Targeted Probing of Compositions and Structures for Complex Sample Analyses by Singlet-Filtered Correlation NMR Technique

Homonuclear proton correlation nuclear magnetic resonance (NMR) spectroscopy [correlation spectroscopy (COSY)] offers an essential method for molecular structure elucidation and composition determination, and its applicability is further promoted by continuously improved pulse sequence techniques. However, in practical applications, mainly to complex chemical and biological samples, existing 2-D COSY experiments remain subject to the problem of spectral congestion caused by abundant observable signals and limited proton chemical shift ranges. Based on the signal filtering mechanism of spin singlet states, herein we propose a singlet-filtered 2-D COSY NMR method to circumvent spectral congestion and achieve favorable analyses on complex samples by individually probing correlation information of targeted proton groups. Different from standard COSY manner that reveals full coupling correlation information, the singlet-filtered COSY adopts the concept of disassembling full coupling correlation networks into separated parts and respectively recording their simplified correlation information for combined analyses. We demonstrate that the proposed method allows one to perform targeted probing of chemical compositions and molecular structures, like specific probe access to individually targeted proton groups, for analyzing complex chemical solution mixtures containing crowded NMR resonances, even biological samples with enormous metabolites and intrinsic field inhomogeneity. This method provides a promising detection tool for component analyses and molecular structure studies on complex chemical and biological samples.