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Araujo-Andrade C.,Autonomous University of Zacatecas | Giuliano B.M.,University of Coimbra | Gomez-Zavaglia A.,Research Center sarrollo En Criotecnologia Of Alimentos | Gomez-Zavaglia A.,University of Coimbra | Fausto R.,University of Coimbra
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2012

In this work, a combined matrix isolation FTIR and theoretical DFT(B3LYP)/6-311++G(d,p) study of 2-furaldehyde dimethylhydrazone (2FDH) was performed. According to calculations, two E and two Z conformers exist, the E forms having considerably lower energy than the Z forms. The absence of relevant sterical hindrance between the two substituents around the CN bond (dimethylamino and 2-furyl) in the E structures and an extended π-p electron delocalization in the hydrazone moiety determines the higher stability of these species relatively to the Z structures. In the lowest energy form (E-AG) the O-C-CN and CN-N-Lp (Lp = lone electron pair of amine nitrogen atom) dihedral angles are predicted by the calculations to be -177.2° and 93.7°, respectively. The weak (NC)-H⋯O hydrogen bond type interaction (H⋯O distance: 252.2 pm) in form E-AG, together with the absence in this form of the destabilizing interaction between the lone electron pairs of the oxygen and nitrogen atoms existing in E-SG, explains its lower energy in comparison with this latter form. Both E-AG and E-SG conformers could be trapped from room temperature gas phase in low temperature argon and xenon matrices. The high E-SG → E-AG energy barrier (>25 kJ mol-1) explains that, upon increasing the temperature of the matrices no conformational isomerization could be observed. After irradiation of 2FDH with UV-light at λ > 328 and λ > 234 nm, two different photochemistries were observed. Irradiation at lower energy (λ > 328 nm) induced the E-AG → E-SG isomerization. Further irradiation at higher energy (λ > 234 nm) led to a quick consumption of 2FDH and production of furan and dimethylisocyanide. © 2012 Elsevier B.V. All rights reserved. Source

Lopes S.,University of Coimbra | Nunes C.M.,University of Coimbra | Gomez-Zavaglia A.,University of Coimbra | Gomez-Zavaglia A.,Research Center sarrollo En Criotecnologia Of Alimentos | And 2 more authors.
Tetrahedron | Year: 2011

(Z)-3-Azido-3-methoxycarbonyl-2-chloro-acrylophenone (MACBP) has been synthesized, isolated in low temperature argon and xenon matrices and studied by FTIR spectroscopy, complemented by DFT(B3LYP)/6-311++G(d,p) calculations. The molecule was characterized both structurally and spectroscopically, and its photochemistry used to probe the mechanism of photo-induced conversion of 3-azido-acrylophenones into oxazoles. In situ UV irradiation (λ = 235 nm) of matrix-isolated MACBP yielded as primary photoproduct a 2H-azirine, which undergoes subsequent photoisomerization to methyl 4-chloro-5-phenyl-1,3-oxazole- 2-carboxylate. In a competitive process, a ketenimine is also formed upon photolysis of MACBP. The reported results indicate that this ketenimine must be formed from the starting 3-azido-acrylophenone via a Curtius type concerted rearrangement. © 2011 Elsevier Ltd. All rights reserved. Source

Araujo-Andrade C.,Autonomous University of Zacatecas | Gomez-Zavaglia A.,Research Center sarrollo En Criotecnologia Of Alimentos | Gomez-Zavaglia A.,University of Coimbra | Reva I.D.,University of Coimbra | Fausto R.,University of Coimbra
Journal of Physical Chemistry A | Year: 2012

The infrared spectra of furfuryl alcohol (2-furanmethanol, FFA) were investigated for FFA monomers isolated in low-temperature argon matrices. The structural interpretation of the obtained experimental spectra was assisted by analysis of the molecule's conformational landscape. According to the DFT(B3LYP)/6-311++G(d,p) calculations, five different minimum energy structures were found on the potential energy surface of the molecule. They can be defined by the orientation of the OCCO and CCOH dihedral angles: GG′, GG, TG, TT, GT (G = +gauche, G′ = -gauche, T = trans) and have a symmetry equivalent configuration: GG′ = G′G, GG = G′G′, TG = TG′, GT = G′T. When zero-point energies are taken into account, only three (GG′, GG, and TT) out of the five unique minima correspond to stable structures. The most stable conformer GG′ (OCCO, 72.7°; CCOH, -59.3°), which in gas phase at room temperature accounts for ∼65% of the total population, was the only form isolated in the argon matrices at 14 K. The other two relevant forms convert into conformer GG′ during matrix deposition. The low temperature glassy and crystalline states of FFA were also obtained and their infrared spectra assigned, suggesting the sole existence of the GG′ conformer also in these phases. The photochemical behavior of FFA induced in situ, by tunable UV-laser, was also studied. The longest wavelength resulting in photochemical changes in the structure of the irradiated sample was found to be λ = 229 nm. Such UV irradiation of the matrix-isolated FFA led to production of formaldehyde and different isomeric C 4H 4O species. Cycloprop-2-ene-1-carbaldehyde and buta-2,3-dienal (two conformers) are the main initial C 4H 4O photoproducts formed upon short-time excitation at λ = 229 nm. But-3-ynal (two conformers) was the principal photoproduct resulting from prolonged excitation at λ= 229 nm, being consumed upon irradiation at shorter wavelengths (λ < 227.5 nm). Vinyl ketene is produced from FFA in the trans conformation and undergoes isomerization to the cis form upon irradiation at λ < 227.5 nm. Cyclopropene, propyne, allene, and CO were also identified in the irradiated matrices (in particular at the later stages of irradiation), suggesting that the photoproduced aldehydes partially decarbonylate during the performed photochemical experiments. © 2012 American Chemical Society. Source

Massolo J.F.,Research Center sarrollo En Criotecnologia Of Alimentos | Concellon A.,Research Center sarrollo En Criotecnologia Of Alimentos | Chaves A.R.,Research Center sarrollo En Criotecnologia Of Alimentos | Vicente A.R.,Research Center sarrollo En Criotecnologia Of Alimentos | Vicente A.R.,National University of La Plata
CYTA - Journal of Food | Year: 2013

To elucidate the role of ethylene in summer squash [Cucurbita maxima var. Zapallito (Carr.) Millan] postharvest responses, harvested fruit was treated with the inhibitor of ethylene action 1-methylcyclopropene (1-MCP, 1 μL L-1) and stored at 10 or 0°C for 14 or 19 days, respectively. Deterioration, chilling injury (CI), weight loss, surface color, firmness, respiration rate, acidity, sugars, and antioxidants were determined. At 10°C 1-MCP treated fruit showed lower deterioration and weight loss. The inhibition of ethylene action delayed yellowing, softening, and respiration, and prevented the increase of acidity. Chilling injury, manifested as shrunken areas and surface depressions, yellowing and softening were reduced in 1-MCP-treated fruit stored at 0°C. Sugars and antioxidants were not affected. Results suggest that ethylene is involved in senescence and CI development in summer squash. Inhibition of its action by 1-MCP could be useful to prevent deterioration and maintain quality. © 2012 Taylor & Francis. Source

Quilaqueo Gutierrez M.,Fundacion de Desarrollo Educacional y Tecnologico la Araucania FUDEAUFRO | Echeverria I.,Research Center sarrollo En Criotecnologia Of Alimentos | Ihl M.,Fundacion de Desarrollo Educacional y Tecnologico la Araucania FUDEAUFRO | Ihl M.,University of the Frontier | And 2 more authors.
Carbohydrate Polymers | Year: 2012

The functionality of nanocomposite films based on carboxymethylcellulose (CMC) and montmorillonite (MMT) activated with murta (Ugni molinae Turcz) leaves extract was studied. Films were prepared by casting from film-forming dispersions containing CMC, glycerol (used as plasticizer) and different concentrations of MMT, using water or murta extract as solvent. The addition of MMT increased the tensile strength and the elasticity modulus of the films, and decreased their permeabilities to water vapor, oxygen and carbon dioxide. Besides the antioxidants properties provided to the films, the addition of murta leaves extract changed the gas permeability in different forms according to the MMT content, and plasticized the nanocomposite matrix. © 2011 Elsevier Ltd. All rights reserved. Source

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