Relationship of moleculated radical anion abundance and calculated lowest unoccupied molecular orbital energies for polychlorinated dibenzofurans and dibenzodioxins in electron capture negative ion mass spectrometry: Evidence for negative metastable ions

Abstract

Relationships were found between experimentally measured molecular radical anion abundances and calculated lowest unoccupied molecular orbital energies (epsilon LUMO) for polychlorodibenzofurans and polychlorodibenzo-p-dioxins. Anion abundances were measured using standard mass spectrometric techniques, while epsilon LUMO were calculated by the 'Complete Neglect of Differential Overlap' method. Polychlorodibenzofurans with calculated epsilon LUMO greater than or equal to 1.6 eV show 0% molecular radical anion and those with epsilon LUMO less than or equal to 1.4 eV show greater than or equal to 80% molecular radical anion abundance. Similarly, the molecular radical anion is absent for polychlorodibenzo-p-dioxins with calculated epsilon LUMO greater than or equal to 2.0 eV. A trend towards greater molecular radical ion relative abundance appears for 2.0 eV greater than or equal to epsilon LUMO greater than or equal to 1.0 eV and a maximum is reached around 1 eV, whereupon the molecular ion abundance diminishes with lower epsilon LUMO. B/E linked scan analysis indicates that chlorodioxins with epsilon LUMO less than 1 eV give increasing amounts of metastable anions.

Electron monochromator-mass spectrometer instrument for negative ion analysis of electronegative compounds

“…This relationship is observed for the five congeners, ranging from trichloro-to hexachlorodioxins, which show negative ion resonances within a narrow electron energy range of 0.09 eV (Table 4). Lower chlorinated dioxins yield no apparent molecular ions; those data are consistent with the known behavior of these compounds under standard ECNI-MS conditions (68).…”

“…The electron energy required for chloride ion production decreases from 0.55 eV for dichlorodioxin to 0.22 eV for hexachlorodioxin. This pattern is consistent with a lowering of the LUMO energies for more highly chlorinated compounds (8,68). (b) Polychlorobiphenyls (PCBs).…”

Electron Affinity for the Most Toxic 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD): A Density Functional Theory Study

“…Previously reported electron affinities for PCDDs calculated by using AM1, CNDO, and MNDO are not quantitatively reliable. Our research group has already demonstrated that the calculated structures, energies, vibrational frequencies, and ionization potentials of 2,3,7,8-TCDD agree well with the experimental values …”

Evidence for radical anion formation during liquid secondary ion mass spectrometry analysis of oligonucleotides and synthetic oligomeric analogs: a deconvolution algorithm for molecular ion region clusters

“…The compu-2521,5 2526,5 The histogram (dotted line) in part a Is the theoretical fit using (M -2H)•", ( -)-, M*", and ( + H)" ion abundances from the deconvolution procedure (Figure 2). tation hardware and software has been previously described (19,20). An orbital restriction of up to 75 minimal base functions did not allow us to directly perform the calculations for the complete dimers and tetramers.…”

“…Figure 5. Experimental electron affinities versus íLUM0 calculated by MNDO method (19,20): (1) tetrafluoro-1,4-benzoquinone (24)\ (2) tetrachtoro-1,4-benzoquinone (24)(25)(26); (3) chlorine (27, 28); (4) mdinltrobenzene (26); (5) p-benzoquinone (24, 25); ( 6) hexachkxoethane (24, 29); ( 7) nitrobenzene (30, 31); (8) blacetyl (31); ( 9) naphthalene (32, 33); ( 10) chlorobenzene (34, 35); ( 11) pyridine ( 23); (12) biphenyl ( 36); ( 13) benzene ( 35); ( 14) pyrrole ( 23); (15) ethylene (24).…”