Oxidative stress description

The scientific community has been discussing for quite some time now the relationship between oxidative stress, defined as the imbalance between oxidant and antioxidants [45], and the health-disease status. An impressive amount of information available in the literature deals with the effects of the classic antioxidants, ascorbic acid, a-tocopherol, and jS-carotene in a huge series of pathophysiological situations in experimental animals and humans. Concerning the effects of the classic antioxidants on mitochondrial function in situations of oxidative stress, the information is not so vast and most of the time it is not conclusive. However, substantial progress has been made in the description of the mitochondrial alterations in neurodegenerative diseases and in the a-tocopherol effects,both as prevention and as treatment [46]. We will briefly review some reports related to vitamin E and mitochondrial dysfunction in oxidative metaboHc disorders and in the neurodegenerative Alzheimer s and Parkinson s diseases. 

Many dietary factors are believed to exert their potent antidisease effects because they possess strong antioxidant activities. However, direct compelling evidence for this supposition is lacking [22] and is difficult to obtain. A multitude of descriptive studies correlating the presence of resveratrol and protection against oxidative stress have been performed over the past 1-2 years. Almost all of these reports present indirect, correlative evidence. The data clearly support an antioxidant function for resveratrol but do very little to provide mechanistic evidence for its action in vivo. However, a few of the most recent studies are highlighted. 

The predominant effect of flavonoid and isoflavonoid supplementation in ex vivo cell culture models appears to be one of promoting apoptosis [54—57]. This is repeatedly observed in studies witti transformed cancer cells, leading to the descriptions cytoprotective and/or chemopreventive [6,58]. Two poly-phenolic compounds that have been extensively studied in anticancer research are quercetin and genistein, a flavonoid and isoflavone, respectively. However, ex vivo studies with primary cultured cells in 2000 and 2001 showed that some flavonoids can prevent apoptosis promoted by agents that induce oxidative stress [7,8,59]. The outcome of flavonoid treatment is expected to show a complex dependence on a number of factors, including the type of flavonoid, its concentration, the type of cell (e.g., transformed versus nontransformed), the mechanisms of action of the flavonoid, the nature of the proapoptotic stimulus, and the specific apoptotic signaling pathway that is activated. 

FIGURE 6.9 Lewis structure representations of oxygen species involved in oxidative stress processes. Although triplet (ground state) molecular oxygen molecules are sometimes depicted by the simplified Lewis structural formulas shown, a complete description of the electronic behavior of these molecules requires use of molecular orbital theory, which is beyond the scope of this work. 

Oxidation state is a frequently used (and indeed misused) concept which apportions charges and electrons within complex molecules and ions. We stress that oxidation state is a formal concept, rather than an accurate statement of the charge distributions within compounds. The oxidation state of a metal is defined as the formal charge which would be placed upon that metal in a purely ionic description. For example, the metals in the gas phase ions Mn + and Cu are assigned oxidation states of +3 and +1 respectively. These are usually denoted by placing the formal oxidation state in Roman numerals in parentheses after the element name the ions Mn- " and Cu+ are examples of manganese(iii) and copper(i). 

Because charge defects will polarize other ions in the lattice, ionic polarizability must be incorporated into the potential model. The shell modeP provides a simple description of such effects and has proven to be effective in simulating the dielectric and lattice dynamical properties of ceramic oxides. It should be stressed, as argued previously, that employing such a potential model does not necessarily mean that the electron distribution corresponds to a fully ionic system, and that the general validity of the model is assessed primarily by its ability to reproduce observed crystal properties. In practice, it is found that potential models based on formal charges work well even for some scmi-covalent compounds such as silicates and zeolites. 

The forced degradation studies should be part of impurity characterization. When identification of the impurity is not feasible, incorporate the description of unsuccessful experiments (including those conducted in stress-testing studies) in the text of the application. The most frequently encountered protein variants include truncated fragments, deamidated, oxidized, isomerized, aggregated forms, and mismatched disulfide links. 

The paper is outlined as follows. After a brief description of the specimen preparation and the stress measurement by OFS, crack and spallation patterns on oxidised NiAl specimens are shown, which have been produced by bend and indentation tests at room or oxidation temperature. In the second part of the paper, first attempts to an interpretation of the crack patterns are presented. In particular, the possibility to derive the oxide fracture toughness and tensile strength from the crack patterns is discussed. 

Speciation and reactivity of actinide compounds comprise an important area for quantum chemical research. Even more so than in the case of lanthanides, f-type atomic orbitals of actinides can affect the chemistry of these elements [185,186] the more diffuse 5f-orbitals [187] lead to a larger number of accessible oxidation states and to a richer chemistry [188]. The obvious importance of relativistic effects for a proper description of actinides is often stressed [189-192]. A major differences in chemical behavior predicted by relativistic models in comparison to nonrelativistic models are bond contraction and changes in valency. The relativistic contribution to the actinide contraction [189,190] is more pronounced than in the case of the lanthanides [191,192]. For the 5f elements, the stabilization of valence s and p orbitals and the destabilization of d and f orbitals due to relativity as well as the spin-orbit interaction are directly reflected in the different chemical properties of this family of elements as compared with their lighter 4f congeners. Aside from a fundamental interest, radioactivity and toxicity of actinide compounds as well as associated experimental difficulties motivate theoretical studies as an independent or complementary tool, capable of providing useful chemical information. 

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