Rapid revelation of radiocarbon records with laser ablation Accelerator Mass Spectrometry.

By focusing high-intensity laser pulses on carbonate samples carbon dioxide is generated and can be directly introduced into the gas ion source (GIS) of an Accelerator Mass Spectrometer (AMS). This new technique allows rapid radiocarbon analyses at high spatial resolution. The design of the deignated laser ablation cell as well as first results on a stalagmite sample are presented.

On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration.

Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet-droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet-droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet-droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet-droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 µs. This work gives a clear picture of droplet-droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.

Synthesis and investigation of tryptophan-amphotericin B conjugates.

Anchors aweigh! The synthesis of tryptophan-amphotericin B conjugates (see figure) is described. The membrane-anchoring effect of tryptophane was thus combined with the pore-formation effect of amphotericin B leading to high channel activity in sterol-free liposomes.

Energy-resolved collision-induced dissociation cross sections of 2:1 bis-oxazoline copper complexes. Nonbonded interactions and nonlinear effects.

Absolute ligand binding energies are determined for the 2:1 complexes of bis-oxazoline ligands and Cu(I) in the gas phase by the fitting of energy-resolved collision-induced dissociation cross sections. The complexes were chosen for their occurrence in asymmetric catalysis for which the phenomenon of nonlinear effects is explained by differences in stability for homochiral and heterochiral complexes. Pseudo-enantiomeric ligands are used so that mass spectrometric measurements can be employed. The measurements find that the sterically similar, but electronically different, isopropyl versus phenyl substituents lead to a different stability ordering of the homo- versus heterochiral complexes, which then leads to the prediction of nonlinear effects in asymmetric catalysis by the complexes with isopropyl-substituted ligands. The origin of the difference in stability order is found in noncovalent interactions between the phenyl groups on the ligands, which are poorly described by DFT calculations.

Fourier transform ion mobility measurement of chain branching in mass-selected, chemically trapped oligomers from methylalumoxane-activated, metallocene-catalyzed polymerization of ethylene.

Fourier transform ion mobility spectrometry is used to determine the branching in mass-selected, chemically trapped oligomers produced in the polymerization of ethylene by a metallocene catalyst activated by methylalumoxane. The measured branching is included in a kinetic analysis to extract the activation energies for the elementary steps in polyethylene formation. Propagation, chain transfer, and chain walking have activation energies of 4.1, 11, and 11 kcal/mol.