Delocalization-Assisted Transport through Nucleic Acids in Molecular Junctions.

The flow of charge through molecules is central to the function of supramolecular machines, and charge transport in nucleic acids is implicated in molecular signaling and DNA repair. We examine the transport of electrons through nucleic acids to understand the interplay of resonant and nonresonant charge carrier transport mechanisms. This study reports STM break junction measurements of peptide nucleic acids (PNAs) with a G-block structure and contrasts the findings with previous results for DNA duplexes. The conductance of G-block PNA duplexes is much higher than that of the corresponding DNA duplexes of the same sequence; however, they do not display the strong even-odd dependence conductance oscillations found in G-block DNA. Theoretical analysis finds that the conductance oscillation magnitude in PNA is suppressed because of the increased level of electronic coupling interaction between G-blocks in PNA and the stronger PNA-electrode interaction compared to that in DNA duplexes. The strong interactions in the G-block PNA duplexes produce molecular conductances as high as 3% G0, where G0 is the quantum of conductance, for 5 nm duplexes.

Colossal anisotropic absorption of spin currents induced by chirality.

The chiral induced spin selectivity (CISS) effect, in which the structural chirality of a material determines the preference for the transmission of electrons with one spin orientation over that of the other, is emerging as a design principle for creating next-generation spintronic devices. CISS implies that the spin preference of chiral structures persists upon injection of pure spin currents and can act as a spin analyzer without the need for a ferromagnet. Here, we report an anomalous spin current absorption in chiral metal oxides that manifests a colossal anisotropic nonlocal Gilbert damping with a maximum-to-minimum ratio of up to 1000%. A twofold symmetry of the damping is shown to result from differential spin transmission and backscattering that arise from chirality-induced spin splitting along the chiral axis. These studies reveal the rich interplay of chirality and spin dynamics and identify how chiral materials can be implemented to direct the transport of spin current.

Chiral electrocatalysts eclipse water splitting metrics through spin control.

Continual progress in technologies that rely on water splitting are often hampered by the slow kinetics associated with the oxygen evolution reaction (OER). Here, we show that the efficiency of top-performing catalysts can be improved, beyond typical thermodynamic considerations, through control over reaction intermediate spin alignment during electrolysis. Spin alignment is achieved using the chiral induced spin selectivity (CISS) effect and the improvement in OER manifests as an increase in Faradaic efficiency, decrease in reaction overpotential, and change in the rate determining step for chiral nanocatalysts over compositionally analogous achiral nanocatalysts. These studies illustrate that a defined spatial orientation of the nanocatalysts is not necessary to exhibit spin selectivity and therefore represent a viable platform for employing the transformative role of chirality in other reaction pathways and processes.

Examining the Effects of Homochirality for Electron Transfer in Protein Assemblies.

Protein voltammetry studies of cytochrome c, immobilized on chiral tripeptide monolayer films, reveal the importance of the electron spin and the film's homochirality on electron transfer kinetics. Magnetic film electrodes are used to examine how an asymmetry in the standard heterogeneous electron transfer rate constant arises from changes in the electron spin direction and the enantiomer composition of the tripeptide monolayer; rate constant asymmetries as large as 60% are observed. These findings are rationalized in terms of the chiral induced spin selectivity effect and spin-dependent changes in electronic coupling. Lastly, marked differences in the average rate constant are shown between homochiral ensembles, in which the peptide and protein possess the same enantiomeric form, compared to heterochiral ensembles, where the handedness of the peptide layer is opposite to that of the protein or itself comprises heterochiral building blocks. These data demonstrate a compelling rationale for why nature is homochiral; namely, spin alignment in homochiral systems enables more efficient energy transduction.