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ANALYTICAL CURRENTS

Increased electron transport in "wired" electrodes Because the rate of electron transport through cross-linked redox hydrogels is controlled by segmental motion of the polymer chains, Adam Heller and col­leagues at the University of Texas at Aus­tin have found that increasing the charge density on the backbone of the polymer "wires" through quaternization of the pyri­dine nitrogens significantly enhances the rate of electron transport. They have now extended their study of quaternization en­hancement to include glucose elec­trodes. Glucose electrodes based on the "wiring" of glucose oxidase via poly(vi-nylpyridine) and poly(vinylimidazole) re­dox hydrogels have no leachable compo­nents and do not require oxygen for their operation

Redox polymers based on the poly(vi-nylpyridine) complex of [Os(bpy)2Cl]+/2* were quaternized with methyl iodide and used to "wire" glucose oxidase. Heller

and co-workers report that quaternization enhanced the rate of electron transport and the strength of the electrostatic com­plex that formed between the polycationic redox polymer and the polyanionic glu­cose oxidase.

Optimal electrode performance is achieved when one-third of the pyridines are quaternized and the enzyme "wiring"

polymer has about one [Os(bpy)2Cl]+/2+

redox center per six pyridine rings (when about half of the rings are quaternized). Glucose electrodes that are made with such a polymer have an activation en­ergy of ~ 46 ± 2 kj/mol and an appaaent Michaelis constant of 15 mM in the ab­sence of a diffusion-limiting membrane. (J. Phys. Chem. 1996,100, 37,9-27)

Schematic representation of the "wired" glucose electrode.

Analyzing combinatorial peptide libraries

Combinatorial libraries offer a promising new approach for obtaining large num­bers of peptides for pharmacological screening. However, the analytical investi­gation of these libraries, which can con­tain millions of individual molecules, has not been well documented. Jean Boutin and his colleagues at the Institut de Recherches Servier (France) have used NMR MS, and HPCE to provide exten­sive data on the composition of peptide and pseudopeptide libraries.

They applied various techniques to tet-rapeptide libraries (13,824 compounds per reactor) made from building blocks of 24 amino acids. According to the authors, 2-D NMR provides information on the incor­poration of a given, exotic amino acid into the peptide chain compared with other amino acids in the library, and tandem MS

can be used to determine the presence of the individual amino acids as well as resid­ual protecting groups and byproducts. 13C NMR is used to survey solid-phase synthesis of nonpeptide combinatorial

libraries, whereas HPCE is used to sepa­rate the libraries into charged families. FABMS was also used to characterize certain libraries. (Anal. Biochem. 1996, 234,126-41)

Automated synthesis of combinatorial libraries using mixture chamber reactor set, five amino acid racks, and, in the center, a robotic transfer arm.

Analytical Chemistry News & Features, May 1, 1996 293 A