Quantitative monitoring of yeast fermentation using Raman spectroscopy

Compared to traditional IR methods, Raman spectroscopy has the advantage of only minimal interference from water when measuring aqueous samples, which makes this method potentially useful for in situ monitoring of important industrial bioprocesses. This study demonstrates real-time monitoring of a Saccharomyces cerevisiae fermentation process using a Raman spectroscopy instrument equipped with a robust sapphire ball probe. A method was developed to correct the Raman signal for the attenuation caused by light scattering cell particulate, hence enabling quantification of reaction components and possibly measurement of yeast cell concentrations. Extinction of Raman intensities to more than 50 % during fermentation was normalized with approximated extinction expressions using Raman signal of water around 1,627 cm^?1 as internal standard to correct for the effect of scattering. Complicated standard multi-variant chemometric techniques, such as PLS, were avoided in the quantification model, as an attempt to keep the monitoring method as simple as possible and still get satisfactory estimations. Instead, estimations were made with a two-step approach, where initial scattering correction of attenuated signals was followed by linear regression. In situ quantification measurements of the fermentation resulted in root mean square errors of prediction (RMSEP) of 2.357, 1.611, and 0.633 g/L for glucose, ethanol, and yeast concentrations, respectively.     

Analytical approaches for the determination of PCB metabolites in blood: a review

Polychlorinated biphenyls (PCBs) are among the most ubiquitous pollutants in the environment, and their metabolism leads to the formation of hydroxylated PCBs (OH-PCBs) and methyl sulfone PCBs (MeSO₂-PCBs). These metabolites are generally more hydrophilic than the parent compound, and therefore are more easily eliminated from the body. However, some congeners have been shown to be strongly retained in human blood, binding to transthyretin with an affinity that is, in general, greater than that of the natural ligand thyroxin itself, which could result in toxicological effects, particularly on the thyroid system. Currently available analytical methods require, in general, extensive sample preparation, which includes a series of time-consuming and low-throughput liquid–liquid and back extractions, evaporations, several cleanup steps, and in some cases, derivatization prior to analysis by gas chromatography (GC) or liquid chromatography (LC) coupled with mass spectrometry (MS). Recent developments in the use of LC coupled with tandem MS (MS/MS) have brought some improvements in terms of sample preparation for the determination of PCB metabolites in blood, although there are still possibilities for continued development. The selected literature has evidenced few studies of LC–MS/MS-based methods, a lack of analytical standards, nonassessment of lower-chlorinated OH-PCBs, and scarce attention to MeSO₂-PCBs in blood. This review aims to evaluate critically the currently available analytical methods for determination of OH-PCBs and MeSO₂-PCBs in blood.     

Efficient Access to Substituted Silafluorenes by Nickel‐Catalyzed Reactions of Biphenylenes with Et2SiH2

The reaction of biphenylene ( 1 ) with Et₂SiH₂ in the presence of [Ni(PPhMe₂)₄] results in the formation of a mixture of 2‐diethylhydrosilylbiphenyl [ 2 (Et₂HSi)] and 9,9,‐diethyl‐9‐silafluorene ( 3 ). Silafluorene 3 was isolated in 37.5 % and 2 (Et₂HSi) in 36.9 % yield. The underlying reaction mechanism was elucidated by DFT calculations. 4‐Methyl‐9,9‐diethyl‐9‐silafluorene ( 7 ) was obtained selectively from the [Ni(PPhMe₂)₄]‐catalyzed reaction of Et₂SiH₂ and 1‐methylbiphenylene. By contrast, no selectivity could be found in the Ni‐catalyzed reaction between Et₂SiH₂ and the biphenylene derivative that bears tBu substituents in the 2‐ and 7‐positions. Therefore, two pairs of isomers of tBu‐substituted silafluorenes and of the related diethylhydrosilylbiphenyls were formed in this reaction. However, a subsequent dehydrogenation of the diethylhydrosilylbiphenyls with Wilkinson’s catalyst yielded a mixture of 2,7‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 8 ) and 3,6‐di‐tert‐butyl‐9,9‐diethyl‐9‐silafluorene ( 9 ). Silafluorenes 8 and 9 were separated by column chromatography.     

Determination of iron by Z-GFAAS and the influence of short-term precision and long-term precision

A detailed method validation of graphite-furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction was performed. The aim is to perform a detailed investigation of short-term precision as opposed to long-term precision. It was suggested that release of graphite flakes into the light path during measurement significantly influenced the performance of the method. It was found that significant deviations with respect to the certified values were frequent and an estimate of reliable uncertainties was obtained only after a high number of repetitions. Uncertainty of Interlaboratory testing was evaluated as a method to estimate uncertainties that are comparable to uncertainties that were obtained by Interlaboratory testing and to uncertainties predicted by the Horwitz curve. To a large extent, the uncertainty in measurement that was predicted by pooled calibrations corresponded to the uncertainties that were obtained from multiple determinations of unknowns. It was thus proposed that a large proportion of the difference in uncertainty in measurement between laboratories could be explained by properties of the different detectors. In order to support accuracy, it is suggested that a higher level of uncertainty should be accepted in analytical investigations.     

Performance Optimization for the Parallel Gauss–Seidel Smoother

Simulation, e.g., in the field of computational fluid dynamics, accounts for a major part of the computing time on highperformance systems. Many simulation packages still rely on Gauss–Seidel iteration, either as the main linear solver or as a smoother for multigrid schemes. Straight-forward implementations of this solver have efficiency problems on today's most common high-performance computers, i.e., multiprocessor clusters with pronounced memory hierarchies. In this work we present two simple techniques for improving the performance of the parallel Gauss–Seidel method for the 3D Poisson equation by optimizing cache usage as well as reducing the number of communication steps. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Historische Pigmente unter Laserbestrahlung: Restaurierung von Kulturgütern

The possibility to use laser radiation to clean historical objects has been established for several years. A complex case and widely met problem are polychromes. They react very sensitive towards laser radiation. In this study the reaction of pigments was investigated in dependency on the incident wavelength and energy density. The chemical and also the physical interactions were investigated. It turned out, that the colour change of the pigments can have multiple origins (laser induced oxidation, reduction, phase changing).