109 research outputs found
EPR Spectroscopy in the Study of 2D Graphene-based Nanomaterials and Nanographites
No full textGraphene-based nanomaterials and nanographites represent 2D and 3D materials, where the transition from one type of materials to the other is without clear boundaryies. In this type of materials, where the leitmotiv is represented by the presence of single or multi-stacked graphene layers, EPR has been fruitfully employed as spectroscopy for structural characterization, as well as for the quantification of paramagnetic defects and for the study of magnetic properties. In this type of carbon-based materials, a fundamental role is played by two main actors a) conduction electrons, belonging to the extended π-system, and b) edge states: electrons described by wavefunctions of limited extension associated to zigzag termination of the graphenic layers. A strong interaction between conduction and localized electrons, and in the presence of other minor paramagnetic contributions like other types of defects (crystal vacancies), or so-called molecular states (very small graphenic fragments), a vast spectrum of magnetic responses is obtained from the materials, from a ferromagnetic to an antiferromagnetic behavior. In this Chapter, methodological and introductory Sections are followed by a list of examples which highlight the use of EPR in this field
Magnetic interactions in spin-labeled Au nanoparticles
No full text© 2014 American Chemical Society. A series of gold nanoparticles functionalized with TEMPO-modified disulfide 2 have been prepared and studied by electron paramagnetic resonance (EPR) spectroscopy, UV-vis, transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and thermogravimetric analysis (TGA). In order to increase the packing of spin labels on the particle surface, heat-induced size evolution and ligand exchange reactions were used. The optimized synthesis included a one-pot reaction at room temperature that led to gold nanoparticles with a controlled large size (ca. 7 nm) and high coverage of radicals. These nanoparticles showed a |Δms| = 2 transition at half-field, which gives direct evidence of the presence of a high-spin state and permits an EPR study of the nature of the magnetic coupling between the spins. The results showed dominant antiferromagnetic interactions between radicals, but at lower temperatures, a ferromagnetic contribution was observed.This work was supported by the University of York Research Visitor Scheme, the DGI grant CONSOLIDERC (CTQ2006-06333), CSIC-PIF RAPCAM (PIF-08-017-3), AGAUR (2009-SGR-00516), and DGI grant POMAs (CTQ2010-19501). CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions, and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Peer Reviewe
Tuning the properties of nitroxide spin labels for use in electron paramagnetic resonance spectroscopy through chemical modification of the nitroxide framework
No full textSpin labels containing nitroxyl radicals possess many properties that render them useful
for electron paramagnetic resonance (EPR) spectroscopy. This review describes the
relationships between the structure and properties of nitroxide spin labels, methods for
their synthesis, advances in methods for their incorporation into biomolecules, and
selected examples of applications in biomolecule structural investigations. </p
Molecules as electron spin qubits
No full textElectron spins confined to molecular compounds are promising candidates to base the elementary unit of a quantum computer: the qubit. The major advantage of molecular spin qubits stems from the ability to tailor their performance properties using synthetic chemistry and devise inexpensive of new systems for experimental study. The article details the latest developments the design and testing of new molecular spin qubits and how they are addressing the key challenges in the field of quantum computing
Applications of electron paramagnetic resonance spectroscopy for interrogating catalytic systems
No full textSpecies bearing unpaired electrons, including paramagnetic redox metal centres, surface defect centres, reactive oxygen species, adsorbed radical anions, are often involved in catalytic reactions. These species can be readily and thoroughly interrogated using Electron Paramagnetic Resonance (EPR) spectroscopy, providing information on the identity, chemical composition and even the dynamics of the centres themselves, thereby helping to elucidate the involvement of the radicals in the reaction cycles. This review will summarise and highlight the applications of EPR in heterogeneous, homogeneous, photocatalytic and microporous materials, all of which are of vital importance to the field of catalysis
Applications of light-induced hyperpolarization in EPR and NMR
No full textMagnetic resonance methods are widely used to provide atomic level information on the structure and dynamics of chemical and biochemical systems, but often suffer from poor sensitivity. This review examines how optical excitation can provide increased electron spin-polarization, and how this can be used to increase sensitivity and/or information content in both Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy
Homogeneous catalytic transformations investigated by EPR spectroscopy
No full textCatalytic reactions are used to drive a large number of important chemical transformations. In general, these catalytic reactions are more energy efficient and produce less waste. Therefore new catalysts are constantly being developed for a wide range of applications ranging from alternative energy sources to synthesis of pure drugs. Many of these catalyzed reactions involve paramagnetic redox centres and reactive intermediates, so a detailed understanding of their role in the mechanistic pathways is required in order to improve the catalyst design. In this chapter, we will provide an overview to illustrate how EPR is used to characterise various transition metal based homogeneous catalysts, by focusing on the literature from the past five years
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