Intramolecular singlet and triplet excimers of triply bridged [3.3.N](3,6,9)carbazolophanes

Intermoiety electronic interactions in the singlet and triplet excimer states of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n=3-6) were studied by emission and transient absorption measurements. In these [3.3.n]Cz molecules, the dihedral angle and the separation distance r between fully overlapped two carbazole rings change systematically from nearly parallel (n=3, r=3.35 A) to oblique (n=6, r=4.03 A). In rigid glass at 77 K, [3.3.n]Cz (n=3, 4) (r<4 A) exhibited red-shifted and structureless excimer fluorescence and phosphorescence while [3.3.n]Cz (n=5, 6) (r>4 A) exhibited monomer-like vibrational fluorescence and phosphorescence. In solution at 130 K, all [3.3.n]Cz molecules exhibited an excimeric fluorescence band while [3.3.5]Cz still exhibited monomer-like phosphorescence. Transient absorption spectra measured at 294 K exhibited local excitation and charge-transfer bands for all [3.3.n]Cz molecules in the excited singlet and triplet states, suggesting that not only singlet but also triplet excimers of carbazole are formed at room temperature. Furthermore, the singlet-triplet energy gap decreased with the decrease in n, suggesting that electrons are effectively delocalized over the two carbazole moieties. These findings showed that both singlet and triplet excimers of carbazole are formed with a separation distance shorter than about 4 A and are most stable in the parallel-sandwich structure and that the configurational mixing between exciton resonance and charge resonance states plays an essential role in the formation of singlet and triplet excimers of carbazole.     

Preliminary electrochemical studies of the flavohaemoprotein from Ralstonia eutropha entrapped in a film of methyl cellulose: Activation of the reduction of dioxygen

A flavohaemoprotein (FHP) from Ralstonia eutropha, obtained in a pure and active form, has been entrapped in a film of methyl cellulose on the electrode surface and gives a stable and reproducible electrochemical response at pH 7.00 when subject to cyclic voltammetry using a glassy carbon electrode. To our knowledge, no previous direct electrochemistry had been achieved with a bacterial flavohaemoglobin, which possess both a FAD and a haem. A single couple is observed which is assigned to the haem moiety of the protein, since the same result is obtained with a semi-apo form of the protein deprived of FAD (semi-apo FHP). The data collected were further confirmed by potentiometry with a platinum electrode, and the homogeneous electron transfer rate estimated by double potential step chronocoulometry at a bare glassy carbon electrode in the presence of methyl viologen (MV). The presence of FAD in the holoprotein is easily confirmed by UV-Vis spectrophotometry, but its expected electron relay role remains elusive. The protein activates the reduction of dioxygen by about 400 mV, the reduction current being proportional to the concentration of dioxygen up to 10% in volume in the gas mixture.     

Chemometric and microscopic analyses for the size growth of monolayer-protected gold nanoparticles during their superlattice formation

Superlattices of gold nanoparticles have been produced at an air/solution interface under a highly acidic condition. The nanoparticle surface is protected by N-acetylglutathione (NAG). During the course of the superlattice formation, size growth of nanoparticles was observed: The superlattices were composed of nanoparticles of 6.6 nm in core diameter, whereas the as-prepared nanoparticles had the core diameter of 1.4 nm. The growth kinetics was pursued by the time evolution of the UV-vis absorption spectra for the sample solution. The change in the absorption spectral profiles was so small that we conducted principal-component analysis (PCA), which is known as a chemometric technique to resolve (or extract) spectra of minute chemical species submerged in the original spectra. Scanning transmission electron microscopy (STEM) corroborated the PCA results, yielding a successful explanation of the growth scheme of the NAG-protected gold nanoparticles.     

A pyrazine-bridged trimer of oxo-centered triruthenium–carbonyl clusters and the supramolecular assembly built from multiple noncovalent contacts

The crystal structure of a new pyrazine-bridged trimer of oxo-centered triruthenium–carbonyl clusters formulated as [Ru₃O(EtCOO)₆(CO)(pyrazine)]₂[Ru₃O(EtCOO)₆(CO)(μ-pyrazine)₂] ( 1 ) has been unequivocally determined by single-crystal X-ray diffraction (SC-XRD) analysis at 100 K. A supramolecular cyclic assembly of two trimers was formed via intermolecular CO⋯CO contacts, which is further assembled into a three-dimensional orthogonal layer-by-layer stack via hydrogen bonds.     

Drug Release Behavior of a Drug-Loaded Polylactide Nanofiber Web Prepared via Laser-Electrospinning

In recent years drug-loaded nanofibers prepared using solution electrospinning methods have been actively studied. However, there are a number of problems connected to their solution electrospinning with respect to medical applications because of the hazards associated with the residual solvents. To avoid the use of solvents in this study we prepared and evaluated drug-loaded polylactide (PLA) fiber webs using a laser-electrospinning (LES) type of a melt electrospinning process. The structures and properties of the obtained drug-loaded PLA fiber webs were evaluated by scanning electron microscopy, fluorescence microscopy, wide-angle X-ray diffraction and UV–vis spectrometry. As shown by the various characterization techniques, we employed LES to prepare PLA nanofiber webs with average fiber diameters of 4.21 and 0.67?μm. Additionally, the webs were loaded with argatroban, a thrombin inhibitor, resulting in amorphous structures for both the argatroban and the PLA matrix. An in-vitro investigation of the drug release behavior of the webs revealed that higher release rates occurred for the fiber samples with the small fiber diameters, particularly in comparison with melt spun fibers with an average diameter of 150?μm. Overall, we expect that the herein described drug-loaded PLA nanofiber webs can be applied as medical materials with drug delivery system functions.     

New speckle control technique using high-speed electro-optic modulators with resonant electrode and polarization-reversed structures

We propose a new technique for reducing speckle noise in laser displays utilizing a high-speed optical phase modulator for expanding the laser beam spectrum. By adopting standing-wave resonant electrodes and polarization-reversed structures to LiTaO₃ electro-optic modulators, high-efficiency phase modulation with a large modulation index at high microwave frequency ranges is obtainable for different color laser beams at the same time. This enables us to expand laser spectra to over 100 GHz and reduce speckle noise. The device design, fabrication, and experimental demonstration for speckle control are reported.     

Controlled polymerization and self-assembly of halogen-bridged diruthenium complexes in organic media and their dielectrophoretic alignment

Lipophilic paddlewheel biruthenium complexes [Ru(2)(μ-O(2)CR)(3)X](n) (O(2)CR = 3,4,5-tridodecyloxybenzoate, X = Cl, I) self-assemble in organic media to form halogen-bridged coordination polymers. The polymerization is accompanied by spectral changes in π(RuO,Ru(2)) → π*(Ru(2)) and π(axial ligand) → π*(Ru(2)) absorption bands. These polymeric complexes form lyotropic liquid crystals in n-decane at concentrations above ~100 unit mM. The bridging halogen axial ligands (X = Cl or I) exert significant influences on their electronic structures and self-assembling characteristics: the chloride-bridged polymers give hexagonally aligned ordered columnar structure (columnar hexagonal phase, Col(h)), whereas the iodide-bridged polymers form less ordered columnar nematic (Col(n)) phase, as revealed by small-angle X-ray diffraction measurements. Chloro-bridged coordination polymers dispersed in n-decane are thermally intact even at the elevated temperature of 70 °C. In contrast, iodo-bridged polymers show reversible dissociation and reassembly phenomena depending on temperature. These halogen-bridged coordination polymers show unidirectional alignment upon applying alternating current (ac) electric field as investigated by crossed polarizing optical microscopy and scanning electron microscopy. The unidirectionally oriented columns of chloro-bridged polymers are accumulated upon repetitive application of the ac voltage, whereas iodo-bridged coordination polymers show faster and reversible alignment changes in response to turning on-and-off the electric field. The controlled self-assembly of electronically conjugated linear complexes provide a potential platform to design electric field-responsive nanomaterials.