Two-dimensional infrared spectroscopy of peptides by phase-controlled femtosecond vibrational photon echoes

TLDR

Two-dimensional infrared spectroscopy of peptides provides spectra analogous to two‑ and three‑pulse multiple quantum NMR. The technique employs phase matching and heterodyning to extract the phase and amplitude of vibrational photon echoes across multiple pulse delays. The method yields picosecond‑resolution structural information, including line‑narrowed spectra and cross‑peaks revealing amide‑I coupling, solvent‑dependent differences in a dipeptide, and demonstrates promise for monitoring biological structural changes across diverse timescales.

Abstract

Two-dimensional infrared spectra of peptides are introduced that are the direct analogues of two- and three-pulse multiple quantum NMR. Phase matching and heterodyning are used to isolate the phase and amplitudes of the electric fields of vibrational photon echoes as a function of multiple pulse delays. Structural information is made available on the time scale of a few picoseconds. Line narrowed spectra of acyl-proline-NH 2 and cross peaks implying the coupling between its amide-I modes are obtained, as are the phases of the various contributions to the signals. Solvent-sensitive structural differences are seen for the dipeptide. The methods show great promise to measure structure changes in biology on a wide range of time scales.