Reflectance divalent elements

Metallic and Inorganic Mercury. Data on the distribution of ingested elemental mercury were not located, and data on the ingestion of inorganic mercury are limited. The metallic mercury that is absorbed from an oral exposure is expected to resemble many aspects of the distribution of mercuric salts because metallic mercury is oxidized to mercuric ion in biological fluids, and the resulting distribution reflects that of the mercuric ion. Unlike elemental mercury, however, the amount of divalent mercury that crosses the blood-brain and placental barriers is much lower because of its lower lipid solubility (Clarkson 1989). 

Once inhaled, mercury vapour is relatively lipid soluble and crosses the lung alveoli into the bloodstream and red blood cells. Here, it is largely converted to an inorganic divalent (mercuric, Hg ) form by the enzyme catalase which is present in the red blood cells. However, small amounts of non-oxidised elemental mercury continue to persist and readily cross the blood/brain barrier into the central nervous system, where toxic effects are caused. These may reflect the subsequent conversion of mercury into ionised forms which are then trapped in the tissues. The characteristic symptoms are of tremor, especially in activities requiring fine... 

The most metallic of the Group IV elements, lead, exists only in a ccp, metallic form. This is a reflection both of its preference for divalence rather than tetravalence and of the relatively low stability of the Pb—Pb bond. 

In the case of metallothionein, we will reflect upon how " Cd substitution and the establishment of specific Cd to Cys residue connectivity by proton-detected heteronuclear H- Cd multiple-quantum coherence methods (HMQC) was essential for the initial establishment of the 3D structure of metaUothioneins, a protein family deficient in the regular secondary strucmral elements of a-helix and p-sheet and the first native protein identified with bound Cd. The Cd NMR smdies also enabled the characterization of the affinity of the individual sites for Cd and, in competition experiments, for other divalent metal ions Zn, Cu, and Hg. 

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