Temperature Dependence of the Melittin Folding Equilibrium Studied by Means of Fluorescence Excitation Spectra

The temperature dependence of fluorescence excitation spectra is investigated. This gives information on melittin folding equilibrium complementary to that obtained from fluorescence emission studies. A fit of the excitation spectra of melittin with three Gaussian functions gives good results. It suggests that in melittin a reversal of La and Lb electronic states of tryptophane takes place. The separate La and Lb bands exhibit a temperature dependence of the width and maximum.     

Effects of anomalous relaxation in the ESR spectra of Na pyrazine in DME

The ESR spectra of Na pyrazine in dimethoxyethane have been studied in the region of rapid intramolecular sodium exchange. Under this condition, the spectra show effects of cross terms in the relaxation caused by the simultaneous modulation of the nitrogen and the proton hyperfine splittings of the pyrazine radical anion has been established.     

Sensitized room-temperature phosphorescence for detection in continuous flow and chromatographic systems

Summary It is shown that sensitized room-temperature phosphorescence in liquid solutions can be successfully applied as a detection method in continuous flow and chromatographic systems. The limits of detection for a series of halogenated naphthalenes and biphenyls obtained by plug injection are roughly the same as those in batch experiments — in the subnanogram region. Liquid chromatograms of mixtures of PCBs, PCNs and polychlorodibenzofurans are given.     

Laser-induced fluorescence detection at 266 nm in capillary electrophoresis. Polycyclic aromatic hydrocarbon metabolites in biota

The separation of five phenolic polycyclic aromatic hydrocarbon metabolites (hydroxy-PAHs) has been performed by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) using a 30 mM borate buffer (pH 9.0) containing 60 mM sodium dodecyl sulfate and varying concentrations of gamma-cyclodextrin (gamma-CD). A concentration of 12.5 mM gamma-CD was found to provide a baseline separation of the five hydroxy-PAHs. We applied conventional fluorescence and laser-induced fluorescence (LIF) detection, using a new, small-size, quadrupled Nd-YAG laser emitting at 266 nm. The best limits of detection, in the low ng/ml range, were achieved using LIF detection. For all analytes, linearity was observed up to ca. 100 ng/ml. As an application, conjugated pyrene metabolites in hepatopancreas samples from the terrestrial isopods Oniscus asellus and Porcellio scaber were separated and detected. Finally, flatfish bile samples from individuals exposed to polluted sediment or crude oil, which were part of an interlaboratory study, were analyzed by CD-MEKC with conventional fluorescence and LIF detection to determine the 1-hydroxypyrene concentrations.     

A reduction approach to the repeated assignment problem

We consider the repeated assignment problem (RAP), which is a K-fold repetition of the n × n linear assignment problem (LAP), with the additional requirement that no assignment can be repeated more than once. In actual applications K is typically much smaller than n. First, we derive upper and lower bounds respectively by a heuristic together with local search, and an efficient method solving the continuous relaxation. The latter also solves a Lagrangian relaxation, such that the related pegging test, to fix variables at zero or one, decomposes into K independent pegging tests to LAPs. These can be solved exactly by transforming them into all-pairs shortest path problems. Together with these procedures, we also employ a virtual pegging test and reduce RAP in size. Numerical experiments show that the reduced instances, with K ? n, can be solved exactly using standard MIP solvers.     

Conformation and dynamics of DNA confined in slitlike nanofluidic channels

Using laser fluorescence microscopy, we study the shape and dynamics of individual DNA molecules in slitlike nanochannels confined to a fraction of their bulk radius of gyration. With a confinement size spanning 2 orders of magnitude, we observe a transition from the de Gennes regime to the Odijk regime in the scaling of both the radius of gyration and the relaxation time. The radius of gyration and the relaxation time follow the predicted scaling in the de Gennes regime, while, unexpectedly, the relaxation time shows a sharp decrease in the Odijk regime. The radius of gyration remains constant in the Odijk regime. Additionally, we report the first measurements of the effect of confinement on the shape anisotropy.     

Hybrid Rayleigh,Raman and two‐photon excited fluorescence spectral confocal microscopy of living cells

A hybrid fluorescence–Raman confocal microscopy platform is presented, which integrates low‐wavenumber‐resolution Raman imaging, Rayleigh scatter imaging and two‐photon fluorescence (TPE) spectral imaging, fast ‘amplitude‐only’ TPE‐fluorescence imaging and high‐spectral‐resolution Raman imaging. This multi‐dimensional fluorescence–Raman microscopy platform enables rapid imaging along the fluorescence emission and/or Rayleigh scatter dimensions. It is shown that optical contrast in these images can be used to select an area of interest prior to subsequent investigation with high spatially and spectrally resolved Raman imaging. This new microscopy platform combines the strengths of Raman ‘chemical’ imaging with light scattering microscopy and fluorescence microscopy and provides new modes of correlative light microscopy. Simultaneous acquisition of TPE hyperspectral fluorescence imaging and Raman imaging illustrates spatial relationships of fluorophores, water, lipid and protein in cells. The fluorescence–Raman microscope is demonstrated in an application to living human bone marrow stromal stem cells. Copyright © 2009 John Wiley & Sons, Ltd.     

New functional polymers for liquid crystal displays review of some recent developments

Polymeric materials play an important role in the construction and performance of liquid crystal displays. New functional polymers are developed to improve the displays on brightness, power efficiency and viewing angle performance. Polymer films with a controlled molecular structure and architecture provide new polarization optics to convert non‐polarized light into polarized light with higher efficiency than the traditional polarizers based on stretched iodine doped poly(vinyl alcohol). Other films provide a polarization compensation function to maintain an angular invariant net optical retardation of the display device and therewith a better contrast to wider viewing angles. Color generation by non‐absorbing methods is believed to improve on the display brightness. Special control of the liquid crystal alignment by photo‐sensitive orientation layers, polymer protrusions or photo‐formed polymer walls provide multiple director patterns within a single pixel to average out angular LC effects.