Mössbauer parameters of a highly anisotropic low-spin ferric compound: Bis[tris(N-methylimidazol-2-yl) hydroxymethane] ferrate (III) tetrafluoroborate

We have analyzed the Mössbauer spectra of a highly anisotropic low-spin ferric compound, [Fe(TICOH)₂](BF₄)₃, taken in frozen solution as a function of temperature and field. Unlike other low-spin ferric compounds, [Fe(TICOH)₂](BF₄)₃ shows a sharp six-line pattern with an overall s;litting of 14.2 mm/s in an applied field at 4.2 K. Good simulations are obtained using the model of Oosterhuis and Lang with a crystal field of axial symmetry. At higher temperature spin fluctuations become important, and a dynamic lineshape model with temperature- and field-dependent relaxation rates is used to simulate the data.     

Scalable scheme for entangling multiple ququarts using linear optical elements

We report a scalable linear optical scheme for generating entangled states of multiple ququarts in which the individual single-ququart state is prepared with the biphoton polarization state of frequency-nondegenerate spontaneous parametric down-conversion. The output state is calculated with the full consideration of the higher order effect (double-pair events) of spontaneous parametric down-conversion. Scalability to multiple-ququart entanglement is demonstrated with examples: linear optical entanglement of three and four individual biphoton ququarts.     

Two-Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin-film through solvothermal method and on-solid-surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin-film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin-film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two-dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF-PP or 2D BECOF-PN ) by employing a surfactant-monolayer-assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF-PP is featured as free-standing thin film with large single-crystalline domains up to ≈60 μm² and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF-PP film on silicon nanowire-based field-effect transistor is demonstrated as a bio-inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process.     

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory-Impairing Anti-Parallel Aβ Dimers

Amyloid-β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti-parallel variants of Aβ(1–40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti-parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA-approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer-specific molecules.     

Revealing Isolated M−N3C1 Active Sites for Efficient Collaborative Oxygen Reduction Catalysis

Single atom catalysts (SACs) are of great importance for oxygen reduction, a critical process in renewable energy technologies. The catalytic performance of SACs largely depends on the structure of their active sites, but explorations of highly active structures for SAC active sites are still limited. Herein, we demonstrate a combined experimental and theoretical study of oxygen reduction catalysis on SACs, which incorporate M−N₃C₁ site structure, composed of atomically dispersed transition metals (e.g., Fe, Co, and Cu) in nitrogenated carbon nanosheets. The resulting SACs with M−N₃C₁ sites exhibited prominent oxygen reduction catalytic activities in both acidic and alkaline media, following the trend Fe−N₃C₁ > Co−N₃C₁ > Cu−N₃C₁. Theoretical calculations suggest the C atoms in these structures behave as collaborative adsorption sites to M atoms, thanks to interactions between the d/p orbitals of the M/C atoms in the M−N₃C₁ sites, enabling dual site oxygen reduction.     

Novel quinoxaline-based organic sensitizers for dye-sensitized solar cells

Novel quinoxaline-based organic sensitizers using vertical (RC-21) and horizontal (RC-22) conjugation between an electron-donating triphenylamine unit and electron-accepting quinoxaline unit have been synthesized and used for dye-sensitized solar cells (DSSCs), leading to the relatively high power conversion efficiencies of 3.30 and 5.56% for RC-21 and RC-22, respectively. This result indicates that the quinoxaline electron-accepting unit is quite a promising candidate in organic sensitizers.     

Human salivary gland stem cells ameliorate hyposalivation of radiation-damaged rat salivary glands

Salivary function in mammals may be defective for various reasons, such as aging, Sjogren''s syndrome or radiation therapy in head and neck cancer patients. Recently, tissue-specific stem cell therapy has attracted public attention as a next-generation therapeutic reagent. In the present study, we isolated tissue-specific stem cells from the human submandibular salivary gland (hSGSCs). To efficiently isolate and amplify hSGSCs in large amounts, we developed a culture system (lasting 4–5 weeks) without any selection. After five passages, we obtained adherent cells that expressed mesenchymal stem cell surface antigen markers, such as CD44, CD49f, CD90 and CD105, but not the hematopoietic stem cell markers, CD34 and CD45, and that were able to undergo adipogenic, osteogenic and chondrogenic differentiation. In addition, hSGSCs were differentiated into amylase-expressing cells by using a two-step differentiation method. Transplantation of hSGSCs to radiation-damaged rat salivary glands rescued hyposalivation and body weight loss, restored acinar and duct cell structure, and decreased the amount of apoptotic cells. These data suggest that the isolated hSGSCs, which may have characteristics of mesenchymal-like stem cells, could be used as a cell therapy agent for the damaged salivary gland.     

Regioselective inversion of the hydroxyl group in D-ribo-phytosphingosine via a cyclic sulfate and bis-sulfonate intermediate

The selective synthesis of D-xylo- and D-lyxo-phytosphingosines from commercially available D-ribo-phytosphingosine is described. Thermolysis of the N-carbonyl protected cyclic sulfate led to an inversion of configuration of the proximal hydroxyl group to give the xylo-isomer, whereas the corresponding bis-sulfonate resulted in an inversion of configuration of the distal hydroxyl group to give the lyxo-isomer. This study allowed the comparison between a cyclic sulfate and a bis-sulfonate in an intramolecular substitution reaction involving a carbonyl oxygen nucleophile.     

Micropatterning of proteins on ion beam‐induced poly(acrylic acid)‐grafted polyethylene film

Micropatterns of proteins were created by using patterned ion beam irradiation onto a polyethylene film and graft polymerization of acrylic acid. Acrylic acid was selectively graft polymerized on the irradiated regions. The results of the grafting study revealed that the optimum fluence to achieve the maximum grafting degree was 1 × 10¹⁵ ions/cm². Biotin was covalently immobilized on the grafted regions of the polyethylene film. Protein patterning was achieved through specific binding of biotin and streptavidin. The resolved protein patterns with the maximum fluorescence intensity were achieved on the poly(acrylic acid) (PAA)‐grafted polyethylene films prepared at the fluence of 1 × 10¹⁵ ions/cm². This method can be used for patterning of various biomolecules and for further biological applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Mössbauer study of intergranular phase in Nd 8 Fe86 − x Nb x B6(x = 0, 1, 2, 3) nanocomposite magnet

Nd₈Fe_86???x Nb _x B₆ (x = 0, 1, 2, 3) nanocomposite magnet has been studied by Mössbauer spectroscopy and nanostructure observation. It was found that intergranular phase formed between α-Fe and Nd₂Fe₁₄B phase in NdFeNbB alloys plays a significant role on the magnetic properties. By the addition of Nb into Nd₈Fe₈₆B₆ composition, coercivity was found to increase by 25% due to the grain refinement of both the soft and hard magnetic phases which was decreased from 50 nm of virgin Nd₈Fe₈₆B₆ to 25 nm in Nd₈Fe₈₅Nb₁B₆ alloys. The role of Nb addition was confirmed to stabilize the Nd₂Fe₁₄B lattice preventing from thermal vibration of the corresponding sites at where Fe atoms are substituted by Nb in the Nd₂Fe₁₄B lattice. The enhanced coercivity was originated from the exchange hardening of soft and amorphous phases surrounding the hard magnetic Nd₂Fe₁₄B crystal.