Matrix-free dynamic nuclear polarization enables solid-state NMR C-13-C-13 correlation spectroscopy of proteins at natural isotopic abundance

We introduce a general approach for dynamic nuclear polarization (DNP) enhanced solid-state NMR that overcomes the current problems in DNP experiments caused by the use of frozen solutions. Notably, we report for the first time a 2D C-13-C-13 correlation spectrum of a protein without the use of isotopic labeling.