Molecular and supramolecular chirality: R2PI spectroscopy as a tool for the gas-phase recognition of chiral systems of biological interest.

A review. In life sciences, diastereomeric chiral mol./chiral receptor complexes are held together by a different combination of intermol. forces and are therefore endowed with different stability and reactivity. Detn. of these forces, which are normally affected in the condensed phase by solvent and supramol. interactions, can be accomplished through the generation of diastereomeric complexes in the isolated state and their spectroscopic investigation. This review presents a detailed discussion of the mass resolved Resonant Two Photon Ionization (R2PI-TOF) technique in supersonic beams and introduces an overview of various other technologies currently available for the spectroscopic study of gas phase chiral mols. and supramol. systems. It reports case studies primarily from the authors' recent work using R2PI-TOF methodol. for chiral recognition in clusters contg. mols. of biol. interest. The measurement of absorption spectra, ionization and fragmentation thresholds of diastereomeric clusters by this technique allow the detn. of the nature of the intrinsic interactions, which control their formation and which affect their stability and reactivity

Chiral recognition between 1-(4-fluorophenyl)ethanol and 2-butanol: higher binding energy of homochiral complexes in the gas phase

Diastereomeric adducts between (S)-1-(4-fluorophenyl)-ethanol and R and S 2-butanol, formed by supersonic expansion, were studied by a combination of mass selected resonant two-photon ionization-spectroscopy and IR depletion spectroscopy. Chiral recognition is evidenced by the specific spectroscopic signatures of the S1 S0 electronic transition as well as different frequencies and intensities of the OH stretch vibrational mode in the ground state. D-DFT calcns. were performed to assist in the anal. of the spectra and the detn. of the structures. The homochiral and heterochiral complexes show slight structural differences, in particular in the interaction of the alkyl groups of 2-butanol with the arom. ring. The homochiral [FESBS] complex is more stable than the heterochiral [FESBR] diastereomer in both the ground and excited states. The binding energy difference was evaluated to be >0.60 kcal mol-1

Ionic route to atmospheric relevant HO2 and protonated formaldehyde from methanol cation and O2

Gas-phase ion chemistry influences atmospheric processes, particularly in the formation of cloud condensation nuclei by producing ionic and neutral species in the upper troposphere–stratosphere region impacted by cosmic rays. This work investigates an exothermic ionic route to the formation of hydroperoxyl radical (HO2) and protonated formaldehyde from methanol radical cation and molecular oxygen. Methanol, a key atmospheric component, contributes to global emissions and participates in various chemical reactions affecting atmospheric composition. The two reactant species are of fundamental interest due to their role in atmospheric photochemical reactions, and HO2 is also notable for its production during lightning events. Our experimental investigations using synchrotron radiation reveal a fast hydrogen transfer from the methyl group of methanol to oxygen, leading to the formation of CH2OH+ and HO2. Computational analysis corroborates the experimental findings, elucidating the reaction dynamics and hydrogen transfer pathway. The rate coefficients are obtained from experimental data and shows that this reaction is fast and governed by capture theory. Our study contributes to a deeper understanding of atmospheric processes and highlights the role of ion-driven reactions in atmospheric chemistry

Childhood bullying, paranoid thinking, and the misappraisal of social threat: trouble at school

Background:Experiences of bullying predict the development of paranoia in school-age adolescents. While many instances of psychotic phenomena are transitory, maintained victimization can lead to increasingly distressing paranoid thinking. Furthermore, paranoid thinkers perceive threat in neutral social stimuli and are vigilant for environmental risk. Aims:The present paper investigated the association between different forms of bullying and paranoid thinking, and the extent to which school-age paranoid thinkers overestimate threat in interpersonal situations. Methods: Two hundred and thirty participants, aged between eleven and fourteen, were recruited from one secondary school in the UK. Participants completed a series of questionnaires hosted on the Bristol Online Survey tool. All data were collected in a classroom setting in quiet and standardized conditions. Results: A significant and positive relationship was found between experiences of bullying and paranoid thinking: greater severity of bullying predicted more distressing paranoid thinking. Further, paranoid thinking mediated the relationship between bullying and overestimation of threat in neutral social stimuli. Conclusion: Exposure to bullying is associated with distressing paranoid thinking and subsequent misappraisal of threat. As paranoid thinkers experience real and overestimated threat, the phenomena may persist

Excited state dynamics of Zn–salophen complexes

Zn-salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV-Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn-Sal) and the effect of the interaction between Zn-Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn-Sal ethanol solution, a longer relaxation constant, in comparison to Zn-Sal, was measured, indicative of the interaction between Zn-Sal and ADP. After a few days, the Zn-Sal-ADP solution displayed the same static and dynamic behavior of a solution containing only the Sal ligand, demonstrating that the coordination of the ADP anion to Zn(II)leads to the demetallation of the Sal ligand. Fluorescence measurements also revealed an enhanced fluorescence at 375 nm following the addition of ADP to the solution, caused by the presence of 2,3-diamino naphthalene that is formed by demetallation and partial decomposition of the Sal ligand. The efficient fluorescence of this species at 375 nm could be selectively detected and used as a probe for the detection of ADP in solution.[GRAPHICS]

Solvent free interactions in contact pairs of molecules of biological interest: Laser spectroscopic and electrospray mass spectrometric studies

A laser spectroscopic and mass spectrometric study of ionic and molecular clusters of biological interest is reported. The molecules of interest and their aggregates were generated in a supersonic beam and analyzed by mass resolved resonant two photon absorption and ionization (R2PI) and by collision induced mass spectrometry (CID-MS). The absence of the solvent allows to study these systems in the isolated state free of undesired solvent effects which may level off the differences in their properties. The gas phase results have been compared to theoretical estimates of the structure and stability of the systems under investigation

Production of clusters and thin films of nitrides, oxides and carbides by pulsed laser ablation and deposition

A short introduction on the principles of laser-matter interaction, material evaporation, plume formation, its reactivity with suitable gases and finally deposition are here illustrated. Experiments by mass spectrometry of formation of clusters, precursors of thin films and nanoparticles of oxides, nitrides and carbides by pulsed laser ablation (PLA) are reported. Pulsed laser ablation of targets combined with an intense atomic source produced by radiofrequency (RF), are discussed in terms of generating chemical reactions or supplying the loss of volatile components

Influence of diameter on temperature dynamics of hot carriers in photoexcited GaAsP nanowires

Semiconductor nanowires (NWs) often present different structural and opto-electronic properties than their thin film counterparts. The thinner they are, the larger these differences are. Here, we present femtosecond transient absorbance measurements on GaAs0.8P0.2 NWs of two different diameters, 36 and 51 nm. The results show that thinner NWs sustain a higher carrier temperature for longer times than thicker NWs. This observation suggests that, in thinner NWs, the buildup of a hot-phonon bottleneck is easier than in thicker NWs because of the increased phonon scattering at the NW sidewalls, which facilitates the buildup of a large phonon density. Moreover, the important observation that the carrier temperature in thin NWs is higher than in thick NWs already at the beginning of the hot carrier regime suggests that the phonon-mediated scattering processes in the nonthermal regime play a major role at least for the carrier densities investigated here (8 × 1018 to 4 × 1019 cm–3). Our results also suggest that the phonon scattering at crystal defects is negligible compared with the phonon scattering at the NW sidewalls