N-15,N-15 spin-spin coupling constants across N-H-N and N-H+-N hydrogen bonds: can coupling constants provide reliable estimates of N-N distances in biomolecules?

摘要

Predictive quantum chemical methods based upon coupled cluster theory of spin-spin coupling constants offer a direct tool to explore a variety of questions concerning the relationship between coupling constants and intermolecular distances, molecular orientation, changes in hybridization and related issues. Of particular interest are (2h)J(N-15,N-15) couplings across hydrogen bonds. In this work we present EOM-CCSD coupling constants [(2h)J(N-15,N-15)] for a series of cationic complexes stabilized by either traditional or proton-shared N - H+ - N hydrogen bonds, and relate these to N-15,N-15 coupling constants in neutral complexes with N-H-N hydrogen bonds. The computed N-15,N-15 coupling constants in these complexes vary smoothly with N-N distance, regardless of the charge or the particular binding at the N atoms. We propose that the curves which show this dependence have sufficient generality that they should be useful for determining N - N distances from experimentally measured coupling constants. Copyright (C) 2001 John Wiley & Sons, Ltd. [References: 35]