Extension of the ν-metric

We extend the ν-metric introduced by Vinnicombe in robust control theory for rational plants to the case of infinite-dimensional systems/classes of nonrational transfer functions.     

Performance monitoring of a mammalian cell based bioprocess using Raman spectroscopy

Being able to predict the final product yield at all stages in long-running, industrial, mammalian cell culture processes is vital for both operational efficiency, process consistency, and the implementation of quality by design (QbD) practices. Here we used Raman spectroscopy to monitor (in terms of glycoprotein yield prediction) a fed-batch fermentation from start to finish. Raman data were collected from 12 different time points in a Chinese hamster ovary (CHO) based manufacturing process and across 37 separate production runs. The samples comprised of clarified bioprocess broths extracted from the CHO cell based process with varying amounts of fresh and spent cell culture media. Competitive adaptive reweighted sampling (CoAdReS) and ant colony optimization (ACO) variable selection methods were used to enhance the predictive ability of the chemometric models by removing unnecessary spectral information. Using CoAdReS accurate prediction models (relative error of predictions between 2.1% and 3.3%) were built for the final glycoprotein yield at every stage of the bioprocess from small scale up to the final 5000 L bioreactor. This result reinforces our previous studies which indicate that media quality is one of the most significant factors determining the efficiency of industrial CHO-cell processes. This Raman based approach could thus be used to manage production in terms of selecting which small scale batches are progressed to large-scale manufacture, thus improving process efficiency significantly.     

Approaches to the Synthesis of Gibberellic Acid. Construction of the B,C and D Ring System

One of the most challenging aspects of the synthesis of gibberellic acid² and structurally related compounds such as steviol³ is the construction of the bicyclo[3.2.1]octane system with the unusual features of an exocyclic methylene group adjacent to a bridgehead tertiary hydroxyl group. In gibberellic acid this structural feature comprises the C, D ring system, which is fused to the five-membered B ring.     

Improving neutron activation analysis accuracy for the measurement of gold in the characterization of heterogeneous catalysts using a TRIGA reactor

To measure the gold content of a catalyst accurately, neutron activation analysis (NAA) is one of the methods of choice. NAA is preferred for such heterogeneous catalysts because: (1) it requires minimal sample preparation; (2) NAA provides consistent and accurate results; and (3) in most cases results are obtained much quicker than competing methods. NAA is also used as a referee for the other elemental techniques when results do not fall within expected statistical uncertainties. However, at very high gold concentrations, applying NAA to determine the gold in a heterogeneous catalyst is more challenging than a routine NAA procedure. On the one hand, the neutron absorption cross section for gold is very high, resulting in significant self-shielding related errors. On the other hand, gold exhibits low energy resonance neutron absorptions. In this application the self-shielding minimization effort was handled more rigorously than the classic suppression of neutron flux within a specimen. This non-routine approach was used because: (1) for most applications, high accuracy, <3 % relative, is desired, (2) the low energy resonances of gold make its neutron reaction rate complex and (3) the TRIGA reactor flux profile used in this study contains both thermal and significant epithermal neutron fluxes. Accuracy and precision, using this new approach, are expected to improve from 15 % to better than 3 % relative uncertainty. This has been accomplished through a rigorous assessment of the observed effects of low energy resonance on the neutron flux spectral shape within the sample and designing an experiment to minimize the effects.     

Input,flux, and persistence of six select pesticides in San Francisco Bay

Temporal patterns of pesticide inputs to San Francisco Bay were identified and correlated with timing of application and transport mechanism. Fluxes were calculated from measured concentrations and estimated flow. Persistence of the pesticides under typical riverine or estuarine conditions were estimated from laboratory experiments. Simazine was detected most frequently and had the highest flux into the Bay, which could be explained by its continuous use and long half-life. In comparison, diazinon was detected at lower concentrations and had a lower flux which corresponded to its lower use and shorter half-life. The order-of-magnitude lower fluxes of carbofuran and methidathion corresponded to their lower use and expected hydrolysis. Molinate was detected at the highest concentration but its flux was lower than expected, considering its very high use and persistence in the laboratory experiments. Additional loss of molinate is likely to occur from volatilization and photodegradation on the rice fields. Although thiobencarb had the second highest use, it had the lowest flux of the six pesticides, which can be attributed to its loss via hydrolysis, photodegradation, volatilization, and sorption to sediments. Fluxes into San Francisco Bay were equal to or greater than those reported for other estuaries, except for the Gulf of Mexico.     

Deuterodehalogenation—a mild method for synthesising deuterated heterocycles

We report a mild and efficient method for introducing deuterium into a range of heterocycles by reacting readily available halide analogues in a deuterodehalogenation reaction using D₈-IPA or Et₃SiD under palladium-catalysed conditions.     

A TEMPO-catalyzed oxidation–reduction method to probe surface and anhydrous crystalline-core domains of cellulose microfibril bundles

Cellulose - A modified TEMPO-catalyzed oxidation of the solvent-exposed glucosyl units of cellulose to uronic acids, followed by carboxyl reduction with NaBD4 to 6-deutero- and...     

Membrane Proteins Have Distinct Fast Internal Motion and Residual Conformational Entropy

The internal motions of integral membrane proteins have largely eluded comprehensive experimental characterization. Here the fast side‐chain dynamics of the α‐helical sensory rhodopsin II and the β‐barrel outer membrane protein W have been investigated in lipid bilayers and detergent micelles by solution NMR relaxation techniques. Despite their differing topologies, both proteins have a similar distribution of methyl‐bearing side‐chain motion that is largely independent of membrane mimetic. The methyl‐bearing side chains of both proteins are, on average, more dynamic in the ps–ns timescale than any soluble protein characterized to date. Accordingly, both proteins retain an extraordinary residual conformational entropy in the folded state, which provides a counterbalance to the absence of the hydrophobic effect. Furthermore, the high conformational entropy could greatly influence the thermodynamics underlying membrane‐protein functions, including ligand binding, allostery, and signaling.