Characterization of low molecular weight hydrocarbon oligomers by laser desorption/ionization time-of-flight mass spectrometry using a solvent-free sample preparation method.

A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards.     

THE NON-RADIATIVE DISSIPATION OF EXCITATION ENERGY IN SOLID CINNAMIC ACID BY DIMER FORMATION

Abstract— The quantum efficiency for the photodimerization of trans -cinnamic acid in the solid state is independent of intensity and is found to have a value approaching two. Thus, the reaction involves one excited and one un-excited molecule.
During the exposure, a dimer film developing on the surface of the cinnamic acid layer attenuates the intensity of the radiation incident on the unreacted cinnamic acid. This gives the appearance of a decrease in the quantum yield with increasing number of photons incident.     

Sequestering of Eu(III) by a GAAA RNA tetraloop

The site-specific binding of metal ions maintains an important role in the structure, thermal stability, and function of folded RNA structures. RNA tetraloops of the "GNRA" family (where N = any base and R = any purine), which owe their unusual stability to base stacking and an extensive hydrogen bonding network, have been observed to bind metal ions having different chemical and geometric properties. We have used laser-induced lanthanide luminescence and isothermal titration calorimetry (ITC) to examine the metal-binding properties of an RNA stem loop of the GNRA family. Previous research has shown that a single Eu(III) ion binds the stem loop fragment in a highly dehydrated site with a K(d) of approximately 12 microM. Curve-fitting analysis of the broad luminescence excitation spectrum of Eu(III) upon complexation with the tetraloop fragment indicates the possibility of two microenvironments that do not differ in hydration number. Binding of Eu(III) to the loop was accompanied by positive enthalpic changes, consistent with energetic cost of removal of water molecules and suggesting that the binding is entropically driven. By comparison, binding of Mg(II) or Mn(II) to the RNA loop, or Eu(III) to the DNA analogue of the loop, was associated with exothermic changes, consistent with predominantly outer-sphere coordination. These results suggest specific binding, most probably involving ligands on the 5' side of the loop.     

Pimaricin—VIII : Structural and configurational studies by electron impact and field desorption mass spectrometry, 13C (25.2MHz) and 1H (270 MHz)-NMR spectroscopy

Attempts to obtain a molecular ion from the polyene macrolide antibiotic pimaricin by EI and FD mass spectrometry were unsuccessful The loss of carbon dioxide and a varying number of water molecules from the molecular ion made a molecular-weight determination impossible ¹³C NMR spectroscopy of N-acetylpimaricin, its dodecahydroderivative, and of HH-2, a hydrogenation-hydrogenolysis product of N-acetylpimaricin, confirmed that the antibiotic has structure 3 containing a hemi-ketalic ring and lacking an OH group at C-8. The value of the anomeric coupling constant, J_c-1-h-1, indicates that the mycosamine moiety is β-glycosidically bound to the aglycone.The structure and configuration of the antibiotic have been studied by analysis of the 270 MHz ¹H-NMR spectra of N acetylpimaricin and HH-2. By comparison of the two spectra and by extensive decoupling experiments, all signals in the spectrum of N-acetylpimaricin have been assigned to the protons in structure 3. From chemical-shift, coupling constant, and integral values, it was deduced that the mycosamine ring is pyranoid with a chair conformation, the hemi-ketal is 6 membered and occupies a chair conformation with the substituents in equatorial positions, the epoxy protons as well as the olefinic protons are trans to each other, and the antibiotic is diastereomerically pure.     

Splitless on-line coupling of capillary high-performance liquid chromatography,capillary electrochromatography and pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

A mixture of unsaturated fatty acid methyl esters was separated with a new splitless capillary set-up. With the employed apparatus configuration different capillary separation techniques such as capillary high-performance liquid chromatography (cHPLC), capillary electrochromatography (CEC) and pressurized capillary electrochromatography (pCEC) could be applied. The detection and identification of the sample compounds were accomplished by hyphenating these capillary separation techniques with nuclear magnetic resonance (NMR) spectroscopy using a novel configuration of the detection capillary set-up. Using modified electrokinetically driven separation techniques, the electric field was applied solely across the separation column. With this improved interface for capillary liquid chromatography-NMR on-line coupling, the stereochemical assignment of the cis and trans configuration of unsaturated fatty acids could be easily accomplished. Finally, the results of cHPLC-NMR, CEC-NMR and pCEC-NMR coupling experiments were compared.Dedicated to Professor Günter Häfelinger on the occasion of his 65th birthday     

Back-Transformation into Physical Configuration Space after Model Order Reduction onto a General Subspace

Model order reduction (MOR) techniques that project onto a general subspace are common practice. In Elastic Multi-Body-Dynamics (EMBD) distinct interface coordinates are required for the interconnection of the elastic structure and the multi-body system. For that reason, a physical interpretation of the coordinates is mandatory, which is not the case for reduced order models in a general subspace. To make alternative MOR techniques accessible for EMBD, a back-projection approach was introduced by [1]. Therein, the system is projected back onto the physical configuration space, which requires the inversion of the master partition of the projection matrix. But the procedure lacks of robustness and generality. A novel approach is introduced by generating additional master coordinates using sensor placement methods, e.g. the Effective-Independence-algorithm (EfI) [2]. By using a rank criterion for the automatic selection of additional coordinates, the improved back-transformation performs properly and without damaging the reduced order model at a fairly small computational overhead, which is demonstrated at the example of a gear box housing. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)