Caspar Demuth

Reversible chemical reactions as the basis for optical sensors used to detect amines, alcohols and humidity

A new class of indicator dyes for use in analytical chemistry is presented. In contrast to most existing indicator dyes, which change colour upon complexation or protonation/deprotonation, the dyes presented here perform reversible chemical reactions with the analyte, resulting in changes in absorbance or fluorescence. Specifically, azo and stilbene dyes which exhibit a reactive trifluoroacetyl group, reversibly interact with alcohols, amines or water to give the respective diol, hemiaminal, hemiacetal or zwitterion. Indicator dyes that combine the properties of a chemical reagent and a ligand molecule are termed ‘chromo-’ or ‘fluororeactands’. They are embedded in various polymer materials and have been characterised for the optical sensing of aliphatic amines, alcohols and humidity. Furthermore, methacrylate derivatives of the dyes have been tested. They were prepared to link the dyes covalently to the polymer matrix. The optical and physical properties of the dye methacrylates make them promising candidates not only for optical sensing but also for applications in molecularly imprinted polymers and non-linear optics.

Comparison of different methods for determining the selectivity coefficient using a magnesium-selective electrode

A lot of effort has been put into correctly describing the selectivity of ion-selective membrane electrodes (ISEs). The fact that the selectivity coefficients of ions with different charge numbers cannot be exchanged for each other was of major practical and theoretical concern. Therefore the “matched potential method” (MPM) was recommended by IUPAC for reporting the selectivity coefficients Kpoti,j correctly when ions of unequal charge numbers are involved. In our experiments, however, the MPM was found to be inaccurate, inconsistent, and not practical. The MPM was made use of in order to investigate the selectivity pattern of magnesium-selective membrane electrodes incorporating the ionophore ETHT 5506. The drawbacks and problems are discussed. Furthermore, a consistent selectivity coefficient Kconsi,j is defined, and an algorithm is derived mathematically from the Nernst and Nickolsky equations which describe the electrode response, and allows to report consistent selectivity coefficients for a primary and an interfering ion of different charge number and vice versa.

Photodissociation of CFCl3 at 193 nm investigated by photofragment translational spectroscopy

Abstract The collisionless photodissociation of CFCl 3 at 193 nm has been studied with the method of crossed laser and molecular beams. The primary dissociation is shown to produce exclusively the fragment pairs CFCl 2 + Cl with a non-thermal translational energy distribution. The average kinetic energy of 32 kcal/mol corresponds to 42% of the available energy and implies an average internal energy of CFCl 2 of 43 kcal/mol. From the recoil anisotropy parameter β = +0.74 ± 0.15 the photoexcitation is inferred to proceed via an E ← A 1 transition polarized perpendicular to the C–F bond. At higher laser fluence a fraction of the nascent CFCl 2 radicals absorbs a further photon and dissociates into CFCl + Cl; the cross section for this secondary process is estimated to be approximately twice as large as that of the primary photodissociation.

Novel probes for pH and dissolved oxygen measurements in cultivations from millilitre to benchtop scale

AbstractpH value and the concentration of dissolved oxygen (DO) are key parameters to monitor and control cell growth in cultivation studies. Reliable, robust and accurate methods to measure these parameters in cultivation systems in real time guarantee high product yield and quality. This mini-review summarises the current state of the art of pH and DO sensors that are applied to bioprocesses from millilitre to benchtop scale by means of a short introduction on measuring principles and selected applications. Special emphasis is placed on single-use bioreactors, which have been increasingly employed in bioprocess development and production in recent years. Working principles, applications and the particular requirements of sensors in these cultivation systems are given. In such processes, optical sensors for pH and DO are often preferred to electrochemical probes, as they allow semi-invasive measurements and can be miniaturised to micrometre scale or lower. In addition, selected measuring principles of novel sensing technologies for pH and DO are discussed. These include solid-state sensors and miniaturised devices that are not yet commercially available, but show promising characteristics for possible use in bioprocesses in the near future.

A rationally designed oligopeptide shows significant conformational changes upon binding to sulphate ions

Oligopeptides that interact with oxoanions were developed by rational design methods. The substrate-binding site of the enzyme purine nucleoside phosphorylase served as a model for the design of the ionophores. The amino acids involved in the complexation of oxoanions were linked through flexible spacer residues. These spacers were chosen such that the relative orientation of the interacting amino acids was conserved. Several peptide sequences were preselected based on intermolecular H-bond frequencies. These frequencies were calculated from molecular dynamics trajectories of the corresponding peptide-anion complexes and used to score the binding properties of the peptides. The most promising peptides were prepared using solid phase peptide synthesis. Anion binding of the peptide ionophores was screened using circular dichroism (CD) and confirmed by NMR spectroscopy. CD measurements performed in methanol revealed a significant conformational change of a linear undecapeptide upon binding to sulphate ions. Two-dimensional-NMR experiments confirmed that a conformation with high helical content is formed in the presence of sulphate ions. These conformational changes induced by the anion stimulate the development of new transduction mechanisms in chemical sensors.

Pitzer ion activities in mixed electrolytes for calibration of ion-selective electrodes used in clinical chemistry

Metrological comparability as well as reliability of ion activity results measured with ion-selective electrodes (ISE) was investigated within the framework of an interlaboratory comparison between eight partners from national metrology institutes and expert laboratories. Two electrolyte solutions containing the clinically most relevant ions sodium, potassium, magnesium, calcium and chloride having ion activities near the physiological range served as samples. The calibration of the measurement set-ups of the participants was carried out using gravimetrically prepared aqueous electrolyte solutions. The ion activities of these calibration standards were calculated by means of the semi-empirical Pitzer model. The measurement uncertainty of the measurement results was calculated according to the guide to the expression of uncertainty in measurement, GUM. Based on a new scale for ion activities traceable to the SI system of units, comparability and reliability of ISE measurement results of clinically relevant ions is realised.

BioTech 2017 Conference Report, Wädenswil, 7./8.9.2017

Almost 200 scientists and professionals from academia and industry attended the BioTech 2017 conference at the Zurich University of Applied Sciences (ZHAW) in Wädenswil on 7./8. September 2017. The focus of this years conference was (bio) process analytics and sensor technology, taking into account the increasingly prominent role of online measurement and control in the process industry.