FABMS

FABMS Fast-atom bombardment mass spectrometry... 

Fast-atom Bombardment Mass Spectroscopy (FABMS)... 

The treatment of sucrose with anhydrous HF89 results in the formation of a complex mixture of pseudooligo- and poly-saccharides up to dp 14, which were detected by fast-atom-bombardment mass spectrometry (FABMS). Some of the smaller products were isolated and identified by comparison with the known compounds prepared86 88 a-D-Fru/-1,2 2,1 -p-D-Fru/j (1), either free or variously glucosylated, was a major product, and this is in accord with the known stability of the compound. The mechanism of formation of the products in the case of sucrose involves preliminary condensation of two fructose residues. The resultant dianhydride is then glucosylated by glucopyranosyl cation.89 The characterization of this type of compound was an important step because it has permitted an increased understanding of the chemical nature of caramels. 

FABMS has shown that the bulky Pr PCEhCHhPPr forms the dimeric [ TcNCl2(P-P) 2]. The 3,PNMR spectrum indicates a chlorine bridged structure [57]. The reaction of MePhNNH2/dppe/[TcOCl4] in MeOH, however, yields a cationic complex formulated as the oxo-imido tra .v-[TcO(NH)(dppe)2]+. Few details are available, but the crystal structure determination showed marked asymmetry in the bonding of the two axial ligands [74]. A distinction between the [HN=Tc=OJ+ core and the tautomeric [N=Tc-OH]+ core should be possible... 

In addition to these examples, several polynuclear mercury alkynyl derivatives have been prepared. Examples of such derivatives include compounds 50-56 which have been obtained by reaction of the MeHgGl with the primary alkyne in basic methanolic conditions.67,68 The phenyl analogs have also been isolated. Most of these compounds have been characterized by FTIR, NMR, and FABMS, and in the case of 51-53 by single crystal X-ray diffraction. 

The structure of the stable germanethione 31 (see reaction 14 in Section V) was characterized by FT-Raman spectrum (i Ge=s 521 cm-1, in good agreement with 518 cm-1 reported for Me2Ge=S), UVV spectrum (/,max = 450 nm, el00, Ge=S n-n transition) and FABMS (field absorption). See also Tables 2 and 353. 

FABMS. A germanethione stabilized by bulky aryl substituents/... 

Dwyer et al. (43) have also reported that dealumination of Y zeolites by a steam/acid leaching process produces a more uniform composition than dealumination by EDTA. The later method caused a depletion of Al in the outermost surface layer, producing a compositional gradient in the zeolite crystals. The conclusions reached by J. Dwyer in his studies of aluminum-deficient zeolites using the FABMS method are summarized in Table IV. 

The bis-benzo-15-crown-5 ferrocene compound [7] containing two vinylic linkages was formed in a mixture of three isomeric components, the cis-cis, cis-trans and trans-trans isomers, which proved inseparable. However, the precedent of insignificant differences found between the magnitudes of the metal cation-induced anodic shifts in the ferrocenyl redox potentials of the respective separated cis and trans isomers [2a] and [2b] led us to use the same isomeric mixture of [7] throughout the subsequent FABMS and electrochemical group 1 and 2 metal cation complexation experiments,... 

FABMS has been used as a semiquantitative indication of the selectivity of receptors for particular guest metal cations (Johnstone and Rose, 1983). The FABMS competition experiment on [7] with equimolar amounts of the nitrates of sodium, potassium, rubidium and caesium gave gas-phase complex ions of ([7] + K)+ ion (m/z 809) and a minor peak ([7] + Rb)+ ion (m/z 855) exclusively. The relative peak intensities therefore suggested a selectivity order of K+ Rb+ Na+, Cs+, indicative of the bis-crown effect, the ability of bis-crown ether ligands to complex a metal cation of size larger than the cavity of a single crown ether unit, forming a sandwich structure. 

Alexander, A.J. Hogg, A.M. Characterization of a Saddle-Field Discharge Gun for FABMS Using Different Discharge Vapors. Int. J. Mass Spectrom. Ion Proc. 1986,69, 297-311. 

Sim, P.G. Boyd, R.K. Calibration and Mass Measurement in Negative-Ion FABMS. Rapid Commun. Mass Spectrom. 1991, 5, 538-542. 

FABMS, 39 340-342 isolobal analogies, 39 378-381 ligand addition, elimination, and substitution reactions, 39 337-338 Mossbauer spectroscopic studies, 39 342-344... 

Assembling [2] rotaxanes (wheel and axle) can involve three basic processes (Scheme 13). One of these (93CC1269) involves slippage, in which the axle (115) is linked by a 4,4 -bipyridine, and the wheel (116) is a bisparaphenylene-34-crown-10 ether. Heating the two components in acetonitrile at 60°C yields the rotaxane, which can be characterized by FABMS and H and l3C NMR, but extrusion of the wheel occurs at 100°C. In other developments (94NAT(369)133), the pyridine component may be incorporated in the wheel, as in structure (117), where two bipyridinium units are connected by p-xylyl groups, and here the rotaxane acts as molecular switch. At room temperature in acetonitrile the wheel... 

Analogous to the previously synthesized dicopper(I) knots [97], Cu2(K-84)p+ gives characteristic 1H NMR and FABMS spectroscopy data [102], In particular, some of the aromatic protons of the bis-chelates are strongly shielded, which indicates that Cu2(K-84)p is compact and that its helical core is geometrically very similar to that observed in 32. This was fully confirmed by subsequent X-ray structure determination. 

Protected methyl ester 76 (0.14 g, 0.38 mmol) was dissolved in a soln of MeOH saturated with ammonia. This mixture was stirred for 3 h at rt, at which time the MeOH was removed under reduced pressure. The resulting residue was chromatographed (silica gel column, EtOAc/hexane 5 2) to give 77 as a white solid yield 0.1 g (76%) mp 162-163 °C [a]D +143.4 (c 1.0, MeOH) FABMS mlz [M+H]+ 350. 

The ecteinascidins constitute a group of very complex alkaloid tris(tetrahydroisoquinolines) with potent in vivo antitumor activity and were isolated from the colonian Caribbean tunicate Ecteinascidia turbinata. The compounds are abbreviated as Et followed by a number that represents the value of the highest mass ion observed in the (+)-FABMS. Reports of the potent in vivo activity of extracts of that tunicate date back to 1969, when it was reported that such extracts gave T/C values of up to 272 vs P388, with four of six cures in one experiment, and they were also found to be powerful immunomodulators [72]. After a decade of effort, two research groups reported at the same time the structures of four [Et 743 (1), Et 729 (63), Et 745 (64), and Et 770 (66)] [72] and two [Et 743 (1), Et 729(63)] [73] ecteinascidins, respectively. The development of an isolation process that was efficient on a large scale allowed Rinehart s group to obtain additional ecteinascidins, Et 743 V2-oxide (67), Et 722... 

Thus as a starting point for understanding the bombardment process we have developed a classical dynamics procedure to model the motion of atomic nuclei. The predictions of the classical model for the observables can be compared to the data from sputtering, spectrometry (SIMS), fast atom bombardment mass spectrometry (FABMS), and plasma desorption mass spectrometry (PDMS) experiments. In the circumstances where there is favorable agreement between the results from the classical model and experimental data It can be concluded that collision cascades are Important. The classical model then can be used to look at the microscopic processes which are not accessible from experiments In order to give us further insight into the ejection mechanisms. 

A classical dynamics model has been developed to Investigate the Importance of colllslonal processes In heavy particle bombardment experiments. This procedure Is very powerful for describing colllslonal events and provides a working hypothesis against which experimental data can be compared. He have shown numerous examples from SIMS experiments where the calculations have fit experimental data very well. The time has come for the experimentalists to conceive and execute experiments aimed at uncovering the fundamental processes Involved In the SIMS and FABMS procedures. 

A convincing body of experimental, information, now available in the literature, serves as confirmation for the possibility to desorb molecular ions out of the condensed phase even for organic molecules which are generally considered nonvolatile and/or fragile and do therefore not lend themselves to classical mass spectrometric analysis. Here the laser-MS competes with techniques such as static SIMS or FABMS, plasma- and field-desorption. 

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