Browsing by Author "Cristiano, Maria L. S."

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    4-Hydroxyquinolin-2(1H)-One Isolated in Cryogenic Argon and Xenon Matrices: Tautomers and Photochemistry
    (Elsevier, 2024) Secrieru, A.; Lopes, S.; Nikitin, T.; Cristiano, Maria L. S.; FAUSTO, RUI
    4-Hydroxyquinolin-2(1H)-one (4HQ2O) was synthesized, isolated in cryogenic matrices (argon and xenon), and studied by infrared spectroscopy. Quantum chemical calculations carried out at the DFT(B3LYP)/6-311++G (3df,3pd) level of theory were used to determine the conformational and tautomeric properties of the molecule. Two tautomeric forms were identified in the as-deposited matrices with the help of the theoretical data. To investigate the photochemistry of the compound, in situ broadband ultraviolet (lambda > 283 nm) irradiation of the asdeposited argon matrix was performed. This irradiation led to the generation of an additional tautomer, together with the products of fragmentation of the heterocyclic ring of the molecule, specifically isocyanic acid and carbon monoxide. Photoproducts such as 1,3-dihydro-2H-indol-2-one and cyclohepta-1,2,4,6-tetraene were also observed in the photolyzed argon matrix. A comprehensive assignment of the infrared spectra of all the species observed experimentally is presented.
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    Molecular and Crystal Structure, Spectroscopy, and Photochemistry of a Dispiro Compound Bearing the Tetraoxane Pharmacophore
    (Wiley-VCH Verlag GmbH, 2023) Amado, Patricia S. M.; Lopes, Susy; Bras, Elisa M.; Paixao, Jose A.; Takano, Ma-aya; Abe, Manabu; FAUSTO, RUI; Cristiano, Maria L. S.
    The molecular structure and photochemistry of dispiro[cyclohexane-1,3 & PRIME;-[1,2,4,5]tetraoxane-6 & PRIME;,2 & PRIME;& PRIME;-tricyclo[3.3.1.1(3,7)]decan]-4-one (TX), an antiparasitic 1,2,4,5-tetraoxane was investigated using matrix isolation IR and EPR spectroscopies, together with quantum chemical calculations undertaken at the DFT(B3LYP)/6-311++G(3df,3pd) level of theory, with and without Grimme's dispersion correction. Photolysis of the matrix-isolated TX, induced by in situ broadband (& lambda;>235 nm) or narrowband (& lambda; in the range 220-263 nm) irradiation, led to new bands in the infrared spectrum that could be ascribed to two distinct photoproducts, oxepane-2,5-dione, and 4-oxohomoadamantan-5-one. Our studies show that these photoproducts result from initial photoinduced cleavage of an O-O bond, with the formation of an oxygen-centered diradical that regioselectivity rearranges to a more stable (secondary carbon-centered)/(oxygen-centered) diradical, yielding the final products. Formation of the diradical species was confirmed by EPR measurements, upon photolysis of the compound at & lambda;=266 nm, in acetonitrile ice (T=10-80 K). Single-crystal X-ray diffraction (XRD) studies demonstrated that the TX molecule adopts nearly the same conformation in the crystal and matrix-isolation conditions, revealing that the intermolecular interactions in the TX crystal are weak. This result is in keeping with observed similarities between the infrared spectrum of the crystalline material and that of matrix-isolated TX. The detailed structural, vibrational, and photochemical data reported here appear relevant to the practical uses of TX in medicinal chemistry, considering its efficient and broad parasiticidal properties.