IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid monomers and clusters: Propanoic acid

Antihyperglycemic and cholesterol-lowering potential of dietary fibre from lemongrass (Cymbopogon citratus Stapf.)

BACKGROUND: The major component of lemongrass by weight is dietary fibre (DF), but no literature has been reported on its DF components and fermentation products when ingested. OBJECTIVE: This study analysed DF components of lemongrass, investigated the potential of the major product from total DF (TDF) fermentation to inhibit α-amylase and HMG-CoA reductase, key enzymes of diabetes mellitus and hypercholesterolemia, respectively, and determined the serum glucose- and cholesterol-lowering potential of TDF in an animal model. METHODS: Lemongrass DF components were analysed, TDF was fermented in vitro; the major fermentation product was isolated for enzyme inhibitory assays; and postprandial blood glucose- and cholesterol-lowering potential of TDF was determined in Sprague-Dawley rats. RESULTS: TDF in lemongrass was 65.7 g/100g and soluble DF, 2.8 g/100 g. Significant amount of propionate (10.9 mM/g TDF) was produced after TDF fermentation; propionate inhibited 20.4% α-amylase activity, and 13.1 % HMG-CoA reductase activity in vitro. TDF further exhibited antihyperglycemic and cholesterol-lowering potential in an animal model. CONCLUSIONS: DF from lemongrass was shown to reduce hyperglycemia and hypercholesterolemia in an animal model, through mild inhibition of α-amylase and HMG-CoA reductase. Thus, lemongrass DF may have a significant role in mitigating the risk of type 2 diabetes mellitus and hypercholesterolemia.

Probing Elusive Cations: Infrared Spectroscopy of Protonated Acetic Acid

Protonated carboxylic acids, (RCOOH)H⁺, are the initial intermediates in acid-catalyzed (Fischer) esterification reactions. However, the identity of the isomeric form has been debated. Surprisingly, no optical spectra have been reported for any isomer of the protonated carboxylic acid monomer, despite it being a fundamental organic cation. Here, we address these issues by using a new approach to prepare cold He-tagged cations of protonated acetic acid (AA), which entails electron ionization of helium nanodroplets containing metastable dimers of AA. The protonated species is subsequently probed using infrared photodissociation spectroscopy, and following a comparison with calculations, we identify the two isomers whose roles in Fischer esterification are debated. These are the carbonyl-protonated E, Z isomer and the metastable hydroxyl-protonated isomer. Our technique provides a novel approach that can be applied to other elusive ionic species.

Ionization of carboxylic acid clusters in the gas phase and on free ArN and (H2O)N nanoparticles: valeric acid as a model for small carboxylic acids

In ionized valeric acid clusters, not only the expected proton transfer reaction, but also anhydride formation is observed. Could this be a common motif in the ionization chemistry of small carboxylic acid clusters?

New insights into the mechanism of interaction between CO2 and polymers from thermodynamic parameters obtained by in situ ATR-FTIR spectroscopy

This work reports new physical insights of the thermodynamic parameters and mechanisms of possible interactions occurring in polymers subjected to high-pressure CO2. ATR-FTIR spectroscopy has been used in situ to determine the thermodynamic parameters of the intermolecular interactions between CO2 and different functional groups of the polymers capable of specific interactions with sorbed CO2 molecules. Based on the measured ATR-FTIR spectra of the polymer samples subjected to high-pressure CO2 (30 bar) at different temperatures (300-340 K), it was possible to characterize polymer-polymer and CO2-polymer interactions. Particularly, the enthalpy and entropy of the formation of the specific non-covalent complexes between CO2 and the hydroxy (-OH), carbonyl (C[double bond, length as m-dash]O) and hydroxyimino ([double bond, length as m-dash]N-OH) functional groups of the polymer samples have been measured. Furthermore, the obtained spectroscopic results have provided an opportunity for the structure of these complexes to be proposed. An interesting phenomenon regarding the behavior of CO2/polymer systems has also been observed. It has been found that only for the polyketone, the value of enthalpy was negative indicating an exothermic process during the formation of the CO2-polymer non-covalent complexes. Conversely, for the polyoxime and polyalcohol samples there is a positive enthalpy determined. This is a result of the initial polymer-polymer interactions requiring more energy to break than is released during the formation of the CO2-polymer complex. The effect of increasing temperature to facilitate the breaking of the polymer-polymer interactions has also been observed. Hence, a mechanism for the formation of CO2-polymer complexes was suggested based on these results, which occurs via a two-step process: (1) the breaking of the existing polymer-polymer interactions followed by (2) the formation of new CO2-polymer non-covalent interactions.

Mass-selected IR-VUV (118 nm) spectroscopic studies of radicals, aliphatic molecules, and their clusters

Mass-selected IR plus UV/VUV spectroscopy and mass spectrometry have been coupled into a powerful technique to investigate chemical, physical, structural, and electronic properties of radicals, molecules, and clusters. Advantages of the use of vacuum ultraviolet (VUV) radiation to create ions for mass spectrometry are its application to nearly all compounds with ionization potentials below the energy of a single VUV photon, its circumventing the requirement of UV chromophore group, its inability to ionize background gases, and its greatly reduced fragmenting capabilities. In this review, mass-selected IR plus VUV (118 nm) spectroscopy is introduced first in a general manner. Selected application examples of this spectroscopy are presented, which include the detections and structural analysis of radicals, molecules, and molecular clusters in a supersonic jet.