Browsing by Author "Nogueira, Bernardo A."

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5-Methylhydantoin: from isolated molecules in a low-temperature argon matrix to solid state polymorphs characterization
(Amer Chemical Soc, 1155 16th St, Nw, Washington, Dc 20036 USA, 2017-07-20) Nogueira, Bernardo A.; Canotilho, J.; Eusebio, M. E. S.; Henriques, M. S. C.; Paixao, J. A.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326
The molecular structure, vibrational spectra and photochemistry of 5-methylhydantoin (C4H6N2O2; 5-MH) were studied by matrix isolation infrared spectroscopy and theoretical calculations at the DFT(B3LYP)/6-311++G(d,p) theory level. The natural bond orbital (NBO) analysis approach was used to study in detail the electronic structure of the minimum energy structure of 5-MH, namely the specific characteristics of the sigma and pi electronic systems of the molecule and the stabilizing orbital interactions. UV irradiation of 5-MH isolated in argon matrix resulted in its photofragmentation through a single photochemical pathway, yielding isocyanic acid, ethanimine, and carbon monoxide, thus following a pattern already observed before for the parent hydantoin and 1-methylhydantoin molecules. The investigation of the thermal properties of 5-MH was undertaken by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM) and Raman spectroscopy. Four different polymorphs of 5-MH were identified. The crystal structure of one of the polymorphs, for which it was possible to grow up suitable crystals, was determined by X-ray diffraction (XRD). Two of the additional polymorphs were characterized by powder XRD, which confirmed the molecules pack in different crystallographic arrangements.
Open Access
Di-Alkyl Adipates as New Phase Change Material for Low Temperature Energy Storage
(Springer/Plenum Publishers, 2023) Sequeira, Maria C. M.; Nogueira, Bernardo A.; Caetano, Fernando J. P.; Diogo, Herminio P.; Fareleira, Joao M. N. A.; FAUSTO, RUI
This work is a contribution to the thermal characterization of a selected binary system of two di-n-alkyl adipates that can be used as phase change material for thermal energy storage at low temperatures. The construction of the solid-liquid phase diagram using differential scanning calorimetry (DSC), complemented with Raman Spectroscopy studies for the system composed by diethyl and dibutyl adipates is presented. The solidus and liquidus equilibrium temperatures were determined by DSC for the pure components and 30 binary mixtures at selected molar compositions were used to construct the corresponding solid-liquid phase diagram. The binary system of diethyl and dibutyl adipates presents eutectic behaviour at low temperatures. The eutectic temperature was found at 240.46 K, and the eutectic composition was determined to occur at the molar fraction xdibutyl = 0.46. Additionally, the system shows a polymorphic transition, characteristic of dibutyl adipate, occurring at ca. 238 K, confirmed by optical microscopy. To the best of our knowledge, no reference to the phase diagram of the present system could be found in the literature. Raman spectroscopy was essential to complement the construction of the phase equilibrium diagram, enabling the identification of the solid and liquid phases of the system. Finally, the liquidus curve of the phase diagram was also successfully predicted using a suitable fitting equation, being the root mean square deviation of the data from the correlation equal to 0.54 K. In addition, this fitting operation enabled a correct prediction of the eutectic composition of the system.
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Hydantoins and mercaptoimidazoles: Vibrational spectroscopy as a probe of structure and reactivity in different environments, from the isolated molecule to polymorphs
(2019) Fausto, Rui; Brás, E.M.; Nogueira, Bernardo A.; ILDIZ, GÜLCE ÖĞRÜÇ
In this chapter, we highlight the power of vibrational spectroscopy as central technique to investigate the structure and reactivity of two relevant families of nitrogen-containing heterocyclic molecules: hydantoins and mercaptoimidazoles. Infrared spectroscopy is used in connection with the matrix isolation technique to investigate the structures of the isolated molecules and their photochemistry, while both infrared and Raman spectroscopies, supplemented by thermodynamics, microscopy, and diffraction techniques, are used to investigate neat condensed phases of the compounds and transitions between these phases. The experimental studies are supported by extensive computational studies, which include several approaches for detailed analysis of the electron density.
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Molecular Structure, Infrared Spectra, Photochemistry, and Thermal Properties of 1-Methylhydantoin
(Amer Chemical Soc, 1155 16Th St, Nw, Washington, Dc 20036 Usa, 2014-08-07) Nogueira, Bernardo A.; Canotilho, Joao; Eusebio, M. Ermelinda S.; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326
The structural, vibrational, and photochemical study of 1-methylhydantoin (1-MM, C4H6N2O2) was undertaken by matrix isolation infrared spectroscopy (in argon matrix; 10 K), complemented by quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The theoretical calculations yielded the C-s symmetry structure, with planar heavy atom skeleton, as the minimum energy structure on the potential energy surface of the molecule. The electronic structure of this minimum energy structure of 1-MH was then studied in detail by means of the natural bond orbital (NBO) and atoms in molecules (AIM) approaches, allowing for the elucidation of specific characteristics of the molecule's sigma and pi electronic systems. The infrared spectrum of the matrix-isolated 1-MH was fully assigned, also with the help of the theoretically predicted spectrum of the compound, and its UV-induced unimolecular photochemistry (lambda >= 230 nm) was investigated. The compound was found to fragment to CO, isocyanic acid, methylenimine, and N-methyl-methylenimine. Finally, a thermal behavior investigation on 1-MM samples was carried out using infrared spectroscopy (10 K until melting), differential scanning calorimetry and polarized light thermal microscopy. A new polymorph of 1-MH was identified. The IR spectra of the different observed phases were recorded and interpreted.
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Polymorphism in 1-Methylhydantoin: Investigation by Periodic DFT Calculations and Characterization of the Third Polymorph
(Royal Society of Chemistry, 2020) Nogueira, Bernardo A.; Milani, Alberto; ILDIZ, GÜLCE ÖĞRÜÇ; Paixão, José A.; Castiglioni, Chiara; Fausto, Rui
In previous studies [Puszyńska-Tuszkanow et al. Polyhedron, 2011, 30(12), 2016; Nogueira et al. J. Phys. Chem. A, 2014, 118(31), 5994; Nogueira et al., J. Mol. Struct., 2017, 1148, 111], two different polymorphs of 1-methylhydantoin (1-MH, C4H6N2O2) were identified (forms I and II) and characterized using infrared and Raman spectroscopies, as well as by X-ray diffraction. In this work, a new polymorph of the compound (form III) is described. The new polymorph was characterized spectroscopically and its structure was determined for the first time by single crystal X-ray diffraction. Very interestingly, the crystal of polymorph III was found to exhibit a high-Z′ (Z′ = 3) asymmetric unit and 12 molecules in the unit cell (Z = 12), which contrasts with the simpler crystal structures found previously for forms I and II (Z = 4; Z′ = 1). Besides, a thorough study of the polymorphism of 1-MH was performed with the help of state-of-the-art first principles fully periodic calculations of the structure, as well as infrared and Raman spectra of the different polymorphs of the compound. Marker-bands in the infrared and Raman spectra of the polymorphs are proposed for fast spectroscopic identification of the polymorphs.
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Revisiting Structural, Vibrational, and Photochemical Data of Matrix-Isolated Simple Hydantoins — Common Features and Substituent Effects
(American Institute of Physics, 2024) FAUSTO, RUI; ILDIZ, GÜLCE ÖĞRÜÇ; Nogueira, Bernardo A.
Characteristic features of the structure (geometries, electronic structures), vibrational spectra (infrared), and photochemistry of a series of simple hydantoins (parent hydantoin, 1-methylhydantoin, 5-methylhydantoin, and 5-acetic acid hydantoin), and effects of substituent on these properties, are reviewed in a comparative comprehensive perspective taken as a basis the low-temperature matrix isolation infrared spectroscopy and electronic structure quantum chemistry data we have reported before for the individual compounds. It is shown that the hydantoin moiety shows a general tendency towards planarity (or quasi-planarity), mostly determined by the π-electron delocalization in the system, in which the two nitrogen atoms are extensively involved and, in the molecules studied, also counts with the involvement of the π-type orbitals of the -C5H2- or -C5HR- (with R ˭ CH3 or CH2COOH in 5-methylhydantoin and 5-acetic acid hydantoin, respectively) fragment (hyperconjugation). The geometries and charge density analyses of the compounds also show that the main electronic effects in the hydantoin ring are the N-to-(C ˭ O) π-electron donation, and the σ system back-donation from the σ-lone electron pairs of the oxygen atoms to the ring. The frequencies of the bands observed in the matrix-isolation infrared spectra (Ar; 10 K) of the different compounds that are assigned to the carbonyl and amine fragments are discussed comparatively, and substituent effects are assessed. Finally, the UV-induced (λ = 320 nm) photochemistry of the hydantoins is shown to share a common pattern, leading to the concerted extrusion of isocyanic acid and carbon monoxide, accompanied by an imine derivative that depends upon the specific hydantoin reactant. An additional photofragmentation pathway, most probably involving nitrene intermediacy, also takes place for 1-methylhydantoin, indicating a specific effect of the substitution at position 1 of the hydantoin ring on the photofragmentation of hydantoins. © 2024 Author(s).
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The ROY Family's Growing Palette: Insights Into Recent Compound Additions and Color Range Expansion - A Short Review
(Elsevier, 2024) Nogueira, Bernardo A.; FAUSTO, RUI
The ROY (systematic name: 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophene-carbonitrile) molecule family stands as the most renowned group of color polymorphic organic compounds. This article offers a concise overview of the main structural characteristics of the 13 known polymorphs of ROY, systematizing their diverse colors in a context where recent data (2022-2024) obtained for novel members of the family are also taken into account, in particular information extracted from our own studies on AcROY, ROY-ol and ROY-CAM. The new findings have extended the spectrum of ROY-based polymorphs' colors to include burgundy and, notably, green tones.
Open Access
Solid-Liquid Phase Equilibrium: Alkane Systems for Low-Temperature Energy Storage
(Springer/Plenum Publishers, 2024) Sequeira, Maria C. M.; Nogueira, Bernardo A.; Caetano, Fernando J. P.; Diogo, Herminio P.; Fareleira, Joao M. N. A.; FAUSTO, RUI
The thermal characterization of two binary systems of n-alkanes that can be used as Phase Change Materials (PCMs) for thermal energy storage at low temperatures is reported in this work. The construction of the solid-liquid binary phase diagrams was achieved using differential scanning calorimetry (DSC) and Raman spectroscopy. The solidus and liquidus equilibrium temperatures were determined using DSC for thirty-nine different samples, three for the pure n-alkanes and the remaining for binary mixtures at selected molar compositions and used to acquire the corresponding solid-liquid phase diagrams. The two binary systems of n-octane/n-decane (C8/C10) and n-decane/n-dodecane (C10/C12) are characterized by a eutectic behavior at low temperatures. The eutectic temperature for the system C8/C10 was found at 211.95 K and the eutectic composition appeared at the molar fraction xoctane = 0.87. For the system C10/C12, the eutectic temperature was found at 237.85 K, and the eutectic composition appeared for the molar fraction xdecane = 0.78. This work aims to fulfill the lack of available data in the existing literature, considering the potential application of these systems for low-temperature thermal energy storage. Raman spectroscopy was used to complement the DSC data for the construction of the solid-liquid phase equilibrium diagrams, enabling the identification of the solid and liquid phases of the system. Additionally, the liquidus curve of the phase diagram was successfully described using a modified freezing point depression curve as fitting equation, the absolute root mean square deviation for the data correlation of the C8/C10 and C10/C12 systems being 2.56 K and 1.22 K, respectively. Ultimately, the fitting procedure also enabled a good prediction of the eutectic point for both studied systems.
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Structural and spectroscopic characterization of the second polymorph of 1-methylhydantoin
(Elsevier Science Bv, Po Box 211, 1000 AE Amsterdam, Netherlands, 2017-11-15) Nogueira, Bernardo A.; Henriques, Marta S. C.; Paixao, Jose Antonio; Fausto, Rui; ILDIZ, GÜLCE ÖĞRÜÇ; 107326
In a previous study [Nogueira, B.A.; Ildiz, G.O.; Canotilho, J.; Eusebio, M. E. S.; Fausto, R. J. Phys. Chem. A, 2014, 118, 5994-6008], two different polymorphs of 1-methylhydantoin (1-MH, C4H6N2O2) were identified using infrared spectroscopy, differential scanning calorimetry and polarized-light thermal microscopy. Unfortunately, at that time it was not possible to structurally characterize in detail the second polymorph (polymorph II) of the compound, due to lack of suitable crystals for X-ray diffraction structure determination. In this article, a throughout investigation of the polymorphism of 1-MH is presented. Screening for polymorphs was performed by recrystallization from different solvents, and the structure of polymorph II was determined for the first time by single crystal X-ray diffraction. The spectroscopic characterization of this polymorph was also undertaken, by Raman spectroscopy, which was also used to follow the phase transition between the two polymorphs (the well-known polymorph I, and the newly described polymorph II), showing that even though their structures are significantly distinct, the transition is a non-destructive one. (C) 2017 Elsevier B.V. All rights reserved.
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Unveiling the Red and Brownish-Green Polymorphs of a Novel ROY Derivative: 2-(4-((3-Cyanothiophen-2-yl)amino)-3-nitrophenyl)Acetic Acid
(American Chemical Society, 2024) Nogueira, Bernardo A.; Lopes, Susana M. M.; Rodrigues, Ana Clara B.; Eusebio, M. Ermelinda S.; Andre, Vania; Duarte, Teresa; Paixao, J. A.; Melo, Teresa M. V. D. Pinho e; FAUSTO, RUI
Polymorphism has been the subject of many studies in the last decades, including a particular type of polymorphism where the colors exhibited by the polymorphs differ. However, only relatively limited or narrow differences in color were observed in color polymorphs of the same compound. Indeed, to this date, almost all compounds known to show color polymorphism exhibit red, orange, or yellow tones, as is the case of the notable ROY molecule (5-methyl-2-[(2-nitrophenyl)-amino]-3-thiophenecarbonitrile), which is the compound with more polymorphs reported and structurally characterized hitherto. In this work, we report a new color polymorphic material derived from ROY, (2-(4-((3-cyanothiophen-2-yl)-amino)-3-nitrophenyl)-acetic acid; or ROY-CAM), synthesized for the first time by nucleophilic aromatic substitution reaction between 2-(4-fluoro-3-nitrophenyl)-acetic acid and 2-aminothiophene-3-carbonitrile, which exhibits a red (P21/n, m.p.: 184 C-degrees and theta = -4.4(degrees) and 3.0(degrees)) and a brownish-green polymorph (P1, m.p.: 190 C-degrees and theta = -66.1(degrees)). This is the first time a member of the ROY family of compounds was observed to exhibit a brownish-green polymorph and, more importantly, the first time that a molecular compound exhibits a red and a greenish polymorphs, i.e., this is the first example of an organic molecule that originates polymorphs covering such a wide range of color. The isolated molecule of ROY-CAM has 11 low-energy conformers, which were accessed by DFT calculations, with two of these conformers being identified in the observed polymorphs of the compound: in the brownish-green polymorph, the most stable conformer exists, while the red polymorph is composed of molecules assuming a conformation similar to that of the third most stable conformer. In the latter polymorph, the intramolecularly disfavored conformation assumed by the molecules is stabilized in the crystal lattice through interactions between carboxylic acid groups of neighboring molecules, resulting in dimeric units formed between pairs of the two distinct molecules that constitute the asymmetric unit of the crystal. The two identified polymorphs were characterized vibrationally (by both IR and Raman spectroscopies), and a thermal study is also presented (based on DSC, PLTM, and TGA measurements). Furthermore, the brownish-green and red colors exhibited by the polymorphs of ROY-CAM are explained based on the differences in the structures of the molecules that are present in these crystals.