Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 97: Organic Molecules on Inorganic Substrates: Electronic, Optical and Other Properties II

O 97.8: Talk

Friday, March 21, 2025, 12:15–12:30, H6

Insights into Nonlinear CD-ee Dependence in Tryptophan Thin Films — •Charitini Panagiotopoulou, Changseop Jeong, Ueli Heiz, and Aras Kartouzian — Chair of Physical Chemistry, School of Natural Sciences & Catalysis Research Center, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany

Chiral analysis is essential, especially for enantio-separation and -enrichment, with Circular Dichroism (CD) spectroscopy being a fast and straightforward method for studying enantiomeric excess (ee) and its dependence on circular dichroism (CD-ee dependence). While most systems show linear CD-ee dependence, studies reporting non-linear CD-ee behaviour are relatively rare and, thus, more attractive for research. Building on our earliest findings of negative nonlinear CD-ee dependence in polycrystalline BINOL thin films (Liang et al. 2023), we extend this study to a different system: the well-known amino acid responsible for synthesizing important proteins in humans, Tryptophan. We prove our hypothesis that the non-linear CD-ee dependence is not limited to BINOL films and can be applied to biomolecules, and we outline this non-linear dependence with different methods, such as CD spectroscopy, SHG-CD spectroscopy and FTIR study. This behaviour is linked to the structural characteristics of Tryptophan when a series of different enantiomeric excesses are deposited onto thin films via molecular evaporation. This approach paves the way for extensive exploration in the field of biomolecular chirality.

Keywords: Chirality; Thin Films; Surface Spectroscopy; Circular Dichroism Spectroscopy; Second Harmonic Generation