Flexible C−C Bonds: Reversible Expansion,Contraction, Formation,and Scission of Extremely Elongated Single Bonds

Since carbon–carbon (C−C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp³)−C(sp³) single bond by light and heat. This flexibility of a C−C bond was demonstrated by X-ray analysis and Raman spectroscopy of hexaphenylethane (HPE)-type hydrocarbons with two spiro-dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single-crystalline phase. The force constant of the contracted C−C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C−C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C−C bond can be deactivated/activated by light/heat.     

Hexaarylbutadiene: A Versatile Scaffold with Tunable Redox Properties towards Organic Near‐Infrared Electrochromic Material

When the 1,1,4,4‐tetraanilinobutadiene skeleton is attached with two halogenated aryl units at the 2,3‐positions, they undergo facile two‐electron oxidation to give stable dicationic dyes which exhibit a near‐infrared (NIR) absorption whereas the neutral dienes show only pale color. Therefore, a distinct electrochromic response with an absorption change in the NIR region is achieved, which is attracting considerable recent attention from the viewpoint of bioimaging. Herein, we demonstrate that the redox potentials of the 1,1,4,4‐tetraanilinobutadiene can be precisely controlled by the donating properties of the amino group on the aniline unit as well as the number of halogen atoms on the aryl units at 2,3‐positions on the butadiene. In contrast, the NIR absorption bands mainly depend on the number of halogen atoms irrespective to the donating properties of aniline unit. Thus, the hexaarylbutadiene skeleton is proven to be a versatile scaffold to develop less‐explored organic NIR electrochromic materials, whose redox and spectroscopic properties can be finely tuned by modifying/attaching the proper substituents.     

Cavitand‐Based Pd‐Pyridyl Coordination Capsules: Guest‐Induced Homo‐ or Heterocapsule Selection and Applications of Homocapsules to the Protection of a Photosensitive Guest and Chiral Capsule Formation

A 2 : 4 mixture of tetrakis[4‐(4‐pyridyl)phenyl]cavitand ( 1 ) or tetrakis[4‐(4‐pyridyl)phenylethynyl]cavitand ( 2 ) and Pd(dppp)(OTf)₂ self‐assembles into a homocapsule { 1 ₂ ? [Pd(dppp)]₄}⁸⁺ ? (TfO^?)₈ ( C1 ) or { 2 ₂ ? [Pd(dppp)]₄}⁸⁺ ? (TfO^?)₈ ( C2 ), respectively, through Pd?Npy coordination bonds. A 1 : 1 : 4 mixture of 1 , 2 , and Pd(dppp)(OTf)₂ produced a mixture of homocapsules C1 , C2 , and a heterocapsule { 1 ? 2 ? [Pd(dppp)]₄}⁸⁺ ? (TfO^?)₈ ( C3 ) in a 1 : 1 : 0.98 mole ratio. Selective formation (self‐sorting) of homocapsules C1 and C2 or heterocapsule C3 was controlled by guest‐induced encapsulation under thermodynamic control. Applications of Pd?Npy coordination capsules with the use of 1 were demonstrated. Capsule C1 serves as a guard nanocontainer for trans‐4,4′‐diacetoxyazobenzene to protect against the trans‐to‐cis photoisomerization by encapsulation. A chiral capsule { 1 ₂ ? [Pd((R)‐BINAP)]₄}⁸⁺ ? (TfO^?)₈ ( C5 ) was also constructed. Capsule C5 induces supramolecular chirality with respect to prochiral 2,2′‐bis(alkoxycarbonyl)‐4,4′‐bis(1‐propynyl)biphenyls by diastereomeric encapsulation through the asymmetric suppression of rotation around the axis of the prochiral biphenyl moiety.     

Development of tubulin-polymerization inhibitors based on the thalidomide skeleton

We synthesized a series of compounds based on the potent tubulin-polymerization inhibitor 5-hydroxy-2-(2,6-diisopropylphenyl)-1H-isoindole-1,3-dione [5HPP-33 (3)], which is structurally derived from thalidomide (1), and investigated their inhibitory effects on tubulin polymerization. Direct interaction between 5HPP-33 (3) and alpha,beta-tubulin heterodimer protein was demonstrated by means of a surface plasmon resonance study.     

Chromic and fluorescence response system based on the dihydrophenanthroline-bipyridine skeleton: dynamic redox behavior and metal binding properties

The spiro-acridan/acridinium-based dynamic redox pair (1/2²⁺) transduces the electrochemical input into UV-vis and fluorescence spectra, whereas the 2,2′-bipyridine units in 1 works as a bidentate ligand for metal ions. X-ray structural analyses of this redox pair and the corresponding Zn-complexes [1-ZnI₂/2²⁺-Zn²⁺(OTf⁻)₄] demonstrate drastic structural changes upon electron-transfer, thus metal binding properties are modified by redox reactions.     

Contribution of stress wave and cavitation bubble in evaluation of cell–cell adhesion by femtosecond laser-induced impulse

When an intense femtosecond laser is focused in a cell culture medium, shock wave, stress wave, and cavitation bubble are generated at the laser focal point. Cell–cell adhesion can be broken at the cellular level by the impacts of these factors. We have applied this breaking of the adhesion to an estimation of the cell–cell adhesion strength. In this application, it is important to identify which of these factors is the dominant factor that breaks the adhesion. Here we investigated this issue using streptavidin-coated microbeads adhering to a biotin-coated substrate as a mimic of the cell–cell adhesion. The results indicated that the break was induced mainly by the stress wave, not by the impact of the cavitation bubble.     

Irreversible magnetovolume effect in Nd7Rh3 single crystal

Magnetovolume effect in Nd₇Rh₃ single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2 K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.     

Temperature effect on the surface phase transitions of monolayer films of C12E1 at air/water interface

The temperature-dependent conformational states of a monolayer film of ethylene glycol monododecyl ether (C₁₂E₁) at the air/water interface have been investigated using ellipsometry, surface tension, external reflection–absorption FTIR spectroscopy and two-dimensional infrared (2DIR) correlation analysis. The ellipticity coefficients and the entropy associated with C₁₂E₁ adsorption changed almost discontinuously at certain temperatures, which manifested the interfacial phase transitions. The phase transition and coexistence of two phases were further clarified using 2DIR correlation analysis with temperature perturbation. The asynchronous correlation maps revealed that both bands of asymmetric and symmetric C–H stretching vibration in one-dimensional IR were split into two components, which confirmed the coexistence of two phases at the interface.     

A purification system for 64Cu produced by a biomedical cyclotron for antibody PET imaging

Ion exchange is a simple and efficient method for separating no-carrier-added ⁶⁴Cu from an irradiated Ni target. We developed a semi-automated two-round ⁶⁴Cu separation system equipped with a strong-base anion exchange resin column. We first verified the efficiency of the system using a non-radioactive substitute consisting of 25 mg of Ni and 127 ng of Cu, and confirmed that Cu was completely eluted at the second round of the separation step. After the bombardment, separation of ⁶⁴Cu from the Ni target was achieved with high radiochemical purity. ⁶⁴Cu produced and separated in this study had an extremely low level of Ni impurity. It could be used for labeling monoclonal antibodies for antibody positron emission tomography imaging and synthesizing radiopharmaceuticals.     

Unique inclusion behaviour of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetraaminothiacalix[4]-arene towards small organic molecules

Tetraaminothiacalixarene 3, bearing four amino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different from those of compound 2 towards small organic molecules upon crystallisation from neat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds.