The novel use of gas chromatography-ion mobility-time of flight mass spectrometry with secondary electrospray ionization for complex mixture analysis

Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry (GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils, were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components, were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses of complex chemical and biological mixtures.     

How many amorphous ices are there?

Many acronyms are used in the literature for describing different kinds of amorphous ice, mainly because many different preparation routes and many different sample histories need to be distinguished. We here introduce these amorphous ices and discuss the question of how many of these forms are of relevance in the context of polyamorphism. We employ the criterion of reversible transitions between amorphous "states" in finite intervals of pressure and temperature to discriminate between independent metastable amorphous "states" and between "substates" of the same amorphous "state". We argue that the experimental evidence suggests we should consider there to be three polyamorphic "states" of ice, namely low-(LDA), high-(HDA) and very high-density amorphous ice (VHDA). In addition to the realization of reversible transitions between them, they differ in terms of their properties, e.g., compressibility, or number of "interstitial" water molecules. Thus they cannot be regarded as structurally relaxed variants of each other and so we suggest considering them as three distinct megabasins in an energy landscape visualization.     

Strong solutions to the Stokes equations of a flow around a rotating body in weighted Lq spaces

We consider the motion of a fluid in the exterior of a rotating obstacle. This leads to a modified version of the Stokes system which we consider in the whole space ${\mathds R}^n$, n = 2 or n = 3 and in an exterior domain $D\subset {\mathds R}^3$. For every q ∈ (1, ∞) we prove existence of solutions and estimates in function spaces with weights taken from a subclass of the Muckenhoupt class A_q. Moreover, uniqueness is shown modulo a vector space of dimension 3. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Paracyclophanes as model compounds for strongly interacting π-systems, part 3: influence of the substitution pattern on photoabsorption properties

The structures and energetics of the ground and first excited states of [2.2]paracyclophane (PC) and its pseudo-para- (p-DHPC) and pseudo-ortho-dihydroxy (o-DHPC) as well as monohydroxy derivates (MHPC) are investigated by quantum chemical calculations, X-ray crystallography, and resonance-enhanced multiphoton ionization spectroscopy (REMPI) in a free jet. We show that substitution of the aromatic hydrogens in PC causes significant changes of the structure and in particular its change between the ground and the excited state. The structural changes include a breathing mode as well as shift and rotation of the benzene moieties and are rationalized by the electronic structure changes upon excitation. Spin-component-scaled second-order M?ller-Plesset perturbation method (SCS-MP2) reproduces the experimental X-ray structure correctly and performs significantly better than ordinary MP2 and the B3LYP methods. The parent propagation method, SCS-approximate coupled cluster second order (SCS-CC2), yields adiabatic excitation energies within 0.1 eV of the experimental values for PC and the investigated hydroxyl derivates as well as the related aromatic molecules benzene and phenol. It is shown that zero-point vibration energy corrections at the time dependent density functional (B3LYP) level are no more accurate enough for that level of theory and have to be substituted by SCS-CC2 values. While the structures of PC and o-DHPC are only slightly modified upon excitation, p-DHPC changes its structural parameters substantially. This is in line with [1 + 1] REMPI-spectra of these substances, which are interpreted with the help of Franck-Condon simulations.     

NMR spectroscopy of intermetallic compounds: an experimental and theoretical approach to local atomic arrangements in binary gallides

The results of the investigation of MGa(2) with M = Ca, Sr, Ba and of MGa(4) with M = Na, Ca, Sr, Ba by a combined application of NMR spectroscopy and quantum mechanical calculations are comprehensively evaluated. The electric-field gradient (EFG) was identified as the most reliable measure to study intermetallic compounds, since it is accessible with high precision by quantum mechanical calculations and, for nuclear spin I>1/2, by NMR spectroscopy. The EFG values obtained by NMR spectroscopy and quantum mechanical calculations agree very well for both series of investigated compounds. A deconvolution of the calculated EFGs into their contributions reveals its sensitivity to the local environment of the atoms. The EFGs of the investigated di- and tetragallides are dominated by the population of the p(x)-, p(y)-, and p(z)-like states of the Ga atoms. A general combined approach for the investigation of disordered intermetallic compounds by application of diffraction methods, NMR spectroscopy, and quantum mechanical calculations is suggested. This scheme can also be applied to other classes of crystalline disordered inorganic materials.     

Synthesis and characterization of polystyrene chains on the surface of silica nanoparticles: comparison of SANS, SAXS, and DLS results

An extensive characterization of well-defined polystyrene (PS)-grafted silica nanoparticles is reported. Bare SiO₂ particles (diameter 50 nm) were functionalized with a suitable initiator for the surface-initiated anionic polymerization of styrene. Both grafted and free PS chains were characterized and compared by size-exclusion chromatography (SEC). PS-grafted particles were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS), and dynamic light scattering (DLS). The thickness of the grafted PS chains was obtained by SANS and DLS and scaled with $M_{\mathrm {w}}^{0.6}$ displaying similar behavior with free PS chains in the same solvent used, tetrahydrofuran (THF). Grafting densities obtained from SANS data and TGA were found to be small, and the thickness of the grafted PS chains determined by SANS was found to be similar to $2R_{\mathrm {g}}$ of free PS chains in THF. Both results are consistent with a “coil-like” conformation of the grafted PS chains.     

Fluorescently Labeled Substrates for Monitoring α1,3‐Fucosyltransferase IX Activity

Fucosylation is often the final process in glycan biosynthesis. The resulting glycans are involved in a variety of biological processes, such as cell adhesion, inflammation, or tumor metastasis. Fucosyltransferases catalyze the transfer of fucose residues from the activated donor molecule GDP‐β‐L ‐fucose to various acceptor molecules. However, detailed information about the reaction processes is still lacking for most fucosyltransferases. In this work we have monitored α1,3‐fucosyltransferase activity. For both donor and acceptor substrates, the introduction of a fluorescent ATTO dye was the last step in the synthesis. The subsequent conversion of these substrates into fluorescently labeled products by α1,3‐fucosyltransferases was examined by high‐performance thin‐layer chromatography coupled with mass spectrometry as well as dual‐color fluorescence cross‐correlation spectroscopy, which revealed that both fluorescently labeled donor GDP‐β‐L ‐fucose‐ATTO 550 and acceptor N‐acetyllactosamine‐ATTO 647N were accepted by recombinant human fucosyltransferase IX and Helicobacter pylori α1,3‐fucosyltransferase, respectively. Analysis by fluorescence cross‐correlation spectroscopy allowed a quick and versatile estimation of the progress of the enzymatic reaction and therefore this method can be used as an alternative method for investigating fucosyltransferase reactions.     

Self-organized synchronization and voltage stability in networks of synchronous machines

The integration of renewable energy sources in the course of the energy transition is accompanied by grid decentralization and fluctuating power feed-in characteristics. This development raises novel challenges for power system stability and design. We investigate power system stability from the viewpoint of self-organized synchronization aspects. In this approach, the power grid is represented by a network of synchronous machines. We supplement the classical Kuramoto-like network model, which assumes constant voltages, with dynamical voltage equations, and thus obtain an extended model, that incorporates the coupled categories voltage stability and rotor angle synchronization. We compare disturbance scenarios in small systems simulated on the basis of both classical and extended model and we discuss resultant implications and possible applications to complex modern power grids.     

Friedelin aus Kork

Cork of the cork oak is a fascinating natural material, used since ancient times. According to a close sight at cork, in 1665 the term “cell” was coined for use in biology. Friedelin, a complex pentacyclic triterpene ketone, is a constituent of cork. The isolation of friedeline is described as well as its history. All analytical spectra were recorded and are reproduced either in the main part or in the supporting information. The NMR‐ and mass‐spectra have been interpreted and compared with theoretical calculations of the ¹³C chemical shifts. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

Masked Rhodamine Dyes of Five Principal Colors Revealed by Photolysis of a 2‐Diazo‐1‐Indanone Caging Group: Synthesis,Photophysics, and Light Microscopy Applications

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as “hidden” markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2‐diazo‐1‐indanone group can be irreversibly photoactivated, either by irradiation with UV‐ or violet light (one‐photon process), or by exposure to intense red light (λ～750 nm; two‐photon mode). All dyes possess a very small 2‐diazoketone caging group incorporated into the 2‐diazo‐1‐indanone residue with a quaternary carbon atom (C‐3) and a spiro‐9H‐xanthene fragment. Initially they are non‐colored (pale yellow), non‐fluorescent, and absorb at λ=330–350 nm (molar extinction coefficient (ε)≈10⁴ M^?1 cm^?1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511–633 and 525–653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε= 3–8×10⁴ M^?1 cm^?1 and fluorescence quantum yields (?)=40–85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water‐soluble caged red‐emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino‐reactive N‐hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375–420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3–6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (?=20–38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10–40 % of the non‐fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a “dark” non‐emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super‐resolution optical microscopy is exemplified.