The B-DNA double helix can dynamically accommodate G–C and A–T base pairs in either Watson-Crick or Hoogsteen configurations. Here, we show that G–C+ and A–U Hoogsteen base pairs are strongly disfavored in A-RNA. As a result, N1-methyl adenosine and N1-methyl guanosine, which occur in DNA as a form of alkylation damage, and in RNA as a posttranscriptional modification, have dramatically different consequences. They create G–C+ and A–U Hoogsteen base pairs in duplex DNA that maintain the structural integrity of the double helix, but block base pairing all together and induce local duplex melting in RNA, providing a mechanism for potently disrupting RNA structure through posttranscriptional modifications. The markedly different propensities to form Hoogsteen base pairs in B-DNA and A-RNA may help meet the opposing requirements of maintaining genome stability on one hand, and dynamically modulating the structure of the epitranscriptome on the other.
Developing noble metal-free water oxidation catalysts is essential for many energy conversion/storage processes (e.g., water splitting). Herein, we report the facile synthesis of hollow Co3O4 microspheres composed of porous, ultrathin (<5 nm), single-crystal-like nanosheets via a novel "self-template" route. The successful preparation of these hollow Co3O4 nanomaterials includes three main steps: (1) the synthesis of solid cobalt alkoxide microspheres, (2) their subsequent self-template conversion into hollow cobalt hydroxide microspheres composed of ultrathin nanosheets, and finally (3) thermal treatment of hollow cobalt hydroxide microspheres into the hollow Co3O4 material. The as-obtained hollow Co3O4 nanomaterial possesses a high BET surface area (∼180 m(2) g(-1)), and can serve as an active and stable water oxidation catalyst under both electrochemical and photochemical reaction conditions, owing to its unique structural features. In the electrochemical water oxidation, this catalyst affords a current density of 10 mA cm(-2) (a value related to practical relevance) at an overpotential of ∼0.40 V. Moreover, with the assistance of a sensitizer [Ru(bpy)3](2+) (bpy = 2,2'-bipyridine), this nanomaterial can catalyze water oxidation reactions under visible light irradiation with an O2 evolution rate of ∼12 218 μmol g(-1) h(-1). Our results suggest that delicate nanostructuring can offer unique advantages for developing efficient water oxidation catalysts.
Nitrogen-doped (N-doped) photoluminescent carbon dots (CDs) were prepared by a one-pot microwave-assisted hydrothermal treatment using histidine as the sole carbon source in the absence of acid, alkali, or metal ions. With a diameter of 2-5 nm, the synthesized CDs had apparent lattice fringes and exhibited an excitation-dependent photoluminescent behavior. The CDs were highly yielded, well-dispersed in aqueous solution, and showed high photostability in the solutions of a wide range of pH and salinity. They were used as probes to identify the presence of Fe(3+) ions with a detection limit of 10 nM. With confirmed nontoxicity, these CDs could enter the cancer cells, indicating a practical potential for cellular imaging and labeling.
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