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1. Effect of Intra-Molecular Coupling Within Double Segmented Molecules on Equilibrium Magnetic Properties of Molecular Spintronics Devices 

   Suh, Pius ; Savadkoohi, Marzieh ; Mutunga, Eva ; Grizzle, Andrew ; Dahal, Bishnu R. ; D’Angelo, Christopher ; Tyagi, Pawan ( January 2022 , EMC-2022, Columbus, OH)

   The intra-molecular coupling within multiple units of paramagnetic molecules can produce various effects on molecular spintronics devices (MSD). The effect of the nature of the strong magnetic coupling between a multi-segmented molecule with two ferromagnetic (FM) electrodes is unexplored. Such knowledge is of critical importance for magnetic tunnel junction-based molecular spintronics devices (MTJMSD). MTJMSD architecture experimentally allows very strong bonding between complex molecules and ferromagnetic electrodes. In our prior studies, we have extensively studied the atomic analog of the single molecular magnet. That means whole molecular geometry and internal features were approximated to appear as one atom representing that molecule. To advance the understanding of the impact of internal molecular structure on MTJMSD, we have focused on multi-segmented molecules. This research aims to fill the knowledge gap about the intramolecular coupling role in the magnetic properties of the MTJMSD. This study explored a double-segmented molecule containing two atomic sections, each with a net spin state and interacting via Heisenberg exchange coupling within molecules and with ferromagnetic electrodes. The effect of thermal energy was explored on the impact of intra-molecular coupling on the MTJMSD Heisenberg model. We performed Monte Carlo simulations(MCS) to study various possibilities in the strong molecule-ferromagnet coupling regime. This research provides insights into the influence of complex molecules on MSD that can be employed in futuristic computers and novel magnetic meta-materials. 

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2. Biological nanopores elucidate the differences between isomers of mercaptobenzoic-capped gold clusters

   https://doi.org/10.1039/D0CP05671E  

   Cox, Bobby D. ; Martin, Charles R. ; Bertino, Massimo F. ; Reiner, Joseph E. ( January 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   Identification of isomers using traditional mass spectroscopy methods has proven an interesting challenge due to their identical mass to charge ratios. This proves particularly consequential for gold clusters, as subtle variations in the ligand and cluster structure can have drastic effects on the cluster functionalization, solubility, and chemical properties. Biological nanopores have proven an effective tool in identifying subtle variations at the single molecule limit. This paper reports on the ability of an α-hemolysin (αHL) pore to differentiate between para -, meta -, and ortho - ( p -, m -, and o -, respectively) mercaptobenzoic acid ligands attached to gold clusters at the single cluster limit. Detecting differences between p -MBA and m -MBA requires pH-dependent studies that illustrate the role inter-ligand binding plays in stabilizing m -MBA-capped clusters. Additionally, this paper investigates the difference in behavior for these clusters when isolated, and when surrounded by small ligand–Au complexes (Au n L m , n = 0, 1, 2… and m = 1, 2,…) that are present following cluster synthesis. It is found that continuous exposure of clusters to freely diffusing ligand complexes stabilizes the clusters, while isolated clusters either disintegrate or exit the nanopore in seconds. This has implications for long term cluster stability. 

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3. Dramatic Effects of Electrode Metal on Tunnel Junction-Based Molecular Spintronic Devices

   Pawan Tyagi ; Eva Mutunga, Hayden Brown ( January 2022 , MRS 2022, Hawaii)

   Magnetic tunnel junction (MTJ) can serve as an excellent testbed for connecting Molecule between two ferromagnetic electrodes. A paramagnetic molecule covalently bonded to two ferromagnetic electrodes with two thiol functional groups can produce intriguing transport and magnetic properties. We have chemically bonded paramagnetic molecules between two ferromagnetic electrodes of a MTJ along the exposed side edges. In this paper we discussed the observation of Molecule induced dramatic changes in the magnetic and transport properties of the conventional magnetic tunnel junctions. Paramagnetic molecules were chemically bonded to ferromagnetic electrodes to bridge them across the insulating spacer along the exposed edges. Paramagnetic molecular channels along the tunnel junction edges decreased the overall current, through tunnel barrier and molecular channels, > 5 orders of magnitude below the leakage current of the bare tunnel junction at room temperature. These molecules caused significant changes in the spin density of states due to potential spin filtering effect. Also, paramagnetic molecules produced antiferromagnetic coupling between the affected magnetic electrodes. In this state spin transport in the magnetic tunnel junction based molecular devices plummeted by several orders. It is also noteworthy that our experimental studies provide a platform to connect a vast variety of ferromagnetic leads to the even broader array of high potential molecules such as single molecular magnets, porphyrin, and single ion molecules. The strength of exchange coupling between ferromagnetic electrodes and molecules can be tailored by utilizing different tethers and terminal functional groups. The MTJMSD can provide an advanced form of logic and memory devices, including a testbed for the Molecule based quantum computation devices. Future study about the interaction between molecular magnets and ferromagnets and interaction of thiol ended alkanes with ferromagnets will be of very valuable. This study indicates the potential of magnetic molecules as a mean to transforming conventional magnetic tunnel junctions and producing unprecedented magnetic and transport properties. 

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4. N-Type Bismuth Telluride Nanocomposite Materials Optimization for Thermoelectric Generators in Wearable Applications

   https://doi.org/10.3390/ma12091529  

   Nozariasbmarz, Amin ; Krasinski, Jerzy S. ; Vashaee, Daryoosh ( May 2019 , Materials)

   Thermoelectric materials could play a crucial role in the future of wearable electronic devices. They can continuously generate electricity from body heat. For efficient operation in wearable systems, in addition to a high thermoelectric figure of merit, zT, the thermoelectric material must have low thermal conductivity and a high Seebeck coefficient. In this study, we successfully synthesized high-performance nanocomposites of n-type Bi2Te2.7Se0.3, optimized especially for body heat harvesting and power generation applications. Different techniques such as dopant optimization, glass inclusion, microwave radiation in a single mode microwave cavity, and sintering conditions were used to optimize the temperature-dependent thermoelectric properties of Bi2Te2.7Se0.3. The effects of these techniques were studied and compared with each other. A room temperature thermal conductivity as low as 0.65 W/mK and high Seebeck coefficient of −297 μV/K were obtained for a wearable application, while maintaining a high thermoelectric figure of merit, zT, of 0.87 and an average zT of 0.82 over the entire temperature range of 25 °C to 225 °C, which makes the material appropriate for a variety of power generation applications. 

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5. Road-blocker HSP disease mutation disrupts pre-organization for ATP hydrolysis in kinesin through a second sphere control

   https://doi.org/10.1073/pnas.2215170120  

   Manna, Rabindra Nath ; Onuchic, José N. ; Jana, Biman ( January 2023 , Proceedings of the National Academy of Sciences)

   Kinesin motor proteins perform several essential cellular functions powered by the adenosine triphosphate (ATP) hydrolysis reaction. Several single-point mutations in the kinesin motor protein KIF5A have been implicated to hereditary spastic paraplegia disease (HSP), a lethal neurodegenerative disease in humans. In earlier studies, we have shown that a series of HSP-related mutations can impair the kinesin’s long-distance displacement or processivity by modulating the order–disorder transition of the linker connecting the heads to the coiled coil. On the other hand, the reduction of kinesin’s ATP hydrolysis reaction rate by a distal asparagine-to-serine mutation is also known to cause HSP disease. However, the molecular mechanism of the ATP hydrolysis reaction in kinesin by this distal mutation is still not fully understood. Using classical molecular dynamics simulations combined with quantum mechanics/molecular mechanics calculations, the pre-organization geometry required for optimal hydrolysis in kinesin motor bound to α/β-tubulin is determined. This optimal geometry has only a single salt-bridge (of the possible two) between Arg203-Glu236, putting a reactive water molecule at a perfect position for hydrolysis. Such geometry is also needed to create the appropriate configuration for proton translocation during ATP hydrolysis. The distal asparagine-to-serine mutation is found to disrupt this optimal geometry. Therefore, the current study along with our previous one demonstrates how two different effects on kinesin dynamics (processivity and ATP hydrolysis), caused by a different set of genotypes, can give rise to the same phenotype leading to HSP disease. 

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