title: Conformational switching in pyruvic acid isolated in Ar and N₂ matrixes: spectroscopic analysis, anharmonic simulation, and tunneling.
abstract: Monomers of pyruvic acid (PA) isolated in cryogenic argon and nitrogen matrixes were characterized by mid- and near-infrared spectroscopy. Interpretation of the experiments was aided by fully anharmonic calculations of the fundamental modes, overtones, and combinations up to two quanta, including their infrared intensities. The initially dominating PA conformer (Tc) has a cis CCOH arrangement and is stabilized by a strong intramolecular H-bond. Selective near-infrared excitation of Tc at the first OH overtone (6630 cm(-1) in Ar, 6643 cm(-1) in N2) induced a large scale conformational conversion to the higher-energy conformer (Tt) with trans CCOH arrangement. Tt was then converted back to Tc by selective NIR irradiation at the first Tt OH overtone (6940 cm(-1) in Ar, 6894 cm(-1) in N2). In N2 matrix, the Tt form was stabilized due to interaction between the OH group and the matrix molecules. This stabilization manifested itself in the absence of Tt → Tc relaxation and in a considerable change of the vibrational Tt signature upon going from argon to nitrogen matrix. In argon, the Tt form spontaneously decayed back to Tc in the dark (characteristic lifetime +16 h). In the presence of broad-band near-infrared light, the Tt → Tc relaxation speed considerably increased. The decay mechanisms are discussed.
authors.affiliation: †CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Igor
authors.initials: I
authors.lastname: Reva
authors.affiliation: †CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Cláudio
authors.initials: C
authors.lastname: M Nunes
authors.affiliation: ‡Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy.|§Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti OrganoMetallici (ICCOM-CNR), UOS di Pisa, Area della Ricerca CNR, Via G. Moruzzi 1, I-56124 Pisa, Italy.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Biczysko
authors.affiliation: †CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Rui
authors.initials: R
authors.lastname: Fausto
mesh_terms: D001128:Argon / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D019289:Pyruvic Acid / Q000737:chemistry* / Q000302:isolation & purification*; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
chemical_list: D001128:Argon; D019289:Pyruvic Acid; D009584:Nitrogen