Structural and Chiroptical Properties of the Two Coordination Isomers of YbDOTA-Type Complexes

Abstract

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)NO 2 BnDOTMA and S(SSSS)NO 2 BnDOTMA 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 nearinfrared 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.

Structure, Dynamics, and Computational Studies of Lanthanide‐Based Contrast Agents

“…However, the same configuration in both types of centers defines a TSA geometry. This was confirmed by a 1 [323,324]. The single bulky nitrobenzyl ring substituent with S configuration locks the ring in a single (δδδδ) conformation with the substituent in an equatorial position, as shown by 1 H EXSY spectra of [Eu(NO 2 BnDOTA)] − , where the exchange between the two diastereoisomeric coordination isomers of the four possible ones occurs through arm rotation alone, as ring inversion is blocked.…”

Static and Dynamic Stereochemistry of Chiral Ln DOTA Analogues

“…[17] On each of them there are an equatorial and an axial protons, giving rise, in principle, to four distinct 1 …”

“…[12,15] As we saw before, the introduction of a bulky 4-nitrobenzyl group on cyclen freezes macrocycle inversion: combination with side-arm chirality leads to a conformationally locked system, whose stereochemical correlations are summarized in Table 2. [17] Inspection of Figure 6 demonstrates that the NIR-ECD spectra of : * (RRRR) Yb DOTMA and S(SSSS) Yb p-NO 2 Bz DOTMA are practically mirror images, in agreement with the fact that the first coordination spheres of these two complexes are enantiomeric; * S(SSSS) Yb p-NO 2 Bz DOTMA and R(SSSS) Yb p-NO 2 Bz DOTMA are completely different, because one is TSA, the other is SA.…”

“…NIR-ECD spectra of (RRRR) Yb DOTMA (c), [15] S(SSSS) Yb p-NO 2 Bz DOTMA (g), and S(RRRR) Yb p-NO 2 Bz DOTMA (a). [17] Table 2. Stereochemical correlations of DOTMA analogues.…”

Lanthanide complexes as chiral probes exploiting circularly polarized luminescence

“…[89][90][91] NMR experiments have shown that these species may be thought of as regioisomers, with their existence being attributed to the fact that it is possible for the ring substituent to be located in one of two nonequivalent positions (Figure 1.20). …”