226 research outputs found
Characterization of a liquid-core waveguide cell for studying the chemistry of light-induced degradation
Many organic compounds undergo changes under the influence of light. This might be beneficial in, for example, water purification, but undesirable when cultural-heritage objects fade or when food ingredients (e.g., vitamins) degrade. It is often challenging to establish a strong link between photodegradation products and their parent molecules due to the complexity of the sample. To allow effective study of light-induced degradation (LID), a low-volume exposure cell was created in which solutes are efficiently illuminated (especially at low concentrations) while simultaneously analysed by absorbance spectroscopy. The new LID cell encompasses a gas-permeable liquid-core waveguide (LCW) connected to a spectrograph allowing collection of spectral data in real-time. The aim of the current study was to evaluate the overall performance of the LID cell by assessing its transmission characteristics, the absolute photon flux achieved in the LCW, and its capacity to study solute degradation in presence of oxygen. The potential of the LID set-up for light-exposure studies was successfully demonstrated by monitoring the degradation of the dyes eosin Y and crystal violet
Circular spectropolarimetric sensing of chiral photosystems in decaying leaves
Circular polarization spectroscopy has proven to be an indispensable tool in
photosynthesis research and (bio)-molecular research in general. Oxygenic
photosystems typically display an asymmetric Cotton effect around the
chlorophyll absorbance maximum with a signal . In vegetation, these
signals are the direct result of the chirality of the supramolecular
aggregates. The circular polarization is thus directly influenced by the
composition and architecture of the photosynthetic macrodomains, and is thereby
linked to photosynthetic functioning. Although ordinarily measured only on a
molecular level, we have developed a new spectropolarimetric instrument,
TreePol, that allows for both laboratory and in-the-field measurements. Through
spectral multiplexing, TreePol is capable of fast measurements with a
sensitivity of and is therefore suitable of non-destructively
probing the molecular architecture of whole plant leaves. We have measured the
chiroptical evolution of \textit{Hedera helix} leaves for a period of 22 days.
Spectrally resolved circular polarization measurements (450-900 nm) on whole
leaves in transmission exhibit a strong decrease in the polarization signal
over time after plucking, which we accredit to the deterioration of chiral
macro-aggregates. Chlorophyll \textit{a} levels measured over the same period
by means of UV-Vis absorption and fluorescence spectroscopy showed a much
smaller decrease. With these results we are able to distinguish healthy from
deteriorating leaves. Hereby we indicate the potency of circular polarization
spectroscopy on whole and intact leaves as a nondestructive tool for structural
and plant stress assessment. Additionally, we underline the establishment of
circular polarization signals as remotely accessible means of detecting the
presence of extraterrestrial life.Comment: 29 pages, 6 figure
Optimized signal-to-noise ratio with shot noise limited detection in Stimulated Raman Scattering microscopy
We describe our set-up for Stimulated Raman Scattering (SRS) microscopy with shot noise limited detection for a broad window of biologically relevant laser powers. This set-up is used to demonstrate that the highest signal-to-noise ratio (SNR) in SRS with shot noise limited detection is achieved with a time-averaged laser power ratio of 1:2 of the unmodulated and modulated beam. In SRS, two different coloured laser beams are incident on a sample. If the energy difference between them matches a molecular vibration of a molecule, energy can be transferred from one beam to the other. By applying amplitude modulation to one of the beams, the modulation transfer to the other beam can be measured. The efficiency of this process is a direct measure for the number of molecules of interest in the focal volume. Combined with laser scanning microscopy, this technique allows for fast and sensitive imaging with sub-micrometre resolution. Recent technological advances have resulted in an improvement of the sensitivity of SRS applications, but few show shot noise limited detection.The dominant noise source in this SRS microscope is the shot noise of the unmodulated, detected beam. Under the assumption that photodamage is linear with the total laser power, the optimal SNR shifts away from equal beam powers, where the most signal is generated, to a 1:2 power ratio. Under these conditions the SNR is maximized and the total laser power that could induce photodamage is minimized. Compared to using a 1:1 laser power ratio, we show improved image quality and a signal-to-noise ratio improvement of 8 % in polystyrene beads and C. Elegans worms. Including a non-linear damage mechanism in the analysis, we find that the optimal power ratio converges to a 1:1 ratio with increasing order of the non-linear damage mechanism
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 γ-cyclodextrin (γ-CD). A concentration of 12.5 mM γ-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.The authors wish to thank the Dutch Foundation for the Advancement of Science (NOW) for financial support and equipment (grant No. 344-006). Also, the technical assistance of Mr. J. Buijs is much appreciated
Conformational studies of stereoisomeric tetraols serived form syn- and anti-dibenzo [a,l]pyrene diolepoxides
An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-positions of dibenzo[a,l]pyrene (DB[a,l]P) is essential for the spectroscopic identification of DNA adducts derived from the biologically highly active fjord region syn- and anti-DB[a,l]P-11,12- diol 13,14-epoxides. Conformational effects are expected to play an important role in DNA-DB[a,l]P diol epoxide reactivity, base-sequence specificity, and conformation dependent repair. The results of conformational studies on trans-anti-, cis-anti-, and cis-syn-DB[a,l]P tetrol isomers are presented and compared to the results obtained previously for trans-syn-DB[a,l]P tetrol (Carcinogenesis 17, 829-837, 1996). Molecular mechanics, dynamical simulations, and semiempirical calculations of electronic transitions are used to interpret the low-temperature fluorescence spectra an
- …