Browsing by Department "Chemistry"

Now showing 1 - 20 of 42

A Multiscale Approach to Magnesium Intercalation Batteries: Safer, Lighter, and Longer-Lasting: Justin Andrews
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/219; NASA-Washington
1. EXECUTIVE SUMMARY: Research Goal: The goal of this research has been to design and develop the basic building blocks of inherently safer electrochemical energy storage vectors as replacements for conventional Li-ion batteries. A focus was placed on exploring metastable phase space to identify viable vanadium oxide cathode materials that are capable of reversibly inserting multivalent ions and Li ions from aqueous electrolytes. These materials have been developed with an eye towards the design of all-printed batteries. Brief Background and Motivation: Lithium-ion batteries are the gold-standard for electrochemical energy storage due to their unrivaled combination of high voltage and exceptional specific and volumetric energy densities; however, the development of ‘beyond-Li-ion’ battery technologies has received considerable attention in an attempt to mitigate growing safety concerns, rising materials criticality constraints, and energy storage limitations enforced by the monovalency of the Li-ion. Safety issues in Li-ion batteries are derived from the intrinsic reactivity of Li and manifest in catastrophic failure arising from dendrite formation and1,2 thermal runaway,2,3 which are further exacerbated by the high flammability of most Li-ion battery electrolytes2. These safety problems are of great concern, particularly in applications, such as manned space flight, where safety and device endurance are paramount. The development of inherently safer battery technologies that do not compromise on energy storage capacity is thus an urgent imperative. In the case of Mg-ion batteries, it has been argued that the full realization of Mg batteries (i.e., an Mg battery which includes a metallic Mg anode) would enable significant improvements to both safety (e.g., it has been claimed that Mg is not dendrite forming, Mg has a higher melting point than Li thereby reducing the risk of thermal runaway)12 and energy storage density thereby making them safer, lighter and longer-lasting. Indeed, the projected improvements in the volumetric and specific energy densities enabled by this technological pivot would lead to transformational reductions in weight and volume of the packaged cells, relative to existing Li-ion cells, in principle establishing Mg batteries an immediately attractive alternative to Li-ion technology.19 However, the lack of suitable cathode materials capable of reversibly storing the highly polarizing Mg2+ (only a couple of viable oxide materials)17,20–25 has significantly stymied progress towards their full realization. In an effort to address this technological knowledge gap, this research has focused on leveraging the discovery of a successful ?-V2O5 Mg-ion cathode, a major breakthrough during the first year of this NASA NSTR fellowship, towards the development and optimization of additional cathode materials. A closed-loop design approach, has been implemented to elucidate cathode design principles based on experimental evaluation of V2O5 intercalation cathode materials and aided by first-principles calculations and synchrotron characterization techniques.20,26 This approach has led to the discovery of several new V2O5 polymorphs (?’-V2O5, ?-V2O5, ?-V2O5) that have exhibited promising results as cathode materials in Li-ion, multivalent ion, and aqueous Li-ion batteries. Attention has furthermore been given to scaling the synthesis of these materials to enable the design of large-scale prototypes. While this research has focused on the fundamental aspects of the chemistry of these materials it has also sought to achieve functional devices, with a focus on 3D printing of these materials for the design of flexible batteries.
A New Cryo-Ion Mobility Spectrometer for Studies of Biomolecule Hydration
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/527; National Science Foundation
With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor David Russell at Texas A&M University is developing a novel instrument to study charged species surrounded by a few water molecules. The instrument being developed is called cryo-ion mobility-mass spectrometer (c-IM-MS) and it can determine the size and structure of the charge species by monitoring how they fly in a long tube under an extreme low temperature. Professor Russell's study are providing information to help understand the role of water molecules in affecting protein structure and function, especially those in direct contact with proteins. The gained knowledge will ultimately enable better understanding of many important biological and chemical questions, such as how antifreeze proteins protect plants and fish living in cold climates. The students working on this project have the opportunity to gain experience for both instrument building and biomolecule studies. The instrument design will be shared with other scientists in the field so the to-be-developed approach can be widely used to answer structural questions about how proteins and other biomolecules behave in water. During the past decade, the Russell laboratory has developed several prototype c-IM-MS instruments and described proof-of-concept studies that illustrate the unparalleled capabilities of the c-IM-MS instrument. The ability to experimentally observe structural changes that are a function of the extent of hydration is critical for establishing structure/function relationships. Such studies compliment the rapid growth in computational studies of biomolecule structure/function relationships---the ability to draw correlations between theoretical and experimental results. In this project, Professor Russell focuses on the design of the next-generation instrument by incorporating a number of recent technological innovations to include studies of larger proteins and protein complexes. He evaluates the overall instrument performance in terms of ion transmission and effects on ion dehydration and benchmark instrument performance against existing MS analyzers. The ultimate goals are to develop an instrument that is capable of better understanding peptide-water interactions and answering questions such as how does hydration affect peptide conformational preferences, and how does the peptide alter the structure of water.
Applications of Carbon-Fluorine Bond Activation by Main Group Electrophilic Catalysts to PFAS Remediation
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/458; DOD-Navy-Naval Research Laboratory
Significantly fluorinated triarylmethyl cations have long attracted attention as potentially accessible highly reactive carbocations, but their isolation in a convenient form has proved elusive. We show that abstraction of chloride with a cationic silylium reagent leads to the facile formation of di-, tetra-, and hexafluorinated trityl cations, which could be isolated as analytically pure salts with the [HCB11Cl11] counterion and are compatible with (halo)arene solvents. The F6Tr+ cation carrying six meta-F substituents was computationally predicted to possess up to 20% higher hydride affinity than the parent triphenylmethyl cation Tr+. We report that indeed F6Tr+ displays reactivity unmatched by Tr+. F6Tr+ at ambient temperature abstracts hydrides from the C–H bonds in tetraethylsilane, mesitylene, methylcyclohexane, and catalyzes Friedel–Crafts alkylation of arenes with ethylene, while Tr+ does none of these.
CAREER: Conformational Control of pi-Conjugated Polymeric Materials Through Dynamic Bonds
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
NON-TECHNICAL SUMMARY This project aims to investigate the fundamental correlation between the geometry of electrically semiconducting polymer molecules and their corresponding materials properties. Most polymeric molecules possess structural flexibility at the nanometer and subnanometer scales, which leads to various 3D shapes that they can adopt. Such geometric variability impacts a wide range of polymer properties that are important for their applications, especially those related to electronic and optical properties. Precision control of the molecular shapes of semiconducting polymers, however, has been a long-standing scientific challenge. This CAREER project tackles this problem by synthesizing molecules with reversible and controllable interactions between different segments along the polymer chain. Through this approach, planarized geometries of these polymer molecules can be enforced and disrupted on demand, leading to tailored properties as a result of the switchable molecular shapes. Establishment of this structural control may not only enable the access of improved functional performance, but also allow for feasible processing of polymer materials into application-relevant forms. In addition, the knowledge gained in this project will advance fundamental understanding in materials-related sciences and benefit multiple research disciplines and STEM education. The educational component of this program focuses on connecting scientific concepts and real-world personal knowledge for the students through relevant experiments in the lab and immersive learning experiences. The societal impacts of this project include benefits from scientific publications, new course components, educational software, and trained STEM students for academia and industry. TECHNICAL SUMMARY This program integrates research, education, and outreach activities under the overarching theme of functional polymer materials. Through a synergistic approach combining chemical synthesis, process engineering, and materials characterization, the research project seeks to establish clear fundamental correlations between controlled torsional conformation and materials properties of pi-conjugated systems. This plan is driven by the underlining hypothesis that active control over torsional conformation can significantly impact polymer properties and processability. The key strategy to achieve this objective is the incorporation of controllable intramolecular dynamic bonds into polymer backbones. A systematic design principle to the synthesis and process engineering of such polymers will be developed on the basis of theoretical simulations and experimental feedback. Structure-property relationships of these materials will be investigated through iterative design-test-feedback-optimization cycles. The ultimate goal is to draw a clear structure-property correlation and to establish design principles for tailoring the integrated properties of conjugated polymeric materials. In parallel, educational and outreach activities are planned to enhance chemistry and broad STEM learning outcome synergistically with the research program. The pedagogical focus is to make the essential connections between scientific knowledge and real-life experiences for the next generation of STEM students through an integrated plan combining course development, undergraduate research programs and outreach activities.
Cationic Gold-Antimony Complexes: Synthesis and Electrophilic Properties
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/224; National Science Foundation
A catalyst is a substance that speeds or otherwise facilitates a chemical reaction. Catalysts are critical to the chemical and pharmaceutical industries, where they are used to reduce the energy required for chemical reactions and to guide the details of precise chemical transformations. While gold is an expensive element, many catalysts incorporate it. Improving gold catalysts is an important area of investigation. In this project, funded by the Chemical Synthesis Program of the Chemistry Division, Professor Francois Gabbai of the Department of Chemistry at Texas A&M University seeks to improve the catalytic properties of gold by combining it with antimony, a non-metallic element. The antimony is able to combine with gold in a way that enhances gold's reactivity. The gold-antimony compounds that are isolated are developed into catalysts for the activation of alkenes, which are major chemical industry feedstocks. Professor Gabbai participates in outreach programs to K-6 students in Spanish/English dual language programs in order to interest young students in science and technology. This research project investigates the chemistry of gold (Au) complexes featuring ambiphilic ligands comprised of two phosphine donors and an antimony moiety. The central objective is to determine if the charge of the antimony (Sb) ligand can be used to modulate the electrophilic character and catalytic properties of the gold center. A series of dinuclear complexes with a gold atom held in close proximity to a pentavalent antimony center are synthesized and ligand abstraction reactions generate complexes in which the pentavalent antimony center is either monocationic or dicationic. Structural, spectroscopic and computational studies indicate if the accumulation of positive character on the antimony ligand promotes a donor-acceptor Au-Sb interaction. A correlation between the charge of the antimony ligand and the electrophilic reactivity of the gold center is indicated by the catalytic activation of alkenes in polymerization and hydroamination reactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Cationic Gold-Antimony Complexes: Synthesis and Electrophilic Properties
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/224; National Science Foundation
A catalyst is a substance that speeds or otherwise facilitates a chemical reaction. Catalysts are critical to the chemical and pharmaceutical industries, where they are used to reduce the energy required for chemical reactions and to guide the details of precise chemical transformations. While gold is an expensive element, many catalysts incorporate it. Improving gold catalysts is an important area of investigation. In this project, funded by the Chemical Synthesis Program of the Chemistry Division, Professor Francois Gabbai of the Department of Chemistry at Texas A&M University seeks to improve the catalytic properties of gold by combining it with antimony, a non-metallic element. The antimony is able to combine with gold in a way that enhances gold's reactivity. The gold-antimony compounds that are isolated are developed into catalysts for the activation of alkenes, which are major chemical industry feedstocks. Professor Gabbai participates in outreach programs to K-6 students in Spanish/English dual language programs in order to interest young students in science and technology. This research project investigates the chemistry of gold (Au) complexes featuring ambiphilic ligands comprised of two phosphine donors and an antimony moiety. The central objective is to determine if the charge of the antimony (Sb) ligand can be used to modulate the electrophilic character and catalytic properties of the gold center. A series of dinuclear complexes with a gold atom held in close proximity to a pentavalent antimony center are synthesized and ligand abstraction reactions generate complexes in which the pentavalent antimony center is either monocationic or dicationic. Structural, spectroscopic and computational studies indicate if the accumulation of positive character on the antimony ligand promotes a donor-acceptor Au-Sb interaction. A correlation between the charge of the antimony ligand and the electrophilic reactivity of the gold center is indicated by the catalytic activation of alkenes in polymerization and hydroamination reactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria
CDS&E: Cyclic Tetrapeptide Probes for Protein Binding
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/216; National Science Foundation
With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Kevin Burgess of Texas A & M University to discover small molecules that affect how some proteins bind to each other. Protein-protein interactions are important to many biological processes in cells. Thus having small molecules that can either aid or or hinder protein-protein interactions could lead to potential new drugs to help treat various diseases. The project is creating new small molecules and studying their effect on protein-protein interactions. It also combines chemical synthesis, computer-aided molecular design and data-mining training for graduate and undergraduate students to help them tackle problems in contemporary life science. Cyclic peptides are known to mimic key regions involved in protein-protein interactions, i.e. to be Protein-Protein Interface (PPI) mimics. While cyclic pentapeptides are easy to make they tend to equilibrate between conformers. Conversely cyclic tetrapeptides from natural amino acids are difficult to make but are more conformationally stable. Thus, easily synthesized cyclic peptides from genetically encoded amino acids linked by main-chain amides can have ring sizes of 9, 12, 15, etc. i.e. 3n atoms, (n = # amino acids) which misses ring sizes between 12 and 15 that combine conformational rigidity with ease of synthesis. This work is showing that contrary to some earlier reports, cyclic Tetrapeptides from natural amino acids are conformationally rigid and are more synthetically accessible than previously thought. It is also showing that replacement of a genetically encoded residue with some rigid unnatural amino acids can be used to give cyclic tetrapeptides that rest at a useful crossroads between ease of synthesis and conformational rigidity.
CLAP-seq: An Aptamer-Based Platform for Transcriptome-Wide Mapping of RNA Modifications
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/200; DHHS-NIH-Eunice Kennedy Shriver National Institute of Child Health & Human Development
Project Summary/Abstract Beginning in the 1950s, more than 100 types of posttranscriptional modifications have been identified in cellular RNA. Today, the study of RNA post-transcriptional modifications – known as epitranscriptomics – is a rapidly developing field, which promises to greatly enhance our understanding of human health and disease. Despite the profound implications already assigned to many RNA modifications, their precise functions remain poorly understood. This can be attributed to the lack of sensitive and robust sequencing technologies to detect these epitranscriptomics marks in a transcriptome-wide manner. A key bottleneck is the lack of sensitive and specific enrichment techniques (affinity- or reactivity-based) for RNA molecules containing these modifications. The proposed research takes direct aim at this critical deficit using the aptamer approach, employing in vitro selection methods to identify nucleic acid molecules that bind chemically modified RNAs. These aptamers are unique in that they are comprised of L-(deoxy)ribose-based nucleic acids (L-DNA and L-RNA), which are mirror images (enantiomers) of natural D-nucleotides. L-Aptamers, which are completely orthogonal to natural biology, are extremely well suited for binding RNA targets. Therefore, in vitro selection will be used to isolate novel L- aptamers capable of binding chemically modified mononucleotides, which will enable selective capture of RNA molecules containing the same modified residue. These L-aptamers will then be used in Cross-Linking- Aptamer Pull-down and sequencing (CLAP-seq), the first transcriptome-wide profiling technology employing aptamer-based RNA enrichment prior to next-generation sequencing. CLAP-seq not only promises to open a general and robust route towards transcriptome-wide profiling of the growing list of RNA modifications, but also promises to reinforce our current view of the epitranscriptome. Accordingly, the development of CLAP-seq will have a profound impact on the field of epitranscriptomics, which is well aligned with the mission of the NICHD and the goal of this FOA: to promote research into the role of RNA chemical modifications in development and related disease.
Collaborative Research: Understanding and Tuning the Molecular Arrangement and Charge Storage Properties of Textured Graphene-Ionic Liquid Interface
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/223; National Science Foundation
Non-technical summary With the ever-increasing need for electrical power on demand, next generation energy storage devices (batteries and supercapacitors) must be designed that can support higher energy densities than current technologies. Therefore, new electrolyte and electrode materials must be explored that allow for higher electrolyte packing densities. To improve electrode/electrolyte interfaces, this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, seeks to understand how the structure of ionic liquids and their arrangement at electrode interfaces may be tuned by precisely controlling electrode geometry on the nanoscale. Single-layer graphene, a carbon-based material, just one-atom thick, which can function as a conductive electrode that is highly flexible, is used to created textured electrodes for this study. The research team investigates the influence of the electrode morphology on the organization of the ionic liquid electrolyte and how it impacts charge storage. In addition to exploring these fundamental science questions, this project supports the education and training of undergraduate and graduate students from diverse backgrounds, at the intersection of materials and surface science, contributing to the development of the energy sector work force in the U.S., by training students in cross-cutting research in a coordinated collaborative environment between the labs of the principle investigators at UIUC and TAMU. Technical summary With this grant, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, the principle investigators (Espinosa-Marzal at UIUC and Batteas at TAMU) test the fundamental hypothesis that by controlling surface morphology and substrate-induced charge doping, along with the chemical composition of the ionic liquids, the local packing density of the liquid on graphene can be precisely modulated. This in turn is expected to afford better control over their charge storage properties. To fill the outlined knowledge gap, the team pursues three major lines of research. New methods to prepare graphene surfaces with precisely controlled charge doping and morphology from the atomic to the nanoscale are developed. In addition, the effects of substrate morphology and charge doping on the interfacial structure of ionic liquids and on the characteristics of the electrical double layer are investigated by Atomic Force Microscopy in an electrochemical cell. Furthermore, local and global electrochemical impedance spectroscopy are used to relate the electrical double layer to the differential capacitance of the textured interfaces. These studies allow determining the relative contributions of graphene roughness, charge doping and ionic liquid composition on the electrical double layer and its capacitance. The knowledge gained from this project is expected to enable control of the interfacial assembly of the liquids and stored charge through the modulation of the graphene texture. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Understanding and Tuning the Molecular Arrangement and Charge Storage Properties of Textured Graphene-Ionic Liquid Interface
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/606; National Science Foundation
Non-technical summary With the ever-increasing need for electrical power on demand, next generation energy storage devices (batteries and supercapacitors) must be designed that can support higher energy densities than current technologies. Therefore, new electrolyte and electrode materials must be explored that allow for higher electrolyte packing densities. To improve electrode/electrolyte interfaces, this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, seeks to understand how the structure of ionic liquids and their arrangement at electrode interfaces may be tuned by precisely controlling electrode geometry on the nanoscale. Single-layer graphene, a carbon-based material, just one-atom thick, which can function as a conductive electrode that is highly flexible, is used to created textured electrodes for this study. The research team investigates the influence of the electrode morphology on the organization of the ionic liquid electrolyte and how it impacts charge storage. In addition to exploring these fundamental science questions, this project supports the education and training of undergraduate and graduate students from diverse backgrounds, at the intersection of materials and surface science, contributing to the development of the energy sector work force in the U.S., by training students in cross-cutting research in a coordinated collaborative environment between the labs of the principle investigators at UIUC and TAMU. Technical summary With this grant, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, the principle investigators (Espinosa-Marzal at UIUC and Batteas at TAMU) test the fundamental hypothesis that by controlling surface morphology and substrate-induced charge doping, along with the chemical composition of the ionic liquids, the local packing density of the liquid on graphene can be precisely modulated. This in turn is expected to afford better control over their charge storage properties. To fill the outlined knowledge gap, the team pursues three major lines of research. New methods to prepare graphene surfaces with precisely controlled charge doping and morphology from the atomic to the nanoscale are developed. In addition, the effects of substrate morphology and charge doping on the interfacial structure of ionic liquids and on the characteristics of the electrical double layer are investigated by Atomic Force Microscopy in an electrochemical cell. Furthermore, local and global electrochemical impedance spectroscopy are used to relate the electrical double layer to the differential capacitance of the textured interfaces. These studies allow determining the relative contributions of graphene roughness, charge doping and ionic liquid composition on the electrical double layer and its capacitance. The knowledge gained from this project is expected to enable control of the interfacial assembly of the liquids and stored charge through the modulation of the graphene texture. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Directing Charge Transport in Hierarchical Molecular Assemblies
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/606; National Science Foundation
In this project funded by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professor James Batteas of the Texas A & M University and Professor Charles Drain of Hunter College of the City University of New York study the molecular assembly and electron transport properties of molecules that might help in electronic device miniaturization. Moore's Law, which has held for the last four decades, states that the density of transistors on an electronic device "chip" will double approximately every two years, making electronic devices smaller, faster and more powerful. A pressing question is whether Moore's Law will continue into the future or has it reached its fundamental limits. Professors Batteas and Drain study metal-organic complexes known as porphyrinoids, found in nature as the active component of hemoglobin and chlorophyll, to aid in these developments. They design, synthesize and evaluate the conductive properties of porphyrinoids assembled into specific structures on surfaces. Using imaging techniques such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM), the team can place individual molecules into precise arrangements on surfaces and measure not only their assembled structure at the molecular level but also how the structure controls the movement of electrons through the molecules. This research has broader impacts in science and technology, and enables the rational design of potential molecular electronic devices, including enhanced photovoltaics, chemical sensors and molecular electronics. The team also trains students, for broader impacts in education, in fundamental materials chemistry, preparing them for the 21st century high technology jobs sector. Professor Batteas and Professor Drain study how to design, synthesize and evaluate the conductive properties of porphyrinoids assembled on metal surfaces with an eye toward the implementation of hybrid molecular-based devices for photonics applications, including enhanced photovoltaics, chemical sensors and molecular based electronics. The electroactive properties and self-assembly of robust porphyrinoids can be readily tuned through chemical synthesis using simple high yield reactions that facilitate commercial viability, making them attractive targets to be integrated as active components in electronic devices. In this project porphryinoids are assembled on Au surfaces in precise architectures via a combination of nanolithography and directed click-chemical reactions to create nanoscopic assemblies of less than 10 nm in lateral dimension. Characterization methods (time resolved florescence, UV-visible absorption, STM and AFM) are applied to understand how local molecular interactions influence electron transport properties in small molecule assemblies, how spatial confinement of molecules on a surface influence their resulting assembly process and the structures that can be formed, and how the assembled architectures control electron transport. Broader impacts of the research result in an improved fundamental understanding of the assembly and electron transport properties of the porphryiods, with potential to influence molecular electronic device and solar light harvesting applications. Broader impacts through education and outreach incorporate aspects of the work, including atomic scale imaging, nanolithography, molecular self-assembly and nanoscale electronics, into demonstrations for elementary school students as part of a weeklong summer camp on Nanotechnology (at Texas A&M University), and into the undergraduate and graduate classrooms at Texas A&M University and CUNY Hunter College.
Collaborative Research: Synthesis and Rigidity Quantification of Ladder Polymers with Controlled Structural Defects
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professors Lei Fang of Texas A&M University and Xiaodan Gu of University of Southern Mississippi are investigating how chain flexibility influences the physical properties of conjugated ladder polymers. Conjugated polymers are a unique class of non-metallic polymers with semiconducting properties resembling that of the chemical element silicon. These long chain carbon-based molecules can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). Conjugated polymers are extensively used in solar cells, LED screens and other applications that utilize the conversion of electricity to light. Ladder polymers, on the other hand, are a type of double stranded polymers with the connectivity of a ladder. This is achieved by interconnecting repeating units along the main polymer chain by four chemical bonds, instead of the two bonds typically seen in conventional plastics. In this research, conjugated ladder polymers with varied structural features are synthesized. Control polymers are prepared with deliberately introduced backbone defects that consist of small molecules. Detailed studies are then conducted to correlate backbone composition and length with the flexibility of the polymer chains. These studies are enabled by employing neutron and light scattering techniques which provide accuracy at lengths ranging from sub 1 nanometer (1/100,000 of human hair diameter) to well beyond 10 micrometers (the width of cotton fiber). Correlations established as a result of this work may provide knowledge that could lead to the development of materials with better optical and electronic performance. Educational innovation tackles the problems associated with outdated contents in undergraduate organic chemistry laboratory courses. The newly designed ?Nobel Prize Reactions? are first implemented at both universities and then disseminated at national and international scales. Outreach activities expose undergraduate and high school students to modern chemical research. This work is specifically designed to benefit a large number of underrepresented minorities and economically disadvantaged students in Mississippi. The primary goal of this research is to establish the fundamental correlations between backbone constitution and the chain rigidity for rigid ladder conjugated polymers. The research is conducted through the design and synthesis of model ladder polymers with varied structural features, and controls with deliberately introduced backbone defects, followed by quantitative evaluation of their chain persistence length and correlation with structural features. Chain rigidity of the ladder polymer models and controls is quantified using combined modern characterization tools with an emphasis on neutron and light scattering. Studies are also performed to understand the influence of chain bending energy on persistent length for ladder polymers. Comprehensive structural-rigidity correlation through iterative design-synthesis-measurement-design cycles is established. Results associated with this award have the potential to advance knowledge on how the chain rigidity (or flexibility) determines the fundamental properties and practical applications of a wide range of polymers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Synthesis and Rigidity Quantification of Ladder Polymers with Controlled Structural Defects
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/236; National Science Foundation
With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professors Lei Fang of Texas A&M University and Xiaodan Gu of University of Southern Mississippi are investigating how chain flexibility influences the physical properties of conjugated ladder polymers. Conjugated polymers are a unique class of non-metallic polymers with semiconducting properties resembling that of the chemical element silicon. These long chain carbon-based molecules can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). Conjugated polymers are extensively used in solar cells, LED screens and other applications that utilize the conversion of electricity to light. Ladder polymers, on the other hand, are a type of double stranded polymers with the connectivity of a ladder. This is achieved by interconnecting repeating units along the main polymer chain by four chemical bonds, instead of the two bonds typically seen in conventional plastics. In this research, conjugated ladder polymers with varied structural features are synthesized. Control polymers are prepared with deliberately introduced backbone defects that consist of small molecules. Detailed studies are then conducted to correlate backbone composition and length with the flexibility of the polymer chains. These studies are enabled by employing neutron and light scattering techniques which provide accuracy at lengths ranging from sub 1 nanometer (1/100,000 of human hair diameter) to well beyond 10 micrometers (the width of cotton fiber). Correlations established as a result of this work may provide knowledge that could lead to the development of materials with better optical and electronic performance. Educational innovation tackles the problems associated with outdated contents in undergraduate organic chemistry laboratory courses. The newly designed ?Nobel Prize Reactions? are first implemented at both universities and then disseminated at national and international scales. Outreach activities expose undergraduate and high school students to modern chemical research. This work is specifically designed to benefit a large number of underrepresented minorities and economically disadvantaged students in Mississippi. The primary goal of this research is to establish the fundamental correlations between backbone constitution and the chain rigidity for rigid ladder conjugated polymers. The research is conducted through the design and synthesis of model ladder polymers with varied structural features, and controls with deliberately introduced backbone defects, followed by quantitative evaluation of their chain persistence length and correlation with structural features. Chain rigidity of the ladder polymer models and controls is quantified using combined modern characterization tools with an emphasis on neutron and light scattering. Studies are also performed to understand the influence of chain bending energy on persistent length for ladder polymers. Comprehensive structural-rigidity correlation through iterative design-synthesis-measurement-design cycles is established. Results associated with this award have the potential to advance knowledge on how the chain rigidity (or flexibility) determines the fundamental properties and practical applications of a wide range of polymers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Design and Testing of Math Models of Iron Trafficking and Regulation in Eukaryotes
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/415; National Science Foundation
Iron is an essential micronutrient of eukaryotic cells. It is required to generate most of the chemical energy in our bodies. Iron-bound enzymes catalyze hundreds of reactions in cells, including processes as fundamental as DNA replication and repair. In this project, the principal investigator's aim is to develop mathematical models that simulate the movement of iron in eukaryotic cells and to investigate how that iron is regulated by cells. Like cars driving into a city at rush-hour, iron "traffic" occurs on different pathways in the main cytosol region of the cell, and different iron species end up at different locations in the cell such as in mitochondria, the nucleus, or other organelles. The cell regulates these traffic patterns so it can survive and prosper under various environmental situations (too much iron or too little iron). However, the details of this regulation - at the level of molecules - are poorly understood. In this project, the investigator's main objective is to develop a comprehensive math model that accounts for all of the iron-containing species in the cell that will help explain complex iron "traffic" within cells. As part of the broader impacts of the project, the PI will engage graduate and undergraduate students, including members of underrepresented groups in science, in interdisciplinary research training. The PI will also develop a website offering free downloads, sample data and video tutorials related to the project. The overall objective of this project is to develop molecular-level mechanistically-based math models of iron trafficking and regulation that can simulate the comprehensive iron content and iron-based reactivity of a yeast cell. The PI will construct a model that accounts for iron in the cytosol, mitochondria, vacuoles, ER/Golgi, nuclei, and cell wall. The ordinary-differential-equations-based models will reflect all of the ca. 120 iron-containing species in yeast cells, with species being represented as groups of aggregated components. Models will share "housekeeping" processes but each model will have a unique emphasis that will be expanded in detail. In developing the models, the investigator will focus on: a) respiration and reactive oxygen species; b) cytosolic iron metabolism (involving the cytosolic iron sulfur cluster assembly (CIA) and iron-related chemistry in the nucleus; c) mitochondrial iron-sulfur and heme chemistry; d) nutrient iron import and metabolism; e) iron homeostasis and regulation. Each model will be optimized in terms of kinetic parameters against experimental data obtained in the PI's lab or elsewhere. Models will be tested by determining whether predictions made by the model (e.g. the effects of deleting or overexpressing a gene related to iron metabolism) are realized experimentally. Models will also guide the design of new experiments, generating a unique synergy between experiments and modeling that will advance our understanding of the cell biology of iron metabolism. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Development of Polycarbonate Micelles for Encapsulation of Dinitrosyl Iron and Diiron Hydrogenase Biomimetics
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/431; National Science Foundation
Nature often encapsulates highly reactive molecules within an environment that offers protection from unwanted reactions. The goal of this research is to prepare similar encapsulation devices (micelles) that are made from plastics and are capable of protecting their pharmaceutical drug "cargoes" until they reach their destination in the human body. This project is funded by the Chemical Synthesis Program of the Chemistry Division. Professors Marcetta Y. Darensbourg and Donald J. Darensbourg of Texas A&M University are preparing the plastic micelles from the abundant gas, carbon dioxide. Since the micelles are biodegradable, they fall apart in living organisms and slowly release their drug cargo. One of the specific systems to be investigated involves entrapping nitric oxide (NO)-releasing drugs. Nitric oxide is implicated in vasoregulation and immune function. The broader impact of this work is to heighten students' awareness of the roles chemists play in issues of societal importance, like medicine. Professor Marcetta Darensbourg and her group are leaders in programs such as Women in Science and Engineering, Broadening Horizons for 6th Grade Girls, and the Chemistry Olympiad. These activities reach out to school children in the Bryan/College Station communities. Professor Donald Darensbourg focuses on carbon dioxide utilization and its impacts on carbon management. He develops courses and education materials on Green Chemistry for advanced undergraduates in chemistry and chemical engineering. This project focuses on the preparation of triblock, "ABA", polycarbonates that, on addition of water, self-assemble into micelles as the A blocks are hydrophilic and the B blocks are hydrophobic. The hydrophobic interiors of the micelles are loaded with molecular payloads of pharmaceutical potential, binding either by non-covalent van der Waals interactions or by covalent attachment. Syntheses and full characterization of the polymers are conducted. The protection of reactive NO-release drugs within the hydrophobic region of a biodegradable micelle may tune and control NO delivery in biological/pharmaceutical applications. Chemical assays and cell studies (cytotoxicity and cell uptake) test this assumption and compare dinitrosyl iron complexes of NO release ability in solution and imbedded within the micelles. Further, the synthesis of polymer immobilized diiron complexes, linked by cyanide to metallo-porphyrin photosensitizers are oriented towards development as hydrogen production catalysts, initially in the absence of water. The research team looks for the stabilization of the fragile diiron or nickel-iron complexes by attachment to (organic solvent) soluble polymers, generating base metal, organometallic catalysts protected from oxygen degradation and aggregation.
DMREF: Collaborative Research: A Blueprint for Photocatalytic Water Splitting: Mapping Multidimensional Compositional Space to Simultaneously Optimize Thermodynamics and Kinetics
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/219; National Science Foundation
NON-TECHNICAL DESCRIPTION: Sunlight is a vast source of renewable energy but its intermittent nature means that its utilization requires a means of storing this energy. One attractive approach for solar energy storage is to harness the energy of sunlight to split water into hydrogen and oxygen i.e. solar generated fuels. The solar generated fuels can be combusted to release energy efficiently with water as the only by-product. As a result, this approach avoids the deleterious consequences of greenhouse emissions that accompany the combustion of conventional fossil fuels. The complex cascade of reactions required to harvest sunlight and split water into hydrogen and oxygen present a formidable scientific challenge. The project seeks to develop hybrid materials as the catalyst for water splitting, such that individual components are assembled and function synergistically. The project further works towards employing components that are highly tunable in terms of their energy levels, thereby providing a versatile platform that can be optimized for converting sunlight and water into fuel. Employing a judicious mix of calculations from supercomputers and selective experiments accelerates the rationally design of materials for efficient solar energy storage within chemical bonds. The project team mentors young scientists from underrepresented groups and engages K-12 students and teachers in activities that emphasize the opportunities made available by big data and solar energy. TECHNICAL DESCRIPTION: The project explores the design of programmable heterostructured platforms for photocatalytic water splitting based on interfacing ternary vanadium oxide bronzes with semiconductor quantum dots. In the former compounds, metal cations are intercalated within a variety of open vanadium oxide frameworks, enabling a multitude of compositional possibilities and considerable energy level tuning. Moreover, the energy levels of quantum dots can also be tuned as a function of composition as well as size and the presence of cores. Photocatalytic water splitting requires not just the appropriate alignment of energy levels but also precise control of charge transfer dynamics. Interfacing two versatile and tunable components yields a rich multidimensional space for identification of effective photocatalytic architectures for water oxidation that yield holes at potentials only minimally positive to the water oxidation potential, thereby allowing for efficient conversion of sunlight to solar fuels. The multidimensional parameter space is mapped through a closely integrated and iterative combination of first-principles structure prediction, electronic structure calculations, diversified materials synthesis, detailed spectroscopy, high-throughput screening, and big data analytics. The activity involves development of an open-source platform for statistical analysis and mining of spectroscopic data. A summer research activity engages undergraduates from diverse backgrounds.
DMREF: Collaborative Research: A Blueprint for Photocatalytic Water Splitting: Mapping Multidimensional Compositional Space to Simultaneously Optimize Thermodynamics and Kinetics
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/219; National Science Foundation
NON-TECHNICAL DESCRIPTION: Sunlight is a vast source of renewable energy but its intermittent nature means that its utilization requires a means of storing this energy. One attractive approach for solar energy storage is to harness the energy of sunlight to split water into hydrogen and oxygen i.e. solar generated fuels. The solar generated fuels can be combusted to release energy efficiently with water as the only by-product. As a result, this approach avoids the deleterious consequences of greenhouse emissions that accompany the combustion of conventional fossil fuels. The complex cascade of reactions required to harvest sunlight and split water into hydrogen and oxygen present a formidable scientific challenge. The project seeks to develop hybrid materials as the catalyst for water splitting, such that individual components are assembled and function synergistically. The project further works towards employing components that are highly tunable in terms of their energy levels, thereby providing a versatile platform that can be optimized for converting sunlight and water into fuel. Employing a judicious mix of calculations from supercomputers and selective experiments accelerates the rationally design of materials for efficient solar energy storage within chemical bonds. The project team mentors young scientists from underrepresented groups and engages K-12 students and teachers in activities that emphasize the opportunities made available by big data and solar energy. TECHNICAL DESCRIPTION: The project explores the design of programmable heterostructured platforms for photocatalytic water splitting based on interfacing ternary vanadium oxide bronzes with semiconductor quantum dots. In the former compounds, metal cations are intercalated within a variety of open vanadium oxide frameworks, enabling a multitude of compositional possibilities and considerable energy level tuning. Moreover, the energy levels of quantum dots can also be tuned as a function of composition as well as size and the presence of cores. Photocatalytic water splitting requires not just the appropriate alignment of energy levels but also precise control of charge transfer dynamics. Interfacing two versatile and tunable components yields a rich multidimensional space for identification of effective photocatalytic architectures for water oxidation that yield holes at potentials only minimally positive to the water oxidation potential, thereby allowing for efficient conversion of sunlight to solar fuels. The multidimensional parameter space is mapped through a closely integrated and iterative combination of first-principles structure prediction, electronic structure calculations, diversified materials synthesis, detailed spectroscopy, high-throughput screening, and big data analytics. The activity involves development of an open-source platform for statistical analysis and mining of spectroscopic data. A summer research activity engages undergraduates from diverse backgrounds.
DMREF: Collaborative Research: Interface-promoted Assembly and Disassembly Processes for Rapid Manufacture and Transport of Complex Hybrid Nanomaterials-
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/598; National Science Foundation
NON-TECHNICAL DESCRIPTION: The intimate combination of inorganic nanoparticles and organic polymers within nanoscopic packages of controlled sizes and shapes includes many challenges with the processes for their production and many opportunities for unique materials properties. Organic polymers are typically considered as plastics and they have physical and mechanical properties that allow them to serve common roles, such as elastic materials (clothing, tents, parachutes, etc.), containment vessels (cups, plastic bags, etc.), and high technology needs, such as optical materials (eye glasses, OLED devices, etc.), engineering materials (airplane parts, football helmets, etc.), among many others. Inorganic nanoparticles are typically rigid and often possess characteristics of magnetism, optical signaling or catalytic reactivity. This project will develop computational methods to guide approaches to rapidly discover and manufacture hybrid inorganic-organic nanostructured objects (HIONs) possessing complexity of compositions, structures, properties and functions. TECHNICAL DESCRIPTION: The primary hypothesis driving our project is that the contrasting interactions of polymers vs nanoparticles vs HIONs with each other and with surfaces and flow fields in porous media and other designed interfaces can be harnessed to develop methods for scalable production. The assembly of organic polymers or inorganic particles or their co-assembly is usually conducted in either the solution state or in the bulk. Although simulations have guided polymer and particle assembly processes, this research activity adds the complexity of assembly/disassembly in a flow field and in an adaptive resolution solvent(s) model, and will elucidate how interfaces impact assembly/disassembly. Experimentally, HION assembly/disassembly at solution-solid substrate interfaces in a flow system or at solvent-solvent interfaces represent new frontiers. Only recently has incorporation of discrete nanoscale heterogeneity on surfaces been demonstrated to allow quantitative mechanistic prediction of particle retention on unfavorable surfaces, as well as mechanistic prediction of release in response to perturbations in solution ionic strength and fluid velocity. Ultimately, the primary goal is to be able to conduct high throughput, tunable manufacturing of complex HIONs that exhibit compositions, structures, morphologies and properties for diverse technological applications.
Enzymatic Hydrolysis of Organophosphate Esters
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/498; National Institutes of Health
The primary objective for the research described in this proposal is the elucidation of the chemical reaction mechanism and three-dimensional structure of a novel phosphotriesterase recently identified from the bacterium Spingobium sp. strain TCM1 (Sb-PTE). The high toxicity of many organophosphate triesters has been exploited as the active component in many commercial agricultural and household insecticides and as ultra-potent chemical warfare agents. Other, less toxic, organophosphate compounds have been widely utilized as flame retardants, plasticizers, and as prodrugs for viral infections. The catalytic properties and three-dimensional structure of the wild- type Sb-PTE are significantly different from those exhibited by the phosphotriesterase from Pseudomonas diminuta (Pd-PTE) or any other enzyme identified to date. We propose to utilize this enzyme as a template for the design and creation of new biological catalysts that can be exploited for the detection, destruction, and detoxification of toxic organophosphate nerve agents that are currently being used as agricultural and household insecticides, plasticizers, and chemical warfare agents. The chemical mechanism for this enzyme will be elucidated by determining the stereochemical course of the reaction with chiral substrates and by monitoring the fate of 18-oxygen labels in the substrate and enzyme. These experiments will be complemented by measurement of heavy atom isotope effects, determination of the substrate/activity profile, and the identification of potent enzyme inhibitors. In preliminary experiments we have succeeded in the crystallization of Sb-PTE and determination of its three dimensional structure by X-ray diffraction methods. Further structures will be pursued in a focused attempt to determine the mode of substrate binding within the active site of this enzyme. These structures will be utilized as a guide for the design and creation of novel enzyme variants with unique substrate profiles. Rational and combinatorial libraries of mutant enzymes will be constructed and those variants with enhanced catalytic proficiency for the hydrolysis of toxic organophosphates will be identified through unique screening and selection procedures. The changes in the amino acid sequence of the Sb-PTE mutants will be correlated with enhancements in the catalytic properties and alterations in the structure within the active site.
Evaluation of Trk Probes in Models for Dry Eye Disease
Chemistry; TAMU; https://hdl.handle.net/20.500.14641/216; DHHS-NIH-National Eye Institute
Evaluation Of Trk Probes In Models For Dry Eye Disease A. Project Summary In previous work, the PI designed small molecules that resemble turn regions in nerve growth factor (NGF) and in neurotrophin-3 (NT-3), for two reasons. First, ?-turn regions in the neurotrophins seem to be hot-spots for their interactions with the tropomyosin receptor kinase (Trk). Second, whereas neurotrophins activate both the Trk receptors and another receptor called p75, the small molecules should only activate the Trk receptors; this is important because activation of p75 has been associated with induction of apoptosis. In the event, several partial agonists were found, and one of them progress to phase 3 clinical trials (Mimetogen) for treatment of dry eye disease, and its fate as a pharmaceutical has yet to be decided. Most of the compounds prepared in that study, however, were not tested for applications in dry eye disease (they were just screened for properties as Trk ligands), and none of them were designed or tested for binding to TrkB (selective receptor for brain derived neurotrophic factor, BDNF). The central hypotheses of this proposal are that: (i) re-synthesis and testing of some of the original hit NGF and NT3 binding-compounds may afford other leads for treatment of dry eye disease; (ii) design principles similar to those used before could be enacted to obtain small molecule ligands that bind TrkB; and, (iii) side-by-side comparison of TrkA, B, and C probes in models for dry eye disease (cellular and in vivo) will reveal the relative impact of these compounds, and, by inference, the relative importance of stimulating those receptors in treatment of dry eye disease.