Time Resolved Transient Circular Dichroism Spectroscopy Using Synchrotron Natural Polarisation

Ultraviolet (UV) synchrotron radiation circular dichroism (SRCD) spectroscopy has made an important contribution to the determination and understanding of the structure of biomolecules. In this paper, we demonstrate an innovative time-resolved SRCD (tr-SRCD) technique, overcoming limitations of current broadband UV SRCD setups, to access ultrafast (down to nanoseconds) time-scales, previously measurable only by other techniques, such as infrared (IR), nuclear magnetic resonance (NMR), fluorescence and absorbance spectroscopies and small angle X-ray scattering (SAXS). The tr-SRCD setup takes advantage of the natural polarisation of the synchrotron radiation emitted by a bending magnet to record broadband UV CD faster than any current SRCD setup, improving the acquisition speed from 10 mHz to 130 Hz and the accessible temporal resolution by 11 orders of magnitude. We illustrate the new approach by following the photoisomerization of an azopeptide. This breakthrough in SRCD spectroscopy opens up a wide range of potential applications to the detailed characterisation of biological processes, such as protein folding, protein-ligand binding and DNA nano-structure formation.