Comparison between vacuum sublimed matrices and conventional dried droplet preparation in MALDI-TOF mass spectrometry

The properties of several cinnamic acid compounds used as matrices for matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were investigated as standard dried droplet (DD) and vacuum sublimed preparations. The differences between both preparation methods were analyzed with regard to matrix grain size, internal ion energy, initial velocity, analyte intensity, and analyte incorporation depth. Some of the used cinnamic acid derivatives exhibit clearly reduced grain sizes as sublimed preparations compared with standard DD approaches. In these cases higher effective temperatures could be measured accompanied by increased analyte intensities, which can be explained by stronger volatilization processes caused by a hindered heat dissipation resulting in a raised analyte transfer into the gas phase. For all sublimed compounds, a strong increase of the initial ion velocity compared with DD preparations could be measured. Higher initial ion velocities correlate with a decrease in internal ion energy which might be attributed to the very uniform crystal morphology exhibited by sublimed compounds. For sublimed matrices without reduced grain size, at least slightly higher analyte intensities could be detected at raised laser fluences. Analyte accumulation in the uppermost matrix layers or the detected higher ion stability can be explanations for these results.     

Stimuli-Responsive Polymers in Solution Investigated by NMR and Infrared Spectroscopy

Summary: Temperature-induced and solvent composition-induced phase separation in solutions of poly(N-isopropylmethacrylamide) (PIPMAm) and other thermoresponsive polymers as studied by NMR and infrared (IR) spectroscopy is discussed. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters characterizing the coil-globule phase transition induced by temperature, were determined from reduced integrated intensities in high-resolution ¹H NMR spectra. This approach can be especially useful in investigations of phase separation in solutions of binary polymer systems. Information on behaviour of water during temperature-induced phase transition was obtained from measurements of ¹H NMR relaxation times of HDO molecules. NMR and IR spectroscopy were used to investigate PIPMAm solutions in water/ethanol (D₂O/EtOH) mixtures where the phase separation can be induced by solvent composition (cononsolvency). Some differences in globular-like structures induced by temperature and solvent composition were revealed by these methods.     

A semi-quantitative dipstick assay for microcystin

An immunochromatographic lateral flow dipstick assay for the fast detection of microcystin-LR was developed. Colloid gold particles with diameters of 40 nm were used as red-colored antibody labels for the visual detection of the antigen. The new dipstick sensor is capable of detecting down to 5 μg·l⁻¹ (ppb; total inversion of the color signal) or 1 ppb (observation of color grading) of microcystin-LR. The course of the labeling reaction was observed via spectrometric wave shifts caused by the change of particle size during the binding of antibodies. Different stabilizing reagents showed that especially bovine serum albumin (BSA) and casein increase the assays sensitivity and the conjugate stability. Performance of the dipsticks was quantified by pattern processing of capture zone CCD images. Storage stability of dipsticks and conjugate suspensions over 115 days under different conditions were monitored. The ready-to-use dipsticks were successfully tested with microcystin-LR-spiked samples of outdoor drinking- and salt water and applied to the tissue of microcystin-fed mussels. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

NMR Investigations of Temperature-Induced Phase Transition in Aqueous Polymer Solutions

The different dynamics of polymer segments forming phase-separated globular structures in aqueous (D₂O) solutions affects both the shape of NMR spectra and NMR relaxation times of polymer and solvent. Two types of the approach are discussed. The first one is based on the reduction of integrated intensities of polymer NMR lines in high-resolution NMR spectra in the system undergoing the coil-globule phase transition. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters ΔH and ΔS characterizing the coil-globule phase transition can be determined. The second approach is based on measurements of ¹H NMR relaxation times of water (HDO) which provide information on behaviour of water during phase transition. The power of both approaches is demonstrated on results obtained with solutions of several thermoresponsive homopolymers and copolymers.     

Metal‐Catalyzed Derivatization of Cα‐Tetrasubstituted Amino Acids and Their Use in the Synthesis of Cyclic Peptides

Making circles with N and O : Cyclic tripeptides containing an unnatural C^α‐tetrasubstituted THF amino acid are prepared by copper(I) and palladium(0)‐catalyzed N‐ and O‐arylation reactions. The reactions give access to side chain‐modified derivatives of the unnatural amino acid and macrocyclic peptidomimetics.

     

Hecke algebras from groups acting on trees and HNN extensions

We study Hecke algebras of groups acting on trees with respect to geometrically defined subgroups. In particular, we consider Hecke algebras of groups of automorphisms of locally finite trees with respect to vertex and edge stabilizers and the stabilizer of an end relative to a vertex stabilizer, assuming that the actions are sufficiently transitive. We focus on identifying the structure of the resulting Hecke algebras, give explicit multiplication tables of the canonical generators and determine whether the Hecke algebra has a universal $C^1$-completion. The paper unifies algebraic and analytic approaches by focusing on the common geometric thread. The results have implications for the general theory of totally disconnected locally compact groups.     

Investigations on the numerical solution of the Fokker-Planck equation with discontinuous Galerkin Methods

Nonlinear dynamic systems under stochastic excitation possess Markov characteristics. Thus, their stochastic equation of motion can be transformed into the Fokker-Planck equation which describes the evolution of the probability density. A discontinuous Galerkin (DG) method is applied to solve the Fokker-Planck equation. This method provides numerical stability as well as accuracy and is able to treat discontinuities of the solution. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On locally strongly convex affine hypersurfaces with parallel cubic form. Part I

In this paper, we study locally strongly convex affine hypersurfaces of Rn+1 that have parallel cubic form with respect to the Levi-Civita connection of the affine Berwald-Blaschke metric; it is known that they are affine spheres. In dimension n?7 we give a complete classification of such hypersurfaces; in particular, we present new examples of affine spheres.