Molecules in motion: Capturing and controlling molecular dynamics through chirality

This talk will be followed by coffee in the DB crush area. An abstract is included below:

The capability to follow changes in molecular structure during a chemical reaction or biological activity is a central ambition of the molecular sciences. However, resolving the structural dynamics of the fastest (bio-)chemical processes has remained a formidable challenge in their native solution phase, where even established methods reach important limitations: nuclear magnetic resonance is limited to millisecond real-time resolution, while ultrafast solution X-Ray scattering requires large-scale free-electron laser facilities. This firmly motivates the need for complementary techniques that combine structural sensitivity in solution with ultrafast time resolution.

A promising laboratory-based approach is circular dichroism (CD) spectroscopy, which measures the absorption difference of left- and right-handed circularly polarized light in chiral molecules. CD encodes the spatial arrangement of light-absorbing chemical groups within the molecular system and is especially attractive in the far and middle ultraviolet (UV) <300 nm, where it is routinely used to characterise the equilibrium structures of proteins, DNA and chiral organic complexes. However, taking this technique to the time-domain has remained a challenge for over three decades, with only few isolated reports with sub-nanosecond time-resolution [1].

In this talk, I will present a novel time-resolved CD spectrometer that combines ultra-sensitive broadband detection in the deep-UV (250-370 nm) with sub-picosecond time-resolution [2]. This has opened the path to measure the CD spectra of photoexcited chiral molecules in solution and to follow the encoded structural dynamics with ultrafast time-resolution. In my talk I will illustrate these new experimental capabilities with two recent studies: 1) the application of a site-specific CD-label for capturing conformational dynamics in peptides [3], and 2) the identification and control of a new reaction coordinate in the spin-crossover dynamics of chiral Fe(II) complexes [4].

J. Meyer-Ilse, D. Akimov, and B. Dietzek, ‘Recent advances in ultrafast time-resolved chiralitymeasurements: perspective and outlook’, Laser Photon. Rev. 7, 495 (2013). https://doi.org/10.1002/lpor.201200065
M. Oppermann, B. Bauer, T. Rossi, F. Zinna, J. Helbing, J. Lacour, and M. Chergui, ‘Ultrafast broadband circular dichroism in the deep ultraviolet’, Optica 6, 1, 56-60 (2019). https://doi.org/10.1364/OPTICA.6.000056
M. Oppermann, J. Spekowius, B. Bauer, R. Pfister, M. Chergui, and J. Helbing, ‘Broad-Band Ultraviolet CD Spectroscopy of Ultrafast Peptide Backbone Conformational Dynamics’, J. Phys. Chem. Lett. 10, 11, 2700-2705 (2019). https://doi.org/10.1021/acs.jpclett.9b01253
M. Oppermann, F. Zinna, J. Lacour, and M. Chergui, ‘Chiral control of spin-crossover dynamics in Fe(II) complexes’, Nat. Chem. 14, 739-745 (2022). https://doi.org/10.1038/s41557-022-00933-0