Acridino-Diaza-20-Crown-6 Ethers: New Macrocyclic Hosts for Optochemical Metal Ion Sensing

Acridino-diaza-20-crown-6 ether derivatives as new turn-on type fluorescent chemosensors with an excellent functionality and photophysical properties have been designed and synthesized for metal ion-selective optochemical sensing applications. Spectroscopic studies revealed that in an acetonitrile-based semi-aqueous medium, the sensor molecules exhibited a remarkable fluorescence enhancement with high sensitivity only toward Zn²⁺, Al³⁺ and Bi³⁺, among 23 different metal ions. Studies on complexation showed a great coordinating ability of logK > 4.7 with a 1:1 complex stoichiometry in each case. The detection limits were found to be from 59 nM to micromoles. The new ionophores enabled an optical response without being affected either by the pH in the range of 5.5–7.5, or the presence of various anions or competing metal ions. Varying the N-substituents of the new host-backbone provides diverse opportunities in both immobilization and practical applications without influencing the molecular recognition abilities.     

Self-Assembly and Fluorescence of Tetracationic Liquid Crystalline Tetraphenylethene

A series of tetraguanidinium tetraphenylethene (TPE) arylsulfonates with different chain lengths was prepared via ionic self-assembly of tetraguanidinium TPE chloride and the respective methyl arylsulfonates. Liquid crystalline properties were studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. Tetraguanidinium TPE arylsulfonates with chain lengths of C₈–C₁₂ displayed hexagonal columnar mesophases over a broad temperature range, while derivatives with longer chains showed oblique columnar phases. In solution all compounds displayed aggregation-induced emission behaviour. Temperature-dependent luminescence spectra of the bulk phase of the tetraguanidinium TPE arylsulfonate with C₁₄ side chains revealed a strong luminescence both in the solid state and the oblique columnar mesophase. The emission behaviour was rationalized by a unique combination of restriction of intramolecular rotation of the TPE core, Coulomb interaction between the guanidinium cations and π–π interactions of the anionic arylsulfonate moieties.     

Surface‐enhanced Raman microscopy of hemispherical shells stripped from templates of anodized aluminum

We report on the optical characterization of plasmonic metal nanostructures representing highly ordered interconnected hemispherical gold and silver shells that can be iteratively stripped from the same embossed templates (without template degradation) made from selectively etched anodized aluminum. By performing scanning high‐resolution confocal Raman microscopy of p‐aminothiophenol and Rhodamine 6G molecules homogeneously adsorbed to samples with different radii of shell curvature, we systematically investigate the applicability of the fabricated structures for surface‐enhanced Raman spectroscopy and correlate the results with linear reflection spectroscopy. We trace the origin of strong Raman signal enhancements (average relative enhancement of up to ~120) to electromagnetic hot‐spots located in sharp grooves and crevices at hemisphere shell junctions. Copyright © 2011 John Wiley & Sons, Ltd.     

Fragmentation by electron impact ionization and intracluster reactions of size selected (N2H4) n and (OCS) n clusters

The hydrogen-bonded (N₂H₄) _n clusters and the van der Waals (OCS) _n clusters are size selected in a scattering experiment with a He beam up to the cluster sizen=6. By measuring the angular distributions of the scattered clusters the complete fragmentation pattern of electron impact ionization is obtained. For Hydrazine the two main fragment masses are the protonated species (N₂H₄) _n?1H⁺ and with somewhat weaker intensities also the nominal ion mass (N₂H₄) _n ⁺ . The largest intensity is observed for the monomer ion N₂H ₄ ⁺ to which clusters up ton=5 fragment. For carbonylsulfide, completely different results are obtained. Aside from the fragments of the OCS monomer and the van der Waals cluster fragments (OCS) ₂ ⁺ and (OCS) ₃ ⁺ signals at mass S ₂ ⁺ , S ₃ ⁺ and S₂OCS⁺ are detected. This indicates a fast chemical reaction in the cluster according to: S + OCS → CO + S₂ which occurs for clusters of sizen ≥ 2. Peaks at S ₃ ⁺ and S₂OCS⁺ are seen for the first time forn ≥ 5 according to a further reaction of S₂ in the cluster.     

Monte Carlo simulations of jet quenching in heavy ion collisions

Jet quenching is one of the major discoveries of the heavy-ion program at Rhic. While there is a wealth of data from Rhic that will soon be supplemented with measurements at the Lhc, on the theoretical side the situation is less clear. A thorough understanding of jet quenching is, however, beneficial, as it is expected that medium-induced modifications of jets allow one to characterise properties of the QCD matter produced in heavy ion collisions. This talk aims at summarising the main ideas and concepts of the currently available Monte Carlo models for jet quenching.     

New Polymerizable Tetraaza Macrocycle Containing Two Acridine Units for Selective Fluorescence Sensing of Metal Ions

A new fluorescent bis(acridino)-macrocycle containing two allyl groups was synthesized and photophysically studied. Studies were carried out on metal ion recognition and selectivity-influencing effects including the determination of the relevant thermodynamic constants as logK and pK_a. The proposed sensor molecule is recommended for the development of Zn²⁺-selective optochemical analyzers based on covalently immobilized ionophores as it has a unique pH-independent metal ion recognition ability, which is not influenced by anions and other potentially occurring metal ions in biological samples.

     

Coherent radiative parton energy loss beyond the BDMPS-Z limit

It is widely accepted that a phenomenologically viable theory of jet quenching for heavy ion collisions requires the understanding of medium-induced parton energy loss beyond the limit of eikonal kinematics formulated by Baier–Dokshitzer–Mueller–Peigné–Schiff and Zakharov (BDMPS-Z). Here, we supplement a recently developed exact Monte Carlo implementation of the BDMPS-Z formalism with elementary physical requirements including exact energy-momentum conservation, a refined formulation of jet-medium interactions and a treatment of all parton branchings on the same footing. We document the changes induced by these physical requirements and we describe their kinematic origin.     

IR-photodissociation of size selected molecular clusters and their structures

Infrared photodissociation spectra of (CH₃NH₂) _n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm^?1 using a cw-CO₂ laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm^?1) and a blue (1048 cm^?1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm^?1 and 1046.0 cm^?1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C₂H₄-CH₃COCH₃ and C₂H₄-(CH₃COCH₃)₂ were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C₂H₄ at 949 cm^?1, shows two peaks at 946.2 cm^?1 and 961.3 cm^?1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer.