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Transuranium Elements: A Half Century eveloped from an international jrattmmitium symposium commemorating the fiements 50th Anniversary of the discovery ί lid/ il\Î"»·' of transuranium elements, this volume honors the chemists, physicists, materials scientists, and engineers who were the pioneers of transuranium research in the 1940s. Opening with a comprehensive review by Glenn T. Seaborg of the discovery of transuranium elements and his perspec tive on the future of the field, the volume offers an outline of the discoveries of transuranium elements and of the chemical foundations of transuranium research, written by the pioneers themselves. The volume also emphasizes contemporary research with articles on nuclear chemistry and physics; spectroscopy, photophysics, and photochemistry; inor ganic and analytical chemistry; materials physics and chemistry; and solution and environmental chemistry of the transuranium elements. Contents • Historical Viewpoints · Materials Physics • Nuclear Physics and Chemistry · Materials Chemistry • Chemistry · Analytical Chemistry • Separations, Thermodynamics
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254 A • ANALYTICAL CHEMISTRY, VOL. 65, NO. 5, MARCH 1, 1993
other ionization methods for larger biomolecules (including ESI), MALDI is generally insensitive to contami n a n t s , such as salts, buffers, and surfactants, which are difficult to completely eliminate from a biologi cal sample (41). The combination of MALDI with FTMS was initially demonstrated for the generation of molecular ions from small peptides (43, 44) and oligonu cleotides (45, 46). The presence of the m a t r i x s u b s t a n t i a l l y reduced t h e amount of fragmentation of these biomolecules. This technique proved to be useful for determining the mo lecular weights, sequences, and ad duction sites for a number of small oli gonucleotides at the low-picomole level (45, 46). The negative-ion MALDIFTMS spectra for these biomolecules revealed abundant (M-H)~ ions and fragment ions that provided the infor mation necessary to determine oli gonucleotide sequence, as shown in F i g u r e 4a for t h e t e t r a n u c l e o t i d e d(AGCT), as well as differentiate iso mers. The primary fragmentation of these compounds was observed to be cleavage of the phosphate ester bonds with the resulting charge retained on the 3' end of the oligomer, yielding fragment ions at m/z 939, 610, and 321 for d(AGCT). Fragmentation in the reverse di rection with the charge retained on the 5' end was observed to be minor. This preferential fragmentation pro vides information that is sufficient not only to determine the sequence of an oligomer but also to identify the 3' nucleotide of the oligomer, and it can be used to differentiate sequence isomers such as d(5'-CGCG-3') and d(5'-CCGG-3') as well as isomers dif fering only in the location of the 3' end, such as d(5'-CGCG-3') and d(5'-GCGC-3') (43). Figure 4b shows the CAD spec trum of the (M-H)~ ion at m/z 1172 for d(AGCT). The fragment ions are identical to those generated by the LD process shown in Figure 4a and indicate a preference for fragmenta tion of the phosphate ester linkages with the charge retained on the 3' end of the oligomer. MALDI-FTMS was also found to be useful for the structural charac t e r i z a t i o n of modified oligonucle otides. For example, mass spectra for t h e tetranucleotide d(TGCA) were compared with m a s s spectra of a modified version of this t e t r a m e r , d(TG*CA), where G* is 0 6 - m e t h y l guanine. Inspection of the differences among the fragment ions for these similar biomolecules verified t h a t the methyl adduct was present on the
