NOEMOL: integrated molecular graphics and the simulation of Nuclear Overhauser effects in NMR spectroscopy

Nuclear Overhauser effects (NOEs) are a widely used method of determining the spatial proximity of spins in Nuclear Magnetic Resonance (NMR) spectroscopy. This paper describes a C program developed for the Sun-3 workstation family that allows the computation of multispin NOE effects for a given molecular structure and given NMR parameters (i.e., resonance frequency and correlation time for molecular reorientation). The integration of these facilities with simple molecular graphics display routines allows modifications to the molecular conformation (such as bond rotations) to be performed, and the effect of these modifications on the NOE effects can then be rapidly calculated and easily visualized. Using the Sun windowing system, the NOE effects can be calculated for two (or more) candidate structures and compared to experimental NMR results. The overall molecular reorientation can be modeled by either isotropic or symmetric top diffusion models, and the internal motions of methyl groups are modeled using an algorithm reported by Tropp.