Erratum: Why is the ground state electron configuration for Lithium 1s(2)2s ?

For the variational calculation involving the 1s22s state, we inadvertently filed energy contributions into the wrong categories, with the result that the Virial Theorem appeared to be violated. The overall calculation of the energy was done correctly, and appropriate assignment of the different energy contributions now confirms that the Virial Theorem is obeyed. Obviously, our conclusions are unchanged.

Ground-State Electron Transfer as an Initiation Mechanism for Asymmetric Hydroalkylations in Radical Biocatalysis

<p>Stereoselective bond-forming reactions are essential tools in modern organic synthesis. However, catalytic strategies for controlling the stereochemical outcome of radical-mediated C–C bond formation remain underdeveloped.<b> </b>Here, we report an ‘ene’-reductase catalyzed asymmetric hydroalkylation of olefins using α-bromoketones as radical precursors. In these reactions, radical initiation occurs <i>via</i> ground-state electron transfer from the flavin cofactor located within the enzyme active site, representing a mechanistic departure from previous photoenzymatic hydroalkylations. Four rounds of site saturation mutagenesis based on wild-type nicotinamide-dependent cyclohexanone reductase (NCR) were deployed to access a variant capable of catalyzing a cyclization to furnish β-chiral cyclopentanones with high levels of enantioselectivity. Additionally, the wild-type NCR was identified that could catalyze the intermolecular coupling with precise stereochemical control over the radical termination step. This report demonstrates this enzyme family’s catalytic versatility and highlights the opportunity for protein engineering to address reactivity and selectivity challenges in radical biocatalysis. </p>

Ground-State Electron Transfer as an Initiation Mechanism for Asymmetric Hydroalkylations in Radical Biocatalysis

<p>Stereoselective bond-forming reactions are essential tools in modern organic synthesis. However, catalytic strategies for controlling the stereochemical outcome of radical-mediated C–C bond formation remain underdeveloped.<b> </b>Here, we report an ‘ene’-reductase catalyzed asymmetric hydroalkylation of olefins using α-bromoketones as radical precursors. In these reactions, radical initiation occurs <i>via</i> ground-state electron transfer from the flavin cofactor located within the enzyme active site, representing a mechanistic departure from previous photoenzymatic hydroalkylations. Four rounds of site saturation mutagenesis based on wild-type nicotinamide-dependent cyclohexanone reductase (NCR) were deployed to access a variant capable of catalyzing a cyclization to furnish β-chiral cyclopentanones with high levels of enantioselectivity. Additionally, the wild-type NCR was identified that could catalyze the intermolecular coupling with precise stereochemical control over the radical termination step. This report demonstrates this enzyme family’s catalytic versatility and highlights the opportunity for protein engineering to address reactivity and selectivity challenges in radical biocatalysis. </p>

Chromophore-radical excited state antiferromagnetic exchange controls the sign of photoinduced ground state spin polarization

A change in the sign of the ground state electron spin polarization (ESP) is reported in complexes where an organic radical (nitronylnitroxide, NN) is covalently attached to a donor–acceptor chromophore via two different meta-phenylene bridges.

Orbital-based Descriptions of Electron Configurations, Ionization, Excitation, and Bonding

This chapter deals with quantitative aspects of molecular orbital (MO) theory: Construction of an orbital diagram, bonding and antibonding overlap, Koopmans’ theorem, orbital energies versus total energies, an explanation of the unintuitive ground state electron configurations seen for some neutral transition metals, and a discussion of orbital energy gaps versus electronic excitations and other observable energy gaps. Localized MOs show the chemical bonds expected from the Lewis structure more readily than the canonical orbitals obtained from solving the SCF equations. It is shown that the delocalization of localized, not the canonical, MOs shows whether a system is delocalized. Algorithms by which to obtain localized MOs are sketched.

Universal coherence protection in a solid-state spin qubit

Decoherence limits the physical realization of qubits, and its mitigation is critical for the development of quantum science and technology. We construct a robust qubit embedded in a decoherence-protected subspace, obtained by applying microwave dressing to a clock transition of the ground-state electron spin of a silicon carbide divacancy defect. The qubit is universally protected from magnetic, electric, and temperature fluctuations, which account for nearly all relevant decoherence channels in the solid state. This culminates in an increase of the qubit’s inhomogeneous dephasing time by more than four orders of magnitude (to >22 milliseconds), while its Hahn-echo coherence time approaches 64 milliseconds. Requiring few key platform-independent components, this result suggests that substantial coherence improvements can be achieved in a wide selection of quantum architectures.