Pseudoequivalent nitrogen atoms in aqueous imidazole distinguished by chemical shifts in photoelectron spectroscopy

The photoelectron spectra of aqueous imidazole are presented, and the N 1s and C 1s binding energies are assigned aided by density functional theory calculations. The chemical equivalency of the two nitrogens of the cationic form is directly identified by the occurrence of a single N 1s photoelectron peak, which results from the delocalization of the positive charge over the molecule as a consequence of the Cv symmetry of the system. In contrast to NMR measurements, the photoemission process is faster than the rapid proton exchange in the aqueous environment, making the pseudoequivalent nitrogens of the neutral state clearly distinguishable with a N 1s binding energy shift of 1.7 eV.     

C60 in intense short pulse laser fields down to 9 fs: excitation on time scales below e-e and e-phonon coupling

The interaction of C60 fullerenes with 765-797 nm laser pulses as short as 9 fs at intensities of up to 3.7 x 10(14) W cm(-2) is investigated with photoion spectroscopy. The excitation time thus addressed lies well below the characteristic time scales for electron-electron and electron-phonon couplings. Thus, energy deposition into the system is separated from energy redistribution among the various electronic and nuclear degrees of freedom. Insight into fundamental photoinduced processes such as ionization and fragmentation is obtained from the analysis of the resulting mass spectra as a function of pulse duration, laser intensity, and time delay between pump and probe pulses, the latter revealing a memory effect for storing electronic energy in the system with a relaxation time of about 50 fs. Saturation intensities and relative abundances of (multiply charged) parent and fragment ions (C60(q+), q=1-6) are fingerprints for the ionization and fragmentation mechanisms. The observations indicate that for final charge states q>1 the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments even with 9 fs pulses through a nonadiabatic multielectron dynamics. In contrast, for energetic reasons singly charged ions are generated by an essentially adiabatic single active electron mechanism and negligible fragmentation is found when 9 fs pulses are used. These findings promise to unravel a long standing puzzle in understanding C60 mass spectra generated by intense femtosecond laser pulses.     

Quantitative Comparison of the Antimicrobial Efficiency of Leaching versus Nonleaching Polymer Materials

New antimicrobial materials will be more and more in the focus for hygienic and clinical disease control. Antimicrobial materials have to be distinguished in leaching and nonleaching materials. For many applications of antimicrobial materials on implants the use of nonleaching materials is essential. Therefore, the antimicrobial efficiency of leaching and nonleaching polymers has been investigated quantitatively in vitro in direct comparison on a highly relevant implant of central venous catheters (CVCs) using a well‐established called Certika test. This test is especially designed to test antimicrobial properties of leachable and nonleachable materials. This contribution demonstrates that newly developed nonleaching antimicrobial CVCs are equivalent to conventional leaching CVC systems in their antimicrobial performance against gram‐positive and gram‐negative bacteria, as well as Candida species. The use of new nonleaching antimicrobial polymers as shown here for CVCs represents a different mode of action with the aim to prevent infections also with antibiotic‐resistant strains and reduced side effects.

     

POLYMERS BEYOND THE YEAR 2000

At the turn of the century, the global polymer industry is undergoing the most rapid and dramatic changes in itshistory. Emerging markets, particularly in Asia, and their polymer consumption are catching up with other parts of the world,creating new business opportunities. Economy of scale, combined with optimized logistic concepts, is becoming a keyeconomic success factor, thus forcing smaller suppliers out of business and creating a major hurdle for newcomers and theintroduction of new products. Globalization of polymer customers and cost pressure lead to a consolidation of suppliers andproducts. Today standard thermoplastics have a dominant position in the market and they will retain this position in future.Engineering thermoplastics are facing growing competition due to the increased efficiency of standard polymers. This leadsto a displacement process where standard polymers substitute engineering thermoplastics. Simultaneously engineeringpolymers are pushing into new markets or applications or displacing materials like glass, wood or metal. The recent historyand future trends have a strong impact on R&D activity in the polymer industry. Competition on a global scale andincreasing cost pressure are turning innovation into an essential precondition of commercial success, thus determining theobjectives of industrial polymer research and development.     

Determination of the xenoestrogens 4-nonylphenol and bisphenol A by high-performance liquid chromatography and fluorescence detection after derivatisation with dansyl chloride

An easily performable and highly selective method for the determination of the xenoestrogens bisphenol A (BPA) and technical 4-nonylphenol (mixture of isomers) from environmental samples was developed. The method consists of fluorigenic labelling of the substances by dansylation followed by HPLC separation of the derivatives. Specific wavelengths (lembda(ex)=354 nm, lambda(em)=545 nm) for detection of the dansylated phenols were determined in order to reduce the signals of interfering compounds. The applicablility of the method for environmental samples was demonstrated by using sewage sludge spiked with BPA and 4-n-nonylphenol (as internal standard).     

Ultrasound technique as a tool for high-rate incorporation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in NiCo layers

NiCo–Al₂O₃ composite coatings were prepared by electrodeposition in a sulfamate plating bath containing Al₂O₃ particles to be co-deposited under sonication. For reliable determination of the microstructure, detailed studies on composite cross-sections were carried out by energy-dispersive spectrometer (matrix composition, particle content) and FE-SEM/electron backscattered diffraction data (particle distribution, grain size), accompanied by XRD analyses concerning texture, lattice parameter, grain size, and residual stress. The NiCo matrix with a Co/Co + Ni ratio up to 0.4 is a face-centered cubic solid solution with <100> and <110> fiber textures. The distribution of the particles (size 250 nm) was well-dispersed and enhanced up to 15 wt.% by ultrasound application during plating. Vickers hardness increased up to 50% by dispersion hardening. First-order residual stress in the matrix increased with rising Co content, thus decreasing wear resistance and revealing the complex of composite properties with partially opposite effects.     

Acoustic cavitation, bubble dynamics and sonoluminescence

Basic facts on the dynamics of bubbles in water are presented. Measurements on the free and forced radial oscillations of single spherical bubbles and their acoustic (shock waves) and optic (luminescence) emissions are given in photographic series and diagrams. Bubble cloud patterns and their dynamics and light emission in standing acoustic fields are discussed.     

Application of digital holographic microscopy to investigate the sedimentation of intact red blood cells and their interaction with artificial surfaces

Red blood cells are able to undergo shape change from the "normal" discocyte to either echinocytes or stomatocytes depending on a large variety of membrane and cytoplasmic parameters. Such shape changes can be relatively fast (within seconds) during the sedimentation of the cells in suspension or after the cells are getting in contact with artificial surfaces. High resolution digital holographic microscopy has been applied to study these processes. This method represents a new set-up allowing a contact-less and marker-free quantitative phase-contrast imaging of living cells under conventional laboratory conditions. With the applied technique we were able to detect and analyse fast shape changes of red blood cells.     

Electronic structure of adenine and thymine base pairs studied by femtosecond electron-ion coincidence spectroscopy

Femtosecond pump-probe spectroscopy was combined with photoelectron-photoion coincidence detection to investigate the electronic structure and dynamics of isolated adenine (A) and thymine (T) dimers and the adenine-thymine (AT) base pair. The photoelectron spectra show that pipi* and npi* states are only weakly perturbed in the hydrogen-bound dimers as compared to the monomers. For cationic base pairs with internal energies greater than 1 eV, we observed considerable cluster fragmentation into protonated monomers. This process selectively removed signals from the npi* --> n-1 ionization channel in all dimers. The photoelectron spectra are compared to time-resolved mass spectra and confirm the assignment of short-lived pipi* and npi* populations in the adenine, thymine, and mixed AT dimers.