A chiroptical molecular switch with distinct chiral and photochromic entities and its application in optical switching of a cholesteric liquid crystal

Two new structurally related photoswitches are described, in which azobenzene photochromism is combined with the chirality of a 2,2'-dihydroxy-1,1'-binaphthyl unit. In system 1 the chiral binaphthyl moiety is bridged by a methylene tether, locking the biaryl chirality while in system 2 the biaryl core is unbridged and has considerable conformational flexibility. Both compound are capable of inducing cholesteric liquid crystalline phases and proved to be good photoswitches both in solution and in a liquid crystalline matrix. Compound 2 is capable of completely reversing the liquid crystalline chirality which is unique for a chiroptical molecular switch where the switching unit and the chiral moiety are separate entities.     

Self-assembly of a nucleotide-calixarene hybrid in a triangular supramolecule

The self-assembly of a thymine nucleotide-calixarene hybrid (1) in CDCl₃ as a solvent was investigated. FT-IR, ESI-MS, ¹H and DOSY-NMR spectra evidenced that compound 1 (ammonium or sodium salt) self-assembles in a triangular trimeric supramolecule by thymine-thymine hydrogen bonding. The saline form is crucial for the arrangement in the cyclic trimer as the protonation of the nucleotide phosphate groups leads the assembly toward a dimeric species.     

Single-wall carbon nanotube chemical attachment at platinum electrodes

Self-assembled monolayer (SAM) techniques were used to adsorb 4-aminothiophenol (4-ATP) on platinum electrodes in order to obtain an amino-terminated SAM as the base for the chemical attachment of single-wall carbon nanotubes (SWCNTs). A physico-chemical, morphological and electrochemical characterizations of SWCNTs attached onto the modified Pt electrodes was done by using reflection-absorption infrared spectroscopy (RAIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cyclic voltammetry (CV) techniques. The SWNTs/4-ATP/Pt surface had regions of small, medium, and large thickness of carbon nanotubes with heights of 100-200 nm, 700 nm to 1.5 μm, and 1.0-3.0 μm, respectively. Cyclic voltammetries (CVs) in sulfuric acid demonstrated that attachment of SWNTs on 4-ATP/Pt is markedly stable, even after 30 potential cycles. CV in ruthenium hexamine was similar to bare Pt electrodes, suggesting that SWNTs assembly is similar to a closely packed microelectrode array.     

High temperature treatment allows the detection of episesamin in paulownia wood extractives

Abstract

The composition and the relative variation of secondary metabolites of Paulownia tomentosa S. wood under thermal effect is a little explored area. Wood material was previously thermo-treated at 210?°C for 3?hours using a press vacuum technology. Extractives of untreated and thermo-treated wood material achieved with Soxhlet extraction techniques were obtained. Then the extracts were chromatographed by using thin layer chromatography. Component groups in extracts were determined by gas chromatography in combination with mass spectrometry. In terms of wood change the thermo-treatment of wood induces a darkening of wood color surface (ΔL* = 28.3), an increase of mass loss (3.5%) and an increase of the amount of extractives and lignin content as well as an increase of the chloroform soluble fraction. This work mainly describes the chemical exploration of the extract from paulownia wood, leading to the isolation and identification of episesamin.     

Wrapping of single-walled carbon nanotubes by a pi-conjugated polymer: the role of polymer conformation-controlled size selectivity

Wrapping of a single-walled carbon nanotube (SWNT) was examined by using a poly[( m-phenylenevinylene)- alt-( p-phenylenevinylene)] (PmPV) derivative. The polymer's intrinsic ability in forming a helical conformation was found to play an essential role in the separation of nanotubes. Among about 15 tubes present in the pure SWNT (HiPcoTM) sample, the polymer was found to selectively pick up the tubes (11,6), (11,7) and (12,6), which correspond to tube diameters of 1.19, 1.25 and 1.24 nm, respectively. The SWNTs of smaller diameters were held loosely by the PmPV, and were gradually dropped out under centrifugation. The suspension solution prepared from the SWNT and PmPV was not permanently stable, with precipitation occurring after a few weeks. Irradiation in the UV-vis region exhibited a catalytic effect to shorten the precipitation time to hours. Those tubes, which were held loosely by PmPV, were quickly separated from the suspension during the irradiation process.     

Photoexcitation of 209Bi and natHg using neutron-capture γ-rays from cobalt

Using neutron-capture γ-rays from cobalt, the ²⁰⁹Bi(γ,γ') and ^natHg(γ,γ') reactions were studied using a 53 cm³ Ge(Li) detector and the reactor facility at the Rhode Island Nuclear Science Center. Resonant scattering was observed at 4.924±0.005 MeV for ^natHg. Resonant scattering was observed at 5.609±0.005 MeV in ²⁰⁹Bi, with an effective cross section of 348±70 mb. The ratio of intensity scattered at 150° to that scattered at 100° was found to be 1.18±0.12 for ²⁰⁹Bi. This is consistent with a dipole transition to a $\text{9}\text{2}$ state but does not eliminate other transitions and spin assignments. No significant inelastic structure was found in the spectra from either sample. The improved energy specification in the present experiments has led to different energy assignments for the resonant states and hence, different incident intensities are producing the observed scattering. These differences lead to higher effective cross sections than those previously reported. Minimum ground state level widths for ²⁰⁹Bi and ^natHg were estimated to be 0.032 eV and 0.43 eV respectively. The need for high-resolution survey data to re-establish systematics is suggested.     

Calix[4]arene-based ligands as endotoxin receptors

Three new calix[4]arene-based receptors as potential antimicrobial agents have been synthesized. Their recognition ability towards lipopolysaccharides of Gram-negative bacteria has been studied by NMR and UV titrations.     

N-tert-Butyldimethylsilyl Imines as Intermediates for the Synthesis of Amines and Ketones

Grignard reagents add to benzonitrile at low temperature catalyzed by CuBr and TBSCl affording N-TBS ketimines, which were investigated as intermediaries for the synthesis of primary amines and ketones. N-silylimines were easily obtained by an organolithium addition to benzonitrile followed by a reaction with TBSCl in CH₂Cl₂. In situ reduction of these imines by BH₃ and 1,3,2-oxazaborolidines 1 or 2 as chiral templates afforded the corresponding amines with modest to good enantiomeric excess.