Nickel, biological significance

The existence of copper-nitrosyl complexes of biological significance has been briefly discussed here (Section VII). It is worth pointing out that nitrosyl complexes of other metal-containing proteins may form, and that these may be important in understanding the effects of NO on living cells. Nitrosyl complexes of many other metals are well documented (e.g., Werner and Karrer, 1918 Moeller, 1952) and include complexes of nickel, cobalt, and ruthenium. Some such complexes may be less obvious than the paramagnetic and often colorful... 

The Ni(III) oxidation state is biologically significant (101,102). Moreover, high-valent nickel species may be intermediates in some catalytic oxidations (97) and in the nickel-mediated sequence-specific oxidative cleavage of DNA by designed metalloproteins (103) as discussed in Section I,G. The chemistry of Ni(III) macrocyclic complexes has been... 

Redox chemistry of nickel(II) hydroporphyrins has gained importance because of its biological significance. F430 involves both Ni(II) and Ni(I) during catalytic cycle for the conversion of C02 to methane. The redox chemistry performed on various Ni(II) hydroporphyrin systems concludes that the reduction of only Ni(II) F43o and isobacteriochlorins unambiguously results in Ni(I) species whereas porphyrins, chlorins, hexahydro- and octahydro-porphyrins yield anions variously ascribed to Ni(I) or Ni(II) 7t-radicals with some metal character [96],... 

A. Biological Significance of Iron, Zinc, Copper, Molybdenum, Cobalt, Chromium, Vanadium, and Nickel... 

Even though the Mossbauer effect has been observed for almost 50 different elements and ca. 100 different nuclides, only a few of these elements are widely used as Mossbauer effect probes. The nuclides which are both experimentally viable and yield useful chemical information are iron-57, tin-119, antimony-121, and europium-151. More difficult to use but of importance in coordination chemistry are gold-197, nickel-61, ruthenium-99, tellurium-125, iodine-129, dysprosium-161, tungsten-182, and neptunium-237. Among these isotopes, iron-57 is by far the easiest, most informative, and most widely used nuclide in both traditional coordination chemistry and in studies of biologically significant coordination complexes. 

It is also clear that copper is of little significance in most of these organisms relative to its multitude of roles in multicellular eukaryotes, while in these eukaryotes the role of nickel and cobalt is further diminished. We may conjecture that biological systems did not use copper extensively before the advent of an oxidizing atmosphere based on dioxygen (Frausto da Silva and Williams, 1991). 

The effects of catalysts on the oxidation temperature can be significant. For example, lead (Pb), copper (Cu), silver (Ag), iron (Fe), platinum (Pt), and nickel (Ni) were found to lower the ignition temperature of graphite powder from 740°C to 382°C, 570°C, 585°C, 593°C, 602°C, and 613°C, respectively [21]. In all of these cases, the concentration of the metal in the sample was <0.2 wt.%. While catalysts are widely used for large-scale production of chemicals and play an important role in biological processes, they are considered as impurities in the case of carbon nanomaterials as they alter their properties and limit the number of potential applications. 

Biological, chemical, and physical effects of airborne metals are a direct function of particle size, concentration, and composition. The major parameter governing the significance of natural and anthropogenic emissions of environmentally important metals is particle size. Metals associated with fine particulates are of concern particles larger than about 3-fjim aerodynamic equivalent diameter are minimally respirable, are ineffective in atmospheric interactions, and have a short air residence time. Seventeen environmentally important metals are identified arsenic, beryllium, cadmium, chromium, copper, iron, mercury, magnesium, manganese, nickel, lead, antimony, selenium, tin, vanadium, and zinc. This report reviews the major sources of these metals with emphasis on fine particulate emissions. 

The determination of trace metal impurities in pharmaceuticals requires a more sensitive methodology. Flame atomic absorption and emission spectroscopy have been the major tools used for this purpose. Metal contaminants such as Pb, Sb, Bi, Ag, Ba, Ni, and Sr have been identified and quantitated by these methods (59,66-68). Specific analysis is necessary for the detection of the presence of palladium in semisynthetic penicillins, where it is used as a catalyst (57), and for silicon in streptomycin (69). Furnace atomic absorption may find a significant role in the determination of known impurities, due to higher sensitivity (Table 2). Atomic absorption is used to detect quantities of known toxic substances in the blood, such as lead (70-72). If the exact impurities are not known, qualitative as well as quantitative analysis is required, and a general multielemental method such as ICP spectrometry with a rapid-scanning monochromator may be utilized. Inductively coupled plasma atomic emission spectroscopy may also be used in the analysis of biological fluids in order to detect contamination by environmental metals such as mercury (73), and to test serum and tissues for the presence of aluminum, lead, cadmium, nickel, and other trace metals (74-77). 

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