Increasing 13C CP-MAS NMR resolution using single crystals: application to model octaethyl porphyrins.
Octaethyl porphyrin (OEP) and its Ni and Zn derivatives are considered as model compounds in biochemical, photophysical, and fossil fuel chemistry. They have thus been investigated by high-resolution solid-state (13)C NMR using powders, but peak assignment has been difficult because of large line widths. Arguing that a significant cause of broadening might be the anisotropic bulk magnetic susceptibility, we utilized single crystals in our (13)C cross-polarization magic angle spinning (CP-MAS) measurements and observed a nearly 2-fold line narrowing. This enhanced resolution enabled us to assign chemical shifts to each carbon for all the three compounds. The new assignments are now in agreement with X-ray structural data and allowed us to probe the motional dynamics of the methyl and methylene carbons of the OEP side chains. It is apparent that the use of single crystals in (13)C CP-MAS measurements has a significantly wider impact than previously thought.
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
Sneha
S
Dugar
Riqiang
R
Fu
Naresh S
NS
Dalal
D002247:Carbon Isotopes / Q000737:chemistry; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011166:Porphyrins / Q000737:chemistry*
D002247:Carbon Isotopes; D011166:Porphyrins; C488938:octaethylporphyrin