The authors thank the National Institutes of Health [EB-04285 (M.W.) and CA-84697 and RR-02584—Division of Research Resources (A.D.S.)]; the Robert A. Welch Foundation [AT-584 (A.D.S.)]; the Texas Advanced Technology Program (A.D.S.); and the Ministero dell’Istruzione, dell’Università e della Ricerca (L.D.B.) for financial support of this work.
Ligands (Biochemistry), Conformational analysis, Molecular structure -- Mathematical models, Contrast media (Diagnostic imaging)
Studies of the structural, physical, and chemical properties of the lanthanide(III) complexes of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and related ligands are often complicated by the presence of two coordination isomers in solution. Since these coordination isomers are in exchange and cannot be separated, many techniques offer information only on the weighted average of the two isomers. Lanthanide ion complexes formed with the ligands S(RRRR)NO2BnDOTMA and S(SSSS)NO2BnDOTMA preferentially adopt only one of the two common coordination isomers in solution, so the ytterbium complexes of these ligands offer a unique opportunity to study the near-infrared circular dichroism (NIR-CD) characteristics of each coordination geometry in isolation. The spectra acquired support many of the conclusions and assumptions of previous studies and demonstrate that this spectroscopy is particularly sensitive to the distortion of the coordination polyhedron. This will have particularly relevant consequences when studying achiral YbDOTA-like systems forming labile adducts with (chiral) hosts and receptors.
Di Bari, L., Pescitelli, G., Sherry, A. D., & Woods, M. (2005). Structural and chiroptical properties of the two coordination isomers of YbDOTA-type complexes. Inorganic chemistry, 44(23), 8391-8398.