Synthesis and properties of water soluble molecular clips and tweezers. Molecular recognition of biological relevant substrates.

Die vorliegende Arbeit befasst sich mit der supramolekularen Chemie, die ein wichtiges Teilgebiet der Chemie darstellt. Diese basiert auf nicht-kovalenten Wechselwirkungen, die zur Bildung von Molekülassoziaten führen. Die Untersuchung dieser nicht-kovalenten Wechselwirkungen kann anhand von kleinen Modellsystemen erfolgen. In der vorliegenden Arbeit dienen molekulare Klammern und Pinzetten als solche Modellsysteme. Diese wurden mit Phosphatgruppen substituiert, um sie wasserlöslich zu machen. Die supramolekularen Eigenschaften dieser wasserlöslichen molekularen Klammern und Pinzetten wurden anhand von Proton-NMR- und Fluoreszenztitrationen gegenüber einer breiten Palette von biologisch wichtigen Substraten untersucht. Die Phosphat-substituierten molekularen Klammern und Pinzetten bilden stabile Wirt-Gast-Komplexe vor allem mit elektronenarmen, biologisch wichtigen Substraten wie Nucleosiden, Nucleotiden, Enzym-Cofaktoren und Aminosäuren aus. Die molekulare Klammer ist hierbei selektiv gegenüber sterisch anspruchsvollen Verbindungen, wie den Enzym-Cofaktoren NAD+ und SAM oder den Xanthinen Coffein und Theophyllin. Die molekulare Pinzette bindet dagegen bevorzugt Verbindungen mit geringem sterischen Anspruch wie z. B. die aliphatische Aminosäure Lysin

Evaluation and validation of detailed and simplified models of the uncertainty of unified pHabsH2O measurements in aqueous solutions

Highlights • First detailed evaluation of the uncertainty of pHabsH2O measurements. • Bottom-up uncertainty evaluations proven valid for 95% confidence. • Monte Carlo Simulation of pHabsH2O measurement ladder with least-squares minimisation. • Described simplified and detailed bottom-up uncertainty evaluations are equivalent. • Measurements from 2 to 10 pHabsH2O with a 95% expanded uncertainty of 0.26–0.51.The use of the unified pH concept, pHabsH2O, applicable to aqueous and non-aqueous solutions, which allows interpreting and comparison of the acidity of different types of solutions, requires reliable and objective determination. The pHabsH2O can be determined by a single differential potentiometry measurement referenced to an aqueous reference buffer or by a ladder of differential potentiometric measurements that allows minimisation of inconsistencies of various determinations. This work describes and assesses bottom-up evaluations of the uncertainty of these measurements, where uncertainty components are combined by the Monte Carlo Method (MCM) or Taylor Series Approximation (TSM). The MCM allows a detailed simulation of the measurements, including an iterative process involving in minimising ladder deviations. On the other hand, the TSM requires the approximate determination of minimisation uncertainty. The uncertainty evaluation was successfully applied to measuring aqueous buffers with pH of 2.00, 4.00, 7.00, and 10.00, with a standard uncertainty of 0.01. The reference and estimated values from both approaches are metrologically compatible for a 95% confidence level even when a negligible contribution of liquid junction potential uncertainty is assumed. The MCM estimated pH values with an expanded uncertainty, for the 95% confidence level, between 0.26 and 0.51, depending on the pH value and ladder inconsistencies. The minimisation uncertainty is negligible or responsible for up to 87% of the measurement uncertainty. The TSM quantified measurement uncertainties on average only 0.05 units larger than the MCM estimated ones. Additional experimental tests should be performed to test these uncertainty models for analysis performed in other laboratories and on non-aqueous solutions

Traceable pH and ISE measurements in clinical chemistry (Mesuragestraçable de pH et ISE dans la chimie clinique)

Reliable analysis results are indispensable in clinical chemistry for unambiguous diagnosis. Hence today traceability of the patient measurement to the SI system is established within the scope of a traceability system consisting of a national metrology institute and routine- and reference laboratories

Data_sheet_1_Metrology for pH Measurements in Brackish Waters—Part 1: Extending Electrochemical pHT Measurements of TRIS Buffers to Salinities 5–20.pdf

<p>Harned cell pH_T measurements were performed on 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) buffered artificial seawater solutions in the salinity range 5–20, at three equimolal buffer concentrations (0.01, 0.025, 0.04 mol·kg-H₂O⁻¹), and in the temperature range 278.15–318.15 K. Measurement uncertainties were assigned to the pH_T values of the buffer solutions and ranged from 0.002 to 0.004 over the investigated salinity and temperature ranges. The pH_T values were combined with previous results from literature covering salinities from 20 to 40. A model function expressing pH_T as a function of salinity, temperature and TRIS/TRIS·H⁺ molality was fitted to the combined data set. The results can be used to reliably calibrate pH instruments traceable to primary standards and over the salinity range 5–40, in particular, covering the low salinity range of brackish water for the first time. At salinities 5–20 and 35, the measured dependence of pH_T on the TRIS/TRIS·H⁺ molality enables extrapolation of quantities calibrated against the pH_T values, e.g., the dissociation constants of pH indicator dyes, to be extrapolated to zero TRIS molality. Extrapolated quantities then refer to pure synthetic seawater conditions and define a true hydrogen ion concentration scale in seawater media.</p

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 semiempirical 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

Symmetric Potentiometric Cells for the Measurement of Unified pH Values

A unified pH scale of absolute values (pHabs scale) enables the comparison of acidities in different solvents. To date, very few different experimental setups have been used for the measurement of values on this scale. The article describes the design and performance of the different symmetric cells used for unified pH measurement by several institutions. Well-established and reliable standard aqueous buffer solutions are the first step of method validation necessary to achieve a robust metrological level for more complex media. The pH of aqueous standard buffers was measured by differential potentiometry, where the potential between two glass electrodes is measured directly. All the tested electrochemical cells prove to be suitable for unified pH measurements. This validation highlights that the method is, to a large extent, independent of the used equipment, including the cell geometry. The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of obtained results