Despite the notable progress in the stabilization of main group radicals by NHCs and cAACs, no germanium radicals have been isolated so far due to synthetic challenges. Stabilization of neutral [:E I R] • (E = Si, Ge) radicals is an uphill task, as these reactive transient species are highly susceptible to dimerization. Herein, we report the synthesis of acyclic neutral germanium(I) radicals Cy-cAAC:GeN(SiMe 3 )Dip (1) and Me-cAAC:GeN(SiPh 3 )Mes (2) obtained by the reduction of [Ar(SiR 3 )NGeCl 3 ] with KC 8 in the presence of cAAC. Compounds 1 and 2 are well characterized by single crystal X-ray structural analysis, cyclic voltammetry, and EPR spectroscopy. Furthermore, the structure and bonding of compounds 1 and 2 have been investigated by theoretical methods.

Multidomain carboxylic acid reductases (CARs) can reduce a wide range of carboxylic acids to the corresponding aldehydes in the presence of ATP and NADPH. Recent X-ray structures of the individual (di)­domains of Segniliparus rugosus CAR (SrCAR) shed light on the catalysis mechanism and revealed domain dynamics during the different states of the reaction. However, the details of the catalytic mechanism of each step operated by the corresponding domains are still elusive. Toward this end, several models based on the crystal structures were constructed, and molecular dynamics simulations along with density functional theory (DFT) calculations were employed to elucidate the conformational dynamics and catalytic mechanism of SrCAR concealed to static crystallography. We investigated the roles of the key residues in the substrate binding pocket involved in the adenylation and thiolation reactions and especially determined the roles played by a nonconserved Lys528 residue in the thiolation step, which were further verified by site-directed mutagenesis. The reduction mechanism of SrCAR, including the natures of the transition states for hydride and proton transfer, was also explored theoretically using the DFT method B3LYP. The information presented here is useful as a guide for the future rational design of CARs.

Quantum chemical calculations using ab initio methods at the CCSD(T) level with large basis sets and DFT calculations using the BP86 functional have been carried out for O 2 2+ and N 2 . An energy decomposition analysis of the chemical bonds suggests that the shorter bond in O 2 2+ compared with isoelectronic N 2 is due to the weaker Pauli repulsion in the dication, which overcompensates the weakening of attractive interactions that are operative in N 2 . At the equilibrium distance of N 2 , the orbital (covalent) bonding in O 2 2+ is weaker than in N 2 , and the attractive Coulomb interactions in the neutral diatomic system become repulsive in the dication, but the weakening of the Pauli repulsion caused by the shrinking of the orbitals in O 2 2+ compensates for these forces and leads to a shortening of the bond. The results also show that the bond dissociation energy is not a reliable indicator for the strength of bond, which is more faithfully given by the (local) force constant.