Synthesis, Behavior, and Applications of Molecules with Redox-Switchable Properties

Molecules with reversible, redox-switchable properties have potential application in many fields, including catalysis, electronics, waste remediation, and energy storage. To further this field, a detailed understanding of the relationship between chemical structure and electronic properties must be developed for different systems. Here, we first examine this relationship for phthalocyanines, a well-studied class of macrocyclic ligand. We first discuss generalized synthesis and characterization of a library of soluble, metal phthalocyanine species, and then proceed to investigate the electronic character of this macrocyclic ligand in extreme detail with modern experimental and computational methods, and discuss a fundamental discovery regarding a terminal manganese nitride phthalocyanine (EtOPcMnN) that is the first reported molecular species capable of reversibly switching between aromatic, non-aromatic, and anti-aromatic states. We then discuss possible reasons for the extreme stability of EtOPcMnN, and discuss more generalized conclusions pertaining to the electronic character of other phthalocyanines and related aromatic macrocycles.Further studies leverage the unusual stability of EtOPcMnN for energy storage applications, revealing a potential use as a symmetric redox-flow battery charge carrier. Electrochemical kinetics and battery measurements are performed, revealing that EtOPcMnN can function as a 2-electron symmetric charge carrier capable of functioning as both anolyte and catholyte in a redox flow battery. A new architecture for redox-flow batteries is also developed, in which a redox-active “sediment” is utilized in lieu of a traditional solution-state charge carrier, and represents a possible strategy for increasing charge carrier loading beyond the solubility limit while preventing the high viscosity typically associated with slurry-based systems.Finally, the redox-switchable properties of another class of ligand, carboranes, are examined for application as reversible chelating agents. It is demonstrated with a carborane phosphine species that redox events can be accessed to induce a C-C bond scission which results in a structural distortion of the carborane that can be utilized as a “molecular switch” capable of changing the bond angle of the phosphine ligands, resulting in a convenient electrochemical switch for the capture and release of metal ions. We demonstrate a proof-of-concept system in which uranyl can be electrochemically captured and released from biphasic systems in a reversible manner, and discuss the application of such systems for new nuclear waste remediation strategies

X-ray Diffraction of Functional Materials

Demand for advanced X-ray scattering techniques has increased tremendously in recent years with the development of new functional materials. These characterizations have a huge impact on evaluating the microstructure and structure–property relation in functional materials. Thanks to its non-destructive character and adaptability to various environments, the X-ray is a powerful tool, being irreplaceable for novel in situ and operando studies. This book is dedicated to the latest advances in X-ray diffraction using both synchrotron radiation as well as laboratory sources for analyzing the microstructure and morphology in a broad range (organic, inorganic, hybrid, etc.) of functional materials

Determining Material Structures and Surface Chemistry by Genetic Algorithms and Quantum Chemical Simulations

With the advent of modern computing, the use of simulation in chemistry has become just as important as experiment. Simulations were originally only applicable to small molecules, but modern techniques, such as density functional theory (DFT) allow extension to materials science. While there are many valuable techniques for synthesis and characterization in chemistry laboratories, there are far more materials possible than can be synthesized, each with an entire host of surfaces. This wealth of chemical space to explore begs the use of computational chemistry to mimic synthesis and experimental characterization. In this work, genetic algorithms (GA), for the former, and DFT calculations, for the latter, are developed and used for the in silico exploration of materials chemistry. Genetic algorithms were first theorized in 1975 by John Holland and over the years subsequently expanded and developed for a variety of purposes. The first application to chemistry came in the early 1990’s and surface chemistry, specifically, appeared soon after. To complement the ability of a GA to explore chemical space is a second algorithmic technique: machine learning (ML) wherein a program is able to categorize or predict properties of an input after reviewing many, many examples of similar inputs. ML has more nebulous origins than GA, but applications to chemistry also appeared in the 1990’s. A history perspective and assessment of these techniques towards surface chemistry follows in this work. A GA designed to find the crystal structure of layered chemical materials given the material’s X-ray diffraction pattern is then developed. The approach reduces crystals into layers of atoms that are transformed and stacked until they repeat. In this manner, an entire crystal need only be represented by its base layer (or two, in some cases) and a set of instructions on how the layers are to be arranged and stacked. Molecules that may be present may not quite behave in this fashion, and so a second set of descriptors exist to determine the molecule’s position and orientation. Finally, the lattice of the unit cell is specified, and the structure is built to match. The GA determines the structure’s X-ray diffraction pattern, compares it against a provided experimental pattern, and assigns it a fitness value, where a higher value indicates a better match and a more fit individual. The most fit individuals mate, exchanging genetic material (which may mutate) to produce offspring which are further subjected to the same procedure. This GA can find the structure of bulk, layered, organic, and inorganic materials. Once a material’s bulk structure has been determined, surfaces of the material can be derived and analyzed by DFT. In this thesis, DFT is used to validate results from the GA regarding lithium-aluminum layered double hydroxide. Surface chemistry is more directly explored in the prediction of adsorbates on surfaces of lithiated nickel-manganese-cobalt oxide, a common cathode material in lithium-ion batteries. Surfaces are evaluated at the DFT+U level of theory, which reduces electron over-delocalization, and the energies of the surfaces both bare and with adsorbates are compared. By applying first-principles thermodynamics to predict system energies under varying temperatures and pressures, the behavior of these surfaces in experimental conditions is predicted to be mostly pristine and bare of adsorbates. For breadth, this thesis also presents an investigation of the electronic and optical properties of organic semiconductors via DFT and time-dependent DFT calculations

The preparation of magnetic nanoparticle assemblies for biomedical applications

Magnetic nanoparticles and their assemblies are subjects of considerable scientific interest for basic research, but also for applications as contrast agents in magnetic resonance imaging (MRI) and for hyperthermia. Such applications depend on the production of stable suspensions of the particles, it is important therefore to characterise the particles in suspension. In this work photon correlation spectroscopy was used to measure of the hydrodynamic size of the particles. NMR techniques were used to determine the stability and to quantify the contrast efficiency (relaxivity) of the suspensions. This work has also provided insight into the nature of the nanoclusters in suspension and into the mechanisms of their growth. In the first part of this thesis the synthesis, stabilisation and magnetic properties of aqueous magnetite nanocomposite suspensions which are formed in the presence of fatty acids or DNA are presented. For fatty-acid stabilised nanocomposites the NMR response is sensitively dependent on the method of preparation, which cab result in magnetically blocked or superparamagnetic nanoclusters. In the case of the DNA nanocomposites, the biomolecule acts as a template for the preparation of low dimensional assemblies, or magnetic nanowires, whose suspensions exhibit high relaxivity at low magnetic field. In this second part the synthesis, stabilisation and magnetic properties of magnetite nanoparticle suspensions formed in organic solvents in the presence of long chain surfactants are presented. The influence of nanoparticle size on the magnetic properties is discussed in detail. The NMR response of the particles in non-aqueous suspension is shown to conform to a model previously developed for aqueous suspensions of magnetite. Studies of the controlled clustering of the nanoparticles in organic solvents are presented. The mechanism and kinetics of nanocluster growth are discussed

Annual Report 2010 - Institute of Radiochemistry

At the beginning of 2011, the former Forschungszentrum Dresden-Rossendorf (FZD) was fully integrated into the Helmholtz Association, as Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Therefore, the present Annual Report 2010 of the Institute of Radiochemistry (IRC) is published as the first HZDR-Report. The Institute of Radiochemistry is one of the six Research Institutes of this centre. IRC contributes to the research program “Nuclear Safety Research” in the “Research Field of Energy” and performs basic and applied research in radiochemistry and radioecology. Motivation and background of our research are environmental processes relevant for the installation of nuclear waste repositories, for remediation of uranium mining and milling sites, and for radioactive contaminations caused by nuclear accidents and fallout. Because of their high radiotoxicity and long half-life the actinides are of special interest

A Comparative Density Functional Theory and Density Functional Tight Binding Study of Phases of Nitrogen Including a High Energy Density Material N8

We present a comparative dispersion-corrected Density Functional Theory (DFT) and Density Functional Tight Binding (DFTB-D) study of several phases of nitrogen, including the well-known alpha, beta, and gamma phases as well as recently discovered highly energetic phases: covalently bound cubic gauche (cg) nitrogen and molecular (vdW-bound) N8 crystals. Among several tested parametrizations of N–N interactions for DFTB, we identify only one that is suitable for modeling of all these phases. This work therefore establishes the applicability of DFTB-D to studies of phases, including highly metastable phases, of nitrogen, which will be of great use for modelling of dynamics of reactions involving these phases, which may not be practical with DFT due to large required space and time scales. We also derive a dispersion-corrected DFT (DFT-D) setup (atom-centered basis parameters and Grimme dispersion parameters) tuned for accurate description simultaneously of several nitrogen allotropes including covalently and vdW-bound crystals and including high-energy phases