Conspectus Catalysts for light-driven water oxidation are a critical component for development of solar fuels technology. The multielectron redox chemistry required for this process has been ...successfully deployed on a global scale in natural photosynthesis by green plants and cyanobacteria using photosystem II (PSII). PSII employs a conserved, cuboidal Mn4CaOX cluster called the O2-evolving complex (OEC) that offers inspiration for artificial O2-evolution catalysts. In this Account, we describe our work on manganese model chemistry relevant to PSII, particularly the functional model MnIII/IV 2(terpy)2(μ-O)2(OH2)2(NO3)3 complex (terpy = 2,2′;6′,2″-terpyridine), a mixed-valent di-μ-oxo Mn dimer with two terminal aqua ligands. In the presence of oxo-donor oxidants such as HSO5 –, this complex evolves O2 by two pathways, one of which incorporates solvent water in an O–O bond-forming reaction. Deactivation pathways of this catalyst include comproportionation to form an inactive MnIVMnIV dimer and also degradation to MnO2, a consequence of ligand loss when the oxidation state of the complex is reduced to labile MnII upon release of O2. The catalyst’s versatility has been shown by its continued catalytic activity after direct binding to the semiconductor titanium dioxide. In addition, after binding to the surface of TiO2 via a chromophoric linker, the catalyst can be oxidized by a photoinduced electron-transfer mechanism, mimicking the natural PSII process. Model oxomanganese complexes have also aided in interpreting biophysical and computational studies on PSII. In particular, the μ-oxo exchange rates of the Mn–terpy dimer have been instrumental in establishing that the time scale for μ-oxo exchange of high-valent oxomanganese complexes with terminal water ligands is slower than O2 evolution in the natural photosynthetic system. Furthermore, computational studies on the Mn–terpy dimer and the OEC point to similar MnIV–oxyl intermediates in the O–O bond-forming mechanism. Comparison between the OEC and the Mn–terpy dimer indicates that challenges remain in the development of synthetic Mn water-oxidation catalysts. These include redox leveling to couple multielectron reactions with one-electron steps, avoiding labile MnII species during the catalytic cycle, and protecting the catalyst active site from undesired side reactions. As the first example of a functional manganese O2-evolution catalyst, the Mn–terpy dimer exemplifies the interrelatedness of biomimetic chemistry with biophysical studies. The design of functional model complexes enriches the study of the natural photosynthetic system, while biology continues to provide inspiration for artificial photosynthetic technologies to meet global energy demand.
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Four manganese complexes of pentadentate ligands have been studied for their ability to act as oxygen evolution catalysts in the presence of Oxone or hydrogen peroxide. The complexes ...Mn(PaPy3)(NO3)(ClO4) (1) (PaPy3H = N,N-bis(2-pyridylmethyl)-amine-N-ethyl-2-pyridine-2-carboxamide) and Mn(PaPy3)(μ-O)(PaPy3)Mn(ClO4)2 (2) feature an anionic carboxamido ligand trans to the labile sixth coordination site, while Mn(N4Py)OTf(OTf) (3) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and Mn(PY5)(OH2)(ClO4)2 (4) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)-pyridine) have neutral ligands of varying flexibility. 1 and 2 are shown to evolve oxygen in the presence of either Oxone or hydrogen peroxide, but 3 evolves oxygen only in the presence of hydrogen peroxide. 4 is inactive. The activity of 1 and 2 with Oxone suggests that the presence of an anionic N-donor ligand plays a role in stabilizing putative high-valent intermediates. Anionic N-donor ligands may be viewed as alternatives to μ-oxo ligands that are prone to protonation in low-valent Mn species formed during a catalytic cycle, resulting in loss of catalyst structure.
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Light-driven water oxidation for solar fuels Young, Karin J.; Martini, Lauren A.; Milot, Rebecca L. ...
Coordination chemistry reviews,
November 2012, 2012-11-01, 2012-11-00, 20121101, Volume:
256, Issue:
21-22
Journal Article
Peer reviewed
Open access
. Display omitted
► Anodes for light-driven water oxidation. ► Design includes semiconductor, light-harvesting molecule, and catalyst. ► Integration of components is greatest challenge.
Light-driven ...water oxidation is an essential step for conversion of sunlight into storable chemical fuels. Fujishima and Honda reported the first example of photoelectrochemical water oxidation in 1972. In their system, TiO2 was irradiated with ultraviolet light, producing oxygen at the anode and hydrogen at a platinum cathode. Inspired by this system, more recent work has focused on functionalizing nanoporous TiO2 or other semiconductor surfaces with molecular adsorbates, including chromophores and catalysts that absorb visible light and generate electricity (i.e., dye-sensitized solar cells) or trigger water oxidation at low overpotentials (i.e., photocatalytic cells). The physics involved in harnessing multiple photochemical events for multi-electron reactions, as required in the four-electron water-oxidation process, has been the subject of much experimental and computational study. In spite of significant advances with regard to individual components, the development of highly efficient photocatalytic cells for solar water splitting remains an outstanding challenge. This article reviews recent progress in the field with emphasis on water-oxidation photoanodes inspired by the design of functionalized thin-film semiconductors of typical dye-sensitized solar cells.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Creating instructional activities and assessments that align with expected learning outcomes can improve student learning. Communicating learning expectations to students may lead to better student ...performance and an increase in student perceptions of the fairness of the assessment tools. One tool for communicating learning outcomes is the distribution of an exam “blueprint”, a document that correlates student learning outcomes with the expected level of performance and the relative weight on the exam. In this study, exam blueprints were prepared and distributed to students in an inorganic chemistry course. Students were surveyed about their use of the blueprints after each exam and interviewed about their perceptions of the congruence between assessments and instruction as well as their use of the blueprints. Students report using the blueprints as both organizational and metacognitive tools by emphasizing heavily weighted objectives. Overall, the blueprints were an effective tool for facilitating instructor–student communication as well as generating positive student attitudes toward exams, even though exam scores did not increase.
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Late-transition-metal catalysts for polymerization of olefins have drawn a significant amount of attention owing to their ability to tolerate and incorporate polar comonomers. However, a systematic ...way to experimentally quantify the electronic properties of the ligands used in these systems has not been developed. Quantified ligand parameters will allow for the rational design of tailored polymerization catalysts, which would target specific polymer properties. We report a series of platinum complexes bearing bisphosphinemonoxide ligands, which resemble those used in the polymerization catalysts of Nozaki and Chen. Their electronic properties are investigated experimentally, and trends are rationalized by using computed spectral properties. Benchmarking computational data with known experimental parameters further enhances the utility of both methods for determining optimal ligands for catalytic application.
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Climate change is a critical scientific and social issue of our time, yet the topic is not frequently discussed by the general public. Additionally, misconceptions about the topic persist. One ...important aspect of climate change is the greenhouse effect. This activity adds a greenhouse gas discussion to an existing module about molecular shape and modeling. The module links the greenhouse effect to climate change. The activity has been used in several introductory chemistry settings. A discussion of student-generated answers and student-reported learning gains is presented.
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Elevated fasting blood glucose (FBG) is associated with increased risks of developing type 2 diabetes (T2D) and cardiovascular-associated mortality. G6PC2 is predominantly expressed in islets, ...encodes a glucose-6-phosphatase catalytic subunit that converts glucose-6-phosphate (G6P) to glucose, and has been linked with variations in FBG in genome-wide association studies. Deletion of G6pc2 in mice has been shown to lower FBG without affecting fasting plasma insulin levels in vivo. At 5 mM glucose, pancreatic islets from G6pc2 knockout (KO) mice exhibit no glucose cycling, increased glycolytic flux, and enhanced glucose-stimulated insulin secretion (GSIS). However, the broader effects of G6pc2 KO on β-cell metabolism and redox regulation are unknown. Here we used CRISPR/Cas9 gene editing and metabolic flux analysis in βTC3 cells, a murine pancreatic β-cell line, to examine the role of G6pc2 in regulating glycolytic and mitochondrial fluxes. We found that deletion of G6pc2 led to ∼60% increases in glycolytic and citric acid cycle (CAC) fluxes at both 5 and 11 mM glucose concentrations. Furthermore, intracellular insulin content and GSIS were enhanced by approximately two-fold, along with increased cytosolic redox potential and reductive carboxylation flux. Normalization of fluxes relative to net glucose uptake revealed upregulation in two NADPH-producing pathways in the CAC. These results demonstrate that G6pc2 regulates GSIS by modulating not only glycolysis but also, independently, citric acid cycle activity in β-cells. Overall, our findings implicate G6PC2 as a potential therapeutic target for enhancing insulin secretion and lowering FBG, which could benefit individuals with prediabetes, T2D, and obesity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The G6PC1, G6PC2 and G6PC3 genes encode distinct glucose-6-phosphatase catalytic subunit (G6PC) isoforms. In mice, germline deletion of G6pc2 lowers fasting blood glucose (FBG) without affecting ...fasting plasma insulin (FPI) while, in isolated islets, glucose-6-phosphatase activity and glucose cycling are abolished and glucose-stimulated insulin secretion (GSIS) is enhanced at submaximal but not high glucose. These observations are all consistent with a model in which G6PC2 regulates the sensitivity of GSIS to glucose by opposing the action of glucokinase. G6PC2 is highly expressed in human and mouse islet beta cells however, various studies have shown trace G6PC2 expression in multiple tissues raising the possibility that G6PC2 also affects FBG through non-islet cell actions. Using real-time PCR we show here that expression of G6pc1 and/or G6pc3 are much greater than G6pc2 in peripheral tissues, whereas G6pc2 expression is much higher than G6pc3 in both pancreas and islets with G6pc1 expression not detected. In adult mice, beta cell-specific deletion of G6pc2 was sufficient to reduce FBG without changing FPI. In addition, electronic health record-derived phenotype analyses showed no association between G6PC2 expression and phenotypes clearly unrelated to islet function in humans. Finally, we show that germline G6pc2 deletion enhances glycolysis in mouse islets and that glucose cycling can also be detected in human islets. These observations are all consistent with a mechanism by which G6PC2 action in islets is sufficient to regulate the sensitivity of GSIS to glucose and hence influence FBG without affecting FPI.
In this laboratory experiment, students evaluated three silver(I) complexes as potential additives for dental adhesives based on bacterial growth inhibition, heat stability, water insolubility, and ...cost-effectiveness. Each student prepared and analyzed a cyanoxime ligand and its corresponding silver(I) complex. Students characterized the antibacterial activity of the silver complexes against E. coli using a Kirby–Bauer disk-diffusion test. Laboratory data were shared among students to compare observed properties to determine which derivative is the most suitable. This multiweek experiment was used in inorganic chemistry laboratory courses to demonstrate the application of inorganic chemistry to biomedicine. The framework of the experiment was developed by a multi-institutional collaboration, and we highlight how the general procedures of the experiment were adapted to meet the needs of varying courses and contexts.
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Twenty fifteen marked the year of assessment for the Millennium Development Goals (MDGs). The MDGs that achieved the greatest success were those where evidence-based practice (EBP) interventions were ...implemented. The ability to practice evidence-based medicine is grounded in the creation of and access to medical literature that synthesizes research findings. The role that global health literature played in the success of the MDGs demonstrates that medical libraries and librarians have a role to play in achieving the Sustainable Development Goals (SDGs). Librarians can hold capacity-building workshops that provide instruction on how to access evidence-based literature and also train health professionals to conduct synthesis research. Research findings conducted by in-country health professionals are more likely to address issues being faced by local communities and will afford the possibility of obtaining the necessary evidence-based answers that can then be used to implement policies to resolve public health issues identified in the SDGs. This paper discusses how an international team of librarians leveraged funding from a Medical Library Association/Librarians without Borders/Elsevier Foundation/Research4Life grant to hold a capacity-building workshop in Zimbabwe and follow-up online trainings. The workshop focused on accessing evidence-based resources and conducting synthesis research. Outcomes included the creation and policy implementation of evidence-based knowledge products in alignment with local needs and galvanizing a multisectoral group of key individuals who have gone on to collaborate toward the vision of creating a Zimbabwe innovation hub. Looking ahead, such grants can be leveraged to conduct capacity-building to support knowledge translation and other local training needs.
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DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK, VSZLJ
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