Demonstration of Capture, Cooling, Tagging, and Spectroscopic Characterization of UV Photoproduct Ions in a Cryogenic Ion Trap: Application to 266 nm Photofragment Ions from Rhodamine 6G.

We demonstrate a method to determine the structures of the primary photodissociation products from a cryogenically cooled parent ion. In this approach, a target ion is cooled by a pulse of buffer gas and tagged in a 20 K Paul trap. The cold ion is then photodissociated by pulsed (∼5 ns) UV laser excitation, and the ionic products are trapped, cooled, and tagged by introduction of a second buffer gas pulse in the same trap. The tagged fragments are then ejected into a triple focusing, UV/vis/IR time-of-flight photofragmentation mass spectrometer which yields vibrational and electronic spectra of the mass-selected photofragments. These methods are demonstrated by application to the 266 nm photodissociation of the Rhodamine 6G cation to yield the R575 fragment ion based on loss of ethene as well as to a weaker secondary fragment arising from loss of m/z 43.

Spectroscopic Evidence for Doubly Hydrogen-Bonded Cationic Dimers in the Solid, Liquid, and Gaseous Phases of Carboxyl-Functionalized Ionic Liquids.

Intermolecular interactions determine whether matter sticks together, gases condense into liquids, or liquids freeze into solids. The most prominent example is hydrogen bonding in water, responsible for the anomalous properties in the liquid phase and polymorphism in ice. The physical properties are also exceptional for ionic liquids (ILs), wherein a delicate balance of Coulomb interactions, hydrogen bonds, and dispersion interactions results in a broad liquid range and the vaporization of ILs as ion pairs. In this study, we show that strong, local, and directional hydrogen bonds govern the structures and arrangements in the solid, liquid, and gaseous phases of carboxyl-functionalized ILs. For that purpose, we explored the H-bonded motifs by X-ray diffraction and attenuated total reflection (ATR) infrared (IR) spectroscopy in the solid state, by ATR and transmission IR spectroscopy in the liquid phase, and by cryogenic ion vibrational predissociation spectroscopy (CIVPS) in the gaseous phase at low temperature. The analysis of the CO stretching bands reveals doubly hydrogen-bonded cationic dimers (c═c), resembling the archetype H-bond motif known for carboxylic acids. The like-charge doubly hydrogen-bonded ion pairs are present in the crystal structure of the IL, survive phase transition into the liquid state, and are still present in the gaseous phase even in (2,1) complexes wherein one counterion is removed and repulsive Coulomb interaction increased. The interpretation of the vibrational spectra is supported by quantum chemical methods. These observations have implications for the fundamental nature of the hydrogen bond between ions of like charge.

Hydrogen Tag Shifts as Vibrational Reporters for Positional Isomers of Formylphenides: Surprising Mobility of the Carbanion Center upon Collisional Decarboxylation of the Parent Benzoates.

Infrared photodissociation of weakly bound "mass tags" is widely used to determine the structures of ions by analyzing their vibrational spectra. Molecular hydrogen is a common choice for tagging in cryogenic radio-frequency ion traps. Although the H2 molecules can introduce distortions in the target species, we demonstrate an advantage of H2 tagging in the analysis of positional isomers adopted by the molecular anions derived from decarboxylation of formylbenzoates. Attachment of H2 to the carbanion centers of three such isomers yields distinct shifts in the H2 stretch, which can be used to determine the distribution of isomers in an unknown sample. Electronic structure calculations indicate that the position-dependent shifts are due to different reactivities of the carbanion sites with respect to an intracluster proton-transfer reaction with the H2 molecule. We exploit this spectroscopic method to quantify the surprisingly facile migrations of the anionic center that have been previously reported for phenide rearrangements.

Structures and Chemical Rearrangements of Benzoate Derivatives Following Gas Phase Decarboxylation.

Decarboxylation of carboxylate ions in the gas phase provides a useful window into the chemistry displayed by these reactive carbanion intermediates. Here, we explore the species generated by decarboxylation of two benzoate derivatives: 2-formylbenzoate (2FBA) and 2-benzoylbenzoate (2BBA). The nascent product anions are transferred to a cryogenic ion trap where they are cooled to ∼15 K and analyzed by their pattern of vibrational bands obtained with IR photodissociation spectroscopy of weakly bound H2 molecules. The structures of the quenched species are then determined by comparison of these spectra with those predicted by electronic structure calculations for local minima on the potential energy surface. The 2-phenide carbanion generated by decarboxylation of 2FBA occurs in two isomeric forms that differ in the orientation of the formyl group, both of which yield a very large (∼110 cm-1) redshift in the stretching frequency of the H2 molecule attached to the anionic carbon center. Although calculated to be a local minimum, the analogous 2-phenide species could not be isolated upon decarboxylation of 2BBA. Rather, the anionic product adopts a ring-closed structure, indicating efficient nucleophilic attack on the pendant phenyl group by the nascent phenide. The barrier for ring closing is evaluated with electronic structure calculations.

Relationship Between Respiratory Muscle Strength, Handgrip Strength, and Muscle Mass in Hospitalized Patients.

BACKGROUND: Minimal information is available to validate measurement of respiratory muscle strength (RMS) in the clinical setting. The purpose of this study was to determine the correlation between maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and sniff nasal inspiratory pressure (SNIP) with handgrip strength (HGS) and cross sectional muscle area obtained via diagnostic abdominal computed tomography (CT). MATERIALS AND METHODS: Measures of MIP, MEP, SNIP, and HGS were obtained from individuals that participated in a previously published study; individuals who had an abdominal CT completed with (±)7 days of obtaining RMS measures were included. Both RMS and HGS were measured within 48-72 hours of admission; for RMS, the highest absolute (cm H2 O) and percent predicted values were recorded, and the average of 3 HGS measurements (kg) was documented. Cross-sectional muscle area (cm2 ) at the third lumbar region was recorded. Spearman's correlation coefficient was used to assess the relationship between variables. RESULTS: A total of 35 participants were included. HGS was correlated to absolute MIP (rs = 0.62, rs = 0.61), MEP (rs = 0.74, rs = 0.73), and SNIP (rs = 0.58, rs = 0.54) for males and females, respectively. Crosss-sectional muscle area was correlated with absolute MIP (rs = 0.66), MEP (rs = 0.58), and SNIP (rs = 0.783) for men and absolute SNIP (rs = 0.56) among women. CONCLUSION: Measures of RMS represent a promising assessment of muscle mass and function among hospitalized patients.

Differences in Respiratory Muscle Strength Measures in Well-Nourished and Malnourished Hospitalized Patients.

BACKGROUND: Objective indicators of nutritional status are essential for accurate identification of malnutrition. Previous research has indicated an association between measures of respiratory muscle strength (RMS) and nutritional status. Measurement of RMS-including maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and sniff nasal inspiratory pressure (SNIP)-may provide evidence to support the assessment of nutritional status in hospitalized patients. OBJECTIVE: The purpose of this study was to determine whether there was a difference in MIP, MEP, and SNIP between well-nourished and malnourished hospitalized patients. DESIGN: A cross-sectional study was conducted. PARTICIPANTS/SETTING: Patients were screened for eligibility criteria on admission by means of electronic medical records in general medical or surgical units at a tertiary care hospital in Chicago, IL, from January 2016 to January 2017. A total of 140 patients were included for analysis. MAIN OUTCOMES MEASURED: The primary outcome was detection of differences in measures of RMS between malnourished and well-nourished hospitalized patients. Nutritional status was assessed using subjective global assessment and Academy of Nutrition and Dietetics/American Society for Parenteral and Enteral Nutrition (Academy/ASPEN) criteria recommended to identify malnutrition. The MIP, MEP, and SNIP measures were obtained and reported as absolute values (expressed in centimeters of water) and percent of predicted values. STATISTICAL ANALYSIS: Independent t tests or Mann-Whitney U tests were used to determine differences in RMS measures between patients assessed as well nourished and those assessed as malnourished, depending on normality. RESULTS: Compared with well-nourished patients, malnourished patients identified by subjective global assessment criteria had significantly lower absolute SNIP (73.7±28.7 vs 59.5±27.1 cm H2O, P=0.004) and percent of predicted SNIP (78.6%±26.3% vs 64.8%± 30.0% predicted, P=0.006). Similarly, compared with well-nourished patients when Academy/ASPEN guidelines were used, malnourished individuals had significantly lower absolute SNIP (76.5±28.6 vs 58.3±26.3 cm H2O, P<0.001), percent of predicted SNIP (81.4%±26.4% vs 63.5%±28.7% predicted, P<0.001), absolute MIP (83.5±34.6 vs 71.1±33.6 cm H2O, P=0.05), and absolute MEP (108.7±36.6 vs 94.2±39.9 cm H2O, P=0.04). CONCLUSION: Differences in RMS between well-nourished and malnourished patients were observed when SNIP measures were used. However, there were no differences in MIP and MEP measures. Further research is needed to build on the findings from this study.