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We studied the impact of aliphatic side chains on the stability and conformational landscape of the local anaesthetics benzocaine, butamben and isobutamben, combining high-resolution rotational spectroscopy in the microwave and millimetre regions and molecular modelling. The study reveals the connections between alkyl chain flexibility and molecular conformations.

One of the most fascinating questions in chemistry is why nature chose CGAT as the alphabet of life. Very likely, such selection was the result of multiple factors and a long period of refinement. Here, we explore how the intermolecular interactions influenced such process, by characterizing the formation of dimers between adenine, theobromine and 4-aminopyrimidine. Using a combination of mass-resolved excitation spectroscopy and DFT calculations, we determined the structure of adenine-theobromine and 4-aminopyrimidine-theobromine dimers. The binding energy of these dimers is very close to the canonical adenine-thymine nucleobases. Likewise, the dimers are able to adopt Watson-Crick conformations. These findings seem to indicate that there were many options available to build the first versions of the informational polymers, which also had to compete with other molecules, such as 4-aminopyrimidine, which does not have a valid attaching point for a saccharide. For some reason, nature did not select the most strongly-bonded partners or if it did, such proto-bases were later replaced by the nowadays canonical CGAT., We thank MICIU (PGC2018-098561-B-C21) and the Basque Government (IT1162-19) for financial support. A.C. thank the Basque Government for a pre-doctoral fellowship.

The role of non-covalent interactions (NCIs) has broadened with the inclusion of new types of interactions and a plethora of weak donor/acceptor partners. This work illustrates the potential of chirped-pulse Fourier transform microwave technique, which has revolutionized the field of rotational spectroscopy. In particular, it has been exploited to reveal the role of NCIs' in the molecular self-aggregation of difluoromethane where a pentamer, two hexamers and a heptamer were detected. The development of a new automated assignment program and a sophisticated computational screening protocol was essential for identifying the homoclusters in conditions of spectral congestion. The major role of dispersion forces leads to less directional interactions and more distorted structures than those found in polar clusters, although a detailed analysis demonstrates that the dominant interaction energy is the pairwise interaction. The tetramer cluster is identified as a structural unit in larger clusters, representing the maximum expression of bond between dimers., We thank MINECO (CTQ2017-89150-R), Basque Government (IT1162-19 and PIBA 2018-11), the UPV/EHU (PPG17/10, GIU18/207), CSIC (2018FR0036, LINKA20249), University of Bologna (RFO), Fondazione CARISBO (2018/0353) and NSF (CHE-1903871 and CHE-2018427) for the financial support. C.C thanks MINECO for a Juan de la Cierva contract., L.E. was supported by Marie Curie fellowship PIOF-GA-2012-328405.

The pure rotational spectrum of CF3CCl3 (1,1,1-trichloro-2,2,2-trifluoroethane, CFC-113a) was investigated at 4–18 GHz in supersonic expansion with chirped pulse and cavity Fourier-transform rotational spectroscopy, and at 94–309 GHz with broadband millimetre wave spectroscopy. Spectroscopic constants for all four possible chlorine isotopic species have been considerably updated. Global fits of hyperfine-resolved and hyperfine-unresolved data are reported and triple chlorine nucleus hyperfine structure has been analysed for all four isotopologues to within experimental accuracy. The new measurements have been augmented with anharmonic force field calculations in an evaluation of the semi-experimental equilibrium geometry for CF3CCl3. Interactions between hyperfine sublevels contributing to frequencies of the lowest J transitions allowed determination of the axial rotational constant A = 1326.24(15) MHz for CF3C35Cl3 from analysis of pure rotational transitions.

The pure rotational spectrum of CF3CH2Cl (1-choro-2,2,2-trifluoroethane, HCFC-133a) was investigated at 8–18 GHz in supersonic expansion with chirped pulse and cavity rotational spectroscopy, and at 94–309 GHz with broadband millimetre wave spectroscopy. Spectroscopic constants for the two principal isotopic species have been considerably updated from global fits over extensive data sets, numbering close to 3000 lines for the ground state of CF3CH2 35 Cl and 1800 lines for CF3CH2 37 Cl. Four different 13 C containing isotopologues have been assigned, as well as several new low lying vibrational states. The new measurements have been augmented with anharmonic force field calculations in an evaluation of the semi-experimental equilibrium geometry for CF3CH2Cl.

Understanding the conformational preferences and intramolecular dynamics of carbohydrates is crucial to explain the interactions with their biological targets and, in turn, to improve their use as therapeutic agents. Herein, we present experimental evidence that resolves the conformational analysis of the monosaccharide D‑lyxose, for which quantum mechanical (QM) calculations offered model‑dependent results. The study compares the structural preferences in the gas phase, determined by rotational spectroscopy, with the solution, resolved by combining NMR and molecular dynamics (MD) simulations. Rotational results show that D‑lyxose adopts only pyranose forms in the gas phase. The α‑anomer exhibits both the 4C1 and 1C4 chairs with a ratio of 60:40, while the β‑anomer, whose effective structure at atomic resolution was determined by (13C, 2H and 18O) monoisotopic enriched samples, displays exclusively 4C1 form. Conversely, in water solution, the most populated conformation is the α‑anomer, which features a 1C4 chair. Moreover, the thorough solvation studies indicate that the β‑anomer is poorly solvated. This result, together with the larger dipole moment exhibited by the 1C4 form of the α‑anomer, may explain the preferences observed in solution, proving the active role of water in the conformational preferences of this monosaccharide. Markedly, the main conformers found in the gas phase (β‑anomer in a 4C1 chair) and in solution (α‑anomer in a 1C4 form) are characterized by the lack of the stabilizing anomeric effect. From a mechanism perspective, rotational spectroscopy together with solid‑state NMR experiments, corroborates that α«β or furanose«pyranose interconversions are prevented in gas phase. The multidisciplinary strategy presented here provides a powerful way of unravelling the role of water in the conformational preferences of challenging molecules, such as flexible monosaccharides.

The potential of non-invasive ventilation procedures and new minimally invasive techniques has resulted in the research of alternative approaches as the aerosolization for the treatment of respiratory distress syndrome (RDS). The aim of this work was to design two nebulizer prototypes and to evaluate them studying the particle size distribution of the inhaled droplets generated with distilled water and two perfluorocarbons (PFCs). Different experiments were performed with driving pressures of 1⁻3 bar for each compound. An Aerodynamic Particle Sizer was used to measure the aerodynamic diameter (Da), the mass median aerodynamic diameter (MMAD) and the geometric standard deviation (GSD). The results showed that both prototypes produced heterodisperse aerosols with Da mean values in all cases below 5 m. The initial experiments with distilled water showed MMAD values lower than 9 m and up to 15 m with prototype 1 and prototype 2, respectively. Regarding the PFCs, relatively uniform MMAD values close to 12 m were achieved. The air delivery with outer lumens of prototype 1 presented more suitable mass distribution for the generation and delivery of a uniform aerosol than the two half-circular ring geometry proposed in the prototype 2. Funding: This work has been supported by Consolidated Groups from the Basque Government and Fundation VITAL Fundazioa.

The investigation of an isolated ribofuranose unit in the gas phase reveals the intrinsic conformational landscape of the biologically active sugar form.We report the rotational spectra of two conformers of methyl b-D-ribofuranoside in a supersonic jet expansion. Both conformers adopt a near twisted (3T2) ring conformation with the methoxy and hydroxymethyl substituents involved in various intramolecular hydrogen bonds., MINECO-FEDER CTQ2015-68148-C2-P

The potential energy surface (PES) of the general anesthetic fluoroxene (2,2,2-trifluoroethyl vinyl ether) was probed in a supersonic jet expansion using broadband chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy and theoretical calculations. The PES is dominated by a single conformation, as other stable minima are shown to kinetically relax in the expansion to the global minimum. Consistently, the rotational spectrum reveals a single conformation. Fluoroxene adopts a CS heavy-atom planar skeleton structure in the gas phase, with a cis-trans conformation (cis for the CH2=CH-O-CH2- and trans for the =CH-O-CH2-CF3 part). The sensitivity of a recently-built CP-FTMW spectrometer at the UPV/EHU is demonstrated by the detection of five isotopologues of fluoroxene in natural abundance, corresponding to the (13)C and (18)O monosubstituted species. The rS and r0 structures were determined and are in good agreement with theoretical predictions using the MP2, B3LYP and M06-2X methods.

Exo-2,3-epoxynorbornane is studied in the gas phase by pulsed jet Fourier transform microwave spectroscopy in the 4-18 GHz region. Six isotopologues were observed and characterized in their natural abundance. The experimental substitution and effective structures were obtained. Comparison with the structure of norbornane shows significant differences in several bond lengths and valence angles upon introduction of the epoxy group. All the work is supported by quantum chemical calculations.

Succinic acid, a dicarboxylic acid molecule, has been investigated spectroscopically with computational support to elucidate the complex aspects of its conformational composition. Due to the torsional freedom of the carbon backbone and hydroxy groups, a large number of potentially plausible conformers can be generated with an indication that the gauche conformer is favored over the trans form. The microwave and millimeter wave spectra have been analyzed and accurate spectroscopic constants have been derived that correlate best with those of the lowest energy gauche conformer. For an unambiguous conformational identification measurements were extended to the monosubstituted isotopologues, precisely determining the structural properties. Besides bond distances and angles, particularly the dihedral angle has been determined to be 67.76(11)°, confirming the anomalous tendency of the methylene units to favor gauche conformers when a short aliphatic segment is placed between two carbonyl groups. Spanish Ministry of Science and Innovation/CTQ2011-22923 Spanish Ministry of Science and Innovation/CGL2011-22441

In order to accurately assess the influence of fatty acids on the hygroscopic and other physicochemical properties of sea salt aerosols, hexanoic, octanoic or lauric acid together with sodium halide salts (NaCl, NaBr and NaI) have been chosen to be investigated in this study. The hygroscopic properties of sodium halide sub-micrometre particles covered with organic acids have been examined by Fourier-transform infrared spectroscopy in an aerosol flow cell. Covered particles were generated by flowing atomized sodium halide particles (either dry or aqueous) through a heated oven containing the gaseous acid. The obtained results indicate that gaseous organic acids easily nucleate onto dry and aqueous sodium halide particles. On the other hand, scanning electron microscopy (SEM) images indicate that lauric acid coating on NaCl particles makes them to aggregate in small clusters. The hygroscopic behaviour of covered sodium halide particles in deliquescence mode shows different features with the exchange of the halide ion, whereas the organic surfactant has little effect in NaBr particles, NaCl and NaI covered particles experience appreciable shifts in their deliquescence relative humidities, with different trends observed for each of the acids studied. In efflorescence mode, the overall effect of the organic covering is to retard the loss of water in the particles. It has been observed that the presence of gaseous water in heterogeneously nucleated particles tends to displace the cover of hexanoic acid to energetically stabilize the system. The authors are grateful to Ministerio de Ciencia e Innovacion (Madrid) for grant-in-aids (CGL2011-22441 and Consolider CSD-2007-00013), to Gobierno Vasco/Eusko Jaurlaritza (Vitoria-Gasteiz) for a Consolidated Research Group grant (IT520-10), and UPV/EHU for UFI11/23, SEM facilities (SGI/IZO-SGIker) and general support. L. Minambres thanks UPV/EHU for a postdoctoral research grant. We are grateful to Cristina Gutierrez from UPV/EHU for the use of the butanol CPC.

Carbohydrates are one of the most versatile biochemical building blocks, widely acting in energetic, structural, or recognition processes. The interpretation of the biological activity of saccharides is based on the structure and relative stability of their conformers. One of the obstacles to resolving the basic structure issues arises from their ability to form strong intermolecular hydrogen bonds with polar solvents, which in turn can result in conformational changes. A clear picture of the conformational panorama of isolated 2-deoxyd-ribose has been revealed using Fourier-transform microwave spectroscopy in conjunction with a UV ultrafast laser ablation source. Additionally, the availability of rotational data has been the main bottle-neck for examining the presence of these building blocks in interstellar space, so these studies could also be useful to the astrochemistry community. 2-Deoxy-d-ribose (2DR, C5H10O4; Figure 1a) is an important naturally occurring monosaccharide, present in nucleotides, which are the building blocks for DNA. In DNA, 2DR is present in the furanose (five-membered) ring form, whereas free in aqueous solution it cyclizes into fiveor six-membered rings, with the latter—the pyranoid form—being dominant. By closing the chain into a six-membered ring, the C1 carbon atom is converted into an asymmetric center, yielding two possible stereochemical a and b anomeric species (Figure 1b). In aqueous solution, 2DR primarily exists as a mixture of nearly equal amounts of a and b pyranose forms, present in their low-energy chair conformations, C1 and C4 (Figure 1c). [4] Such configurations are connected through ring inversion, thus establishing the axial or equatorial position of the OH group for each conformer. In addition, the monossacharides exhibit an unusual preferential stabilization of pyranose rings containing an axial OH group at the C1 carbon over the equatorial orientation, widely known as the anomeric effect, although its physical origin remains controversial. Nevertheless, structural analysis of 2DRmust take into consideration the intramolecular hydrogen bonding between adjacent OH groups. The formation of hydrogenbond networks reinforces their stability owing to hydrogenbond cooperativity effects. Such networks are fundamental to the molecular recognition of carbohydrates. By dissecting all these factors we can determine the most stable conformers of 2DR and the relative arrangement of the different hydroxy groups under isolated conditions, such as in the gas phase. In vacuo theoretical calculations, carried out on a-/bpyranoses, a-/b-furanoses, and open-chain conformations, predict 15 furanose and pyranose forms (Figure 1d, Table 1) in an energy window of 12 kJmol 1 above the predicted cc-apyr C1 global minimum. The notation used to label the different conformers include the symbols a and b to denote the anomer type, C1 and C4 to denote the pyranose chair form, C2-endo or C3-endo to denote the furanose envelope forms, and “c” or “cc” to indicate a clockwise or counterclockwise configuration of the adjacent OH bonds, respectively. A number is added to provide theMP2 energy ordering within the same family. To validate the predicted conformational behavior, comparison with precise experimental data of 2DR is needed. Previous experiments to determine the conformation of monosaccharides were based on X-ray and NMR measurements. However, these data are influenced by environmental effects associated with the solvent or crystal lattice. Recently, an IR spectrum of 2DR in an inert matrix in

The structural isomerization of scopine into scopoline (oscine) has been observed in a supersonic jet expansion using microwave spectroscopy. The rotational spectrum evidences a single structure in the gas phase, providing a first description of the (three-ring) structurally distorted tropane in scopoline. The absence of rotational signatures of any scopine conformation suggests a practically quantitative isomerization at the vaporization temperatures of the experiment (ca. 90 °C). The determined rotational parameters of scopoline reveal the structural consequences of the intramolecular cyclation of scopine, which breaks the original epoxy group and creates a new ether bridge and a 7β-hydroxytropane configuration. The hydroxy group further stabilizes the molecule by an O-H⋅⋅⋅N intramolecular hydrogen bond, which, in turn, forces the N-methyl group to the less stable axial form. Supporting ab initio (MP2) and DFT (B3LYP, M06-2X) calculations are included.

Tropospheric aerosols are usually mixtures of inorganic and organic compounds in variable proportions, and the relative amount of organic fraction can influence the hygroscopic properties of the particles. Infrared spectra of submicrometer internally mixed dry particles of ammonium sulfate (AS) with various dicarboxylic acids (oxalic, malonic, maleic, glutaric and pimelic) have been measured in an aerosol flow tube at several solute mass ratios. The spectra show a notable broadening in the bandwidth of sulfate ion ν3 vibrational band near 1115 cm−1 with respect to pure AS. We attribute these perturbations, that are biggest at AS/organic acid mass ratio near unity, to intermolecular interactions between inorganic ions and organic acid molecules in the internally mixed solids. The water uptake behavior of internally mixed particles has been measured by recording the infrared integrated absorbance of liquid water as a function of relative humidity (RH). The amount of water present in the particles prior to deliquescence correlates partially with the water solubilities of the dicarboxylic acids, and also with the relative magnitudes of intermolecular interactions in the internally mixed dry solids. Phase change of ammonium sulfate in the internally mixed particles with RH has been spectrally monitored, and it is shown that water uptaken before full deliquescence produces structural changes in the particles that are revealed by their vibrational spectra.

Producción Científica, The rotational spectrum of the tropane alkaloid scopine has been detected by Fourier transform microwave spectroscopy in a pulsed supersonic jet. A non-conventional method for bringing the molecules intact into the gas phase was used, mixing scopine syrup with solid glycine powder and vaporizing the solid mixture with an UV ultrafast laser beam. Laser vaporization prevented the easy isomerization to scopoline previously observed when conventional heating. A single conformer was unambiguously observed in the supersonic jet, which corresponds to the energetically most stable species according to quantum chemistry calculations. Rotational and centrifugal distortion constants have been accurately determined. The spectrum reveals hyperfine splittings due to the combined effect of hindered rotation of the methyl group and the presence of a quadrupolar nucleus (14N). This additional information allowed determining the angle of N-methyl inversion between the N- CH3 bond and the bicyclic C-N-C plane (135o), as well as the internal rotation barrier of the methyl group (6.24(1) kJ mol-1)., 2017-12-31, MINECO-FEDER CTQ-2014-54464-R, CTQ-2015-68148

2-Azabicyclo[2.2.1]hept-5-en-3-one (ABH or Vince lactam) and its monohydrated complex (ABH···H(2)O) have been observed in a supersonic jet by Fourier transform microwave spectroscopy. ABH is broadly used in the synthesis of therapeutic drugs, whereas the ABH···H(2)O system offers a simple model to explain the conformational preferences of water linked to a constrained peptidic bond. A single predominant form of the Vince lactam and its singly hydrated complex have been detected, determining the rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling tensor. The monohydrated complex is stabilized by two hydrogen bonds (C═O···H-O and N-H···O) closing a six-membered ring. The complexation energy has been estimated to be ∼10 kJ mol(-1) from experimental results. In addition, the observed structure in the gas phase has been compared with solid-phase diffraction data. The structural parameters and binding energies of ABH···H(2)O have also been compared with similar molecules containing peptide bonds. Ab initio (MP2) and density functional (M06-2X and B3LYP) methods have supported the experimental work, describing the rotational parameters and conformational landscape of the title compound and its singly hydrated complex.

sugar to be detected in the gas phase, isreported by E. J. Cocinero, A. Lesarri, and co-workers in their Communication on page3119 ff. Six conformers were detected by a combination of laser vaporization andmicrowave spectroscopy. All adopt a pyranoside (pyr) structure, stabilized bycooperative hydrogen-bond networks, rather than the furanose form usually found inbiological compounds. This rotational spectrum opens the door to the radio-astronom-ical detection of the first sugar in space.

Sea salt aerosols include appreciable fractions of organic material, that can affect properties such as hygroscopicity, phase transition or chemical reactivity. Although sodium chloride is the major component of marine salt, bromide and iodide ions tend to accumulate onto particle surfaces and influence their behaviour. The hygroscopic properties of internally mixed submicrometric particles composed of succinic acid (SA) and NaX (where X = F, Cl, Br or I) have been studied by infrared absorption spectroscopy in an aerosol flow cell at ambient temperature for different relative succinic acid/NaX compositions. The results show that deliquescence relative humidities of SA/NaF and SA/NaCl are equal to those of the pure sodium halides. SA/NaBr particles, on the other hand, deliquesce at lower relative humidities than pure NaBr particles, the effect being more marked as the SA/NaBr mass ratio approaches unity. The SA/NaI system behaves as a non-deliquescent system, absorbing liquid water at all relative humidities, as in pure NaI. Succinic acid phase in the particles has been spectroscopically monitored at given values of both RH and SA/NaX solute mass ratio. The different hygroscopic properties as the halogen ion is changed can be rationalized in terms of simple thermodynamic arguments and can be attributed to the relative contributions of ion–molecule interactions in the solid particles. The observed behaviour is of interest for tropospheric sea salt aerosols mixed with organic acids.

The conformational preferences of o -vanillin have been investigated in a supersonic jet expansion using Fourier transform microwave (FT-MW) spectroscopy. Three molecular conformations were derived from the rotational spectrum. The two most stable structures are characterized by a moderate O H···O C hydrogen bond between the aldehyde and the hydroxyl groups, with the methoxy side chain either in plane (global minimum a- cis–trans ) or out of plane (a- cis-gauche ) with respect to the aromatic ring. In the third conformer the aldehyde group is rotated by ca. 180°, forming a O H···O hydrogen bond between the methoxy and hydroxyl groups (s- trans–trans ). Rotational parameters and relative populations are provided for the three conformations, which are compared with the results of ab initio (MP2) and density-functional (B3LYP, M05–2X) theoretical predictions.

The diode laser absorption infrared spectrum of fluorobenzene has been recorded near 1230 cm −1 after cooling the molecules in a supersonic pulsed jet. Spectral lines have been assigned to the ν 7a fundamental band. Transitions of J between 32 and 49 have been recorded, that show characteristic line groupings in the P branch. Analysis of the spectrum gives the vibrational band origin and rotational and centrifugal distortion constants of the molecule in the ν 7a = 1 state.

The diode laser absorption infrared spectrum of chlorobenzene has been recorded near 1500 cm −1 by cooling the molecules in a supersonic pulsed jet. Spectral lines have been assigned to the 2 ν 10b overtone. Transitions of J between 34 and 73 have been recorded and the most intense ones assigned to the C 6 H 5 35 Cl isotope. The spectra show characteristic line groupings in the R branch. Analysis of the spectrum gives the vibrational band origin and rotational constants of the molecule in the ν 10b = 2 state.

Atmospheric aerosols typically consist of inorganic and organic material. Although the organic fraction can affect the behavior of mixed organic/inorganic particles, their physical properties are not well-understood. In this work, infrared spectra of internally mixed submicrometer particles of ammonium sulfate and succinic acid have been studied at ambient temperature in an aerosol flow cell. The spectra of dried particles show distinct features relative to the pure components, as a result of ion-molecule interactions between the inorganic and organic species. The hygroscopic behavior of the particles has been followed for several organic/inorganic mass ratios, showing that around equimolar composition, the mixed particles uptake water in a broad range of relative humidities (30-80%), substantially lower than the deliquescence relative humidity of the mixed system near 80%. Infrared spectra at predeliquescence relative humidities reveal that succinic acid is partially or completely in the liquid phase at much higher concentrations that those corresponding to a saturated solution of succinic acid. This behavior is proposed to arise from the ion-molecule interactions between the organic and inorganic components, which unstabilize the crystal structure relative to the pure solids and cause loss of translational order in the crystal, bringing about an increase in the Gibbs energy of the solid particles and allowing the uptake of water molecules prior to the deliquescence point. The obtained results show that water absorption prior to full deliquescence in this system has to be taken into account because it extends the range of relative humidities at which particles are partially or completely liquid.

Respiratory distress syndrome (RDS) represents one of the major causes of mortality among preterm infants, and the best approach to treat it is an open research issue. The use of perfluorocarbons (PFC) along with non-invasive respiratory support techniques has proven the usefulness of PFC as a complementary substance to achieve a more homogeneous surfactant distribution. The aim of this work was to study the inhaled particles generated by means of an intracorporeal inhalation catheter, evaluating the size and mass distribution of different PFC aerosols. In this article, we discuss different experiments with the PFC perfluorodecalin (PFD) and FC75 with a driving pressure of 4-5 bar, evaluating properties such as the aerodynamic diameter (Da), since its value is directly linked to particle deposition in the lung. Furthermore, we develop a numerical model with computational fluid dynamics (CFD) techniques. The computational results showed an accurate prediction of the airflow axial velocity at different downstream positions when compared with the data gathered from the real experiments. The numerical validation of the cumulative mass distribution for PFD particles also confirmed a closer match with the experimental data measured at the optimal distance of 60 mm from the catheter tip. In the case of FC75, the cumulative mass fraction for particles above 10 mu m was considerable higher with a driving pressure of 5 bar. These numerical models could be a helpful tool to assist parametric studies of new non-invasive devices for the treatment of RDS in preterm infants. Consolidated Groups from the Basque Government supported this work. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU) is gratefully acknowledged.

An experimental study of the evolution of nanosecond pulsed lasers absorbed by Ni metal is presented. The ions ejected near fluence threshold fit single Maxwell–Boltzmann distributions (MBDs) whereas the ion distributions at higher fluences have side-bands whose maxima match accurately those of the ionization and recombination precursors. It is demonstrated that ions are trapped for ≈1 μs and further ejected in a few picoseconds whereas electrons have shorter dead time (≈10 ns) and continue evaporating for as long as ≈1 μs. Radiation is partially trapped during the creation of the electric field that ejects ions. The evolution also applies to other metals.

A crossed-beam experiment of well characterized kinetic energy (KE) electrons and supersonic halomethanes CCl 3 F and CClF 3 in Ar carrier has been carried out in order to quantify the kinetic energy distributions (KEDs), the appearance energies (AEs) and the channels involved in the production of nascent ions. The ion KEDs were derived from the band profiles of the time-of-flight mass spectrum and the total KEDs computed using conservation laws. Heavier ions are created with KED peaked at thermal energies in contrast with low mass atoms or other fragments, where the distribution is broader and the maximum is at much higher energies. A discussion of the dissociative ionization pathways derived from the appearance energies, total average KEDs, thermodynamic enthalpies and computed electron dissociation energies is reported. The role of the vibrational and rotational energies into the dissociative processes is also discussed.

2-Colour REMPI and ZEKE-PFI spectra of the 4-amino-3-ethylbenzonitrile (EtABN) molecule are reported for the first time. EtABN S 1 ← S 0 0 0 0 transition is located at 33 578 cm −1 , and its adiabatic ionisation threshold, as determined by ZEKE-PFI spectroscopy is 64 799 ± 4 cm −1 . A comparison with the spectra of 4-aminobenzonitrile (ABN) shows that the ethyl substituent gives rise to a rich spectroscopy, mainly involving the Ph–Et rocking mode.

The vibration–rotation spectrum of the ν3 band of CF2 radical has been recorded in a supersonic expansion by tunable diode laser absorption spectroscopy near 1114 cm−1. The radical was prepared by pulse pyrolysis of hexafluoropropylene oxide, which decomposes at relatively low temperatures. The rotational temperature of CF2 has been evaluated to be 260 ± 15 K for a heating nozzle temperature of 1225 K. The average absolute number density of the radical at the nozzle exit in the jet has been obtained, and the efficiency of precursor conversion into CF2 is shown to be nearly unity at 1225 K.

The high-resolution infrared spectrum of the ν 19 a band of fluorobenzene has been recorded near 1500 cm −1 . Fluorobenzene was cooled to ca. 25 K in a jet expansion with He. A tunable diode laser was used as excitation source, and a multipass system was employed. The spectrum shows groupings of lines in the P and R regions, similar to pseudo Q branches. The analysis of the spectrum yields accurate values for the band origin, rotational constants, and the off-diagonal quadratic centrifugal distortion constants.

The diode laser absorption spectrum of the ν 19a band of aniline cooled in a supersonic expansion has been recorded and transitions with low J , K a and K c values (2–28) are reported. The band center has been found at ν 0 =1504.297 cm −1 and rotational constants for the upper state have been determined from a least-squares fitting to the experimental data. The effect of the centrifugal distortion has also been studied, and approximate values of quartic constants are provided. In addition, the possible effect of the inversion mode of the NH 2 group on the ν 19a mode is analyzed.

A rotational spectroscopy investigation has resolved the conformational equilibrium and structural properties of the alkaloid pseudopelletierine. Two different conformers, which originate from inversion of the N-methyl group from an axial to an equatorial position, have been unambiguously identified in the gas phase, and nine independent isotopologues have been recorded by Fourier-transform microwave spectroscopy in a jet expansion. Both conformers share a chair-chair configuration of the two bridged six-membered rings. The conformational equilibrium is displaced towards the axial form, with a relative population in the supersonic jet of Naxial /Nequatorial ≈2/1. An accurate equilibrium structure has been determined by using the semiexperimental mixed-estimation method and alternatively computed by quantum-chemical methods up to the coupled-cluster level of theory. A comparison with the N-methyl inversion equilibria in related tropanes is also presented.

Nicotinoids are agonists of the acetylcholine receptor (nAChR) and play important biochemical and pharmacological roles. Here we report on the structural and conformational landscape of cotinine, and compare its molecular properties with the nicotine prototype, from which it only differs in the addition of a carbonyl group. The investigation of cotinine included a theoretical survey of the effects of rotamerization of the pyridine moiety, the puckering of the pyrrolidinone ring and the internal rotation of the methyl group. The experimental work examined the rotational spectrum of the molecule in a supersonic expansion, using both broadband chirped-pulse excitation techniques and cavity microwave spectrometers. Two conformers were observed for cotinine, and the fine and hyperfine structures arising from the two quadrupolar 14N nuclei and the methyl internal rotor were fully analyzed. The two observed conformers share the same twisted conformation of the five-membered ring, but differ in a ~180o rotamerization around the C-C bond connecting the two cycles. The barrier heights for the internal rotation of the methyl top in cotinine (4.55(4) and 4.64(3) kJ/mol, respectively) are much lower than in nicotine (estimated in 16.5 kJ/mol). The combination of different intramolecular electronic effects, hydrogen bonding and possible binding differences to receptor molecules arising from the carbonyl group could explain the lower affinity of cotinine for nAChRs.

The mephenesin molecule (3-(2-methylphenoxy)propane-1,2-diol) serves as a test bank to explore several structural and dynamical issues, such as conformational flexibility, the orientation of the carbon linear chain relative to the benzene plane, or the effect of substituent position on the rotational barrier of a methyl group. The molecule has been studied by rotational spectroscopy in the 4-18 GHz frequency range by Fourier-transform methods in a supersonic expansion. The experiment has been backed by a previous conformational search plus optimization of the lowest energy structures by ab initio and density functional quantum calculations. The three lowest-lying conformers that can interconvert to each other by simple bond rotations have been detected in the jet. Rotational parameters for all structures have been obtained, and methyl torsional barriers have been determined for the two lowest-lying rotamers. The lowest-lying structure of mephenesin is highly planar, with all carbon atoms lying nearly in the benzene ring plane, and is stabilized by the formation of cooperative intramolecular hydrogen bonding. An estimation of the relative abundance of the detected conformers indicates that the energetically most stable conformer will have an abundance near 80% at temperatures relevant for biological activity.

Objective: Aerosol delivery holds potential to release surfactant or perfluorocarbon (PFC) to the lungs of neonates with respiratory distress syndrome with minimal airway manipulation. Nevertheless, lung deposition in neonates tends to be very low due to extremely low lung volumes, narrow airways and high respiratory rates. In the present study, the feasibility of enhancing lung deposition by intracorporeal delivery of aerosols was investigated using a physical model of neonatal conducting airways. Methods: The main characteristics of the surfactant and PFC aerosols produced by a nebulization system, including the distal air pressure and air flow rate, liquid flow rate and mass median aerodynamic diameter (MMAD), were measured at different driving pressures (4-7 bar). Then, a three-dimensional model of the upper conducting airways of a neonate was manufactured by rapid prototyping and a deposition study was conducted. Results: The nebulization system produced relatively large amounts of aerosol ranging between 0.3 +/- 0.0 ml/min for surfactant at a driving pressure of 4 bar, and 2.0 +/- 0.1 ml/min for distilled water (H(2)Od) at 6 bar, with MMADs between 2.61 +/- 0.1 mu m for PFD at 7 bar and 10.18 +/- 0.4 mu m for FC-75 at 6 bar. The deposition study showed that for surfactant and H(2)Od aerosols, the highest percentage of the aerosolized mass (similar to 65%) was collected beyond the third generation of branching in the airway model. The use of this delivery system in combination with continuous positive airway pressure set at 5 cmH(2)O only increased total airway pressure by 1.59 cmH(2)O at the highest driving pressure (7 bar). Conclusion: This aerosol generating system has the potential to deliver relatively large amounts of surfactant and PFC beyond the third generation of branching in a neonatal airway model with minimal alteration of pre-set respiratory support. This work has been supported by the SAIOTEK 2011 program of the Basque Government (HODEI01, SA-2011/00227) and by the University of the Basque Country (consolidated groups IT 583-13, IT 520-10 and UFI 11/23). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The diode laser absorption spectrum of the v19a band of fluorobenzene molecule near 1500 cm−1 has been measured in a pulsed supersonic jet and transitions from low J, Ka, and Kc. values (2–24) are reported. The band centre has been found at and rotational constants for the upper state as determined from a least-squares fitting to experimental data have been found to be A19a, = 0.188 77(5), B19a = 0.08569(5) and C19a = 0.058 94(1) cm−1. In addition, a number of weak transitions assigned to δKa = ±2, δKc = ±1. ±3 have been observed, with higher intensities than those expected in the rigid rotor model. A discussion of their origin is presented.

International audience; Organic isocyanides have an interesting astrochemistry and some of these molecules have been detected in the interstellar medium (ISM). However, rotational spectral data for this class of compounds are still scarce. We provide laboratory spectra of the four-carbon allyl isocyanide covering the full microwave region, thus allowing a potential astrophysical identification in the ISM. We assigned the rotational spectrum of the two cis (synperiplanar) and gauche (anticlinal) conformations of allyl isocyanide in the centimeter-wave region (4-18 GHz), resolved its 14N nuclear quadrupole coupling (NQC) hyperfine structure, and extended the measurements into the millimeter and submillimeter-wave (150-900 GHz) ranges for the title compound. Rotational constants for all the monosubstituted 13C and 15N isotopologues are additionally provided. Laboratory observations are supplemented with initial radioastronomical observations. Following analysis of an extensive dataset (>11000 rotational transitions), accurate ground-state molecular parameters are reported for the cis and gauche conformations of the molecule, including rotational constants, NQC parameters, and centrifugal distortion terms up to octic contributions. Molecular parameters have also been obtained for the two first excited states of the cis conformation, with a dataset of more than 3300 lines. The isotopic data allowed determining substitution and effective structures for the title compound. We did not detect allyl isocyanide either in the IRAM 30 m line survey of Orion KL or in the PRIMOS survey toward SgrB2. Nevertheless, we provided an upper limit to its column density in Orion KL.

The diode laser absorption spectrum of the nu(13) band of benzene cooled in a supersonic expansion has been recorded with the help of a multipass optical system built inside the vacuum chamber. Transitions from low J, K values (0-10) are reported for the first time for this band. The observed frequencies agree with the ones computed with previously existing spectroscopic constants. The rotational temperature of the expansion has been evaluated to be 8 +/- 5 K when using He as buffer gas at a stagnation pressure of 1.5 bar. This value lowers in 1:10 mixtures of Ar:He at the same pressure. The effect of the carrier gas on the linewidth is also discussed. Copyright 1999 Academic Press.

The intrinsic conformational and structural properties of the bicycle exo-2-aminonorbornane have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy and quantum chemical calculations. The rotational spectrum revealed two different conformers arising from the internal rotation of the amino group, exhibiting small (MHz) hyperfine patterns originated by the (14)N nuclear quadrupole coupling interaction. Complementary ab initio (MP2) and DFT (B3LYP and M05-2X) calculations provided comparative predictions for the structural properties, rotational and centrifugal distortion data, hyperfine parameters, and isomerization barriers. Due to the similarity of the rotational constants, the structural assignment of the observed rotamers and the calculation of the torsion angles of the amino group were based on the conformational dependence of the (14)N nuclear quadrupole coupling hyperfine tensor. In the most stable conformation (ss), the two amino N-H bonds are staggered with respect to the adjacent C-H bond. In the second conformer (st), only one of the N-H bonds is staggered and the other is trans. A third predicted conformer (ts) was not detected, consistent with a predicted conformational relaxation to conformer ss through a low barrier of 5.2 kJ mol(-1).

Velocity and kinetic energy distributions (VDs, KEDs) of metal ions generated by nanosecond (ns) pulsed laser ablation under high vacuum have been determined using an electrostatic analyzer plus time-of-flight coupled system. A number of metal and alloy targets, principally involving Fe and Ni, have been studied at different laser fluences. At low fluence, the ion distributions have been shown to fit single Maxwell-Boltzmann-Coulomb (MBC) distributions; for medium and higher fluences, each ion distribution is found to comprise that of the surviving ``precursor'' ion, itself, overlapped with sidebands which arise from ion-electron recombination and/or ionization. The so-called surviving ``precursor'' ion of a distribution is that which underwent no change of charge. The Coulomb velocities of the surviving ``precursor'' ions and those of the ion products resulting from ion-electron collisions have been compared. Ion velocities are correlated with the local electric field resulting from ejection of the photoelectrons following laser ablation. Under identical conditions of laser fluence, the ions are seen to experience an electrical field nearly independent of their charge. The transit times of ions in the plasma have been estimated to be of the order of $1\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. An overall quantitative mechanism for metal ablation on this basis is presented, including the ejection time for photoelectrons and differences in ion distributions resulting from employing laser pulses in the nanosecond (ns) and femtosecond (fs) regimes.

The diode-laser absorption spectrum of the nu(19a) band of the chlorobenzene molecule cooled in a supersonic jet is presented and transitions from low J, K(a), and K(c) values (0-14) are reported. The C(6)H(5)(35)Cl band center has been found at nu(0) = 1483.894 cm(-1) and rotational constants for the upper state have been determined from a least-squares fitting to experimental data. The band center for the C(6)H(5)(37)Cl isotope has also been obtained. Copyright 2000 Academic Press.