Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (Azo-1) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of Azo-1 (crystallized from a mixture of DMSO and H2O) reveal that it possesses supramolecular columnar packing along the b axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the Azo-1 fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the Azo-1 supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in Azo-1 is demonstrated by the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence of fluoride anions.

Two-dimensional (2-D) metal dichalcogenides like molybdenum disulfide (MoS 2 ) may provide a pathway to high-mobility channel materials that are needed for beyondcomplementary metal-oxide-semiconductor (CMOS) devices. Controlling the thickness of these materials at the atomic level will be a key factor in the future development of MoS 2 devices. In this study, we propose a layer-by-layer removal of MoS 2 using the atomic layer etching (ALET) that is composed of the cyclic processing of chlorine (Cl)-radical adsorption and argon (Ar) + ion-beam desorption. MoS 2 etching was not observed with only the Clradical adsorption or low-energy (< 20 eV) Ar + ion-beam desorption steps; however, the use of sequential etching that is composed of the Cl-radical adsorption step and a subsequent Ar + ion-beam desorption step resulted in the complete etching of one monolayer MoS 2 . Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) indicated the removal of one monolayer MoS 2 with each ALET cycle; therefore, the number of MoS 2 layers could be precisely controlled by using this cyclical etch method. In addition, no noticeable damage or etch residue was observed on the exposed MoS 2 .

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Histidine state (deprotonated, neutral, and protonated) is considered an important factor influencing the structural properties and aggregation mechanisms in amyloid β-peptides (Aβ), which are associated with the pathogenesis of Alzheimer's disease. Understanding the structural properties and aggregation mechanisms is a great challenge because two forms (the N-H or N-H tautomer) can exist in the free neutral state of histidine. Here, replica-exchange molecular dynamics simulation was performed to elucidate the changes in structure and the mechanism of aggregation influenced by tautomeric behaviors of histidine in Aβ(1-40). Our results show that sheet-dominating conformations can be found in the His6(δ)-His13(δ)-His14(δ) (δδδ) isomer with significant antiparallel sheet structures between R5-D7 and L34-G38, as well as between L17-F20 and L34-G38, implying that a new aggregation mechanism may exist to promote the generation of oligomers and/or aggregates. This work is helpful in understanding the fundamental tautomeric behaviors of neutral histidine in the process of aggregation.

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