The MS/MS and H/D-exchange results are comparable with the recently published NMR structure of RES-701-1. The naturally occurring peptide has a highly ordered structure with a "tail" that passes through a "ring", which the authors refer to as a "lasso-type" structure. The structure could not be duplicated synthetically. RES-701-1 has an unusually stable structure that can withstand the solution-to-gas phase transition and CAD processes. The authors believe the stability is caused by electrostatic forces. Other peptide complexes that are held together by hydrophobic interactions not exhibit such high stability under vacuum conditions. (J. Am. Chem. Soc. 1998 120 4542-43)
Controlling the assembly of electroactive films Iron heme enzymes, such as cytochrome P450 (cyt P450), which is found in the liver, are known to act as catalysts in the oxidation of lipophilic pollutants and drugs. The oxidation cycle begins with the reduction of heme Fe m to Fe11. To study the enzymecatalyzed activation of pollutants by electrochemical methods, this key reduction must take place on an electrode surface. Proteinsurfactant films on pyrolytic graphite electrodes that simulate enzymatic reductive catalysis of organohalide pollutants have been previously reported Suchfilmsare useful for electrochemical applications bethey "turn on" protein electrontransfer reactions; however their structures are based on the molecular ties that guide the self-assembly process In other words the researcher has no control over the final structure of the films To gain more control over the design of specific films, Yuri M. Lvov, James F. Rusling, and co-workers at the University of Connecticut explore alternating the ad-
Nanoelectrospray source
capillaries are inserted into the reservoir as a pickup line and a pressure/vent llne. The latter capillary is connected to a presWith its ultralow flow rate and small sure regulation station. The pickup line sample consumption, nanoelectrospray connects to the ion spray body, which (nanoES) has greatly improved peptide and protein analysis. Its original concep- consists of a stainless steel microvolume union. The ion spray needle is a tapered tion, however, precludes precise flow 3-cm fused-silica capillary with an inner rate control and analysis of more than diameter of 1-5 um. The ion spray potenone sample. Paul Tempst and co-worktial was applied to the ion spray body, ers at Memorial Sloan-Kettering Canrather than the needle, so the needle cer Center have designed a nanoES source that they call injection adaptable lasted for several days. fine ionizatton source QaFIS) )or continJaFIS was interfaced with a tripleuous-flow nanoES. quadrupole mass spectrometer and used to analyze a control peptide mixThe JaFIS is constructed with a ture, consisting of 50 fmol/uL P-galacto0.2-mL polymerase chain reaction tube as the sample reservoir. Two fused-silica sidase tryptic digest. Standards and multiple samples could be analyzed consecutively with the same needle. Samples were changed by switching the sample reservoir. With JaFIS, flow rates of 10-100 nL/ min and sensitivity of 25 fmol/uL obtained (Rabid Commun Ma,s Shedrom 1998 12 551-56)
sorption of polycations and polyanions, which act as "electrostatic glue", onto polymerfilms.Ultrathin (5-10 nm) electroactive films of myoglobin (Mb) and cyt P450cam are assembled onto gold electrodes, layer by layer, with polyions of opposite charge. Quartz crystal microbalance and voltammetric methods are used to confirm that each step in the process provides a new monolayer of adsorbate. In all cases, only thefirstprotein monolayer was fully electroactive, indicating that the distance from the electrode is a critical parameter for electroactivity. Direct, reversible electron transfer between the proteins and the electrodes was observed under aerobic conditions, allowing the films to be used for enzymelike catalysis. Both the Mb and cyt P450 films are shown to catalyze the oxidation of styrene to styrene oxide. (J. Am. Chem. Soc. 1998 Various film architectures of Mb located at different 120 4073-80) distances above a Au electrode.
A complex ionization process Metal complexation could provide an alternative method of ionization for pharmaceutical compounds. Jennifer S. Brodbelt and Erwin J. Alvarez of the University of Texas at Austin used pyridyl and polyether compounds as auxiliary ligands to promote the formation of metal complexes with pharmaceutical compounds in electrospray ionization. The structure of the complexes was probed with collisionally activated dissociation (CAD). The goal was to form complexes that provided richer fragmentation information than their protonated counterparts. Eleven pharmaceutical compounds (the analytes) and eight auxiliary ligands were used in the MS studies. The auxiliary ligands were needed because metal complexes did not form efficiently with a simple solution of the metal (cobalt, copper, and nickel salts) and the analyte. Electrospray experiments with the pharmaceutical/
Analytical Chemistry News & Features, July 1, 1998 441 A
