Formation kinetics and stability studies on the lanthanide complexes of 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid by capillary electrophoresis.
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 x 10(-2) mM(-1)min(-1), 5.20 x 10(-2) mM(-1)min(-1), 4.56 x 10(-2) mM(-1)min(-1) and 4.54 x 10(-2) mM(-1)min(-1) at 25 degrees 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 degrees 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.
Zhu
Xiaofeng
X
Department of Chemistry, University of Missouri at Columbia, 65211, USA.
Lever
Susan Z
SZ
D002021:Buffers; D002614:Chelating Agents / Q000032:analysis* / Q000737:chemistry; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D004355:Drug Stability; D006573:Heterocyclic Compounds, 1-Ring / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D028581:Lanthanoid Series Elements / Q000032:analysis* / Q000737:chemistry; D009942:Organometallic Compounds / Q000032:analysis / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
D002021:Buffers; D002614:Chelating Agents; D006573:Heterocyclic Compounds, 1-Ring; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid