Remarkable Problem-Solving Ability of Unicellular Amoeboid Organism and its Mechanism

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Surface Structure, Adsorption, and Thermal Desorption Behaviors of Methaneselenolate Monolayers on Au(111) from Dimethyl Diselenides

To understand the effect of headgroups (i.e., sulfur and selenium) on surface structure, adsorption states, and thermal desorption behaviors of self-assembled monolayers (SAMs) on Au(111), we examined methanethiolate (CH₃–S, MS) and metheneselenolate (CH₃–Se, MSe) monolayers formed from dimethyl disulfide (DMDS) and dimethyl diselenide (DMDSe) molecules by ambient vapor-phase deposition. Scanning tunneling microscopy imaging revealed that DMDS molecules on Au(111) after a 1 h deposition form MS monolayers containing a disordered phase and an ordered row phase with an inter-row spacing of 1.51 nm, whereas DMDSe molecules form long-range-ordered MSe monolayers with a (√3 × 3√3)<i>R</i>30° structure. X-ray photoelectron spectroscopy measurements showed that MS or MSe monolayers chemisorbed on Au(111) were formed via S–S bond cleavage of DMDS or Se–Se bond cleavage of DMDSe. On the other hand, we monitored three main desorption fragments for MS and MSe monolayers using TDS monomers (CH₃S⁺, CH₃Se⁺), parent mass species (CH₃SH⁺, CH₃SeH⁺), and dimers (CH₃S–SCH₃⁺, CH₃Se–SeCH₃⁺). Interestingly, we found that thermal desorption behaviors of MSe monolayers were markedly different from those of MS monolayers. All desorption peaks for MSe monolayers were observed at a higher temperature compared with MS monolayers, suggesting that the adsorption affinity of selenium atoms for the Au(111) surface is stronger than that of sulfur atoms. In addition, the desorption intensity of dimer fragments for MSe monolayers was much lower than for MS monolayers, indicating that selenolate SAMs on Au(111) did not undergo their dimerization efficiently during thermal heating compared with thiolate SAMs. Our results provide new insight into understanding the surface structure and thermal desorption behavior of MSe monolayers on Au(111) surface by comparing those of MS monolayers

Stimulus-Responsive Azobenzene Supramolecules: Fibers, Gels, and Hollow Spheres

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-((<i>E</i>)-phenyldiazenyl)­phenyl)­benzene-1,3,5-tricarboxamide (<b>Azo-1</b>) 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 <b>Azo-1</b> (crystallized from a mixture of DMSO and H₂O) reveal that it possesses supramolecular columnar packing along the <i>b</i> axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the <b>Azo-1</b> 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 <b>Azo-1</b> 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 <b>Azo-1</b> is demonstrated by the behavior of the analogous, ester-containing tris­(4-((<i>E</i>)-phenyldiazenyl)­phenyl)­benzene-1,3,5-tricarboxylate (<b>Azo-2</b>) and by the hydrogen abstraction in the presence of fluoride anions

Stimulus-Responsive Azobenzene Supramolecules: Fibers, Gels, and Hollow Spheres

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-((<i>E</i>)-phenyldiazenyl)­phenyl)­benzene-1,3,5-tricarboxamide (<b>Azo-1</b>) 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 <b>Azo-1</b> (crystallized from a mixture of DMSO and H₂O) reveal that it possesses supramolecular columnar packing along the <i>b</i> axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the <b>Azo-1</b> 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 <b>Azo-1</b> 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 <b>Azo-1</b> is demonstrated by the behavior of the analogous, ester-containing tris­(4-((<i>E</i>)-phenyldiazenyl)­phenyl)­benzene-1,3,5-tricarboxylate (<b>Azo-2</b>) and by the hydrogen abstraction in the presence of fluoride anions