Confirmation of a nanohybrid shish‐kebab (NHSK) structure in composites of PET and MWCNTs

Here, the confirmation of an oriented nanohybrid shish‐kebab (NHSK) crystalline structure in a series of composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNTs) is reported. The combined use of small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and thermal analysis has been used to investigate the morphology development in PET‐MWCNT nanocomposites under hot isothermal crystallization conditions. The MWCNTs act as both heterogeneous nucleating agents and surfaces (oriented shish structures) for the epitaxial growth of PET crystallites (kebabs) giving an oriented crystalline morphology. In contrast, the PET homopolymer does not show any residual oriented crystalline morphology during isothermal crystallization but gave a sporadic nucleation of a classic unoriented lamellar structure with slower crystallization kinetics. The results provide a valuable insight into the role of MWCNTs as nanoparticulate fillers in the morphology development and subsequent modification of physical properties in engineering polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 132–137     

A high-throughput assay format for determination of nitrate reductase and nitrite reductase enzyme activities

The authors describe a microplate-based high-throughput procedure for rapid assay of the enzyme activities of nitrate reductase and nitrite reductase, using extremely small volumes of reagents. The new procedure offers the advantages of rapidity, small sample size-nanoliter volumes, low cost, and a dramatic increase in the throughput sample number that can be analyzed simultaneously. Additional advantages can be accessed by using microplate reader application software packages that permit assigning a group type to the wells, recording of the data on exportable data files and exercising the option of using the kinetic or endpoint reading modes. The assay can also be used independently for detecting nitrite residues/contamination in environmental/food samples.     

Fullerene bridged metallocyclodextrin donor-acceptor complexes: optical spectroscopy and photophysics

Two pyridine substituted beta-cyclodextrins have been synthesized and coordinated to the photoactive metal centres, [Ru(II)(bpy)2] and [Re(I)(CO)3bpy], where bpy is 2,2'-bipyridyl. The photophysical and electrochemical properties of these model complexes have been examined and compared with dinuclear complexes formed when C60 was included between two cyclodextrin cavities of the metallocyclodextrin units. On inclusion of C60, significant quenching of the emission of the luminophores is observed. Concentration and laser power dependence confirm that this quenching is intramolecular. The quenching process is interpreted in terms of a photoinduced electron transfer between the photosensitizer and C60 centre on the basis of spectroscopic and electrochemical evidence. Rate constants of 1.3 +/- 0.1 x 10(8) and 7.0 +/- 0.4 x 10(7) s(-1) have been determined for the Ru and Re based complexes, respectively. Significantly, these large rate constants indicate that that there is substantial electronic communication across the cyclodextrin at least for excited state processes.     

Rhodium-catalyzed intermolecular chelation controlled alkene and alkyne hydroacylation: synthetic scope of beta-S-substituted aldehyde substrates

The use of beta-S-substituted aldehydes in rhodium-catalyzed intermolecular hydroacylation reactions is reported. Aldehydes substituted with either sulfide or thioacetal groups undergo efficient hydroacylation with a variety of electron-poor alkenes, such as enoates, in Stetter-like processes and with both electron-poor and neutral alkynes. In general, the reactions with electron-poor alkenes demonstrate good selectivity for the linear regioisomer, and the reactions with alkynes provide enone products with excellent selectivity for the E-isomers. The scope of the process was shown to be broad, tolerating a variety of substitution patterns and functional groups on both reaction components. A novel CN-directing effect was shown to be responsible for reversing the regioselectivity in a number of alkyne hydroacylation reactions. Catalyst loadings as low as 0.1 mol % were achievable.     

Colloidal transition-metal-doped ZnO quantum dots

Methods for introducing new magnetic, optical, electronic, photophysical, or photochemical properties to semiconductor nanocrystals are attracting intense applications-oriented interest. In this communication, we report the preparation and electronic absorption spectroscopy of colloidal ZnO DMS-QDs. Our synthetic procedure involves modification of literature methods known to yield highly crystalline and relatively monodisperse nanocrystals of pure ZnO to allow introduction of transition-metal dopants. We use ligand-field electronic absorption spectroscopy as a dopant-specific optical probe to monitor dopant incorporation during nanocrystal growth and to verify internal substitutional doping in Co2+:ZnO and Ni2+:ZnO DMS-QDs. To the best of our knowledge, these are the first free-standing oxide DMS-QDs reported. The synthesis of colloidal oxide DMS-QDs introduces a new category of magnetic semiconductor materials available for detailed physical study and application in nanotechnology.     

A Pyridine–Pyridine Cross‐Coupling Reaction via Dearomatized Radical Intermediates

A pyridine–pyridine coupling reaction has been developed between pyridyl phosphonium salts and cyanopyridines using B₂pin₂ as an electron‐transfer reagent. Complete regio‐ and cross‐selectivity are observed when forming a range of valuable 2,4′‐bipyridines. Phosphonium salts were found to be the only viable radical precursors in this process, and mechanistic studies indicate that the process does not proceed through a Minisci‐type coupling involving a pyridyl radical. Instead, a radical–radical coupling process between a boryl phosphonium pyridyl radical and a boryl‐stabilized cyanopyridine radical explains the C?C bond‐forming step.