Browsing by Author "Lopes, Susy"

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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.
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    Structure, Conformational Landscape and UV-Induced Selective Rotamerization of 2-Aminoacetanilide
    (Elsevier Science SA, 2023) Brito, Anna Luiza B.; Justino, Licinia L. G.; Çatıkkaş, Berna; Lopes, Susy; ILDIZ, GÜLCE ÖĞRÜÇ; Fausto, Rui
    The molecular structure, conformational space and UV-induced rotamerization and decarbonylation of 2-aminoacetanilide (2AA) were investigated by matrix isolation infrared spectroscopy and quantum chemical electronic structure calculations. The compound was isolated in a cryogenic (15 K) argon matrix, and four conformers were spectroscopically identified: two trans-amide (O--C-N-H dihedral - 180 degrees) conformers (trans-I and trans-II), and two higher-energy cis-amide (O--C-N-H dihedral - 0 degrees) conformers (cis-I and cis-II). These four conformers were found to be present in the as-deposited matrix of 2AA in a population ratio matching well that predicted by the calculations for the gas-phase equilibrium at the temperature of the vapor of the compound before deposition (60 degrees C = 333.15 K). The calculations predicted also the existence of an additional higherenergy trans-amide conformer (trans-III) which was not observed experimentally. In situ broadband UV irradiation (lambda > 235 nm) of the matrix-isolated compound was found to induce selective conversion of conformer trans-I into conformer trans-II, in a few minutes (55 % after 2 min. of irradiation; 70 % after 10 min.), while the populations of the cis-amide conformers did not change. Prolonged UV irradiation was found to result in decomposition of the compound, leading to generation of carbon monoxide and 2-amine-N-methylaniline. The infrared spectra of the experimentally relevant conformers of 2AA were interpreted and assigned with help of normal coordinate analysis, and the different behavior of the conformers of 2AA upon UV-irradiation of the argon matrix was explained with help of time-dependent DFT (TD-DFT) calculations.
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    Structure, Vibrational Spectra, and Cryogenic MatrixPhotochemistry of 6-Bromopyridine-2-Carbaldehyde: From the Single Molecule of the Compound to the Neat Crystalline Material
    (MDPI, 2023) Brito, Anna Luiza B.; Lopes, Susy; ILDIZ, GÜLCE ÖĞRÜÇ; Fausto, Rui
    6-Bromopyridine-2-carbaldehyde (abbreviated as BPCA) is used both as a building block in supramolecular chemistry and as a ligand for transition metal catalysts and luminescent complexes. In this study, the structure and vibrational spectra of BPCA were investigated in both the room temperature neat crystalline phase and for the compound isolated in cryogenic Ar, Kr and Xe matrices. The experimental studies were complemented by quantum chemical DFT(B3LYP)/6-311++G(d,p) calculations. For the crystalline compound, infrared and Raman spectra were obtained and interpreted. Comparison of the obtained infrared spectrum of the crystal with those obtained for the isolated molecules of BPCA in the studied cryomatrices helped to conclude that the intermolecular interactions in the crystal do not significantly perturb the intramolecular vibrational potential. Structural analysis further supports the existence of weak coupling between the intermolecular interactions and the structure of the constituting molecular units in crystalline state. The intermolecular interactions in the BPCA crystal were also evaluated by means of Hirshfeld analysis, which revealed that the most important interactions are weak and of the (HN)-N- horizontal ellipsis , (HO)-O- horizontal ellipsis , (HH)-H- horizontal ellipsis , (HBr)-Br- horizontal ellipsis and (BrBr)-Br- horizontal ellipsis types. The conformer of BPCA present in the crystal was found to correspond to the most stable form of the isolated molecule (trans), which bears stabilizing C-(HO)-O- horizontal ellipsis =C and C(=O)(HN)-N- horizontal ellipsis interactions. This conformer was shown to be the single conformer present in the as-deposited cryogenic matrices prepared from the room temperature gaseous compound. Broadband UV irradiation of matrix-isolated BPCA (lambda >= 235 nm) resulted in the conversion of the trans conformer into the higher-energy cis conformer, where repulsive C-(HH)-H- horizontal ellipsis -C(=O) and C=(OLPLPN)-N- horizontal ellipsis (where LP designates a lone electron pair) interactions are present, and decarbonylation of the compound with formation of 2-bromopyridine (plus CO). The decarbonylation reaction was found to be more efficient in the more polarizable Xe matrix, indicating stabilization of the radicals initially formed upon breaking of the C-C(HO) and C-H (aldehyde) bonds in this medium, and testifying the occurrence of the decarbonylation reaction with involvement of radical species. TD-DFT calculations were used to access the nature of the excited states associated with the observed UV-induced reactions. As a whole, this study provides fundamental data to understand the physicochemical behavior of the compound, bridging the properties of the isolated molecule to those of the neat crystalline com-pound. Such information is of fundamental importance for the understanding of the role of BPCA in supramolecular chemistry and to potentiate its applications in synthesis and as a ligand for transition metal catalysts and luminescent complexes.