Singly aquated and diaquated species are key intermediates in the mechanism responsible for the antitumor activity of cisplatin. Aqua complexes [PtX(NH₃)₂(H₂O)]⁺ (X = Cl, OH), obtained in water by hydrolysis of cisplatin and of the inactive isomer transplatin, are transferred into the gas-phase by electrospray ionization. The so-formed ions, cis- and trans-[PtX(NH₃)₂(H₂O)]⁺, have been allowed to react with selected ligands, representing platination targets in the biological environment. The reaction kinetics monitored in the gas-phase show consistently higher reactivity for the chloro complexes, [PtCl(NH₃)₂(H₂O)]⁺, with respect to the hydroxo counterparts, [Pt(OH)(NH₃)₂(H₂O)]⁺. The latter species, both cis- and trans-isomers, have been assayed by IRMPD spectroscopy in the NH/OH stretching region and their vibrational and geometric features are compared with the ones pertaining to the already described chloro complexes, cis- and trans-[PtCl(NH₃)₂(H₂O)]⁺.

Cisplatin and transplatin (cis- and trans-[PtCl₂(NH₃)₂]) have been allowed to react with methionine (Met) in water solution in a study aimed to characterize the monofunctional complex primarily formed. The thioether function of methionine is known to have a very high affinity for square planar platinum(II) and sulfur-containing biomolecules have been proposed as a cisplatin drug reservoir on the way to platination at DNA. Both cisplatin and transplatin yield [PtCl(NH₃)₂Met]⁺ complexes, delivered by electrospray ionization in the gas phase and sampled as isolated species using tools based on mass spectrometry. The collision induced dissociation spectra of both cis-[PtCl(NH₃)₂Met]⁺ and trans-[PtCl(NH₃)₂Met]⁺ are quite similar and also the transport properties assayed by ion mobility mass spectrometry do not allow any appreciable discrimination. However, the vibrational spectra obtained by IR multiple photon absorption (IRMPD) spectroscopy show distinct features. Their analysis, supported by quantum chemical calculations, has revealed that while cisplatin attack is mainly directed to the sulfur atom of Met, transplatin shows a more balanced partition between sulfur and nitrogen binding. Among the vibrational signatures characterizing cis-[PtCl(NH₃)₂Met]⁺ and trans-[PtCl(NH₃)₂Met]⁺ complexes, the asymmetric NH₂ stretching of the α-amino group of the amino acid at ca. 3440 cm⁻¹ is peculiar and diagnostic of S-platination. IRMPD kinetics evaluated at this frequency support the prevailing S-attack by cisplatin while approximately a 1 : 2 ratio of S- versus N-coordination is observed by transplatin, to be possibly related to the trans effect at the platinum center.

Wavelength and mass resolved resonance-enhanced two photon ionization (R2PI) excitation spectra of (R)-(+)-1-phenyl-1-propanol (P_R) and its complexes with some chiral esters, i.e. methyl lactates (L_R and L_S), methyl 3-hydroxybutyrates (H_R and H_S), and methyl 2-chloropropionates (C_R and C_S), have been recorded after a supersonic molecular beam expansion and interpreted in the light of DFT calculations. The spectral features of the selected complexes were found to depend on the nature of hydrogen-bond interactions within the diasteromeric complexes, whose intensity in turn depends upon the structure and the configuration of the estereal moiety. The study further confirms resonant two-photon ionization spectroscopy, coupled with time-of-flight mass resolution (R2PI-TOF), as an excellent tool for gathering valuable information on the interactive forces in molecular clusters and for the enantiodiscrimination of chiral molecules in the gas phase.