In contrast to the CH₂OO isomers, those of SiH₂OO have received relatively little attention, either theoretically or experimentally. High-level coupled cluster calculations predict a much different energy ordering in comparison to that found for CH₂OO, with the three conformers of Si-dihydroxycarbene, HOSiOH, most stable, followed by the Si-analogues of cis and trans formic acid, and then a cyclic isomer with C_2v symmetry, c-SiH₂OO. Guided by these theoretical predictions, rotational lines of the cis, trans isomer of HOSiOH, as well as c-SiH₂OO, have been detected by Fourier transform microwave spectroscopy. The lines of the cyclic form are sufficiently strong that several rare isotopic species have also been found, enabling, in combination with calculated vibrational corrections, a precise semi-experimental structure to be derived. This talk will provide a status report on our joint study of this unusual isomeric system, and an update on searches for still other isomers.

Terpenes represent one of the largest classes of secondary metabolites in nature and are derived from adding substituents to their core building block, isoprene. They exhibit a huge assortment of structures and thus a variety of chemical and biological activities. We recently investigated a number of monoterpenoids using broadband rotational spectroscopy in the 2-8.5 GHz frequency range. r0pt Figure We present a comparative study of the aromatic monoterpenoids thymol and carvacrol and aliphatic menthone and menthol. The differences in their electronic and steric structures significantly influence molecular properties such as internal rotation barriers and conformational flexibility. These influences are revealed in the rotational spectra. We report the rotational spectra and the experimentally determined molecular parameters. Results from extensive quantum chemical calculations of the conformational spaces of these molecules are compared with the experimentally determined molecular parameters.

Methyl valerate, C₄H₉COOCH₃, belongs to the class of fruit esters, which play an important role in nature as odorants of different fruits, flowers, and wines. A sufficient explanation for the structure–odor relation of is not available. It is known that predicting the odor of a substance is not possible by knowing only its chemical formula. A typical example is the blueberry- or pine apple-like odor of ethyl isovalerate while its isomers ethyl valerate and isoamyl acetate smell like green apple and banana, respectively. Obviously, not only the composition but also the molecular structures are not negligible by determining the odor of a substance. Gas phase structures of fruit esters are thus important for a first step towards the determination of structure–odor relation since the sense of smell starts from gas phase molecules.

For this purpose, a combination of microwave spectroscopy and quantum chemical calculations (QCCs) is an excellent tool. Small esters often have sufficient vapor pressure to be transferred easily in the gas phase for a rotational study but already contain a large number of atoms which makes them too big for classical structure determination by isotopic substitution and requires nowadays a comparison with the structures optimized by QCCs. On the other hand, the results from QCCs have to be validated by the experimental values.

About the internal dynamics, the methoxy methyl group -COOCH₃ of methyl acetate shows internal rotation with a barrier of 424.581(56) cm⁻¹. A similar barrier height of 429.324(23) cm⁻¹was found in methyl propionate, where the acetyl group is extended to the propionyl group. The investigation on methyl valerate fits well in this series of methyl alkynoates. In this talk, the structure of the most energetic favorable conformer as well as the internal rotation shown by the methoxy methyl group will be reported. It could be confirmed that the internal rotation barrier of the methoxy methyl group remains by longer alkyl chain.

Methyl salicylate is a naturally occurring organic ester produced by wintergreen and other plants. It is also found in many over-the-counter remedies, such as muscle ache creams. The rotational spectrum of the methyl salicylate monomer was reported previously, where the most stable, dominant conformer was identified. S. Melandri, B. M. Giuliano, A. Maris, L. B. Favero, P. Ottaviani, B. Velino, W. Caminati, J. Phys. Chem. A. 2007, 111, 9076.he methyl salicylate-water complex was first studied using fluorescence-detected infrared spectroscopy; only one monohydrate conformer was found in that work. A. Mitsuzuka, A. Fujii, T. Ebata, N. Mikami, J. Phys. Chem. A 1998, 102, 9779.n the present study, we employed both broadband chirped and cavity based Fourier transform microwave spectroscopy to examine the competition between intra- and intermolecular hydrogen-bonding interactions and possible large amplitude motions associated with the methyl group and the water subunit. In contrast to the previous infrared study, two monohydrate conformers were identified, with carbonyl O or hydroxyl O as the hydrogen bond acceptors. Detailed analyses of the observed hyperfine structures will be presented, as well as our efforts to extend the study to larger methyl salicylate hydration clusters. S. Melandri, B. M. Giuliano, A. Maris, L. B. Favero, P. Ottaviani, B. Velino, W. Caminati, J. Phys. Chem. A. 2007, 111, 9076.T A. Mitsuzuka, A. Fujii, T. Ebata, N. Mikami, J. Phys. Chem. A 1998, 102, 9779.I

i0pt Figure Alkaloids such as nicotine, cotinine or anabasine share a common floppy structural motif consisting of a two-ring assembly with a 3-pyridil methylamine skeleton. In order to investigate the structure-activity relationship of these biomolecules, structural studies with rotational resolution have been carried out for nicotineJ.-U. Grabow, S. Mata, J. L. Alonso, I. Peña, S. Blanco, J. C. López, C. Cabezas, Phys. Chem. Chem. Phys. 2011, 13, 21063.nd anabasineA. Lesarri, E. J. Cocinero, L. Evangelisti, R. D. Suenram, W. Caminati, J.-U. Grabow, Chem. Eur. J. 2010, 16, 10214.n the gas phase, where these molecules can be probed in an “interaction-free” environment (no solvent or crystal-packing interactions). We hereby present a structural investigation of cotinine in a jet expansion using the chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer recently built at the University of the Basque Country (UPV-EHU). The rotational spectrum (6-18 GHz) reveals the presence of two different conformations. The conformational preferences of cotinine originate from the internal rotation of the two ring moieties, the detected species differing in a near 180^° rotation of pyridine. The final structure is modulated by steric effects.

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Footnotes:

J.-U. Grabow, S. Mata, J. L. Alonso, I. Peña, S. Blanco, J. C. López, C. Cabezas, Phys. Chem. Chem. Phys. 2011, 13, 21063.a A. Lesarri, E. J. Cocinero, L. Evangelisti, R. D. Suenram, W. Caminati, J.-U. Grabow, Chem. Eur. J. 2010, 16, 10214.i

Glutamine is widely known to be found in critical regions of peptides which readily fold into amyloid fibrils, the structures commonly associated with Alzheimer’s disease and glutamine repeat diseases such as Huntington’s disease. Building on previous single-conformation data on Gln-containing peptides containing an aromatic cap on the N-terminus (Z-Gln-OH and Z-Gln-NHMe), we present here single-conformation UV and IR spectra of Ac-Gln-NHBn and Ac-Ala-Gln-NHBn, with its C-terminal benzyl cap. These results point towards side-chain to backbone hydrogen bonds dominating the structures observed in the cold, isolated environment of a molecular beam. We have identified and assigned three main conformers for Ac-Gln-NHBn all involving primary side-chain to backbone interactions. Ac-Ala-Gln-NHBn extends the peptide chain by one amino acid, but affords an improvement in the conformational flexibility. Despite this increase in the flexibility, only a single conformation is observed in the gas-phase: a structure which makes use of both side-chain-to-backbone and backbone-to-backbone hydrogen bonds.

Comprehensive FTIR, MS/MS and NMR of pharmaceuticals are generally readily available but characterization of their metabolites has been an obstacle. Atorvastatin is a statin drug responsible for the maintenance of cholesterol in the body. Diovan is an angiostensin receptor antagonist used to treat high blood pressure and congestive heart failure. The field of metabolomics, however, is struggling to obtain the identity of their structures. We implement mass spectrometry with cryogenic ion spectroscopy to study gaseous ions of the desired metabolites which, in combination, not only identify the mass of the metabolite but also elucidate their structures through isotope-specific infrared spectroscopy.

The efficient extraction of cellulose from biomass and its subsequent conversion to glucose derivatives is an attractive goal in the field of energy science. However, current industrial methods require high ionic strength and harsh conditions. Ionic liquids (IL’s) are a class of “green” compounds that have been shown to dissolve cellulose in concentrations of up to 25 wt%. In order to understand IL’s extraordinary cellulose dissolving power, a molecular level understanding of the IL-cellulose interaction is needed. Toward that end, we have acquired infrared pre-dissociation spectra of M⁺-glucose, where M⁺=Li⁺, Na⁺, or K⁺. Through comparisons with density functional theory calculations, we have determined the relative abundances of various M⁺-glucose binding motifs in both the thermodynamic and kinetic limits. These results provide insight on the hydrogen bonding dynamics of glucose and are a step towards a fuller understanding of cellulose interactions with ionic liquids.

Polyethylene oxides (Polyethylene glycoles) represent a prominent class of water-soluble polymers. Surprisingly, already 1,2-dimethoxyethane as the simplest representative of this polymer family has an undetermined conformational preference in the gas phase. Here, we address this problem by spontaneous Raman scattering in a supersonic jet.
Variation of carrier gas, stagnation pressure, nozzle distance and temperature provides information on the three lowest conformations and their mutual interconversion during collisions in the expansion. The results are compared to quantum chemical calculations of the potential energy landscape and of normal modes.