Enantiosensitive molecular compass

arXiv (Cornell University) · 2025-05-28

Chirality describes the asymmetry between an object and its mirror image and manifests itself in diverse functionalities across all scales of matter - from molecules and aggregates to thin films and bulk chiral materials. A particularly intriguing example is chirality-induced spin selectivity (CISS), where chiral structures orient electron spins enantio-sensitively. Despite extensive research, the fundamental origin of spin-chirality coupling, the unexpectedly large magnitude of the CISS effect, and the possible role of electromagnetic fields in it remain unclear. Here, we address these issues by examining the simplest scenario: spin-resolved photoionization of randomly oriented chiral molecules. We uncover a universal mechanism of spin-selective chiral photodynamics, arising solely from electric-dipole interactions and previously unrecognized. This mechanism embodies a chiral molecular compass - a photoinduced magnetization vector that orients the photoelectron spin. It arises in photoexcited chiral molecules even under isotropic illumination, operates even in isotropic chiral media, and enables a phenomenon central to CISS: locking of the photoelectron spin orientation to molecular geometry. It shows that chiral molecules can sustain time-odd correlations whereas achiral molecules cannot. Our findings have broad implications, from unambiguously identifying the origin of CISS effect in photoionization to harvesting correlations underlying this effect in other forms of CISS in various chiral materials.

Dipole-Induced Inversion of Spin-Dependent Charge Transport through α-Helical Peptide-Based Single-Molecule Junctions

Journal of the American Chemical Society · 2025-09-30 · 3 citations

We report on a remarkable phenomenon of interfacial electric dipole inversion coupled to changes in atomic spin densities that translates into the enantiomeric inversion of electron spin-dependent conductance in a 2-terminal single-molecule junction, consisting of a 22 amino acid chiral α-helical peptide sequence connecting two metal electrodes. This phenomenon is conventionally associated with the Chirality-Induced Spin Selectivity (CISS) effect and how it induces spin polarization and spin filtering of the electron transport along the main peptide axis. Here, the inversion of the spin-dependent charge transport behavior is achieved by keeping constant the chiral symmetry of the junction while inverting the direction of the internal electrical dipole moment running along the main helical peptide axis. Using a spinterface model, in which the electrode-molecule injection barriers are dependent both on the electric dipole and magnetic spin moment, we have been able to rationalize the current pattern as arising from a surface dipole inversion and changes in the atomic spin densities in atoms located within the peptide backbone. Both experimental and computational results show that the observed electric dipole-induced spin-dependent transport inversion in the chiral peptide junction links to an inversion in the spin-dependent resistance due to the combined effect of the helical-based CISS effect and the electrode/molecule spinterface.

Residual charge dependence of spin transport in chiral biomolecules

The Journal of Chemical Physics · 2025-11-03

Electron spin polarization in biomolecules has drawn significant attention as it embodies an unexplored mechanism for information propagation and electron transfer in biological systems. Despite extensive experimental and theoretical investigations of the CISS (Chirality-Induced Spin Selectivity), there are still many unanswered questions about how electrons are spin-polarized after passing through chiral molecules and, furthermore, how this process influences vital electron transfer reactions. Since peptides are excellent models to examine this aspect of the spin polarization phenomenon, calculations were carried out to compare the spin-dependent transport properties of a charge-neutral peptide composed of seven alanine residues (A7) to that containing a negatively charged aspartic acid residue (A6D), a positively charged lysine residue (A6K), and an aromatic tyrosine residue (A6Y). We focus our analysis on the spin polarization arising from both spinterface, that is, the interplay between the interfacial electric and magnetic dipole moments, and spin polarization induced by the CISS effect. We find that the asymmetry between the α and β spin transport channels is particularly pronounced in a peptide containing a tyrosine residue. Furthermore, the secondary structure of the peptide plays a key role in spin-dependent transport, with peptides possessing α-helical conformations exhibiting transmission higher than the corresponding extended structures. Tyrosine is a key molecular fragment in photosynthetic complexes and several other biological electron transfer systems. Our results indicate that the natural selection of tyrosine is linked to its versatile electronic structure that allows for a path to spin polarization, which in turn dramatically modifies the nature of electron transfer processes.

Chirality-encoded molecular wavefunctions

The Journal of Chemical Physics · 2025-11-24

For enantiomers, the ground-state charge densities are mapped into one another by spatial reflection, yet-when spin-orbit coupling (SOC) is present-their occupied spinors need not coincide beyond a global phase. SOC encodes spatially varying, intrinsic phase textures whose gradients leave the density unchanged but enter gauge-invariant response combinations. These phases provide a general mechanism for enantiospecific contributions in response tensors. We show that isotropic pseudoscalar signatures arise only from polar-axial couplings, while same-parity couplings remain mirror-even; in oriented samples, anisotropic tensor components can also flip sign. We derive analytical bounds linking SOC-driven spinor phases and amplitude distortions to measurable tensor differences and validate them with relativistic plane wave density-functional calculations on prototypical chiral molecules. Plane waves are chosen because they faithfully represent delocalized SOC phase textures that standard localized bases struggle to capture. Experiments that couple mirror-odd operators to SOC-induced phases in chiral samples can, in principle, yield enantiospecific responses.

Emerging Non-Local Quantum Time Correlation Phenomena In A Classical System Of Organo-Metallic Microparticles

HAL (Le Centre pour la Communication Scientifique Directe) · 2025-01-01

We investigate enantiomers of chiral organo-metallic particles which exhibit collective memory effect. Under the influence of magnetic field, the millions of particles in solution form macroscopic shapes and when dispersed again at zero field they return to their original shape. The microparticles forming the shaped structures are collectively coupled under the influence of long-range van der Waals exchange interactions which govern the collective macroscopic structure. We recently have found that non-local quantum exchange interactions between particles persist up to ten meters, close to room temperature. Here, we investigate further the perception of time in the system. We find that the particles exhibit temporal correlations between the future and present states of the system. The forces which govern the collective memory effect and shape the macroscopic structure therefore allow to visualize quantum phenomena which extend the classical causality notion into an expanded nonlocal space-time reality. We propose that the observations are attributed to chirality-discriminating van der Waals exchange interactions coupled to vacuum fluctuations.

A first-principles DFT study and molecular dynamics simulation of the mechanism of water adsorption in polyamide-6

Computational and Theoretical Chemistry · 2025-08-31 · 2 citations

A computational study combining Molecular Dynamics (MD) and Density Functional Theory (DFT) explored water interactions with polyamide-6 (PA-6), focusing on hydrogen bonding and water aggregation due to the polymer's amphiphilic nature. Water adsorption affects PA-6's physical and mechanical properties. MD simulations show strong affinity at low water content, supported by radial distribution functions and hydrogen bond analysis. Free energy and interaction energy peak near 5 wt% water, driven by the electrostatics and bonding with amide C O groups. At higher water concentrations, a decline in adhesion work is observed, correlating with the enhanced formation of water aggregates in a solvent-saturated environment. The DFT results support these findings. Furthermore, theoretical infrared (IR) spectra confirm that the driving force behind water–PA-6 interactions is the formation of strong intermolecular hydrogen bonds. The comparison of the Raman spectra for water and nitrogen (IR inactive) moieties, confirms significant differences between the two molecules in the adsorption process. • An integrated MD–DFT computational approach elucidates how hydration affects the structural and energetic properties of PA-6, offering insights into its performance in humid environments and paving the way for experimental verification. • A molecular-level description indicates that at higher water contents, hydrogen bonding is weakened, leading to decreased interaction energy and adhesion, and promoting the formation of water aggregates due to the amphiphilic nature of PA-6. This is confirmed by FTIR spectra simulations.

<span>Emerging Non-Local Quantum Time Correlation Phenomena In A Classical System Of Organo-Metallic Microparticles</span><span></span><span></span>

SSRN Electronic Journal · 2025-01-01

Toward a formulation of a CISS theory with the inclusion of two-particle relativistic effects, electron–phonon coupling, and electron–electron correlation. An application to NMR-based chiral discrimination

The Journal of Chemical Physics · 2025-09-24 · 1 citations

The current status of the theoretical foundations of the Chiral-Induced Spin Selectivity (CISS) effect has substantially improved from its original one-electron formulation. However, there is a need to improve the inclusion of electron-vibrational interaction, the exchange and correlation effects arising from electron-electron interactions, and non-Born-Oppenheimer coupling to enhance the predictive power of the theory and its agreement with experiments. In an attempt to overcome these difficulties, we advance in the present work a microscopic quantum mechanical treatment of CISS based on the relativistic Breit-Pauli many-particle Hamiltonian. In particular, we determine in this context the effect that including non-Born-Oppenheimer components arising in a Taylor expansion of the electron-nuclear potential has on the spin-orbit coupling term of this Hamiltonian. We also consider in this framework the electron-electron exchange and correlation effects and propose some practical approximations based on non-relativistic approaches. Finally, we extend the application of the Breit-Pauli Hamiltonian to describe nuclear-nuclear spin interactions and discuss the possibility of explaining enantiomeric selectivity in cross-polarization nuclear magnetic resonance experiments.

Hybrid mesoporous electrodes evidence CISS effect on water oxidation

The Journal of Chemical Physics · 2024-03-21 · 6 citations

Controlling product selectivity is essential for improving the efficiency of multi-product reactions. Electrochemical water oxidation is a reaction of main importance in different applications, e.g., renewable energy schemes and environmental protection, where H2O2 and O2 are the two principal products. In this Communication, the product selectivity of electrochemical water oxidation was controlled by making use of the chiral induced spin selectivity (CISS) effect at mesoporous-TiO2 on the molecule-modified Au substrate. Our results show a decrease in H2O2 formation when using chiral hetero-helicene molecules adsorbed on the Au substrate. We propose a mechanism for this kinetic effect based on the onset of CISS-induced spin polarization on the Au-helicene chiral interface. We also present a new tunable substrate to investigate the CISS mechanism.

A computational study of the size effect of SiO2 spherical nanoparticles in water solvent

Journal of Molecular Modeling · 2024-11-13 · 1 citations