Biomolecular ions trapped

R. G. Cooks, G. Chen, and C. Weil, Quadrupole mass filters and quadrupole Ion traps, in R. M. Caprioli, A. Malorni, and G. Sindona (eds.). Selected Topics in Mass Spectrometry in the Biomolecular Sciences, Series C, Vol. 504 Kluwer Academic Publishers, Dordrecht, 1997, pp. 213-238. 

SC Flenderson, SJ Valentine, AE Counterman, DE Clemmer. ESI/ion trap/ion mobility/time-of-flight mass spectrometry for rapid and sensitive analysis of biomolecular mixtures. Anal Chem 71 291—301, 1999. 

The mass analyzer is used to separate sample ions. Commonly used analyzers include time-of-flight (TOE), quadrupole (Q), quadrupole ion trap (QIT), and Fourier-transform ion cyclotron resonance (FT-ICR) (9-14). These analyzers provide a wide mass range, high accuracy, and resolution for biomolecular analysis. 

Figure 6.7 Schematics of single-quadrupole (a) and quadrupole ion trap (b) mass analyzers. (Reproduced from Jonscher and Yates with permission from ABRF News the Association of Biomolecular Resource Facilities copyright 1996.)...

Our research group has developed a wide range of new experimental methods that are designed to be performed on ions stored within radio-frequency (RF) ion traps. In this chapter, we wiU phasize the integration of trap technology within different experimental arrangements in order to perform unique scientific measuranents. We will describe measurements of both trapped-ion electron diffraction (TIED) of metal cluster ions and radiative lifetimes of trapped biomolecular ions. Experiments will be discussed in sufficient detail to permit the advantages afforded by ion trap capabilities to be appreciated. This chapter is not intended as an extensive review of trap-related experimental measurements that are referred to and discussed elsewhere in the volumes of this series. 

Fig. 6.7. The Lausanne photofragment-spectrometer for measuring spectra of cold biomolecular ions as well as their clusters with solvent molecules. In the center of the tandem quadrupole mass spectrometer is a 22-pole ion trap which can be cooled to temperatures below 10 K. The ions of interest are produced by an electrospray source, mass-selected in a quadrupole, and then injected into the trap where they are cooled via collisions with cold helium. After irradiating the ions with IR and/or UV laser pulses, the contents of the trap are ejected and sent through an analyzing quadrupole before being detected. Spectra are generated by monitoring the appearance of a particular fragment ion mass as a function of the laser wave length.

To measure the spectra of cold, biomolecular ions, one must first produce them in the gas phase and cool them to low temperatures to eliminate thermal inhomogeneous broadening. Because of their net charge, one can use electric or magnetic fields to trap the ions in space before spectroscopic interrogation. To obtain a spectrum one has to detect the absorption of light, and because the density of ions is low, it is extremely difficult to do so directly. One typically uses some type of action spectroscopy in which the consequences of light absorption are detected... 

In the same year, our group in Lausanne published first results from a similar instrument which was equipped with an electrospray ion source for producing closed-shell biomolecular ions, the first demonstrations of which were the measurement of the UV spectra of cold, protmiated aromatic amino acids, tryptophan [46], tyrosine [46, 122], and phenylalanine [122]. Spectroscopic detection is achieved by measuring the small percentage of parent ions that fragment subsequent to UV absorption. The internal temperature of the ions was estimated to be 11-16 K from an analysis of the intensity of hot band transitions of low frequency vibrational modes. If the temperatures achieved in buffer-gas cooled ion traps are low enough and the spectra sufficiently simple, one can often resolve UV absorption spectra for different stable cOTiformers of the molecule [122]. In this case, one can use the IR-UV double resonance techniques so profitably employed in supersonic molecular beam studies [91,123-128] to measure conformer-specific infrared spectra, and this was applied by Steams et al. to both individual amino acids [129] as well as peptides with up to 12 amino acid residues [130]. Subsequent improvements to the Lausanne machine (Fig. 7) included the addition of an ion funnel to... 

In a completely different approach to all the above-mentioned studies, von Helden and coworkers have combined ion trap technology with superfluid helium nanodroplets to measure spectra of cold biomolecular ions [59]. As illustrated schematically in Fig. 12, after producing gas-phase biomolecules via electrospray, they mass select them, bend them 90° with a static quadrupole deflector, and then trap them in a room temperature ion trap. A pulsed, helium droplet source produces... 

The original ECD implementation by Zubarev, Kelleher, and McLafferty involved an FT-ICR mass analyzer with an ion cell fitted with extra trapping electrodes to allow trapping of both electrons and precursor cations. The FT-ICR mass analyzer is ideally suited for ECD because very light electrons can be stored at the same time as large biomolecular ions, thereby maximizing their interaction. Later FT-ICR... 

Henderson, S. C. Valentine, S. J. Counterman, A. E. Clemmer, D. E., ESFlon Trap/ Ion Mobihty/Time-of-Flight Mass Spectrometry for Rapid and Sensitive Analysis of Biomolecular Mixtures , Ana/. Chem. 1999, 71, 291-301. 

Peroxynitrite. - In terms of its ability to induce biomolecular injury, by far the most important reaction of NO is its combination with 02 to form the oxoperoxonitrate(— 1) ion (ONOO , peroxynitrite ) [k = (6.7-19) x 10 M s ]. Whereas ONOO is relatively stable, peroxynitrous acid (ONOOH, pKa 6.5-6.S) undergoes rapid decay to the harmful OH and NO2 radicals at a yield of ca. 30% (see Tsai et al. and references therein ). Although there are several cellular sources of 02 for combination with NO, spin trapping studies have shown that NOS itself may generate the radical, but not without attracting controversy. 

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