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A new synthetic route to the covalent bonding of an organic monolayer bearing terminal phosphorylcholine (PC) groups onto the surface of silicon oxide is reported; such monolayers prohibit the deposition of enzymes and proteins and can be used to improve surface biocompatibility.

SummaryThis Review reports the more recent applications of radiohalogen labelling in organic compounds. Modern synthetic methods place more emphasis upon substitution at specific sites. Electrophilic substitution, especially at aromatic carbon atoms, involves displacement of halogen or of metals rather than the earlier popular halogen-deprotiation processes. Nucleophilic displacement, at either aliphatic or aromatic sites, has also become widespread since it may be made more selective by the inclusion of appropriate activating groups or suitable displaced groups. Microwave and thermally induced methods are both reported with a critical assessment of the value of each process.

The synthesis of [lSN]-l, 1,3,3-tetrakis(trideuteriomethyl)isoindolin-2-yloxyl and of some S-alkyi derivatives have been achieved by standard synthetic routes. The presence of deuterium improves the sharpness of the signals, and this, together with the incorporation of nitrogen-15, enhances the application of such compounds as spin probes; alkyl substituents at C-5 improve the lipophilicity.

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The Co atom can be methylated by reaction of the Col cobalamin with the PhNMe3+ ion in aqueous solution at 25 "C at a pH-independent rate (pH 4-10) with the second-order rate constant k2 = 2 X 10-3 dm3 mol-1 s-1.Methyl transfer is the simplest nucleophilic substitution reaction, as well as one of the most extensively studied and best understood of all organic reactions.' Little is known, however, about the first transfer of a de novo synthesised Me group from the N5 of N-Me-THFA (THFA = tetrahydrofolic acid) to the S of homocysteine to form methionine, for which nature has evolved two families of enzymes.* In the BIZdependent enzymes the mechanism involves the alternate formation of CoI and Me-Co corrinoids; in the less efficient B12-independent enzymes there is no evidence for any prosthetic group. N-Me donors able to methylate thiols nonenzymatically and provide a model for the B12-independent pathway include N-Me-py+ ,334 PhNMe3+ ,4 N5-Me-THFA