Alex Sheldrick

Alex Sheldrick

Dual M.Sc. in AI and Physics with experience as an AI Engineer at appliedAI and Data Scientist at ExoMatter, specializing in LLM's, 3D Deep Learning and neural rendering, with a strong research background from TUM Visual Computing & AI Group.

Publications

Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumichrome ions (M = Li–Cs) in the gas phase.

Published in Phys. Chem. Chem. Phys., 2018

The photochemical properties of flavins depend sensitively on their environment and are strongly modified by coordination with metal ions. Herein, the electronic spectra of cold complexes of the smallest flavin molecule with alkali ions are measured by photodissociation in the visible range in a cryogenic ion trap coupled to a tandem mass spectrometer and an electrospray ionization source.

Pablo Nieto, David Müller, Alexander Sheldrick, Alan Günther, Mitsuhiko Miyazaki, Otto Dopfer. (2018). Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+ lumichrome ions (M= Li–Cs) in the gas phase. Phys. Chem. Chem. Phys. 2018, 20 (34): 22148-22158. http://dx.doi.org/10.1039/C8CP03950J

Optical spectroscopy of isolated flavins: photodissociation of protonated lumichrome

Published in The Royal Society of Chemistry, 2018

The optical properties of flavins strongly depend on the charge and oxidation states as well as the environment. Herein, the electronic spectrum of cold protonated lumichrome, the smallest flavin molecule, is recorded by means of photodissociation in the visible range (VISPD) in a cryogenic ion trap tandem mass spectrometer coupled to an electrospray ionization source. The vibronic spectrum is assigned to the S1 ← S0 (ππ*) transition of the most stable N5-protonated isomer by comparison with quantum chemical calculations at the PBE0/cc-pVDZ level in combination with multidimensional Franck–Condon simulations. Analysis of the geometric and electronic structures of neutral and protonated lumichrome explains the large red shift of the band origin upon protonation (ΔS1 ∼ −6000 cm−1), which corresponds to the increase in proton affinity upon S1 excitation as a result of charge transfer. N5 protonation greatly modifies the structure of the central pyrazine ring of the chromophore. The orbitals involved in S1 ← S0 excitation include an important fraction of the probability at the central ring and they are, hence, largely influenced by the positive charge of the attached proton. The rich vibronic spectrum indicates the large geometry change upon S1 excitation. This combined experimental and computational approach is shown to be suitable to determine the optical properties of flavins as a function of oxidation, protonation, metalation, and microsolvation state.

Alexander Sheldrick, David Müller, Alan Günther, Pablo Nieto, Otto Dopfer, (2018). "Optical spectroscopy of isolated flavins: photodissociation of protonated lumichrome." The Royal Society of Chemistry. 20 (11): 7407-7414. https://doi.org/10.1039/C8CP00590G

BerlinTrap: A new cryogenic 22-pole ion trap spectrometer

Published in Journal of Molecular Spectroscopy, 2017

The design and first applications of a new tandem mass spectrometer (BerlinTrap) combining an electrospray ion source, a quadrupole mass spectrometer, a cryogenic 22-pole ion trap (4–300 K), and an orthogonal reflectron time-of-flight mass spectrometer are described. The trapped ions are cooled by helium buffer gas cooling. The formation and solvation shell structure of weakly-bound HenH3O+ complexes and the electronic photodissociation spectrum of the protonated amino acid tyrosine are used to calibrate the setup for cooling, tagging, and spectroscopic capabilities. A vibrational temperature below 20 K is inferred for protonated tyrosine. The electronic spectrum of isolated protonated lumichrome, the smallest protonated flavin, is recorded in the visible range and assigned to the most stable N5 isomer by comparison with quantum chemical calculations. These results demonstrate the suitability of the BerlinTrap apparatus for spectroscopy and reactivity studies of small and large (bio-)molecular ions and their clusters.

Günther, Alan, Pablo Nieto, David Müller, Alexander Sheldrick, Dieter Gerlich, and Otto Dopfer. (2017). "BerlinTrap: A new cryogenic 22-pole ion trap spectrometer." Journal of Molecular Spectroscopy. 1(332):8-15. https://doi.org/10.1016/j.jms.2016.08.017