Structural studies of two protonated forms of a C-2 symmetrical optically active cyclam derivative

Detailed structural analyses, including solid-state (X-Ray), solution-state (NMR) and theoretical (AM1) studies of the two most stable protonated form s - di 3H(2)(2+) and tetraprotonated 3H(4)(4+) - of a C-2 symmetrical, opti cally active cyclam derivative 3 have been carried out. Important conformat ional changes in the 14-membered and cyclohexane rings accompany the proton ation. A rigid conformation with C-2 symmetry stabilized by bifurcated intr amolecular hydrogen bonds is obtained for 3H(2)(2+), whereas for 3H(4)(4+) a dynamic system in solution and a loss of the C-2 symmetry in the solid st ate are found. The effects of temperature and the counter-ion are also disc ussed.