One challenge in chemistry is the plethora of often disparate models for rationalizing the electronic structure of molecules. Chemical concepts abound, but their connections are often frail. This work describes a quantum‐mechanical framework that enables a combination of ideas from three approaches common for the analysis of chemical bonds: energy decomposition analysis (EDA), quantum chemical topology, and molecular orbital (MO) theory. The glue to our theory is the electron energy density, interpretable as one part electrons and one part electronegativity. We present a three‐dimensional analysis of the electron energy density and use it to redefine what constitutes an atom in a molecule. Definitions of atomic partial charge and electronegativity follow in a way that connects these concepts to the total energy of a molecule. The formation of polar bonds is predicted to cause inversion of electronegativity, and a new perspective of bonding in diborane and guanine−cytosine base‐pairing is presented. The electronegativity of atoms inside molecules is shown to be predictive of pKa.
Here we report the design of a superfast
bioorthogonal ligation
reactant pair comprising a sterically shielded, sulfonated tetrazole
and bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN). The design involves
placing a pair of water-soluble N-sulfonylpyrrole
substituents at the C-phenyl ring of diphenyltetrazoles to favor the
photoinduced cycloaddition reaction over the competing nucleophilic
additions. First-principles computations provide vital insights into
the origin of the tetrazole–BCN cycloaddition’s superior
kinetics compared to the tetrazole–spirohexene cycloaddition.
The tetrazole–BCN cycloaddition also enabled rapid bioorthogonal
labeling of glucagon receptors on live cells in as little as 15 s.
The anionic cluster [Co 6 As(CO) 16 ]was synthesized through the reaction of Na[Co(CO) 4 ] and arsenic acid in THF at room temperature. Crystallization from MeOH/2-propanol yielded two polymorphs that feature two slightly different isomers of the anion with the same PPh 4 + cation. One of the isomers is very similar to the known [Co 6 P(CO) 16 ]-, formed by four edge fused triangles, partially wrapping the main group atom. The other isomer features a deformed cage, which differs mainly for a non-bonding Co-Co distance. The reasons for this unprecedented stereochemistry, and the factors which may trigger this isomer, have been investigated by DFT calculations.
Here we report the design and synthesis of a new class
of bioorthogonal
reagents called hydrazonyl sultones (HS) that serve as stable tautomers
of highly reactive nitrile imines (NI). Compared to the photogenerated
NI, HS display a broad range of aqueous stability and tunable reactivity
in a 1,3-dipolar cycloaddition reaction, depending on substituents,
sultone ring structure, and solvent conditions. DFT calculations have
provided vital insights into the HS → NI tautomerism, including
a base-mediated anionic tautomerization pathway and a small activation
barrier. Comparative kinetic analysis of tetrazole vs HS-mediated
cycloadditions reveals that a tiny fraction of the reactive NI (∼15
ppm) is present in the tautomeric mixture, underpinning the extraordinary
stability of the six-membered HS. We further demonstrate the utilities
of HS in selective modification of bicyclo[6.1.0]non-4-yn-9-ylmethanol
(BCN)-lysine-containing nanobodies in phosphate buffered saline and
fluorescent labeling of a BCN-lysine-encoded transmembrane glucagon
receptor on live cells.
The breakdown of interaction energy has always been a very important means to appreciate chemical bonding and it has become a seamlessly useful tool for modern supramolecular chemistry. Many interaction...
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