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High-valent iron species are key intermediates in oxidative biological processes, but hexavalent complexes apart from the ferrate ion are exceedingly rare. Here, we report the synthesis and structural and spectroscopic characterization of a stable Fe(VI) complex ( 3 ) prepared by facile one-electron oxidation of an Fe(V) bis(imido) ( 2 ). Single-crystal x-ray diffraction of 2 and 3 revealed four-coordinate Fe centers with an unusual "seesaw" geometry. 57 Fe Mössbauer, x-ray photoelectron, x-ray absorption, and electron-nuclear double resonance (ENDOR) spectroscopies, supported by electronic structure calculations, support a low-spin ( S = 1/2) d 3 Fe(V) configuration in 2 and a diamagnetic ( S = 0) d 2 Fe(VI) configuration in 3 Their shared seesaw geometry is electronically dictated by a balance of Fe-imido σ- and π-bonding interactions., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The N 2 analogue phosphorus nitride (PN) was the first phosphorus-containing compound to be detected in the interstellar medium; however, this thermodynamically unstable compound has a fleeting existence on Earth. Here, we show that reductive coupling of iron(IV) nitride and molybdenum(VI) phosphide complexes assembles PN as a bridging ligand in a structurally characterized bimetallic complex. Reaction with C≡N t Bu releases the mononuclear complex [(N 3 N)Mo-PN] - , N 3 N = [(Me 3 SiNCH 2 CH 2 ) 3 N] 3- ), which undergoes light-induced linkage isomerization to provide [(N 3 N)Mo-NP] - , as revealed by photocrystallography. While structural and spectroscopic characterization, supported by electronic structure calculations, reveals the PN multiple bond character, coordination to molybdenum induces a nucleophilic character at the terminal atom of the PN/NP ligands. Indeed, the linkage isomers can be trapped in solution by reaction with a Rh(I) electrophile., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

A low-coordinate, high spin ( S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η 1 -allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.

The paramagnetic cyano-bridged complex PhB( t BuIm) 3 Fe-NC-Mo(N t BuAr) 3 (Ar = 3,5-Me 2 C 6 H 3 ) is readily assembled from a new four-coordinate, high-spin ( S = 2) iron(II) monocyanide complex and the three-coordinate molybdenum(III) complex Mo(N t BuAr) 3 . X-ray diffraction and IR spectroscopy reveal that delocalization of unpaired electron density into the cyanide π* orbitals leads to a reduction of the C-N bond order. Direct current (dc) magnetic susceptibility measurements, supported by electronic structure calculations, demonstrate the presence of strong antiferromagnetic exchange between spin centers, with a coupling constant of J = -122(2) cm -1 . To our knowledge, this value represents the strongest magnetic exchange coupling ever to be observed through cyanide. These results demonstrate the ability of low-coordinate metal fragments to engender extremely strong magnetic exchange coupling through cyanide by virtue of significant π-backbonding into the cyanide ligand.

Structural and spectroscopic characterization of the dimeric iron hydride complex [Ph 2 B( t BuIm) 2 FeH] 2 reveals an unusual structure in which a tetrahedral iron(II) site ( S = 2) is connected to a square planar iron(II) site ( S = 1) by two bridging hydride ligands. Magnetic susceptibility reveals strong ferromagnetic coupling between iron centers, with a coupling constant of J = +110(12) cm -1 , to give an S = 3 ground state. High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy confirms this model. A qualitative molecular orbital analysis of the electronic structure, as supported by electronic structure calculations, reveals that the observed spin configuration results from the orthogonal alignment of two geometrically distinct four-coordinate iron fragments held together by highly covalent hydride ligands.

The ground state structure of [Ph 2 B( t BuIm) 2 Fe(CO) 2 ] - is trigonal pyramidal (S = 1), with a thermally accessible square planar (S = 0) geometry. Experimentally calibrated electronic structure calculations provide evidence for two-state reactivity, with C-H oxidative addition on the singlet surface providing an iron(ii) product (S = 0).

Bulky tris(carbene)borate ligands provide access to high spin iron(ii) phosphido complexes. The complex PhB(MesIm) 3 FeP(H)Ph is thermally unstable, and [PPh] group insertion into a C-H bond of the supporting ligand is observed. An arrested α-hydride migration mechanism suggests increased nucleophilicity of the phosphorus atom facilitates [PPh] group transfer reactivity.

We investigated the role of glycogen synthase in supranormal resynthesis (supercompensation) of skeletal muscle glycogen after exhaustive exercise. Six healthy men exercised 60 min by cycling with one leg at 75% VO2max, recovered 3 days on a low-carbohydrate diet, exercised again, and recovered 4 days on high-carbohydrate diet. Glycogen and glycogen synthase activities at several glucose-6-phosphate (G6P) concentrations were measured in biopsy samples of m. vastus lateralis. Dietary alterations alone did not affect glycogen, whereas exercise depleted glycogen stores. After the second exercise bout, glycogen returned to normal within 24 h and reached supercompensated levels by 48 h of recovery. Glycogen synthase activation state strikingly increased after exercise in exercised muscle and remained somewhat elevated for the first 48 h of recovery in both muscles. We suggest that 1) forms of glycogen synthase intermediate to I (G6P-independent) and D (G6P-dependent) forms are present in vivo, and 2) glycogen supercompensation can in part be explained by the formation of intermediate forms of glycogen synthase that exhibit relatively low activity ratios, but an increased sensitivity to activation by G6P.

B-endorphin, which is released concomitantly with ACTH from the pituitary during stress, may also alter cardiac performance in hemorrhagic shock. In this study of 36 dogs subjected to hemorrhagic shock without resuscitation, we demonstrate the interaction of high doses of dexamethasone (DEX) or methylprednisolone (M) and opiate receptor blockade with naloxone (NAL). NAL, when given alone, resulted in the most hemodynamic improvement and the longest survival time while those animals receiving DEX or M, even in combination with NAL, did not do as well. These data suggest that corticosteroids block the NAL effect following hemorrhagic shock.

Glycogen synthase kinase was isolated from rat skeletal muscle. This kinase, which is cyclic nucleotide-independent and calcium-independent, was separated from phosphorylase kinase, cyclic AMP-dependent protein kinase and phosvitin kinase by phosphocellulose chromatography. Gel filtration on Sephadex G-100 resolved the glycogen synthase kinase into two fractions with apparent molecular weights of 68 000 (peak I) and 52 000 (peak II). This step also separated glycogen synthase kinase from the catalytic subunit of the cyclic AMP-dependent protein kinase, which had an apparent molecular weight of 39 000. Peak II glycogen synthase kinase activity was not affected by the addition of calcium, EGTA or a number of cyclic nucleotides. In addition to ATP, dATP would serve as the phosphate donor. Other trinucleotides tested were either poor or ineffective substrates. Activity was about 5-fold greater with Mg2+ than with Mn2+. Glycogen stimulated activity about 25%. Modifications of the methods of Soderling et al. ((1970) J. Biol. Chem. 245, 6317--6328) and Nimmo et al. ((1976) Eur. J. Biochem. 68, 21--30) were developed for purification of glycogen synthease (UDPglucose:glycogen 4-alpha D-glucosyltransferase, EC 2.4.1.11) to specific activity of 35 units/mg of protein. Using this preparation of glycogen synthase as substrate, the phosphorylation and inactivation catalyzed by glycogen synthase kinase was compared to that catalyzed by cyclic AMP-dependent protein kinase or phosphorylase kinase. Each of the kinases had different specificities for phosphorylation sites on glycogen synthase.