Synthesis and properties of novel crown ether-annelated 4′,5′-diaza-9′-(1,3-dithiole-2-ylidene)-fluorenes and their ruthenium(II) complexes

Two novel redox-active 1,3-dithiole (DT) ring-fused 4,5-diazafluorene ligands with crown ether moieties (L1 and L2) were synthesized and characterized. The crystal structure of L1 was studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding bis(bipyridine)ruthenium(II) complexes [4: Ru L1(bpy)₂ and 5: Ru L2(bpy)₂], were also been investigated.     

New Criteria for Self-Adjointness and its Application to Dirac–Maxwell Hamiltonian

We present a new theorem concerning a sufficient condition for a symmetric operator acting in a complex Hilbert space to be essentially self-adjoint. By applying the theorem, we prove that the Dirac–Maxwell Hamiltonian, which describes a quantum system of a Dirac particle and a radiation field minimally interacting with each other, is essentially self-adjoint. Our theorem covers the case where the Dirac particle is in the Coulomb-type potential.     

Attaining 186-nm light generation in cooled beta-BaB(2)O(4) crystal

The transparency range of beta-BaB(2)O(4) (BBO) was expanded by means of cooling, and the resulting absorption coefficient at 193.4 nm was reduced to 0.29cm(-1) at 91 K from 1.39cm(-1) at 295 K. Further, generation of light at 186.0 nm (the measurement limit in air) by type I sum-frequency generation (SFG) based on fundamental (744-nm) and third-harmonic (248-nm) light from a Ti:sapphire laser was confirmed for cooled BBO. Calculations based on observed data for SFG wavelengths and phase-matching angles indicate a potential for cooled BBO to generate wavelengths as low as 181.7 nm.     

Copolymerization of Metal Nanoparticles: A Route to Colloidal Plasmonic Copolymers

The resemblance between colloidal and molecular polymerization reactions is very useful in fundamental studies of polymerization reactions, as well as in the development of new nanoscale systems with desired properties. Future applications of colloidal polymers will require nanoparticle ensembles with a high degree of complexity that can be realized by hetero‐assembly of NPs with different dimensions, shapes, and compositions. A method has been developed to apply strategies from molecular copolymerization to the co‐assembly of gold nanorods with different dimensions into random and block copolymer structures (plasmonic copolymers). The approach was extended to the co‐assembly of random copolymers of gold and palladium nanorods. A kinetic model validated and further expanded the kinetic theories developed for molecular copolymerization reactions.     

Anisotropic Self‐Assembly of Citrate‐Coated Gold Nanoparticles on Fluidic Liposomes

The behavior of self‐assembly processes of nanoscale particles on plasma membranes can reveal mechanisms of important biofunctions and/or intractable diseases. Self‐assembly of citrate‐coated gold nanoparticles (cAuNPs) on liposomes was investigated. The adsorbed cAuNPs were initially fixed on the liposome surfaces and did not self‐assemble below the phospholipid phase transition temperature (T_m). In contrast, anisotropic cAuNP self‐assembly was observed upon heating of the composite above the T_m, where the phospholipids became fluid. The number of self‐assembled NPs is conveniently controlled by the initial mixing ratio of cAuNPs and liposomes. Gold nanoparticle protecting agents strongly affected the self‐assembly process on the fluidic membrane.     

Instantaneous inclusion of a polynucleotide and hydrophobic guest molecules into a helical core of cationic beta-1,3-glucan polysaccharide

We succeeded in the quantitative and selective introduction of an ammonium cationic group into the C6 position of Curdlan (CUR) by "Click Chemistry", and the obtained cationic Curdlan (CUR-N+) showed good solubility in water. ORD studies suggested that CUR-N+ adopts a single-stranded structure, different from a right-handed, triple-stranded helical structure of beta-1,3-glucan polysaccharides in water. It has been revealed that the polymeric complexes of CUR-N+ with polymeric guest molecules, such as polycytidylic acid (poly(C)), permethyldecasilane (PMDS), and single-walled carbon nanotubes (SWNTs), can be easily obtained by just mixing them in water with sonication. The characterization of the resultant CUR-N+-poly(C) complexes by UV-vis, CD spectroscopic measurements, and AFM and TEM observations revealed that they have stoichiometric, nanosized fibrous structures. From these experimental results as well as our precedent studies (e.g., refs 6 and 23), we propose that the complexation would be driven by the cooperative action of (1) the hydrogen-bonding interaction between the OH group at the C2 position and hydrogen-bonding sites of the cytosine ring (ref 6d), (2) the electrostatic interaction between the ammonium cation and the phosphate anion (ref 23), as well as (3) the background hydrophobic interaction. In addition, the complexed polynucleotide chain showed a strong resistance against enzymatic hydrolysis. Likewise, the dispersion of PMDS and SWNTs in water by CUR-N+ and the fibrous structures of the complexes were confirmed by spectroscopic measurements as well as microscopic observations. These binding properties of CUR-N+, which can proceed spontaneously in water, clearly differ from those of schizophyllan (SPG), which inevitably require a denature-renature process corresponding to a conversion of a triple strand to single strands induced by DMSO or base for inclusion of polymeric guest molecules.     

Effects of surface water on gas sorption capacities of gravimetric sensing layers analyzed by molecular descriptors of organic adsorbates

The gas sorption capacities of sputtered carbonaceous films are evaluated with quartz crystal resonators. These films are sensitive to 20 ppm organic vapors and exhibit structure-dependent responses. Films derived from synthetic polymers are hydrophobic, whereas films derived from biomaterials are amphiphilic or hydrophilic. Polyethylene (PE) film has an extremely high sorption capacity for a wide range of vapors. Transient sorption responses are investigated using a humidified carrier by employing carboxylic acid esters, whose aliphatic groups are systematically changed. Small esters with a higher affinity to water induce negative U-shaped responses from amphiphilic films derived from biomaterials. On the other hand, polymeric films exhibit positive exponential response curves. Even if the concentrations are decreased, the response intensities are enhanced with the incremental expansion of carbon chains of aliphatic groups. Only fluoropolymer film shows the opposite tendency. The modeling of quantitative structure property relationships has indicated that the sorption capacities of the PE film to the carboxylic acid esters are fundamentally governed by electrostatic interactions. The intermolecular attractive forces are basically attributable to interactions between the positively polarized sites in esters and the negatively polarized/charged sites in PE film.     

Experimental detection of domain wall propagation above the Walker field

The domain wall (DW) velocity above the Walker field drops abruptly with increasing magnetic field, because of the so-called Walker breakdown, where the DW moves with a precessional mode. On applying the higher field, the DW velocity again starts to increase gradually. We report the DW propagation around this local minimum regime in detail, investigated through the time-resolved electrical detection technique, with a magnetic tunnel junction. Just above the Walker field, we succeeded in detecting the precessional motion of the DW in a real-time regime, while a different mode appeared around the local minimum of the DW velocity.