Extra virgin olive oil (EVOO) consumption has been traditionally related to a higher longevity in the human population. EVOO effects on health are often attributed to its unique mixture of phenolic compounds with tyrosol and hydroxityrosol being the most biologically active. Although these compounds have been extensively studied in terms of their antioxidant potential and its role in different pathologies, their actual connection with longevity remains unexplored. This study utilized the nematode Caenorhabditis elegans to investigate the possible effects of tyrosol in metazoan longevity. Significant lifespan extension was observed at one specific tyrosol concentration, which also induced a higher resistance to thermal and oxidative stress and delayed the appearance of a biomarker of ageing. We also report that, although tyrosol was efficiently taken up by these nematodes, it did not induce changes in development, body length or reproduction. In addition, lifespan experiments with several mutant strains revealed that components of the heat shock response (HSF-1) and the insulin pathway (DAF-2 and DAF-16) might be implicated in mediating tyrosol effects in lifespan, while caloric restriction and sirtuins do not seem to mediate its effects. Together, our results point to hormesis as a possible mechanism to explain the effects of tyrosol on longevity in C. elegans.

pH is an important biomarker for many human diseases and great efforts are being made to develop new pH probes for bioimaging and biomedical applications. Here, the use of three different CdSe/ZnS QDs, functionalized with D-penicillamine and small peptides, as pH probes for fluorescence lifetime imaging microscopy (FLIM) is investigated. The fluorescence pH sensitivity of the nanoparticles is analyzed in different experimental media: aqueous solution, synthetic intracellular medium, and mesenchymal C3H10T1/2 and tumoral SK-MEL-2 cell lines. Different experiments along with theoretical calculations are conducted to unravel the mechanisms causing pH sensitivity of the nanoparticles and the effect of the length and composition of the peripheral branches on their photophysical properties. Absolute intracellular pH values measured in live cells with FLIM using a fluorescent probe based on a QD are reported here for the first time (intracellular pH values of 7.0 and 7.1 for C3H10T1/2 and SK-MEL-2 cells, respectively). These fluorescent nanoprobes can also be used to distinguish between different types of cells in cocultures on the basis of their different fluorescence lifetimes in dissimilar intracellular environments.

The dependence of the fluorescence on pH for two 1,3,5-tristyrylbenzenes decorated with polyamine (compound 1) and poly­(amidoamine) (compound 2) chains at the periphery was investigated. The highest fluorescence intensities were observed under acidic conditions because electrostatic repulsions between positively charged molecules reduce the fluorescence quenching. The slopes observed in the fluorescence pH titration curves were associated with deprotonation of the different types of amine groups, which results in quenching by photoinduced electron transfer and aggregation processes. The linear dependence of fluorescence lifetime observed for different pH ranges is a valuable property for applications in the field of fluorescence lifetime sensors and imaging microscopy. The influence of the pH and the peripheral chains on the aggregation processes was also analyzed by absorption and emission spectroscopy, dynamic light scattering measurements, and transmission electron microscopy. For compound 1, bands associated with the formation of aggregates were detected along with micrometric aggregates surrounded by fibers with lattice fringes typical of columnar mesophases. For compound 2, which contains longer peripheral chains with a higher degree of branching, aggregates with lower internal order were observed. In this case, the peripheral chains hindered aggregation by π-stacking although the amine groups did allow hydrogen bonding.

In this work, we have investigated the dependence on the pH of the photophysical properties of a functionalized perylene bisimide (PBI) and its potential pH sensing applications. Observed was the presence of aggregates which diminishes at acid pH values and low concentrations, without totally disappearing until a temperature of 80 °C was reached. At basic pH, significant changes in the absorption spectrum were observed, which were associated with more strongly coupled aggregates. The 1 H NMR spectra of the PBI dye in D 2 O/TFA also showed the dependence of aggregation on concentration and temperature. PBI fluorescence intensity and lifetime were also sensitive to pH values. The maximum fluorescence intensity and lifetime were observed in acid medium, in which protonation of the secondary amines on the PBI side chains likely hinders the formation of strongly coupled aggregates. On the contrary, the fluorescence intensity significantly decreased in basic medium, due to deprotonation of the amine groups and the formation of stronger aggregates. Density functional theory calculations corroborated that π-stacked aggregates of PBI derivatives are stable in the protonated state, but their supramolecular structure changes. In the aggregate, monomeric units slide over their adjacent ones and increase the intermolecular distance upon the protonation. Intermolecular hydrogen bonds can help maintain the stability of the protonated aggregate. Fluorescence lifetime showed a sigmoidal dependence on pH, with a linear response range between pH 6 and 8, both in Tris•HCl buffered solutions and in a synthetic buffer mimicking the intracellular environment. The biocompatibility of the PBI dye was tested in C3H10T1/2 mesenchymal cells. The cellular uptake was confirmed by confocal fluorescence microscopy. No significant effects on cellular viability and morphology were observed at the conditions in which compound 1 can be used as a fluorescent probe. This work supports the idea that PBI derivatives can be suitable dyes for fluorescence lifetime sensing applications.

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