Paramagnetic Relaxation Enhancement to Improve Sensitivity of 1,1-ADEQUATE NMR

Abstract. The 1,1-ADEQUATE NMR experiment provides easily interpretable spectra to identify two-bond proton-carbon correlations in the structural analysis of small molecules. Despite this, the low natural abundance of ¹³C drastically reduces the efficacy of this experiment due to its dependence on C-C magnetization transfers. A reduction of T₁ and T₂ relaxation times via paramagnetic relaxation enhancement (PRE) represents an opportunity to improve sensitivity and reduce experiment times by facilitating a reduction in recycle delays. In this work, we demonstrate Cr³⁺ at a concentration of 10 mM to be an excellent PRE agent. Paramagnetic relaxation enhancement was then applied in 1,1-ADEQUATE analysis of several compounds, limonene, camphor, amoxapine and quinidine, demonstrating signal-to-noise improvements up to 4.5-fold over diamagnetic conditions.