[show abstract][hide abstract] ABSTRACT: A non-conventional vaporization method, using laser ablation of solid NaCl doped with d-erythrose, has been used to bring this sugar into the gas phase for rotational study. The jet cooled rotational spectrum of this C4 monosaccharide reveals the existence of two furanose forms, one α envelope and one β twist. Cooperative hydrogen bond networks and the anomeric effect have been found to be the main stabilization factors of the detected structures.
Chemical Communications 10/2013; · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: Crystalline samples of d-xylose have been vaporized by laser ablation and probed in the gas phase using Fourier transform microwave spectroscopy. The rotational spectrum revealed the existence of two α-d-xylopyranose conformers stabilized by the anomeric effect and cooperative hydrogen bond networks. The experiment spectroscopically tracked fine structural changes upon clockwise and counterclockwise arrangements of the OH groups in the observed conformers. The five monosubstituted (13)C species of the most abundant conformer cc-α-(4)C1 have also been observed in their natural abundance, and its structure has been derived. This work demonstrates the pivotal role that the intramolecular hydrogen-bonding network plays in the conformational behavior of free monosaccharides.
Physical Chemistry Chemical Physics 09/2013; · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: A clear picture of the conformations of isolated 2-deoxy-D-ribose was obtained using chirped pulse and Balle–Flygare Fourier-transform microwave spectrometers, both coupled with laser ablation sources. Two conformers of α-D-deoxyribopyranose and four of β-D-deoxyribopyranose were found on the basis of the spectroscopic rotational parameters and ab initio predictions. The substitution and effective structures of the most abundant conformer have been determined.
Angewandte Chemie International Edition 09/2013; · 13.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The computational composite scheme purposely set up for accurately describing the electronic structure and spectroscopic properties of small biomolecules has been applied to the first study of the rotational spectrum of 2-thiouracil. The experimental investigation was made possible thanks to the combination of the laser ablation technique with Fourier transform microwave spectrometers. The joint experimental-computational study allowed us to determine the accurate molecular structure and spectroscopic properties of the title molecule, but more importantly, it demonstrates a reliable approach for the accurate investigation of isolated small biomolecules.
Physical Chemistry Chemical Physics 09/2013; · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: The small peptide derived from proline, N-acetyl-prolinamide (Ac-Pro-NH2 ), has been investigated using a combination of Fourier transform microwave spectroscopy with laser ablation. Spectral signatures belonging to only one conformer have been detected in the supersonic expansion. Rotational constants and nuclear quadrupole coupling constants of the two (14) N nuclei have been used in the characterization of a γ-turn structure in the gas phase, which is stabilized by a CO⋅⋅⋅HN intramolecular hydrogen bond closing a seven-membered ring. A methyl group internal rotation barrier of 354 cm(-1) has been determined from the analysis of the A-E splittings.
[show abstract][hide abstract] ABSTRACT: The complex of glycine with two water molecules glycine-(H2O)2 has been generated by laser ablation in a supersonic expansion and characterised using rotational spectroscopy. The water molecules bind to the carboxylic group of glycine and to each other through three intermolecular hydrogen bonds, closing an eight-membered ring. In the complex, glycine adopts the conformation found to be the most stable for bare glycine.
Chemical Communications 03/2013; · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: Two conformers of D-fructopyranose are characterized using laser ablation and broadband Fourier-transform microwave spectroscopy. Both species are stabilized by complicated intramolecular hydrogen-bonding networks. Structural motifs related to the sweetness of D-fructopyranose are revealed for the most stable conformer.
[show abstract][hide abstract] ABSTRACT: Give me five! All five tautomers and conformers of cytosine were characterized in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy. The spectra were assigned unambiguously on the basis of the hyperfine structure due to the three (14) N nuclei (see picture; N blue, O red). The relative energies of the identified species were estimated from the relative intensities of the spectra.
Angewandte Chemie International Edition 01/2013; · 13.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Microwave spectroscopy has been applied to characterize the conformations adopted in the gas phase by a small peptide derived from alanine, N-acetyl-l-alaninamide (Ac-Ala-NH(2)). This compound was vaporized by laser ablation and shown to exist as a mixture of C and C(5) conformers stabilized by a COHN intramolecular hydrogen bond closing a seven- or a five-membered ring, respectively. The complicated quadrupole hyperfine structure originated from two (14)N nuclei has been completely resolved for both species and the derived nuclear quadrupole coupling constants have been used to determine the Ramachandran angles that describe their molecular shapes.
Physical Chemistry Chemical Physics 01/2013; · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: A laser ablation device in combination with a molecular beam Fourier-transform microwave spectrometer has allowed the observation of the rotational spectrum of serotonin for the first time. Three conformers of the neurotransmitter have been detected and characterized in the 4-10 GHz frequency range. The complicated hyperfine structure arising from the presence of two (14)N nuclei has been fully resolved for all conformers and used for their identification. Nuclear quadrupole coupling constants of the nitrogen atom of the side chain have been used to determine the orientation of the amino group probing the existence of N-Hπ interactions involving the amino group and the pyrrole unit in the Gauche-Phenyl conformer (GPh) or the phenyl unit in the Gauche-Pyrrole (GPy) ones.
Physical Chemistry Chemical Physics 09/2012; 14(39):13618-23. · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rotational spectra of β-propiolactone-(H_2O)_n (n=1-5) adducts
have been extensively analyzed by broadband microwave spectroscopy
(CP-FTMW). Unambiguous identification of their structures has been
achieved from the spectra of the parent species and H_218O
single substitution clusters and Stark effect measurements. In addition
to our previous work, the substitution structures for two n=4 and one
n=5 complexes are presented. The three structures show a cyclic
arrangement in the oxygen framework. For both n=4 structures, the water
molecules form a quasiplanar ring that sits above the BPL unit. The
structural differences between these two n=4 complexes are discussed in
terms of the water oxygen atom positions and dipole moment orientations,
enabling to distinguish between isomers with certainty by CP-FTMW
spectroscopy. For n=5, a cyclic arrangement similar to n=4 was found
with water molecules making a puckered five-water ring. Substitution
coordinates for the oxygen framework support the assignment. Our results
show that complexation with BPL induces measurable structural changes in
the (H_2O)_n (n = 3, 4, 5) pure water clusters. This fact is also
discussed in terms of the variation in O-O distances within pure and
complexed water clusters.
[show abstract][hide abstract] ABSTRACT: One dominant structure has been identified analysing the rotational spectrum of asparagine in sharp contrast with the multiconformational behaviour for other amino acids with polar side chains. This locking of the conformational variety to a single conformer has been ascribed to an intramolecular hydrogen bonding network involving α-amine, α-carboxylic and amide groups.
Chemical Communications 05/2012; 48(47):5934-6. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: The first high-resolution study of isolated gas-phase acetyl salicylic acid (aspirin) is reported. Solid aspirin was vaporized by laser ablation, expanded in a supersonic jet, and characterized by Fourier transform microwave spectroscopy (see picture). Two different neutral structures have been identified from the analysis of the rotational spectrum.
Angewandte Chemie International Edition 02/2012; 51(6):1375-8. · 13.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Using a combination of laser ablation and jet cooled FT-MW spectroscopy the pure rotational spectrum of AlCCH and AgCCH in the (X1Σ+) electronic ground state has been recorded and assigned in the 6–20 GHz region. A newly constructed ablation-discharge source has been coupled to our LA-MB-FTMW spectrometer and tested as a generator of metal acetylides. Laser ablation of the pure metal has been demonstrated as a very efficient method to create unstable compounds in the gas phase. The high spectral resolution of our instrument provided an accurate set of rotational, quadrupole (only for AlCCH) and centrifugal distortion constants which are reported for the first time.
[show abstract][hide abstract] ABSTRACT: The molecular shape of proteinogenic glutamic acid has been determined for the first time. Vaporization of the solid amino acid by laser ablation in combination with Fourier transform microwave spectroscopy made possible the detection of five different structures in a supersonic jet. These structures have been identified through their rotational and (14)N quadrupole coupling constants. All conformers show hydrogen bonds linking the amino and alpha carboxylic group through N-H···O═C (type I) or N···H-O (type II) interactions. In three of them there are additional hydrogen bonds established between the amino group and the carboxylic group in the gamma position. Entropic effects related to the side chain have been found to be significant in determining the most populated conformations.
Journal of the American Chemical Society 12/2011; 134(4):2305-12. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nicotine has been investigated in the gas phase and two conformational forms were characterized through their rotational spectra. Two spectroscopic techniques have been used to obtain the spectra: a new design of broadband Fourier transform microwave (FTMW) spectroscopy with an in-phase/quadrature-phase-modulation passage-acquired-coherence technique (IMPACT) and narrowband FTMW spectroscopy with coaxially oriented beam-resonator arrangement (COBRA). The rotational, centrifugal distortion and hyperfine quadrupole coupling constants of two conformers of nicotine have been determined and found to be in N-methyl trans configurations with the pyridine and pyrrolidine rings perpendicular to one another. The quadrupole hyperfine structure originated by two (14)N nuclei has been completely resolved for both conformers and used for their unambiguous identification.
Physical Chemistry Chemical Physics 12/2011; 13(47):21063-9. · 3.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: The natural nonproteinogenic α-amino acid 1-aminocyclopropanecarboxylic acid (Ac(3)c) has been vaporized by laser ablation and studied in the gas phase by molecular-beam Fourier transform microwave spectroscopy. Comparison of the experimental rotational and (14)N nuclear quadrupole coupling constants with the values predicted ab initio for these parameters has allowed the unambiguous identification of three Ac(3)c conformers differing in the hydrogen bonding pattern. Two of them resemble those characterized before for the coded aliphatic α-amino acids. Remarkably, a third conformer predicted to be energetically accessible for all of these amino acids but never observed (the so-called "missing conformer") has been found for Ac(3)c, close in energy to the global minimum. This is the first time that such a conformer, stabilized by an N-H···O(H) hydrogen bond, is detected in the rotational spectrum of a gaseous α-amino acid with a nonpolar side chain. The conjugative interaction established between the cyclopropane ring and the adjacent carbonyl group seems to be responsible for the unique conformational properties exhibited by Ac(3)c.
Journal of the American Chemical Society 06/2011; 133(27):10621-8. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rotational spectrum of neutral phenylalanine has been recorded for the first time using laser-ablation molecular-beam Fourier transform microwave spectroscopy (LA-MB-FTMW). Two conformers stabilized by conjugative O-H···N and N-H···π hydrogen bond interactions have been conclusively identified on the basis of experimental values of rotational and (14)N nuclear quadrupole coupling constants. The nonobservation of the rotational spectra of the other low-energy conformers has been attributed to the photofragmentation that takes place in the laser ablation process. Nuclear quadrupole coupling interactions have been used directly to determine the orientation of the amino group and to identify and experimentally characterize the N-H···π interactions.
The Journal of Physical Chemistry A 05/2011; 115(34):9653-7. · 2.77 Impact Factor