The effect of pendant-arm modification and ring size on the dynamics of cyclic polyamines

Carbon-13 relaxation studies have been performed on two cyclic polyamines—1,4,8,11-tetraazacyclotetradecane, N4R4_H, (cyclam) and 1,4,7,10,13,16-hexaazacyclooctadecane, N6R6_H, (hexacyclen), and on two synthesized N-substituted cyclam derivatives—1,4,8,11-tetrahexanoyl-1,4,8,11-tetraazacyclotetradecane, N4R4_CO(CH2)4CH3, with aliphatic and 1,4,8,11-tetranaftalenesulfonyl-1,4,8,11-tetraazacyclotetradecane, N4R4_SO2C10H7, with aromatic substituents. Longitudinal T1 relaxation and NOE measurements were performed in extreme narrowing region for basic polyamines and outside extreme narrowing region for substituted derivatives at room temperature and for magnetic strengths 400 and 500 MHz. The main ring and the pendant-arms in substituted compounds were considered separately. The obtained relaxation rates and NOE factors for N4R4_CO(CH2)4CH3 and N4R4_SO2C10H7 molecules were fitted to overall and internal correlation times and order parameters using Lipari–Szabo ‘model-free’ formalism. The chemical shift anisotropy was determined for N4R4_SO2C10H7 compound. The meaningful differences were observed between carbons in the main part of molecules and carbons from pendant-arms.