Optimizing "Lipari-Szabo model free" parameters to heteronuclear relaxation data.


Modelfree is a program to fit the extended model free spectral density function to NMR spin relaxation data. The program can analyze the spin-lattice relaxation rate constant (R1), the spin-spin relaxation rate constant (R2), and the heteronuclear steady-state {1H}-X nuclear Overhauser effect (NOE) for any combination of 13C and 15N spins at up to five static magnetic fields. The algorithm assumes dipolar and chemical shift anisotropy (CSA) relaxation mechanisms for R1, R2 and the NOE and includes an additive term to account for chemical exchange broadening of R2. The exchange broadening parameter is scaled quadratically with respect to the static magnetic field if data for more than one field is available. Descriptions of the main principles utilized in the program for model selection, optimization and error analysis using Monte Carlo simulations have been published previously (Palmer et al., 1991; Mandel et al., 1995).



NMRbox Version Software Version
1.0.0 4.0,
2.0.0 4.0,
3.0.0 4.0,


  • Relaxation Analysis


Backbone Dynamics of Escherichia coli Ribonuclease HI: Correlations with Structure and Function in an Active Enzyme
Mandel Arthur M, Akke Mikael, Palmer III Arthur G,
Journal of molecular biology. 1995; 246(1): 144--163