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Updated: Apr 23, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Structural melting of an amino acid dimer upon intersystem crossing
Ulrich J Lorenz1, Thomas R Rizzo
1Laboratoire de Chimie Physique Moléculaire, École Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
Abstract:
We present a spectroscopic investigation of the excited-state dynamics of the phenylalanine (Phe)/serine (Ser) protonated dimer in the gas phase. Using an ultraviolet (UV) laser pulse, we promote individual isomers to the S1 state and probe their fate with an infrared (IR) pulse. We find that the S1 state has a lifetime of ~70 ns and undergoes intersystem crossing (ISC) to the T1 state. Time-resolved IR spectra allow us to follow the structural evolution of the dimer. In the S1 state, the different isomers retain the hydrogen-bonding pattern of the ground state. Intersystem crossing triggers a sudden increase of the vibrational energy, so that the dimers can overcome isomerization barriers and explore large parts of the potential energy surface (PES). Their broad IR spectra largely resemble one another and indicate that the dimers adopt a molten structure.
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