Methoxyquinoline-diethylenetriamine conjugate as a fluorescent zinc sensor

A 6-methoxyquinoline conjugated diethylenetriamine derivative, N,N'-bis(6-methoxy-2-quinolylmethyl)diethylenetriamine (6-MeOBQDIEN) has been synthesized and its fluorescent response toward zinc ion was investigated. In the presence of zinc ion, 6-MeOBQDIEN exhibits fluorescence (λ(ex) = 329 nm, λ(em) = 418 nm, φ = 0.039). The fluorescent intensity of the zinc complex of the compound is two times higher than the parent BQDIEN (φ = 0.021) under the same conditions. The crystal structure of 6-MeOBQDIEN-Zn complex shows that all five nitrogen atoms participate to the metal coordination in a distorted square-pyramidal geometry (τ = 0.145) with the aliphatic nitrogen in an apical position. Fluorescent microscopic analysis using 6-MeOBQDIEN reveals the zinc ion concentration change in living cells.     

Electronic Stabilization Effect of a Spin‐Delocalized Neutral Radical: Synthesis of an 8‐Cyano‐6‐oxophenalenoxyl Derivative and Quantitative Evaluation of the Electronic Spin Structure in terms of Resonance Structures

A new 2,5‐di‐tert‐butyl‐6‐oxophenalenoxyl (6OPO) derivative with a cyano group at the 8‐position, where a large spin density resides, has been synthesized. This neutral radical exhibits high stability in the solid state in air despite the low steric protection on the 8‐position; the stability is comparable to that of a corresponding 8‐tert‐butylated 6OPO derivative. EPR/¹H‐ENDOR/TRIPLE (electron paramagnetic resonance/¹H‐electron‐nuclear double resonance/TRIPLE) spectroscopy and cyclic voltammetry showed an extended spin delocalization on the cyano group and a significant increase in electron‐accepting ability relative to that of the 8‐tert‐butylated 6OPO derivative. DFT calculations indicated the extension of a singly occupied molecular orbital (SOMO) onto the cyano group and the lower‐lying SOMO and LUMO in comparison with those of the 8‐tert‐butylated 6OPO derivative, which was consistent with experimental results. Furthermore, the extended nature of π conjugation onto the cyano group was quantitatively evaluated by calculating the contributing weights of resonance structures in terms of a molecular orbital (MO)‐based valence‐bond (VB) method. Herein, the synthesis and physical properties of the 8‐cyano‐6OPO derivative are described, emphasizing that the high stability arises from the electronic effect of the cyano group. Also, the usefulness of the quantitative resonance structure analysis is shown.     

Novel sequential 1,4-Brook rearrangement-Wittig reaction: new one-pot approach for silyl dienol ethers

A novel one-pot synthetic method of silyl dienol ethers via 1,4-Brook rearrangement-Wittig reaction sequence has been developed. This tandem reaction proceeded via the intramolecular silyl migration step, which enabled stereoselective formation of phosphorane intermediates. The reaction is operationally simple and high yielding, thus providing a new useful formula for silyl dienol ether synthesis.     

Biopharmaceutical Study on Nobiletin-Loaded Amorphous Solid Dispersion with Improved Hypouricemic Effect

The present study aimed to develop an amorphous solid dispersion of nobiletin (ASD/NOB) using hydroxypropyl cellulose-SSL (HPC-SSL) to improve the pharmacokinetic properties and hypouricemic effect of NOB. ASD/NOB was prepared by the freeze-drying method (ASD/NOB). ASD/NOB was characterized with a focus on crystallinity, dissolution, pharmacokinetic behavior, and hypouricemic action in a rat model of hyperuricemia. ASD/NOB showed significant improvement in dissolution behavior, as evidenced by a 4.4-fold higher dissolved NOB concentration than crystalline NOB at 2 h in distilled water. After the oral administration of ASD/NOB (50 mg NOB/kg) in rats, higher systemic exposure to NOB was observed with an 18-fold enhancement in oral bioavailability, and the T_max value of orally administered ASD/NOB was 60% shorter than that of orally administered crystalline NOB. In a rat model of hyperuricemia, orally dosed ASD/NOB showed an improved hypouricemic effect by a 16% reduction in the plasma uric acid level compared with orally administered crystalline NOB. Based on these findings, ASD/NOB may be an efficacious dosage option to improve the nutraceutical potential of NOB for the treatment of hyperuricemia.     

Differential photoelectron holography: a new approach for three-dimensional atomic imaging

We propose differential holography as a method to overcome the long-standing forward-scattering problem in photoelectron holography and related techniques for the three-dimensional imaging of atoms. Atomic images reconstructed from experimental and theoretical Cu 3p holograms from Cu(001) demonstrate that this method suppresses strong forward-scattering effects so as to yield more accurate three-dimensional images of side- and backscattering atoms.     

Synthesis of Phenanthrene Derivatives by Intramolecular Cyclization Utilizing the [1,2]‐Phospha‐Brook Rearrangement Catalyzed by a Brønsted Base

The synthesis of functionalized phenanthrene derivatives was achieved by intramolecular cyclization utilizing the [1,2]‐phospha‐Brook rearrangement under Brønsted base catalysis. Treatment of biaryl compounds having an α‐ketoester moiety and an alkyne moiety at the 2 and 2′ positions, respectively, with diisopropyl phosphite in the presence of a catalytic amount of phosphazene base P2‐tBu provides 9,10‐disubstituted phenanthrene derivatives in high yields. This reaction involves the generation of an ester enolate through an umpolung process, that is, addition of diisopropyl phosphite to a keto moiety followed by the [1,2]‐phospha‐Brook rearrangement, the intramolecular addition to an alkyne, and the [3,3] rearrangement of the allylic phosphate moiety in a consecutive fashion.     

Electron transfer from axial ligand to S1- and S2-excited phosphorus tetraphenylporphyrin

Photoinduced processes of a series of phosphorus tetraphenylporphyrin (PTPP) derivatives ([PTPP-(NHC6H4X)2]+Cl-, X = OCH3, CH3, H, Cl, CF3, and CN) have been investigated by using femtosecond laser flash photolysis mainly. PTPP with OH as an axial ligand showed S2 fluorescence upon excitation of the Soret band. The S2 fluorescence lifetime was estimated to be 1.5 ps. On the other hand, both S2 and S1 fluorescence bands of PTPP-(NHC6H4X)2 were difficult to observe, indicating the existence of an additional deactivation process such as charge separation (CS). From MO calculation and cyclic voltammetry, PTPP and the axial ligand are expected to act as an acceptor and a donor, respectively, upon excitation of PTPP. CS via the S2 state was confirmed during the femtosecond laser flash photolysis by observing the transient absorption of radical anion of PTPP. Furthermore, CS via the S1 state of PTPP was also observed. The CS rate via the S1 state was faster than that from the S2 state. The free energy dependence of the electron-transfer rates was discussed on the basis of Marcus theory.     

Brønsted Base-Catalyzed Formal Reductive [3+2] Annulation of 4,4,4-Trifluorocrotonate and α-Iminoketones

A formal reductive [3+2] annulation of 4,4,4-trifluorocrotonate and α-iminoketones was developed under Brønsted base catalysis. A single phosphazene base efficiently catalyzes the one-pot tandem reaction involving two mechanistically different elementary processes, namely the chemoselective reduction of an imine moiety of α-iminoketones with thiols as the reductant and the subsequent intermolecular Michael addition of an enolate of α-aminoketones concomitant with lactam formation. This operationally simple method provides β-trifluoromethyl-substituted γ-lactams with a tetrasubstituted carbon as a single diastereomer.     

Surface treatments toward obtaining clean GaN(0 0 0 1) from commercial hydride vapor phase epitaxy and metal-organic chemical vapor deposition substrates in ultrahigh vacuum

We studied processes of cleaning GaN(0 0 0 1) surfaces on four different types of wafers: two types were hydride vapor phase epitaxy (HVPE) free-standing substrates and two types were metal-organic chemical vapor deposition (MOCVD) films grown on these HVPE substrates and prepared by annealing and/or Ar ion sputtering in ultra high vacuum. We observed the surfaces through treatments using in situ low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy, and also using ex situ temperature programmed desorption, X-ray photoelectron spectroscopy, X-ray diffraction, and secondary ion mass spectrometry. For HVPE samples, we obtained relatively clean surfaces under optimized three-step annealing conditions (200 °C for 12 h + 400 °C for 1 h + 500 °C for 5 min) without sputtering, after which the surface contamination of oxide and carbide was reduced to ∼20% of that before annealing. Clear GaN(0 0 0 1)1×1 patterns were obtained by LEED and RHEED. STM images showed flat terraces of ∼10 nm size and steps of ∼0.5 nm height. Upon annealing the HVPE-GaN samples at a much higher temperature (C), three-dimensional (3D) islands with facets were formed and the surface stoichiometry was broken down with the desorption of nitrogen in the form of ammonia, since the samples include hydrogen as an impurity. Ar⁺ sputtering was effective for removing surface contamination, however, postannealing could not recover the surface roughness but promoted the formation of 3D islands on the surface. For MOCVD/HVPE homoepitaxial samples, the surfaces are terminated by hydrogen and the as-introduced samples showed a clear 1×1 structure. Upon annealing at 500-600 °C, the surface hydrogen was removed and a 3×3 reconstruction structure partially appeared, although a 1×1 structure was dominant. We summarize the structure differences among the samples under the same treatment and clarify the effect of crystal quality, such as dislocations, the concentration of hydrogen impurities, and the residual reactant molecules in GaN films, on the surface structure.