A Simple,High‐Yield Synthesis of DNA Duplexes Containing a Covalent,Thermally Cleavable Interstrand Cross‐Link at a Defined Location

Interstrand DNA–DNA cross‐links are highly toxic to cells because these lesions block the extraction of information from the genetic material. The pathways by which cells repair cross‐links are important, but not well understood. The preparation of chemically well‐defined cross‐linked DNA substrates represents a significant challenge in the study of cross‐link repair. Here a simple method is reported that employs “post‐synthetic” modifications of commercially available 2′‐deoxyoligonucleotides to install a single cross‐link in high yield at a specified location within a DNA duplex. The cross‐linking process exploits the formation of a hydrazone between a non‐natural N⁴‐amino‐2′‐deoxycytidine nucleobase and the aldehyde residue of an abasic site in duplex DNA. The resulting cross‐link is stable under physiological conditions, but can be readily dissociated and re‐formed through heating–cooling cycles.     

The Role of Alkali Metal in α‐MnO2 Catalyzed Ammonia‐Selective Catalysis

The unexpected phenomenon and mechanism of the alkali metal involved NH₃ selective catalysis are reported. Incorporation of K⁺ (4.22 wt %) in the tunnels of α‐MnO₂ greatly improved its activity at low temperature (50–200 °C, 100 % conversion of NO_x vs. 50.6 % conversion over pristine α‐MnO₂ at 150 °C). Experiment and theory demonstrated the atomic role of incorporated K⁺ in α‐MnO₂. Results showed that K⁺ in the tunnels could form a stable coordination with eight nearby O atoms. The columbic interaction between the trapped K⁺ and O atoms can rearrange the charge population of nearby Mn and O atoms, thus making the topmost five‐coordinated unsaturated Mn cations (Mn_5c, the Lewis acid sites) more positive. Therefore, the more positively charged Mn_5c can better chemically adsorb and activate the NH₃ molecules compared with its pristine counterpart, which is crucial for subsequent reactions.