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The iron-molybdenum cofactor of nitrogenase (FeMoco) catalyzes fixation of N 2 via Fe hydride intermediates. Our understanding of these species has relied heavily on the characterization of well-defined 3d metal hydride complexes, which serve as putative spectroscopic models. Although the Fe ions in FeMoco, a weak-field cluster, are expected to adopt locally high-spin Fe 2+/3+ configurations, synthetically accessible hydride complexes featuring d 5 or d 6 electron counts are almost exclusively low-spin. We report herein the isolation of a terminal hydride complex of four-coordinate, high-spin (d 5 ; S = 5/2) Mn 2+ . Electron paramagnetic resonance and electron-nuclear double resonance studies reveal an unusually large degree of spin density on the hydrido ligand. In light of the isoelectronic relationship between Mn 2+ and Fe 3+ , our results are expected to inform our understanding of the valence electronic structures of reactive hydride intermediates derived from FeMoco.

Appreciating that the role of the solute-solvent and other outer-sphere interactions is essential for understanding chemistry and chemical dynamics in solution, experimental approaches are needed to address the structural consequences of these interactions, complementing condensed-matter simulations and coarse-grained theories. High-energy X-ray scattering (HEXS) combined with pair distribution function analysis presents the opportunity to probe these structures directly and to develop quantitative, atomistic models of molecular systems in situ in the solution phase. However, at concentrations relevant to solution-phase chemistry, the total scattering signal is dominated by the bulk solvent, prompting researchers to adopt a differential approach to eliminate this unwanted background. Though similar approaches are well established in quantitative structural studies of macromolecules in solution by small- and wide-angle X-ray scattering (SAXS/WAXS), analogous studies in the HEXS regime-where sub-ångström spatial resolution is achieved-remain underdeveloped, in part due to the lack of a rigorous theoretical description of the experiment. To address this, herein we develop a framework for differential solution scattering experiments conducted at high energies, which includes concepts of the solvent-excluded volume introduced to describe SAXS/WAXS data, as well as concepts from the time-resolved X-ray scattering community. Our theory is supported by numerical simulations and experiment and paves the way for establishing quantitative methods to determine the atomic structures of small molecules in solution with resolution approaching that of crystallography., (open access.)

We report herein the synthesis and characterization of a terminal Co(III) imido complex supported by an intermediate field N,N,C heteroscorpionate. This chemistry is enabled through the development of an additional member of this ligand type featuring Ph 2 (CH 3 )C- substituents, one of which weakly binds and stabilizes Co in the corresponding Co(I) precursor. The Co(III) imide is low-spin with no evidence for thermal population of open-shell excited states. Unusually, the imido ligand in this molecule tilts markedly toward the C alkyl donor. DFT calculations suggest this structural feature to be largely a result of strong Co-C covalency, underscoring the importance of M-C bonding in determining the (electronic) structure of metal centers supported by this class of ligand., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The application of grazing-incidence total X-ray scattering (GITXS) for pair distribution function (PDF) analysis using >50 keV X-rays from synchrotron light sources has created new opportunities for structural characterization of supported thin films with high resolution. Compared with grazing-incidence wide-angle X-ray scattering, which is only useful for highly ordered materials, GITXS/PDFs expand such analysis to largely disordered or nanostructured materials by examining the atomic pair correlations dependent on the direction relative to the surface of the supporting substrate. A characterization of nanocrystalline In 2 O 3 -derived thin films is presented here with in-plane-isotropic and out-of-plane-anisotropic orientational ordering of the atomic structure, each synthesized using different techniques. The atomic orientations of such films are known to vary based on the synthetic conditions. Here, an azimuthal orientational analysis of these films using GITXS with a single incident angle is shown to resolve the markedly different orientations of the atomic structures with respect to the planar support and the different degrees of long-range order, and hence, the terminal surface chemistries. It is anticipated that orientational analysis of GITXS/PDF data will offer opportunities to extend structural analyses of thin films by providing a means to qualitatively determine the major atomic orientation within nanocrystalline and, eventually, non-crystalline films., (open access.)

Nature employs weak-field metalloclusters to support a wide range of biological processes. The most ubiquitous metalloclusters are the cuboidal Fe-S clusters, which are comprised of Fe sites with locally high-spin electronic configurations. Such configurations enhance rates of ligand exchange and imbue the clusters with a degree of structural plasticity that is increasingly thought to be functionally relevant. Here, we examine this phenomenon using isotope tracing experiments. Specifically, we demonstrate that synthetic [Fe 4 S 4 ] and [MoFe 3 S 4 ] clusters exchange their Fe atoms with Fe 2+ ions dissolved in solution, a process that involves the reversible cleavage and reformation of every Fe-S bond in the cluster core. This exchange is facile-in most cases occurring at room temperature on the timescale of minutes-and documented over a range of cluster core oxidation states and terminal ligation patterns. In addition to suggesting a highly dynamic picture of cluster structure, these results provide a method for isotopically labeling pre-formed clusters with spin-active nuclei, such as 57 Fe. Such a protocol is demonstrated for the radical S -adenosyl-l-methionine enzyme, RlmN.

Inspired by mechanistic proposals for N 2 reduction at the nitrogenase FeMo cofactor, we report herein a new, strongly σ-donating heteroscorpionate ligand featuring two weak-field pyrazoles and an alkyl donor. This ligand supports four-coordinate Fe(I)-N 2 , Fe(II)-Cl, and Fe(III)-imido complexes, which we have characterized using a variety of spectroscopic and computational methods. Structural and quantum mechanical analysis reveal the nature of the Fe-C bonds to be essentially invariant between the complexes, with conversion between the (formally) low-valent Fe-N 2 and high-valent Fe-imido complexes mediated by pyrazole hemilability. This presents a useful strategy for substrate reduction at such low-coordinate centers and suggests a mechanism by which FeMoco might accommodate the binding of both π-acidic and π-basic nitrogenous substrates.

Although biological iron-sulfur (Fe-S) clusters perform some of the most difficult redox reactions in nature, they are thought to be composed exclusively of Fe 2+ and Fe 3+ ions, as well as mixed-valent pairs with average oxidation states of Fe 2.5+ . We herein show that Fe-S clusters formally composed of these valences can access a wider range of electronic configurations─in particular, those featuring low-valent Fe 1+ centers. We demonstrate that CO binding to a synthetic [Fe 4 S 4 ] 0 cluster supported by N -heterocyclic carbene ligands induces the generation of Fe 1+ centers via intracluster electron transfer, wherein a neighboring pair of Fe 2+ sites reduces the CO-bound site to a low-valent Fe 1+ state. Similarly, CO binding to an [Fe 4 S 4 ] + cluster induces electron delocalization with a neighboring Fe site to form a mixed-valent Fe 1.5+ Fe 2.5+ pair in which the CO-bound site adopts partial low-valent character. These low-valent configurations engender remarkable C-O bond activation without having to traverse highly negative and physiologically inaccessible [Fe 4 S 4 ] 0 /[Fe 4 S 4 ] - redox couples.

Although the overall complication rate of volar plating approaches 15%, less than 5% require reoperation. Certain factors involving the patient, the fracture, and/or the surgeon may affect the overall complication risk. Patient factors, including body mass index greater than 35 and diabetes mellitus, may increase complication risk with volar plating, but older patient age does not seem to significantly alter risk., Competing Interests: Disclosure Neither the authors nor their immediate families received any financial payments or other benefits from any commercial entity related to this article., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Scaphoid fractures are common injuries in athletes. Most can be treated with cast immobilization, with an expected rate of union of 90% to 95%. Cast treatment, however, has the disadvantages of longer immobilization time, joint stiffness, reduced grip strength, and longer time to return to manual work or athletics. Closed reduction and percutaneous screw fixation generally are preferred in athletes to allow a quicker return to sport; if closed reduction cannot be obtained, open reduction and internal fixation may be required., Competing Interests: Disclosure The authors have nothing to disclose., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Alkyl-ligated iron-sulfur clusters in the [Fe 4 S 4 ] 3+ charge state have been proposed as short-lived intermediates in a number of enzymatic reactions. To better understand the properties of these intermediates, we have prepared and characterized the first synthetic [Fe 4 S 4 ] 3+ -alkyl cluster. Isolation of this highly reactive species was made possible by the development of an expanded scorpionate ligand suited to the encapsulation of cuboidal clusters. Like the proposed enzymatic intermediates, this synthetic [Fe 4 S 4 ] 3+ -alkyl cluster adopts an S = 1 / 2 ground state with g iso > 2. Mössbauer spectroscopic studies reveal that the alkylated Fe has an unusually low isomer shift, which reflects the highly covalent Fe-C bond and the localization of Fe 3+ at the alkylated site in the solid state. Paramagnetic 1 H NMR studies establish that this valence localization persists in solution at physiologically relevant temperatures, an effect that has not been observed for [Fe 4 S 4 ] 3+ clusters outside of a protein. These findings establish the unusual electronic-structure effects imparted by the strong-field alkyl ligand and lay the foundation for understanding the electronic structures of [Fe 4 S 4 ] 3+ -alkyl intermediates in biology.

Background: The purpose of the study was to compare the histopathologic and immunophenotypic features of central centrifugal cicatricial alopecia (CCCA) and lichen planopilaris (LPP) to better characterize and differentiate these two clinical entities. CCCA remains an ill-defined and still-unsettled histologic entity and many hair loss experts regard CCCA to be histologically indistinguishable from LPP. Given the overlapping histologic features of these two lymphocyte-predominant cicatricial alopecias, and the lack of consensus regarding the significance of proposed distinctions, dermatopathologists face difficulty in providing clinicians and patients certainty with a definitive diagnosis of CCCA vs LPP., Methods: We performed a retrospective review of 51 scalp biopsies of patients with either the clinical diagnosis of CCCA (27 cases) or LPP (24 cases). Clinical information, histologic features of hematoxylin-eosin-stained sections, and a panel of immunohistochemical markers were evaluated on scalp biopsies. Tested parameters were quantified, and statistical analysis was performed., Results: Our study found no differences on either histologic assessment or immunophenotypic characterization between cases of classic LPP and CCCA., Conclusion: The conclusion of this study is that the inflammatory infiltrates in CCCA and LPP are not only histologically similar but also immunophenotypically indistinguishable., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Although alkyl complexes of [Fe 4 S 4 ] clusters have been invoked as intermediates in a number of enzymatic reactions, obtaining a detailed understanding of their reactivity patterns and electronic structures has been difficult owing to their transient nature. To address this challenge, we herein report the synthesis and characterization of a 3:1 site-differentiated [Fe 4 S 4 ] 2+ -alkyl cluster. Whereas [Fe 4 S 4 ] 2+ clusters typically exhibit pairwise delocalized electronic structures in which each Fe has a formal valence of 2.5+, Mössbauer spectroscopic and computational studies suggest that the highly electron-releasing alkyl group partially localizes the charge distribution within the cubane, an effect that has not been previously observed in tetrahedrally coordinated [Fe 4 S 4 ] clusters.

Species with 2-center, 3-electron (2c/3e - ) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d 9 ) trigonal pyramidal Rh and Ir complexes that feature 2c/3e - σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X-ray diffraction, continuous wave and pulse electron paramagnetic resonance, density-functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e - bonding framework with a σ*-SOMO of metal 4- or 5d z 2 parentage that is partially stabilized by significant mixing with Si (3p z ) and metal (5- or 6p z ) orbitals. Metal-ligand covalency thus buffers the expected destabilization of transition-metal (TM)-silyl σ*-orbitals by d-p mixing, affording well-characterized examples of TM-main group, and hence polar, 2c/3e - σ "half-bonds"., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The intermediacy of metal-NNH 2 complexes has been implicated in the catalytic cycles of several examples of transition-metal-mediated nitrogen (N 2 ) fixation. In this context, we have shown that triphosphine-supported Fe(N 2 ) complexes can be reduced and protonated at the distal N atom to yield Fe(NNH 2 ) complexes over an array of charge and oxidation states. Upon exposure to further H + /e - equivalents, these species either continue down a distal-type Chatt pathway to yield a terminal iron(IV) nitride or instead follow a distal-to-alternating pathway resulting in N-H bond formation at the proximal N atom. To understand the origin of this divergent selectivity, herein we synthesize and elucidate the electronic structures of a redox series of Fe(NNMe 2 ) complexes, which serve as spectroscopic models for their reactive protonated congeners. Using a combination of spectroscopies, in concert with density functional theory and correlated ab initio calculations, we evidence one-electron redox noninnocence of the "NNMe 2 " moiety. Specifically, although two closed-shell configurations of the "NNR 2 " ligand have been commonly considered in the literature-isodiazene and hydrazido(2-)-we provide evidence suggesting that, in their reduced forms, the present iron complexes are best viewed in terms of an open-shell [NNR 2 ] •- ligand coupled antiferromagnetically to the Fe center. This one-electron redox noninnocence resembles that of the classically noninnocent ligand NO and may have mechanistic implications for selectivity in N 2 fixation activity.

A point-projection soft X-ray Opacity Spectrometer (OpSpec) has been implemented to measure X-ray spectra from ∼1 to 2 keV on the National Ignition Facility (NIF). Measurement of such soft X-rays with open-aperture point-projection detectors is challenging because only very thin filters may be used to shield the detector from the hostile environment. OpSpec diffracts X-rays from 540 to 2100 eV off a potassium (or rubidium) acid phthalate (KAP or RbAP) crystal onto either image plates or, most recently, X-ray films. A "sacrificial front filter" strategy is used to prevent crystal damage, while 2 or 3 rear filters protect the data. Since May 2017, OpSpec has been recording X-ray transmission data for iron-magnesium plasmas on the NIF, at "Anchor 1" plasma conditions (temperature ∼150 eV, density ∼7 × 10 21 e - /cm 3 ). Upgrades improved OpSpec's performance on 6 NIF shots in August and December 2017, with reduced backgrounds and 100% data return using filter stacks as thin as 2.9 μ m (total). Photometric noise is beginning to meet requirements, and further work will reduce systematic errors.

The cost of carpal tunnel release (CTR) surgery can be decreased and patient satisfaction increased by a few relatively simple changes. Although cost estimates vary in the literature, most investigators agree that open CTR costs less than endoscopic CTR, and the clinic procedure room or ambulatory surgery center is cheaper than the ambulatory surgery center, which is less than the hospital. Patient satisfaction can be increased by making office visits more patient-centered and improving the quality of dialogue between the surgeon and patient., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Carpal tunnel syndrome (CTS) is one of the most common musculoskeletal disorders of the upper extremity. Comorbidities associated with the development of CTS include diabetes and obesity. Although a high rate of repetitive hand/wrist motions is a risk factor, there is insufficient evidence to implicate computer use in the development of CTS. Initial treatment generally is nonoperative, with the strongest evidence supporting bracing/splinting. Strong evidence supports operative treatment, regardless of technique, as superior to nonoperative treatment. Complications are infrequent and most are minor and transient., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The purpose of this study was to describe long-term outcomes of partial trapeziectomy with capsular interposition (PTCI) arthroplasty for patients with osteoarthritis of the basal joint of the thumb. A total of 27 patients (20 women, 7 men; 32 thumbs) with a mean age of 61 years (range, 47-74 years) agreed to return for follow-up and were included in the study. Mean postoperative follow-up was 64.3 months (range, 28-112 months). Evaluation included tests for grip and pinch strength; range of motion of the metacarpophalangeal joint; measurement of the first web space; completion of the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire; visual analog scale (VAS) measurements; and radiographic examination of the hand. A paired, 2-tailed t test was used to determine statistical significance (P<.05) of pre- and postoperative values. Postoperative values for grip strength were significantly increased from preoperative values. No significant loss of pinch strength was noted. Excessive hyperextension of the metacarpophalangeal joint did not occur, and the first web space was maintained. The mean DASH questionnaire and VAS scores were 5.06 (range, 0-26.5) and 0.32, respectively. Use of PTCI arthroplasty resulted in minimal loss in thumb height (7%) and significantly reduced thumb metacarpal subluxation (13%). There were no reported complications. The low DASH questionnaire and VAS scores compare well with other studies and indicate good functional outcomes. In treating thumb basal joint osteoarthritis, use of PTCI arthroplasty may result in improved thumb stability and grip strength, minimal subsidence of the thumb metacarpal, and reduced joint subluxation. [Orthopedics. 2018; 41(2):e228-e233.]., (Copyright 2018, SLACK Incorporated.)

Outpatient surgery, especially in free-standing ambulatory surgery centers (ASC), provides a safe, cost-effective option for a variety of surgical procedures and has become the preferred choice over inpatient and hospital-based outpatient surgery for most hand and wrist procedures. Complication rates after ASC hand surgery are low (0.2%-2.5%). Patient dissatisfaction with ASC surgery is primarily associated with postoperative nausea and vomiting and inadequate pain control., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl comonomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over 2 orders of magnitude (0.36 M -1 s -1 < k homo < 82 M -1 s -1 ). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(d,l-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by nonlinear least-squares fitting of the instantaneous comonomer concentrations according to the Mayo-Lewis terminal model. In-depth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r 1 /r 2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

Terminal iron nitrides (Fe≡N) have been proposed as intermediates of (bio)catalytic nitrogen fixation, yet experimental evidence to support this hypothesis has been lacking. In particular, no prior synthetic examples of terminal Fe≡N species have been derived from N 2 . Here we show that a nitrogen-fixing Fe-N 2 catalyst can be protonated to form a neutral Fe(NNH 2 ) hydrazido(2-) intermediate, which, upon further protonation, heterolytically cleaves the N-N bond to release [Fe IV ≡N] + and NH 3 . These observations provide direct evidence for the viability of a Chatt-type (distal) mechanism for Fe-mediated N 2 -to-NH 3 conversion. The physical oxidation state range of the Fe complexes in this transformation is buffered by covalency with the ligand, a feature of possible relevance to catalyst design in synthetic and natural systems that facilitate multiproton/multielectron redox processes.

We report the synthesis, characterization, and reactivity of [LFe 3 (PhPz) 3 OMn( s PhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene-metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57 Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2 Fe II Mn II vs. Fe III 3 Mn II ) influence oxygen atom transfer in tetranuclear Fe 3 Mn clusters. In particular, a one-electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe-N2 complexes of tetradentate P3(E) ligands (E = B, C) generate catalytic yields of NH3 under an atmosphere of N2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings. Nearly an order of magnitude improvement in yield of NH3 for each Fe catalyst has been realized (up to 64 equiv of NH3 produced per Fe for P3(B) and up to 47 equiv for P3(C)) by increasing acid/reductant loading with highly purified acid. Cyclic voltammetry shows the apparent onset of catalysis at the P3(B)Fe-N2/P3(B)Fe-N2(-) couple and controlled-potential electrolysis of P3(B)Fe(+) at -45 °C demonstrates that electrolytic N2 reduction to NH3 is feasible. Kinetic studies reveal first-order rate dependence on Fe catalyst concentration (P3(B)), consistent with a single-site catalyst model. An isostructural system (P3(Si)) is shown to be appreciably more selective for hydrogen evolution. In situ freeze-quench Mössbauer spectroscopy during turnover reveals an iron-borohydrido-hydride complex as a likely resting state of the P3(B)Fe catalyst system. We postulate that hydrogen-evolving reaction activity may prevent iron hydride formation from poisoning the P3(B)Fe system. This idea may be important to consider in the design of synthetic nitrogenases and may also have broader significance given that intermediate metal hydrides and hydrogen evolution may play a key role in biological nitrogen fixation., Competing Interests: The authors declare no competing financial interests.

Herein we report the intramolecular arene C-H and C-F bond oxygenation by tetranuclear iron complexes. Treatment of [LFe3(PhPz)3OFe][OTf]2 (1) or its fluorinated analog [LFe3(F2ArPz)3OFe][OTf]2 (5) with iodosobenzene results in the regioselective hydroxylation of a bridging pyrazolate ligand, converting a C-H or C-F bond into a C-O bond. The observed reactivity suggests the formation of terminal and reactive Fe-oxo intermediates. With the possibility of intramolecular electron transfer within clusters in 1 and 5, different reaction pathways (Fe(IV)-oxo vs Fe(III)-oxo) might be responsible for the observed arene hydroxylation.

A series of tetranuclear iron complexes displaying a site-differentiated metal center was synthesized. Three of the metal centers are coordinated to our previously reported ligand, based on a 1,3,5-triarylbenzene motif with nitrogen and oxygen donors. The fourth (apical) iron center is coordinatively unsaturated and appended to the trinuclear core through three bridging pyrazolates and an interstitial μ4-oxide moiety. Electrochemical studies of complex [LFe3(PhPz)3OFe][OTf]2 revealed three reversible redox events assigned to the Fe(II)4/Fe(II)3Fe(III) (-1.733 V), Fe(II)3Fe(III)/Fe(II)2Fe(III)2 (-0.727 V), and Fe(II)2Fe(III)2/Fe(II)Fe(III)3 (0.018 V) redox couples. Combined Mössbauer and crystallographic studies indicate that the change in oxidation state is exclusively localized at the triiron core, without changing the oxidation state of the apical metal center. This phenomenon is assigned to differences in the coordination environment of the two metal sites and provides a strategy for storing electron and hole equivalents without affecting the oxidation state of the coordinatively unsaturated metal. The presence of a ligand-binding site allowed the effect of redox modulation on nitric oxide activation by an Fe(II) metal center to be studied. Treatment of the clusters with nitric oxide resulted in binding of NO to the apical iron center, generating a {FeNO}(7) moiety. As with the NO-free precursors, the three reversible redox events are localized at the iron centers distal from the NO ligand. Altering the redox state of the triiron core resulted in significant change in the NO stretching frequency, by as much as 100 cm(-1). The increased activation of NO is attributed to structural changes within the clusters, in particular, those related to the interaction of the metal centers with the interstitial atom. The differences in NO activation were further shown to lead to differential reactivity, with NO disproportionation and N2O formation performed by the more electron-rich cluster.

Well-defined molecular catalysts for the reduction of N2 to NH3 with protons and electrons remain very rare despite decades of interest and are currently limited to systems featuring molybdenum or iron. This report details the synthesis of a molecular cobalt complex that generates superstoichiometric yields of NH3 (>200% NH3 per Co-N2 precursor) via the direct reduction of N2 with protons and electrons. While the NH3 yields reported herein are modest by comparison to those of previously described iron and molybdenum systems, they intimate that other metals are likely to be viable as molecular N2 reduction catalysts. Additionally, a comparison of the featured tris(phosphine)borane Co-N2 complex with structurally related Co-N2 and Fe-N2 species shows how remarkably sensitive the N2 reduction performance of potential precatalysts is. These studies enable consideration of the structural and electronic effects that are likely relevant to N2 conversion activity, including the π basicity, charge state, and geometric flexibility.

Background: Certain fracture configurations, especially spiral fractures, are often thought to be indicative of nonaccidental trauma in children. The purpose of this study was to determine whether femoral fracture morphology, as determined by an objective measurement (fracture ratio), was indicative of nonaccidental trauma in young children., Methods: Consecutive patients who were three years of age or younger and had a closed, isolated femoral shaft fracture treated at an urban pediatric level-I trauma center between 2005 and 2013 were identified. Anteroposterior and lateral fracture ratios (fracture length/bone diameter) were calculated for each patient by a fellowship-trained pediatric orthopaedic surgeon who was blinded to the patient's clinical history. The presence or absence of a Child Protective Services referral as well as institutional Child Assessment Program evaluations were reviewed. Nonaccidental trauma was deemed to be present, absent, or indeterminate by Child Protective Services or an on-site Child Assessment Program team. To further evaluate and quantify the likelihood of nonaccidental trauma, the criteria of the Modified Maltreatment Classification System were used., Results: Of 122 patients identified, ninety-five met the inclusion criteria for this study. Of these ninety-five, fifty-one (54%) had either a Child Protective Services or a Child Assessment Program consultation because of suspected nonaccidental trauma. Thirteen (25%) were found to have nonaccidental trauma as determined by Child Protective Services or the Child Assessment Program team and seven (14%) had indeterminate Child Protective Services or Child Assessment Program investigations. All thirteen patients with nonaccidental trauma, as well as the seven patients with an indeterminate Child Protective Services or Child Assessment Program investigation, had positive Modified Maltreatment Classification System scores for physical abuse. Patients who had nonaccidental trauma had significantly decreased mean anteroposterior fracture ratios compared with those who had confirmed accidental trauma (p < 0.0001)., Conclusions: The fracture ratio can be helpful to determine fracture morphology and can be used as part of the assessment of a child with suspected nonaccidental trauma. While not diagnostic, the presence of a transverse diaphyseal femoral fracture in a young child should raise the index of suspicion for nonaccidental trauma., Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence., (Copyright © 2015 by The Journal of Bone and Joint Surgery, Incorporated.)

Acquired coarctation of the thoracic aorta is a rare phenomenon in adults. The etiology is often idiopathic, but severe stenosis can develop from prior surgery, blunt thoracic aortic injuries, or severe atherosclerotic/atheroembolic disease. Common symptomatic presentations include refractory upper extremity hypertension and new-onset congestive heart failure. We present the case of a 52-year-old man who developed acquired thoracic aortic coarctation 30 years after a blunt trauma and deceleration injuries to the aorta requiring open surgical aortic repair. He presented with poorly controlled hypertension and new-onset heart failure and was treated surgically with endovascular repair., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Spiral fractures of long bones have long been cited as indications of non-accidental trauma (NAT) in children; however, fracture types are only loosely defined in the literature, and intraobserver and interobserver variability in defining femoral fracture patterns is rarely mentioned. We sought to determine reliability in classifying femoral fractures in young children using a standard series of radiographs shown to physicians with varied backgrounds and training and to determine if a quantitative approach based on objective measurements made on plain radiographs could improve definition of these fractures., Methods: On 50 radiographs, the fracture ratio--fracture length divided by bone diameter--was determined and radiographs were reviewed by 14 observers, including pediatric orthopaedic surgeons, emergency room physicians, and musculoskeletal radiologists, who classified the fractures as transverse, oblique, or spiral. A second review of the images in a different order was carried out at least 10 days after the first., Results: Overall, intraobserver agreement was strong, whereas interobserver reliability was moderate. Experience level did not correlate with either result. Complete agreement among all observers occurred for only 5 fractures: 3 transverse and 2 spiral. An average fracture ratio near 1.0 appeared to be predictive of a transverse fracture and a ratio of >3.0, a spiral fracture; ratios between these 2 values resulted in essentially random classification., Conclusions: The ability to reproducibly classify femoral fractures in young children is highly variable among physicians of different specialties. These results support the belief that fracture morphology has little predictive value in NAT because of the wide variability in what observers classify as a spiral fracture of the femur. Caution should be used in the use of descriptive terms such as spiral, oblique, or transverse when classifying femoral fractures, as well as when evaluating children for possible NAT, because of the variability in classification., Level of Evidence: Level III-diagnostic study.