Showing items related by title, author, creator and subject.

• 

  1,4‐Addition of TMSCCl3 to nitroalkenes: efficient reaction conditions and mechanistic understanding

  Wu, Na (Anna); Wahl, B.; Woodward, S.; Lewis, W. (2014-06)

  Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70 %) and excellent purity. Compounds of the type NBu4X [X=Ph3SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4‐additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (1H, 19F, 13C and 29Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13 M ) at −20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me3SiF, Ph3SiF and NBu4CCl3. The latter is stable to at least 0 °C and does not add nitroalkene from −20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13 M at −20 °C), when treated with TBAT, leads to immediate formation of the 1,4‐addition product, suggesting the reaction proceeds via a transient [Me3Si(alkene)CCl3] species, in which (alkene) indicates an Si⋅⋅⋅O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3− addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4[CH2=NO2] is an efficient promoter. Use of H2C=CH(CH2)2CH=CHNO2 in air affords radical‐derived bicyclic products arising from aerobic oxidation.
• Nanoscale ZrRGOCuFe layered double hydroxide composites for enhanced photocatalytic degradation of dye contaminant

  Kumar, O.P.; Ashiq, M.N.; Shah, S.S.A.; Akhtar, S.; Mudhar, M.A.; Mujtaba, Iqbal M.; Rehman, A. ur (2021-06-15)

  Coprecipitation method was used to prepare non-stoichiometric pristine copper and iron layered double hydroxide (LDH) doped with zirconium and embedded with reduced graphene oxide. The composite materials (ZrRGOCuFe LDHs) were studied for the photodegradation of methylene blue (MB) dye as a model contaminant from an aqueous solution. These composites were fully characterized by X-rays diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Photoluminescence (PL), Raman spectroscopy and Electrochemical Impedance Spectroscopy (EIS). The results of Raman, Photoluminescence and Electrochemical Impedance Spectroscopy revealed the presence of oxygen defects level in the composites. Such defects are believed to be essential for boosting the catalytic potential of the composites. The secondary pollution manifested by transition metal ions is usually tackled by inducing heterogeneous catalysis. Herein, pristine CuFe LDH has been doped with Zr and RGO moieties to realize heterogeneous catalysis within ZrRGOCuFe LDH dopants. An admirable band ranging between 1.74 and 2.0 eV was obtained for the doped materials. The remarkable photodegradation efficiency of 95.2% was achieved by using heterogeneous photocatlyst Zr0.6RGOCuFe LDH within 75 min at a pH of 7, photocatalyst dosage of 1.0 g/L and methylene blue dye solution of 10 ppm under visible light irradiation. The total organic content (TOC) analysis has revealed removal of 92% organic content. Moreover, the catalyst has the potentia to maitain sufficient stability and reusability capacity even after three successive cycles. The reaction kinetics and proposed photocatalytic mechanism were also explained in detail.
• Sequence-dependent structure/function relationships of catalytic peptide-enabled gold nanoparticles generated under ambient synthetic conditions

  Bedford, N.M.; Hughes, Zak E.; Tang, Z.; Li, Y.; Briggs, B.D.; Ren, Y.; Swihart, M.T.; Petkov, V.G.; Naik, R.R.; Knecht, M.R.; et al. (2016-01)

  Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction data and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancemen