Iron mobilization from intact ferritin: effect of differential redox activity of quinone derivatives with NADH/O2 and in situ-generated ROS.

Ferritins are multimeric nanocage proteins that sequester/concentrate excess of free iron and catalytically synthesize a hydrated ferric oxyhydroxide bio-mineral. Besides functioning as the primary intracellular iron storehouses, these supramolecular assemblies also oversee the controlled release of iron to meet physiologic demands. By virtue of the reducing nature of the cytosol, reductive dissolution of ferritin-iron bio-mineral by physiologic reducing agents might be a probable pathway operating in vivo. Herein, to explore this reductive iron-release pathway, a series of quinone analogs differing in size, position/nature of substituents and redox potentials were employed to relay electrons from physiologic reducing agent, NADH, to the ferritin core. Quinones are well known natural electron/proton mediators capable of facilitating both 1/2 electron transfer processes and have been implicated in iron/nutrient acquisition in plants and energy transduction. Our findings on the structure-reactivity of quinone mediators highlight that iron release from ferritin is dictated by electron-relay capability (dependent on E1/2 values) of quinones, their molecular structure (i.e., the presence of iron-chelation sites and the propensity for H-bonding) and the type/amount of reactive oxygen species (ROS) they generate in situ. Juglone/Plumbagin released maximum iron due to their intermediate E1/2 values, presence of iron chelation sites, the ability to inhibit in situ generation of H2O2 and form intramolecular H-bonding (possibly promotes semiquinone formation). This study may strengthen our understanding of the ferritin-iron-release process and their significance in bioenergetics/O2-based cellular metabolism/toxicity while providing insights on microbial/plant iron acquisition and the dynamic host-pathogen interactions.

Porphyrin nanoribbon-based spin filtering devices.

Advancement in molecular electronics opens up another new domain with a new possibility of realizing its spin-polarized version, which is called molecular spintronics. This novel domain has a range of applications such as high-capacity storage devices and quantum computers. Several contemporary researchers have considered porphyrin molecules and their derivatives as potential candidates for molecular devices. Herein, using the first-principles calculations, we propose a porphyrin nanoribbon-based system for spin-filtering applications. Such a system shows robust half-metallicity and also exhibits itinerant magnetism. Our calculated spin transport properties exhibit that our device can give 100% spin-polarizing efficiency, which is very promising for next-generation spin-filtering applications.

Ferromagnetism in magnesium chloride monolayer with an unusually large spin-up gap.

The primary research target of the rapidly evolving spintronic industry is to design highly efficient novel materials that consume very low power and operate with high speed. Main group based ferromagnetic half-metallic materials are very promising due to their long spin-relaxation time. In recent years, the discovery of superconducting state with high critical temperature in a magnesium based system (MgB2) invigorated researchers due to its simple crystal structure and intriguing results, leading to its use as a good material for large scale application in electronic devices. Here, we report ferromagnetism and strong half-metallicity in another Mg-based system, which can be a promising material for spintronics based devices rather than for electronic devices (such as MgB2). Based on the first principle calculations, we report here a series of magnetic half-metallic magnesium chloride based monolayers [Mg0.89δ0.11Cl2, Mg0.78δ0.22Cl2, and Mg0.67δ0.33Cl2 (MgCl3)]. This MgCl3 phase has a similar pattern as that in CrI3, which has drawn remarkable attention worldwide as the first intrinsic 2D magnet. These magnesium chloride monolayer based systems are 100% spin-polarized, and promising for scattering-less transport due to strong half-metallicity and large spin-up gap (∼6.135-6.431 eV). The unusually large spin-up gap in our proposed system may shield spin current leakage even in nanoscale device. Further investigation explores a ferromagnetic ordering in Mg0.89δ0.11Cl2 with a Curie temperature of 250 K, which makes the system viable for operation at temperatures slightly lower than the room temperature. High magnetic anisotropy energy (MAE) in Mg0.89δ0.11Cl2 (452.84 µeV) indicates that the energy required to flip the spin is high, and therefore inhibits spin fluctuation. These results suggest a promising way to discover MgCl2-based 2D spin valves, GMR, TMR and other spintronics devices.

First-Principles Study of Magnesium Peroxide Nucleation for Mg-Air Battery.

Recently, rechargeable non-aqueous Mg-air batteries have gained a lot of interest as the next-generation energy storage device due to the high theoretical volumetric density (3832 Ah L-1 for Mg anode vs. 2062 Ah L-1 for Li), low cost and safety. The field of Mg-air batteries is in the initial stage of development having a limited number of experimental and theoretical reports, in which mainly a carbon cathode is used; however, the information regarding the structural form of carbon is still missing. In this work, using first-principles density functional theory (DFT) calculations, we demonstrate the possibility of graphene and graphite as a cathode material towards Mg-air batteries by studying the initial MgO and MgO2 nucleation processes on the surfaces of graphene and graphite. The calculated free energy diagrams for the redox reactions of oxygen are used to identify the rate-determining step controlling the overpotentials for initial nucleation of MgO and MgO2 . We observe that graphene and graphite surfaces show similar reactivity towards the nucleation of MgO or MgO2 , and the overpotential of the controlling steps for MgO2 nucleation is comparatively less than that of MgO nucleation, which is supported by a recent experimental study, where a higher discharge voltage was observed in a cell having a mixed MgO/MgO2 discharge product than MgO-based cells. Furthermore, the preferable formation of MgO2 cluster compared to MgO on the graphene surface during the ab initio molecular dynamic (AIMD) simulations confirms the selectivity of MgO2 formation over MgO as the final discharge product. We believe that our study will be helpful in understanding the initial nucleation processes during the oxygen reduction reaction (ORR) mechanism and development of suitable cathodes for the future Mg-air batteries.

High Curie temperature and half-metallicity in an atomically thin main group-based boron phosphide system: long range ferromagnetism.

Transition metal-free magnetism and half-metallicity are currently drawing remarkable attention due to their potential future applications in spintronics devices. Using state-of-the-art density functional theory (DFT) calculations, we have considered Be and Mg incorporated in atomically thin boron phosphide (BP) systems for possible spintronics applications. Interestingly, our results reveal that Mg and Be substitution at P-sites exhibits ferromagnetism and half-metallicity. We also found long range ferromagnetism and a high Curie temperature (TC = ∼494 K) in the MgP@BP system; this Curie temperature is remarkably high amongst the existing main group-based 2D materials reported to date. The calculated magnetic anisotropy energy (MAE) is as high as 21.6 µeV per Mg. The stability study of the Mg-doped BP systems shows excellent dynamical, thermal and mechanical properties. Thus, a material with this high Curie temperature can function at elevated temperatures for future nano-spintronics device applications.