Kinetic isotope effects in the thermal gas phase reactions of 1, 2-epoxycyclohexane-3, 3, 6, 6-d4

First-order rate constants for formation of cyclohexanone and 2-cyclohexen-1-ol from 1,2-epoxycyclohexane and 1,2-epoxycyclohexane-3,3,6,6-d₄ have been determined over the temperature range of 677–746°K. The observed kinetic isotope effects are used in an attempt to determine the mechanism for formation of products. A distinction between a biradical and a concerted mechanism for the alcohol formation could not be made. However, if a common biradical is the precursor of both cyclohexanone and 2-cyclohexenl-ol then the rate of ring closure of this biradical must be much faster than the rates of hydrogen transfer to give the ketone and the alcohol.     

A Synthetic,Structural, Spectroscopic and DFT study of ReI,CuI, RuII and IrIII Complexes Containing Functionalised Dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz)

The ligands 11‐cyanodipyrido[3,2‐a:2′,3′‐c]phenazine and 2‐(11‐dipyrido[3,2‐a:2′,3′‐c]phenazine)‐5‐phenyl‐1,3,4‐oxadiazole have been coordinated to Re^I, Cu^I, Ru^II and Ir^III metal centres. Single‐crystal X‐ray analyses were performed on fac‐chlorotricarbonyl(11‐cyanodipyrido[3,2‐a:2′,3′‐c]phenazine)rhenium (C₂₂H₉ClN₅O₃Re, a=6.509(5), b=12.403(5), c=13.907(5) Å, α=96.88(5), β=92.41(5), γ=92.13(5)°, triclinic, P , Z=2) and bis‐2,2′‐bipyridyl(2‐(11‐dipyrido[3,2‐a:2′,3′‐c]phenazine)‐5‐phenyl‐1,3,4‐oxadiazole)ruthenium triflate ? 2 CH₃CN (C₅₂H₃₆F₆N₁₂O₈RuS₂, a=10.601(5), b=12.420(5), c=20.066(5) Å, α=92.846(5), β=96.493(5), γ=103.720(5)°, triclinic, P , Z=2). The ground‐ and excited‐state properties of the ligands and complexes have been investigated with a range of techniques, including electrochemistry, absorption and emission spectroscopy, spectroelectrochemistry and excited‐state lifetime studies. Spectroscopic, time‐resolved and DFT studies reveal that the ligand‐centred (LC) transitions and their resultant excited states play an important role in the photophysical properties of the complexes. Evidence for the presence of lower‐lying metal‐to‐ligand charge‐transfer transitions is obtained from resonance Raman spectroscopy, but nanosecond transient Raman experiments suggest that once excited, the ³LC state is populated.     

Multi-Pesticide Analysis in Sediment by GC-EI-MS/MS Using Programmed Temperature Vaporization–Large Volume Injection Technique

A sensitive, selective and high throughput gas chromatography–tandem mass spectrometry method using programmable temperature vaporization–large volume injection mode (PTV-LVI-GC-MS/MS) for the analysis of 30 organochlorine pesticides (OCPs) including toxaphenes in sediments was developed. The PTV-LV injection settings, viz. inlet temperature, split flow, injection phase time, and injection speed were optimized for 50 µL injection. A significant increase in sensitivity was accomplished as compared with that obtained by the conventional 1 µL cold splitless injection. Average LVI recoveries for OCPs were in the range 58–133 % with low % RSD in instrument precision (<12 %). The method detection limits achieved were 0.04–0.92 µg kg^?1. The method recovery ranged from 80 to 120 % with <10 % RSD for more than 83 % of targeted analytes fortified at 10 µg kg^?1 in sediments. The PTV-LVI-GC-MS/MS allows simultaneous determination and unambiguous confirmation of trace OCPs and toxaphene congeners, which significantly streamlines and improves the trace organic analysis in the environmental surveillance and monitoring.     

De novo asymmetric synthesis of fridamycin E

A de novo asymmetric synthesis of (R)- and (S)-fridamycin E has been achieved. The entirely linear route required only nine steps from commercially available starting materials (16% overall yield). Key transformations included a Claisen rearrangement, a Sharpless dihydroxylation and a cobalt-catalyzed epoxide carbonylation to give a β-lactone intermediate. Antibacterial activities were determined for both enantiomers using two strains of E. coli, with the natural (R)-enantiomer showing significant inhibition against a Gram-(+)-like imp strain (MIC = 8 μM).     

Remarkable regioselective position-10 bromination of bacteriopyropheophorbide-a and ring-B reduced pyropheophorbide-a

Both bacteriopyropheophorbide-a and ring-B reduced pyropheophorbide-a on reacting with NBS (N-bromosuccinamide) undergo electrophilic bromination to provide 10-bromo analogs. The electronic nature of the substituents present at position-3 did not make any difference in the regioselective outcome of the brominated products. These relatively stable brominated chlorins and bacteriochlorins provide an easy way of introducing a wide variety of functionalities, which could be extremely useful in developing improved agents for biomedical applications and supramolecular chemistry.     

A Note on Schnyder’s Theorem

We give an alternate proof of Schnyder’s Theorem, that the incidence poset of a graph G has dimension at most three if and only if G is planar.     

Zeolite synthesis from waste fly ash and its application in CO<Subscript>2</Subscript> capture from flue gas streams

Zeolite A and A + X mixtures were prepared from coal-fly ash procured from China by using an alkali fusion method. X-ray diffraction showed that both the materials were crystalline and reproducible. Scanning Microscopy revealed that pure zeolite A particles have cubic morphology while the mixture shows intergrowth of cubic and pyramidal crystals. The surface area for A + X mixture was around 330 m²/g which is higher than zeolite A, however, lower than typical X zeolite. CO₂ and N₂ adsorption isotherms were measured and the data was fitted by the Dual Site Langmuir equation. These zeolites were then tested for CO₂ capture at different temperatures in a process with a nine step cycle. When compared with 13X zeolites at higher temperature (∼90 °C), both the zeolite A + X mixture and zeolite A prepared from fly ash showed better performance in CO₂ capture from flue gas because they have higher selectivity of CO₂ over N₂.     

XPS investigation of vacuum annealed vertically aligned ultralong ZnO nanowires

The surface properties of vertically aligned ZnO nanowires grown by chemical vapour deposition on GaN using a gold layer as a catalyst are investigated by X-ray Photoelectron Spectroscopy as a function of annealing temperature in ultra high vacuum (UHV). The nanowires are 8.5 μm long and 60 nm wide. 87% of the surface carbon content was removed after annealing at 500 °C in UHV. Analysis of the gold intensity suggests diffusion into the nanowires after annealing at 600 °C. Annealing at 300 °C removes surface water contamination and induces a 0.2 eV upward band bending, indicating that adsorbed water molecules act as surface electron donors. The contaminants re-adsorbed after 10 days in UHV and the surface band bending caused by the water removal was reversed. The UHV experiment also affected the nanowires arrangement causing them to bunch together. These results have clear implications for gas sensing applications with ZnO NWs.     

The Influence of Silkworm Species on Cellular Interactions with Novel PVA/Silk Sericin Hydrogels

Sericin peptides and PVA are chemically modified with methacrylate groups to produce a covalent PVA/sericin hydrogel. Preservation of the sericin bioactivity following methacrylation is confirmed, and PVA/sericin hydrogels are fabricated for both B. mori and A. mylitta sericin. Cell adhesion studies confirm the preservation of sericin bioactivity post incorporation in PVA gels. PVA/A. mylitta gels are observed to facilitate cell adhesion to a significantly greater degree than PVA/B. mori gels. Overall, the incorporation of sericin does not alter the physical properties of the PVA hydrogels but does result in significantly improved cellular interaction, particularly from A. mylitta gels.

     

Packing and Covering Triangles in Planar Graphs

Tuza conjectured that if a simple graph G does not contain more than k pairwise edge-disjoint triangles, then there exists a set of at most 2k edges that meets all triangles in G. It has been shown that this conjecture is true for planar graphs and the bound is sharp. In this paper, we characterize the set of extremal planar graphs.