DNA duplexes comprising 6-(1H-pyrazol-1-yl)-9Hpurine (6PP), 1-deaza-6PP (1D 6PP), 7-deaza-6PP (7D 6PP) and 1,7-dideaza-6PP (1,7D 6PP) 2'-deoxyribonucleosides, respectively,w ere investigated towards their ability to form metalmediated base pairs in the presenceo fA g I .I n6 PP and 7D 6PP,t he Ag I ion can coordinate to the nucleobase via the endocyclic N1 nitrogena tom, that is, via the Watson-Crick edge. In contrast, this nitrogen atom is not available in 1D 6PP and 1,7D 6PP,s ot hat in 1D 6PP an Ag I coordination is only possible via the Hoogsteen edge (N7). Reference duplexesw ith eithera denine:adenine mispairs or canonical adenine:thymine base pairs were used to investigatet he impact of the pyrazolyl moiety on the Ag I-binding properties. To determine the thermala nd structurald uplex stabilities in the absence or presence of Ag I ,a ll duplexes weree xamined by UV and circulardichroism spectroscopics tudies. These investigations shed light on the questiono fw hether N1-or N7-coordination is preferred in purine-based metal-mediated base pairs.

A series of antiparallel‐stranded and parallel‐stranded DNA duplexes containing hetero base pairs of the artificial nucleobases 6‐(1H‐pyrazol‐1‐yl)‐9H‐purine (6PP), 1‐deaza‐6PP (1D6PP), 7‐deaza‐6PP (7D6PP), and 1,7‐dideaza‐6PP (1,7D6PP) were investigated with respect to their ability to form silver(I)‐mediated base pairs. A close examination of the duplex melting temperatures in the absence and in the presence of silver(I) ions shows a strong sequence‐dependence of the stability of the resulting silver(I)‐mediated base pairs. The most stable silver(I)‐mediated base pairs are formed when 1,7D6PP is located in a purine‐rich strand opposite either 6PP or 7D6PP. This indicates that the silver(I) ions are coordinated via the Watson‐Crick edge of the latter nucleobase, whereas they bind to the pyrazolyl moiety of the former. As a result, a [2+1] coordination environment is proposed for the silver(I) ions.

Films of four different DNA quadruplex-forming (G4) sequences (c-KIT, c-MYC, HTelo, and BCL2) on gold surfaces were investigated by electrochemical impedance spectroscopy (EIS) to evaluate whether they evoke unique electrochemical responses that can be used for their identification. This could render EIS an alternative means for the determination of G4 sequences of unknown structure. Towards, this end, cation-dependent topology changes in the presence of either K+, K+ in combination with Li+, or Pb2+ in the presence of Li+ were first evaluated by circular dichroism (CD) spectroscopy, and electrochemical studies were performed subsequently. As a result, G4-sequence specific charge transfer resistance (RCT) patterns were in fact observed for each G4 sequence, allowing their discrimination by EIS. Graphic abstract