Design, Functionalization, Synthesis and Evaluation of New Chiral Stationary Phases for (U)HPLC and Their Implementation in Drug Analysis, (Enantio)Purification and Structural Elucidation

Das Feld der chiralen Flüssigchromatographie ist von herausragender Bedeutung für eine Vielzahl akademischer und industrieller Anwendungen. Die Entwicklung neuer potenzieller Arzneistoffe, Umweltanalytik, laborgestützte Diagnostik und Strukturaufklärung sind nur einige der Bereiche, aus denen die chirale Flüssigchromatographie heute nicht wegzudenken ist. Aus diesem Grund gibt die vorliegende kumulative Dissertation einen Überblick sowohl über die Entwicklung als auch über die Anwendung chiraler stationärer Phasen für die enantioselektive (Ultra-)Hochleistungsflüssigchromatographie ((U)HPLC). Im ersten Teil dieser Dissertation wuden neue chirale stationäre Phasen (CSPs) basierend auf Anionentauschern und zwitterionischen Ionentauschern entwickelt. Folgende Ziele konnten dabei erreicht werden: Verschiedene Silikapartikel wurden bezüglich ihrer kinetischen Leistung für enantioselektive UHPLC optimiert. Dabei wurde ein detaillierter Einblick in die zahlreichen Interaktionsprozesse zwischen Analyt und stationärer Phase gewonnen [Publikation I]. Die Anbindungschemie und deren Entstehung durch chemische Radikalstarter (thermisch oder UV-initiiert) wurde verglichen und systematisch optimiert. Hier wurde eine neue, lösemittelfreie, UV-initiierte Immobilisierungsstrategie eingeführt, welche zu wenig blutenden, sogenannten „Plattform-Typ“-Phasen führt [Publikation II]. Die Funktionalisierung von Silika, welche als Ausgangspunkt für die Entwicklung CSP-basierter HPLC-Säulen gelten kann, wurde verändert und für schnelle Trennungen optimiert. Dies wurde durch eine Verringerung des Widerstands gegen den Massentransfer erreicht. Dazu wurden Silatrane verwendet, welche einen dünnen, homogenen Film an Thiolgruppen auf der Oberfläche der Silikapartikel formen. Hierzu wurde erst ein mehr- [Publikation III] und anschließend ein einstufiges Verfahren eingeführt [Publikation IV]. Der zweite Teil der vorliegenden Dissertation handelt von der Anwendung chiraler Trennmethoden. Folgende Aspekte wurden dabei ausgearbeitet: Da die Anwendungsfelder der Metabolomik und Lipidomik nach immer mehr chiralen Trennmethoden verlangen, wurde ein Leitfaden zur Trennung verzweigter kurzkettiger Fettsäuren basierend auf Polysaccharidsäulen entwickelt [Publikation V]. Des Weiteren wurde die Chiralität von vorher unbekannten Naturstoffen aufgeklärt [Publikation VI]. Ein Protokoll zur enantiomerenreinen Aufreinigung eines Radiotracers konnte entwickelt und angewandt werden [Publikation VII]. Das Wissen über chirale HPLC-Trennungen sowohl im analytischen als auch im präparativen Maßstab wurde ferner in der Entwicklung neuer Wirkstoffkandidaten angewandt [Publikationen VIII und IX]. Zusammenfassend lässt sich sagen, dass eine umfassende Forschungsarbeit in dem Gebiet der Planung, Funktionalisierung, Synthese und Evaluierung chiraler stationärer Phasen sowie ihren breiten Anwendungsbereichen durchgeführt wurde.Chiral liquid chromatography is a field of utmost importance for a wide range of academic and industrial applications. Drug development, environmental analysis, laboratory-based diagnostics, or structure elucidation among others, strongly rely on chiral liquid chromatography nowadays. For this reason, this cumulative thesis describes the development and applications of chiral stationary phases for enantioselective (ultra-)high performance liquid chromatography ((U)HPLC). In the first part of the thesis, new chiral stationary phases (CSPs) based on anion-exchange and zwitterionic ion exchange chiral selectors were developed. The following goals were achieved during the work on this thesis: Various silica particles were evaluated for their kinetic performance optimization for enantioselective UHPLC and a deep insight into a variety of interactions between analyte and stationary phase was gained [Publication I]. The bonding chemistry and its generation by thermic or UV-driven radical starter was evaluated and systematically optimized by introducing a solvent-free photo-click immobilization strategy resulting in low-bleeding, “platform-type” stationary phases [Publication II]. Furthermore, the functionalization of bare silica, which can be seen as the starting point of the production of a CSP-based HPLC column, was varied and optimized for fast separations by the reduction of mass transfer resistance using silatranes and thus forming thin, homogeneous monolayer of thiol functionalization in a multiple-step [Publication III] and in a single-step approach [Publication IV]. The second part of the thesis focuses on the application of enantiomer separation. This includes the elaboration of the following aspects: Since chiral methods are becoming increasingly important in the fields of metabolomics and lipidomics, a guide for the chiral analysis of branched short-chain fatty acids based on polysaccharide columns was developed [Publication V]. Furthermore, the chirality of previously unknown natural compounds was elucidated [Publication VI]. A protocol for the enantiopurification of a radiotracer was established [Publication VII]. Knowledge about chiral HPLC was used for both analytical and preparative separation in the development of potential new drugs [Publications VIII and IX]. In summary, extensive research on the design, functionalization, synthesis, and evaluation of chiral stationary phases and their scope of applications has been performed

Microwave spectroscopy on heavy-fermion systems: probing the dynamics of charges and magnetic moments

Investigating solids with light gives direct access to charge dynamics, electronic and magnetic excitations. For heavy fermions, one has to adjust the frequency of the probing light to the small characteristic energy scales, leading to spectroscopy with microwaves. We review general concepts of the frequency-dependent conductivity of heavy fermions, including the slow Drude relaxation and the transition to a superconducting state, which we also demonstrate with experimental data taken on UPd2Al3. We discuss the optical response of a Fermi liquid and how it might be observed in heavy fermions. Microwave studies with focus on quantum criticality in heavy fermions concern the charge response, but also the magnetic moments can be addressed via electron spin resonance (ESR). We discuss the case of YbRh2Si2, the open questions concerning ESR of heavy fermions, and how these might be addressed in the future. This includes an overview of the presently available experimental techniques for microwave studies on heavy fermions, with a focus on broadband studies using the Corbino approach and on planar superconducting resonators.Comment: 11 pages, 6 figures, proceedings of QCnP 201

Identification of Functionally Distinct Na-HCO3 Co-Transporters in Colon

Na-HCO3 cotransport (NBC) regulates intracellular pH (pHi) and HCO3 secretion in rat colon. NBC has been characterized as a 5,5′-diisothiocyanato-2-2′-stilbene (DIDS)-sensitive transporter in several tissues, while the colonic NBC is sensitive to both amiloride and DIDS. In addition, the colonic NBC has been identified as critical for pHi regulation as it is activated by intravesicular acid pH. Molecular studies have identified several characteristically distinct NBC isoforms [i.e. electrogenic (NBCe) and electroneutral (NBCn)] that exhibit tissue specific expression. This study was initiated to establish the molecular identity and specific function of NBC isoforms in rat colon. Northern blot and reverse transcriptase PCR (RT-PCR) analyses revealed that electrogenic NBCe1B or NBCe1C (NBCe1B/C) isoform is predominantly expressed in proximal colon, while electroneutral NBCn1C or NBCn1D (NBCn1C/D) is expressed in both proximal and distal colon. Functional analyses revealed that amiloride-insensitive, electrogenic, pH gradient-dependent NBC activity is present only in basolateral membranes of proximal colon. In contrast, amiloride-sensitive, electroneutral, [H+]-dependent NBC activity is present in both proximal and distal colon. Both electrogenic and electroneutral NBC activities are saturable processes with an apparent Km for Na of 7.3 and 4.3 mM, respectively; and are DIDS-sensitive with apparent Ki of 8.9 and 263.8 µM, respectively. In addition to Na-H exchanger isoform-1 (NHE1), pHi acidification is regulated by a HCO3-dependent mechanism that is HOE694-insensitive in colonic crypt glands. We conclude from these data that electroneutral, amiloride-sensitive NBC is encoded by NBCn1C/D and is present in both proximal and distal colon, while NBCe1B/C encodes electrogenic, amiloride-insensitive Na-HCO3 cotransport in proximal colon. We also conclude that NBCn1C/D regulates HCO3-dependent HOE694-insensitive Na-HCO3 cotransport and plays a critical role in pHi regulation in colonic epithelial cells

Equations for solar tracking

Direct Sun light absorption by trace gases can be used to quantify them and investigate atmospheric chemistry. In such experiments, the main optical apparatus is often a grating or a Fourier transform spectrometer. A solar tracker based on motorized rotating mirrors is also needed to direct the light along the spectrometer axis, correcting for the apparent rotation of the Sun. Calculating the Sun azimuth and altitude for a given time and location can be achieved with high accuracy but different sources of angular offsets appear in practice when positioning the mirrors. A feedback on the motors, using a light position sensor closed to the spectrometer is almost always needed. This paper aims to gather the main geometrical formulas necessary for the use of a widely used kind of solar tracker, based on two 45{\deg} mirrors in altazimuthal set-up with a light sensor on the spectrometer, and to illustrate them with a tracker developed for atmospheric research by our group.Comment: 14 pages, 7 figures. Second version of the paper as published in Sensors. Main correction: a rotation matrix converted to a reflection matrix. Main addition: a discussion on how the control theory applies to this kind of tracking syte

DOM files

<p>DOM samples for Daniel, 20230807, neg mode</p&gt