Structural characterization of various dirhodium compounds using fast atom bombardment and collision-induced dissociation mass spectrometry

Abstract

Fast atom bombardment (FAB) and collision-induced dissociation (CID) tandem mass spectra of a series of novel pyrazolato-bridged dirhodium A-frame compounds provide structure confirmation and useful information concerning the structural dependence of lability, based upon fragmentation pathways. CID mass spectra indicate that FAB matrixand beam-induced reduction chemistry can alter the energy and/or the structure of the precursor molecules.However, it appears that FAB matrixand beam-induced oxidation chemistry does not do so delectably.limit the amount of structural information that can be gained from FAB mass spectra. Collision-induced dissociation (CID) MS14•15 coupled with FAB ionization has proven useful in providing structural information for organic compounds like peptides16 and

Binding of DNA Purine Sites to Dirhodium Compounds Probed by Mass Spectrometry

“…The enhanced lability of CF 3 CO 2 - compared to that of the CH 3 CO 2 - ligands is supported by the fact that a different number of bridging groups are retained by the dirhodium core in the reactions of Rh 2 (O 2 CCF 3 ) 4 (prevalent ion [M + Rh 2 − 5H] - (II)) and Rh 2 (O 2 CCH 3 ) 4 (prevalent ion [M + Rh 2 (O 2 CCH 3 ) − 3H] (III)) with GG sequences (Figures S2, S5B, and S6 (Supporting Information)) and by the presence of an intense monotrifluoroacetate adduct ion peak for [M + Rh 2 (O 2 CCF 3 ) − 3H] - (IIIa) observed mainly by ESI (Supporting Information, Figure S6) because of the softness of the ionization process . The higher reactivity of Rh 2 (O 2 CCF 3 ) 4 compared to that of Rh 2 (O 2 CCH 3 ) 4 correlates with the increased basicity of CH 3 CO 2 - (p K b 9.25) compared to that of CF 3 CO 2 - (p K b > 13), which makes the latter a better leaving group, , whereas the enhanced reactivity of [Rh 2 (O 2 CCH 3 ) 2 (CH 3 CN) 6 ] 2+ compared to that of Rh 2 (O 2 CCH 3 ) 4 , upon reaction with DNA oligonucleotides, is justified on the basis of the presence of more labile monodentate eq acetonitrile groups compared to bidentate acetate bridges. The latter point is further confirmed by the fact that the acetate ligands remain attached to the dirhodium core, in favor of the eq acetonitrile groups, during the desorption and ionization process in the MALDI mass spectra of [Rh 2 (O 2 CCH 3 ) 2 (CH 3 CN) 6 ] 2+ adducts with GG sequences (Figure ); that is, no dirhodium acetonitrile-containing species are observed in the MALDI spectra.…”

“…The comparable reaction time scale of cis-[Pt(NH 3 ) 2 -(OH 2 ) 2 ] 2+ and Rh 2 (O 2 CCF 3 ) 4 with DNA oligonucleotides indicates that trifluoroacetate groups are highly labile; in fact, the Rh 2 (O 2 CCF 3 ) 4 reaction is complete within the first day of incubation (Supporting Information, Figure S9). The enhanced lability of CF 3 CO 2compared to that of the CH 3 CO 2ligands is supported by the fact that a different number of bridging groups are retained by the dirhodium core in the reactions of Rh leaving group, 55,88 Effects of Oligonucleotide Length on Reactivity and Specificity of Products. The observed trend of dodecamers and octamers reacting faster than tetramers, for a given metal complex and the same purine motif (except for the case of [Rh 2 (O 2 CCH 3 ) 2 (CH 3 CN) 6 ] 2+ which reacts faster with the GG octamers than with the dodecamers, Figures 1 and 2) was established by MALDI MS. An enhanced rate of reactivity with increasing oligonucleotide length has been noted for platinum compounds and is attributed to initial weak preassociation (due to electrostatic interactions) between the positively charged metal species and the negatively charged phosphate backbone prior to covalent binding.…”