Publications

Abstract <jats:p>Brown carbon is a type of strong light-absorbing carbonaceous aerosol associated with radiative forcing. Nevertheless, the difficulty in correlating the chemical composition of brown carbon with its light absorption properties impairs the proper elucidation of its role in radiative forcing. Here, we have used a time-dependent density functional theory (TD-DFT)-based procedure to revisit the “real-world” absorption spectra of polycyclic aromatic hydrocarbons (PAHs) over the city of Porto, in Portugal, while correcting the spectra for their quantity in PM10 particulate matter. Our aim is to, by comparing these new results with those obtained previously regarding PM2.5 data, evaluate the role of different groupings of particulate matter in the light absorption of brown carbon. The results indicate that irrespective of the absorption spectra corresponding to their PM10 or PM2.5 data, the studied PAHs should contribute to radiative forcing by light absorption at UVA and (sub)visible wavelengths. However, the identity of the individual PAH species that contribute the most for the considered wavelengths can be quite different. Thus, different groupings of particulate matter appear to provide distinct contributions to light absorption and radiative forcing over the same location, even when considering the same class of molecular compounds.</jats:p>

Abstract Marine Coelenterazine is one of the most well-known chemi-/bioluminescent systems, and in which reaction the chemi-/bioluminophore (Coelenteramide) is generated and chemiexcited to singlet excited states (leading to light emission). Recent studies have shown that the bromination of compounds associated with the marine Coelenterazine system can provide them with new properties, such as anticancer activity and enhanced emission. Given this, our objective is to characterize the photophysical properties of a previously reported brominated Coelenteramide analog, by employing a combined experimental and theoretical approach. To better analyze the potential halogen effect, we have also synthesized and characterized, for the first time, two new fluorinated and chlorinated Coelenteramide analogs. These compounds show similar emission spectra in aqueous solution, but with different fluorescence quantum yields, in a trend that can be correlated with the heavy-atom effect (F > Cl > Br). A blue shift in emission in other solvents is also verified with the F-Cl-Br trend. More relevantly, the fluorescence quantum yield of the brominated analog is particularly sensitive to changes in solvent, which indicates that this compound has potential use as a microenvironment fluorescence probe. Theoretical calculations indicate that the observed excited state transitions result from local excitations involving the pyrazine ring. The obtained information should be useful for the further exploration of halogenated Coelenteramides and their luminescent properties.

Abstract Currently, salinity and heat are two critical threats to crop production and food security which are being aggravated by the global climatic instability. In this scenario, it is imperative to understand plant responses to simultaneous exposure to different stressors and the cross-talk between underlying functional mechanisms. Thus, in this study, the physiological and biochemical responses of tomato plants (Solanum lycopersicum L.) to the combination of salinity (100 mM NaCl) and heat (42 degrees C; 4 h/day) stress were evaluated. After 21 days of co-exposure, the accumulation of Na+ in plant tissues was superior when salt-treated plants were also exposed to high temperatures compared to the individual saline treatment, leading to the depletion of other nutrients and a harsher negative effect on plant growth. Despite that, neither oxidative damage nor a major accumulation of reactive oxygen species took place under stress conditions, mostly due to the accumulation of antioxidant (AOX) metabolites alongside the activation of several AOX enzymes. Nonetheless, the plausible allocation of resources towards the defense pathways related to oxidative and osmotic stress, along with severe Na toxicity, heavily compromised the ability of plants to grow properly when the combination of salinity and heat was imposed.