Radical Mechanisms in the Metallocenes
A special class of sandwich complexes is the metallocenes. The best-known members are the metallocenes of the formula M(C5H5)2, where M = zirconium, zinc, titanium, hafnium, vanadium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, rhodium, and nickel. Besides the two cyclopentadienyl rings, the metal can have additional ligands depending on its valence state. These species are also called bis(cyclopentadienyl)metal complexes. Bis(cyclopentadienyl) complexes are called metallocenes or sandwich compounds. Metal-centred radical and cyclopentadienyl radical structures can occur in the metallocene. The anion and cation radicals can also be formed by charge transfer transition.
Part of the book: Recent Progress in Organometallic Chemistry
Magnetic resonance is divided into electron spin resonance (ESR) [electron paramagnetic resonance (EPR)] and nuclear magnetic resonance (NMR) according to the working region in the electromagnetic spectrum. If the studied region is in the microwave region, this resonance type is electron spin resonance. If the region studied is the radio frequency region, then nuclear magnetic resonance is mentioned. ESR and NMR are similar in terms of their basic theorem.
Part of the book: Resonance
Potassium Nutrition in Plants and Its Interactions with Other Nutrients in Hydroponic Culture
Potassium is an essential major nutrient for plant growth and development. Plants absorb more K (potassium) than any other element, with the exception of N. Most plant-available forms of essential plant nutrients are ionic. Among the many plant mineral nutrients, K stands out as a cation having the strongest influence on quality attributes. Potassium ions are involved in many processes that result from ionic activity in the hydroponic nutrient solution and often provide positive contributions. Due to the presence of potassium cation ions, some elements increase in nutrient solution, whereas others decrease.
Part of the book: Potassium
EPR Analysis of Antioxidant Compounds
A free radical is a molecular species having an unpaired electron and it is a highly reactive entity and unstable. A free radical is a molecule with one or more unpaired electrons in its outer shell. Free radicals can be formed by chemical bond breakage from molecules or by redox reactions. When cells use oxygen, the oxidative stress occurs. The oxidative stress causes free radical formation. Free radicals can also be generated from ionizing radiations, ozone, heavy metal poisoning, cigarette smoking, and chronic alcohol intake. These free radicals are highly reactive and oxidize biomolecules leading to tissue injury and cell death. They also cause toxic effects and diseases. Antioxidants neutralize free radicals resulting from oxidative stress. Antioxidants play an important role in the treatment of diseases. The most suitable method for the analysis of free radicals is the electron paramagnetic resonance (EPR) spectroscopy method. The EPR method detects a paramagnetic center with a single electron. It gives information about the interactions with other nuclei around one electron. It provides information on the structure and environment of radicals.
Part of the book: Free Radicals, Antioxidants and Diseases
Free radicals may participate in biological processes. An enzymatic dehydrogenation involved free radical intermediates. The oxidations of organic molecules, although they are bivalent, proceed in two successive steps, the intermediate state being a free radical. In an attempt to correlate the action of such a variety of carcinogenic agents as sodium hydroxide, ultraviolet and ionizing radiations and thousands of organic compounds, a free radical intermediate always suggests itself. Electron paramagnetic resonance (EPR) has brought sufficient sensitivity and discrimination to observe free radical intermediates directly in many of these reactions. EPR is aided by an increased sensitivity in many cases and has made a much greater contribution by distinguishing among paramagnetic ions, odd molecules and free radicals.
Part of the book: Topics From EPR Research
Dipolar Interactions: Hyperfine Structure Interaction and Fine Structure InteractionsView all chapters
The interaction between the nuclear spin and the electron spin creates a hyperfine structure. Hyperfine structure interaction occurs in paramagnetic structures with unpaired electrons. Therefore, hyperfine structure interaction is the most important of the fundamental parameters investigated by electron paramagnetic resonance (EPR) spectroscopy. For EPR spectroscopy the two effective Hamiltonian terms are the hyperfine structure interaction and the electronic Zeeman interaction. The hyperfine structure interaction has two types as isotropic and anisotropic hyperfine structure interactions. The zero-field splitting term (electronic quadrupole fine structure), the nuclear Zeeman term, and the nuclear quadrupole interaction term are among the Hamiltonian terms used in EPR. However, their effects are not as much as the term of the hyperfine structure interaction. The zero-field splitting term and the nuclear quadrupole interaction term are the fine structure terms. The interaction of two electron spins create a zero-field splitting, the interaction between the two nucleus spins form the nuclear quadrupole interaction. Hyperfine structure interaction, zero-field interaction, and nuclear quadrupole interaction are subclasses of dipolar interaction. Interaction tensors are available for all three interactions.
Part of the book: Quantum Mechanics