Publications

Abstract Steady-state and time-resolved optical spectroscopy techniques were employed to study the photo physics and photochemistry of 4- (4HC) and 3-hydroxycoumarin (3HC). We found that the p K-a of 4HC in aqueous solutions is about 7.5 and the p K-a* is only 4.5. We also found that the nonradiative rate of 4-hydroxycoumarin is high and the excited state proton transfer (ESPT) rate to water is rather slow and so an ESPT process is not observed. Quantum mechanical calculations confirm that the ESPT rate should be slow and the intersystem crossing rate St -> 4 T is large. An ESPT process was also not observed for 3HC, but it might still take place and not being observed as the fluorescence quantum yield of the anion is two orders of magnitude smaller than that of the protonated form. The nonradiative decay of protonated 3HC is explained with an H-atom abstraction mechanism, leading to the formation of a radical species.

Abstract Coelenterazine, a member of the imidazopyrazinone class of chemiluminescent substrates, presents significant potential as a dynamic probe of reactive oxygen species in a biological environment, such as a superoxide anion, in which these species are important in cellular biology and pathology. The objective of the current study was to understand in what way the efficiency of singlet and triplet chemiexcitation could be modulated, towards a more efficient use of imidazopyrazinone-based compounds as dynamic chemiluminescent probes. To this end the thermolysis of imidazopyrazinone dioxetanone, substituted at the C-8-position with electron-donating or electron-withdrawing groups, was characterized with a theoretical approach based on density functional theory. Substituents with different electron-donating/withdrawing characters have only a limited effect on the singlet chemiexcitation of anionic dioxetanone. For neutral dioxetanone, both electron-withdrawing and weak electron-donating substituents increase singlet chemiexcitation, to the contrary of strong electron-donating groups. During their thermolysis reaction, all molecules presented regions of degeneracy with triplet states, thereby indicating the possibility of triplet chemiexcitation.

Abstract In this work carbon quantum dot (CQD) nanoparticles are synthesized from D-lactose using a hydrothermal method and then they are coated with polyethylene glycol (CQDs@PEG). These particles exhibit a monodisperse spherical morphology with an average particle size of similar to 4 nm. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy showed the presence of the hydroxyl groups from the ethylene glycol molecules grafted onto the CQDs' surfaces, which confirms that PEG was covalently attached to the nanoparticles' surfaces. Fluorescence analysis demonstrates a shift in the emission at 495 nm after PEG coating. Modified carbon dots were introduced into thermo-responsive pNIPAM microgels. The resultant pNIPAM-CQDs@PEG hybrid system exhibits interesting fluorescence properties. Transmission electron microscopy (TEM), fluorescence microscopy, and energy-dispersive X-ray (EDX) spectroscopy confirm the incorporation of CQD particles into the microgels. Finally, dynamic light scattering (DLS) analysis confirms that further hybrid microgels based on pNIPAM are thermo-responsive, with a transition temperature similar to that of a system with an ionic component.

Abstract AimsThe aim of this study was to investigate the antibiofilm potential of five essential oil (EO) components with cyclic (sabineneSAB, carveolC1, carvoneC2) and acyclic (citronellolC3 and citronellalC4) structures against Escherichia coli and Staphylococcus aureus. Methods and ResultsThe selected EO components prevented biofilm set-up, with C3 and C4 causing remarkable effects. When applied against pre-established biofilms, they promoted high biomass removal and inactivation of biofilm cells. Moreover, no viable E.coli biofilm cells were detected after exposure to SAB at 5xMIC and 10xMIC, and a significant viability decrease was observed for both bacteria with the other EO components. SAB, C3 and C4 caused the most prominent effects apparently due to their octanol-water partition coefficient (Po/w), the number of rotatable bonds (n-ROTB) and the free hydroxyl groups. ConclusionsThe overall results demonstrated that the selected EO components, particularly SAB, C3 and C4 are of interest as new lead molecules to both prevent biofilm set-up and to control pre-established biofilms of E.coli and S. aureus. Significance and Impact of the StudyThe tested EO components exhibited prominent antibiofilm properties against E.coli and S. aureus providing a novel and effective alternative/complementary approach to counteract chronic infections and the transmission of diseases in clinical settings.

Abstract Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-alpha, omega-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM). The various critical concentrations and the enthalpy changes of the corresponding phase transitions for the oppositely charged system were obtained from the plots of the observed enthalpy change (DHobs) and turbidity measurements as a function of gemini concentration. The morphologies of the aggregates in various phases were observed by Cryo-TEM. Altogether these results suggest the critical role of gemini as a dual linker. At the concentrations where the crosslink between the pendant aggregates happens, the free gemini concentration is proximately zero and the aggregate retains its negative charge. The analysis of various factors involved in the interaction allowed a rationalization of the driving forces for mixed aggregate formation, which will contribute to a subsequent rational design of drug delivery systems based on this polymer/surfactant system.

Abstract Mycobacterial infections cause a significant burden of disease and death worldwide. Their treatment is long, toxic, costly, and increasingly prone to failure due to bacterial resistance to currently available antibiotics. New therapeutic options are thus clearly needed. Antimicrobial peptides represent an important source of new antimicrobial molecules, both for their direct activity and for their immunomodulatory potential. We have previously reported that a short version of the bovine antimicrobial peptide lactoferricin with amino acids 17 to 30 (LFcin17-30), along with its variants obtained by specific amino acid substitutions, killed Mycobacterium avium in broth culture. In the present work, those peptides were tested against M. avium living inside its natural host cell, the macrophage. We found that the peptides increased the antimicrobial action of the conventional antibiotic ethambutol inside macrophages. Moreover, the D-enantiomer of the lactoferricin peptide (D-LFcin17-30) was more stable and induced significant killing of intracellular mycobacteria by itself. Interestingly, D-LFcin17-30 did not localize to M. avium-harboring phagosomes but induced the production of proinflammatory cytokines and increased the formation of lysosomes and autophagosome-like vesicles. These results lead us to conclude that D-LFcin17-30 primes macrophages for intracellular microbial digestion through phagosomal maturation and/or autophagy, culminating in mycobacterial killing. IMPORTANCE The genus Mycobacterium comprises several pathogenic species, including M. tuberculosis, M. leprae, M. avium, etc. Infections caused by these bacteria are particularly difficult to treat due to their intrinsic impermeability, low growth rate, and intracellular localization. Antimicrobial peptides are increasingly acknowledged as potential treatment tools, as they have a high spectrum of activity, low tendency to induce bacterial resistance, and immunomodulatory properties. In this study, we show that peptides derived from bovine lactoferricin (LFcin) improve the antimicrobial activity of ethambutol against Mycobacterium avium growing inside macrophages. Moreover, the D-enantiomer of a short version of lactoferricin containing amino acids 17 to 30 (D-LFcin17-30) causes intramacrophagic death of M. avium by increasing the formation of lysosomes and autophagosomes. This work opens the way to the use of lactoferricin-derived peptides to treat infections caused by mycobacteria and highlights important modulatory effects of D-FLcin17-30 on macrophages, which may be useful under other conditions in which macrophage activation is needed.

Abstract This work aims to calculate the carbon footprint of the ICB produced by a Portuguese company and to compare it with other insulation materials available in the market. A Life Cycle Thinking approach and the ISO/TS 14067 (2013) requirements were followed in this work to perform a “cradle-to-gate” life cycle analysis. The inventory analysis mainly uses primary data collected from a Portuguese ICB producing company, complemented with secondary data from commercial life cycle databases and literature concerning respectively, the external transportation of the cork raw-material and the emission factors of electricity and fuel production and use. Results of this study show that ICB has a carbon footprint of −116.229 kg CO2 equivalent per m3 of ICB. It is the only insulation material present in the market with a negative carbon footprint, which is mainly due to the utilization of cork, a renewable raw material, the proximity of its source to the factory, and the use of biomass for generating the steam needed for its production process. To the authors’ knowledge, this is the first study to report the carbon footprint of ICB and to compare it with other building insulation materials. © 2016 Elsevier Ltd

Abstract The ohmic heating also known as direct Joule heating, is an advanced thermal processing method, mainly used in the food industry to rapidly increase the temperature for either cooking or sterilization purposes. Its use in organic synthesis, in the heating of chemical reactors, is an emerging method that shows great potential, the development of which has started recently. This Concept article focuses on the use of ohmic heating as a new tool for organic synthesis. It presents the fundamentals of ohmic heating and makes a qualitative and quantitative comparison with other common heating methods. A brief description of the ohmic reactor prototype in operation is presented as well as recent examples of its use in organic synthesis at laboratory scale, thus showing the current state of the research. The advantages and limitations of this heating method, as well as its main current applications are also discussed. Finally, the prospects and potential implications of ohmic heating in future research in chemical synthesis are proposed.

Abstract Microwave synthetized sulfur and nitrogen co-doped carbon dots responded selectively to nitric oxide (NO) at pH 7. Citric acid, urea and sodium thiosulfate in the proportion of 1:1:3 were used respectively as carbon, nitrogen and sulfur sources in the carbon dots microwave synthesis. For this synthesis, the three compounds were diluted in 15 mL of water and exposed for 5 min to a microwave radiation of 700 W. It is observed that the main factor contributing to the increased sensitivity and selectivity response to NO at pH 7 is the sodium thiosulfate used as sulfur source. A linear response range from 1 to 25 mu M with a sensitivity of 16 mu M-1 and a detection limit of 0.3 mu M were obtained. The NO quantification capability was assessed in standard and in fortified serum solutions.