513 research outputs found

    Using Green Chemistry to Build Community: How Transformational Learning Impacts the Building of a Community of Practice

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    Green Chemistry education is a widening field, seeking to include educators at all levels collaboratively in the process of transforming outdated chemistry practices. Qualitative research methods were used to interview three key collaborator groups at Beyond Benign, a green chemistry education organization, who are considered part of the Green Chemistry Community of Practice (GCCoP). This was done to develop a strategic plan to 1) explore how the Beyond Benign team and K-12 teachers see themselves as part of one GCCoP; 2) to ascertain how to bring the K-12 program into alignment with the organization’s evolving mission; and 3) to discover approaches for improving K-12 and Higher Ed collaboration and engagement, creating new possibilities for K-12, and bringing the two communities back into one evolving GCCoP. What was discovered through interviews with the Beyond Benign team, K-12 teachers, and higher ed faculty was that there were several challenges, but many possibilities for collaboration. Transformational learning that generates engagement, agency, and a desire for change was a theme that educators at all levels, from elementary through grad school, described as important to learning and building community around green chemistry to generate changes in the wider world, and draw more people into GCCoP

    A quantum crystallographic approach to study properties of molecules in crystals

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    In this dissertation, the behaviour of atoms, bonds, functional groups and molecules in vacuo but especially also in the crystal is studied using quantum crystallographic methods. The goal is to deepen the understanding of the properties of these building blocks as well as of the interactions among them, because good comprehension of the microscopic units and their interplay also enables us to explain the macroscopic properties of crystals. The first part (chapters 1-3) and second part (chapter 4) of this dissertation contain theoretical introductions about quantum crystallography. On the one hand, this expression contains the termquantum referring to quantumchemistry. Therefore, the very first chapter gives a brief overview about this field. The second chapter addresses different options to partition quantum chemical entities, such as the electron density or the bonding energy, into their components. On the other hand, quantumcrystallography consists obviously of the crystallographic part and chapter 3 covers these aspects focusing predominantly on X-ray diffraction. A more detailed introduction to quantum crystallography itself is presented in the second part (chapter 4). The third part (chapters 5-9) starts with an overview of the goals of this work followed by the results organized in four chapters. The goal is to deepen the understanding of properties of crystals by theoretically analysing their building block. It is for example studied how electrons and orbitals rearrange due to the electric field in a crystal or how high pressure leads to the formation of new bonds. Ultimately, these findings shall help to rationally design materials with desired properties such as high refractive index or semiconductivity.Mithilfe quantenkristallografischer Methoden werden Atome, Bindungen, funktionellen Gruppen und MolekĂŒle in vacuo aber vor allem auch in Kristallen untersucht. Das Ziel ist es die Eigenschaften dieser Bestandteile zu verstehen und wie sie miteinander interagieren. Das VerstĂ€ndnis der Verhaltensweise der einzelnen Bausteine sowie deren Zusammenspiel auf mikroskopischer Ebene kann auch die makroskopischen Eigenschaften von Kristallen erklĂ€ren. Der erste Teil dieser Doktorarbeit (Kapitel 1-3) beinhaltet eine theoretische Einleitung in die verschiedenen Bereiche der Quantenkristallografie. Wie der Name Quantenkristallografie besagt, besteht diese zum einen aus dem quantenchemischen Teil, weswegen das erste Kapitel eine kurze EinfĂŒhrung in die Quantenchemie gibt. Das zweite Kapitel widmet sich den verschiedenen Möglichkeiten quantenchemische Grössen wie zum Beispiel die Elektronendichte oder Bindungsenergien in Einzelteile zu zerlegen. Zum anderen trĂ€gt der kristallografische Teil zur Quantenkristallografie bei. Kapitel drei besteht daher aus einem kurzen Überblick ĂŒber die Kristallografie mit Fokus auf der Röntgenbeugung. Anschliessend folgt im zweiten Teil (Kapitel 4) eine ausfĂŒhrlichere Einleitung in die Quantenkristallografie selbst. Der dritte Teil (Kapitel 5-9) beginnt mit einer kurzen Übersicht ĂŒber die Ziele dieser Arbeit worauf die Resultate, gegliedert in vier verschiedene Kapitel, folgen. Das Ziel dieser Arbeit ist es die Eigenschaften von Kristallen besser zu verstehen, indem man ihre Einzelteile theoretisch analysiert und mit verschiedenen Methoden rationalisiert. Beispielsweise wird untersucht wie sich Elektronen und Orbitale aufgrund des elektrischen Feldes in Kristallen neu anordnen oder wie unter hohem Druck Bindungen neu geformt werden. Schlussendlich können all diese Erkenntnisse helfen, Materialien mit spezifischen gewĂŒnschten Eigenschaften herzustellen.Les atomes, les liaisons entre eux, les groupes fonctionnels et les molĂ©cules sont examinĂ©s en utilisant des mĂ©thodes de la cristallographie quantique. Le but est de comprendre les propriĂ©tĂ©s de ces composants et comment ils interagissent in vacuo mais surtout aussi dans les cristaux. En comprenant leurs caractĂ©ristiques et interactions au niveau microscopique, on peut aussi rationaliser les propriĂ©tĂ©s macroscopiques des cristaux. La premiĂšre partie (chapitres 1-3) de cette thĂšse de doctorat contient une introduction brĂšve Ă  la cristallographie quantique. Comme le noml’indique, ce domaine de recherche est composĂ© de la chimie quantique et la cristallographie. Pour cette raison le premier chapitre donne une introduction Ă  la chimie quantique. Le deuxiĂšme chapitre prĂ©sente quelques mĂ©thodes de dĂ©composition des quantitĂ©s de la chimie quantique comme la densitĂ© Ă©lectronique ou l’énergie de liaison. Le troisiĂšme chapitre couvre la partie cristallographique. Ensuite dans la deuxiĂšme partie (chapitre 4) une introduction plus dĂ©taillĂ©e sur la cristallographie quantique elle-mĂȘme est donnĂ©e. La troisiĂšme partie (chapitres 5-9) commence par un aperçu des objectives de cette dissertation suivis des rĂ©sultats structurĂ©s en quatre chapitres. Le but est de comprendre les propriĂ©tĂ©s des cristaux en analysant leurs building blocks avec diffĂ©rentes mĂ©thodes thĂ©oriques. Il Ă©tait par example examinĂ© comment les Ă©lectrons et les orbitales se rĂ©organisent dans un cristal Ă  cause du champ Ă©lectrique ou comment des nouvelles liaisons sont formĂ©es sous pression. Finalement on peut utiliser ces conclusions pour modeler des matĂ©riaux avec des propriĂ©tĂ©s dĂ©sirĂ©es

    Endangered by Sprawl: How Runaway Development Threatens America's Wildlife

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    Estimates the growth of land consumption in metropolitan areas over the next 25 years, investigates locally implemented strategies to protect natural lands from overdevelopment, and offers "smart growth" as an option for reducing suburban sprawl

    Strength and Nature of Host‐Guest Interactions in Metal‐Organic Frameworks from a Quantum‐Chemical Perspective

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    Metal-organic frameworks (MOFs) offer a convenient means for capturing, transporting, and releasing small molecules. Their rational design requires an in-depth understanding of the underlying non-covalent host-guest interactions, and the ability to easily and rapidly pre-screen candidate architectures in silico. In this work, we devised a recipe for computing the strength and analysing the nature of the host-guest interactions in MOFs. By assessing a range of density functional theory methods across periodic and finite supramolecular cluster scale we find that appropriately constructed clusters readily reproduce the key interactions occurring in periodic models at a fraction of the computational cost. Host-guest interaction energies can be reliably computed with dispersion-corrected density functional theory methods; however, decoding their precise nature demands insights from energy decomposition schemes and quantum-chemical tools for bonding analysis such as the quantum theory of atoms in molecules, the non-covalent interactions index or the density overlap regions indicator

    Engineering Host–Guest Interactions in Organic Framework Materials for Drug Delivery

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    Metal-organic frameworks (MOF) and covalent organic frameworks (COFs) are promising nanocarriers for targeted drug delivery. Noncovalent interactions between frameworks and drugs play a fundamental role in the therapeutic uptake and release of the latter. However, the scope of framework functionalizations and deliverable drugs remains underexplored. Using a multilevel approach combining molecular docking and density functional theory, we show for a range of drugs and frameworks that experimentally reported release metrics are in good agreement with the in silico computed host–guest interaction energies. Functional groups within the framework significantly impact the strength of these host–guest interactions, while a given framework can serve as an efficient delivery agent for drugs beyond the prototypical few. Our findings identify the interaction energy as a reliable and relatively easy to compute descriptor of organic framework materials for drug delivery, able to facilitate their high-throughput screening and targeted design towards extended-release times

    Host–guest interactions in framework materials:Insight from modeling

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    The performance of metal–organic and covalent organic framework materials in sought-after applications—capture, storage, and delivery of gases and molecules, and separation of their mixtures—heavily depends on the host–guest interactions established inside the pores of these materials. Computational modeling provides information about the structures of these host–guest complexes and the strength and nature of the interactions present at a level of detail and precision that is often unobtainable from experiment. In this Review, we summarize the key simulation techniques spanning from molecular dynamics and Monte Carlo methods to correlate ab initio approaches and energy, density, and wavefunction partitioning schemes. We provide illustrative literature examples of their uses in analyzing and designing organic framework hosts. We also describe modern approaches to the high-throughput screening of thousands of existing and hypothetical metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) and emerging machine learning techniques for predicting their properties and performances. Finally, we discuss the key methodological challenges on the path toward computation-driven design and reliable prediction of high-performing MOF and COF adsorbents and catalysts and suggest possible solutions and future directions in this exciting field of computational materials science

    Locating Guest Molecules inside Metal–Organic Framework Pores with a Multilevel Computational Approach

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    Molecular docking has traditionally mostly been employed in the field of protein–ligand binding. Here, we extend this method, in combination with DFT-level geometry optimizations, to locate guest molecules inside the pores of metal–organic frameworks. The position and nature of the guest molecules tune the physicochemical properties of the host–guest systems. Therefore, it is essential to be able to reliably locate them to rationally enhance the performance of the known metal–organic frameworks and facilitate new material discovery. The results obtained with this approach are compared to experimental data. We show that the presented method can, in general, accurately locate adsorption sites and structures of the host–guest complexes. We therefore propose our approach as a computational alternative when no experimental structures of guest-loaded MOFs are available. Additional information on the adsorption strength in the studied host–guest systems emerges from the computed interaction energies. Our findings provide the basis for other computational studies on MOF–guest systems and contribute to a better understanding of the structure–interaction–property interplay associated with them
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