pH-induced interconversion between J-aggregates and H-aggregates of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in polyelectrolyte multilayer films

We fabricated a layer-by-layer (LbL) film composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(allylamine) (PAA) and investigated its pH response by UV-visible spectrometry. When the (PAA/TPPS)5PAA film was immersed in a pH 1.5 solution, J-aggregate bands were observed at 484 and 691 nm. Above pH 3.0, the J-aggregates were completely dissociated and an H-aggregate band was observed at 405 nm. The interconversion between the J-aggregates and H-aggregates in the LbL film was repeatable and controllable by changing the pH of the solutions.     

Stereospecific morphogenesis of aspartic acid helical crystals through molecular recognition

Helical morphologies were generated from aspartic acid (Asp) crystals in agar gel matrix. The morphogenesis stereospecifically proceeded in the helical crystal growth: D- and L-Asp provided left- and right-handed structures, respectively. The backbone of the helical morphology was twisted twins of tilted unit crystals, as was the case with inorganic helical crystals. The molecular recognition between the Asp crystals and agar matrix molecules resulted in the stereospecific morphogenesis. The chirality in Asp and agar molecules, the enantiomorph of unit crystals, and the resultant macroscopic helix were exquisitely associated with each other.     

Application of High-Sensitivity UV photoemission Spectroscopy to Examine the Electronic Structure of Thermophilic Rhodopsin

Abstract

The electronic structures of materials such as HOMO and LUMO are essential information to understand their functions. Photoemission spectroscopy, which is the most standard technique to examine the electronic structures of various materials, has been not well applied to biomolecules mostly due to sample charging and poor sensitivity. Very recently, we have developed high-sensitivity photoemission spectroscopy (HS-PES) using low photon energy. In this study, HS-PES has been successfully applied to a thermophilic rhodopsin (TR) film. The high sensitivity of our technique enabled to observe the HOMO region of retinal part in TR without any problem due to sample charging. This technique is expected to explore the electronic structures of various proteins.     

An Electrochemical Immunosensor Based on SPA and rGO-PEI-Ag-Nf for the Detection of Arsanilic Acid

A sensitive electrochemical immunosensor was prepared for rapid detection of ASA based on arsanilic acid (ASA) monoclonal antibody with high affinity. In the preparation of nanomaterials, polyethyleneimine (PEI) improved the stability of the solution and acted as a reducing agent to generate reduced graphene oxide (rGO) with relatively strong conductivity, thereby promoting the transfer of electrons. The dual conductivity of rGO and silver nanoparticles (AgNPs) improved the sensitivity of the sensor. The synthesis of nanomaterials were confirmed by UV-Vis spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. In the optimal experiment conditions, the sensor could achieve the detection range of 0.50–500 ng mL⁻¹ and the limit of detection (LOD) of 0.38 ng mL⁻¹ (S/N = 3). Moreover, the sensor exhibited excellent specificity and acceptable stability, suggesting that the proposed sensor possessed a good potential in ASA detection. Thus, the as-prepared biosensor may be a potential way for detecting other antibiotics in meat and animal-derived foods.     

Amplification of weak chiral inductions for excellent control over the helical orientation of discrete topologically chiral (M3L2)n polyhedra

Superb control over the helical chirality of discrete (M₃L₂)_n polyhedra (n = 2,4,8, M = Cu^I or Ag^I) created from the self-assembly of propeller-shaped ligands (L) equipped with chiral side chains is demonstrated here. Almost perfect chiral induction (>99 : 1) of the helical orientation of the framework was achieved for the largest (M₃L₂)₈ cube with 48 small chiral side chains (diameter: ∼5 nm), while no or moderate chiral induction was observed for smaller polyhedra (n = 2, 4). Thus, amplification of the weak chiral inductions of each ligand unit is an efficient way to control the chirality of large discrete nanostructures with high structural complexity.

Superb control over the helical chirality of highly-entangled (M₃L₂)_n polyhedra (M = Cu(i), Ag(i); n = 2,4,8) was achieved via multiplication of weak chiral inductions by side chains accumulated on the huge polyhedral surfaces.     

Union carbide polymerization catalysts: from uncovering active site structures to designing molecularly-defined analogs

The Union Carbide (UC) ethylene polymerization catalysts, based on chromocene dispersed on silica, show distinct features from the Phillips catalysts, but share the same heated debate regarding the structure of their active sites. Based on a combination of IR, EPR spectroscopies, labeling experiments, and DFT modeling, we identified monomeric surface-supported Cr(iii) hydrides, ( SiO)Cr(Cp)–H, as the active sites of the UC catalyst. These sites are formed in the presence of grafted and adsorbed chromocene as well as residual surface OH groups, only possible at high Cr loading, and involve a C–H activation of the Cp ring. These Cr-hydrides initiate polymerization, yielding Cr(iii) alkyl species that insert ethylene through a Cossee–Arlman-type mechanism, as evidenced by spectroscopic studies. These insights inspired the design of a well-defined analog, CpCr(CH(SiMe₃)₂)₂ grafted on partially dehydroxylated silica, that shows similar spectroscopic and polymer structure to the UC catalyst, further supporting the proposed active site structure.

A combined SOMC and DFT studies on the Union Carbide catalyst enable to propose that Cr(iii)-H, formed at high-loading, are active in ethylene polymerization. We therefore design a well-defined supported CpCr(iii)-R ethylene polymerization catalyst.     

Switchable Chemoselectivity of Reactive Intermediates Formation and Their Direct Use in A Flow Microreactor

A chemoselectivity switchable microflow reaction was developed to generate reactive and unstable intermediates. The switchable chemoselectivity of this reaction enables a selection for one of two different intermediates, an aryllithium or a benzyl lithium, at will from the same starting material. Starting from bromo-substituted styrenes, the aryllithium intermediates were converted to the substituted styrenes, whereas the benzyl lithium intermediates were engaged in an anionic polymerization. These chemoselectivity-switchable reactions can be integrated to produce polymers that cannot be formed during typical polymerization reactions.     

Advanced carbon electrode for electrochemical capacitors

Journal of Solid State Electrochemistry - Electrochemical capacitors are high-power energy storage devices having long cycle durability in comparison to secondary batteries. The energy storage...     

A sensitive analysis of sulfadimethoxine using an AuNPs/Ag-GO-Nf-based electrochemical immunosensor

Journal of Solid State Electrochemistry - Herein, a strategy was put forward for high-sensitive detection of sulfadimethoxine (SDM) using a label-free electrochemical immunosensor....     

Synthesis of Cage-Shaped Borates Bearing Pyrenylmethyl Groups: Efficient Lewis Acid Catalyst for Photoactivated Glycosylations Driven by Intramolecular Excimer Formation

We describe the synthesis and characterization of a photoactivated boron-based Lewis acid catalyst based on a cage-shaped triphenolic ligand with three pyrenylmethyl moieties. The obtained cage-shaped borate functioned as a photoactivated Lewis acid catalyst thanks to the flexible three pyrenylmethyl moieties. The deformation of the cage-shaped scaffold driven by intramolecular excimer formations of the pyrenes is a critical factor in realizing the photoactivation. Mannich-type reactions and glycosylations significantly were accelerated under 370 nm light irradiations. It is noteworthy that various glycosyl fluorides, which are not easily activated in photocatalytic systems due to their high C−F bond stability, are activated by the photoimproved catalytic activity of the catalyst.