Tunable band gap in few-layer graphene by surface adsorption

There is a tunable band gap in ABC-stacked few-layer graphene (FLG) via applying a vertical electric field, but the operation of FLG-based field effect transistor (FET) requires two gates to create a band gap and tune channel's conductance individually. Using first principle calculations, we propose an alternative scheme to open a band gap in ABC-stacked FLG namely via single-side adsorption. The band gap is generally proportional to the charge transfer density. The capability to open a band gap of metal adsorption decreases in this order: K/Al > Cu/Ag/Au > Pt. Moreover, we find that even the band gap of ABA-stacked FLG can be opened if the bond symmetry is broken. Finally, a single-gated FET based on Cu-adsorbed ABC-stacked trilayer graphene is simulated. A clear transmission gap is observed, which is comparable with the band gap. This renders metal-adsorbed FLG a promising channel in a single-gated FET device

Quantum Chemical Study on the Antioxidation Mechanism of Piceatannol and Isorhapontigenin toward Hydroxyl and Hydroperoxyl Radicals.

A systematic study of the antioxidation mechanisms behind hydroxyl (•OH) and hydroperoxyl (•OOH) radical scavenging activity of piceatannol (PIC) and isorhapontigenin (ISO) was carried out using density functional theory (DFT) method. Two reaction mechanisms, abstraction (ABS) and radical adduct formation (RAF), were discussed. A total of 24 reaction pathways of scavenging •OH and •OOH with PIC and ISO were investigated in the gas phase and solution. The thermodynamic and kinetic properties of all pathways were calculated. Based on these results, we evaluated the antioxidant activity of every active site of PIC and ISO and compared the abilities of PIC and ISO to scavenge radicals. According to our results, PIC and ISO may act as effective •OH and •OOH scavengers in organism. A4-hydroxyl group is a very important active site for PIC and ISO to scavenge radicals. The introducing of -OH or -OCH3 group to the ortho-position of A4-hydroxyl group would increase its antioxidant activity. Meanwhile, the conformational effect was researched, the results suggest that the presence and pattern of intramolecular hydrogen bond (IHB) are considerable in determining the antioxidant activity of PIC and ISO

Kinetic Reaction Mechanism of Sinapic Acid Scavenging NO₂ and OH Radicals: A Theoretical Study

<div><p>The mechanism and kinetics underlying reactions between the naturally-occurring antioxidant sinapic acid (SA) and the very damaging ·NO₂ and ·OH were investigated through the density functional theory (DFT). Two most possible reaction mechanisms were studied: hydrogen atom transfer (HAT) and radical adduct formation (RAF). Different reaction channels of neutral and anionic sinapic acid (SA^-) scavenging radicals in both atmosphere and water medium were traced independently, and the thermodynamic and kinetic parameters were calculated. We find the most active site of SA/SA^- scavenging ·NO₂ and ·OH is the –OH group in benzene ring by HAT mechanism, while the RAF mechanism for SA/SA^- scavenging ·NO₂ seems thermodynamically unfavorable. In water phase, at 298 K, the total rate constants of SA eliminating ·NO₂ and ·OH are 1.30×10⁸ and 9.20×10⁹ M^-1 S^-1 respectively, indicating that sinapic acid is an efficient scavenger for both ·NO₂ and ·OH.</p></div

The reaction enthalpies (Δ<i>H</i>), reaction Gibbs energies (Δ<i>G</i>) and energy barrier heights with ZPE corrections (Δ<i>E</i>+ZPE), at 298 K, for the reactions of SA^- with ·NO₂ and ·OH in water phase (in kJ/mol).

<p>The reaction enthalpies (Δ<i>H</i>), reaction Gibbs energies (Δ<i>G</i>) and energy barrier heights with ZPE corrections (Δ<i>E</i>+ZPE), at 298 K, for the reactions of SA^- with ·NO₂ and ·OH in water phase (in kJ/mol).</p