金澤 宏樹

<jats:p>Significant efforts have been invested in unraveling the stucture-property relationship of DNA-AgNCs using relatively short DNA sequences. Due to the limited sequence length, two or more strands are often required...</jats:p>

<jats:p>Gold‐mediated base pairing in nucleic acids has remained poorly understood, despite structural analogies with mercury and silver ions known to coordinate selectively to mismatched base pairs. Here, the crystal structures of a CAu(I)C base pair and a CGAu(I)C base triple formed with natural nucleobases are reported. Although solution‐phase thermodynamic analysis of Au(I) coordination is technically unfeasible, structural evidence supports its selective insertion into the base mismatches. In contrast, duplexes incorporating 2‐thiocytosine form square‐planar complexes with Au(III), and melting temperature analysis shows significant thermal stabilization. The distinct coordination geometries of Au(I) and Au(III) arise from differences in oxidation state and preferred coordination numbers, with Au(I) favoring linear two‐coordinate structures and Au(III) forming square‐planar complexes stabilized by thiocarbonyl donors. These findings establish a structure‐guided strategy for oxidation‐state‐selective metal coordination in nucleic acids, paving the way for the design of metal‐responsive DNA architectures with tunable properties.</jats:p>

<jats:p>Fluorescence imaging is a key tool in biological and medical sciences. Despite the potential for increased imaging depth in the near‐infrared range, the limited availability of bright emitters hinders its widespread implementation. In this work, a DNA‐stabilized silver nanocluster (DNA–AgNC) with bright emission at 960 nm in solution is presented, which redshifts further to 1055 nm in the solid and crystalline states. The atomic structure, composition and charge of this DNA–AgNC are determined by combining single‐crystal X‐ray diffraction and electrospray ionization–mass spectrometry. This unique atomically precise silver nanocluster consists of 28 silver atoms, of which are neutral (Ag<jats:sub>28</jats:sub> <jats:sup>16+</jats:sup>), arranged in a rodlike shape, and measures just over 2 nm in length. Interestingly, differences are observed in the number of chlorido ligands between the solution and crystalline states, highlighting the important but not yet fully understood role of chlorides in fine‐tuning the optical properties of this class of emitters. The structure of this silver nanorod, along with the fully characterized photophysical properties, represents a cornerstone for understanding the intricate interactions between silver and DNA bases, as well as paving the way for the rational design of the next‐generation imaging probes.</jats:p>

Abstract Aminoglycosides (AG) are antibiotics that lower the accuracy of protein synthesis by targeting a highly conserved RNA helix of the ribosomal A‐site. The discovery of AGs that selectively target the eukaryotic ribosome, but lack activity in prokaryotes, are promising as antiprotozoals for the treatment of neglected tropical diseases, and as therapies to read‐through point‐mutation genetic diseases. However, a single nucleobase change A1408G in the eukaryotic A‐site leads to negligible affinity for most AGs. Herein we report the synthesis of 6′‐fluorosisomicin, the first 6′‐fluorinated aminoglycoside, which specifically interacts with the protozoal cytoplasmic rRNA A‐site, but not the bacterial A‐site, as evidenced by X‐ray co‐crystal structures. The respective dispositions of 6′‐fluorosisomicin within the bacterial and protozoal A‐sites reveal that the fluorine atom acts only as a hydrogen‐bond acceptor to favorably interact with G1408 of the protozoal A‐site. Unlike aminoglycosides containing a 6′‐ammonium group, 6′‐fluorosisomicin cannot participate in the hydrogen‐bonding pattern that characterizes stable pseudo‐base‐pairs with A1408 of the bacterial A‐sites. Based on these structural observations it may be possible to shift the biological activity of aminoglycosides to act preferentially as antiprotozoal agents. These findings expand the repertoire of small molecules targeting the eukaryotic ribosome and demonstrate the usefulness of fluorine as a design element.