arXiv subjects

Ron Naaman

Publications and source records attributed to Ron Naaman.

14 recordsLinked to original sources

arXiv2026

Spin-Dependent Electron Transport through Bacterial Cell Surface Multiheme Electron Conduits

Multiheme cytochromes, located on the bacterial cell surface, function as long-distance (> 10 nm) electron conduits linking intracellular reactions to external surfaces. This extracellular electron transfer process, which allows microorganisms to gain energy by respiring solid redox-active minerals, also facilitates the wiring of cells to electrodes. While recent studies suggested that a chiral induced spin selectivity effect is linked to efficient electron transmission through biomolecules, this phenomenon has not been investigated in the extracellular electron conduits. Using magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin-dependent electrochemistry of the decaheme cytochromes MtrF and OmcA from the metal-reducing bacterium Shewanella oneidensis MR-1, we show that electron transport through these extracellular conduits is spin-selective. Our study has implications for understanding how spin-dependent interactions and magnetic fields may control electron transport across biotic-abiotic interfaces in both natural and biotechnological systems. Electron

physics.chem-ph↗

arXiv2026

Control of Electrons Spin Eliminates Hydrogen Peroxide Formation During Water Splitting

The production of hydrogen through water splitting in a photoelectrochemical cell suffers from an overpotential that limits the efficiencies. In addition, hydrogen-peroxide formation is identified as a competing process affecting the oxidative stability of photoelectrodes. We impose spin-selectivity by coating the anode with chiral organic semiconductors from helically-aggregated dyes as sensitizers; Zn-porphyrins and triarylamines. Hydrogen peroxide formation is dramatically suppressed, while the overall current through the cell, correlating with the water splitting process, is enhanced. Evidence for a strong spin-selection in the chiral semiconductors is presented by magnetic conducting (mc-)AFM measurements, where chiral and achiral Zn-porphyrins are compared. These findings contribute to our understanding of the underlying mechanism of spin selectivity in multiple electron-transfer reactions and pave the way towards better chiral dye-sensitized photoelectrochemical cells.

physics.chem-ph↗

arXiv2026

Dynamic Breaking of Mirror Symmetry in Spin-Dependent Electron Transport through Chiral Media Causes Enantiomeric Excesses

Two fundamental questions have puzzled scientists for more than 150 years. How did life become homochiral and why was this specific handedness selected. Recently, it has been shown that homochirality could have emerged through the enantioselective interactions of molecules with magnetic substrates due to the asymmetric crystallization of an RNA precursor on a magnetite substrate, abundant on early Earth. This phenomenon is based on the chirality-induced spin selectivity,CISS, effect. Despite its robustness, this model could not provide an answer to the second question: why one specific handedness, D for RNA, was selected. Here we demonstrate that spin-involving processes can have different outcomes in the two enantiomers of chiral molecules. In chiral molecules with unpaired electrons or while electrons are passing through them, the total angular momentum vector, J, is aligned along the easy axis, which is defined by the magnetic anisotropy induced by the spin-orbit coupling and asymmetry of the molecular field. The magnitude J is the same for both enantiomers, but the vectors may be aligned differently relative to the molecular frame in the two enantiomers. This difference can be quantified by, for example, by the angle between J and electric dipole moment of the molecule. We show by direct measurements, theory, and ab initio calculations that dynamic spin processes in chiral molecules could result in different efficiencies of spin-related phenomena, including the interaction of chiral molecules with magnetic surfaces. The findings may provide an explanation for the specific homochirality in nature.

physics.chem-ph↗

arXiv2026

Control of protein activity by photoinduced spin polarized charge reorganization

Considerable electric fields are present within living cells, and the role of bioelectricity has been well established at the organismal level. Yet little is known about electric-field effects on protein function. Here we use phototriggered charge injection from a site-specifically attached ruthenium photosensitizer to directly demonstrate the effects of charge redistribution within a protein. We find that binding of an antibody to phosphoglycerate kinase (PGK) is increased two folds under illumination. Remarkably, illumination is found to suppress the enzymatic activity of PGK by a factor as large as three. These responses are sensitive to the photosensitizer position on the protein. Surprisingly, left (but not right) circularly polarized light elicits these responses, indicating that the electrons involved in the observed dynamics are spin polarized, due to spin filtration by protein chiral structures. Our results directly establish the contribution of electrical polarization as an allosteric signal within proteins. Future experiments with phototriggered charge injection will allow delineation of charge rearrangement pathways within proteins and will further depict their effects on protein function.

physics.chem-ph↗

arXiv2026

Chiral-Induced Spin Selectivity Effect in a 1 nm Thin 1,1'-Binaphthyl-2,2'-diyl Hydrogenphosphate Self-Assembled Monolayer on Nickel Oxide

The chiral-induced spin selectivity (CISS) effect describes an observed correlation between the orientation of an electron spin transported or transferred through a molecule and that molecule's chirality. Suitable molecules are usually arranged as self-assembled monolayers (SAMs), and the primary CISS systems are based on multiple nanometer-long biomolecules exhibiting helical chirality. Aside from these typically thiolate-anchored molecules, phosphonic and phosphoric acid SAMs may well become significant for those CISS applications that require a more robust molecular coupling to metal oxide surfaces. In this work, we report on our studies, employing the aromatic, low-molecular-mass, axially chiral organophosphoric acid derivative 1,1'-binaphthyl-2,2'-diyl hydrogenphosphate (BNP). Grown as a roughly 1 nm thin SAM on top of a NiOx/Ni substrate, a strong circular dichroism signal indicates that the thin films preserved chirality. The CISS response exhibits a high magnetoresistance with a spin polarization of 50-80% when measured using magnetic-conductive atomic force microscopy. For biases above 0.5 V, the magnetoresistance curves could be well fitted to the Fowler-Nordheim (FN) tunneling model. Using a minimal FN model, we determined that, depending on the magnetization direction and the handedness of the molecules, electrons of a certain spin direction face an effective tunneling barrier at high bias, which is either 80 % higher or 40 % lower compared to the barrier for electrons of the opposite spin direction. Due to the small size of the molecules, their compatibility with oxide materials, and their commercial availability, they are excellent candidates for the realization of novel (nanoscale) organic spintronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Insights into the Mechanism underlying the Chiral-Induced Spin Selectivity: The effect of an Angle-Dependent Magnetic Field and Temperature

Chiral oligopeptide monolayers were adsorbed on a ferromagnetic surface and their magnetoresistance was measured as a function of the angle between the magnetization of the ferromagnet and the surface normal. These measurements were conducted as a function of temperature for both enantiomers. The angle dependence was found to follow the cosine square function. Quantum simulations revealed that the angular distribution could be obtained only if the monolayer has significant effective spin orbit coupling (SOC), that includes contribution from the vibrations. The model shows that SOC only in the leads cannot reproduce the observed angular dependence. The simulation can reproduce the experiments only if it included electron-phonon interactions and dissipation.

cond-mat.mes-hall↗

arXiv2023

Chirality-Induced Magnetization of Magnetite by an RNA Precursor

Life is homochiral and homochirality is a fundamental feature of living systems on Earth. While the exact mechanism that led to homochirality is still not fully understood, any realistic scenario on the origins of life needs to address the emergence of homochirality. In order to impose and maintain chirality in a prebiotic network, an environmental factor functioning as a chiral agent is demanded. Magnetized surfaces are prebiotically plausible chiral agents, shown to be effective in enantioseparation of ribose-aminooxazoline (RAO), a ribonucleic acid (RNA) precursor, due to the chiral-induced spin selectivity (CISS) effect. As such, mechanisms for breaking the magnetic symmetry of magnetic minerals are of the utmost importance. Here we report the avalanche magnetization of magnetite $(Fe_{3}O_{4})$ by the crystallization of enantiopure RAO. The observed breaking of the magnetic symmetry is induced by the chiral molecules due to the CISS effect and spreads out across the magnetic surface like an avalanche, providing a way to uniformly magnetize a magnetic surface without fully covering it. Considered together with our previous results on enantioseparation by crystallization on a magnetic surface, chirality-induced avalanche magnetization paves the way for a cooperative feedback between chiral molecules and magnetic surfaces. With this feedback, a weak natural bias in the net magnetization can be amplified and spin-selective processes can be accommodated on magnetic minerals on a persistent basis.

physics.chem-ph↗

arXiv2021

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

We provide a critical overview of the theory of the chirality-induced spin selectivity (CISS) effect, i.e., phenomena in which the chirality of molecular species imparts significant spin selectivity to various electron processes. Based on discussions in a recently held workshop, and further work published since, we review the status of CISS effects - in electron transmission, electron transport, and chemical reactions. For each, we provide a detailed discussion of the state-of-the-art in theoretical understanding and identify remaining challenges and research opportunities.

cond-mat.mtrl-sci↗

arXiv2021

The temperature-dependent chiral-induced spin selectivity effect: Experiments and theory

The theoretical explanation for the chiral-induced spin selectivity effect, in which electrons' passage through a chiral system depends on their spin and the handedness of the system, remains vague. Although most experimental work was performed at room temperature, most of the proposed theories did not include vibrations. Here, we present temperature-dependent experiments and a theoretical model that captures all observations and provides spin polarization values that are consistent with the experimental results. The model includes vibrational contribution to the spin orbit coupling. It shows the importance of dissipation and the relation between the effect and the optical activity.

cond-mat.mes-hall↗

arXiv2021

Substrates modulate charge-reorganization allosteric effects in protein-protein association

Protein function may be modulated by an event occurring far away from the functional site, a phenomenon termed allostery. While classically allostery involves conformational changes, we recently observed that charge redistribution within an antibody can also lead to an allosteric effect, modulating the kinetics of binding to target antigen. In the present study, we study the association of a poly-histidine tagged enzyme (phosphoglycerate kinase, PGK) to surface-immobilized anti-His antibodies, finding a significant Charge-Reorganization Allostery (CRA) effect. We further observe that the negatively charged nucleotide substrates of PGK modulate CRA substantially, even though they bind far away from the His-tag-antibody interaction interface. In particular, binding of ATP reduces CRA by more than 50%. The results indicate that CRA may be affected by charged substrates bound to a protein and provide further insight into the role of charge redistribution in protein function.

physics.bio-ph↗

arXiv2020

A Chirality-Based Quantum Leap

Chiral degrees of freedom occur in matter and in electromagnetic fields and constitute an area of research that is experiencing renewed interest driven by recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials. The CISS effect underpins the fact that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision. Any technology that relies on optimal charge transport, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which is presently lacking. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking perspective provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and presents a vision for their future roles in enabling room-temperature quantum technologies.

cond-mat.mes-hall↗

arXiv2016

Origin of spin dependent tunneling through chiral molecules

The functionality of many biological systems depends on reliable electron transfer with minimal heating. Unlike man-made electric circuits, nature realizes electron transport via insulating chiral molecules. Here we include spin into the analysis of tunneling through these molecules, and demonstrate its importance for efficient transport. We show that the helical geometry induces robust spin filtering accompanied by, and intimately related to, strongly enhanced transmission. Thus, we resolve two key questions posed by transport measurements through organic molecules, demonstrating their common origin.

cond-mat.mes-hall↗

arXiv2011

Increased superconducting transition temperature of a niobium thin-film proximity-coupled to gold nanoparticles using linking organic molecules

The superconducting critical temperature, TC, of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The TC increases by up to 10% for certain linker length and NPs size. No change is observed when the nanoparticles are physisorbed with non-linking molecules. Electron tunneling spectra acquired on the linked NPs below TC typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

cond-mat.supr-con↗

arXiv2008

Chiral control of electron transmission through molecules

Electron transmission through chiral molecules induced by circularly polarized light can be very different for mirror-image structures, a peculiar fact given that the electronic energy spectra of the systems are identical. We propose that this asymmetry - as large as 10% for resonance transport- arises from different dynamical responses of the mirrored structures to coherent excitation. This behaviour is described in the context of a general novel phenomenon, current transfer, transfer of charge with its momentum information, that is outlined in terms of a simple tight binding model. This analysis makes it possible to account for the observed asymmetry in and off resonance, to characterize its dependence on the length of the molecular bridge and to examine effects of dephasing processes.

physics.chem-ph↗