Operational variables in high-performance liquid chromatography-electrospray ionization mass spectrometry of peptides and proteins using poly(styrene-divinylbenzene) monoliths

Capillary reversed-phase high-performance liquid chromatography (RP-HPLC) utilizing monolithic poly(styrene-divinylbenzene) columns was optimized for the coupling to electrospray ionization mass spectrometry (ESI-MS) by the application of various temperatures and mobile phase additives during peptide and protein analysis. Peak widths at half height improved significantly upon increasing the temperature and ranged from 2.0 to 5.4 s for peptide and protein separations at 70 degrees. Selectivity of peptide elution was significantly modulated by temperature, whereas the effect on proteins was only minor. A comparison of 0.10% formic acid (FA), 0.050% trifluoroacetic acid (TFA), and 0.050% heptafluorobutyric acid (HFBA) as mobile phase additives revealed that highest chromatographic efficiency but poorest mass spectrometric detectabilities were achieved with HFBA. Clusters of HFBA, water, and acetonitrile were observed in the mass spectra at m/z values >500. Although the signal-to-noise ratios for the individual peptides diverged considerably both in the selected ion chromatograms and extracted mass spectra, the average mass spectrometric detectabilities varied only by a factor of less than 1.7 measured with the different additives. Limits of detection for peptides with 500 nl sample volumes injected onto a 60 mm x 0.20 mm monolithic column were in the 0.2-13 fmol range. In the analysis of hydrophobic membrane proteins, HFBA enabled highest separation selectivity at the cost of lower mass spectral quality. The use of 0.050% TFA as mobile phase additive turned out to be the best compromise between chromatographic and mass spectrometric performance in the analysis of peptides and proteins by RP-HPLC-ESI-MS using monolithic separation columns.     

Existence of pulses in excitable media with nonlocal coupling

We prove the existence of fast traveling pulse solutions in excitable media with non-local coupling. Existence results had been known, until now, in the case of local, diffusive coupling and in the case of a discrete medium, with finite-range, non-local coupling. Our approach replaces methods from geometric singular perturbation theory, that had been crucial in previous existence proofs, by a PDE oriented approach, relying on exponential weights, Fredholm theory, and commutator estimates.     

Thermal processes in the systems with Li-battery cathode materials and LiPF6 -based organic solutions

Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li₂MnO₃, xLi₂MnO₃ ^.(1???x)Li(MnNiCo)O₂,LiNi_0.33Mn_0.33Co_0.33O₂, LiNi_0.4Mn_0.4Co_0.2O₂, LiNi_0.8Co_0.15Al_0.05O₂ LiMn_1.5Ni_0.5O₄, LiMn(or Fe)PO₄, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF₆ salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF₆-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li₂CO₃ is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures.     

Superspiral structures of meandering and drifting spiral waves

The spatiotemporal superstructure of meandering and drifting spiral waves is explained analytically. It is also demonstrated that the Hopf eigenmode that causes the transition to meandering waves is weakly exponentially localized at onset but grows exponentially slightly before onset.     

Molecules on kepler orbits: An experimental study

We have demonstrated experimentally that polar molecules revolve around the inner electrode of a charged cylindrical capacitor in helical trajectories that result from a superposition of a translational motion along and an orbital motion around the cylinder axis. In this way molecular beams can be guided over any given distance. The results have been obtained for nozzle beams of NaCl, NaBr, and NaI seeded in Kr. The capacitor bent into a toroid may be used as a storage ring for polar molecules in high field seeking rotational states.