Andrzej Rajca - US grants

This project by Andrzej Rajca at Kansas State University within the Organic Dynamics Program, is aimed at the development of organic compounds with superconducting and ferromagnetic properties. Very few examples are currently known, with such properties most often confined to inorganic solids. The use of organics with metallic-like properties will provide a wealth of possibilities due to ease of fabrication and subsequent modification of properties by standard methods of organic synthesis. Because the electronic structure and bonding of molecules and solids is affected by topology (and symmetry), a topological approach to organic superconductors and ferromagnets will be employed. Multi-carbanions, radicals, and radical anions of pi-conjugated hydrocarbons with highly degenerate highest occupied, non-bonding molecular orbitals will be prepared. The degeneracy and unique delocalization of these orbitals have a topological rather than symmetry origin. First, theoretical predictions about the impact of the special topology on the charge distribution, ground state multiplicities, and other molecular properties will be tested. Second, solids will be prepared; density of states at the Fermi level, band width, and other important solid state properties will be obtained and compared to their molecular counterparts. Finally, the solids will be examined with respect to ferromagnetism and superconductivity.

The Department of Chemistry at Kansas State University will use this award from the Chemistry Research Instrumentation Program to help acquire a mass spectrometer system. The areas of chemical research that will enhance by the acquisition include the following: 1) Diels - Alder Chemistry of Activated Cyclobutenes, 2) Asymmetric Synthesis of Natural Products and Molecules of Biomedical Interest, 3) Organic Molecule Fragmentations on the Surfaces of Nano-scale Metal Oxide Particles, 4) Performance of SMAD Catalysts Organic Precursors to Carbon Monosulfide (CS), 5) p-Phenylenediimido-Bridged Dimers and Polymers. A New Class of Conjugated Inorganic Systems, and 6) Toward a Hydrocarbon Ferromagnet: Polyarylmethyls. Mass spectrometry is a technique used to probe intimate structural details and to obtain the molecular compositions of a vast array of organic, bioorganic and organometallic molecules. When combined with a high performance liquid chromatograph, the resulting system affords the chemist one of the most powerful tools available for the separation and characterization of compounds. The acquisition of a mass spectrometer is essential for the prosecution of frontier research in many fields of chemistry.

This SQUID-based sample magnetometer will perform fast, precise measurements of the magnetic properties of materials over a broad range of temperatures and applied magnetic fields. It has a complete and sophisticated computer operating system for control and analysis and allows for total automation. The proposed instrument exceeds current equipment ability in sensitivity, temperature control, and computer control. The system will be used by four faculty members of the Physics and Chemistry departments for fundamental materials research, and will aid in training of undergraduates and graduate students (20), and postdocs (3). The SQUID magnetometer is a central measurement and characterization apparatus for several projects: measurement of magnetic properties of ultrafine parcticles prepared via novel synthetic techniques having unique compositions and structures; studies of storage and relaxation processes of photoexcited charge carriers in II-VI mixed crystals and related critical phenomena; studies of magnetic anisotropy and interface exchange in multilayers of rare-earth metals and transition metals and their oxides and studies of critical phenomena in these systems; and measurements of organic ferromagnets.//

A series of high spin polyradical molecules with distinct three-dimensional shapes will be synthesized and characterized. The polyradical shapes will be imposed by either steric hindrance (dendrimers) or covalent bond networks (cages). Magnetic analysis will be accomplished by utilizing SQUID, NMR, and ESR techniques. Molecular solids comprised of high spin polyradicals will be developed and investigated, and the feasibility of making ultra high spin polyradicals will be demonstrated. The investigation will provide a general model for electron spin ordering as a function of distance and number of unpaired electrons. %%% This grant from the Organic Dynamics Program supports the work of Professor Andrzej Rajca at the University of Nebraska on the synthesis and characterization of high spin organic molecules that possess several unpaired electrons. Electrons in typical organic molecules are paired and thus have no magnetic properties, whereas the target molecules will be prototype building blocks for novel organic magnets. This investigation should provide basic information required to produce magnets on a molecular level for a variety of technical and scientific applications impacting on the electronics and communications fields.

This research is concerned with the preparation and study of ultrathin magnetic films of high-spin organic polyradicals having two to nine unpaired electrons. These polyradicals, considered to be superparamagnetic building blocks for a magnet, will be used in the form of a thin film with a thickness of one to hundred monolayers. Langmuir-Blodgett technique will be used to control the structure and the thickness of the films. The study of the materials and their magnetooptical properties will be examined. The results of this research will ultimately lead to the development of magneto-optical storage media that are erasable and rewritable at high speed.

This award iq made jointly by the Organic Dynamic Program and the Advanced Materials Program in the Chemistry Division in support of the continuing research of Dr. Andrzej Rajca. Two major efforts will be supported; (1) the design, synthesis and characterization of very high spin macrocyclic poyradical systems, and (2) computational and experimental studies on the synthesis and properties of new carbon allotropes and highly condensed network solids based on tetra o-phenylene structural units. In the first research area, polyradicals, all of the triarylmethyl type will be prepared from the corresponding triarylmethyl-methyl ethers by alkali metal reduction to the carbopolyanions followed by iodine oxidation. These elongated macrocyclic polyradicals will have greater than ten spin-coupled electrons and will be designed to minimize defects which interrupt spin-coupling. In the second research area, solid-state and molecular calculations using MNDO, EHT, and MM3 methods will provide thermodynamic stabilities and band structure-properties of the solids. Experiments will evaluate the structures of the network solids, including their response to doping. Molecular and polymeric fragments of the solids will be synthesized, and their solution redox chemistry investigated. Understanding the behavior of macrocyclic polyradicals and controlling spin coupling defects will allow the researcher to use them as building blocks for two and three dimensional network polyradicals, with the potential to be organic ferromagnets with high Curie temperatures. Synthesis and doping of highly condensed carbon networks will facilitate preparation of radical ion-and dianion -based molecular solids which will lead to promising new materials with conducting properties.

This research focuses on the development of new synthetic methodologies for the synthesis of novel mesoscopic molecular architectures that serve as scaffolds for very-high-spin polyradicals, and the experimental and computational characterization of the polyradicals. The principles of fractal geometry will be applied to achieve connectivities differing from those obtainable with the current dendritic approach. MNDO, EHT and MM3 molecular calculations of the electronic structure of these, and mesoscopic systems possessing chiral pi-conjugated systems, will be correlated with measurements of the magnetic and electronic properties of the two- and three-dimensional polyradicals to achieve spin-coupled organic magnets with high Curie temperatures. Graduate and postdoctoral students carrying out the experiments will be trained in the synthesis of molecules of mesoscopic dimensions, and the experimental and theoretical characterization of their electronic properties. With this award, the Organic and Macromolecular Chemistry Program and the Advanced Materials Program support the educational and research activities of Dr. Andrzej Rajca of the Chemistry Department at the University of Nebraska. Dr. Rajca will focus his research efforts on developing synthetic routes to relatively large molecules, referred to as mesoscopic molecules. These multi-dimensional molecules serve as scaffolds for a relatively large number of sites possessing an unpaired electron, and are key intermediates in the development of organic magnets. Dr. Rajca will correlate the magnetic properties of these mesoscopic molecules with theoretical analyses to achieve organic materials that exhibit room temperature magnetic properties. Dr. Rajca's educational activities involve training graduate and postdoctoral students in the synthetic methodology needed to achieve molecules of mesoscopic dimensions, and their experimental and theoretical characterization.

This is a joint award from the Major Research Instrumentation program and the NSF/EPSCoR program to the University of Nebraska (UN). The award supports the acquisition of a focussed ion beam (FIB) workstation for processing of single crystals and nanometer size materials in order to investigate their magnetic and magneto-optic properties. FIB is an ultra-high precision tool for etching and writing with 10-nanometer resolution. The workstation will complement existing facility at UN and will be used in a number of currently funded projects at the institution. It provides new capability for the study of devices at the nano scale with a high probability for discovery of new phenomena. The instrument will benefit the education and training of a large number of graduate and undergraduate students as well as postdocs at the University of Nebraska.
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This is a joint award from the Major Research Instrumentation program and the NSF/EPSCoR program to the University of Nebraska (UN). The award supports the acquisition of a focussed ion beam (FIB) workstation for processing of single crystals and nanometer size materials in order to investigate their magnetic and magneto-optic properties. FIB is an ultra-high precision tool for etching and writing with 10-nanometer resolution. The workstation will complement existing facility at UN and will be used in a number of currently funded projects at the institution. It provides new capability for the study of devices at the nano scale with a high probability for discovery of new phenomena. The instrument will benefit the education and training of a large number of graduate and undergraduate students as well as postdocs at the University of Nebraska.

With this renewal award, the Organic and Macromolecular Chemistry Program continues its support of the work of Professor Andrzej Rajca of the Department of Chemistry at the University of Nebraska, Lincoln, NE. The research will extend the PI's research on high-spin polyradicals and chiral conjugated pi-systems. In the area of polyradicals, the PI will synthesize molecules having multiple unpaired electrons that are expected to be stable at ambient temperatures. Stability will be enhanced through the use of nitroxides as carriers of electron spin. These will be materials with high-spin electronic ground states that exhibit strong ferromagnetic coupling, giving them the potential to function as organic magnets. In the area of chiral conjugated systems, the PI will synthesize enantiopure helicenes with more than seven fused aromatic rings in order to understand the principles governing the rational design of strongly chiral organic materials.

These multidisciplinary studies are expected to provide important fundamental information that will contribute to the development of lightweight organic magnets and of chiral materials with novel optical and electronic properties. In addition, the research will provide students with diverse training in physical organic chemistry, organic synthesis, solid-state chemistry, and magnetism.

This grant supports the purchase of a continuous wave electron paramagnetic resonance (EPR) spectrometer, which is essential in the synthesis of novel organic magnetic materials and is valuable in the characterization of other magnetic materials. The EPR spectrometer system will replace the current 20+ year-old X-band EPR instrument that is no longer functional. The superior capabilities of this new EPR spectrometer will be tailored to materials research in magnetism, which will complement existing bulk magnetic measurement capabilities based upon superconducting quantum interference device (SQUID) magnetometry/susceptometry. This new spectrometer will have a significant impact on the following projects: (1) synthesis of organic polymer magnets with stability at ambient conditions; (2) coordinating organic ligands with a few unpaired electrons (high-spin organic molecules) for new organometallic magnets with improved ordering temperatures; (3) organic molecules for potential magnetic resonance imaging contrast agents and radical ions of molecules and polymers with chiral p -conjugated systems; and (4) inorganic metal-based magnets, transition metal complexes, magnetic nanostructures and films.
The results of the indicated projects will be disseminated in the peer review journals, conference presentations, and web-based publications. In particular, the significant progress toward practical organic polymer magnet is expected to attract wide attention, promoting better understanding of basic research in materials.

These research activities will advance fundamental understanding of magnetic materials and may have a significant impact on the future electronic technology through the development of soft magnets based upon conjugated organic polymers. The EPR spectrometer is indispensable in the training and education of students and postdoctoral associates in the interdisciplinary area of organic magnetism. The spectrometer will make possible a more advanced computer-controlled operation that will facilitate the training of undergraduate and graduate students. The overall infrastructure for materials research at the University of Nebraska-Lincoln will be enhanced, which will benefit other researchers studying magnetic films, nanostructures, and metal-based inorganic magnets and complexes.

With this award, the Organic and Macromolecular Chemistry Program supports the work of Professor Andrzej Rajca of the University of Nebraska-Lincoln. This research consists of two areas directed toward the synthesis and characterization of stable high-spin poly-radicals (multiple unpaired electrons) and chiral (not superimposable on its mirror image) pi-conjugated systems. In the area of poly-radicals, high-spin organic molecules with very strong ferromagnetic coupling and with stability at ambient conditions will be synthesized and characterized. The research approach is based upon annelated pi-systems of poly-radicals, for which both nitrogen-centered radicals and nitroxide radicals will be used as carriers of electron spin. In the area of chiral conjugated systems, chiral helicenes with more than eleven ortho-fused aromatic rings and related highly annelated pi-systems, including radical cations of helicenes, will be synthesized and studied. These studies are designed to advance the development of organic magnets and of other materials based upon high-spin organic molecules and to provide an understanding of the principles governing the rational design of strongly chiral organic materials.

The proposed research involves organic synthesis and comprehensive physical characterization of organic molecules, in particular magnetic measurements. These multidisciplinary studies are expected to provide important fundamental information that will contribute to development of lightweight organic magnets and of chiral materials with novel optical and electronic properties. A group of undergraduate, graduate and postdoctoral students, who will carry out these studies, will receive diverse training in physical organic chemistry, organic synthesis, solid-state chemistry, and magnetism. The research experience will promote learning, by approaching and solving complex problems. Furthermore, the materials obtained from this project will be made available to other research groups in the United States and abroad.

DESCRIPTION (provided by applicant): Nitroxide radicals are being investigated for many biological and biomedical applications, such as spin probes, antioxidants, radiation protectors, electron paramagnetic resonance imaging (EPRI), and magnetic resonance imaging (MRI). These applications rely mainly on the use of nitroxide monoradicals with the total spin quantum number (S) of 1/2. This R21 project will explore a new class of radicals, high-spin nitroxide diradicals with S = 1, for biomedical imaging applications. Because the signal intensity in MRI scales with the factor of S(S + 1) of paramagnetic agent, we expect that significant increases in sensitivity could be attained using high-spin S >1/2 radicals as contrast agents. The specific hypothesis behind this proposal is that the S = 1 diradicals, especially the rigid scaffolds of S = 1 diradicals, can be made to possess adequate relaxivity and redox properties for functional MRI contrast agents. Diradicals and scaffolds of diradicals with rigid structure will be prepared by organic synthesis and their selected properties affecting 1H water relaxivity will be studied. Values of S(S + 1) will be measured by superconducting quantum interference device (SQUID) magnetometry and EPR spectroscopy. Rotational correlation times and electron spin relaxation times (T1 and T2) will be measured by EPR spectroscopy. Stability in the presence of ascorbate will be determined. Nitroxides with most promising relaxivities and redox properties will be subjected to an in vivo study. This information will provide an assessment of the key factors affecting the 1H water relaxivity of the nitroxide radicals, a foundation for our long term goal of the development of highly sensitive, functional, and safe MRI contrast agents based upon stable, redox-active high-spin nitroxide polyradicals with large values of S. Development of contrast agents based on organic compounds with strong paramagnetic properties will expand the frontier of biomedical imaging research. Various structural modifications of organic compounds for specific targeting and property tuning (magnetism, redox, solubility, toxicity) can be efficiently implemented by organic synthesis. Organic-based contrast agents will provide an alternative to metal-based agents, in which the property tuning is limited and their applications have been associated with the risk of exposure to highly toxic metal ions. Such organic-based agents should render safe, effective tools for early detection and diagnosis of diseases and for modern approaches to drug discovery. PUBLIC HEALTH RELEVANCE: Contrast agents based on organic compounds with strong paramagnetic properties provide alternative MRI contrast media to the metal-based agents, avoiding the risk factors associated with the release of highly toxic metal ions. This project will explore the feasibility of sensitive and safe contrast agents based on organic radicals. Such agents may ultimately render effective tools for early detection and diagnosis of diseases, and for modern approaches to drug discovery.

This award from the Division of Chemistry supports a Research Experience for Undergraduates (REU) site at the University of Nebraska led by Andrzej Rajca, Mark Griep, and Marilyne Stains for three summers, commencing in 2012. The site will support nine students per summer in a ten week program. The projects focus on chemical assembly and are specifically tailored to stimulate student curiosity by provoking students to ask, "Why?" and "How?" about their research. Sample projects include: (1) assembling nanocluster catalysts; (2) late stage introduction of fluorine into drug-like molecules; (3) synthesis of conjugation/linking elements for nanohybrid materials; (4) rapid analysis of drug-protein interactions; (5) electrochemical sensors using biomolecules; (6) organic radicals for organic magnets, spin labels, and MRI contrast agents; (7) composite biomaterials for bone grafts; (8) assembly of graphene nanostructures with semiconductive properties; (9) macromolecular assembly as a switch for protein function; (10) noble metal nanocrystals with high index facets. In addition, students will develop skills in communicating their research to scientists (meeting abstract, poster and oral presentations) and science learners (development and enactment of a mini-lesson), they will learn about careers in both industry (through field trips) and academia, and they will be trained on state of the art instruments and in ethics. Through a competition, five students each year will receive a travel grant to travel and to present their research at a regional or national meeting of the American Chemical Society.

Young scientists need exposure to modern research methods and tools as part of their training. This REU site aims to provide cutting-edge research training in chemical assembly of relevance to innovations in the areas of information technology, targeted medicines, functional materials, energy storage, and beyond. The site will provide opportunities for research to a significant number of students who might not otherwise be reached. The diverse student cohort participating in research at this site will be well-prepared for graduate school, and eventual employment as part of the country's technical workforce.

In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Andrzej Rajca of the Department of Chemistry at the University of Nebraska-Lincoln will investigate structure and property relationships of organic molecules and macromolecules that are relevant to the development of novel magnetic and optical technology. The goal of this research is to synthesize and study high-spin nitrogen-centered radicals (aminyls) and chiral helical radical cations. The aminyls with strong through-bond ferromagnetic coupling and with persistence at room temperature are important to the development of lightweight, soft organic magnets. In addition, such organic radicals could benefit the development of metal-free paramagnetic contrast agents for magnetic resonance imaging (MRI), agents for paramagnetic relaxation enhancement nuclear magnetic resonance (NMR) spectroscopy, as well as materials for spintronics. The helical radical cations, which possess an unpaired electron confined to a helix, could facilitate the discovery of new organic magneto-optic materials and devices. This interdisciplinary research project involves multi-step organic synthesis, diverse physical characterization of organic molecules, and computations, and is therefore well suited to the education of scientists at all levels, with exceptional opportunities to gain a broad education as well as to develop a wide range of skills. This group is also well-positioned to provide the highest level of education and training for students underrepresented in science.

The proposed aminyls are high-spin radicals based upon annelated pi-systems of nitrogen-centered radicals that are made persistent by steric shielding of radical centers and isotopic substitution to prevent decay of radicals. The proposed radicals will be prepared by modern organic synthetic methodologies and characterized by electron spin resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, as well as computations. Aminyl diradicals with very strong pairwise ferromagnetic coupling between electron spins and persistence at room temperature, with half-life that would permit isolation of the radicals, will be investigated and compared to analogous nitroxide diradicals, to provide an insight into the degree of spin delocalization in the pi-system. Aminyl triradical will be prepared and extended to the synthesis of aminyl polyradical polymers with very large magnetic moment. The proposed chiral helical radical cations are based on nitrogen-centered radical cations of helical pi-systems, which would be configurationally persistent at room temperature. Helical radical cations are intriguing molecules with a combination of chiral pi-systems and paramagnetism. Helical, ladder-type pi-systems of n ortho-annelated aromatic rings, such as [n]helicenes, are among molecules with the strongest chiral properties. Paramagnetism of radical cations within the three-dimensional helical pi-system would render unique properties, a combination of helicene chirality and delocalized electronic spin, for development of novel paramagnetic materials with inherently strong chiral properties. Radical cations of aza-thio-[7]helicene and conjoined [5]helicene will be prepared and studied by electrochemistry, UV-vis-NIR, circular dichroism (CD), EPR spectroscopies, as well as computations.

? DESCRIPTION (provided by applicant): The overall goal of this project is the development of biostable organic radicals as contrast agent (CA) for magnetic resonance imaging (MRI). Such metal-free, organic-based CAs will provide a breakthrough in contrast-enhanced MRI while avoiding the risk associated with toxic metal ions. While the agents would especially benefit patients with impaired kidney function, who are at increased risk of developing nephrogenic systemic fibrosis (NSF) following administration of paramagnetic gadolinium chelates (GBCAs) for MRI procedures, the new agents may also benefit the general population. The objective of the proposed work is to synthesize organic radical contrast agents (ORCAs) that provide high quality in vivo MR images. The long-standing obstacle in the development of a practical ORCA for MRI is the design and synthesis of paramagnetic organic compounds of moderate molecular size that possess sufficiently long in vivo lifetime, high 1H water relaxivity (r1), and high water solubility. We propose a design strategy to prepare ORCAs from nitroxide radicals that are highly resistant to reduction and exploit prior knowledge about dendrimers and PEGylation, particularly their applications to drug design, to achieve agents with optimized MRI properties. The proposed project has three specific aims. Specific aim 1: optimize 1H water relaxivity r1 (at 3 Tesla) and hydrophilicity of ORCAs to achieve molecular r1 = 10 mMs, at least twice that of the clinical CAs (molecular r1 ??5 mM?¹s?¹). The ORCAs are derived from nitroxides conjuated to a generation 4 polypropylenimine (PPI-G4) dendrimer through PEGylation with long linear and/or branched PEG chains. The proposed work will provide a foundation for specific aim 2: optimize molecular size of the ORCAs with molecular r1 = 10 mM?¹s?¹ to achieve agents with th radii 1 nm ? rSE ? 2 nm that would undergo efficient renal filtration/excretion. In vitro toxicty and water relaxivity of the ORCAs, as well as the properties that affect molecular r1, such as rotational correlation time and electron spin relaxation time, will be determined, to identify the four best ORCAs. Specific aim 3: evaluate effectiveness of ORCAs for in vivo MRI. Lowest effective dose, time course, and tumor vascular permeability (transfer constant Ktrans) for the four selected ORCAs will be determined at the clinical field of 3 Tesla by MRI of normal mice and by dynamic contrast enhanced (DCE) MRI of mice bearing tumor xenografts. Preliminary toxicity of the ORCA will be evaluated by histological examination. The most effective ORCA will be selected, labeled with a fluorescence probe, and then subjected to ex vivo biodistribution studies by electron paramagnetic resonance and fluorescence spectroscopy. These studies will determine suitability of ORCA for further development towards human use. Development of metal-free MRI contrast agents based on biostable organic radicals will expand the frontier of biomedical imaging. Modularity of organic synthesis enables efficient structural modifications for specific property tuning (redox, solubility, and toxicity). Such organic-based agents will improve early detection and diagnosis of diseases.

DESCRIPTION (provided by applicant): The overall goal of this project is the development of biostable organic radicals as contrast agent (CA) for magnetic resonance imaging (MRI). Such metal-free, organic-based CAs will provide a breakthrough in contrast-enhanced MRI while avoiding the risk associated with toxic metal ions. While the agents would especially benefit patients with impaired kidney function, who are at increased risk of developing nephrogenic systemic fibrosis (NSF) following administration of paramagnetic gadolinium chelates (GBCAs) for MRI procedures, the new agents may also benefit the general population. The objective of the proposed work is to synthesize organic radical contrast agents (ORCAs) that provide high quality in vivo MR images. The long-standing obstacle in the development of a practical ORCA for MRI is the design and synthesis of paramagnetic organic compounds of moderate molecular size that possess sufficiently long in vivo lifetime, high 1H water relaxivity (r1), and high water solubility. We propose a design strategy to prepare ORCAs from nitroxide radicals that are highly resistant to reduction and exploit prior knowledge about dendrimers and PEGylation, particularly their applications to drug design, to achieve agents with optimized MRI properties. The proposed project has three specific aims. Specific aim 1: optimize 1H water relaxivity r1 (at 3 Tesla) and hydrophilicity of ORCAs to achieve molecular r1 = 10 mMs, at least twice that of the clinical CAs (molecular r1 ? 5 mM?¹s?¹). The ORCAs are derived from nitroxides conjuated to a generation 4 polypropylenimine (PPI-G4) dendrimer through PEGylation with long linear and/or branched PEG chains. The proposed work will provide a foundation for specific aim 2: optimize molecular size of the ORCAs with molecular r1 ? 10 mM?¹s?¹ to achieve agents with th radii 1 nm ? rSE ? 2 nm that would undergo efficient renal filtration/excretion. In vitro toxicty and water relaxivity of the ORCAs, as well as the properties that affect molecular r1, such as rotational correlation time and electron spin relaxation time, will be determined, to identify the four best ORCAs. Specific aim 3: evaluate effectiveness of ORCAs for in vivo MRI. Lowest effective dose, time course, and tumor vascular permeability (transfer constant Ktrans) for the four selected ORCAs will be determined at the clinical field of 3 Tesla by MRI of normal mice and by dynamic contrast enhanced (DCE) MRI of mice bearing tumor xenografts. Preliminary toxicity of the ORCA will be evaluated by histological examination. The most effective ORCA will be selected, labeled with a fluorescence probe, and then subjected to ex vivo biodistribution studies by electron paramagnetic resonance and fluorescence spectroscopy. These studies will determine suitability of ORCA for further development towards human use. Development of metal-free MRI contrast agents based on biostable organic radicals will expand the frontier of biomedical imaging. Modularity of organic synthesis enables efficient structural modifications for specific property tuning (redox, solubility, and toxicity). Such organic-based agents will improve early detection and diagnosis of diseases.

In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Andrzej Rajca of the Department of Chemistry at the University of Nebraska-Lincoln investigates stable organic polyradicals that are relevant to novel magnetic materials and optical technology. With stable organic polyradicals, lightweight, soft organic magnets, which have applications in wearable electronics, can be developed. Stable organic polyradicals can also assist the development of contrast agents for magnetic resonance imaging, which is widely used in medical diagnosis. This interdisciplinary research project is well positioned to provide the highest level of the training and education of scientists at all levels, including those currently underrepresented in science.

The specific objectives of this project are high-spin nitrogen (aminyl) centered di-, tri- and polyradicals, helically folded high-spin carbon-centered polyradicals, helical and double helical oligothiophene-based radicals. The high-spin aminyl radicals derive from a molecular design based upon annelated, cross-conjugated structures that facilitate delocalization of electron spin density into the ferromagnetic coupler. These radicals are expected to possess a long half-life at room temperature that would permit isolation and/or thermal robustness permitting sublimation under vacuum to prepare thin films. The helical and double helical oligothiophene-based radicals are intriguing novel molecules with a combination of chiral pi-systems and paramagnetism. Paramagnetism associated with helical or double helical pi-system may render unique properties due to the combination of chirality and delocalized electronic spin, providing an avenue for development of novel paramagnetic materials with inherently strong chiral properties that could facilitate discovery of new organic magneto-optic materials and devices. The proposed radicals are being prepared by modern organic synthetic methodologies and characterized by electron spin resonance spectroscopy, superconducting quantum interference device magnetometry, as well as computations.

Project Summary Nitroxide spin labels are useful probes for investigation of biomacromolecules such as proteins DNA, and RNA. In a typical approach, doubly-labeled proteins are prepared by site-directed spin labeling (SDSL) and a set of distances between spin labels is measured using pulsed electron paramagnetic resonance (EPR) dipolar spectroscopy (PDS). Double electron electron resonance (DEER) is the most widely used PDS method. The temperatures at which the DEER measurements currently can be made are limited by the dynamic averaging effects associated with methyl group rotation in the typical nitroxide spin label, and therefore have to be performed at about 50 ? 70 K, requiring use of liquid helium, or with lower sensitivity at 80 K with liquid nitrogen. In addition, application of the SDSL methodology to in vivo measurements is hampered by the short in vivo lifetime of the currently available nitroxide spin labels. The objective of the proposed work is to synthesize and evaluate new nitroxide spin labels for DEER distance measurements in proteins at physiological temperature and for in vivo DEER at cryogenic temperature. The proposed project has three specific aims. Aim 1: synthesize ultra-rigid, small-sized, and polar nitroxide spin labels for distance measurements at physiological temperatures (D-Labels). The target labels are novel nitroxides devoid of methyl groups with structure motifs that address the problem of conformational flexibility, molecular size and hydrophobicity. Aim 2: synthesize nitroxide spin labels for in vivo DEER distance measurements (C-Labels). The targets labels are biostable gem-diethyl and gem-dicarboxylate nitroxide spin labels. Aim 3: evaluate effectiveness of the synthesized spin labels for SDSL-DEER distance measurements at physiological temperatures and for in vivo DEER distance measurements. All labels synthesized in Aims 1 and 2 will be tested for their electron spin relaxation times (Tm and T1) as a function of temperature up to 310 K and for the rate of reduction in ascorbate/glutathione solutions. SDSL-DEER distance measurements at physiological temperature will be calibrated using T4 Lysozyme (T4L) that is doubly spin labelled with D-Labels and immobilized in carbohydrate matrix. C-Labels will be tested for in vivo DEER distance measurements at cryogenic temperature, via SDSL of selected proteins in live mitochondria and in E. coli. Collaborating laboratories will carry out these studies and set the stage for the general adoption of the proposed spin labels by highlighting their properties and defining the range of their applications. These studies will provide structural information at physiological temperature and/or in the native cellular environment, which is characterized by factors and conditions that may have a crucial role in determining the biologically relevant conformation of the proteins under investigation. The wealth of information enabled by the proposed labels will be close to ideal for understanding diseases and the approaches to developing cures for diseases.