Bipyridine-Modified DNA Three-Way Junctions with Amide linkers: Metal-Dependent Structure Induction and Self-Sorting

DNA three-way junction (3WJ) structures are essential building blocks for the construction of DNA nanoarchitectures. We have synthesized a bipyridine (bpy)-modified DNA 3WJ by using a newly designed bpy-modified nucleoside, U_bpy- 3 , in which a bpy ligand is tethered via a stable amide linker. The thermal stability of the bpy-modified 3WJ was greatly enhanced by the formation of an interstrand Ni^II(bpy)₃ complex at the junction core (ΔT_m=+17.7 °C). Although the stereochemistry of the modification site differs from that of the previously reported bpy-modified nucleoside U_bpy- 2 , the degree of the Ni^II-mediated stabilization observed with U_bpy- 3 was comparable to that of U_bpy- 2 . Structure induction of the 3WJs and the duplexes was carried out by the addition or removal of Ni^II ions. Furthermore, Ni^II-mediated self-sorting of 3WJs was performed by using the bpy-modified strands and their unmodified counterparts. Both transformations were driven by the formation of Ni^II(bpy)₃ complexes. The structural induction and self-sorting of bpy-modified 3WJs are expected to have many potential applications in the development of metal-responsive DNA materials.     

New Size-Expanded Fluorescent Thymine Analogue: Synthesis,Characterization, and Application

Here, the synthesis, photophysical characterization, and application of a new size-expanded thymine nucleoside, ^diox T , is described. ^diox T has desirable qualities as a T surrogate, including excellent quantum yield (0.36) and high environmental sensitivity. When incorporated into single- and double-stranded DNA, ^diox T showed excellent photophysical characteristics including a high quantum yield (average 0.20), and unlike BgQ, demonstrated dependence on neighboring bases without significant destabilization of the duplex. Interestingly, the matched base pair of adenine (A) and ^diox T has the unique property that it exhibits higher fluorescence than mismatched base pairs, and ^diox T has self-quenching effects. As one example of the possible applications of these promising features, single nucleoside polymorphism typing is demonstrated for discrimination of A by using ^diox T . The results suggest that ^diox T can be used for a broad range of applications in chemical biology.     

Facile Redox-Induced Aromatic–Antiaromatic Interconversion of a β-Tetracyano-21,23-Dithiaporphyrin under Ambient Conditions

Facile redox-induced aromatic–antiaromatic interconversions were accomplished by using β-tetracyano-21,23-dithiaporphyrin (CN₄S₂Por). Introduced cyano groups not only increased the reduction potential of the porphyrin core but also stabilized the antiaromatic isophlorin (CN₄S₂Iph) by π conjugation. The reduction of CN₄S₂Por with hydrazine in polar solvents quantitatively affords CN₄S₂Iph, even under ambient conditions. CN₄S₂Iph retains a nearly planar conformation and exhibits considerable antiaromaticity. Aerobic oxidation of CN₄S₂Iph to CN₄S₂Por occurs in nonpolar solvents. This study was conducted to contribute to the understanding of the structure–antiaromaticity relationship.     

Enantioselective Construction of 3‐Hydroxypiperidine Scaffolds by Sequential Action of Light and Rhodium upon N‐Allylglyoxylamides

3‐Hydroxypiperidine scaffolds were enantioselectively constructed in an atom‐economical way by sequential action of light and rhodium upon N‐allylglyoxylamides. In a formal sense, the allylic C? H bond was selectively cleaved and enantioselectively added across the ketonic carbonyl group with migration of the double bond (carbonyl‐ene‐type reaction).     

Single-particle spectral density of the unitary Fermi gas: Novel approach based on the operator product expansion,sum rules and the maximum entropy method

Making use of the operator product expansion, we derive a general class of sum rules for the imaginary part of the single-particle self-energy of the unitary Fermi gas. The sum rules are analyzed numerically with the help of the maximum entropy method, which allows us to extract the single-particle spectral density as a function of both energy and momentum. These spectral densities contain basic information on the properties of the unitary Fermi gas, such as the dispersion relation and the superfluid pairing gap, for which we obtain reasonable agreement with the available results based on quantum Monte-Carlo simulations.