Synthesis and Spectroscopic Investigation of a Hexaaza Lanthanum(III) Macrocycle with a Hybrid-Type G4 DNA Stabilizing Effect

[Image: see text] Herein we present a mononuclear lanthanum(III) complex obtained in a template cyclocondensation reaction of lanthanum(III) nitrate salt, 1,2-propanediamine, and 2,6-diacetylpyridine (LaPA complex). A preliminary investigation of the biological potential of this compound was conducted using a biomedically relevant target Tel26. We found that, different from parallel G4, antiparallel G4, and duplex DNA, only a hybrid-type G4 structure of Tel26 in a K(+) solution was significantly stabilized by ≥7 °C, which emerged in our UV melting studies. Moreover, LaPA induced structural changes in the Tel26 structure in a K(+)-deprived solution, suggesting that it may also lead to conformational changes in “non-G4” telomeric DNA.