Poly(3-decylthiophene) Radical Anions and Cations in Solution: Single and Multiple Polarons and Their Delocalization Lengths in Conjugated Polymers

Optical absorption spectra of anions and cations of poly­(3-decylthiophene) (P3DT) in solution were identified as single polarons. Pulse radiolysis of P3DT in THF determined the spatial extent of one negative polaron to be ∼11.5 thiophene units by observing transient absorption of P3DT–• radical ions, which are prinicpally free ions, at 850 nm with ε = (7.25 ± 0.47) × 104 M–1 cm–1 and bleaching of the neutral absorption band at 450 nm. P3DT–• was formed in a combination of diffusive reactions and fast “step” processes. Similarly, a positive polaron of P3DT was estimated to delocalize over ∼8.7 thiophene units by pulse radiolysis in chloroform. Chemical reduction by sodium and oxidation by FeCl3 injected multiple charges into a single P3DT chain while showing absorption spectra in the early stages of reaction resembling those observed by pulse radiolysis. The results indicated that multiple polarons exist in a single chain of P3DT before coalescing into bipolarons or transforming into other forms of polaron

Adsorption Morphology, Light Absorption, and Sensitization Yields for Squaraine Dyes on SnS₂ Surfaces

The sensitization properties of two squaraine dyes adsorbed onto the van der Waals surface of n-doped tin disulfide single crystals were studied using atomic force microscopy (AFM), vis−NIR absorption spectroscopy, and photoelectrochemical techniques. Quantum yield per absorbed photon (QYAP) values of near unity were observed for submonolayer coverages of 2,4-bis(4-(N-methyl-N-hexylamino)phenyl)squaraine (1-6SQ) in aqueous electrolyte when a sufficiently positive bias was applied, demonstrating the advantages of SnS2 as a photoanode for fundamental studies of dye sensitization. Islandlike and microcrystalline morphologies, associated with aggregate formation and revealed by AFM, could be correlated with spectral shifts in both the absorbance and photoaction spectra. A related dye, 2,4-bis(4-(N,N-dimethyl)-2-hydroxyphenyl)squaraine (1-1OHSQ), at similar coverages showed slightly lower QYAP, ascribed to a recombination path due to the different aggregate structures

Highly Effective Synthetic Methods for Substituted 2-Arylbenzofurans Using [3,3]-Sigmatropic Rearrangement: Short Syntheses of Stemofuran A and Eupomatenoid 6

A new and efficient synthesis of 2-arylbenzofurans has been achieved via a route involving acylation and subsequent [3,3]-sigmatropic rearrangement of oxime ethers. Its synthetic utility is demonstrated by a short synthesis of stemofuran A and eupomatenoid 6 in which no procedure for protection of the phenolic hydroxyl groups is needed

Nature and Energies of Electrons and Holes in a Conjugated Polymer, Polyfluorene

Electrons and holes were injected selectively into poly-2,7-(9,9-dihexylfluorene) (pF) dissolved in a tetrahydrofuran (THF) and a 1,2-dichloroethane (DCE) solution, respectively, using pulse radiolysis. Transient absorption spectra of monoions of both signs revealed two bands attributable to formation of polarons, one in the visible region (pF+• at 580 nm, pF-• at 600 nm) and another in the near-IR region. Additional confirmation for the identification of pF+• and pF-• comes from bimolecular charge-transfer reactions, such as bithiophene-• + pF → pF-• or pF+• + TTA → +TTA+• (TTA = tri-p-tolylamine), in which known radical ions transfer charge to pF or from pF. Difference absorption spectra of pF chemically reduced by sodium in THF provided a ratio of absorbance of anions formed to bleaching of the neutral band at 380 nm. In conjunction with pulse-radiolysis results, the data show that each polaron occupies 4.5 ± 0.5 fluorene units, most probably contiguous units. Extensive reduction of pF by sodium also revealed resistance to formation of bipolarons:  excess electrons reside as separate polarons when two or more electrons were injected. Redox equilibria with pyrene and terthiophene by pulse radiolysis established reversible one-electron redox potentials of E0(pF+/0) = +0.66 V and E0(pF0/-) = −2.65 V vs Fc+/0. Together with the excited-state energy, these results predict a singlet exciton binding energy of 0.2 eV for pF in the presence of 0.1 M tetrabutylammonium tetrafluoroborate. This binding energy would increase substantially without an electrolyte

Evaluation of Achiral Templates with Fluxional Brønsted Basic Substituents in Enantioselective Conjugate Additions

Enantioselective conjugate addition of malononitrile to pyrazolidinone-derived enoates proceeds in excellent yields and high enantioselectivities. A comparison of fluxional substituents with and without a Brønsted basic site and their impact on selectivity is detailed. Molecular sieves as an additive were found to be essential to achieve high enantioselectivity

Anhydrous Hydrogen Iodide-Mediated Reductive Indolization of In Situ-Generated Cyclopropyl Hydrazones

Fischer-type indolization of N-aryl-C-cyclopropyl hydrazones generated in situ followed by chemoselective reduction using tert-butyl iodide as an anhydrous HI generator was developed. This protocol provides indoles bearing carboxylic acid derivative units. A series of control experiments indicated the HI-mediated formation and reduction of spirocyclopropyl indolenines. Anhydrous HI functions as a Brønsted acid as well as a reducing agent, facilitating the successful conversion of unstable reaction intermediates and iodinated mixtures in equilibrium

Regiodivergent Ring-Opening Reaction of Trichloromethylcyclopropane Carboxylates

Reagent-controlled regiodivergent ring-opening reactions of trichloromethylcyclopropane carboxylates have been developed. The regioselectivity of bond cleavage is completely controlled by the proper choice of silver salts; the treatment of trichloromethylcyclopropane with AgBF₄ led to C2–C3 bond cleavage and fluorination to afford fluorinated β,γ-unsaturated ester with high stereoselectivity, while the reaction with AgOAc in THF gave a γ,δ-unsaturated ester through the reductive cleavage of the C1–C2 bond

Faster Dissociation: Measured Rates and Computed Effects on Barriers in Aryl Halide Radical Anions

Carbon−halogen bond dissociation rates for a series of aryl halide radical anions (ArX-•:  X = Cl, Br) in NMP were measured at room temperature by pulse radiolysis with 10-11 s time resolution. To obtain accurate dissociation rates, care was taken to measure and correct for competing decay channels. The observed rates correlated well with activation energies computed in the gas phase by density functional (DFT) calculations. The rates did not correlate well with electron affinities or dissociation energies obtained by the same computational methods, although such correlations are reported in the literature and are expected on the basis of simple models. The calculations also found that the transition state structures had bent carbon−halogen bonds. Bending enables large reductions of the activation energies by an electronic effect involving mixing of π* and σ* states. This bending-induced mixing is computed to increase the dissociation rates by a few orders of magnitude and is thus essential to understanding these reactions

Supplementary Figures 1-16 from Pyruvate Dehydrogenase PDH-E1β Controls Tumor Progression by Altering the Metabolic Status of Cancer Cells

Supplementary Figure 1: Viability assay for the breast cancer cell lines pre-treated with normoxia or hypoxia. Supplementary Figure 2: Decrease of PDH-E1β expression in different cell types. Supplementary Figure 3: PDH-E1β expression increases upon HIF-1α depletion by siRNA. Supplementary Figure 4: Effect of HIF-1 knockdown on PDH-E1β expression in HeLa cells. Supplementary Figure 5: Effect of HIF-1 knockdown on PDH-E1β expression in MB231 cells. Supplementary Figure 6: Induction of transcriptional repressors in hypoxia. Supplementary Figure 7: Expression of PDH-E1α and PDH-E1β in PDH-E1α and PDH-E1β-KD MB231 cells. Supplementary Figure 8: Protein degradation of PDH-E1β is not mediated by proteasome or lysosome. Supplementary Figure 9: Depletion of mitochondria matrix proteases by siRNA. Supplementary Figure 10: Metabolic state of PDH-E1α and PDH-E1β-depleted MB231 and MCF7 cells. Supplementary Figure 11: Metabolic state of PDH-E1α and PDH-E1β-depleted MCF7 cells. Supplementary Figure 12: Depletion of PDH-E1α and PDH-E1β in tumors. Supplementary Figure 13: Expression of PDH-E1α and PDH-E1β in MCF7 cells ectopically expressing PDH-E1β (MCF7+E1β). Supplementary Figure 14: Formation of PDH complex in MCF7 cells ectopically expressing PDH-E1β (MCF7+E1β). Supplementary Figure 15: Tumor formation of breast cancer cells pre-treated with normoxia or hypoxia. Supplementary Figure 16: ChIP assay for the PDH-E1β promoter region in MCF7 cells.</p

Sc(OTf)₃‑Catalyzed Iodocyclization/Ritter-Type Amidation of <i>N</i>‑Alkoxypropiolamides: A Synthetic Strategy for Isoxazol-3(2<i>H</i>)‑ones

A Sc­(OTf)3-catalyzed iodocyclization/Ritter-type amidation of N-alkoxypropiolamides for the synthesis of 4-iodoisoxazol-3­(2H)-ones bearing an amide group has been developed. This domino protocol allows the construction of a valuable heterocycle, isoxazol-3­(2H)-one, as well as the introduction of two functional groups. The reaction has a broad substrate scope and can be carried out on a large scale. Control experiments suggest that Sc­(OTf)3 acts as a dual activator for both the iodocyclization and amidation steps. In addition, the N-alkoxy group in the substrate suppresses some of the side reactions