Europium(III) Macrocyclic Chelates Appended with Tyrosine‐based Chromophores and Di‐(2‐picolyl)amine‐based Receptors: Turn‐On Luminescent Chemosensors Selective to Zinc(II) Ions

Abstract

Zinc ions play an important role in many biological processes in the human body. To selectively detect Zn 2 + , two EuDO3A-based complexes (DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid) appended with tyrosine as a chromophore and di-(2-picolyl)amine (DPA) as the Zn 2 + recognition moiety were developed as suitable luminescent sensors. Their luminescence intensity is affected by the photoinduced electron transfer mechanism. Upon addition of Zn 2 + , both probes display an up to sevenfold enhancement in Eu 3 + emission. Competition experiments demonstrated their specificity toward Zn 2 + over other metal ions, while also revealing the nonspecificity of the derivatives lacking the DPA-moiety, thus confirming the essential role of the DPA for the recognition of Zn 2 + . The induced emission changes of Eu 3 + allow for precise quantitative analysis of Zn 2 + , establishing these lanthanide-based complexes as viable chemosensors for biological applications.

Highly Potent MRI Contrast Agent Displaying Outstanding Sensitivity to Zinc Ions

“…The obtained dissociation constant resulted in the values K d(GdZnL) =543±39 and 552±76 nM in HEPES and PBS, respectively. This is in line with the values we obtained for the luminescence sensor with a similar structure; [12] also, the results indicate that the binding affinity is not affected by the ternary complex formation between the phosphates and Gd 3+ (vide supra).…”

“…Consequently, the 13 C signals of the carbons in the phenylacetate recover in intensity, multiplicity and the usual frequency shift in 13 C NMR for the respective functional groups. Moreover, the minor change in the shift of doublets between 1–2 equiv of Zn 2+ indicates that EuL* :Zn 2+ stoichiometry likely moves from 1:1 to 1:2 complex formation, which was also observed in the case of the luminescent phenoxy analogue [12] . However, it is obvious that, irrespective of the type of formed species (1:1 or 1:2), already the first equiv of Zn 2+ causes the decoordination of the phenoxyacetate from the paramagnetic metal center.…”

“…To push the limits of Zn 2+ detection at high magnetic fields with SCAs, we approached the problem by using a structural motif we recently discovered, which shows an excellent “turn‐on” luminescence emission response to Zn 2+ [12] . The SCA molecule we designed was based on the di‐(2‐picolyl)amine (DPA) as the Zn 2+ recognition moiety, 1,4,7,10‐tetraazacyclododecane‐1,4,7‐tricarboxylic acid (DO3A) as chelator for Gd 3+ and a tyrosine (Tyr) unit as a spacer.…”

“…The preparation of the desired complex GdL (Figure 1) was done in analogy to the recently reported luminescence chemosensor [12] . Additionally, phenoxyacetate was installed by the alkylation of the phenolic ‐OH of 1 at room temperature to smoothly provide 2 within 12 h (Scheme S1 in SI).…”

Highly Potent MRI Contrast Agent Displaying Outstanding Sensitivity to Zinc Ions

“…[9a, 11] To push the limits of Zn 2+ detection at high magnetic fields with SCAs, we approached the problem by using a structural motif we recently discovered, which shows an excellent "turn-on" luminescence emission response to Zn 2+ . [12] The SCA molecule we designed was based on the di-(2-picolyl)amine (DPA) as the Zn 2+ recognition moiety, 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid (DO3A) as chelator for Gd 3+ and a tyrosine (Tyr) unit as a spacer. Herein, we protected the carboxylate of Tyr as the methyl ester, and deliberately appended an acetate moiety on the phenolic oxygen, which can act as a bridge between the DPA moiety and the DO3A chelator.…”