Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon’s high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and −CO2 – groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si–N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.
Different cryo‐EM derived atomic models of in vivo tau filaments from patients with tauopathies consisted of R3 and R4 repeats of the microtubule‐binding domain. In comparison, only the R3 repeat forms the core of the heparin‐induced fibrils of the three repeat tau isoforms. For developing therapeutics, it is desirable to have an in vitro tau aggregation system producing fibrils corresponding to the disease morphology. Here we report the self‐aggregation of truncated tau segment R3R4 peptide without requiring heparin for aggregation induction. We used NMR spectroscopy and other biophysical methods to monitor the self‐aggregation of R3R4. We identified the hexapeptide region in R3 and β‐turn region in R4 as the aggregation initiating region of the protein. The solid‐state NMR of self‐aggregated R3R4 fibrils demonstrated that in addition to R3 residues, residues of R4 were also part of the fibril filaments. The presence of both R3 and R4 residues in the aggregation process and the core of fibril filaments suggest that the aggregation of R3R4 might resemble the in vivo aggregation process.
The sodium storage mechanism related to a high voltage slope region and a low voltage plateau region observed commonly in hard carbon (HC) is still a topic of debate. The difference in physicochemical properties of controllably synthesized carbon reflects the ambiguity in explaining their charge storage mechanism. Herein, we attempt to unravel the sodium storage mechanism using HCs with controlled 'closed' and 'open' porosities. Opening the 'closed' pores diminishes the plateau region but does not affect the slope region. Electrochemical measurements coupled with N 2 and CO 2 gas adsorption studies reveal a strong correlation between closed pores with a diameter (d), 0.4 < d < 1.5 nm and capacity contribution from the plateau region, supporting the adsorption/intercalationpore filling model. Solid-state NMR measurements confirm the near metallic state of sodium in the 'closed' micropores of HCs at potentials close to 0 V (vs. Na).
Sulfide-based solid electrolytes are one of the potential candidates for all-solid-state batteries due to their high ionic conductivity and low synthesis temperature compared to their oxide counterparts. However, the preparation methods involve the requirement of an inert atmosphere for ball milling, heating, and quenching facilities that severely limit their implementation, which necessitates a resurgence of interest in alternate synthesis approaches. Herein, a simple, accelerated, and energy-efficient method for the synthesis of highly crystalline cubic sodium thiophosphate solid electrolyte (Na 3 PS 4 ) is developed using the microwaveassisted irradiation technique. Along with impedance studies, 23 Na solid-state NMR spin-lattice relaxation experiments are performed to obtain insights into Na-ion mobility in Na 3 PS 4 solid electrolytes. The electrochemical properties and the interfacial stability of the electrolyte with the metallic sodium anode are thoroughly investigated and presented in this work. Further, a prototype full-cell constructed using a Na 3 V 2 (PO 4 ) 3 cathode, a Na 3 PS 4 solid electrolyte, and a modified sodium anode showed promising electrochemical properties. Although numerous studies focus on solid electrolyte interface modification and design, the simple and energy-efficient approach for sodium-ion solid electrolyte synthesis presented here will provide a meaningful advance to the accelerated synthesis of sulfide electrolyte-based all-solid-state batteries.
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