Effect of an inhibitor on high-speed turbulent flames and the transition to detonation

The influence of an inhibitor (CF₃Br or Halon 1301) on the propagation of high-speed turbulent flames, quasi-detonations and the transition to detonation has been investigated for methane-air, propane-air and acetylene-air mixtures. The experiments are carried out in a 13 m tube (15 cm diameter) filled with regularly spaced orifice plates (blockage ratio of 0.39) to ensure rapid flame acceleration. In all cases, the addition of the inhibitor reduces the turbulent flame velocity and extinguishes the flame with sufficient inhibitor concentration (2.7% and 7.5% for methane-air and propane-air, respectively). For acetylene-air mixtures, the quasi-detonation speed is progressively reduced with increasing inhibitor concentration and eventually causes the failure of the quasi-detonation and transition back to a fast turbulent flame. The inhibitor also narrows the propagation limits in all cases. To elucidate the inhibition mechanism, detailed modelling of both the turbulent flame structure as well as the chemical kinetics are required.     

Energy Landscape Exploration of Sub‐Nanometre Copper–Silver Clusters

The energy landscapes of sub‐nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low‐lying minima along with their permutational isomers are located for the Cu${_4 }$ Ag${_4 }$ cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo‐planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters.     

Biosynthetic insights provided by unusual sesterterpenes from the medicinal herb Aletris farinosa

A series of novel sesterterpenes (2–6) have been isolated from the roots of Aletris farinosa and structurally characterized by MS, NMR, and X-ray crystallography in conjunction with computational modeling. Their structures provide new insights into the mechanisms of sesterterpene biosynthesis. Specifically, we propose with support from density functional theory computations that the configuration at a single stereocenter determines the fate of a key tetracyclic carbocationic intermediate, derived from an oxidogeranylfarnesol precursor. Whereas one epimer of the carbocation undergoes H⁺ elimination to give 6, the other undergoes a spectacular cascade of seven 1,2-methyl and hydride migrations leading to the previously unreported carbon skeleton of 5. Theoretical calculations suggest that the cascade is triggered by substrate preorganization in the enzyme active site.     

Well‐Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water

Herein, we describe the use of Pd nanoparticles immobilized on an amino‐functionalized siliceous mesocellular foam for the catalytic oxidation of H₂O. The Pd nanocatalyst proved to be capable of mediating the four‐electron oxidation of H₂O to O₂, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar‐fuel production.     

A flow environment for studying vortex interactions

The vortex formed at the tip of a propeller interacting with the vortex formed at the tip of a stator vane provides a unique environment for the study of vortex interactions. Changes in the relative vortex strengths and vortex rotational directions were determined to impact the resulting vortex structures and are easily implemented with the experimental apparatus described herein. Study of the development of the vortex interaction was determined to be possible by increasing the initial separation between the two vortices. Vortex interaction phenomenon has been observed using smoke flow visualization.The authors would like to thank the NASA Lewis Research Center for their funding of propeller related research from which this experiment evolved and the National Sciences and Engineering Research Council of Canada for R. Johnston's Post Graduate Scholarships.     

Vortex generating jets; effects of jet-hole inlet geometry

An experimental study of flow downstream of round, pitched and skewed wall-jets (vortex generating jets) is presented to illustrate the effects of changing the geometric inlet conditions of the jet-holes. In one case the jet-hole has a smoothly contoured inlet, and in the other the inlet was a sharp-edged, sudden contraction. The test region geometry, mean jet flow and cross-flow conditions were otherwise identical. In both cases, dominant streamwise vortex structures are seen in the boundary layer downstream; the flow and turbulence is nearly the same in the far-field starting downstream of x/D=5. In the near-field, for x/D<5, there are significant differences; turbulence levels are higher, and the start of the dominant vortex shape is less clear for the sharp-edged case. This is believed to be the result of flow separation and free shear layer instability inside the jet-hole which are not present for the smoothly contoured case.     

Engineered hydrogen-bonded polymer multilayers: from assembly to biomedical applications

Over the last two decades the layer-by-layer (LbL) assembly technique has become a highly versatile platform for the synthesis of nanoengineered thin films and particles. The widespread need for highly functional and responsive materials for applications in biomedicine-such as drug and gene delivery-has recently led to considerable efforts in the assembly of LbL materials, particularly films that can be subsequently stabilised and functionalised through a range of chemistries. In this tutorial review, recent developments in hydrogen-bonded LbL-assembled materials will be discussed, focusing on the design of materials with enhanced stimuli-responsive characteristics. Emphasis will be given to materials engineered for biomedical applications, specifically films/capsules that afford controlled loading and release of therapeutic cargo for application in vitro and in vivo.     

Selective targeting of antibody conjugated multifunctional nanoclusters (nanoroses) to epidermal growth factor receptors in cancer cells

The ability of smaller than 100 nm antibody (Ab) nanoparticle conjugates to target and modulate the biology of specific cell types may enable major advancements in cellular imaging and therapy in cancer. A key challenge is to load a high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. A versatile method called thin autocatalytic growth on substrate (TAGs) has been developed in our previous study to form ultrathin and asymmetric gold coatings on iron oxide nanocluster cores producing exceptional near-infrared (NIR) absorbance. AlexaFluor 488 labeled Abs were used to correlate the number of Abs conjugated to iron oxide/gold nanoclusters (nanoroses) with the hydrodynamic size. A transition from submonolayer to multilayer aggregates of Abs on the nanorose surface was observed for 54 Abs and an overall particle diameter of ～60-65 nm. The hydrodynamic diameter indicated coverage of a monolayer of 54 Abs, in agreement with the prediction of a geometric model, by assuming a circular footprint of 16.9 nm diameter per Ab molecule. The targeting efficacy of nanoclusters conjugated with monoclonal Abs specific for epidermal growth factor receptor (EGFR) was evaluated in A431 cancer cells using dark field microscopy and atomic absorbance spectrometry (AAS) analysis. Intense NIR scattering was achieved from both high uptake of nanoclusters in cells and high intrinsic NIR absorbance of individual nanoclusters. Dual mode imaging with dark field reflectance microscopy and fluorescence microscopy indicates the Abs remained attached to the Au surfaces upon the uptake by the cancer cells. The ability to load intense multifunctionality, specifically strong NIR absorbance, conjugation of an Ab monolayer in addition to a strong r2 MRI contrast that was previously demonstrated in a total particle size of only 63 nm, is an important step forward in development of theranostic agents for combined molecular specific imaging and therapy.     

Tuning of the electronic properties of a cyclopentadienylruthenium catalyst to match racemization of electron-rich and electron-deficient alcohols

The synthesis of a new series of cyclopentadienylruthenium catalysts with varying electronic properties and their application in racemization of secondary alcohols are described. These racemizations involve two key steps: 1) β-hydride elimination (dehydrogenation) and 2) re-addition of the hydride to the intermediate ketone. The results obtained confirm our previous theory that the electronic properties of the substrate determine which of these two steps is rate determining. For an electron-deficient alcohol the rate-determining step is the β-hydride elimination (dehydrogenation), whereas for an electron-rich alcohol the re-addition of the hydride becomes the rate-determining step. By matching the electronic properties of the catalyst with the electronic properties of the alcohol, we have now shown that a dramatic increase in racemization rate can be obtained. For example, electron-deficient alcohol 15 racemized 30 times faster with electron-deficient catalyst 6 than with the unmodified standard catalyst 4. The application of these protocols will extend the scope of cyclopentadienylruthenium catalysts in racemization and dynamic kinetic resolution.     

Automated optimization and construction of chemometric models based on highly variable raw chromatographic data

Direct chemometric interpretation of raw chromatographic data (as opposed to integrated peak tables) has been shown to be advantageous in many circumstances. However, this approach presents two significant challenges: data alignment and feature selection. In order to interpret the data, the time axes must be precisely aligned so that the signal from each analyte is recorded at the same coordinates in the data matrix for each and every analyzed sample. Several alignment approaches exist in the literature and they work well when the samples being aligned are reasonably similar. In cases where the background matrix for a series of samples to be modeled is highly variable, the performance of these approaches suffers. Considering the challenge of feature selection, when the raw data are used each signal at each time is viewed as an individual, independent variable; with the data rates of modern chromatographic systems, this generates hundreds of thousands of candidate variables, or tens of millions of candidate variables if multivariate detectors such as mass spectrometers are utilized. Consequently, an automated approach to identify and select appropriate variables for inclusion in a model is desirable. In this research we present an alignment approach that relies on a series of deuterated alkanes which act as retention anchors for an alignment signal, and couple this with an automated feature selection routine based on our novel cluster resolution metric for the construction of a chemometric model. The model system that we use to demonstrate these approaches is a series of simulated arson debris samples analyzed by passive headspace extraction, GC-MS, and interpreted using partial least squares discriminant analysis (PLS-DA).