2D-IR is a great tool to investigate protein dynamics on the picosecond timescale. For light-sensitive proteins or protein folding studies, different approaches of transient 2D-IR to induce non-equilibrum dynamics, have been demonstrated. All aproaches rely on a reversible sample system. In the reseach area of serial crystallography (SX, e.g. at XFELs) this is not the case - originally considered as the biggest problem for these techniques, the protein sample has to be exchanged between every shot, this emerges now as a strong feature: Experiments can cover time-delays from fs to 10s of minutes and allow to access non-reversible reactions. A lot of the latest developments in SX have been enabled by another way to prepare and deliver samples, including fixed target sample delivery. In this contribution I will outline the general concept of fixed target sample delivery, as originally developed for SX, and first results of IR and 2D-IR spectroscopy of protein samples on fixed targets developed for applications in the mid-IR. By comparing to a recent crystallographic study of an irreversible enzymatic reaction, triggered by a photocaged substrate, I will illustrate how 2D-IR can benefit from transfering latest methodology from a neighbouring area in protein dynamics. Serial 2D-IR with fixed targets will evolve as another approach to cover time-scales of seconds and minutes during biochemical reactions yet with the intrinsic time-resolution and sensitivitiy for conformational and solvent dynamics on the ps scale.

2D-IR spectroscopy for long time-delays: What can we learn from serial crystallography?

ACS Fall 2021

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