Structure Determination of an AgI‐Mediated Cytosine–Cytosine Base Pair within DNA Duplex in Solution with 1H/15N/109Ag 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 ¹⁵N‐¹⁰⁹Ag J‐coupling (¹J(¹⁵N,¹⁰⁹Ag): 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 (?NH₂), 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 ¹⁰⁹Ag NMR chemical shift of C‐Ag^I‐C was recorded for cytidine/Ag^I complex (δ(¹⁰⁹Ag): 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.     

4-Nitro-9,10-di­hydro­phenanthrene and a polymorphic form of 4-nitro­phenanthrene

The crystal structures of 4-nitro-9,10-di­hydro­phenanthrene, C₁₄H₁₁NO₂, (I), and 4-nitro­phenanthrene, C₁₄H₉NO₂, (II), the latter having two crystallographically independent mol­ecules, show that the mol­ecules are not planar. The dihedral angles between the phenyl rings of the bi­phenyl skeletons are 28.64 (8)° for (I), and 10.34 (15) and 11.75 (13)° for the two mol­ecules of (II). The differences in the dihedral angles have an effect on the photochemical reactivity of the mol­ecules.     

Dark energy from modified gravity with Lagrange multipliers

We study scalar–tensor theory, k-essence and modified gravity with Lagrange multiplier constraint which role is to reduce the number of degrees of freedom. Dark Energy cosmology of different types (ΛCDM, unified inflation with DE, smooth non-phantom/phantom transition epoch) is reconstructed in such models. It is demonstrated that presence of Lagrange multiplier simplifies the reconstruction scenario. It is shown that mathematical equivalence between scalar theory and F(R)$F(R)$ gravity is broken due to presence of constraint. The cosmological evolution is defined by the second F₂(R)$F_2(R)$ function dictated by the constraint. The convenient F(R)$F(R)$ gravity sector is relevant for local tests. This opens the possibility to make originally non-realistic theory to be viable by adding the corresponding constraint. A general discussion on the role of Lagrange multipliers to make higher-derivative gravity canonical is developed.     

Facile synthesis of acetylenecarboxylates by the oxidative carbonylation of terminal acetylenes catalyzed by PdCl2 under mild conditions

Terminal acetylenes were converted to acetylenecarboxylates in high yields under atmospheric pressure of carbon monoxide at room temperature using a catalytic amount of PdCl₂ and a stoichiometric amount of CuCl₂.