molecular catalyst for this reaction. The FePc complex belongs to the non-precious catalysts group, whose active site, FeN4, emulates catalytic centers of biocatalysts such as Cytochrome c. This study presents an experimental platform involving FePc self-assembled to a gold electrode surface using chiral peptides (L and D enantiomers), i.e., chiro-self-assembled FePc systems (CSAFePc). The chiral peptides behave as spin filters axial ligands of the FePc. One of the main findings is that the peptides' handedness and length in CSAFePc can optimize the kinetics and thermodynamic factors governing ORR. Moreover, the D-enantiomer promotes the highest electrocatalytic activity of FePc for ORR, shifting the onset potential up to 1.01 V vs. RHE in an alkaline medium, a potential close to the reversible potential of the O2 /H2 O couple. Therefore, this work has exciting implications for developing highly efficient and bioinspired catalysts, considering that, in biological organisms, biocatalysts that promote O2 reduction to water comprise L-enantiomers.

Electrochemical Performance of Metal-Free Carbon-Based Catalysts from Different Hydrothermal Carbonization Treatments for Oxygen Reduction Reaction

This research investigates the difference between products obtained through two hydrothermal carbonization treatments. Our aim is to synthesize metal-free, carbon-based catalysts for the oxygen reduction reaction (ORR) to serve as efficient and cost-effective alternatives to platinum-based catalysts. Catalysts synthesized using the traditional hydrothermal approach exhibit a higher electrocatalytic activity for ORR in alkaline media, despite their more energy-intensive production process. The superior performance is attributed to differences in the particle morphology and the chemical composition of the particle surfaces. The presence of functional groups on the surfaces of catalysts obtained via a traditional approach significantly enhances ORR activity by facilitating deprotonation reactions in an alkaline environment. Our research aims to provide a reference for future investigations, shifting the focus to the fine-tuning of surface chemical compositions and morphologies of metal-free catalysts to enhance ORR activity.

Does Coherence Affect the Multielectron Oxygen Reduction Reaction?

The oxygen reduction reaction (ORR) is the key for oxygen-based respiration and the operation of fuel cells. It involves the transmission of two pairs of electrons. We probed what type of interaction between the electrons is required to enable their efficient transfer into the oxygen. We show experimentally that the transfer of the electrons is controlled by the "hidden property" and present a theoretical model suggesting that it is related to coherent phase relations between the two electrons. Using spin polarization electrochemical measurements, with electrodes coated with different thicknesses of chiral coating, we confirm the special relation between the electrons. This relation is destroyed by multiple scattering events that result in the formation of hydrogen peroxide, which indicates a reduction in the ORR efficiency. Another indication for the possible role of coherence is the fluctuations in the reaction efficiency as a function of thickness of the chiral coated electrode.