Examination of Protonation-Induced Dinitrogen Splitting by in Situ EXAFS Spectroscopy

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage

Active RNA Polymerases: Mobile or Immobile Molecular Machines?

Although it is widely assumed that active RNA polymerase tracks along its template, we find that DNA, not the polymerase, moves, suggesting that polymerase works by reeling in the template

Carbamazepine inhibits angiotensin I-converting enzyme, linking it to the pathogenesis of temporal lobe epilepsy

We find that a common mutation that increases angiotensin I-converting enzyme activity occurs with higher frequency in male patients suffering from refractory temporal lobe epilepsy. However, in their brains, the activity of the enzyme is downregulated. As an explanation, we surprisingly find that carbamazepine, commonly used to treat epilepsy, is an inhibitor of the enzyme, thus providing a direct link between epilepsy and the renin–angiotensin and kallikrein–kinin systems

Fusicoccin Counteracts the Toxic Effect of Cadmium on the Growth of Maize Coleoptile Segments

The effects of cadmium (Cd; 0.1–1000 μM) and fusicoccin (FC) on growth, Cd2+ content, and membrane potential (Em) in maize coleoptile segments were studied. In addition, the Em changes and accumulation of Cd and calcium (Ca) in coleoptile segments treated with Cd2+ combined with 1 μM FC or 30 mM tetraethylammonium (TEA) chloride (K+-channel blocker) were also determined. In this study, the effects of Ca2+-channel blockers [lanthanum (La) and verapamil (Ver)] on growth and content of Cd2+ and Ca2+ in coleoptile segments were also investigated. It was found that Cd at high concentrations (100 and 1000 μM) significantly inhibited endogenous growth of coleoptile segments and simultaneously measured proton extrusion. FC combined with Cd2+ counteracted the toxic effect of Cd2+ on endogenous growth and significantly decreased Cd2+ content (not the case for Cd2+ at the highest concentration) in coleoptile segments. Addition of Cd to the control medium caused depolarization of Em, the extent of which was dependent on Cd concentration and time of treatment with Cd2+. Hyperpolarization of Em induced by FC was suppressed in the presence of Cd2+ at 1000 μM but not Cd2+ at 100 μM. It was also found that treatment of maize coleoptile segments with 30 mM TEA chloride caused hyperpolarization of Em and decreased Cd2+ content in coleoptile segments, suggesting that, in the same way as for FC, accumulation of Cd2+ was dependent on plasma membrane (PM) hyperpolarization. Similar to FC, TEA chloride also decreased Ca2+ content in coleoptile segments. La and Ver combined with Cd2+ (100 μM) significantly decreased Cd content in maize coleoptile segments, but only La completely abolished the toxic effect of Cd2+ on endogenous growth and growth in the presence of FC. Taken together, these results suggest that the mechanism by which FC counteracts the toxic effect of Cd2+ (except at 1000 μM Cd2+) on the growth of maize coleoptile segments involves both stimulation of PM H+-ATPase activity by FC as well as Cd2+-permeable, voltage-dependent Ca channels, which are blocked by FC and TEA chloride-induced PM hyperpolarization

Complex Reorganization and Predominant Non-Homologous Repair Following Chromosomal Breakage in Karyotypically Balanced Germline Rearrangements and Transgenic Integration

We defined the genetic landscape of balanced chromosomal rearrangements at nucleotide resolution by sequencing 141 breakpoints from cytogenetically-interpreted translocations and inversions. We confirm that the recently described phenomenon of “chromothripsis” (massive chromosomal shattering and reorganization) is not unique to cancer cells but also occurs in the germline where it can resolve to a karyotypically balanced state with frequent inversions. We detected a high incidence of complex rearrangements (19.2%) and substantially less reliance on microhomology (31%) than previously observed in benign CNVs. We compared these results to experimentally-generated DNA breakage-repair by sequencing seven transgenic animals, and revealed extensive rearrangement of the transgene and host genome with similar complexity to human germline alterations. Inversion is the most common rearrangement, suggesting that a combined mechanism involving template switching and non-homologous repair mediates the formation of balanced complex rearrangements that are viable, stably replicated and transmitted unaltered to subsequent generations

A platinum(II) metallonitrene with a triplet ground state

Metallonitrenes (M–N) are complexes with a subvalent atomic nitrogen ligand that have been proposed as key reactive intermediates in nitrogen atom transfer reactions. However, in contrast to the common classes of nitride complexes (M≡N) and organic nitrenes (R–N), structurally and spectroscopically well defined ‘authentic’ metallonitrenes with a monovalent atomic nitrogen ligand remain elusive. Here we report that the photolysis of a platinum(II) pincer azide complex enabled the crystallographic, spectroscopic, magnetic and computational characterization of a metallonitrene that is best described as a singly bonded atomic nitrogen diradical ligand bound to platinum(II). The photoproduct exhibits selective C–H, B–H and B–C nitrogen atom insertion reactivity. Despite the subvalent metallonitrene character, mechanistic analysis for aldehyde C–H amidation shows nucleophilic reactivity of the N-diradical ligand. Ambiphilic reactivity of the metallonitrene is indicated by reactions with CO and PMe3 to form isocyanate and phosphoraneiminato platinum(II) complexes, respectively

Stabilizing P≡P: P22–, P2⋅–, and P20 as bridging ligands

The bigger picture: Chemical synthesis relies on strategies to stabilize well-defined molecular building blocks while also retaining their fundamental reactivity. This is illustrated by the classic pnictogen dichotomy. In contrast to highly stable N2, the higher homologs Pn2 evade isolation—and thus synthetic use—as a result of the preference of heavier p-block elements for σ-bonding. Previous strategies to stabilize π-bonded compounds such as P2 by coordination to electron donors have significantly altered their bonding and reactivity. Here, we demonstrate the coordination of redox-inactive transition-metal fragments as a strategy to stabilize P2 under ambient conditions with retention of the P≡P triple bond character, as in the case of free P2. The release of the Lewis-acidic capping agents offers P2 transfer reactivity to molecular products. This work provides a new strategy for the stabilization of highly reactive species with multiply bonded heavy p-block elements and their use as reagents in chemical synthesis. Summary: In contrast to its lighter congener N2, neutral diphosphorus with a P≡P triple bond is a highly reactive species observable only in the gas phase and by matrix isolation. Previous stabilization efforts with Lewis bases (e.g., carbenes) or by transition-metal coordination led to charge transfer to highly electrophilic P2 and thus to significant reduction of the bond order. Here, we report the crystallographic, spectroscopic, and quantum chemical characterization of the redox series [(μ2,η1:η1-P2){Pt(PNP)}2] (PNP = N(CHCHPtBu2)2), which features (P2)2–, (P2)⋅–, and (P2)0 as bridging ligands. Although common for N2, the stabilization as a neutral, triply bonded P≡P ligand is unprecedented for the heavier homolog. It was enabled by coordination of the dipnictogen to redox-inactive Lewis-acidic metal fragments and gave rise to the controlled release of P2 in the condensed phase

An iridium(III/IV/V) redox series featuring a terminal imido complex with triplet ground state

The iridium(III/IV/V) imido redox series [Ir(NtBu){N(CHCHPtBu2)2}]0/+/2+ was synthesized and examined spectroscopically, magnetically, crystallographically and computationally. The monocationic iridium(IV) imide exhibits an electronic doublet ground state with considerable ‘imidyl’ character as a result of covalent Ir–NtBu bonding. Reduction gives the neutral imide [Ir(NtBu){N(CHCHPtBu2)2}] as the first example of an iridium complex with a triplet ground state. Its reactivity with respect to nitrene transfer to selected electrophiles (CO2) and nucleophiles (PMe3), respectively, is reported

Spectroscopic and Computational Studies of an End-on Bound Superoxo-Cu(II) Complex: Geometric and Electronic Factors That Determine the Ground State

A variety of techniques including absorption, magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and resonance Raman (rR) spectroscopies are combined with density functional theory (DFT) calculations to elucidate the electronic structure of the end-on (η1) bound superoxo-Cu(II) complex [TMG3trenCuO2]+ (where TMG3tren is 1,1,1-tris[2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl]amine). The spectral features of [TMG3trenCuO2]+ are assigned, including the first definitive assignment of a superoxo intraligand transition in a metal-superoxo complex, and a detailed description of end-on superoxo-Cu(II) bonding is developed. The lack of overlap between the two magnetic orbitals of [TMG3trenCuO2]+ eliminates antiferromagnetic coupling between the copper(II) and the superoxide, while the significant superoxo π*σ character of the copper dz2 orbital leads to its ferromagnetically coupled, triplet, ground state