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Formation kinetics and stability studies on the lanthanide complexes of 1,4,7,10‐tetraazacyclododecane‐ N , N ', N '', N '''‐tetraacetic acid by capillary electrophoresis
Author(s) -
Zhu Xiaofeng,
Lever Susan Z.
Publication year - 2002
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/1522-2683(200205)23:9<1348::aid-elps1348>3.0.co;2-v
Subject(s) - capillary electrophoresis , lanthanide , kinetics , dota , chemistry , stopped flow , chromatography , biophysics , chelation , inorganic chemistry , physics , biology , organic chemistry , reaction rate constant , ion , quantum mechanics
In this study, the kinetic behaviors of four lanthanide ions, Sm 3&+ , Dy 3+ , Yb 3&+ and Lu 3&+ , when mixed with a polyazamacrocyclic chelating agent 1,4,7,10‐tetraazacyclododecane‐ N , N ', N '', N '''‐tetraacetic acid (DOTA), were investigated by capillary electrophoresis (CE) in the pH range of 2.0–6.0. At pH 2.0, the formation rate of DOTA‐metal complex is extremely low as very little complex was detected after 5 days reaction, whereas almost no free DOTA was found in the mixture of metal ion and DOTA after 4 min at pH 6.0. The second‐order kinetic association rate constants of the four lanthanide ions chelates at pH 4.2 were calculated as 1.44×10 –2 m M –1 min –1 , 5.20×10 –2 m M –1 min –1 , 4.56×10 –2 m M –1 min –1 and 4.54×10 –2 m M –1 min –1 at 25°C with CE, respectively. In addition, the stability constants of the four lanthanide ions with DOTA were determined by CE at pH 3.0 where approximately 80–90% of the metal ions were associated with DOTA at 25°C. The measured stability constants (log K f ) of the four DOTA‐metal complexes were 23.36, 23.93, 23.39 and 23.06, respectively, and correlated well with published data obtained by different methods. The percentage of metal ion bound with DOTA was evaluated as a function of reactant concentration in pH 6.0 buffer. After adding excess strong acid (0.1 M HCl) to each solution of DOTA‐metal was formed at pH 6.0, no released DOTA was detected after 24 h; thus, dissociation of these lanthanide complexes did not occur under strongly acidic conditions. The Ln(DOTA) – species for the four DOTA‐metal complexes were characterized by electrospray ionization‐mass spectroscopy (ESI‐MS), and the results correlated with proposed structures.