Ana Rosa Galego Garcia
@ualg.pt
universidade do algarve
RESEARCH, TEACHING, or OTHER INTERESTS
Chemistry, Materials Chemistry
Scopus Publications
Scopus Publications
Suzana M. Andrade, Vanda Vaz Serra, Carlos J. Bueno-Alejo, Ana Rosa Garcia, M. Fernanda N.N. Carvalho, Laura M. Ilharco, Maria Graça P.M.S. Neves, and Sílvia M.B. Costa
Elsevier BV
Antonino Scurria, Marzia Sciortino, Ana Rosa Garcia, Mario Pagliaro, Giuseppe Avellone, Alexandra Fidalgo, Lorenzo Albanese, Francesco Meneguzzo, Rosaria Ciriminna, and Laura M. Ilharco
MDPI AG
DRIFT, HPLC-MS, and SPME-GC/MS analyses were used to unveil the structure and the main functional compounds of red (blood) orange (Citrus sinensis) and bitter orange (Citrus aurantium). The IntegroPectin samples show evidence that these new citrus pectins are comprised of pectin rich in RG-I hairy regions functionalized with citrus biophenols, chiefly flavonoids and volatile molecules, mostly terpenes. Remarkably, IntegroPectin from the peel of fresh bitter oranges is the first high methoxyl citrus pectin extracted via hydrodynamic cavitation, whereas the red orange IntegroPectin is a low methoxyl pectin. C. aurantium IntegroPectin has a uniquely high concentration of adsorbed flavonoids, especially the flavanone glycosides hesperidin, naringin, and eriocitrin.
João L. Parracha, Giovanni Borsoi, Rosário Veiga, Inês Flores-Colen, Lina Nunes, Ana R. Garcia, Laura M. Ilharco, Amélia Dionísio, and Paulina Faria
Elsevier BV
A. S. Figueiredo, A. R. García, M. Minhalma, L. Ilharco and M. D. Pinho
Integral asymmetric cellulose acetate (CA) membranes were casted by phase-inversion with formamide varying content - 22, 30 and 34% - as pore promoter. These membranes, CA-22, CA-30 and CA-34, were analyzed by infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) to investigate the porous membrane matrix influence on the polymer/water/solute interactions and the selective ultrafiltration of salts. The membranes covered a wide range of hydraulic permeabilities, from 3.5 to 81.0 kg.m-2.h-1.bar-1, and of molecular weight cut-offs, from 4.17 to 31.43 kDa. The experimental apparent rejection coefficients of neutral solutes of increasing molecular weight are related to their intrinsic rejection coefficients through the film model. The surface average pore radius, estimated by an iterative algorithm, ranges from 2.1 to 4.5 nm. The tighter membrane, CA-22, displays experimental apparent rejection coefficients to the Na2SO4, CaSO4, MgSO4 of 50% or higher values and this is in contrast with the lower values, between 14 and 18%, to the NaCl, CaCl2 and MgCl2 salts. The ATR-FTIR evidences that in the membranes with larger pores, CA-30 and CA-34, the water molecules are organized with a liquid-water-like structure, in which most molecules are hydrogen bonded to four or to two others; nevertheless, a fraction of water molecules is strongly bonded to the CA carbonyl groups. For the CA-22 membrane, there are more free carbonyl groups and a larger fraction of free water, both able to interact with solutes, such as the hydrated sulphate ions. Therefore, this ultrafiltration membrane has the capability of differentiating anionic species.
Ana R. Garcia, Maria de Fátima Júlio, and Laura M. Ilharco
American Chemical Society (ACS)
Environmentally friendly nanocomposites were synthesized from a silica precursor and cork under mild conditions and dried at atmospheric pressure. Because of the covalent bonding between the components, these CorSil nanocomposites are homogeneous, light (apparent density in the range 360-750 kg m-3), machinable, with the Shore D hardness up to 67 and compressive strength up to 22.6 MPa. These properties place them as good replacements for wood, other natural products, and thermoplastic polymers, with the advantage of being flame-retardant. The influence of the cork content and grain size on the structure, porosity, and mechanical properties of the nanocomposites was studied using infrared spectroscopy, sorption isotherms, compressive strength, and Shore D hardness measurements.
Frederico Fonseca, Ricardo Brito de Barros, Laura M. Ilharco, and Ana R. Garcia
SAGE Publications
This work aimed at analyzing the performance of direct spectroscopic methods for the quantification of gabapentin (GABAp), given the lack of previous studies, in comparison with the more reviewed and complex derivatization techniques, discussing their susceptibility to the pharmaceutical formulations. All of the methods analyzed showed high selectivity for this pharmaceutical analyte, with recoveries close to 100%. Absorption spectroscopy without derivatization yielded better sensitivity and lower limits of detection and quantification of gabapentin in aqueous solution (AqSol method) when compared with other solvents, such as acidic solution or ethanol/water mixture. Derivatization with sodium hypochlorite presented the highest precision, whereas derivatization with vanillin exhibited the highest accuracy. The best method for GABAp quantification in terms of highest sensitivity, lowest limits of detection, and quantification, and also with good precision and accuracy, proved to be fluorescence with derivatization by 4-chloro-7-nitrobenzofurazan. The effect of the pharmaceutical formulation (nature of excipients) was tested for the most robust and sensitive methods, with and without derivatization, on capsules of five commercial brands. Recoveries in the range of 97.9–101.5% proved that there are no matrix interfering effects. Although not presenting the best performance in all the parameters evaluated, the AqSol method, due to its simplicity, proved to be suitable for the quantification of GABAp in capsules and tables containing the molecule as the active ingredient.
Pedro Morgado, Ana Rosa Garcia, Luís F. G. Martins, Laura M. Ilharco, and Eduardo J. M. Filipe
American Chemical Society (ACS)
In this work, we demonstrate that n-alkanes coil when mixed with perfluoroalkanes, changing their conformational equilibria to more globular states, with a higher number of gauche conformations. The new coiling effect is here observed in fluids governed exclusively by dispersion interactions, contrary to other examples in which hydrogen bonding and polarity play important roles. FTIR spectra of liquid mixtures of n-hexane and perfluorohexane unambiguously reveal that the population of n-hexane molecules in all-trans conformation reduces from 32% in the pure n-alkane to practically zero. The spectra of perfluorohexane remain unchanged, suggesting nanosegregation of the hydrogenated and fluorinated chains. Molecular dynamics simulations support this analysis. The new solvophobic effect is prone to have a major impact on the structure, organization, and therefore thermodynamic properties and phase equilibria of fluids involving mixed hydrogenated and fluorinated chains.
A. R. Garcia, M. F. Júlio, and L. M. Ilharco
Springer Science and Business Media LLC
Francisca Ribeiro, Ana R. Garcia, Beatriz P. Pereira, Maria Fonseca, Nélia C. Mestre, Tainá G. Fonseca, Laura M. Ilharco, and Maria João Bebianno
Elsevier BV
Pedro Morgado, Ana Rosa Garcia, Laura M. Ilharco, João Marcos, Martim Anastácio, Luís F. G. Martins, and Eduardo J. M. Filipe
American Chemical Society (ACS)
This article reports a combined thermodynamic, spectroscopic, and computational study on the interactions and structure of binary mixtures of hydrogenated and fluorinated substances that simultaneously interact through strong hydrogen bonding. Four binary mixtures of hydrogenated and fluorinated alcohols have been studied, namely, (ethanol + 2,2,2-trifluoroethanol (TFE)), (ethanol + 2,2,3,3,4,4,4-heptafluoro-1-butanol), (1-butanol (BuOH) + TFE), and (BuOH + 2,2,3,3,4,4,4-heptafluoro-1-butanol). Excess molar volumes and vibrational spectra of all four binary mixtures have been measured as a function of composition at 298 K, and molecular dynamics simulations have been performed. The systems display a complex behavior when compared with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes. The combined analysis of the results from different approaches indicates that this results from a balance between preferential hydrogen bonding between the hydrogenated and fluorinated alcohols and the unfavorable dispersion forces between the hydrogenated and fluorinated chains. As the chain length increases, the contribution of dispersion increases and overcomes the contribution of H-bonds. In terms of the liquid structure, the simulations suggest the possibility of segregation between the hydrogenated and fluorinated segments, a hypothesis corroborated by the spectroscopic results. Furthermore, a quantitative analysis of the infrared spectra reveals that the presence of fluorinated groups induces conformational changes in the hydrogenated chains from the usually preferred all-trans to more globular arrangements involving gauche conformations. Conformational rearrangements at the CCOH dihedral angle upon mixing are also disclosed by the spectra.
Ana R. Garcia, Luís F. Lopes, Ricardo Brito de Barros, and Laura M. Ilharco
American Chemical Society (ACS)
Attenuated total reflection infrared spectroscopy (ATR-IR) proved to be a promising detection technique for 2,4,6-trichloroanisole (TCA), which confers organoleptic defects to bottled alcoholic beverages, allowing the proposal of a criterion for cork plank acceptance when meant for stopper production. By analysis of a significant number of samples, it was proved that the presence of TCA, even in very low concentrations, imparts subtle changes to the cork spectra, namely, the growth of two new bands at ∼1417 (νC═C of TCA ring) and 1314 cm–1 (a shifted νCC of TCA) and an increase in the relative intensities of the bands at ∼1039 cm–1 (δCO of polysaccharides) and ∼813 cm–1 (τCH of suberin), the latter by overlapping with intense bands of TCA. These relative intensities were evaluated in comparison to a fingerprint of suberin (νasC–O–C), at 1161 cm–1. On the basis of those spectral variables, a multivariate statistics linear analysis (LDA) was performed to obtain a discriminant function that allows classifying the samples according to whether they contain or not TCA. The methodology proposed consists of a demanding acceptance criterion for cork planks destined for stopper production (with the guarantee of nonexistence of TCA) that results from combining the quantitative results with the absence of the two TCA correlated bands. ATR infrared spectroscopy is a nondestructive and easy to apply technique, both on cork planks and on stoppers, and has proven more restrictive than other techniques used in the cork industry that analyze the cleaning solutions. At the level of proof of concept, the method here proposed is appealing for high-value stopper applications.
Ana R. Garcia, Adelino M. Galvão, and Laura M. Ilharco
American Chemical Society (ACS)
Zoran P. Visak, Laura M. Ilharco, Ana Rosa Garcia, Vesna Najdanovic-Visak, João M. N. A. Fareleira, Fernando J. P. Caetano, Mirjana L. Kijevcanin, and Slobodan P. Serbanovic
American Chemical Society (ACS)
Densities and molar excess volumes of the solutions of pyridine or nicotine in liquid polyethylene glycol, PEG200 and PEG400, have been determined at several temperatures. The experimental molar excess volumes are negative, thus indicating strong attractive interactions between the components, as could be expected considering their highly polar nature and good hydrogen bond abilities. For the pyridine systems, this negativity is slightly increased as the temperature rises, while the opposite tendency is observed for the nicotine mixtures. When pyridine and nicotine solutions are compared, the former-particularly those with PEG400-exhibit substantially more negative molar excess volumes than the latter. The effect of the polymer chain length on the results for the nicotine solutions is almost negligible. However, this is not the case when pyridine is one of the components: a longer chain induced considerably higher compression on mixing. The Fourier-transform infrared analysis allowed interpretation of the negative experimental molar excess volumes in terms of specific inter- and intramolecular interactions.
Ana C.T. Teixeira, Ana R. Garcia, Laura M. Ilharco, Amélia M.P.S. Gonçalves da Silva, and Anabela C. Fernandes
Elsevier BV
Luís M. F. Lopes, Ana R. Garcia, Pedro Brogueira, and Laura M. Ilharco
American Chemical Society (ACS)
The interactions between DNA purines (guanine and adenine) and three ruthenium ammine complexes (hexaammineruthenium(III) chloride, hexaammineruthenium(II) chloride, and ruthenium-red) were studied in a confined environment, within sol-gel silica matrixes. Two encapsulation methods were rehearsed (differing in temperature and condensation pH), in order to analyze the effects of the sol-gel processes on the purines and on the Ru complexes separately. The extent of decomposition of the Ru complexes, as well as the interactions established with the purine bases, proved to be determined by the coencapsulation method. Combined results by diffuse reflectance UV-vis and infrared spectroscopies showed that, when coencapsulation is carried out at 60 degrees C, specific H bonding interactions are established between the amine group of Ade and the ammine groups of the Ru complex or the hydroxo group of an early decomposition product. These are responsible for the important role of the purine in inhibiting the oxidation reactions of the Ru(II) and Ru(III) complexes. In contrast, Gua establishes preferential H bonds with the matrix (mainly due to the carbonyl group), leading to higher yields in the final oxidation products of the Ru complexes, namely, trimers and dimers. Direct covalent bonding of either purine to the metal was not observed.
Luís M. F. Lopes, Ana R. Garcia, Alexandra Fidalgo, and Laura M. Ilharco
American Chemical Society (ACS)
The interactions between DNA purines (guanine and adenine) and the ruthenium complex Ru(NO)(NO(3))(3) were studied within nanostructured silica matrices prepared by a two-step sol-gel process. By infrared analysis in diffuse reflectance mode, it was proved that encapsulation induces a profound modification on the complex, whereas guanine and adenine preserve their structural integrity. The complex undergoes nitrate ligand exchange and co-condenses with the silica oligomers, but the nitrosyl groups remain stable, which is an unusual behavior in Ru nitrosyl complexes. In turn, the doping molecules affect the sol-gel reactions and eventually the silica structure as it forms: the complex yields a microporous structure, and the purine bases are responsible for the creation of macropores due to hydrogen bonding with the silanol groups of the matrix. In a confined environment, the interactions are much stronger for the coencapsulated pair guanine complex. While adenine only establishes hydrogen bonds or van der Waals interactions with the complex, guanine bonds covalently to Ru by one N atom of the imidazole ring, which becomes strongly perturbed, resulting in a deformation of the complex geometry.
Ana C.T. Teixeira, Ana R. Garcia, Laura M. Ilharco, Amélia M.P.S. Gonçalves da Silva, and Anabela C. Fernandes
Elsevier BV
Ana R. Garcia, Ricardo B. Barros, and Laura M. Ilharco
Elsevier BV
Ana R. Garcia, Ricardo Brito de Barros, João P Lourenço, and Laura M. Ilharco
American Chemical Society (ACS)
The influence of the pH on the infrared spectrum of L-alanine has been analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The amino acid was precipitated from aqueous solutions and dried at 36.5 degrees C, in order to stabilize cationic L-alanine or alaninium [CH3CH(NH3(+))COOH] at pH 1, the zwitterionic form [CH3CH(NH3(+))COO(-)] at pH 6, and anionic L-alanine or alaninate [CH3CH(NH2)COO(-)] at pH 13. New insight on the specific inter and intramolecular interactions in the different forms of L-alanine was reached by a novel methodological approach: an infrared technique not used before to analyze solid amino acid samples (DRIFTS), in combination with a detailed analysis based on spectral deconvolution. The frequency ranges of interest include the carbonyl/carboxyl stretching and amine deformation modes and the OH/NH stretching modes. It was shown that intermolecular hydrogen bonds between the NH3(+) and COO(-) groups are predominant in the zwitterionic form, whereas in cationic L-alanine, H bonds between the COOH groups are responsible for the formation of dimers. In anionic L-alanine, only strong electrostatic interactions between the COO(-) groups and Na(+) ions are proposed, evidencing the relevant role of the counterion.
Ana R. Garcia, Ricardo B. Barros, and Laura M. Ilharco
Wiley
AbstractThe decomposition patterns of hexene and hexyne isomers on clean Ru(001), under ultra‐high vacuum, are overviewed and correlated with functionality and isomerism. The key surface intermediates and products were identified by reflection absorption infrared spectroscopy (RAIRS). The results evidence the relevant role of the unsaturation position over its nature. The effects of steric hindrance and geometrical isomerism are apparent only in the inhibition of some decomposition pathways. The RAIRS data show that 1‐hexene chemisorbs at low temperature (∼90 K) and coverage as a di‐σ complex, whereas 1‐hexyne forms a di‐σ/π complex. By thermal activation, both these species dehydrogenate (in C1), yielding hexylidyne [µ3‐η1‐C(CH2)4CH3], which further decomposes (at 280–290 K) into surface metallocycles, [Ru3C(CH2)4CH2‐Ru] and [Ru3C(CH2)4CRu3]. Eventually, at 300 K, complete CC bond breaking occurs, yielding just adsorbed methylidyne [µ3‐η1‐CH]. The hexene and hexyne isomers with the unsaturation between secondary carbons may follow two surface‐assisted decomposition mechanisms. At low temperatures, they adsorb as the corresponding alkyne di‐σ/π complex, which implies a rehybridization of the sp2 (or sp) carbons with reduction of the bond order, plus, for alkenes, dehydrogenation at the same carbons. These complexes decompose by breaking the CC bonds adjacent to the surface anchors: C1C2 and C3C4 in the case of the 2‐isomer, yielding methylidyne, ethyne di‐σ/π complex [µ3‐η2‐CHCH] and propylidyne [µ3‐η1‐CCH2CH3], and C2C3 and C4C5 in the 3‐isomer, with the formation of the ethyne di‐σ/π complex and ethylidyne [µ3‐η1‐CCH3]. The second decomposition path occurs upon direct adsorption at the reaction temperatures. It involves the scission of the multiple bond, with the formation of shorter chain alkylidynes: propylidyne (for 3‐hexyne and Z‐3‐hexene), ethylidyne and butylidyne [µ3‐η1‐C(CH2)2CH3] (for 2‐hexyne). The reactivity of Z‐2‐hexene revealed to be different, since no evidence was found for the second decomposition path. This was ascribed to a reduced accessibility of the double bond to the surface, due to a steric hindrance effect of the alkyl chain. The influence of geometrical isomerism was particularly clear in the decomposition of E‐3‐hexene, which has a remarkable stability. Copyright © 2008 John Wiley & Sons, Ltd.
Ana R. Garcia, Ricardo Brito de Barros, Alexandra Fidalgo, and Laura M. Ilharco
American Chemical Society (ACS)
The interactions of L-alanine with gamma- and alpha-alumina have been investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). L-alanine/alumina samples were dried from aqueous suspensions, at 36.5 degrees C, with two amino acid concentrations (0.4 and 0.8 mmol g-1) and at different pH values (1, 6, and 13). The vibrational spectra proved that the nature of L-alanine interactions with both aluminas is the same (hydrogen bonding), although the groups involved depend on the L-alanine form and on alumina surface groups, both controlled by the pH. For samples prepared at pH 1, cationic L-alanine [CH3CH(NH3+)COOH] displaces physisorbed water from alumina, and strong hydrogen bonds are established between the carbonyl groups of alanine, as electron donors, and the surface Al-OH2+ groups of alumina. This occurs at the expense of alanine dimer dissociation and breaking of intramolecular bonds. When samples are prepared at pH 6, the interacting groups are Al-OH2+ and the carboxylate groups of zwitterionic L-alanine [CH3CH(NH3+)COO-]. The affinity of L-alanine toward alumina decreases, as the strong NH3+...-OOC intermolecular hydrogen bonds prevail over the interactions with alumina. Thus, for a load of 0.8 mmol g-1, phase segregation is observed. On alpha-alumina, crystal deposition is even observed for a load of 0.4 mmol g-1. At pH 13, the carboxylate groups of anionic L-alanine [CH3CH(NH2)COO-] are not affected by alumina. Instead, hydrogen bond interactions occur between NH2 and the Al-OH surface groups of the substrate. Complementary N2 adsorption-desorption isotherms showed that adsorption of L-alanine occurs onto the alumina pore network for samples prepared at pH 1 and 13, whereas at pH 6 the amino acid/alumina interactions are not strong enough to promote adsorption. The mesoporous structure and the high specific surface area of gamma-alumina make it a more efficient substrate for adsorption of L-alanine. For each alumina, however, it is the nature of the specific interactions and not the porosity of the substrate that determines the adsorption process.
Ana C.T. Teixeira, Anabela C. Fernandes, Ana R. Garcia, Laura M. Ilharco, Pedro Brogueira, and Amélia M.P.S. Gonçalves da Silva
Elsevier BV
Ricardo B. Barros, Ana Rosa Garcia, and Laura M. Ilharco
Elsevier BV
Ricardo B. Barros, Ana Rosa Garcia, and Laura M. Ilharco
Elsevier BV
Ricardo B. Barros, Ana Rosa Garcia, and Laura M. Ilharco
Wiley
AbstractThe influence of oxygen precoverage on the bonding geometry of methoxide on Ru(001) was studied using the isotopically labeled molecule CHD2OH by reflection–absorption infrared spectroscopy (RAIRS). This molecule is an excellent model because the vibrational spectra of CHD2O− may be unambiguously correlated with the adsorption configuration. For Ru(001)O layers with an effective oxygen coverage (θ0) between 0.25 and 0.6 ML (ML=monolayer), the influence of the oxygen precoverage was shown to vary with the initial methanol exposure. For an extremely low dose of [D2]methanol (0.01 L; L=Langmuir, 1 L=10−6 torr s), at 90 K, no oxygen‐coverage effects were detected on the geometry of [D2]methoxide: it adsorbs in an upright orientation (pseudo‐C3v local symmetry), just as on clean Ru(001). An increase in the methanol exposure to 0.1 L, at the same temperature, results in the formation of a disordered layer of tilted methoxide: for θO=0.25 ML, Cs/C1 and intrinsic C1 configurations are present on the surface, whereas for θO≥0.5 ML, only the former species were identified. The thermal activation of these tilted layers to 105 K results in a lower coverage of upright methoxide for any oxygen precoverage, coadsorbed with decomposition products, as confirmed by the detection of adsorbed formaldehyde and, on the denser oxygen layer (θO=0.6 ML), formate. The influence of the oxygen precoverage becomes determinant when annealing a [D2]methanol multilayer to 105 K: for θO=0.25 ML, the RAIR spectrum correlates with a disordered layer of tilted methoxide and formaldehyde, whereas for θO=0.6 ML upright methoxide, formate, and carbon monoxide were identified. On clean Ru(001), for methanol exposures ≥0.1 L, the C3v methoxide configuration was never attained upon thermal activation.