Disentangling crystallographic inequivalence and crystallographic forms of l-arginine by one- and two-dimensional solid-state NMR spectroscopy

Overlapping ¹³C or ¹⁵N solid-state NMR spectra from crystallographically different forms of l-arginine hydrochloride can be separated by exploiting differential proton T₁ relaxation in conjunction with cross-polarization. Dipolar ¹³C-¹³C and ¹⁵N-¹⁵N two-dimensional correlation experiments reveal resonances belonging to crystallographically and magnetically inequivalent molecules.