1,721,054 research outputs found
The effect of bean origin and temperature on grinding roasted coffee
Get PDFCoffee is prepared by the extraction of a complex array of organic molecules from the roasted bean, which has been ground into fine particulates. The extraction depends on temperature, water chemistry and also the accessible surface area of the coffee. Here we investigate whether variations in the production processes of single origin coffee beans affects the particle size distribution upon grinding. We find that the particle size distribution is independent of the bean origin and processing method. Furthermore, we elucidate the influence of bean temperature on particle size distribution, concluding that grinding cold results in a narrower particle size distribution, and reduced mean particle size. We anticipate these results will influence the production of coffee industrially, as well as contribute to how we store and use coffee daily
Enhancing the Antiaromaticity of s-Indacenes Through Heterocycle Fusion
Get PDFAntiaromaticity, while associated with instability, imparts beneficial properties such as decreased HOMO-LUMO energy gaps. Compounds containing antiaromatic subunits are not only of fundamental interest, but of interest as components in organic electronics. Since antiaromatic compounds are generally unstable, various strategies for isolating these compounds, such as annulation of aromatic subunits, have been developed. While this strategy stabilizes the antiaromatic subunit, it generally decreases the degree of antiaromaticity. Thus, methods to stabilize yet maintain or increase the degree of antiaromaticity are desirable. Recently, we found that fusion of aromatic heterocycles to s-indacene, a known antiaromatic molecule, yields isolable compounds with increased antiaromaticity in the s-indacene core. In this dissertation I will discuss the background of s-indacene and an overview of tuning the antiaromaticity of s-indacene, how fusion of naphthothiophene units increases the antiaromaticity of s-indacene and the development a computational understanding for the effect of heterocycle fusion on s-indacene.Chapter I is an overview of the literature about s-indacene followed by a discussion of the methods used to tune the antiaromaticity of s-indacene by the Haley group. Chapter II describes the synthesis of four naphthothiophene-fused s-indacenes, one of which increased the antiaromaticity of the s-indacene core above unsubstituted s-indacene. Chapter III extends the work of Chapter II further developing the synthesis of naphthothiophene-fused s-indacenes, varying the aryl substituents, and providing a detailed comparison of the properties of all isomers. Finally, Chapter IV explores fourteen different benzoheterocycle-fused s-indacenes through a variety of computational techniques to understand the effect of the heteroatom on the antiaromaticity of the s-indacene core.
This dissertation includes previously published and unpublished co-authored material
Tracking a Common Surface-Bound Intermediate During CO₂-to-Fuels Catalysis
No full textRational design of selective CO₂-to-fuels electrocatalysts requires direct knowledge of the electrode surface structure during turnover. Metallic Cu is the most versatile CO₂ -to-fuels catalyst, capable of generating a wide array of value-added products, including methane, ethylene, and ethanol. All of these products are postulated to form via a common surface-bound CO intermediate. Therefore, the kinetics and thermodynamics of CO adsorption to Cu play a central role in determining fuel-formation selectivity and efficiency, highlighting the need for direct observation of CO surface binding equilibria under catalytic conditions. Here, we synthesize nanostructured Cu films adhered to IR-transparent Si prisms, and we find that these Cu surfaces enhance IR absorption of bound molecules. Using these films as electrodes, we examine Cu-catalyzed CO₂ reduction in situ via IR spectroelectrochemistry. We observe that Cu surfaces bind electrogenerated CO, derived from CO₂, beginning at -0.60 V vs RHE with increasing surface population at more negative potentials. Adsorbed CO is in dynamic equilibrium with dissolved 13 CO and exchanges rapidly under catalytic conditions. The CO adsorption profiles are pH independent, but adsorbed CO species undergo a reversible transformation on the surface in modestly alkaline electrolytes. These studies establish the potential, concentration, and pH dependencies of the CO surface population on Cu, which serve to maintain a pool of this vital intermediate primed for further reduction to higher order fuel products.United States. Air Force Office of Scientific Research (Award FA9550-15-1-0135
First Principles Studies of The Metal-Organic Interface in Porous Frameworks
Get PDFDue to their generally poor conductivity, metal–organic frameworks (MOFs) have been limited in electrical applications. In this dissertation we explore structural deformation as a route to augmenting the electronic properties of these high surface area materials. We show that, under hydrostatic negative pressure, metallicity can be installed and we also elucidated the covalent characteristic of the metal-organic interface in 2D MOFs. Continuing our quest, we explore the deformation and phase change within 3D MOFs. Given the stability of metal-organic frameworks under numerous harsh conditions, bonding in MOFs has thought to be static. This project explores the metal-linker interface for a handful of carboxylate-based MOFs under various temperature conditions, which provides evident for dynamic bonding within these frameworks. Our insights to this phenomenon through the lens of density functional theory (DFT) combine with VT-DRIFT spectroscopy reveal specific vibrational modes coming from the carboxylate stretches that give rise to reversible metal-linker bonding within these materials. The metal-linker dynamics resemble the ubiquitous soft modes that trigger important phase transitions offering insights to several important events such as catalysis, negative thermal expansion, post-synthetic exchange that occurred in these frameworks. We applied the same methods onto Fe-based porous frameworks and elucidated Fe metal centers possess properties such as spin-crossover transition, mixed-valency, and cooperativity which together enhance the material's transport properties. With these knowledges, we proposed a design principle of retroffitting 2D Fe-based MOFs into 3D analog to achieve highly conductive MOFs. This study contributes a fundamentally new perspective for the design of next-generation conductive metal–organic materials
Simulation of defects in molecular materials using ab initio methods
Get PDFMolecular materials such as metal-organic frameworks (MOFs) are emerging as an interesting class of materials for their wide range of applications as well as their customizability and tunability. Like other materials, the properties of molecular materials can be modified through the use of defects - however, the nature of these defects in these systems can be much more complex than in conventional materials. Because of this, modifying conventional computational methods is essential for understanding defects in these systems. This research addresses the limitations of traditional approaches by refining techniques for calculating chemical potentials and employing higher levels of theory, such as many- body perturbation theory (MBPT), to model the unique electronic structures of MOFs. These modifications attempt to account for the intricate chemical environments, large unit cells, and significant structural dynamics inherent to molecular materials. We propose that chemical potentials for defects should be calculated based on the reactions that form the defects, thereby incorporating the thermodynamics of covalent bond formation and cleavage, as opposed to referencing them to elemental phases and treating all atoms of a given species as thermodynamically equivalent. We also attempt to use MBPT to more accurately predict the electronic properties of these materials (thereby overcoming the underestimations of fundamental band gaps typical of simpler ab initio methods)which is essential to predict the stability of defects that these materials can host. Finally, a case study on Yttrium-based MOFs with HHTP linkers demonstrated the potential impact of defects and guest ions on conductivity, showcasing the practical implications of accurate defect modeling. Theoretical findings enhance the predictive power of computational methods for MOFs, informing material design and optimization for applications in catalysis, gas storage, and electronic devices. This dissertation includes previously published coauthored material.2025-10-3
Antiaromaticity, s-Indacene, and Molecular Electronics
No full textAlmost 100 years ago, the publication of Hückel’s [4n +2] π-electrons rule for identifying aromatic compounds piqued the interest of theorists and experimentalists alike. F. London published his quantum theory of interatomic currents in aromatic compounds, commonly referred to as London diamagnetism only one year later. The idea in a nutshell, is that the delocalized ring current of π-electrons found in aromatic molecules behaves like a conductive metal wire. In the 1950’s R. Breslow, proposed the idea of antiaromatic [4n] π-electron molecules, (formally referred to as pseudo aromatic) as potentially much more conductive molecular wires. Significant developments in synthetic organic chemistry methodology and techniques over the last 75 years have facilitated the study and isolation of a multitude of antiaromatic and aromatic-antiaromatic hybrid molecules. The valuable molecular properties associated with this class of molecules (such as a small HOMO-LUMO gap, amphoteric redox properties, and low energy absorbance) has motivated further investigation due to their potential materials applications in organic electronics. Antiaromatic molecules have maintained a fundamentally interesting status within the chemistry community because they are extremely reactive, difficult to isolate, and possess interesting electronic properties. In this dissertation I will discuss conductive materials composed of organic molecules, conductivity as it applies to molecular circuits, molecular wires, the structure-property relationships of antiaromatic heterocycle-fused-s-indacene derivatives, and the synthesis and study of donor-acceptor heterocycles fused across s-indacene in a set of structural isomers. Chapter I is a historical review of conductive organic materials, electrical conduction in molecular wires, and explanation of the relationship between paratropic ring current strength and diradical character in antiaromatic molecules. Chapter II describes the synthetic methodology of s-indacene derivatives developed by the Haley lab, the effect of heterocycle fusion on the magnetic properties of s-indacene, and rationalization of such based on physical organic principals and the rule of topological charge stabilization. Chapter III details the synthesis and effects of asymmetric donor-acceptor heterocycle fusion on the s-indacene core and explains the potential impact of this work with reference to superconductivity. Chapter IV is a conclusion. This dissertation includes previously published and unpublished co-authored material
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
One-dimensional Magnus-type platinum double salts
Get PDFInterest in platinum-chain complexes arose from their unusual oxidation states and physical properties. Despite their compositional diversity, isolation of crystalline chains has remained challenging. Here we report a simple crystallization technique that yields a series of dimer-based 1D platinum chains. The colour of the Pt[superscript 2+] compounds can be switched between yellow, orange and blue. Spontaneous oxidation in air is used to form black P[superscript 2.33+] needles. The loss of one electron per double salt results in a metallic d[subscript z[superscript 2]] state, as supported by quantum chemical calculations, and displays conductivity of 11 S cm[superscript −1] at room temperature. This behaviour may open up a new avenue for controllable platinum chemistry.Japan. Ministry of Education, Culture, Sports, Science and Technology (Grant-in-Aid for Scientific Research on Priority Areas)World Premier International Research Center Initiative (WPI) (International Institute for Carbon Neutral Energy Research. Grant WPI-I2CNER)European Research Council (Grant 277757)Royal Society (Great Britain)National Science Foundation (U.S.) (Extreme Science and Engineering Discovery Environment. Grant ACI-1053575
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
