Facile synthesis, crystal structures, and high-spin cationic states of all-para-brominated oligo(N-phenyl-m-aniline)s.

Syntheses of both the dimer (3) and the trimer (4) of all-para-brominated poly(N-phenyl-m-aniline)s (2c) were achieved in a one-pot procedure from the parent nonbrominated oligomers and benzyltrimethylammonium tribromide [(BTMA)Br(3)]. An X-ray crystallographic analysis revealed that 4 has a U-shaped structure, suggesting that 2c easily adopts helical structures. Furthermore, the redox properties were investigated by the UV-vis and EPR measurements. It was confirmed that the both 3 and 4 can be oxidized into the dications 3(2+) and 4(2+) with triplet spin-multiplicity.     

Intermolecular Anionic Rearrangement of the Trimethylgerml Group in Trimethylgermylacetonitrile Anions

Intermolecular anionic rearrangement of the trimethylgermyl group in trimethylgermylacetonitrile, bis(trimethylgermyl)acetonitrile, and tris(trimethylgermyl)acetonitrile is described.     

The use of electrodialysis to prepare aqueous bread extracts for bromate determination by chemiluminescence

A cleanup procedure based on electrodialysis is described for the preparation of aqueous bread extracts for bromate determination by chemiluminescence. The technique utilizes electrophoresis with 3 chambers separated by semipermeable membranes. The relative merits of reverse osmosis (RO), ultrafiltration, and nanofiltration membranes with various molecular weight cutoffs were evaluated. The best results were obtained with an RO membrane manufactured from thin-film (composite) polysulfone as support for polyamide. A 0.14 M sodium sulfate solution in the center or collection chamber provides optimum conductivity. Aqueous hydroxylamine sulfate (30 mM) was selected for the anode compartment as a reductant for the anode oxidation products. The constant current mode at 150 mA with a potential of ca 100 volts was used. After electrophoretic separation, the bromate concentration in the collection chamber was typically 2 to 3 times greater than the concentration in the bread extract. The chemiluminescent reaction of bromate with sulfite with hydrocortisone as the enhancer was selected for detection of bromate. The emission, with a wavelength maximum at 575 nm, was found to "glow" rather than "flash" after the reagents were mixed; therefore, it was possible to optimize the light collection period. The method was validated with a variety of commercial bread products. White bread, hot dog buns, hamburger rolls, and a multigrain bread from 7 different manufacturers were studied.     

Time–frequency two-dimensional mapping of rapid energy transfer in light-harvesting star-shaped dendrimers

Rapid energy transfer dynamics in light-harvesting small dendrimers (star-shaped stilbenoid phthalocyanine: SSS1-Pc) having oligo (p-phenylenevinylene) peripheries was studied by real-time pump-probe imaging spectroscopy implemented on a single-shot basis. Using this method, we could successfully map the time–frequency two-dimensional (2D) image of the transient absorption of SSS1-Pc with a very short accumulation time. Under the selective excitation of the peripheries, the 2D image obtained clearly shows the transient absorption as well as the ground-state bleaching due to the energy transfer to the core with a fast rise time of ～0.3 ps. This fast rise implies that the rapid energy transfer from the peripheries to the core takes place through the short-range interactions due to the overlap of wave functions between the excited states of the peripheries and the core.     

Polaron dynamics of heavily doped regioregular and regiorandom poly(3-alkylthiophenes) revealed by electron spin resonance spectroscopy

Electron spin resonance (ESR) features in heavily doped conjugated polymers are investigated through the comparison of temperature dependences of ESR spectra between head-to-tail coupled regioregular (RR) and regiorandom (RRa) poly(3-octylthiophenes) (P3OTs). RR-P3OT, used as a model of having crystalline grains in the solid film, is found to exhibit anisotropic ESR spectra, whereas RRa-P3OT gives almost isotropic ESR spectra similar to those of usual heavily doped conjugated polymers. This difference in the degree of spectral anisotropy primarily arises from a difference in their film morphology. Spectral simulations show the anisotropy observed in RR-P3OT to be caused by g-anisotropy. The presence of the g-anisotropy in RR-P3OT indicates that its polarons spend most of the time within a single crystalline grain that has some domains with a common direction of the g-tensor. The g-anisotropy turns out to decrease with increasing temperature. This result is explained by thermally activated hopping motions between crystalline grains. We emphasize that the decrease in the g-anisotropy with temperature should be associated with its activated type of temperature dependence of conductivity. In RRa-P3OT, its isotropic ESR spectra are suggested to be caused by the interchain motion as well as the intrachain one.     

N-(Morpholine-4-dithio)phthalimide: A Shelf-Stable,Bilateral Platform Molecule Enabling Access to Diverse Unsymmetrical Disulfides**

Synthetic methods for unsymmetrical disulfides are greatly needed owing to their applications in drug discovery, linker chemistry, and materials sciences. In this study, a new shelf-stable and easy-to-prepare bilateral disulfurating platform molecule, N-(morpholine-4-dithio)phthalimide, has been developed for the divergent synthesis of unsymmetrical disulfides. The amino and imide leaving groups of this reagent can be orthogonally transformed. Under acidic conditions, the amino moiety undergoes selective protonation and thus can be displaced by various carbon nucleophiles, such as allyl trimethylsilanes, alkynyl silanes, and electron-rich arenes, leaving the phthalimide moiety untouched. Meanwhile, the phthalimide leaving group is amenable to substitution under basic or neutral conditions. The combination of these transformations provides rapid access to diverse unsymmetrical disulfides through two C−S bond-forming reactions.     

Functionalization of a Single C−F Bond of Trifluoromethylarenes Assisted by an ortho-Silyl Group Using a Trityl-Based All-in-One Reagent with Ytterbium Triflate Catalyst

Catalytic thiolation and azidation of a single C−F bond of trifluoromethylarenes were achieved assisted by an ortho-silyl group with all-in-one reagents to generate a trityl cation and nucleophiles. The reactions catalyzed by ytterbium triflate efficiently afforded a wide variety of difluoromethylenes avoiding the further C−F bond cleavage, by virtue of the mild conditions without the generation of a Brønsted acid.     

X-ray absorption spectroscopy of transition-metal trichalcogenides

The sulfur K and metal L_III absorption spectra of transition-metal trichalcogenides (TMTC's) were measured. The matrix element effect plays an important role in these spectra. It was considered that the structures up to 5 eV above the absorption edge reflect the chalcogen antibonding band, the metal nonbonding d_z² band, and the metal d bands, and that the higher energy structures are derived from the metal s and p bands. The chalcogen antibonding band arises from chalcogen pairing and the metal d, s, and p bands are the mixture bands with chalcogen p orbitals. Evidence that shows that the lowest conduction band of the group IV TMTC's is the chalcogen antibonding band is presented. The overlap of the metal d and metal s bands is promoted by increasing the atomic number of chalcogen atoms.     

1-Acyl-5-methoxy-8-nitro-1,2-dihydroquinoline: a biologically useful photolabile precursor of carboxylic acids

The synthesis, photochemistry, and biological application of 1-acyl-5-methoxy-8-nitro-1,2-dihydroquinoline (MNDQ-caged carboxylic acid) are described. Optimization experiments were carried out on three acetyl derivatives (3a-c), and the most appropriate analogue for application to the caging of glutamate was determined to be 3c. Thus, a MNDQ-caged glutamate (MNDQ-Glu) was synthesized, and the photochemical release of glutamate by uncaging of MNDQ-Glu was confirmed by NMR, MS, and HPLC analysis. When MNDQ-Glu was tested with pyramidal neurons in hippocampal slices, whole-field UV illumination resulted in a large inward current due to the release of l-glutamate. A short two-photon uncaging of MNDQ-Glu at single dendritic spines induced a transient current that exhibited similar kinetic properties to miniature excitatory postsynaptic currents (mEPSC).