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Nonthrombogenic sensors
adhesion—are significantly lower than those of "NO-free" sensors. The NO-releasing compound used in the experiments was an A^A^-dimethylhexanediamine nitric oxide (DMHD/N2Oj) adduct, a diazeniumdiolate species that spontaneously generates NO in aqueous solutions. The compound was incorporated as a fine disper-
sion into either polyurethane or high molecular weight poly (vinyl chloride) membranes used to construct ion-selective electrodes for H+ and K+. Release of NO was confirmed by One of the "Holy Grails" of analytical chemmeasuring the formation of nitrite by flowistry is the development of implantable injection analysis. The electrodes with or chemical sensors that continuously meawithout the diazeniumdiolate compound sure physiologically important ions (such were tested against platelet-rich sheep as H+ and K+) and gases (such as C0 2 and 0 2 ) in blood. So far, plasma. The devices dischemists have had limited played comparable analytisuccess because these cal performance, but the devices can be thromboNO-releasing sensors had genic and cause vasoconfewer adhered platelets. striction of arteries. Also, the platelets were not activated, as measured by Mark Meyerhoff and the lack of pseudopod exhis colleagues at the Unitensions. Although the poversity of Michigan attential toxicity of this aptacked this problem by proach needs to be investiincorporating a nitric gated the authors calculate oxide-releasing compound that the NO released from into their sensors. NO is a an implanted catheter made potent platelet antiaggregafrom these new films would tion and vasodilation agent be far less than the 1 mol or They report that when low more of NO produced endolevels of NO are emitted, genouslv each dav in huthe thrombogenic properScanning electron micrographs of sensing membranes (A) without and (B) with mans (l.Am Chem Soc ties of the sensor as meaDMHD/N202, showing the difference in platelet adhesion. Top images 1997 119 2321-22) sured by in vitro platelet represent a five-fold increase in magnification of the boxed area on the bottom.
Measuring the carbo load of proteins
A 300-fold increase in sensitivity. (A) MALDI mass spectrum of the underivatized oligosaccharide A2F (disialylated, galactosylated, ,iantennary, core substituted with fucose). (B) MALDI mass spectrum of derivatized A2F. (Adapted with permission from the National Academy of Sciences.)
Many proteins are more than just an amino acid sequence, and a complete characterization of any protein would ideally include the structure of any posttranslational modifications that might affect its behavior. Unfortunately, the structural elucidation of carbohydrates, a moiety frequently found in modified proteins, often proves daunting. Brian T. Chait and co-workers at Rockefeller University and the Scripps Research Institute increased the sensitivity of MS measurements of oligosaccharides by ligating them to an aminooxyacetyl form of a basic peptide. The resulting glycopeptide was digested by an exoglycosidase array, and the digestion products were analyzed by MALDI-MS.
For the glycopeptides, the strongest ion signals were observed using saturated a-cyano-4-hydroxycinnamic acid matrix. The underivatized oligosaccharides were ionized most effectively with a matrix that was a mixture of 2,5-dihydroxybenzoic acid and 1-hydroxy isocarbostyril. The sensitivity of die mass spectrometric measurement increased anywhere from 50- to 1000-fold for derivatized relative to underivatized oligosaccharides because the saccharides were easier to ionize and the mass was in a range better suited for MALDI-MS analysis. Sensitivities for the derivatized oligosaccharides are in the low femtomole range This derivatization method represents an improvement over conventional oligosaccharide sequencing because it provides higher resolution, tolerates oligosaccharide heterogeneity, and can be performed without complete digestion. (Proc. Natl. Acad. Sci. USA 1997, 94, 1629-33)
Analytical Chemistry News & Features, May 1, 1197 277 A
