Tunneling in the Hydrogen-Transfer Reaction from a Vitamin E Analog to an Inclusion Complex of 2,2-Diphenyl-1-picrylhydrazyl Radical with β-Cyclodextrin in an Aqueous Buffer Solution at Ambient Temperature

Recently, increasing attention has been paid to quantum mechanical behavior in biology. In this study, we investigated the involvement of quantum mechanical tunneling in the hydrogen-transfer reaction from Trolox, a water-soluble analog of vitamin E (α-tocopherol), to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) in a phosphate buffer solution (0.05 M, pH 7.0). DPPH• was used as a reactivity model of reactive oxygen species and solubilized in water using β-cyclodextrin (β-CD). The second-order rate constants, kH and kD, in 0.05 M phosphate buffer solutions prepared with H2O (pH 7.0) and D2O (pD 7.0), respectively, were determined for the reaction between Trolox and DPPH•, using a stopped-flow technique at various temperatures (283–303 K). Large kinetic isotope effects (KIE, kH/kD) were observed for the hydrogen-transfer reaction from Trolox to the β-CD-solubilized DPPH• in the whole temperature range. The isotopic ratio of the Arrhenius prefactor (AH/AD = 0.003), as well as the isotopic difference in the activation energies (19 kJ mol−1), indicated that quantum mechanical tunneling plays a role in the reaction.

Theoretical Prediction of Heterogeneous Integration of Dissimilar Semiconductor with Various Ultra-Thin Oxides and 2D Materials

In this paper, we build a numerical p-n Si/GaAs heterojunction model using quantum-mechanical tunneling theory with various quantum tunneling interfacial materials including two-dimensional (2D) materials such as hexagonal boron nitride (h-BN) and graphene, and ALD-enabled oxide materials such as HfO2, Al2O3, and SiO2. Their tunneling efficiencies and tunneling currents with different thicknesses were systematically calculated and compared. Multiphysics modeling was used with the aforementioned tunneling interfacial materials to analyze changes in the strain under different temperature conditions. Considering the transport properties and thermal-induced strain analysis, Al2O3, among three oxide materials, and graphene in 2D materials are favorable material choices that offer the highest heterojunction quality. Overall, our results offer a viable route in guiding the selection of quantum tunneling materials for a myriad of possible combinations of new heterostructures that can be obtained with an ultra-thin tunneling intermediate layer.

Spin-forbidden heavy-atom tunneling in the ring-closure of triplet cyclopentane-1,3-diyl

In 1975, Buchwalter and Closs reported one of the first examples of heavy-atom quantum mechanical tunneling (QMT) by studying the ring closure of triplet cyclopentane-1,3-diyl to singlet bicyclo[2.1.0]pentane in cryogenic...

Contact Electrification by Quantum-Mechanical Tunneling

A simple model of charge transfer by loss-less quantum-mechanical tunneling between two solids is proposed. The model is applicable to electron transport and contact electrification between e.g. a metal and a dielectric solid. Based on a one-dimensional effective-mass Hamiltonian, the tunneling transmission coefficient of electrons through a barrier from one solid to another solid is calculated analytically. The transport rate (current) of electrons is found using the Tsu-Esaki equation and accounting for different Fermi functions of the two solids. We show that the tunneling dynamics is very sensitive to the vacuum potential versus the two solids conduction-band edges and the thickness of the vacuum gap. The relevant time constants for tunneling and contact electrification, relevant for triboelectricity, can vary over several orders of magnitude when the vacuum gap changes by one order of magnitude, say, 1 Å to 10 Å. Coulomb repulsion between electrons on the left and right material surfaces is accounted for in the tunneling dynamics.