Assignment of pH‐dependent NMR spectra of the scorpiand macrocycle: an application of titration profiles and spectral linewidths

Abstract

AbstractRoutine homo‐ and heteronuclear 2D NMR experiments (COSY, HMQC, TOCSY and ROESY) were performed for the complex macrocyclic pentaamine ligand 1‐(2′‐aminoethyl)‐1,4,8,11‐tetraazacyclotetradecane (1, scorpiand), derived from 1,4,8,11‐tetraazacyclotetradecane (cyclam). However, some its 13C and 1H resonances were distinguished only based on the similarity between profiles of relevant pH–chemical shift plots and/or linewidth considerations. Following this empirical method relying on the assumption that titration curves of nuclei in comparable chemical environments have comparable shapes, it was possible to assign all chemical shifts (13C, pH 0.25–13.4; 1H, pH 10–11.5) for some different protonated species Hn1n+. A multiple experimental approach used for recognizing their NMR signals is offered as a general assignment procedure in the case of polyazamacrocycles. Copyright © 2002 John Wiley & Sons, Ltd.