The electrochemistry of microdroplets, shown to be nearly monodisperse, of N,N,N‘,N‘-tetraalkyl-para-phenylenediamine oils (TRPD, R = n-butyl, n-hexyl, n-heptyl, and n-nonyl) immobilized on a basal plane pyrolytic graphite electrode and immersed into aqueous electrolyte solution is studied using cyclic voltammetry. Upon oxidation of the TRPD droplet to the cation radical TRPD+•, anion uptake from, or cation loss into the aqueous solution takes place, so as to maintain electroneutrality within the oily deposit. The former process is shown to produce an ionic liquid, with the anion insertion taking place at the triple phase boundary of electrode |TRPD oil| aqueous electrolyte; the latter process, in contrast, takes place at the interface between the two immiscible liquids, and with two-thirds-order kinetics. The possibility of a chemical reaction taking place between the electrogenerated and inserted ions at the three-phase junction, viz. redox-catalysis or otherwise, is illustrated via reference to two systems (azide and iodide).

The endo-β-N-acetylglucosaminidases (ENGases) are an enzyme class (EC 3.2.1.96) produced by a range of organisms, ranging from bacteria, through fungi, to higher order species, including humans, comprising two-sub families of glycosidases which all cleave the chitobiose core of N-linked glycans. Synthetic applications of these enzymes, i.e. to catalyse the reverse of their natural hydrolytic mode of action, allow the attachment of N-glycans to a wide variety of substrates which contain an N-acetylglucosamine (GlcNAc) residue to act as an 'acceptor' handle. The use of N-glycan oxazolines, high energy intermediates on the hydrolytic pathway, as activated donors allows their high yielding attachment to almost any amino acid, peptide or protein that contains a GlcNAc residue as an acceptor. The synthetic effectiveness of these biocatalysts has been significantly increased by the production of mutant glycosynthases; enzymes which can still catalyse synthetic processes using oxazolines as donors, but which do not hydrolyse the reaction products. ENGase biocatalysts are now finding burgeoning application for the production of biologically active glycopeptides and glycoproteins, including therapeutic monoclonal antibodies (mAbs) for which the oligosaccharides have been remodelled to optimise effector functions.

CommunicationsPrecise mimics of post-translationally modified proteins can be constructed by using a highly selective, selenenylsulfide-mediated method. On the following pages B. G. Davis and co-workers describe the use of this approach for the glycosylation of a protein with a heptasaccharide glycan and for a multiple site-selective, chemical protein glycosylation.