Mg-promoted facile and selective intramolecular cyclization of aromatic δ-ketoesters

Treatment of various types of aromatic δ-ketoesters 2, 7, and 9 with Mg-turnings for Grignard reaction at −5 to 0 °C in N,N-dimethylformamide (DMF) containing trimethylsilyl chloride (TMSCl) brought about selective and reductive intramolecular cyclization to give the corresponding α-aryl-α-hydroxycyclopentanones 5, 8, and 10, respectively, in moderate to good yields. Similar reductive intramolecular cyclization of aromatic δ-ketodiesters 14, followed by acidic hydrolysis and decarboxylation easily gave the corresponding 2-aryl-2-cyclopenten-1-ones 15. The present facile coupling may be initiated through electron transfer from Mg metal to the aromatic carbonyl groups of 2, 7, 9, and 14 to generate the corresponding radical anions, followed by their intramolecular nucleophilic attack to the ester groups to give the corresponding five-membered ring compounds 5, 8, 10, and 15, respectively.     

Protective effect of small amounts of sodium dodecyl sulfate on the helical structure of bovine serum albumin in thermal denaturation

In the presence of sodium dodecyl sulfate (SDS), the secondary structure of bovine serum albumin (BSA) was almost protected against thermal denaturation above 50 degrees C, where the structural change became irreversible. Beyond 30 degrees C, the helicity (66%) of the protein sharply decreased with rise of temperature. In response to this, the proportions of beta-structure and random coil increased. The helicity and the beta-structural proportion were 44% and 13% at 65 degrees C, respectively. The protective effect was observed upon the coexistence of SDS of extremely low concentrations: the molar ratio of [SDS]/[BSA] of 15 was enough to induce the maximal protective effect on the helical structure of the protein. The maximal protected helicity was 58% at 65 degrees C, increasing to 64% upon cooling down to 25 degrees C. This protective effect became greater with an increase of chain length of alkyl sulfate ion. On the other hand, a cationic surfactant did not protect the BSA structure at all against the thermal denaturation. This protective effect was characterized by the specific amphiphilic nature of anionic surfactant. Such an anionic surfactant is considered to protect the protein structure by building bridges between particular nonpolar residues and particular positively charged residues located on different loops of the protein.     

A new N~* resonance as a hadronic molecular state

We report our recent work on a hadronic molecule state of the K(K)N system with I=1/2 and J~P=1/2~+. We assume that the A(1405) resonance and the scalar mesons, f_0(980), a_0(980), are reproduced as quasi-bound states of (K)N and K(K), respectively. Performing non-relativistic three-body calculations with a variational method for this system, we find a quasibound state of the K(K)N system around 1910 MeV below the three-body breakup threshold. This state corresponds to a new baryon resonance of N~* with J~P = 1/2~+. We find also that this resonance has the cluster structure of the two-body bound states keeping their properties as in the isolated two-particle systems. We also briefly discuss another hadronic molecular state composed by two (K) and one (N), which corresponds to a Ξ~* resonance.     

Baryon resonances as hadronic molecule states with kaons

We investigate hadronic molecule states of $K \bar K N$ and $\bar K \bar K N$ systems with I?=?1/2 and J ^P ?=?1/2^?+?, assuming that Λ(1405) and the scalar mesons, f ₀(980), a ₀(980), are reproduced as quasi-bound states of $\bar KN$ and $K \bar K$ . Performing non-relativistic three-body calculations for these systems, we find weakly bound states for $K \bar K N$ and $\bar K \bar K N$ around 1900 MeV, which correspond to new baryon resonances of N ^* and Ξ ^* with J ^P ?=?1/2^?+?. We find that these resonances have cluster structure of the two-body bound state keeping its properties as in the isolated two-particle system.     

Third-order nonlinear optical response in double-walled carbon nanotubes

Resonant behavior and magnitudes of third-order nonlinear optical susceptibilities in double-walled carbon nanotubes (DWNTs) have been investigated by means of femtosecond pump-probe spectroscopy with different pump-photon energies. With the selective excitation of the E₂₂ exciton transition of the inner tubes labeled by the chiral vector indices (7,5) and (7,6), the imaginary part of nonlinear susceptibility Imχ⁽³⁾ has shown the resonant enhancement compared with the case of the nonresonant excitation of the specific tube. The nonlinear response signal at the E₂₂ transition energy of the (8,7) tube has been also enhanced for the excitation of the G-band phonon sideband of its E₂₂ transition. This result is consistent with the phonon-mediated nonlinear optical process observed for the E₂₂ transitions in single-walled carbon nanotubes (SWNTs). It has been also found that the values of the figure of merit Im χ⁽³⁾/α (α: absorption coefficient) of the inner tubes in DWNTs are smaller than those of the corresponding SWNTs, which is interpreted in terms of decay time shortening due to the energy relaxation between the inner and outer tubes.     

Listeria monocytogenes cells injured by high hydrostatic pressure and their recovery in nutrient-rich or -free medium during cold storage

ABSTRACT

Cells of Listeria monocytogenes suspended in phosphate-buffered saline (PBS) were treated by high hydrostatic pressure (HHP; 500?MPa, 25°C, 10?min), diluted by ten folds using trypticase soy broth (TSB) or PBS, and stored at cold temperatures of 0–15°C. Viable cell count in TSB increased logarithmically close to the initial count at each storage temperature, while that in PBS increased temporarily and subsequently decreased to almost nondetectable level except the case at 15°C, where it showed logarithmic increase thereafter. Based on proliferation experiments where their healthy cells were inoculated to TSB or to PBS containing their heat-killed dead cells, it was suggested that increase in the viable count of HHP-treated cells in TSB and PBS could be ascribed to the recovery of colony forming ability and/or proliferation depending on the cold storage temperature.     

Synthesis of a New Thiophene/Quinoxaline CT‐Type Copolymer with High Solubility and Its Basic Optical Properties

A new π‐conjugated charge‐transfer‐type copolymer of electron‐donating thiophene and electron‐accepting quinoxaline was prepared by organometallic polycondensation. The polymer was soluble in organic solvents such as tetrahydrofuran, and showed a UV‐vis peak at long wavelengths of 598 nm in chloroform and 629 nm in the film. Its film exhibited a χ⁽³⁾ peak in the resonance region with a χ⁽³⁾ value comparable to that of regioregular head‐to‐tail poly(3‐hexylthiophene‐2,5‐diyl).

     

Caged bulky organic dyes in a polyaromatic framework and their spectroscopic peculiarities

Host–guest structures and properties have been widely studied using relatively small dyes (<1 nm) without bulky groups, due to their smooth incorporation, efficient host–guest interactions, and high analytical accessibility. In this report, on the other hand, three types of sterically demanding organic dyes trapped by a polyaromatic cage were investigated by spectroscopic analyses on the basis of supramolecular interactions. Coumarins with two bulky substituents are bound by the cage in aqueous solution. The resultant caged dyes show unusual emission enhancement, depending on the difference of a single heteroatom in their substituents. The color of perylene bisimides with two bulky substituents is remarkably changed from yellow to red upon caging. This peculiarity stems from the twist of the substituents in the cage, revealed by the combination of absorption and theoretical studies. Furthermore, tetrasubstituted, bulky porphyrins are caught by the cage in aqueous solution. The caged bulky dyes also display altered color and absorption properties, which remain intact even under acidic conditions. In contrast to typical covalent functionalization and previous host–guest studies toward small and non-bulky dyes, the unusual, non-covalent spectroscopic modulation of the large and bulky dyes can be accomplished for the first time by the present cage, featuring a prolate polyaromatic framework with four openings.

Here we report that the open large cavity of an M₂L₄ polyaromatic cage can efficiently bind sterically demanding organic dyes with coumarin, perylene bisimide, and porphyrin cores in aqueous solution. The spectroscopic properties of the caged dyes are largely modulated in the cavity.