How calcium affects oxygen formation

Calcium is an essential component of the catalyst that forms oxygen from water during photosynthesis. It seems that part of calcium's job is to enable the release of oxygen from this catalyst

Metal-templated ligand architectures for trinuclear chemistry: tricopper complexes and their O_2 reactivity

A trinucleating framework was assembled by templation of a heptadentate ligand around yttrium and lanthanides. The generated complexes orient three sets of two or three N-donors each for binding additional metal centers. Addition of three equivalents of copper(I) leads to the formation of tricopper(I) species. Reactions with dioxygen at low temperatures generate species whose spectroscopic features are consistent with a μ_3,μ_3-dioxo-tricopper complex. Reactivity studies were performed with a variety of substrates. The dioxo-tricopper species deprotonates weak acids, undergoes oxygen atom transfer with triphenylphosphine to yield triphenylphosphine oxide, and performs hydrogen atom abstraction from tetramethylpiperidine-N-hydroxide (TEMPO-H). Thiophenols reduce the oxygenated species to a Cu_3^I complex and liberate two equivalents of disulfide, consistent with a four-electron four-proton process

A trans-Hyponitrite Intermediate in the Reductive Coupling and Deoxygenation of Nitric Oxide by a Tricopper–Lewis Acid Complex

The reduction of nitric oxide (NO) to nitrous oxide (N_2O) is a process relevant to biological chemistry as well as to the abatement of certain environmental pollutants. One of the proposed key intermediates in NO reduction is hyponitrite (N_2O_2^(2–)), the product of reductive coupling of two NO molecules. We report the reductive coupling of NO by an yttrium–tricopper complex generating a trans-hyponitrite moiety supported by two μ-O-bimetallic (Y,Cu) cores, a previously unreported coordination mode. Reaction of the hyponitrite species with Brønsted acids leads to the generation of N_2O, demonstrating the viability of the hyponitrite complex as an intermediate in NO reduction to N_2O. The additional reducing equivalents stored in each tricopper unit are employed in a subsequent step for N_2O reduction to N_2, for an overall (partial) conversion of NO to N_2. The combination of Lewis acid and multiple redox active metals facilitates this four electron conversion via an isolable hyponitrite intermediate

Preparation, Characterization, and Electrochemical Activation of a Model [Cp*Rh] Hydride

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.8b02160.Monomeric half-sandwich rhodium hydride complexes are often proposed as intermediates in catalytic cycles, but relatively few such compounds have been isolated and studied, limiting understanding of their properties. Here, we report preparation and isolation of a monomeric rhodium(III) hydride complex bearing the pentamethylcyclopentadienyl (Cp*) and bis(diphenylphosphino)benzene (dppb) ligands. The hydride complex is formed rapidly upon addition of weak acid to a reduced precursor complex, Cp*Rh(dppb). Single-crystal X-ray diffraction data for the [Cp*Rh] hydride, which were previously unavailable for this class of compounds, provide evidence of the direct Rh–H interaction. Complementary infrared spectra show the Rh–H stretching frequency at 1986 cm−1. In contrast to results with other [Cp*Rh] complexes bearing diimine ligands, treatment of the isolated hydride with strong acid does not result in H2 evolution. Electrochemical studies reveal that the hydride complex can be reduced only at very negative potentials (ca. −2.5 V vs. ferrocenium/ferrocene), resulting in Rh–H bond cleavage and H2 generation. These results are discussed in the context of catalytic H2 generation, and development of design rules for improved catalysts bearing the [Cp*] ligand.University of Kansas Undergraduate Research AwardS10OD016360S10RR024664NSF MRI Grant CHE-162592

Single-Electron Redox Chemistry on the [Cp*Rh] Platform Enabled by a Nitrated Bipyridyl Ligand

This work is licensed under a Creative Commons Attribution 4.0 International License.[Cp*Rh] complexes (Cp* = pentamethylcyclopentadienyl) are attracting renewed interest in coordination chemistry and catalysis, but these useful compounds often undergo net two-electron redox cycling that precludes observation of individual one-electron reduction events. Here, we show that a [Cp*Rh] complex bearing the 4,4′-dinitro-2,2′-bipyridyl ligand (dnbpy) (3) can access a distinctive manifold of five oxidation states in organic electrolytes, contrasting with prior work that found no accessible reductions in aqueous electrolyte. These states are readily generated from a newly isolated and fully characterized rhodium(III) precursor complex 3, formulated as [Cp*Rh(dnbpy)Cl]PF6. Single-crystal X-ray diffraction (XRD) data, previously unavailable for the dnbpy ligand bound to the [Cp*Rh] platform, confirm the presence of both [η5-Cp*] and [κ2-dnbpy]. Four individual one-electron reductions of 3 are observed, contrasting sharply with the single two-electron reductions of other [Cp*Rh] complexes. Chemical preparation and the study of the singly reduced species with electronic absorption and electron paramagnetic resonance spectroscopies indicate that the first reduction is predominantly centered on the dnbpy ligand. Comparative cyclic voltammetry studies with [NBu4][PF6] and [NBu4][Cl] as supporting electrolytes indicate that the chloride ligand can be lost from 3 by ligand exchange upon reduction. Spectroelectrochemical studies with ultraviolet (UV)-visible detection reveal isosbestic behavior, confirming the clean interconversion of the reduced forms of 3 inferred from the voltammetry with [NBu4][PF6] as supporting electrolyte. Electrochemical reduction in the presence of triethylammonium results in an irreversible response, but does not give rise to catalytic H2 evolution, contrasting with the reactivity patterns observed in [Cp*Rh] complexes bearing bipyridyl ligands with less electron-withdrawing substituents.US National Science Foundation award OIA-1833087KU Hall Chemical Research FundCenter for Undergraduate Research at the University of KansasNIH S10OD016360NIH S10RR024664NSF MRI funding (CHE-1625923

Heterometallic Triiron-Oxo/Hydroxo Clusters: Effect of Redox-Inactive Metals

A series of tetranuclear oxo/hydroxo clusters comprised of three Fe centers and a redox-inactive metal (M) of various charge is reported. Crystallographic studies show an unprecedented Fe_3M(μ_4-O)(μ_2-OH) core that remains intact upon changing M or the oxidation state of iron. Electrochemical studies reveal that the reduction potentials (E_(1/2)) span a window of 500 mV and depend upon the Lewis acidity of M. Using the pK_a of the M-aqua complex as a measure of Lewis acidity, these compounds display a linear dependence between E1/2 and acidity, with a slope of ∼70 mV per pK_a unit. The current study of [Fe_3MO(OH)] and previous ones of [Mn_3MO_n] (n = 2,4) moieties support the generality of the above relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidity of incorporated cations, as applied to clusters of different redox-active metals

HandMonizer: a case study for personalized digital musical instrument design

The rapid evolution in technology has found its way to introducing novelty in today’s live music performances. In this context, the development of Digital Musical Instruments (DMIs) has obtained increasing attention in recent years. In this paper, we present the development of a DMI called Handmonizer, an interactive artist-oriented harmonizer for musical performance adapted to the needs of a specific singer. A key component of our work is the combination of hand motion recognition and audio signal processing to obtain a smoother interaction. We describe the development methodology, but we also focus on our collaboration with the artist to conceptualize and then refine this tool until the development of the final product. At the end of this paper, we define an evaluation strategy, collecting feedback with a questionnaire addressed to the singer. Our aim in presenting this evaluation strategy is to help other engineers keen to develop cutting-edge technologies by working in partnership with artists. While results are not definitive, we believe that the chosen methodology could be of interest to other DMI researchers. Moreover, the modular nature of the Handmonizer makes it easily adaptable to further developments concerning the Internet of Sounds (IoS) and Networked Music Performances (NMP)

Age and Gender Affect the Composition of Fungal Population of the Human Gastrointestinal Tract

The fungal component of the human gut microbiota has been neglected for long time due to the low relative abundance of fungi with respect to bacteria, and only recently few reports have explored its composition and dynamics in health or disease. The application of metagenomics methods to the full understanding of fungal communities is currently limited by the under representation of fungal DNA with respect to the bacterial one, as well as by the limited ability to discriminate passengers from colonizers. Here we investigated the gut mycobiota of a cohort of healthy subjects in order to reduce the gap of knowledge concerning fungal intestinal communities in the healthy status further screening for phenotypical traits that could reflect fungi adaptation to the host. We studied the fecal fungal populations of 111 healthy subjects by means of cultivation on fungal selective media and by amplicon-based ITS1 metagenomics analysis on a subset of 57 individuals. We then characterized the isolated fungi for their tolerance to gastrointestinal tract-like challenges and their susceptibility to antifungals. A total of 34 different fungal species were isolated showing several phenotypic characteristics associated with intestinal environment such as tolerance to body temperature (37°C), to acidic and oxidative stress and to bile salts exposure. We found a high frequency of azoles resistance in fungal isolates, with potential and significant clinical impact. Analyses of fungal communities revealed that the human gut mycobiota differs in function of individuals’ life stage in a gender-related fashion. The combination of metagenomics and fungal cultivation allowed an in-depth understanding of the fungal intestinal community structure associated to the healthy status and the commensalism-related traits of isolated fungi. We further discussed comparatively the results of sequencing and cultivation to critically evaluate the application of metagenomics-based approaches to fungal gut populations

Alteration of Fecal Microbiota Profiles in Juvenile Idiopathic Arthritis. Associations with HLA-B27 Allele and Disease Status.

Alteration of gut microbiota is involved in several chronic inflammatory and autoimmune diseases, including rheumatoid arthritis, and gut microbial pro-arthritogenic profiles have been hypothesized. Intestinal inflammation may be involved in spondyloarthropathies and in a subset of patients affected by Juvenile Idiopathic Arthritis (JIA), the most common chronic rheumatic disease of childhood. We compared the fecal microbiota composition of JIA patients with healthy subjects (HS), evaluating differences in microbial profiles between sub-categories of JIA, such as enthesitis-related arthritis (JIA-ERA), in which inflammation of entheses occurs, and polyarticular JIA, non-enthesitis related arthritis (JIA-nERA). Through taxon-level analysis, we discovered alteration of fecal microbiota components that could be involved in subclinical gut inflammation, and promotion of joint inflammation. We observed abundance in Ruminococcaceae in both JIA categories, reduction in Clostridiaceae and Peptostreptococcaceae in JIA-ERA, and increase in Veillonellaceae in JIA-nERA, respectively compared with HS. Among the more relevant genera, we found an increase in Clostridium cluster XIVb, involved in colitis and arthritis, in JIA-ERA patients compared with HS, and a trend of decrease in Faecalibacterium, known for anti-inflammatory properties, in JIA-nERA compared with JIA-ERA and HS. Differential abundant taxa identified JIA patients for the HLA-B27 allele, including Bilophila, Clostridium cluster XIVb, Oscillibacter and Parvimonas. Prediction analysis of metabolic functions showed that JIA-ERA metagenome was differentially enriched in bacterial functions related to cell motility and chemotaxis, suggesting selection of potential virulence traits. We also discovered differential microbial profiles and intra-group variability among active disease and remission, suggesting instability of microbial ecosystem in autoimmune diseases with respect to healthy status. Similarly to other chronic autoimmune and inflammatory diseases, different microbial profiles, as observed among different JIA subgroups compared to HS, and potential functional acquisition related to migration could promote inflammation and contribute to the disease pathogenesis

Effects of Lewis Acidic Metal Ions (M) on Oxygen-Atom Transfer Reactivity of Heterometallic Mn_3MO_4 Cubane and Fe_3MO(OH) and Mn_3MO(OH) Clusters

The modulation of the reactivity of metal oxo species by redox inactive metals has attracted much interest due to the observation of redox inactive metal effects on processes involving electron transfer both in nature (the oxygen-evolving complex of Photosystem II) and in heterogeneous catalysis (mixed-metal oxides). Studies of small-molecule models of these systems have revealed numerous instances of effects of redox inactive metals on electron- and group-transfer reactivity. However, the heterometallic species directly involved in these transformations have rarely been structurally characterized and are often generated in situ. We have previously reported the preparation and structural characterization of multiple series of heterometallic clusters based on Mn_3 and Fe_3 cores and described the effects of Lewis acidity of the heterometal incorporated in these complexes on cluster reduction potential. To determine the effects of Lewis acidity of redox inactive metals on group transfer reactivity in structurally well-defined complexes, we studied [Mn_3MO_4], [Mn_3MO(OH)], and [Fe_3MO(OH)] clusters in oxygen atom transfer (OAT) reactions with phosphine substrates. The qualitative rate of OAT correlates with the Lewis acidity of the redox inactive metal, confirming that Lewis acidic metal centers can affect the chemical reactivity of metal oxo species by modulating cluster electronics