Using computer modeling to predict and optimize separations for comprehensive two-dimensional gas chromatography

In order to fully realize the separation power of comprehensive two-dimensional gas chromatography (GC x GC), a means of predicting and optimizing separations based on operating variables was developed. This approach initially calculates the enthalpy (DeltaH) and entropy (DeltaS) for the target compounds from experimental input data, and then uses this information to simultaneously optimize all column and runtime variables, including stationary phase composition, by comparing the performance of large numbers of simulated separations. This use of computer simulation has been shown to be a useful aid in conventional separations. It becomes almost essential for GC x GC optimization because of the large number of variables involved and their very complex interaction. Agreement between experimental and predicted values of standard test samples (Grob mix) using GC x GC separation shows that this approach is accurate. We believe that this success can be extended to more challenging mixtures resulting in optimizations that are simpler and transferable between GC x GC instruments.     

Biomimetic synthesis of pyrone-derived natural products: exploring chemical pathways from a unique polyketide precursor

Our biomimetic hypothesis proposes that families of diverse natural products with complex core structures such as 9,10-deoxytridachione, photodeoxytridachione and ocellapyrone A are derived in nature from a linear and conformationally strained all-( E) tetraene-pyrone precursor. We therefore synthesized such a precursor and investigated its biomimetic transformation under a variety of reaction conditions, both to the above natural products as well as to diverse isomers which we propose to be natural products "yet to be discovered". We also report herein the first synthesis of the natural product iso-9,10-deoxytridachione.     

Thermal activation and deactivation of grown‐in defects limiting the lifetime of float‐zone silicon

By studying the minority carrier lifetime in recently manufactured commercially available n‐ and p‐type float‐zone (FZ) silicon from five leading suppliers, we observe a very large reduction in the bulk lifetime when FZ silicon is heat‐treated in the range 450–700 °C. Photoluminescence imaging of these samples at the wafer scale revealed concentric circular patterns, with higher recombination occurring in the centre, and far less around the periphery. Deep level transient spectroscopy measurements indicate the presence of recombination active defects, including a dominant center with an energy level at ～E_v + 0.5 eV. Upon annealing FZ silicon at temperatures >1000 °C in oxygen, the lifetime is completely recovered, whereby the defects vanish and do not reappear upon subsequent annealing at 500 °C. We conclude that the heat‐treatments at >1000 °C result in total annihilation of the recombination active defects. Without such high temperature treatments, the minority carrier lifetime in FZ silicon is unstable and will affect the development of high efficiency (>24%) solar cells and surface passivation studies.     

Updating incomplete factorization preconditioners for model order reduction

When solving a sequence of related linear systems by iterative methods, it is common to reuse the preconditioner for several systems, and then to recompute the preconditioner when the matrix has changed significantly. Rather than recomputing the preconditioner from scratch, it is potentially more efficient to update the previous preconditioner. Unfortunately, it is not always known how to update a preconditioner, for example, when the preconditioner is an incomplete factorization. A recently proposed iterative algorithm for computing incomplete factorizations, however, is able to exploit an initial guess, unlike existing algorithms for incomplete factorizations. By treating a previous factorization as an initial guess to this algorithm, an incomplete factorization may thus be updated. We use a sequence of problems from model order reduction. Experimental results using an optimized GPU implementation show that updating a previous factorization can be inexpensive and effective, making solving sequences of linear systems a potential niche problem for the iterative incomplete factorization algorithm.     

High resistance to thermal decomposition in brown cotton is linked to tannins and sodium content

Brown cotton fibers (SA-1 and MC-BL) studied were inferior to a white cotton fiber (Sure-Grow 747) in fiber quality, i.e., a shorter length, fewer twists, and lower crystallinity, but showed superior thermal resistance in thermogravimetric, differential thermogravimetric, and microscale combustion calorimetric (MCC) analyses. Brown cotton fibers yielded 11–23 % smaller total heat release and 20–40 % greater char. Washing fibers in water and a 1 % NaOH solution showed that rich natural inorganic components and the condensed tannins present in brown cotton are responsible for the unusual thermal property. The loss of inorganics from white cotton during a water wash increased the thermal decomposition temperature of cellulose, resulting in no char yield. However, the stronger binding of metal ions for brown cotton as well as its dominant adsorption of sodium ions after a 1 % NaOH wash facilitated the low-temperature thermal-reaction route; the sodium content showed a significant negative correlation with the heat release capacity of the fiber. Condensed tannins greatly enhanced the adsorption of sodium ions to the fiber and exhibited inherent thermal stability. The limiting oxygen indices (LOI) calculated from the MCC parameters indicated the slower burning characteristic of brown cotton, and its LOI was further increased upon adsorption of sodium ions.     

Photobleaching-based dosimetry predicts deposited dose in ALA-PpIX PDT of rodent esophagus

An improved method to estimate dose to esophageal tissue was investigated in the setting of photodynamic therapy with aminolevulinic acid-induced protoporphyrin IX (PpIX) treatment. A model of treatment-induced edema in the esophagus mucosa proved to be a well controlled and useful way to test the dosimetry model, and the light from the treatment laser together with the PpIX fluorescence intensity could be quantified reliably in real time. Dosimetry calculations based upon the detected fluorescence and bleaching kinetics were used to calculate the "effective" dose to the tissue, and a correlation was shown to exist between this metric and the edema induced in the esophagus. The difference between animals with no detectable treatment effect and those with significant edema was predictable based upon the dose calculation. The underlying assumption in the interpretation of the data is that rapid photobleaching of PpIX occurs when there is ample oxygen supply, and this bleaching is not present when oxygen is limited. This leads to the prediction that integration of the light and drug dose, in intervals where appreciable photobleaching occurs, should provide a prediction of the relative dose of singlet oxygen produced. This detection system and rodent model can be used for prospective dosimetry studies that focus on optimization of esophageal PDT.     

Synthesis of the Arctic sponge alkaloid viscosaline and the marine sponge alkaloid theonelladin C

The synthesis of Arctic sponge alkaloid viscosaline (1) is achieved by using the Zincke reaction as the penultimate step. A key synthetic intermediate theonelladin C (6), itself a marine sponge natural product, is synthesised efficiently using a four-step sequence.     

An evaluation of british columbian beetle-killed hybrid spruce for bioethanol production

The development of bioconversion technologies for production of fuels, chemicals, and power from renewable resources is currently a high priority for developed nations such as the United States, Canada, and the European Union as a way to improve national energy security and reduce greenhouse gas emissions. The widespread implementation of such technologies will require a sustainable supply of biomass from forestry and agriculture. Forests are a major source of feedstocks for biofuels production in Canada. Woody biomass includes residues from logging and forest thinning, and from wood processing and pulp production. More recently, damaged wood caused by beetle infestations has become available on a large scale in Western Canada. This study evaluates beetle-killed British Columbian hybrid spruce (HS) (Picea glauca x P. engelmannii) as a feedstock for the production of bioethanol. In the past 30 yr, attack by the beetle Dendroctonus rufipennis and associated fungi has resulted in estimated losses of more than three billion board feet in British Columbia alone. Here we describe the chemical and some physical characteristics of both healthy (HHS) and beetle-killed (BKHS) British Columbian HS and evaluate the technical feasibility of using these feedstocks as a source of biomass for bioethanol production. Untreated HHS and BKHS did not differ significantly in chemical composition except for the moisture content, which was significantly lower in BKHS (approx 10%) compared with HHS (approx 18%). However, the yields of carbohydrates in hydrolyzable and fermentable forms were higher at mild pretreatment conditions (H-Factor <1000) for BKHS compared with HHS. At medium (H-Factor 1000-2000) and severe (H-Factor >2000) pretreatment conditions HHS and BKHS behaved similarly. Organosolv pretreated HHS and BKHS demonstrated good ethanol theoretical yields, approx 70 and 80%, respectively.     

Wormlike micelles from a cage amine metallosurfactant

We have shown that copper and cobalt metallosurfactants derived from Cu(II) and Co(III) complexes of a macrobicyclic hexamine ("cage") can form wormlike micelles in aqueous solution that may coexist with or easily interconvert with vesicle structures. The cylindrical micelle structures are unusual for triple-chain surfactants with a single headgroup and are not easily accounted for using geometrical packing arguments. The solution behavior has been characterized by cryo-TEM and SAXS measurements. Both the Cu and Co compounds display viscoelastic solutions at 1 wt %, indicating that such behavior may be anticipated for the full variety of stable metal complexes formed by the cage headgroup, auguring applications based on the incorporation of metallo aggregates into mesoporous silica structures.