Vibrational Spectroscopy of Platinum(II) Complexes Relevant in Antitumor Activity

International audienceCisplatin (cis-diamminedichloroplatinum(II) is the first platinum-based antitumor agent, and it is still widely used in chemotherapy. In the cytoplasm, the administered drug undergoes spontaneous hydrolysis by nucleophilic substitution of chloride with water. The cationic chloro-monoaqua form, cis-[PtCl(NH3)2(H2O)]+, characterized by a pKa value of 6.5, is the relevant intermediate at physiological pH, that can ultimately give rise to DNA and protein adducts through easy substitution of water by nitrogen/sulfur donor ligands. Electrospray ionization has allowed cis- and trans-[PtCl(NH3)2(H2O)]+ species to be obtained as free ions in the gas phase where they were sampled by infrared multiple photon dissociation (IRMPD) spectroscopy in the NH/OH stretching frequency range (3200−3800 cm−1), using a tabletop optical parametric oscillator/amplifier (OPO/OPA) laser system coupled to a quadrupole ion trap mass spectromete

Uncovering the nature of transient and metastable non-equilibrium phases in 1TT-TaS2_2

Complex systems are characterized by strong coupling between different microscopic degrees of freedom. Photoexcitation of such materials can drive them into new transient and long-lived hidden phases that may not have any counterparts in equilibrium. By exploiting femtosecond time- and angle-resolved photoemission spectroscopy, we probe the photoinduced transient phase and the recovery dynamics of the ground state in a complex material: the charge density wave (CDW)-Mott insulator 1$T$-TaS$_2$. We reveal striking similarities between the band structures of the transient phase and the (equilibrium) structurally undistorted metallic phase, with evidence for the coexistence of the low-temperature Mott insulating phase and high-temperature metallic phase. Following the transient phase, we find that the restoration of the Mott and CDW order begins around the same time. This highlights that the Mott transition is tied to the CDW structural distortion, although earlier studies have shown that the collapse of Mott and CDW phases are decoupled from each other. Interestingly, as the suppressed order starts to recover, a long-lived metastable phase emerges before the material recovers to the ground state. Our results demonstrate that it is the CDW lattice order that drives the material into this metastable phase, which is indeed a commensurate CDW-Mott insulating phase but with a smaller CDW amplitude. Moreover, we find that the long-lived state emerges only under strong photoexcitation and has no evidence when the photoexcitation strength is weak

Probing the competition among different coordination motifs in metal-ciprofloxacin complexes through IRMPD spectroscopy and DFT calculations

The vibrational spectra of ciprofloxacin complexes with monovalent (Li+, Na+, K+, Ag+) and polyvalent (Mg2+, Al3+) metal ions are recorded in the range 1000-1900 cm(-1) by means of infrared multiple-photon dissociation (IRMPD) spectroscopy. The IRMPD spectra are analyzed and interpreted in the light of density functional theory (DFT)-based quantum chemical calculations in order to identify the possible structures present under our experimental conditions. For each metal-ciprofloxacin complex, four isomers are predicted, considering different chelation patterns. A good agreement is found between the measured IRMPD spectrum and the calculated absorption spectrum of the most stable isomer for each complex. Metal ion size and charge are found to drive the competition among the different coordination motifs: small size and high charge density metal ions prefer to coordinate the quinolone between the two carbonyl oxygen atoms, whereas large-size metal ions prefer the carboxylate group as a coordination site. In the latter case, an intramolecular hydrogen bond compensates the weaker interaction established by these cations. The role of the metal cation on the stabilization of ionic and nonionic structures of ciprofloxacin is also investigated. It is found that large-size metal ions preferentially stabilize charge separated motifs and that the increase of metal ion charge has a stabilizing effect on the zwitterionic form of ciprofloxacin

Ultrafast Structural Dynamics along the β − γ Phase Transition Path in MnAs

International audienceWe investigate the orthorhombic distortion and the structural dynamics of epitaxial MnAs layers on GaAs(001) using static and time-resolved x-ray diffraction. Laser-induced intensity oscillations of Bragg reflections allow us to identify the optical phonon associated with orthorhombic distortion and to follow its softening along the path towards an undistorted phase of hexagonal symmetry. The frequency of this mode falls in the THz range, in agreement with recent calculations. Incomplete softening suggests that the $\beta-\gamma$ transformation deviates from a purely second-order displacive transition

Carbon and Nitrogen K-Edge NEXAFS Spectra of Indole, 2,3-Dihydro-7-azaindole, and 3-Formylindole

The near-edge X-ray absorption fine structure (NEXAFS) spectra of indole, 2,3-dihydro-7-azaindole, and 3-formylindole in the gas phase have been measured at the carbon and nitrogen K-edges. The spectral features have been interpreted based on density functional theory (DFT) calculations within the transition potential (TP) scheme, which is accurate enough for a general description of the measured C 1s NEXAFS spectra as well as for the assignment of the most relevant features. For the nitrogen K-edge, the agreement between experimental data and theoretical spectra calculated with TP-DFT was not quite satisfactory. This discrepancy was mainly attributed to the many-body effects associated with the excitation of the core electron, which are better described using the time-dependent density functional theory (TDDFT) with the range-separated hybrid functional CAM-B3LYP. An assignment of the measured N 1s NEXAFS spectral features has been proposed together with a complete description of the observed resonances. Intense transitions from core levels to unoccupied antibonding π* states as well as several transitions with mixed-valence/Rydberg or pure Rydberg character have been observed in the C and N K-edge spectra of all investigated indoles

Clusters of chiral molecules in the isolated state

Chirality, a fundamental property present across different scales in our world, remains a captivating area of exploration. The origins of chirality and the intricate chemical pathways leading to the formation of the first replicable homochiral system are subjects of ongoing studies. This paper, dedicated to the late Prof Anna Giardini, unravels insights into chiral discrimination effects through Resonant Two-Photon Ionization (R2PI) spectroscopy on gas-phase intermolecular complexes. Using theoretical ab-initio calculations, and a range of resonant multiphoton spectroscopic techniques, this study reports on key aspects of chirality. This involves the application of One-color R2PI Spectroscopy, where diastereomeric complexes formed by non-covalent interactions between enantiomers of chiral solvent and a chiral chromophore are discerned. Moving on, Two-color R2PI Spectroscopy is discussed as a tool to measure binding energy differences between homochiral and heterochiral adducts. After which the study of Reaction Thresholds by Two-color R2PI is reported. Here, the impact of asymmetric microsolvation on the photodissociation of Cα-Cβ bonds is explored. This sheds light on how solvent molecules influence activation energies in these processes. Lastly, the investigation into One-color R2PI and IR-R2PI focuses on the effect of fluorine substitution on chiral recognition. The interplay of CH···π, OH···π, and CH···F interactions is analyzed, highlighting the specific molecular interactions crucial in chiral discrimination. This comprehensive exploration underscores the intricate molecular mechanisms governing chiral recognition and enantioselectivity, emphasizing the lasting impact of Prof Anna Giardini’s pioneering work in this field

High-Harmonic Generation Spectroscopy of Gas-Phase Bromoform

High-Harmonic Generation (HHG) spectra of randomly aligned bromoform (CHBr3) molecules have been experimentally measured and theoretically simulated at various laser pulse intensities. From the experiments, we obtained a significant number of harmonics that goes beyond the cutoff limit predicted by the three-step model (3SM) with ionization from HOMO. To interpret the experiment, we resorted to real-time time-dependent configuration interaction with single excitations. We found that electronic bound states provide an appreciable contribution to the harmonics. More in detail, we analyzed the electron dynamics by decomposing the HHG signal in terms of single molecularorbital contributions, to explain the appearance of harmonics around 20−30 eV beyond the expected cutoff due to HOMO. HHG spectra can be therefore explained by considering the contribution at high energy of HOMO−6 and HOMO−9, thus indicating a complex multiple-orbital strong-field dynamics. However, even though the presence of the bromoform cation should be not enough to produce such a signal, we could not exclude a priori that the origin of harmonics in the H29−H45 to be due to the cation, which has more energetic ionization channels