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Co (II) Br/auxiliary ligand solutions were successful for five of the analytes. 2,2'-Dipyridine generated the most abundant ternary complexes with most of the substrates. The authors attribute its success to the proximity of the nitrogen binding sites to one another and to the free rotation along the C-C bond between the pyridyl rings. 4,4'-Dipyridine was the only auxiliary ligand that produced no
ternary complexes with any of the pharmaceuticals. Nickel complexes did not produce as many fragments as cobalt complexes. For three of the pharmaceuticals, the copper complexes demonstrated more fragmentation pathways than the cobalt complexes, indicating that CAD spectra can be tailored by selecting the transition metal. (J. Am. Soc. Mass Spectrom. 1998, 9, 463-72)
No metal required
nanoelectrospray emitter tips that don't need metal coatings and can be made with common laboratory implements. Instead of using abrasion or a capillary puller, the emitter tips are formed in the flame of a Bunsen burner. By pulling 50-pm capillaries, they formed emitter tips with an ~10-)im opening. Theflowrates were in the range of 30-80 nL/min. The emitter tips were used to obtain mass spectra of bovine insulin and angiotensin III. The emitter tips can be used for several hours with different analytes by flushing the tips between samples. (Rapid Schematic illustration of the nanoelectrospray device. Commun. Mass Spectrom. (Adapted with permission. Copyright 1998 John Wiley & 1998,12,443-48) Sons.)
Most nanoelectrospray tips are coated with a thin gold film to apply the electrospray potential. That film tends to deterio rate rapidly (typically in 30 min, but tome have lasted as long as 3 h) )s that each tip can be used for only one sample. David C. Muddiman and James C. Hannis of Virginia Commonwealth University describe
SCIENCE
Sticky nanoparticles Analytical chemists are always in search of selectivity. In the June 1 issue of Analytical Chemistry (p. 2197), Ernst Bayer and doworkers at the Universitat Tubingen describe nanoparticles that provide such selectivity for oligonucleotides. The particles can isolate this class of compounds from any aqueous solution, including those found in biological samples. The 180-nm-diameter nanoparticles are made from a noncrosslinked polystyrene with positively charged end groups. Thanks to an emulsifier-free polymerization technique they are very pure and remain spherical in aqueous solutions over a wide range of pH and ionic strength. (In contrast to cross-linked beads, these nanoparticles are soluble in some organic solvents.) In size and biological function they fall somewhere between micelles
and ion-exchange particles. What makes them unique are their specific hydrophobic and electrostatic interactions with oligonucleotides as short as 10 nucleotide units. This property should be useful in the preparative and analytical isolation of antisense oligonucleotide drugs from body fluids. When the particles are used as an isolation tool, a suspension of nanoparticles is added to the biological fluid, incubated for several minutes, centrifuged, and washed twice; the oligonucleotides can then be desorbed from the particles by the addition of a release buffer at high pH. The released oligonucleotides are then ready for investigation and quantitation by capillary electrophoresis and electrospray MS. "We had to find the optimum conditions by trial and error, but now the protocol is really simple," Bayer explains. "Because the nanopar-
ticles are so small, the centrifugation time is about 20 min, which could be a problem for serial analysis. Therefore we have synthesized 400-nm particles and even larger ones in order to achieve an improved sample workup using automated filtration systems." The development of the extraction method is based on recent work of Bayer's group in which similar cationic nanoparticles were designed for their application as colloidal drug carriers for antisense oligonucleotides (J. Colloid Interface aci. 1997, 195,272-88). These nanoparticles are now used in cell culture experiments to study the transport of antisense drugs directly into cells. The small particles can smoothly enter biological cells, thus acting as vehicles that bring antisense nucleotides to the site where they can block messenger RNA. So far the experiments have demonstrated that the amount of antisense drug needed is only 1/10 as much as needed with conventional application techniques. Bethe nanoparticle-oligonucleotide conjugates are stable at low pH such drugs could be taken orally and would pass the stomach without decomposition Possible applications in humans are still a long way off. In the meantime, Bayer is thinking about applications for nanoparticles in technological fields unrelated to biochemistry. Their synthesis would be unsuitable for mass production because of the difficulty in achieving the charged end group, but they could replace latex beads in many applications. Chemical affinity seems to be limited to polyanionic substances such as oligonucleotides (maybe even long ones), heparins, and nitrophenols. Trace analysis of nitrophenols in environmental water S3.ni-
ples is currently difficult and unsatisfactory. Could the Bayer beads change this for the better? Veronika R. Meyer
A micrograph of the nanoparticles.
