orals 5th Asia-Pacific NMR Symposium 2013

Double Quantum Correlation Experiments in the Solid State for Assignment and Structure (#14)

K V Ramanathan 1
  1. Indian Institute of Science, Bangalore, India

The enormous success of solution state NMR in deciphering structures of molecules of chemical and biological interest has been largely due experiments that could map proton – proton proximities both through scalar and dipolar couplings. Similar approaches to study molecular structures in solids have been evolving and in recent years significant advances have been made for the case of several partially ordered and fully rigid systems. For such studies, it is required that the homonuclear dipolar couplings are eliminated while retaining chemical shifts and the heteronuclear couplings. In the case of protons, the presence of very strong proton-proton interactions requires special techniques and developments in this regard have been continuing. Along with this, multiple quantum correlation spectroscopy in the case of rigid and semi rigid systems can provide useful proximity information, as the coherences can be generated between dipolar coupled spin systems. Here, we present our efforts in utilizing proton double quantum and carbon single quantum correlation experiments for the case of static oriented liquid crystal samples and rigid powder samples of chemical and biological interest. Correlations based on both scalar and dipolar couplings have been explored.  These experiments have the following advantages, viz., (a) provide more definite  assignments; (b) uncertainties in proton chemical shifts can be reduced by making redundant information available due to possibilities of several DQ cross peaks present for the same carbon; (c) provide chemical shifts of protons, bonded to some other atoms such as the amide protons; (d) enable 13C-13C correlation. The application of this technique to liquid crystals oriented in a magnetic field as well to a few synthetic and natural peptides will be presented.