Binding Selectivity of Macrocycle Ionophores in Ionic Liquids versus Aqueous Solution and Solvent-free Conditions.

The understanding of supramolecular recognition in room-temperature ionic liquids (RTILs) is key to develop the full potential of these materials. In this work, we provide insights into the selectivity of the binding of alkali metal cations by standard cyclodextrin and calixarene macrocycles in RTILs. A direct laser desorption/ionization mass spectrometry approach is employed to determine the relative abundances of the inclusion complexes formed through competitive binding in RTIL solutions.

Ultraviolet laser desorption/ionization mass spectrometry of single-core and multi-core polyaromatic hydrocarbons under variable conditions of collisional cooling: insights into the generation of molecular ions, fragments and oligomers.

The ultraviolet laser desorption/ionization of polyaromatic hydrocarbons (PAHs) has been investigated under different background pressures of an inert gas (up to 1.2 mbar of N2) in the ion source of a hybrid, orthogonal-extracting time-of-flight mass spectrometer (oTOF-MS). The study includes an ensemble of six model PAHs with isolated single polyaromatic cores and four ones with multiple cross-linked aromatic and polyaromatic cores.

Cations in a molecular funnel: vibrational spectroscopy of isolated cyclodextrin complexes with alkali metals.

The benchmark inclusion complexes formed by α-cyclodextrin (αCD) with alkali-metal cations are investigated under isolated conditions in the gas phase. The relative αCD-M(+) (M=Li(+), Na(+), K(+), Cs(+)) binding affinities and the structure of the complexes are determined from a combination of mass spectrometry, infrared action spectroscopy and quantum chemical computations. Solvent-free laser desorption measurements reveal a trend of decreasing stability of the isolated complexes with increasing size of the cation guest.

Gas-phase complexes of cyclic and linear polyethers with alkali cations.

The flexibility of polymer backbones constitutes one key aspect in their molecular recognition properties. This investigation characterizes the structure of the gas-phase complexes formed by the cyclic and linear polyethers with the heavier alkali metal cations. In particular, the cyclic 15-crown-5 ether (15c5), (OCH(2)CH(2))(5), and the polyethylene glycol linear chains PEG4 and PEG9, H(OCH(2)CH(2))(n=4,9)OH, are considered.

Emergence of symmetry and chirality in crown ether complexes with alkali metal cations.

Crown ethers provide a valuable benchmark for the comprehension of molecular recognition mediated by inclusion complexes. One of the most relevant crown ethers, 18-crown-6 (18c6), features a flexible six-oxygen cyclic backbone that is well-known for its selective cation binding. This study employs infrared spectroscopy and quantum mechanical calculations to elucidate the structure of the gas-phase complexes formed by the 18c6 ether with the alkali metal cations.

Spectroscopic investigation of the gas-phase conformations of 15-crown-5 ether complexes with K+.

Infrared multiple photon dissociation action spectra of the binary and ternary gas-phase complexes formed by 15-crown-5 ether with potassium cations (15c5-K(+) and 15c5-K(+)-15c5) are reported. The spectra span the 800-1500 cm(-1) infrared range. Particularly significant differences are found in the position and structure of the CO-stretching band of the two types of complexes.

Conformational landscape of supersonically expanded 1-(fluorophenyl)ethanols and their monohydrated clusters.

The effects of the presence of the ring fluorine atom on the conformational landscape of supersonically expanded isomeric 1-(fluorophenyl)ethanols and their monohydrated clusters are investigated by resonant two-photon ionization (R2PI) spectroscopy, coupled with time-of-flight (TOF) mass spectrometry. In contrast to the very simple spectrum of 1-phenylethanol, the lack of structural symmetry of the aromatic rings of isomeric 1-(fluorophenyl)ethanols generates more complicated spectra, characterized by several low-frequency progressions of bands. Their interpretation is based on the strict correspondence with theoretical predictions at the D-B3LYP/6-31G** level of theory.

Solvent-free MALDI investigation of the cationization of linear polyethers with alkali metals.

The MALDI technique with solvent-free sample preparation has been applied to evaluate relative gas-phase affinities of polyether chain polymers with alkali metal cations. The study is performed on poly(ethylene glycol) and poly(propylene glycol) polymers of different lengths (PEG600, PEG1000, PPG425, PPG750) and the alkali metal cations Li(+), Na(+), K(+), and Cs(+). The experiments show that the lattice energy of the alkali metal salts employed as cation precursors can have a strong influence on the outcome of conventional MALDI measurements.

Fragmentation and gas phase aggregation processes in the laser desorption ionization of chlorodiaminotriazines.

Fragmentation and supramolecular aggregation induced during the laser desorption/ionization (LDI) of four chlorodiaminotriazines (simazine, atrazine, terbutylazine and propazine) have been investigated. The laser wavelength employed (266 nm) lies within the first absorption band of the four triazines. The main fragmentation channel observed involves the prompt cleavage of the Cl atom, followed by partial or total fragmentation of the side alkyl chains.

Laser desorption/ionization determination of molecular weight distributions of polyaromatic carbonaceous compounds and their aggregates.

Molecular weight distributions (MWDs) of model polyaromatic hydrocarbons (PAHs) and complex asphaltene samples have been investigated in laser desorption/ionization mass spectrometry (LDI-MS) experiments. Special efforts are devoted to the characterization of aggregation effects during the desorption process. It is found that non-covalent clusters of the PAHs and asphaltenes form readily in the desorbing plume.

On the determination of molecular weight distributions of asphaltenes and their aggregates in laser desorption ionization experiments.

Molecular weight distributions (MWD) of asphaltenes and their aggregates have been investigated in laser desorption ionization (LDI) mass spectrometric experiments. A systematic investigation of the dependence of the measured MWD on the asphaltene sample density and on the laser pulse energy allows the assignment of most probable molecular weights within 300-500 amu and average molecular weights of 800-1000 amu for the monomeric asphaltenes, as well as for the estimation of the contribution from asphaltene clusters in typical LDI measurements. The results serve to reconcile the existing controversy between earlier mass spectrometric characterizations of asphaltenes based on laser desorption techniques by different groups.