X-ray absorption spectroscopy reveals charge transfer in π-stacked aromatic amino acids

X-ray absorption spectroscopy (XAS) and quantum mechanical calculations bear great potential to unravel π stacking side-chain interaction properties and structure in, e.g., proteins. However, core-excited state calculations for proteins and their associated interpretation for π-π interactions are challenging due to the complexity of the non-covalent interactions involved. A theoretical analysis is developed to decompose the core-to-valence transitions into their atomic contributions in order to characterize the π stacking of aromatic amino acids as a function of their non-covalent distance change. Three models were studied as a non-covalent mixed dimers of the phenylalanine, tyrosine and tryptophan amino acids. We found that there are carbon 1s → π* charge transfer transitions associated with the non-covalently paired aromatic amino acids through their side chains. The atomic-centered contributions to the electronic transition density quantify the excited state charge transfer of the pairing amino acid models, highlighting the π stacking interactions between their aromatic side chains.

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539: Matter; Molecular Physics; Atomic and Nuclear physics; Radiation; Quantum Physics

572: Biochemistry

541: Physical; Theoretical

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https://creativecommons.org/licenses/by/3.0/de/

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d4cp04615c.pdf

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X-ray absorption spectroscopy reveals charge transfer in π-stacked aromatic amino acids