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Biological methylation is an enzymatic process in which a methyl group is transferred from one atom to another. For elements having atomic number greater than 11, biological methylation has been most extensively studied for three elements: arsenic, mercury and sulfur. However, many other elements also undergo biological methylation but have received less attention. Recent work on these lessstudied elements and new applications of biological methylation to environmental remediation, along with a description of these reactions in terms of bonding models, is the focus of this review.

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The heaviest main-group elements (mercury through radon and their heavier congenors) often show markedly different chemical properties than their lighter counterparts. Most of these differences arise from changes in the relative energies of the outer-shell atomic orbitals that can be explained by application of Einstein's theory of special relativity ("relativistic effects") to electrons in atoms. Changes include stabilization of lower oxidation states, destabilization of higher states, and greater tendencies towards cluster formation. These will be illustrated by examples of recent research reports, and predictions for the chemistry of elements 112 through 118.

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Traces the synthesis and analysis of potassium trichloro(theylene)platinate(II) monohydrate, named Zeise's salt in honor of its discoverer.

Formation of bonds between methyl groups and heavy elements (metals or metalloids) alters various physical properties such as solubility or volatility. This alteration enhances the mobility of the heavy metal and can play a major role in the environmental cycles for these elements. Environmental methylation has been established as a major factor in the environmental movement of mercury and arsenic, and very probably affects other elements similarly. Two methylating agents (methylcobalamin and methyl iodide) have been found to mobilize metals out of water-insoluble compounds andlor anoxic sediments. These two compounds react with quite different substrates, but the kinetics of the resulting dissolutions follow virtually identical patterns. These reactions proceed through formation of a methylated intermediate on the substrate surface, followed by movement of the heavy element out of the solid lattice into the surrounding solution.