Cisplatin Primary Complex with l-Histidine Target Revealed by IR Multiple Photon Dissociation (IRMPD) Spectroscopy.

The primary complex obtained from cisplatin and l-histidine in water has been detected and isolated by electrospray ionization. The so-obtained cis-[PtCl(NH3 )2 (histidine)]+ complex has been characterized in detail by high-resolution mass spectrometry (MS), tandem MS, IR multiple photon dissociation (IRMPD) spectroscopy, and by quantum chemical calculations. The structural features revealed by IRMPD spectroscopy indicate that platinum binds to the imidazole group, which presents tautomeric forms. Thus, depending on the position of the amino acid pendant on the imidazole ring, isomeric complexes are formed that are remarkably different with respect to the ease with which they undergo fragmentation when activated either by energetic collisions or by multiple IR photon absorption. It is shown here how IRMPD kinetics can allow their relative proportions to be estimated.

Infrared absorption features of gaseous isopropyl carbocations.

C3H7+ ions were formed in the cell of a Fourier transform ion cyclotron resonance mass spectrometer and assayed by their multi-photon dissociation (MPD) behavior, triggered by the absorption of tunable IR radiation from a free-electron laser source providing a high fluence. The derived experimental IRMPD spectrum, which reflects the active vibrational modes of the ion, was compared with the IR spectra calculated for the optimized structures of the most-stable species on the C3H7+ potential energy surface, namely, a chiral iC3H7+ ion of C2 symmetry and an asymmetric corner-protonated cyclopropane, cC3H7+. The significant features in the IRMPD spectra of both the unlabeled and the perdeuterated ions obtained by ionization and fragmentation of isobutane or 2-chloro[D7]propane confirm the presence of the isopropyl cation, the ground-state isomer, whose IR spectroscopic features can thus be comparatively checked in the gas phase and in condensed superacid media. Details of the IRMPD features are suggested to result from the nearly barrierless interconversion of the two C2 enantiomers.