1,4,7,10-Tetraazacyclododecanes

CO3 species was formed and the X-ray structure solved. It is thought that the carbonate species forms on reaction with water, which was problematic in the selected strategy, as water was produced in the formation of the dialkyl carbonates. Other problems included compound solubility and the stability of the monoalkyl carbonate complex. Van Eldik and co-workers also carried out a detailed kinetic study of the hydration of carbon dioxide and the dehydration of bicarbonate both in the presence and absence of the zinc complex of 1,5,9-triazacyclododecane (12[ane]N3). The zinc hydroxo form is shown to catalyze the hydration reaction and only the aquo complex catalyzes the dehydration of bicarbonate. Kinetic data including second order rate constants were discussed in reference to other model systems and the enzyme carbonic anhy-drase.459 The zinc complex of the tetraamine 1,4,7,10-tetraazacyclododecane (cyclen) was also studied as a catalyst for these reactions in aqueous solution and comparison of activity suggests formation of a bidentate bicarbonate intermediate inhibits the catalytic activity. Van Eldik concludes that a unidentate bicarbonate intermediate is most likely to the active species in the enzyme carbonic anhydrase.460... 

Weisman and Reed have developed a route to cyclen (1,4,7,10-tetraazacyclododecane) via a fused 5 6 5 tricyclic system which was formed from condensation of triethylenetetramine 383 and dithiooxamide 381 to give 2,3>5,6,8,9-hexahydrodiimidazo[l,2- 2, l -c]pyrazine 382 in 69% yield (Scheme 30) <1996JOC5186>. 

After our report, many other examples of SIMs based on mononuclear lanthanide complexes have appeared. As relevant examples, we should mention the erbium-organometallic double-decker complexes [11] and the dysprosium-acetylacetonate complexes [12], and the dysprosium-DOTA (H4DOTA, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) complexes reported by Sessoli etal. [13]. 

While the basic and or applied chemistry of saturated macrocyclic polyamines, typically represented by 1,4,7,10-tetraazacyclododecane (cyclen, 1) and 1,4,8,11-tetraazacyclotetradecane (cyclam, 2), have both... 

The use of a lipophilic zinc(II) macrocycle complex, 1-hexadecyl-1,4,7,10-tetraazacyclododecane, to catalyze hydrolysis of lipophilic esters, both phosphate and carboxy (425), links this Section to the previous Section. Here, and in studies of the catalysis of hydrolysis of 4-nitrophenyl acetate by the Zn2+ and Co2+ complexes of tris(4,5-di-n-propyl-2 -imidazolyl)phosphine (426) and of a phosphate triester, a phos-phonate diester, and O-isopropyl methylfluorophosphonate (Sarin) by [Cu(A(A(A/,-trimethyl-A/,-tetradecylethylenediamine)l (427), various micellar effects have been brought into play. Catalysis of carboxylic ester hydrolysis is more effectively catalyzed by A"-methylimidazole-functionalized gold nanoparticles than by micellar catalysis (428). Other reports on mechanisms of metal-assisted carboxy ester hydrolyses deal with copper(II) (429), zinc(II) (430,431), and palladium(II) (432). 

CTAB = cetyltrimethylammonium bromide cyclam = 1,4,8,11-tetraazacyclotetradecane cyclen = 1,4,7,10-tetraazacyclododecane cyst = cysteine... 

A greater stability is observed for [Ln2(L13)3] (see Fig. 10) (56) these complexes are stable in water in the pH range 4-13, with a stability similar to [Ln(DOTA)]- (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The europium complex exhibits a quantum yield of only 0.0137, but has an extremely long lifetime (2.53 ms) in... 

The 12-membered tetraaza-macrocyclic ligand with four pendant pyrazole groups, L6, was synthesized by the reaction of l-(hydroxy-methyDpyrazole with 1,4,7,10-tetraazacyclododecane in MeCN. The Ni(II) complex [NiLe]I2 formed a distorted octahedral structure with... 

MTS containing anchored Mn(II)(dichloride)-l,4,7,10-jV,tetrakis(2-hydroxylpropyl)-27 ,3/ -cyclohexano-1,4,7,10-tetraazacyclododecane 7 was evaluated in the epoxidation of trans P-methylstyrene using iodosylbenzene as oxygen donor. 

From temperature coefficients of polarographic data (ref. 50). h 1,4,7,10-Tetraazacyclododecane, cyclen. 

A second class of MRI contrast agents contains ligands that are derivatives of the macrocydic tetramine, 1.4.7.10-tetraazacyclododecane (cyclen). Gadoterate (Dotarem, Gd-DOTA, Scheme 3, formula 5) was the first macrocydic gadolinium complex which has entered the market. 

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