J-coupling constants for a trialanine peptide as a function of dihedral angles calculated by density functional theory over the full Ramachandran space

Abstract

We present 13 3J, seven 2J and four 1J coupling constants (24 in all) calculated using B3LYP/D95** as a function of the and ψ Ramachandran dihedral angles of the acetyl(Ala) 3NH 2 capped trialanine peptide over the entire Ramachandran space. With the exception of three of these J couplings, all show significant dependence upon both dihedral angles. For each J coupling considered, a two dimensional grid with respect to and ψ angles can be used to interpolate the values for any pair of and ψ values. Such simple interpolation is shown to be very accurate. Most of these calculated J couplings should prove useful for improving the accuracy of the determination of peptide and protein structures from NMR measurements in solution over that provided by the common procedure of treating the J couplings as functions of a single dihedral angle by means of Karplus-type fittings