Type I Toeplitz algebras

The class of Toeplitz algebras associated to ordered groups is important in the analysis of Toeplitz operators on the generalised Hardy spaces defined by such groups. The conditions under which these Toeplitz algebras are Type I C^*-algebras are investigated.     

Magnetic silica colloids for catalysis

Monodisperse magnetizable colloidal silica particles in a stable dispersion have been functionalized with a homogeneous catalyst: a PCP–pincer Pd-complex. In a proof-of-principle experiment we demonstrate the catalytic activity of the colloids in a C–C bond formation reaction. Advantages of the magnetic silica carriers are the large surface-to-volume ratio and the easy recovery by magnetic separation. After magnetic separation, the catalyst-loaded particles are readily redispersed for further use.     

Tetramethyl guanidine-assisted synthesis and thermal crosslinking of multifunctional benzoxazine monomers based on natural phloretic acid

An efficient strategy to synthesize novel biobased multifunctional benzoxazine compounds was developed using the 1,1,3,3-tetramethyl guanidine (TMG)-triggered esterification of natural phloretic acid with organic halides as a key synthetic step. First, phloretic acid was combined with either aniline or furfurylamine to prepare the corresponding carboxylic acid-functional monobenzoxazine monomer. Next, the use of TMG enabled an efficient esterification of these compounds with di-, tri-, and tetra-functional benzyl bromide compounds at room temperature to afford a series of new multi-benzoxazine monomers tethered to an aromatic core. The effect of the functionality of the monomers on the curing process was analyzed, indicating that the reactivity during the thermally induced ring-opening increases with the number of furan and oxazine rings in the monomers. The resulting thermosets revealed good correlation between the number of oxazine rings in the structure of the monomer and the properties of the crosslinked materials. Furfurylamine-based polybenzoxazines showed improved thermal behavior compared to the aniline-based systems, due to the role of furan rings. All materials showed high T_g, good thermal stability, and promising flame retardancy properties.     

Optical parametric oscillation in quasi-phase-matched GaAs

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilizes an all-epitaxially-grown orientation-patterned GaAs crystal that is 0.5 mm thick, 5 mm wide, and 11 mm long, with a domain reversal period of 61.2 microm. Tuning either the near-IR pump wavelength between 1.8 and 2 microm or the temperature of the GaAs crystal allows the mid-IR output to be tuned between 2.28 and 9.14 microm, which is limited only by the spectral range of the OPO mirrors. The pump threshold of the singly resonant OPO is 16 microJ for the 6-ns pump pulses, and the photon conversion slope efficiency reaches 54%. We also show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.     

Mechanism of Intramolecular Photostabilization in Self‐Healing Cyanine Fluorophores

Organic fluorophores, which are popular labels for microscopy applications, intrinsically suffer from transient and irreversible excursions to dark‐states. An alternative to adding photostabilizers at high concentrations to the imaging buffer relies on the direct linkage to the fluorophore. However, the working principles of this approach are not yet fully understood. In this contribution, we investigate the mechanism of intramolecular photostabilization in self‐healing cyanines, in which photodamage is automatically repaired. Experimental evidence is provided to demonstrate that a single photostabilizer, that is, the vitamin E derivative Trolox, efficiently heals the cyanine fluorophore Cy5 in the absence of any photostabilizers in solution. A plausible mechanism is that Trolox interacts with the fluorophore through intramolecular quenching of triplet‐related dark‐states, which is a mechanism that appears to be common for both triplet‐state quenchers (cyclooctatetraene) and redox‐active compounds (Trolox, ascorbic acid, methylviologen). Additionally, the influence of solution‐additives, such as cysteamine and procatechuic acid, on the self‐healing process are studied. The results suggest the potential applicability of self‐healing fluorophores in stochastic optical reconstruction microscopy (STORM) with optical super‐resolution. The presented data contributes to an improved understanding of the mechanism involved in intramolecular photostabilization and has high relevance for the future development of self‐healing fluorophores, including their applications in various research fields.     

Monomers and polymers from plant oils via click chemistry reactions

As a consequence of the depleting of fossil reserves and environmental issues, today, plant oils and fatty acids derived therefrom have a respectable status within the polymer chemistry community. However, maximizing the benefits of these renewable feedstocks requires the utilization of sustainable and efficient chemical transformations. The emergence of click chemistry concept and especially the renaissance of thiol‐ene addition reaction have had an impact on the way to make plant oil‐derived polymers. This highlight discusses the applicability and success of thiol‐ene addition and other click reactions in the transformation of oleochemicals into monomers and polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Quantification of L‐ergothioneine in whole blood by hydrophilic interaction ultra‐performance liquid chromatography and UV‐detection

A new hydrophilic interaction ultra‐performance LC method was established for the whole blood measurement of L‐ergothioneine. Chromatographic separation was achieved in a fairly short time, less than 4 min, on a 100 × 2.1 mm Acquity UPLC BEH HILIC 1.7 μm column with a mobile phase consisting of a mixture of 100 mmol/L ammonium acetate/ACN/water (5:85:10, v/v/v) that flowed isocratically at 0.250 mL/min. The LOD and the limit of quantification were 3.85 and 11.67 μmol/L, respectively. The method exhibited linearity in a concentration range of 15.63–1000 μmol/L (R² > 0.999). Mean recovery was 96.34% whereas intraassay and interassay precision were 1.52 and 1.82% RSD, respectively. On the whole, the developed method is simple, fast, precise, accurate, and sensitive and may be useful for routine analyses.     

Isomerization of a peptidic fragment studied theoretically in vacuum and in explicit water solvent at finite temperature

The cis-trans isomerization of N-methylacetamide, a molecular model of the polypeptide chain, is examined via umbrella sampling Car-Parrinello MD and classical MD, in both gas and solution phases at 300 K. A new analysis of the C(O)-N bond interconversion and a full examination of the solvent shell structure are presented.     

Development of the force field parameters for phosphoimidazole and phosphohistidine

Phosphorylation of histidine-containing proteins is a key step in the mechanism of many phosphate transfer enzymes (kinases, phosphatases) and is the first stage in a wide variety of signal transduction cascades in bacteria, yeast, higher plants, and mammals. Studies of structural and dynamical aspects of such enzymes in the phosphorylated intermediate states are important for understanding the intimate molecular mechanisms of their functioning. Such information may be obtained via molecular dynamics and/or docking simulations, but in this case appropriate force field parameters for phosphohistidine should be explicitly defined. In the present article we describe development of the GROMOS96 force field parameters for phosphoimidazole molecule--a realistic model of the phosphohistidine side chain. The parameterization is based on the results of ab initio quantum chemical calculations with subsequent refinement and testing using molecular mechanics and molecular dynamics simulations. The set of force constants and equilibrium geometry is employed to derive force field for the phosphohistidine moiety. Resulting parameters and topology are incorporated into the molecular modeling package GROMACS and used in molecular dynamics simulations of a phosphohistidine-containing protein in explicit solvent.     

Polynuclear Cu(II), Ni(II) and Cd(II) coordination compounds with bis(pyrimidin-2-yl)amine and dicyanamide

In this study the synthesis, crystal structure and characterization of three new transition metal polynuclear compounds with formula [Cu(dipm)(μ-dca)₂]_n(H₂O) (1), [Ni(dipm)(μ-dca)₂]_n(C₂H₆O)_1/2 (2) and [Cd(dipm)(μ-dca)₂]_n (3) (in which dipm = bis(pyrimidin-2-yl)amine and dca = dicyanamide) are reported. The isostructural compounds 1 and 2 contain a double-bridging end-to-end dca unit connecting two metal ions and a single bridging end-to-end dca unit between subsequent metals. Compound 3 exhibits only single bridging end-to-end dca units, oriented in three directions, giving rise to a 3D framework.