Optimum excitation conditions in spectrographic analysis with the D. C. carbon arc

Summary A previously established expression for the transport mechanism in the arc is applied to the equation for the spectral line intensity. The possibility of a correlation between temperature and electron concentration in the arc is discussed and optimum temperatures are calculated, for which the intensity of an atom line reaches a maximum. The optimum temperature is shown to depend on (a) the excitation potential of the transition and the ionization potential of the element, (b) the magnitude of the electron concentration and its variation with arc temperature and (c) the occurence of transport processes in the arc.

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Zusammenfassung Mit Hilfe einer kürzlich gefundenen Beziehung für den Transportmechanismus im Gleichstrombogen wird eine vollstÄndige Gleichung für die LinienintensitÄt erhalten. Die Möglichkeit einer Korrelation zwischen Temperatur und Elektronenkonzentration im Bogenraum wird diskutiert und optimale Temperaturen werden berechnet, für welche die IntensitÄt einer Atomlinie maximal wird. Die optimale Temperatur hÄngt ab von a) der Anregungsenergie des Spektralübergangs und der Ionisierungsspannung des Elementes, b) der Grö\e der Elektronenzahl und ihrer Änderung mit der Temperatur, und c) dem Transportmechanismus im Bogenraum.

     

Separation and identification of illicit heroin samples by liquid chromatography using an alumina and C18 coupled column system and photodiode array detection

The analysis of illicit heroin and opium samples on a coupled alumina and C18 column system is described. The compounds to be analysed can be divided into two groups: those with low pKa values, such as caffeine, papaverine and noscapine, and those with high pKa values, such as heroin, acetylcodeine, O6-monoacetylmorphine, procaine, codeine, morphine and strychnine. The first group can best be separated on a C18 column, whereas alumina is more suitable for the second group. Previously reported criteria for choosing proper buffer systems for ion-exchange separations on alumina were used together with an iterative regressive optimization procedure developed in our laboratory. The system can be used with and without valve-switching, depending on the sample type. The peak purity of the judicially important components heroin and O6-monoacetylmorphine has been checked with a photodiode array detector and by use of advanced software.     

Enhanced sampling molecular dynamics simulations correctly predict the diverse activities of a series of stiff-stilbene G-quadruplex DNA ligands

Ligands with the capability to bind G-quadruplexes (G4s) specifically, and to control G4 structure and behaviour, offer great potential in the development of novel therapies, technologies and functional materials. Most known ligands bind to a pre-formed topology, but G4s are highly dynamic and a small number of ligands have been discovered that influence these folding equilibria. Such ligands may be useful as probes to understand the dynamic nature of G4 in vivo, or to exploit the polymorphism of G4 in the development of molecular devices. To date, these fascinating molecules have been discovered serendipitously. There is a need for tools to predict such effects to drive ligand design and development, and for molecular-level understanding of ligand binding mechanisms and associated topological perturbation of G4 structures. Here we study the G4 binding mechanisms of a family of stiff-stilbene G4 ligands to human telomeric DNA using molecular dynamics (MD) and enhanced sampling (metadynamics) MD simulations. The simulations predict a variety of binding mechanisms and effects on G4 structure for the different ligands in the series. In parallel, we characterize the binding of the ligands to the G4 target experimentally using NMR and CD spectroscopy. The results show good agreement between the simulated and experimentally observed binding modes, binding affinities and ligand-induced perturbation of the G4 structure. The simulations correctly predict ligands that perturb G4 topology. Metadynamics simulations are shown to be a powerful tool to aid development of molecules to influence G4 structure, both in interpreting experiments and to help in the design of these chemotypes.

Enhanced sampling molecular dynamics simulations and solution-phase experiments come together to demonstrate the diverse effects of G4-interactive small molecules.