Spectroscopic studies of electron spin resonance and Raman scattering on novel hybrid poly-p-phenylenebenzobisoxazole (PBO) fibers with copper phthalocyanine

As was shown in the previous study using X-ray analyses, poly-p-phenylene benzobisoxazole fibers can accommodate copper phthalocyanine molecules with a molecularly-dispersed state in the fiber structure. It is necessary for us to investigate the presence/absence of chemical interactions between the two molecules mentioned above for the purpose to make clear the mechanism why such characteristic structures with the well dispersion of copper phthalocyanine molecules in the hybrid fiber were realized. Spectroscopic analyses based on electron spin resonance and Raman scattering were adopted. Because the copper phthalocyanine molecule take a plane form having D_4h symmetry in an ideal state, the spectra from the molecule would express the consequences based on its symmetry as the shape of the spectrum; the presence of characteristic bands in the spectra would be a proof of the existing state of copper phthalocyanine and poly-p-phenylene benzobisoxazole molecules in the hybrid fiber. It is found that both the spectroscopic methods suggested that there were no chemical bond observed between the two molecules of copper-phthalocyanine and poly-p-phenylene benzobisoxazole in the hybrid fiber.     

Heteroleptic [Bis(oxazoline)](dipyrrinato)zinc(II) Complexes: Bright and Circularly Polarized Luminescence from an Originally Achiral Dipyrrinato Ligand

Heteroleptic zinc(II) complexes synthesized using achiral dipyrrinato and chiral bis(oxazoline) ligands show bright fluorescence with quantum efficiencies of up to 0.70. The fluorescence originates from the ¹π–π^* photoexcited state localized exclusively on the dipyrrinato ligand. Furthermore, the luminescence is circularly polarized despite the achirality of the dipyrrinato ligand. Single‐crystal X‐ray structure analysis discloses that the chiral bis(oxazoline) ligand undergoes intramolecular π–π stacking with the dipyrrinato ligand, inducing axial chirality in the dipyrrinato moiety.     

Electrocatalytic Hydrogen Production by a Nickel(II) Complex with a Phosphinopyridyl Ligand

A novel nickel(II) complex [Ni(L)₂Cl]Cl with a bidentate phosphinopyridyl ligand 6‐((diphenylphosphino)methyl)pyridin‐2‐amine (L) was synthesized as a metal‐complex catalyst for hydrogen production from protons. The ligand can stabilize a low Ni oxidation state and has an amine base as a proton transfer site. The X‐ray structure analysis revealed a distorted square‐pyramidal Ni^II complex with two bidentate L ligands in a trans arrangement in the equatorial plane and a chloride anion at the apex. Electrochemical measurements with the Ni^II complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source. The catalytic current increases with the stepwise addition of protons, and the turnover frequency is 8400 s^?1 in 0.1 m [NBu₄][ClO₄]/MeCN in the presence of acetic acid (290 equiv) at an overpotential of circa 590 mV.     

Switching non-local vector median filter

This paper describes a novel image filtering method that removes random-valued impulse noise superimposed on a natural color image. In impulse noise removal, it is essential to employ a switching-type filtering method, as used in the well-known switching median filter, to preserve the detail of an original image with good quality. In color image filtering, it is generally preferable to deal with the red (R), green (G), and blue (B) components of each pixel of a color image as elements of a vectorized signal, as in the well-known vector median filter, rather than as component-wise signals to prevent a color shift after filtering. By taking these fundamentals into consideration, we propose a switching-type vector median filter with non-local processing that mainly consists of a noise detector and a noise removal filter. Concretely, we propose a noise detector that proactively detects noise-corrupted pixels by focusing attention on the isolation tendencies of pixels of interest not in an input image but in difference images between RGB components. Furthermore, as the noise removal filter, we propose an extended version of the non-local median filter, we proposed previously for grayscale image processing, named the non-local vector median filter, which is designed for color image processing. The proposed method realizes a superior balance between the preservation of detail and impulse noise removal by proactive noise detection and non-local switching vector median filtering, respectively. The effectiveness and validity of the proposed method are verified in a series of experiments using natural color images.     

Synthesis,Characterization, and Catalytic Activity of a Cubic [Mo3S4Pd] Cluster Bearing Bulky Cyclopentadienyl Ligands

A cubic metal-sulfur cluster containing three Mo ions and a Pd ion, [Cp^SiEt3₃Mo₃S₄Pd]Cl ( Mo₃Pd , Cp^SiEt3=C₅Me₄SiEt₃), was synthesized by the incorporation of the Pd ion into a Mo₃S₄ cluster [Cp^SiEt3₃Mo₃S₄] ( Mo₃ ). Mo₃Pd was characterized by ¹H NMR, UV-vis, X-ray crystallography, and cyclic voltammetry measurements. The electrochemical measurements demonstrated reversible one- and two-electron reduction processes for Mo₃Pd , which suggested potential catalytic activity for two-electron substrate reductions such as hydrogen evolution reaction. Controlled potential electrolysis in the presence of Mo₃Pd and trifluoroethanol in THF solvent displayed H₂ formation with a constant current over 60 min. The amount of generated H₂ by Mo₃Pd was two times higher than Mo₃ , indicating the catalytic activity facilitated by the Pd center. The mechanism of the catalytic cycle was determined by density functional theory.     

Crystalline Rhodium-Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

Crystalline {Cryptand(Na⁺)}[(COD)Rh^ICl⋅Sn^II(Pc³⁻)]⁻⋅2C₆H₄Cl₂ ( 1 ) and {Cryptand(Cs⁺)}[(COD)Rh^I⋅Sn^II(Pc⁴⁻)]⁻⋅C₆H₅CH₃ ( 2 ) complexes were obtained via the interaction of [Sn^II(Pc³⁻)]⁻ and [Sn^II(Pc⁴⁻)]²⁻, respectively, with organometallic {(COD)RhCl}₂ dimer (COD is 1,5-cyclooctadiene). Dissociation of {(COD)RhCl}₂ followed by the Rh−Sn binding is observed at the formation of 1 . Elimination of the chlorine atom at the rhodium atom is observed in 2 , and rhodium is additionally coordinated to the imine nitrogen atom of Pc⁴⁻. The complexes contain mono- Pc⋅³⁻ and doubly reduced Pc⁴⁻ species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2 . There is an alternation of C-N_imine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc³⁻ to 0.075 Å in Pc⁴⁻. The formation of 1 is accompanied by an essential blue shift of the Q-band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q-band is observed in the spectrum of 2 , but the band in the near-IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μ_B at 300 K corresponding the contribution of the Pc³⁻ radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc³⁻ species additionally monitored by EPR spectroscopy show a strong temperature dependence of g-factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.     

Intermolecular radical addition of alkylthio- and arylthiodiphenylphosphines to terminal alkynes

Intermolecular radical thiophosphination of terminal alkynes with alkylthio- and arylthiophosphines affords 1-thio-2-phosphino-1-alkenes in good yields. The addition reaction proceeds predominantly in an anti fashion to yield E isomers.     

Palladium-catalyzed benzylic arylation of N-benzylxanthone imine

The direct benzylic arylation of N-benzylxanthone imine with aryl chloride proceeds under palladium catalysis, yielding the corresponding coupling product. The product is readily transformed to benzhydrylamine. Taking into consideration that the imine is readily available from benzylic amine, the overall transformation represents a formal cross-coupling reaction of aryl halide with alpha-aminobenzyl metal.     

Theoretical investigation of the electronic asymmetry of the special pair cation radical in the photosynthetic type-II reaction center

The electronic asymmetry of the special pair cation radical in the photosynthetic reaction center was studied, using density functional calculations with a polarizable continuum model and a point charge model as the protein environment. The calculated spin density distribution between the halves of the special pair from Rhodobacter sphaeroides agreed well with the experimental value due to the protein polarity effect. The differences in the specific orientations of the ester carbonyl groups of the phytyl groups, as well as the methyl ester groups, are one of the origins of the electronic asymmetry. The orientations of these groups are specific, as revealed by the 14 recent X-ray structures of a variety of type-II reaction centers, with a few exceptions. In addition to the spin density distributions of the special pair cation radical from other species, the structural features of the protein surrounding these groups of a variety of type-II reaction centers were investigated to elucidate the generality and mechanisms of the specific orientations of the groups by a structural alignment and a multiple sequence alignment. The determining factors of the electronic asymmetry among type-II reaction centers are discussed.     

Nickel-catalyzed carboxylation of organozinc reagents with CO2

An efficient nickel catalyst system for the carboxylation of organozinc reagents with CO(2) under very mild conditions has been developed. The catalyst system complements the conventional methods and enables the direct synthesis of various saturated carboxylic acid derivatives from the corresponding alkylzinc reagents and CO(2).