Synthesis and magnetic properties of platelet γ-Fe2O3 particles for medical applications using hysteresis-loss heating

Platelet γ-Fe₂O₃ particles of particle size less than 100 nm were prepared for medical applications that use the hysteresis-loss heating of ferromagnetic particles. The γ-Fe₂O₃ particles were obtained through the dehydration, reduction, and oxidation of platelet α-FeOOH particles, which were synthesized by the precipitation of ferric ions in an alkaline solution containing ethanolamine, and the crystals grown using a hydrothermal treatment. The γ-Fe₂O₃ particles contained dimples formed by the dehydration of α-FeOOH particles. The coercive force and the saturation magnetization of the γ-Fe₂O₃ particles were in the ranges 11.9 to 12.7 kA/m (150 to 160 Oe), and 70 to 72 Am²/kg (70 to 72 emu/g), respectively. The specific loss power of the γ-Fe₂O₃ particles, estimated from their temperature-raising property measured under a peak magnetic field of 50.9 kA/m (640 Oe) and at a frequency of 117 kHz, was 590 W/g. This value is higher than that of spherical cobalt-containing iron oxide particles having equivalent coercive force and saturation magnetization, reflecting the larger area of the minor hysteresis loop measured under a peak magnetic field of 50.9 kA/m (640 Oe).     

Resolving vibrational wave-packet dynamics of D2(+) using multicolor probe pulses

We demonstrate the generation and real-time observation of the vibrational wave packet of D(2)(+) by using a sub-10-fs extreme UV high-harmonic pump pulse and a three-color probe laser pulse whose wavelength ranges from near-IR to vacuum UV. This multicolor pump-probe scheme can provide us with a powerful experimental tool for investigating a variety of wave packets evolving with a time scale of ~20 fs.     

Mechanistic Aspects for the Modulation of Enzyme Reactions on the DNA Scaffold

Cells have developed intelligent systems to implement the complex and efficient enzyme cascade reactions via the strategies of organelles, bacterial microcompartments and enzyme complexes. The scaffolds such as the membrane or protein in the cell are believed to assist the co-localization of enzymes and enhance the enzymatic reactions. Inspired by nature, enzymes have been located on a wide variety of carriers, among which DNA scaffolds attract great interest for their programmability and addressability. Integrating these properties with the versatile DNA–protein conjugation methods enables the spatial arrangement of enzymes on the DNA scaffold with precise control over the interenzyme distance and enzyme stoichiometry. In this review, we survey the reactions of a single type of enzyme on the DNA scaffold and discuss the proposed mechanisms for the catalytic enhancement of DNA-scaffolded enzymes. We also review the current progress of enzyme cascade reactions on the DNA scaffold and discuss the factors enhancing the enzyme cascade reaction efficiency. This review highlights the mechanistic aspects for the modulation of enzymatic reactions on the DNA scaffold.     

2,2′-Tethered Binaphthyl-Embedded One-Handed Helical Ladder Polymers: Impact of the Tether Length on Helical Geometry and Chiroptical Property

Synthetic breakthroughs diversify the molecules and polymers available to chemists. We now report the first successful synthesis of a series of optically-pure 2,2′-tethered binaphthyl-embedded helical ladder polymers based on quantitative and chemoselective ladderization by the modified alkyne benzannulations using the 4-alkoxy-2,6-dimethylphenylethynyl group as the alkyne source, inaccessible by the conventional approach lacking the 2,6-dimethyl substituents. Due to the defect-free helix formation, the circular dichroism signal increased by more than 6 times the previously reported value. The resulting helical secondary structure can be fine-tuned by controlling the binaphthyl dihedral angle in the repeating unit with variations in the 2,2′-alkylenedioxy tethering groups by one carbon atom at a time. The optimization of the helical ladder structures led to a strong circularly polarized luminescence with a high fluorescence quantum yield (28 %) and luminescence dissymmetry factor (2.6×10⁻³).     

Hydroxymethylfurfural as an Intermediate of Cellulose Carbonization

Hydrogen bond donor solvents such as aromatic solvents inhibit the secondary degradation of cellulose-derived primary pyrolysis products. In a previous study, we found that the formation of solid carbonized products was completely inhibited during cellulose pyrolysis in aromatic solvents, with 5-hydroxymethylfurfural (5-HMF) recovered in certain yields instead. This indicated that 5-HMF is an intermediate in cellulose carbonization. To confirm this hypothesis, the thermal reactivity of 5-HMF was investigated. At 280 °C, pure 5-HMF polymerized into a hard glassy substance through OH group elimination, but further conversion was slow. When pyrolyzed in the presence of glycerol, a model of coexisting primary pyrolysis products from cellulose, a coupling reaction proceeded. Reactions characteristic of cellulose carbonization then occurred, including the formation of acidic groups and benzene-type structures in the solid products. These results confirmed the above hypothesis. The molecular mechanism of cellulose carbonization is discussed, focusing on the crystalline nature.     

Preparation of polysaccharide derivatives and their chiral recognition mechanism

Several new phenylcarbamate derivatives of cellulose and amylose having fluoro and methyl groups or 4-trimethylsilyl substituent on the phenyl groups were prepared and their chiral recognition abilities as chiral stationary phases for HPLC were evaluated. These derivatives are soluble in chloroform and exhibit chiral discrimination in ¹H NMR spectroscopy. Based on the above results and molecular mechanics calculation of interaction energies between the derivatives and enantiomers, the mechanism of chiral discrimination is discussed.     

One-Handed Helical Tubular Ladder Polymers for Chromatographic Enantioseparation**

Defect-free one-handed contracted helical tubular ladder polymers with a π-electron-rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random-coil precursor polymers containing 6,6′-linked-1,1′-spirobiindane-7,7′-diol-based chiral monomer units. The resulting tightly-twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random-coil precursor polymer and analogous rigid-rod extended helical ribbon-like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π-electron-rich cylindrical helical cavity formed in the tightly-twisted tubular helical ladder structures is of key importance for producing the highly-enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π-π and/or hydrophobic interactions.     

Peculiar ‘Reptational’ Movements of Single Synthetic Polymer Chains on Substrate Observed by AFM

Peculiar ‘reptational’ movements of isotactic PMMA chains on mica are observed by in situ AFM. The polymer molecules comprise long flexible chains that exhibit reptative, or snake‐like, motion on the substrate along the direction of the polymer chain. Intriguingly, some chains underwent forward then backward motion in which the head of the chain moved in a curvilinear manner along the previous contours of the polymer chain. No limitation in the direction of movement for the ends of the polymer chain was anticipated based on an assumed reptational mechanism. As a result, the chains recovered a conformation that had been adopted prior to the initial movement. Several factors that may affect the movement are discussed.

     

Synthesis,Structures, and Complexation with Phenolic Guests of Acridone-Incorporated Arylene–Ethynylene Macrocyclic Compounds

Acridone units were incorporated into the arylene–ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone-2,7-diyl units and three 1,3-phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X-ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. ¹H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×10³ L mol⁻¹ for hydroquinone or resorcinol guests in CDCl₃ at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds.