Publications

Abstract Synthetic amino acid-based surfactants possess versatile aggregation properties and are typically more biocompatible and biodegradable than surfactants with conventional headgroups. This opens the possibility of a myriad of specialty applications, namely in pharmaceutics, cosmetics, biomedicine, and nanotemplating chemistry. In this work, we have investigated the interfacial and self-assembling properties in aqueous medium of novel double-chained lysine-based surfactants, with particular focus on the behavior of the dodecyl derivative, 12Lys12. Upon cooling from dilute isotropic micellar solutions, this surfactant crystallizes into micrometer-sized tubular structures that induce gelation of the system. The tubules have been characterized in terms of morphology, assembly process, thermal behavior, and stability, by using differential scanning calorimetry, light and scanning electron microscopy, and deuterium NMR. Possible mechanisms for tubule assembly are discussed, on the basis of surfactant molecular shape, H-bonding and electrostatic interactions, and chirality effects.

Abstract Solanum nigrum L. plants were exposed for 28 days to 100 and 200 mu mol/L copper (Cu) in a hydroponic system to analyze the antioxidant defense response. A dose-dependent reduction in growth (fresh mass of root and shoot, shoot height, and root elongation) with increasing concentration of Cu was observed, whereas Cu treatments did funt affect total chlorophyll and carotefunids content. An enhanced lipid peroxidation, in terms of malondialdehyde (MDA) content, was quantified in shoots when the plants were subjected to the highest Cu level, while in roots MDA levels showed a dose-dependent increase along the increasing Cu concentrations applied. An increase of proline in roots of plants exposed to 200 mu mol/L Cu was found. Antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) did funt show significant changes with respect to control, in both roots and shoots, despite mRNA-specific accumulations varied between Cu levels and organs. Ascorbate peroxidase (APX) was negatively affected in shoots by the highest Cu level. Gene expression of the subtype 2d metallothioneins (MT) revealed to be Cu-enhanced throughout the plant body and correlated with Cu tissue levels, with the other MT1 and MT2 gene members downregulated in roots and upregulated in shoots, contributing more as antioxidants in the latter organs than in Cu homeostasis. MT3s are not involved in Cu homeostasis and phytochelatin (PC) production was enhanced in roots of plants exposed to 200 mu mol/L Cu, contributing to a higher Cu accumulation in these organs.

Abstract Hydroxycinnamic acids (HCAs) are important phytochemicals possessing significant biological properties. Several investigators have studied in vitro antioxidant activity of HCAs in detail. In this review, we have gathered the studies focused on the structure-activity relationships (SARs) of these compounds that have used medicinal chemistry to generate more potent antioxidant molecules. Most of the reports indicated that the presence of an unsaturated bond on the side chain of HCAs is vital to their activity. The structural features that were reported to be of importance to the antioxidant activity were categorized as follows: modifications of the aromatic ring, which include alterations in the number and position of hydroxy groups and insertion of electron donating or withdrawing moieties as well as modifications of the carboxylic function that include esterification and amidation process. Furthermore, reports that have addressed the influence of physicochemical properties including redox potential, lipid solubility and dissociation constant on the antioxidant activity were also summarized. Finally, the pro-oxidant effect of HCAs in some test systems was addressed. Most of the investigations concluded that the presence of ortho-dihydroxy phenyl group (catechol moiety) is of significant importance to the antioxidant activity, while, the presence of three hydroxy groups does not necessarily improve the activity. Optimization of the structure of molecular leads is an important task of modern medicinal chemistry and its accomplishment relies on the careful assessment of SARs. SAR studies on HCAs can identify the most successful antioxidants that could be useful for management of oxidative stress-related diseases.

Abstract In this paper an optimized enzymatic assay for inorganic sulfate (SO4-2) detection and quantitation in freshwater, relying on adenosine-5'-triphosphate sulfurylase catalyzed reaction coupled to bioluminescent detection by firefly luciferase, is described. Inorganic sulfate is converted, by adenosine-5'-triphosphate sulfurylase, into adenosine-5'-phosphosulfate and inorganic pyrophosphate, with consumption of adenosine-5'-triphosphate. The remaining adenosine-5'-triphosphate is used as a co-factor in the reaction catalyzed by firefly luciferase generating, as a co-product, photons of visible light. The light output is inversely proportional to the inorganic sulfate content. Using sodium sulfate as a model, the assay was optimized through a statistical experimental design methodology and validated in water samples from domestic wells from two municipalities within the Metropolitan Area of Porto plus tap water as control. The optimized method requires 20 mu L of sample in a final reaction volume of 100 mu L. It is linear in the range from 14 to 134 mg L-1 of inorganic sulfate, with limits of detection and quantitation of 10 and 34 mg L-1, respectively. Repeatability, expressed as relative standard deviation, is 7.23% at 34 mg L-1, 6.87% at 68 mg L-1 and 4.67% at 96 mg L-1. The inorganic sulfate concentration in the wells is approximately 124, 182 and 182 mg L-1, whereas it was found to be a value of about 200 mg L-1 in tap water. Samples can be quantified by calibration curves without any pre-treatment other than dilution. The optimized method is fast, simple to perform and robust.

Abstract The chemiluminescence properties of firefly luciferin were studied, in a variety of chemical systems different from those in which it is usually studied. It was found that luciferin is a multifunctional chemiluminescence molecule, as it can behave as a chemiluminescence sensitizer, an emitter and a substrate. The first two roles are here reported for the first time, while we have found a novel way of obtaining excited state oxyluciferin from luciferin. Evidence was also found that does not support the newly proposed radical-mechanism of the formation of firefly dioxetanone. With this study we hope to open the way for novel chemiluminescence applications for firefly luciferin.

Abstract This work presents a new approach for estimating sublimation enthalpies and vapor pressures of substituted benzenes. Proposed estimating equations were based on a collection of selected literature results of vapor pressures of ca. 240 benzene derivatives attached with 30 different substituents. Compared to experimental results, best estimates are obtained from the equations that include the temperature of fusion. A review of the results determined for substituted benzenes using two different calorimetric techniques shows that the results of enthalpies of sublimation derived from vapor pressures seem to be more reliable than those derived from the calorimetric techniques.

Abstract The photophysical properties of four bare firefly bioluminophores were studied in vacuo by means of a density functional theory approach. The objective of this work was to fingerprint the excited-state properties of these molecules without perturbations of the microenvironment (either solution or enzyme active site). It is known that intermolecular interactions formed between the light-emitter and active site molecules govern the bioluminescence multicolor tuning mechanism. However, it is difficult to disentangle the numerous active site-oxyluciferin interactions and understand the effect exerted by each one of these interactions on the color of light emitted. Thus, the study of these isolated bioluminophores allows us to obtain their intrinsic photophysics properties, which can serve as a reference in studies aiming to understand the role of perturbations from the microenvironment.

Abstract A(2B) adenosine receptor antagonists may be beneficial in treating diseases like asthma, diabetes, diabetic retinopathy, and certain cancers. This has stimulated research for the development of potent ligands for this subtype, based on quantitative structure-affinity relationships. In this work, a new ensemble machine learning algorithm is proposed for classification and prediction of the ligand-binding affinity of A(2B) adenosine receptor antagonists. This algorithm is based on the training of different classifier models with multiple training sets (composed of the same compounds but represented by diverse features). The k-nearest neighbor, decision trees, neural networks, and support vector machines were used as single classifiers. To select the base classifiers for combining into the ensemble, several diversity measures were employed. The final multiclassifier prediction results were computed from the output obtained by using a combination of selected base classifiers output, by utilizing different mathematical functions including the following: majority vote, maximum and average probability. In this work, 10-fold cross- and external validation were used. The strategy led to the following results: 0 the single classifiers, together with previous features selections, resulted in good overall accuracy, a comparison between single classifiers, and their combinations in the multiclassifier model, showed that using our ensemble gave a better performance than the single classifier model, and our multiclassifier model performed better than the most widely used multiclassifier models in the literature. The results and statistical analysis demonstrated the supremacy of our multiclassifier approach for predicting the affinity of A(2B) adenosine receptor antagonists, and it can be used to develop other QSAR models.

Abstract Although a few groups have recently published transport properties for extensive sets of imidazoliumand pyridinium-based room-temperature ionic liquids (RTILs) and their solutions, there are still no prediction techniques for the conductivity maximum in these systems. We contribute to the discussion by reporting own conductometric data and establishing implicit empirical correlations between ionic structure, concentration and temperature. Our analysis is based on binary systems containing ionic (RTIL) and molecular (acetonitrile) co-solvent. The molar fraction of RTIL in each system ranges from 0 to 50% whereas temperature ranges from 278.15 to 328.15 K. Imidazolium-based RTILs are sampled by 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium and 1-hexyl-3- methylimidazolium tetrafluoroborates, 1-n-butyl-3- methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium bromide. 1-butyl-4-methylpyridinium tetrafluoroborate is employed to distinguish a role of aromatic ring. Ionic association in all RTIL-AN systems poorly correlates with the cation structure, although strongly depends on the anion size and structure. Cation and anion of RTILs form the 'contact ion pairs' (CIPs) where anion is coordinated by imidazole and pyridine rings. Notably, all binary systems exhibit conductivity maximum between χ(RTIL) = 10 and 20%. This maximum slightly shifts towards smaller χ(RTIL), as counterion gets larger. Smaller cations and anions lead to substantial conductivity growth. Conductivity maximum can be boosted and observed at larger χ(RTIL) even at insignificant temperature increase. Our observations provide novel insights into a complicated functional dependence of ionic conductivity versus ionic concentration and temperature. The results may be of extensive practical application, particularly for construction of high-performance electrolyte systems. © 2013 Elsevier Ltd. All rights reserved.