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 Te126. We found that, different from parallel G4, antiparallel G4, and duplex DNA, only a hybrid-type G4 structure of Te126 in a K+ solution was significantly stabilized by >= 7 degrees C, which emerged in our UV melting studies. Moreover, LaPA induced structural changes in the Te126 structure in a K+-deprived solution, suggesting that it may also lead to conformational changes in "non-G4" telomeric DNA.