Analysis of NMR Spectra in Case of Temperature-Dependent Chemical Exchange Between Two Unequally Populated Sites
Abstract
A new approach is introduced for analysis of nuclear magnetic resonance (NMR) spectra measured under conditions of asymmetric chemical exchange. It is based on a simultaneous least-square fit of a due analytical formula to the experimental NMR spectrum.
For this reason, we derived the analytical solution of Bloch-McConnell equations describing the spectral lineshape in the case of the free induction decay and chemical exchange between two unequally populated sites. The obtained formula is shown to be in agreement with the one derived for continuous wave NMR experiments first published in fifties.
On the other hand, typing errors were found in formulae presented in later monographs. Applicability of the approach to extensive NMR data was demonstrated on proton NMR spectra of a self-complementary oligodeoxynucleotide d(GATGCATC) measured at various temperatures covering the duplex melting.
The lineshape analysis of aromatic proton signals provided us the temperature dependence not only of the equilibrium ratio between duplexes and single strands, but also of the kinetics of duplex formation and dissociation, which is not obtainable for a sample in the state of thermodynamic equilibrium by other methods.