Gonçalo C. Justino

Antioxidant mechanisms of Quercetin and Myricetin in the gas phase and in solution--a comparison and validation of semi-empirical methods.

Flavonoids have long been recognized for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work we have studied the properties of two flavonols, quercetin and myricetin, using semi-empirical methods in order to validate the application of the recent Parametric Model 6 and to understand the fundamental difference between the two molecules. Their geometries have been optimized and important molecular properties have been calculated. The energetic of the possible antioxidant mechanisms have also been analyzed. The two studied flavonols do not differ significantly in their molecular properties, but the antioxidant mechanisms by which they may act in solution can be rather different. Moreover, we also show that the Parametric Model 6 can produce reliable information for this type of compounds.

Structural Analysis of Flavonoids and Related Compounds - A Review of Spectroscopic Applications

In 1936 St. Rusznyak and A. Szent-Gyorgyi described, in a paper in Nature (Rusznyak & Szent-Gyorgy, 1936), the relief of certain pathological conditions, characterized by an increased permeability or fragility of the capillary wall, by extracts of Hungarian red pepper containing flavonols, a type of flavonoids, which were then named “vitamin P”. The following five decades saw a slow but steady rise in the interest in the group of flavonoids, and their benefits in the treatment of a vast number of diseases and conditions, including pregnancy toxaemia, rheumatic fever, diabetes and cancer. In the late 1980s and throughout the 1990s flavonoids were intensely studied concerning their actions as mutagenic agents and as antioxidants and pro-oxidants as their likely roles in biological systems (for example, Aviram & Fuhrman, 1998; Lambert & Elias, 2010). In the early 90s the antioxidant activity of flavonoids was extensively studied in vitro, and it was assumed that such activity would be at the basis of the health promoting benefits of these compounds. However, in the late 90s and early 00s the metabolism of flavonoids was deeply scrutinized, and the results indicated that their antioxidant activity in vivo could not account for the overall actions attributed to them (Fraga et al., 2010). The paradigm for flavonoid action changed towards the establishment of flavonoids as inflammation modulators, and more recently their role in neuroprotection, memory and cognition has been under scrutiny (Gomes et al., 2008; Spencer et al., 2009; Spencer, 2010). However, exact mechanisms for many of the actions attributed to flavonoids have not yet been established, but the relationship between their activity and the presence of specific functional groups in the molecules is undeniable. Moreover, each role attributed to flavonoids has been linked to different structural features – for example, while antioxidant activity depends essentially on the number and location of OH groups in the molecules, their antagonist effect towards adenosine receptors depends more on the overall planarity than on the hydroxyl groups; in fact, the latter even appear to be counter-productive (Gonzalez et al., 2007).

Interaction of [VIV O(acac)2 ] with Human Serum Transferrin and Albumin

[VO(acac)2 ] is a remarkable vanadium compound and has potential as a therapeutic drug. It is important to clarify how it is transported in blood, but the reports addressing its binding to serum proteins have been contradictory. We use several spectroscopic and mass spectrometric techniques (ESI and MALDI-TOF), small-angle X-ray scattering and size exclusion chromatography (SEC) to characterize solutions containing [VO(acac)2 ] and either human serum apotransferrin (apoHTF) or albumin (HSA). DFT and modeling protein calculations are carried out to disclose the type of binding to apoHTF. The measured circular dichroism spectra, SEC and MALDI-TOF data clearly prove that at least two VO-acac moieties may bind to apoHTF, most probably forming [VIV O(acac)(apoHTF)] complexes with residues of the HTF binding sites. No indication of binding of [VO(acac)2 ] to HSA is obtained. We conclude that VIV O-acac species may be transported in blood by transferrin. At very low complex concentrations speciation calculations suggest that [(VO)(apoHTF)] species form.

Electronic communication in linear oligo(azobenzene) radical anions.

The radical anions of five bis(azobenzene) and one tris(azobenzene) compounds were studied by optical and electron paramagnetic resonance (EPR) spectroscopies in polar aprotic solvents. The radicals with planar or almost-planar bridges are charge-delocalized mixed-valence species. Localization of charge occurs only on radicals with highly twisted biphenyl bridges. The electronic coupling between the azobenzene charge-bearing units, calculated as half the energy of the intervalence band for the charge-delocalized and by the Hush equation for the charge-localized radicals, decreases with the distance and torsion angle between azobenzene units. These radicals have smaller electronic couplings between charge-bearing units than other mixed-valence organic radicals with similar bridges. However, the application of a three-stage model to the tris(azobenzene) radical anion intervalence band yields an electronic coupling between consecutive azobenzenes that is higher than in any of the bis(azobenzene) radicals studied.

Demethylation of theophylline (1,3-dimethylxanthine) to 1-methylxanthine: the first step of an antioxidising cascade

Abstract The reaction of theophylline with HO• radical, produced by photolytic methods at pH 7, was studied in aqueous solution and the products characterised by HPLC and GC-MS. In addition to the expected 1,3-dimethyluric acid, the formation of 1-methylxanthine and, to a lesser extent, of 3-methylxanthine was observed. Theoretical calculations confirmed the preferred formation of the former compound. Both demethylated products were also observed upon reaction of theophylline with O•– radical anion at pH∼13, and 1-methylxanthine was consumed faster than 3-methylxanthine after its formation. Molecular oxygen had no significant effect on the formation of the mono-methylxanthine derivatives. A reaction mechanism for the demethylation of theophylline by oxidising radicals is proposed. This demethylation reaction can play an important role in the protection of biological targets against oxidative stress as the first step of an antioxidising cascade.

Camphor-based CCR5 blocker lead compounds – a computational and experimental approach

The C–C chemokine receptor type 5 (CCR5) is a transmembrane receptor that plays a pivotal role as a HIV anchor to human cell membranes, mediating viral entry. CCR5 antagonists, acting by blocking the receptor and preventing its interaction with the HIV proteins, are key agents towards effective anti-viral therapy. This work describes the computational study, synthesis and viral inhibition assay of a number of camphor derivatives as a first step towards new drug leads to block this specific entry pathway. Viral inhibition assays have identified three molecules, camphor carboxylic acid, its tri(hydroxymethyl)aminomethane amide derivative, and an hydroxyl-imide camphor derivative as promising agents to develop new drugs, with IC50 values (0.16, 0.22 and 1.02 μM, respectively) one order below that of maraviroc (0.02 μM), a clinically used CCR5 antagonist.

Antibodies against HDL Components in Ischaemic Stroke and Coronary Artery Disease

Quantitative and qualitative defects of high-density lipoprotein (HDL) are important in atherogenesis. In this study, we investigated whether antibodies against HDL components had additional value to conventional cardiovascular risk factors for the diagnosis of ischaemic stroke (IS) and coronary artery disease (CAD). Cross-sectional study was conducted on 53 patients with IS, 51 with CAD and 55 healthy controls, and in vitro studies to validate findings of the clinical study. We determined serum immunoglobulin G (IgG) antibodies against HDL (aHDL), apolipoproteins (aApoA-I, aApoA-II and aApoC-I) and paraoxonase-1 (aPON1) as well as PON1 activity (PON1a), total antioxidant capacity and biomarkers of endothelial activation (serum nitric oxide metabolites, 3-nitrotyrosine, VCAM-1 and ICAM-1); in vitro assays tested the capacity of IgG aHDL purified from high titer patients to inhibit PON1a and to reverse protective effect of HDL on endothelial cells. IgG aHDL, aApoA-I and aPON1 were higher in IS and CAD than controls (p < 0.001), predicted negatively PON1a and positively VCAM-1 and ICAM-1. By adding IgG aHDL and aApoA-I to a traditional cardiovascular risk factors model for IS and by adding IgG aHDL in a similar model for CAD, we obtained better discrimination of IS and CAD from healthy controls. IgG aHDL purified from IS and CAD inhibited PON1a by 38% (p < 0.01) and abrogated the protective effect of HDL on VCAM-1 expression by 126% compared with non-specific human IgG (p < 0.001). IgG against HDL components interfere with the antioxidant and anti-inflammatory properties of HDL and may represent novel biomarkers for vascular disease that need to be investigated in prospective studies.