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Retracted: Kinetics of Formation for Lanthanide (III) Complexes of DTPA‐(Me‐Trp) 2 used as Imaging Agent
Author(s) -
Tiwari Anjani K.,
Sinha Deepa,
Datta Anupama,
Kakkar Dipti,
Mishra Anil K.
Publication year - 2011
Publication title -
chemical biology and drug design
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.59
H-Index - 77
eISSN - 1747-0285
pISSN - 1747-0277
DOI - 10.1111/j.1747-0285.2011.01103.x
Subject(s) - chemistry , protonation , lanthanide , amide , ionic strength , kinetics , ligand (biochemistry) , dota , reaction rate constant , biodistribution , stability constants of complexes , crystallography , gadolinium , nuclear chemistry , chelation , ion , inorganic chemistry , aqueous solution , organic chemistry , biochemistry , physics , receptor , quantum mechanics , in vitro
Diethlenetriamine‐ N , N , N′N′′N′′ ‐pentaacetic acid (DTPA)‐bis (amide) analogs have been synthesized and evaluated as a potential biomedical imaging agents. Imaging and biodistribution studies were performed in mice that showed a significant accumulation of DTPA analogs in brain. The stability and protonation constants of the complexes formed between the ligand [DTPA‐(Me‐Trp) 2 ] and Gd 3+ , Eu 3+ , and Cu 2+ have been determined by pH potentiometry (Gd 3+ , Eu 3+ ) and spectrophotometry (Cu 2+ ) at 25 °C and at constant ionic strength maintained by 0.10 m KCl. The kinetic inertness of Gd [DTPA‐(Me‐Trp) 2 ] was characterized by the rates of exchange reactions with Zn 2+ and Eu 3+ . In the Eu 3+ exchange, a second‐order [H + ] dependence was found for the pseudo‐first‐order rate constant [ k 0 = (4.5 ± 1.2) × 10 −6 /s; k 1 = 0.58 ± 0.1 / m /s, k 2 = (6.6 ± 0.2) × 10 4 / m 2 /s, k 3 = (4.8 ± 0.8) × 10 −4 / m /s]. In the Eu 3+ exchange, at pH < 5.0, the rate decreases with increasing concentration of the exchanging ion. At physiological pH, the kinetic inertness of [DTPA‐(Me‐Trp) 2 ] is more inert than GdDTPA 2− , the most commonly used MRI contrast agent ( t 1 / 2 = 127 h). High kinetic stability is an important requirement for the Gd complexes used as contrast enhancement agents in magnetic resonance imaging.