A Synthetic Model of the Putative Fe(II)-Iminobenzosemiquinonate Intermediate in the Catalytic Cycle of \u3cem\u3eo\u3c/em\u3e-Aminophenol Dioxygenases

The oxidative ring cleavage of aromatic substrates by nonheme Fe dioxygenases is thought to involve formation of a ferrous–(substrate radical) intermediate. Here we describe the synthesis of the trigonal-bipyramdial complex Fe(Ph2Tp)(ISQtBu) (2), the first synthetic example of an iron(II) center bound to an iminobenzosemiquinonate (ISQ) radical. The unique electronic structure of this S = 3/2 complex and its one-electron oxidized derivative ([3]+) have been established on the basis of crystallographic, spectroscopic, and computational analyses. These findings further demonstrate the viability of Fe2+–ISQ intermediates in the catalytic cycles of o-aminophenol dioxygenases

Dioxygen Reactivity of Biomimetic Fe(II) Complexes with Noninnocent Catecholate, \u3cem\u3eo\u3c/em\u3e-Aminophenolate, and \u3cem\u3eo\u3c/em\u3e-Phenylenediamine Ligands

This study describes the O2 reactivity of a series of high-spin mononuclear Fe(II) complexes each containing the facially coordinating tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (Ph2TIP) ligand and one of the following bidentate, redox-active ligands: 4-tert-butylcatecholate (tBuCatH–), 4,6-di-tert-butyl-2-aminophenolate (tBu2APH–), or 4-tert-butyl-1,2-phenylenediamine (tBuPDA). The preparation and X-ray structural characterization of [Fe2+(Ph2TIP)(tBuCatH)]OTf, [3]OTf and [Fe2+(Ph2TIP)(tBuPDA)](OTf)2, [4](OTf)2 are described here, whereas [Fe2+(Ph2TIP)(tBu2APH)]OTf, [2]OTf was reported in our previous paper [Bittner et al., Chem.—Eur. J. 2013, 19, 9686–9698]. These complexes mimic the substrate-bound active sites of nonheme iron dioxygenases, which catalyze the oxidative ring-cleavage of aromatic substrates like catechols and aminophenols. Each complex is oxidized in the presence of O2, and the geometric and electronic structures of the resulting complexes were examined with spectroscopic (absorption, EPR, Mössbauer, resonance Raman) and density functional theory (DFT) methods. Complex [3]OTf reacts rapidly with O2 to yield the ferric-catecholate species [Fe3+(Ph2TIP)(tBuCat)]+ (3ox), which undergoes further oxidation to generate an extradiol cleavage product. In contrast, complex [4]2+ experiences a two-electron (2e–), ligand-based oxidation to give [Fe2+(Ph2TIP)(tBuDIBQ)]2+ (4ox), where DIBQ is o-diiminobenzoquinone. The reaction of [2]+ with O2 is also a 2e– process, yet in this case both the Fe center and tBu2AP ligand are oxidized; the resulting complex (2ox) is best described as [Fe3+(Ph2TIP)(tBu2ISQ)]+, where ISQ is o-iminobenzosemiquinone. Thus, the oxidized complexes display a remarkable continuum of electronic structures ranging from [Fe3+(L2–)]+ (3ox) to [Fe3+(L•–)]2+ (2ox) to [Fe2+(L0)]2+ (4ox). Notably, the O2 reaction rates vary by a factor of 105 across the series, following the order [3]+ \u3e [2]+ \u3e [4]2+, even though the complexes have similar structures and Fe3+/2+ redox potentials. To account for the kinetic data, we examined the relative abilities of the title complexes to bind O2 and participate in H-atom transfer reactions. We conclude that the trend in O2 reactivity can be rationalized by accounting for the role of proton transfer(s) in the overall reaction

An Ontology for Submarine Feature Representation on Charts

A landform is a subjective individuation of a part of a terrain. Landform recognition is a difficult task because its definition usually relies on a qualitative and fuzzy description. Achieving automatic recognition of landforms requires a formal definition of the landforms properties and their modelling. In the maritime domain, the International Hydrographic Organisation published a standard terminology of undersea feature names which formalises a set of definition mainly for naming and communication purpose. This terminology is here used as a starting point for the definition of an ontology of undersea features and their automatic classification from a terrain model. First, an ontology of undersea features is built. The ontology is composed of an application domain ontology describing the main properties and relationships between features and a representation ontology deals with representation on a chart where features are portrayed by soundings and isobaths. A database model was generated from the ontology. Geometrical properties describing the feature shape are computed from soundings and isobaths and are used for feature classification. An example of automatic classification on a nautical chart is presented and results and on-going research are discussed

Motivic Milnor fibre for nondegenerate function germs on toric singularities

We study function germs on toric varieties which are nondegenerate for their Newton diagram. We express their motivic Milnor fibre in terms of their Newton diagram. We extend a formula for the motivic nearby fibre to the case of a toroidal degeneration. We illustrate this by some examples.Comment: 14 page

Comparison of Evidence-Based Practices for Students with Autism Spectrum Disorder

The Every Student Succeeds Act (ESSA, 2015) reinforces and clearly defines the requirement of school districts to use evidence-based practices (EBPs) to improve student outcomes. The ESSA requires schools to find, evaluate, and implement effective EBPs that support high-quality learning for all students, including those with autism spectrum disorder (ASD). It is necessary for teachers to use identified EBPs when developing individualized education programs and providing necessary interventions for students with ASD. The purpose of this article is to: (a) examine EBPs determined by two national organizations (i.e., National Professional Development Center, National Standards Project Phase 2), (b) compare overlapping EBPs to determine their effectiveness for students with ASD, and (c) make recommendations for educators and other school professionals teaching students with ASD in school settings. Identification and implementation of EBPs is essential for teachers who work with students with ASD to increase their academic and functional achievement and reach their fullest potential

Synthetic, Spectroscopic and DFT Studies of Iron Complexes with Iminobenzo(semi)quinone Ligands: Implications for o-Aminophenol Dioxygenases

The oxidative CC bond cleavage of o-aminophenols by nonheme Fe dioxygenases is a critical step in both human metabolism (the kynurenine pathway) and the microbial degradation of nitroaromatic pollutants. The catalytic cycle of o-aminophenol dioxygenases (APDOs) has been proposed to involve formation of an FeII/O2/iminobenzosemiquinone complex, although the presence of a substrate radical has been called into question by studies of related ring-cleaving dioxygenases. Recently, we reported the first synthesis of an iron(II) complex coordinated to an iminobenzosemiquinone (ISQ) ligand, namely, [Fe(Tp)(tBuISQ)] (2 a; where Tp=hydrotris(3,5-diphenylpyrazol-1-yl)borate and tBuISQ is the radical anion derived from 2-amino-4,6-di-tert-butylphenol). In the current manuscript, density functional theory (DFT) calculations and a wide variety of spectroscopic methods (electronic absorption, Mössbauer, magnetic circular dichroism, and resonance Raman) were employed to obtain detailed electronic-structure descriptions of 2 a and its one-electron oxidized derivative [3 a]+. In addition, we describe the synthesis and characterization of a parallel series of complexes featuring the neutral supporting ligand tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (TIP). The isomer shifts of about 0.97 mm s−1 obtained through Mössbauer experiments confirm that 2 a (and its TIP-based analogue [2 b]+) contain FeII centers, and the presence of an ISQ radical was verified by analysis of the absorption spectra in light of time-dependent DFT calculations. The collective spectroscopic data indicate that one-electron oxidation of the FeII–ISQ complexes yields complexes ([3 a]+ and [3 b]2+) with electronic configurations between the FeIII–ISQ and FeII–IBQ limits (IBQ=iminobenzoquinone), highlighting the ability of o-amidophenolates to access multiple oxidation states. The implications of these results for the mechanism of APDOs and other ring-cleaving dioxygenases are discussed

Ising spins coupled to a four-dimensional discrete Regge skeleton

Regge calculus is a powerful method to approximate a continuous manifold by a simplicial lattice, keeping the connectivities of the underlying lattice fixed and taking the edge lengths as degrees of freedom. The discrete Regge model employed in this work limits the choice of the link lengths to a finite number. To get more precise insight into the behavior of the four-dimensional discrete Regge model, we coupled spins to the fluctuating manifolds. We examined the phase transition of the spin system and the associated critical exponents. The results are obtained from finite-size scaling analyses of Monte Carlo simulations. We find consistency with the mean-field theory of the Ising model on a static four-dimensional lattice.Comment: 19 pages, 7 figure

What makes slow samples slow in the Sherrington-Kirkpatrick model

Using results of a Monte Carlo simulation of the Sherrington-Kirkpatrick model, we try to characterize the slow disorder samples, namely we analyze visually the correlation between the relaxation time for a given disorder sample $J$ with several observables of the system for the same disorder sample. For temperatures below $T_c$ but not too low, fast samples (small relaxation times) are clearly correlated with a small value of the largest eigenvalue of the coupling matrix, a large value of the site averaged local field probability distribution at the origin, or a small value of the squared overlap $$. Within our limited data, the correlation remains as the system size increases but becomes less clear as the temperature is decreased (the correlation with$$ is more robust) . There is a strong correlation between the values of the relaxation time for two distinct values of the temperature, but this correlation decreases as the system size is increased. This may indicate the onset of temperature chaos