Accelerator mass spectrometry structures

Elmore, D., Anantaraman, N., Fulbright, H. W., Gove, H. E., Hans, H. S., Nishiizumi, K., Murrell, M. T., Honda, M., Half-life of 32Si using tandem accelerator mass spectrometry, Nuclear Structure Research Laboratory, University of Rochester, NY, Publication UR-NSRL-220, 11 p., 1980. 

Because use of mass spectrometry by chemists has increased greatly, most U.S. chemists have access to mass spectrometry facilities at their own institutions to confirm synthesis and support structure elucidations. Heavily used national centers provide more expensive instrumentation and more complex experiments. Most notably, a section of the National High Magnetic Field Laboratory at Florida State University provides state-of-the-art Fourier transform ion cyclotron resonance mass spectrometry. The NSF Arizona Accelerator Mass Spectrometry Laboratory is used primarily to provide radiocarbon measurements. NIH funds a number of national mass spectrometry centers to support biomedical research, including those at Boston University and the Pacific Northwest National Laboratory. 

Other experiments have also aimed to identify the chemical structure of potential ochratoxin A adducts. In in vitro studies, incubation of ochratoxin A with DNA or dG in the presence of various activation systems did not reveal any adducts, neither by P-postlabelling nor by liquid chromatography/tandem mass spectrometry (LC-MS/MS). Subsequently, DNA was isolated from the livers and kidneys of male Fischer rats treated with a single dose of P C]ochratoxin A (0.5 mg/kg bw) and analysed by C-accelerated mass spectrometry. No significant difference between control group and treated group could be observed in C activity in isolated DNA from treated animals, and no specific ochratoxin A-DNA adducts were detected with C-accelerated mass spectrometry (Mally et al., 2004). The EFSA opinion pointed out that a concern in the interpretation of these results is that DNA adducts may have been repaired, as DNA was isolated 72 h after a single treatment with a relatively low dose, which is in contrast to other studies, in which DNA was isolated within 24 h after exposure to ochratoxin A (European Food Safety Authority, 2006),... 

Figure 5.45 Structures of (1) Bosentan (C27H29N5O6S [M + H]+ 552.1917) and three of its metabolites, formed by (2) oxidation (C27H29N5O7S [M + H]+ 568.1866), (3) demethylation (C26H27N5O6S [M- -H]+ 538.1760), and (4) demethylation-oxidation (C26H27N5O7S [M + M]+ 554.1709). Reprinted by permission of Elsevier Science from Exact mass measurement of product ions for the structural elucidation of drug metabolites with a tandem quadrupole orthogonal-acceleration time-of-flight mass spectrometer , by Hopfgartner, G., Chemushevich, I. V., Covey, T., Plomley, 1. B. and Bonner, R., Journal of the American Society for Mass Spectrometry, Vol. 10, pp. 1305-1314, Copyright 1999 by the American Society for Mass Spectrometry.

In an effort, to study the effect of introduction of -C=C- on thermal stability of polynitroaromatics, Feng and Boren designed 3,3 -bis((2,2, 4,4, 6,6 -hexanitrostilbene) and azo-3,3 -bis (2,2, 4,4, 6,6 -hexanitrostilbene), synthesized and studied their structural aspects by infrared (IR), NMR, elemental analysis and mass spectrometry [64]. These explosives are expected to have high m.p. and thermal stability in view of their large molecular masses and better molecular symmetry. Further, DSC study of these explosives also proves that thermal stability of an explosive is associated with its m.p. Also decomposition rate is accelerated... 

Some destructive techniques require a thousandth of a gram while some need less than a millionth of a gram. One particularly useful combination of techniques is gas chromatography (GC) linked to mass spectrometry (MS), which together can separate the components of a complex mixture and identify all of them. In M S, molecules in the gaseous state are ionized and then exposed to an electric field. This accelerates them to a speed that enables a magnetic field to deflect them and the extent to which they are deflected depends on the atomic mass of the particle which thereby reveals its constituent atoms, from which its molecular structure can then be deduced. 

Rationalization of known compounds provides a level of usefulness that justifies the rule. But the rule also permits observed molecular stoichiometries of newly synthesized compounds to be translated into acluster shape. For example, [Al Bu ]2-has eve = 50 or sep =13 consistent with n = 12 and a deltahedral structure. The compound has been synthesized and an X-ray diffraction study reveals an icosahe-dral shape. The ability to suggest reasonable structures based on knowledge of a molecular formula generated by a technique like mass spectrometry accelerated the development of cluster chemistry simply because rapid spectroscopic methods can be more productively applied. Although efficient X-ray crystallographic structure determination reduces its importance for compounds that can be isolated in pure crystalline forms, transient intermediates detected in a reaction mixture can now be given reasonable structures. 

Baldwin, M.A. Medzihradszky, K.F. Lock, C.M. Fisher, B. Settineri, T.A. Burhngame, A.L. Matrix-assisted laser desorption/ionization coupled with quadrupole/orthogonal acceleration time-of-flight mass spectrometry for protein discovery, identification, and structural analysis. Ana/. Chem. 2001, 73, 1707-1720. 

---