Photoreversible Supramolecular Polymerisation and Hierarchical Organization of Hydrogen‐Bonded Supramolecular Co‐polymers Composed of Diarylethenes and Oligothiophenes

Diarylethene 1 equipped with two monotopic melamine hydrogen‐bonding sites and oligothiophene‐functionalized ditopic cyanurate (OTCA) were mixed in a nonpolar solvent to form AA‐BB‐type supramolecular co‐polymers (SCPs) bearing photoswitchable moieties in their main chains and extended π systems as side chains. UV/Vis, fluorescence, dynamic light scattering (DLS), TEM, and AFM studies revealed that the two functional co‐monomers formed flexible quasi‐one‐dimensional SCPs in solution that hierarchically self‐organized into helical nanofibers through H‐aggregation of the oligothiophene side chains. Upon irradiating the SCPs with UV light, a transition occurred from the H‐aggregated state to non‐aggregated monomeric oligothiophene side chains, as shown by spectroscopic studies, which indicates the formation of small oligomeric species held together only by hydrogen‐bonding interactions. TEM and AFM visualized unfolded fibrils corresponding to elongated single SCP chains formed upon removal of solvent. The helical nanofibers were regenerated upon irradiating the UVirradiated solution with visible light. These results demonstrated that the supramolecular polymerisation followed by hierarchical organization can be effectively controlled by proper supramolecular designs using diarylethenes and π‐conjugated oligomers.     

Supramolecularly engineered perylene bisimide assemblies exhibiting thermal transition from columnar to multilamellar structures

Perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) was functionalized with ditopic cyanuric acid to organize it into complex columnar architectures through the formation of hydrogen-bonded supermacrocycles (rosette) by complexing with ditopic melamines possessing solubilizing alkoxyphenyl substituents. The aggregation study in solution using UV-vis and NMR spectroscopies showed the formation of extended aggregates through hydrogen-bonding and π-π stacking interactions. The cylindrical fibrillar nanostructures were visualized by microscopic techniques (AFM, TEM), and the formation of lyotropic mesophase was confirmed by polarized optical microscopy and SEM. X-ray diffraction study revealed that a well-defined hexagonal columnar (Col(h)) structure was formed by solution-casting of fibrillar assemblies. All of these results are consistent with the formation of hydrogen-bonded PBI rosettes that spontaneously organize into the Col(h) structure. Upon heating the Col(h) structure in the bulk state, a structural transition to a highly ordered lamellar (Lam) structure was observed by variable-temperature X-ray diffraction, differential scanning calorimetry, and AFM studies. IR study showed that the rearrangement of the hydrogen-bonding motifs occurs during the structural transition. These results suggest that such a striking structural transition is aided by the reorganization in the lowest level of self-organization, i.e., the rearrangement of hydrogen-bonded motifs from rosette to linear tape. A remarkable increase in the transient photoconductivity was observed by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements upon converting the Col(h) structure to the Lam structure. Transient absorption spectroscopy revealed that electron transfer from electron-donating alkoxyphenyl groups of melamine components to electron-deficient PBI moieties takes place, resulting in a higher probability of charge carrier generation in the Lam structure compared to the Col(h) structure.     

Chiral Catalysts Dually Functionalized with Amino Acid and Zn2+ Complex Components for Enantioselective Direct Aldol Reactions Inspired by Natural Aldolases: Design,Synthesis, Complexation Properties,Catalytic Activities,and Mechanistic Study

Aldolases are enzymes that catalyze stereospecific aldol reactions in a reversible manner. Naturally occurring aldolases include class I aldolases, which catalyze aldol reactions via enamine intermediates, and class II aldolases, in which Zn²⁺ enolates of substrates react with acceptor aldehydes. In this work, Zn²⁺ complexes of L ‐prolyl‐pendant[15]aneN₅ (ZnL³), L ‐prolyl‐pendant[12]aneN₄ (ZnL⁴), and L ‐valyl‐pendant[12]aneN₄ (ZnL⁵) were designed and synthesized for use as chiral catalysts for enantioselective aldol reactions. The complexation constants for L³ to L⁵ with Zn²⁺ [logK_s(ZnL)] were determined to be 14.1 (for ZnL³), 7.6 (for ZnL⁴), and 9.6 (for ZnL⁵), indicating that ZnL³ is more stable than ZnL⁴ and ZnL⁵. The deprotonation constants of Zn²⁺‐bound water [pK_a(ZnL) values] for ZnL³, ZnL⁴, and ZnL⁵ were calculated to be 9.2 (for ZnL³), 8.2 (for ZnL⁴), and 8.6 (for ZnL⁵), suggesting that the Zn²⁺ ions in ZnL³ is a less acidic Lewis acid than in ZnL⁴ and ZnL⁵. These values also indicated that the amino groups on the side chains weakly coordinate to Zn²⁺. We carried out aldol reactions between acetone and 2‐chlorobenzaldehyde and other aldehydes in the presence of catalytic amounts of the chiral Zn²⁺ complexes in acetone/H₂O at 25 and 37 °C. Whereas ZnL³ yielded the aldol product in 43 % yield and 1 % ee (R), ZnL⁴ and ZnL⁵ afforded good chemical yields and high enantioselectivities of up to 89 % ee (R). UV titrations of proline and ZnL⁴ with acetylacetone (acac) in DMSO/H₂O (1:2) indicate that ZnL⁴ facilitates the formation of the ZnL⁴ ? (acac)^? complex (K_app=2.1×10² M ^?1), whereas L ‐proline forms a Schiff base with acac with a very small equilibrium constant. These results suggest that the amino acid components and the Zn²⁺ ions in ZnL⁴ and ZnL⁵ function in a cooperative manner to generate the Zn²⁺‐enolate of acetone, thus permitting efficient enantioselective C? C bond formation with aldehydes.     

Orally active GPIIb/IIIa antagonists: synthesis and biological activities of masked amidines as prodrugs of 2-[(3S)-4

To improve the in vivo potency of the potent GPIIb/IIIa antagonist 2-[(3S)-4-[(2S)-2-(4-amidinobenzoylamino)-3-(4-methoxyphenyl)propanoyl]-3-(2-methoxy-2-oxoethyl)-2-oxopiperazinyljacetic acid (4), the amidino group was converted to an oxadiazole ring, thiadiazole ring or substituted amidoxime group. These groups were expected to be metabolized to an amidino group in vivo. The compounds synthesized were evaluated for their potency to inhibit the ex vivo adenosine 5'-diphosphate (ADP)-induced aggregation of guinea pig platelets. Among the compounds examined, the methoxycarbonyloxyamidine 8a exhibited the most potent ex vivo inhibitory activity with a fast onset and prolonged duration of action after oral administration.     

Spherical‐harmonics expansion method for density‐matrix simulations of quantum electron dynamics in continuum states

Spherical‐harmonics expansion method is proposed to solve the quantum time‐evolution equations for density matrices numerically in momentum space. This method facilitates efficient real‐time simulations of quantum electron dynamics in continuum states through extension of our previous formalism developed for discrete states. Numerical accuracy and efficiency are demonstrated through two examples: (i) multiphoton ionization of a one‐electron atom in intense laser field, and (ii) real‐time dynamics of plasma oscillations in electron liquids. In case (i), coupled dynamics of density matrices for bound and continuum states reveals an enhancement of multiphoton ionization over the Keldysh approximation through resonant intermediate states. © 2015 Wiley Periodicals, Inc.     

Tunable photonic band gap crystals based on a liquid crystal-infiltrated inverse opal structure

Composite materials comprised of nematic liquid crystals (LCs) and SiO(2) inverse opal films were fabricated. Their optical properties were quite different from those of inverse opal films without the LCs. The optical properties could be controlled by changing the refractive indices of the LCs, which vary with orientation, phase, and temperature. In particular, the optical properties were drastically changed by thermal or photoinduced isothermal phase transitions of the LCs. This means that the photonic band structure could be controlled, and tunable photonic crystals have been achieved, based on the inverse opal structure. The mechanism of this change was investigated by the evaluation of the effective refractive indices. As a result, it was found that the change in optical properties was derived from the orientation of the LC molecules in the voids in the inverse opal film. Furthermore, once the mechanism was understood, it was also possible to control the position of the reflection peak by changing the alignment of the LCs. Such materials have the possibility for practical use in optical devices and fundamental research systems.     

Photoluminescent dinuclear lanthanide complexes with tris(2-pyridyl)carbinol acting as a new tetradentate bridging ligand

A tripodal ligand, tris(2-pyridyl)carbinol, affords a novel tetradentate coordination mode in homodinuclear lanthanide complexes, which exhibit remarkably short distances between metal ions. The strong luminescences of Eu(III) and Tb(III) complexes with the ligand demonstrate that the ligand has a suitable excited state for energy transfer from the ligand to the Eu(III) and Tb(III) centers, respectively.     

Precise and accurate determination of halogens in organic compounds using an amalgamated gold electrode

Precise and accurate titration of halogens in organic and inorganic materials has been studied. The halogen was titrated with coulometrically generated silver and determined potentiometrically by using an amalgamated gold indicator electrode. An argentometric titration curve using the amalgamated gold indicator electrode showed a large jump in potential at the endpoint as well as in mercurometric determination. Sodium carboxymethyl cellulose (CMC) and aluminum nitrate were added as they are most effective for clarifying the sample solution and eliminating adsorption of the halide ion on the silver halide generated. The electrolytes used were 0.5 M nitric acid containing 0.1% CMC and 0.2 M aluminum nitrate. Approximately 0.2 mmol of chloride, bromide, and iodide ions were titrated with high precision and accuracy. Their standard deviations were 0.03, 0.02, and 0.02%, respectively, with no apparent systematic error. The precise determination of halogens, employing oxygen flask combustion and dissolution of the halide salts in the electrolyte, was carried out with ±0.1% absolute error using samples weighing between 20 and 30 mg.