Untersuchung der Chiralitätseigenschaften von Elektrogesprayten Anionen
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Abstract
The projects worked on had two main focuses. First, the applicability of the ESI-PECD-method
as a tool for chemical analysis was investigated. The corresponding results are
discussed in chapters 4.2 and 4.4. It was shown that the method can reliably determine
molar fractions and enantiomeric excesses, even at a concentration of 10 μmol/L. The
measurement times for these measurements are currently still in the range of 8 to 16
hours, but through targeted further development of the method, there is potential to
use it in the future for the investigation of corresponding substances. Advantages over
other methods include the low concentrations, the possibility of preselecting ions in the
mass spectrometer, independence from sample concentration and independence from
additional reagents (chapter 4.2). The method is currently still in the early stages when
it comes to the analysis of biopolymers such as peptides and proteins. The first steps
toward making it a useful component of analysis were taken in this work. A correlation
was found between the change in the tertiary structure of the Trp-cage and the
determined PECD- and PICD-values (chapter 4.4).
The other focus is on the fundamental understanding of chirality and the measured
asymmetries in the angular distributions of photoelectrons. Here, the PEELD was first
examined in chapter 4.3, and it was observed that it can also scale nonlinearly in the
single-photon case. Until now, nonlinearities have often been attributed to multiphoton
processes, but these explanations fail in case of the results shown. Hopefully, these can
contribute to a new consideration of the origin of the asymmetries and thus to a better
understanding of the effect in general.
The experiments on the interaction of helicity with point chirality in chapter 4.6 have
just started. In the measurements, the helicenes and leucines show PECD-values of
approximately ±0.03 each. Future measurements must show to what extent they expand
the state of knowledge and whether, in the end, transferable conclusions about
the helicity of biological polymers are possible.
In addition, an approach was investigated to enable the examination of samples whose
photodetachment threshold lie above the photon energy. The results are discussed in
chapter 4.5. As has been shown, the photodetachment threshold can be influenced by
halides, and PECD-values of the adducts can be determined. As far as can be judged
from the results obtained so far, this approach could contribute to the investigation of
otherwise difficult-to-access systems.
In addition to the experiments mentioned, the measurement setup was optimized and
adapted at various points. The adjustments are described in chapter 3, and the influence
of the equipment adjustments is described in more detail in chapter 4.1. The
use of the HPLC pump enabled longer continuous operation, and the adjustment of the
ESI improved the ion yields. The effect of the splitter was also presented there, which
resulted in a significant stabilization of the ion yields. In future projects and new apparatus
designs, these findings can help to plan and optimize the measurement systems
in a meaningful way. Overall, it was shown that the apparatus modifications improve
the stability of the measurements and meet the requirements for measurements with
high photon energies. During the measurements, it was found that the PECD-value as
a measurement parameter is relatively robust against instrumental influences. Based
on the observations on instrumental asymmetry and pulse energy of the laser, it is clear
that the method is surprisingly robust against external influences. Even if these, such
as instrumental asymmetry, have a direct effect on the signal.
In addition to the measurable advantages of the modified structures, it was also possible
to achieve some quality-of-life improvements, such as the use of the HPLC-pump
and the reduction in cleaning effort.
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Contributors
Supervisor:
Weitzel, Karl-Michael
Dates
Issued: 2026-03-27
Faculty
FB15:Chemie
Language
de
Keywords
PECDPhotoelektronen Circulardichroismusphotoelectron circualr dichroismPICDPhotoionen Circulardichroismusphotoion circular dichroismCirculardichroismuscircular dichroismAnionenanionsMassenspektrometriemass spectrometryElektrosprayionisationelectrospray ionisationEnantiomerenüberschussenantiomeric excessPEELDPhotoelektronen Elliptischer Dichroismusphotoelectron elliptical dichroism
DFG-subjects
3.13-01 - Physikalische Chemie von Molekülen, Flüssigkeiten und Grenzflächen, Biophysikalische Chemie
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Both, Jon Henrik: Untersuchung der Chiralitätseigenschaften von Elektrogesprayten Anionen. : 2026-03-27.
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