Application of RP-18 TLC Retention Data to the Prediction of the Transdermal Absorption of Drugs

NMR spectroscopy is a powerful tool for structural analysis of solids, especially if it is complemented by computations of NMR observables, such as chemical shifts and quadrupole coupling constants. In paramagnetic solids, chemical shifts can be greatly affected by hyperfine couplings among the unpaired electrons and atomic nuclei. In this study ¹³C MAS NMR spectra of three representative crystalline solids (a simple coordination compound of copper and alanine and two complex copper-based metal–organic framework materials) were measured, and the observed paramagnetic shifts were correlated with the hyperfine coupling constants, calculated along two different density functional theory-based approaches. The first approach employed an isolated-cluster model, and the second one used an extended-lattice model and periodic boundary conditions. For both approaches the calculated isotropic hyperfine coupling constants correlated very well with the measured paramagnetic shifts and thus allowed the assignment of the ¹³C NMR signals, spread over the region of 1000 ppm. This assignment to individual carbon crystallographic sites was in complete agreement with the experimentally derived assignment.