Search for: All records

Abstract The chemical reduction of a bilayer spironanographene,spiro‐NG(C₁₃₇H₁₂₀), with Na and K metals in the presence of [2.2.2]cryptand to yield [Na⁺(2.2.2‐cryptand)](C₁₃₇H₁₂₁⁻) (1) and [K⁺(2.2.2‐cryptand)](C₁₃₇H₁₂₁⁻) (2), respectively, is reported. X‐ray crystallography reveals the formation of a new “naked” anion (spiro‐NG_H⁻), in which spirocyclic ring cleavage and subsequent hydrogenation have occurred. Density Functional Theory (DFT) calculations suggest that the generation of the radical anion of the parent nanographene (spiro‐NG^•−), upon electron acceptance from Na and K metals, induces the cleavage of the strained spirobifluorene core. The resulting spin density localizes on a particular carbon atom, previously attached to the spiranic sp³carbon atom, facilitating a site‐specific hydrogenation to afford (spiro‐NG_H⁻). The electrostatic potential map of this anion reveals electron density concentrated at the five‐membered ring of the readily formed indenyl fragment, thus enhancing the aromaticity of the system. Furthermore, nuclear magnetic resonance (NMR) and UV–vis absorption spectroscopy experiments allowed to follow the in situ reduction and hydrogenation processes in detail. 

Aromaticity is one of the most deeply rooted concepts in chemistry. But why, if two-thirds of existing compounds can be classified as aromatic, is there no consensus on what aromaticity is? σ−, π−, δ−, spherical, Möbius, or all-metal aromaticity… why are so many attributes needed to specify a property? Is aromaticity a dubious concept? This perspective aims to reflect where the aromaticity community is and where it is going. 

The chemical reduction of a corannulene-based molecular nanographene, C 76 H 64 (1), with Na metal in the presence of 18-crown-6 afforded the doubly-reduced state of 1. This reduction provokes a distortion of the helicene core and has a significant impact on the aromaticity of the system. 

Protein-protein interactions play critical roles in biology, but the structures of many eukaryotic protein complexes are unknown, and there are likely many interactions not yet identified. We take advantage of advances in proteome-wide amino acid coevolution analysis and deep-learning–based structure modeling to systematically identify and build accurate models of core eukaryotic protein complexes within the Saccharomyces cerevisiae proteome. We use a combination of RoseTTAFold and AlphaFold to screen through paired multiple sequence alignments for 8.3 million pairs of yeast proteins, identify 1505 likely to interact, and build structure models for 106 previously unidentified assemblies and 806 that have not been structurally characterized. These complexes, which have as many as five subunits, play roles in almost all key processes in eukaryotic cells and provide broad insights into biological function. 

Abstract The chemical reduction of π‐conjugated bilayer nanographene1(C₁₃₈H₁₂₀) with K and Rb in the presence of 18‐crown‐6 affords [K⁺(18‐crown‐6)(THF)₂][{K⁺(18‐crown‐6)}₂(THF)_0.5][C₁₃₈H₁₂₂³⁻] (2) and [Rb⁺(18‐crown‐6)₂][{Rb⁺(18‐crown‐6)}₂(C₁₃₈H₁₂₂³⁻)] (3). Whereas K⁺cations are fully solvent‐separated from the trianionic core thus affording a “naked”1^.3−anion, Rb⁺cations are coordinated to the negatively charged layers of1^.3−. According to DFT calculations, the localization of the first two electrons in the helicene moiety leads to an unprecedented site‐specific hydrogenation process at the carbon atoms located on the edge of the helicene backbone. This uncommon reduction‐induced site‐specific hydrogenation provokes dramatic changes in the (electronic) structure of1as the helicene backbone becomes more compressed and twisted upon chemical reduction, which results in a clear slippage of the bilayers.