The unusual protonation constants of cyclam. A potentiometric, crystallographic and molecular mechanics study

On the Signalling Pathways and CuII‐Mediated Anion Indication of N‐meso‐Substituted Heptamethine Cyanine Dyes

“…These findings can be interpreted as follows: The cyclam unit of 1 is doubly protonated at neutral pH. [43,45,57] The third secondary nitrogen atom in the cyclam unit is then protonated with a pK a value of 3.6. In contrast to the protonation of 2 and 3, this step is reversible.…”

“…The cyclam moiety in 1 is now most probably doubly protonated. [43] All three dyes still fluoresce in water at neutral pH ( Figure S4 in the Supporting Information), however, F f values are reduced to 0.03 for 1, 0.09 for 2 and 0.05 for 3. For comparison, 4 emits with a F f value of 0.04 in this medium.…”

“…Additionally, it is known from many studies of cyclam and related derivatives that these macrocycles can adopt different conformations in the ground state in solution, the most prominent influence being the preference of the single nitrogen atoms to exist in the endo or exo conformation (N atom directed inwards or outwards of the macrocycle, Figure 4), mainly depending on solvent, protonation state and counterions (note that 1 is a cationic dye with a perchlorate counterion), [42] and that the pK a of the first two protonation steps for cyclam are rather high (11.3 and 10.2). [43] Based on the background of these diverse features, we refrained from a theoretical approach to this problem. In the optimised groundstate geometry of all-trans 1, the three nitrogen atoms of the NH groups occupy an endo conformation, the bridgehead nitrogen an exo conformation (Figures 4 and 5).…”

A New Tris(phosphonomethyl) Monoacetic Acid Cyclam Derivative: Synthesis, Acid‐Base and Metal Complexation Studies

“…Similar concerted protonation phenomena have been previously observed for cyclam itself and for several of its derivatives. [18,19,21,[23][24][25]27] Further protonations on the ligand could not be determined as they occur at an extremely low pH.…”

Synthesis of 1,4,7,10‐Tetra‐azacyclododecan‐1,4,7,10‐tetra‐azidoethylacetic Acid (DOTAZA) and Related “Clickable” DOTA Derivatives

“…[30] Routine characterization of DOTAZA esters, like compound 27, by using NMR spectroscopy and MS was complicated by the high affinity of the compounds for sodium ions. After routine work-up by column chromatography on silica gel, DOTAZA ester 27 was isolated as a 2:1 mixture of sodium complex 31 (Scheme 7) and the free ligand (27). The high affinity of DOTA esters for sodium has been reported previously.…”