Hydroxyethylation and its effect on the rate of metal ion ingress into macrocyclic ligands

New Insights into the Complexation of Lead(II) by 1,4,7,10‐Tetrakis(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane (DOTAM): Structural, Thermodynamic, and Kinetic Studies

“…[89,90] Of particular relevance, Rahardjo and Wainwright showed that a minimum of two dangling Nhydroxyethyl chains appended to adjacent amines of 1,4-disubstituted cyclam are required to assist the metal ion capture by the oxygen atoms and speed up its insertion into the diprotonated macrocycle. [91] Following this idea, [Pb (TETAM)] 2+ formation could most probably be initiated by the fast replacement of two water molecules of the fully aquated Pb 2+ ion by the entering amide carbonyl oxygen atoms of TETAMH + and subsequent interaction with the tertiary amines bearing the amide groups, affording an O 2 N 2 -bound intermediate. [15,91] The driving force for such a sequential arm-by-arm binding process is the successive closure of five-membered chelate rings.…”

“…[91] Following this idea, [Pb (TETAM)] 2+ formation could most probably be initiated by the fast replacement of two water molecules of the fully aquated Pb 2+ ion by the entering amide carbonyl oxygen atoms of TETAMH + and subsequent interaction with the tertiary amines bearing the amide groups, affording an O 2 N 2 -bound intermediate. [15,91] The driving force for such a sequential arm-by-arm binding process is the successive closure of five-membered chelate rings. Once the cation has been brought into the vicinity of the cyclam scaffold, the fifth bond formation could presumably involve a nitrogen atom located on the opposite side of the already bound amide arms.…”

Anion and cation binding by a pendant arm cyclam and its macrobicyclic derivatives

“…Coordination to the hydroxyl groups has been shown to be intimately involved in the metal complexation process. 28,31,32 The propyl analogue L 1 is prepared through the high-pressure reaction of cyclam with trimethylene oxide. 26 Yields are almost quantitative due to the reactive nature of the oxetane molecule.…”

External Coordination of Europium(III) Prior to Its Encapsulation within a Cyclen-Based Pendant Donor Macrocycle

“…Structural information concerning such an intermediate would provide knowledge relating to the progression of the metal ion from the solvated state to the fully encapsulated state. In the past, others [5][6][7][8][9] and we ourselves [10][11][12][13][14] have suggested that pre-encapsulation of the metal ion by the pendant donor groups may be responsible for kinetically assisting the metal ion into and out of the macrocyclic cavity, but no intermediate complex, which would substantiate this theory, has been reported.…”