Structure Determination of an Ag I ‐Mediated Cytosine–Cytosine Base Pair within DNA Duplex in Solution with 1 H/ 15 N/ 109 Ag NMR Spectroscopy

The structure of an Ag I ‐mediated cytosine–cytosine base pair, C–Ag I –C, was determined with NMR spectroscopy in solution. The observation of 1‐bond 15 N‐ 109 Ag J ‐coupling ( 1 J ( 15 N, 109 Ag): 83 and 84 Hz) recorded within the C–Ag I –C base pair evidenced the N3–Ag I –N3 linkage in C–Ag I –C. The triplet resonances of the N4 atoms in C–Ag I –C demonstrated that each exocyclic N4 atom exists as an amino group (−NH 2 ), and any isomerization and/or N4–Ag I bonding can be excluded. The 3D structure of Ag I –DNA complex determined with NOEs was classified as a B‐form conformation with a notable propeller twist of C–Ag I –C (−18.3±3.0°). The 109 Ag NMR chemical shift of C‐Ag I ‐C was recorded for cytidine/Ag I complex ( δ ( 109 Ag): 442 ppm) to completed full NMR characterization of the metal linkage. The structural interpretation of NMR data with quantum mechanical calculations corroborated the structure of the C–Ag I –C base pair.