Related Experiment Video
Updated: Aug 18, 2026

NMR 15N Relaxation Experiments for the Investigation of Picosecond to Nanoseconds Structural Dynamics of Proteins
Published on: November 1, 2024
Restricted rotational motion of CO in a protein internal cavity: evidence for nonseparating correlation functions
Jan Helbing1, Karin Nienhaus, G Ulrich Nienhaus
1Physikalisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse, 190, CH-8057 Zürich, Switzerland.
Abstract:
The strongly restricted orientational motion of CO molecules trapped in the Xe4 internal cavity of myoglobin mutant L29W-S108L is investigated by polarization-dependent mid-infrared pump-probe spectroscopy at cryogenic temperatures. Following an ultrafast initial decay, the signal anisotropy reaches an asymptotic value that is significantly larger than the prediction from the well-known relation [see text], based on previously established potential parameters. This discrepancy is explained by showing that the full four-point correlation function describing third-order spectroscopy [see text] does not factorize in systems where its fast decay is dominated by restricted reorientation of the transition dipole moments.
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
NMR Spectroscopy: Spin–Spin Coupling
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
According to Hooke's law, the vibrational frequency is directly proportional to the...
¹H NMR: Long-Range Coupling
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...

