Publications

Abstract Antioxidants are additives largely used in industry for delaying, retarding, or preventing the development of oxidative deterioration. Propyl gallate (E310) is a phenolic antioxidant extensively used in the food, cosmetics, and pharmaceutical industries. A series of lab experiments have been developed to teach students about the importance and significance of antioxidants in industry. In the first laboratory, the antioxidant propyl gallate is obtained and the structure identified. Students become acquainted with laboratory techniques such as extraction, crystallization, and thin-layer chromatography. In the second laboratory, spectroscopic data (IR, H-1 and C-13 NMR) is acquired and interpreted. Students become familiar with the basic concepts of organic compound identification. In the third laboratory, the antioxidant activity of the synthesized additive and gallic acid is evaluated by DPPH (2,2-diphenyl-1-picrythydrazyl) assay using trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) as standard. Concepts such as free radical chemistry, preparation of analytical samples, calibration methods, and UV-vis spectrophotometry, are reviewed. This series of experiments can also be used to explore the effect of substituents on radical stability because structurally related compounds were found to have qualitatively different antioxidant profiles.

Abstract The measurement of aryl-naphthyl rotational barriers, Delta G(double dagger), in various solvents for two substituted 1,8-diarylnaphthalenes by dynamic H-1 NMR showed that Delta G(double dagger) trends in aromatic systems can be fully rationalized only when considering the different types of aromatic interactions that can be established in the ground and transition states, namely, intramolecular interactions involving the aromatic rings and specific solvation interactions.

Abstract The chlorophenoxy herbicide MCPA(4-chloro-2-methylphenoxyacetic acid), widely used for the control of broad-leaf weeds primarily in cereal and grass seed crops, still remains one of the most often used herbicides in Portugal. As the formation of inclusion complexes with cyclodextrins can improve its solubility properties, the interaction between the herbicide MCPA and beta-cyclodextrin was investigated. The stability constants describing the extent of formation of the complexes have been determined by phase-solubility studies. Different analytical techniques [ultraviolet-visible spectroscopy (UV-Vis), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (H-1 NMR)] were employed for a thorough investigation of the structural characteristics of the obtained complexes, which exhibited distinct features and properties from both "guest" and "host" molecules. FTIR and H-1 NMR data obtained for the MCPA/beta-CD complexes gave information about the interaction between MCPA and the nonpolar cyclodextrin cavity. The dramatic change observed in band frequency and proton displacements of OCH2 group and H6 aromatic proton confirmed the inclusion of MCPA in beta-CD. The formation of an inclusion complex between MCPA and beta-CD increased the aqueous solubility of this herbicide which could be a particularly advantageous property for some specific applications, namely to improve commercial formulation and for environmental protection.

Abstract We report a study on the energetics and structural properties of naphthalene-based proton sponges and their corresponding protonated cations. In particular, we have determined the experimental standard enthalpies of formation in the gas phase at T = 298.15 K, Delta fH(m)(o) m (g), for the neutral and protonated DMAN [1,8-bis (dimethylamino)-naphthalene], (221.0 +/- 7.3) and (729.0 +/- 11.1) kJ.mol(-1), respectively. A reliable experimental estimation of enthalpy associated with "strain'' effect and hydrogen bond intramolecular (included within "enhanced basicity'', EB) contributions to the basicity of DMAN, were deduced from isodesmic reactions, -(29.1 +/- 4.6) and (87.1 +/- 11.9) kJ.mol(-1), respectively. The gas-phase basicities (GB) of naphthalene-based proton sponges are compared with the corresponding aqueous basicities (pKa), covering a range of 149 kJ.mol(-1) in GB and 11.5 in pKa. Density functional calculations at the M05-2X/6-311++G(d,p) level of theory were used to check the consistency of the experimental results and also to estimate the unavailable GB values of the considered species.

Abstract In this work, the interplay between structure and energetics in some representative phenylnaphthalenes is discussed from an experimental and theoretical perspective. For the compounds studied, the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were determined by the measurement of the vapor pressures as a function of T, using a Knudsen/quartz crystal effusion apparatus. The standard molar enthalpies of formation in the crystalline state were determined by static bomb combustion calorimetry. From these results, the standard molar enthalpies of formation in the gaseous phase were derived and, altogether with computational chemistry at the B3LYP/6-311++G(d,p) and MP2/cc-pVDZ levels of theory, used to deduce the relative molecular stabilities in various phenylnaphthalenes. X-ray crystallographic structures were obtained for some selected compounds in order to provide structural insights, and relate them to energetics. The thermodynamic quantities for sublimation suggest that molecular symmetry and torsional freedom are major factors affecting entropic differentiation in these molecules, and that cohesive forces are significantly influenced by molecular surface area. The global results obtained support the lack of significant conjugation between aromatic moieties in the alpha position of naphthalene but indicate the existence of significant electron delocalization when the aromatic groups are in the beta position. Evidence for the existence of a quasi T-shaped intramolecular aromatic interaction between the two outer phenyl rings in 1,8-di([1,1-biphenyl]4-yl)naphthalene was found, and the enthalpy of this interaction quantified on pure experimental grounds as -(11.9 +/- 4.8) kJ.mol(-1), in excellent agreement with the literature CCSD(T) theoretical results for the benzene dimer.

Abstract In the recent decades, numerous drug delivery systems based on nanoparticles have been developed. To deliver drugs to a specific site, many vehicles have been designed, including liposomes, lipid and polymeric nanoparticles. However these systems can suffer some limitations such as thermal and physical instability as well as opsonization by reticuloendothelial system. This chapter addresses the development and application of silica gel nanoparticles (nanogels) for drug delivery. The synthesis of nanoparticles by sol-gel technology offers new possibilities and many advantages for embedding organic compounds within silica, controlling their release from the host matrix into a surrounding medium, being a great potential for a variety of drug delivery applications, such as the site-specific delivery and intracellular controlled release of drugs, genes, and other therapeutic agents. © 2012 Springer-Verlag Berlin Heidelberg. All rights are reserved.

Abstract The energetic study of 4-nitro-2,1,3-benzothiadiazole has been developed using experimental techniques together with computational approaches. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of crystalline 4-nitro-2,1,3-benzothiadiazole (181.9 +/- 2.3 kJ . mol(-1)) was determined from the experimental standard molar energy of combustion -(3574.3 +/- 1.3) kJ . mol(-1), in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The standard (p degrees = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K, (101.8 +/- 4.3) kJ . mol(-1), was determined by a direct method, using the vacuum drop micro-calorimetric technique. From the latter value and from the enthalpy of formation of the solid, it was calculated the standard (p degrees = 0.1 MPa) enthalpy of formation of gaseous 4-nitro-2,1,3-benzothiadiazole as (283.7 +/- 4.9) kJ . mol(-1). Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several working reactions in order to derive the standard molar enthalpy of formation 4-nitro-2,1,3-benzothiadiazole. The ab initio results are in good agreement with the experimental data.