Browsing by Author "Justino, Licinia L. G."

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Open Access
Indigo Carmine Binding to Cu(II) in Aqueous Solution and Solid State: Full Structural Characterization Using NMR, FTIR and UV/Vis Spectroscopies and DFT Calculations
(MDPI, 2024) Braz, Sofia; Justino, Licinia L. G.; Ramos, M. Luisa; FAUSTO, RUI
The food industry uses indigo carmine (IC) extensively as a blue colorant to make processed food for young children and the general population more attractive. Given that IC can act as a ligand, this raises concerns about its interactions with essential metal ions in the human body. In view of this interest, in the present investigation, the copper(II)/indigo carmine system was thoroughly investigated in aqueous solution and in the solid state, and the detailed structural characterization of the complexes formed between copper(II) and the ligand was performed using spectroscopic methods, complemented with DFT and TD-DFT calculations. NMR and UV/Vis absorption spectroscopy studies of the ligand in the presence of copper(II) show changes that clearly reveal strong complexation. The results point to the formation of complexes of 1:1, 1:2 and 2:1 Cu(II)/IC stoichiometry in aqueous solution, favored in the pH range 6-10 and stable over time. DFT calculations indicate that the coordination of the ligand to the metal occurs through the adjacent carbonyl and amine groups and that the 1:1 and the 2:1 complexes have distorted tetrahedral metal centers, while the 1:2 structure is five-coordinate with a square pyramidal geometry. FTIR results, together with EDS data and DFT calculations, established that the complex obtained in the solid state likely consists of a polymeric arrangement involving repetition of the 1:2 complex unit. These results are relevant in the context of the study of the toxicity of IC and provide crucial data for future studies of its physiological effects. Although the general population does not normally exceed the maximum recommended daily intake, young children are highly exposed to products containing IC and can easily exceed the recommended dose. It is, therefore, extremely important to understand the interactions between the dye and the various metal ions present in the human body, copper(II) being one of the most relevant due to its essential nature and, as shown in this article, the high stability of the complexes it forms with IC at physiological pH.
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Molecular Structure, Spectroscopy and Photochemistry of Alprazolam
(Elsevier, 2022) ILDIZ, GÜLCE ÖĞRÜÇ; Tabanez, Andreia M.; Nunes, Antonio; Roque, Jose P. L.; Justino, Licinia L. G.; Ramos, M. Luisa; Fausto, Rui
In this article, a comprehensive study of the molecular structure, spectroscopy, and photochemistry of alprazolam (Xanax (R); 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine) is reported. The structure of the isolated molecule of the compound was investigated using density functional theory (DFT), revealing that the molecule exists in a single conformer, which is associated with 12 equivalent-by symmetry minima. The molecules of the compound were trapped from the gas phase into a low temperature (10 K) argon matrix, and the infrared (IR) spectrum of the matrix-isolated monomers was obtained and assigned. The matrix-isolated molecules were then subjected to in situ ultraviolet (UV) irradiation . It was concluded that alprazolam is photostable under these experimental conditions, contrarily to what is known to happen for the compound in solution or in solid state in the presence of excipients used in the pharmaceutical formulations. An explanation for the photostability of the matrix-isolated compound is provided, based on rapid recombinations of the biradical formed from the UV-induced diazepine ring cleavage or the chlorine atom and the complementary radical resulting from the scissoring of the C-Cl bond, which are favored by the cage confinement of the matrix-isolated molecules. The major fragmentation channels of the alprazolam molecule upon electron bombardment (70 eV) were determined by analysis of its electron ionization mass spectrum, which reveals that the major primary fragmentation processes lead to formation of cyanobenzene, N-2 , HCl (Cl-2), and benzene. The compound was also investigated in solution by multinuclear (H-1, C-13 and N-15) nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopies, and in crystalline phase (P-1 polymorph) through IR and Raman spectroscopies. In addition, the structure of the crystal, previously reported in the literature [M. R. Caira, B. Easter, S. Honiball, A. Horne and L. R. Nassimbeni, Structure and Thermal Stability of Alprazolam and Selected Solvates, J. Pharm. Sci., 1995 , 84 , 1379-1384], was revisited in order to evaluate the relative importance of the different types of intermolecular interactions , using Hirshfeld surface analysis, the CE-B3LYP energy decomposition model, and the harmonic oscillator model of aromaticity (HOMA) index. Finally, the enthalpy of sublimation of the crystal was estimated from the CE-B3LYP calculated lattice energy.
Open Access
Nanoscale Study of the Polar and Electronic Properties of a Molecular Erbium(III) Complex Observed via Scanning Probe Microscopy
(MDPI, 2023) Ivanov, Maxim; Grempka, Arkadiusz; Buryakov, Arseniy; Nikitin, Timur; Justino, Licinia L. G.; FAUSTO, RUI; Vilarinho, Paula M.; Paixao, Jose A.
We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)(3)(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale levels. The single crystal X-ray diffraction method demonstrates the monoclinic (noncentrosymmetric space group P2(1)) crystallographic structure of the synthesized samples and scanning electron microscopy exhibits the terrace-ledge morphology of the surface in erbium(III) crystals. By using the piezoelectric force microscopy mode, the origin of the polar properties and the hyperpolarizability in the synthesized samples were assigned to the internal domain structure framed by the characteristic terrace-ledge topography. The direct piezoelectric coefficient (similar to d33) was found to be intensely dependent on the local area and was measured in the range of 4-8 pm/V. A nanoscale study using the kelvin probe force and capacitance force (dC/dz) microscopy modes exposed the effect of the Er ions clustering in the erbium(III) complex. The PFM method applied solely to the Er ion revealed the corresponding direct piezoelectric coefficient (similar to d33) of about 4 pm/V. Given the maximum piezoelectric coefficient in the erbium(III) complex at 8 pm/V, we highlight the significant importance of the spatial coordination between the lanthanide ion and the ligands. The polar coordination between the lanthanide ion and the nitrogen and oxygen atoms was also corroborated by Raman spectroscopy supported by the density functional theory calculations. The obtained results can be of paramount importance for the application of molecular erbium(III) complex crystals in low-magnitude magnetic or electric field devices, which would reduce the energy consumption and speed up the processing switching in nonvolatile memory devices.
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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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Synthesis, Characterization and Sensing Mechanism of a Novel Fluorescence Probe for Fe(III) in Semi-Aqueous Solution Based on a Schiff Base Hexadentate Receptor
(Elsevier Science SA, 2023) Ooshall, Farkhondeh; Jamehbozorgi, Saeed; Golbedaghi, Reza; Justino, Licinia L. G.; Feshalame, Keyvan Mirzaei; Liyaghati-Delshad, Mozhdeh; Anaraki-Ardakani, Hossein; Jaleh, Babak; FAUSTO, RUI
A new acyclic Schiff base chemosensor L was synthesized by the one pot condensation reaction of 2-[3-(formyl phenoxy)2-hydroxypropoxy]benzaldehyde and 2-aminophenol in a 1:2 molar ratio and was characterized by elemental analysis, FTIR, 1H- and 13C NMR, and fluorescence spectroscopies. These studies were complemented with a thorough conformational study at the molecular mechanics and density functional theory (DFT) levels of theory to further elucidate the structure of the compound in solution. The chemosensor L displays high sensitivity and selectivity for Fe3+ in semi-aqueous (H2O-DMF, 1:1) solution, except in the presence of a significant amount of Ni2+, with the presence of Fe3+ being signaled through the total fluorescence quenching of the fluorophore when Fe3+ binds to the recognition unit. The synthesized ligand also shows high selectivity for Fe3+ compared to the metal ions Cu2+, Zn2+, Mg2+, Mn2+, Pb2+, Hg2+, Na+, Ba2+ and Cd2+, and reasonable selectivity in the presence of Ag+, Co2+ and Cr3+. The stoichiometry and structure of the complex formed between Fe3+ and the probe L were determined from a Job's plot and DFT calculations, respectively. The complex was characterized as a high-spin 1:1 octahedral species, in which the ligand coordinates to the metal through the two ether oxygen atoms, two nitrogen atoms and two terminal hydroxyl groups. Time dependent (TD-DFT) calculations were performed to provide information on the type of mechanism causing the quenching of the fluorescence in the presence of Fe3+.