Rui M. D. Nunes

Photoacid for Extremely Long-Lived and Reversible pH-Jumps

The ability to change the acidity of an aqueous solution within the time of a short laser pulse and use the resulting low pH to drive acid-catalyzed reactions in the irradiated volume opens news perspectives for the spatial and temporal control of a variety of processes. Persistent and reversible acidification of an aqueous solution is achieved with a new molecule, 1-(2-nitroethyl)-2-naphthol, that combines the fast photoacid properties of an aromatic alcohol with the slow proton transfer rates of a nitroalkane. The protons released in a few nanoseconds by pulsed laser excitation of the photoacid last for nearly one second in aqueous solutions. We show that acid-base equilibria with other species is established at the lower pHs of the irradiated volume, that the process is reversible and that it can be maintained under continuous irradiation.

Exothermic rate restrictions in long-range photoinduced charge separations in rigid media.

Glycerol/methanol (9:1) mixtures at 255 K behave as rigid media for photoinduced electron transfers that take place within a few hundred nanoseconds. This media also provides enough polarity and plasticity to accommodate charge separations with reaction free energies ranging from +3 to -34 kcal/mol. The distance dependence of the electron transfer rates from electronically excited aromatic hydrocarbons to nitriles in this medium is accurately described by an exponential decay constant of 1.65 per angstrom. These photoinduced electron transfers display, for the first time in charge separations between independent electron donors and acceptors, a free-energy relationship with a maximum rate followed by a decrease in the rate for more exothermic reactions. According to this free-energy relationship, Franck-Condon factors are maximized at DeltaG(0) approximately -15 kcal/mol. It is suggested that the inverted region observed for these first-order photoinduced charge separations originates from a slower increase of their reorganization energies with DeltaG(0) than that of the analogous second-order photoinduced charge separations, for which inverted regions have never been clearly observed.

Dynamics of Radical Ion Pairs following Photoinduced Electron Transfer in Solvents with Low and Intermediate Polarities.

Fluorescence quenching of p-xylene, naphthalene, or pyrene by fumaronitrile in apolar solvents and in solvents of intermediate polarities leads to weakly fluorescent radical ion pairs. This emission is assigned to ion pairs in close contact on the basis of their solvent polarity dependence, kinetics, and thermodynamics. The temperature-dependence of the intensity and fluorescence emission maxima of ion pairs in methyl acetate reveals that they have decay channels competitive with their thermal equilibration. The results presented in this work are consistent with the direct formation of contact ion pairs in weakly polar solvents and in solvents of intermediate polarities as the result of bimolecular photoinduced electron transfer reactions between aromatic hydrocarbons and nitriles. The implications of these findings in free-energy relationships of electron transfer reactions are discussed.

Spectroscopic properties and photodynamic effects of new lipophilic porphyrin derivatives: Efficacy, localisation and cell death pathways [Journal of Photochemistry and Photobiology B: Biology 84 (2006) 1–14]

Photodynamic therapy (PDT) and photodynamic diagnostics (PDD) of cancer are based on the use of non-toxic dyes (photosensitisers) in combination with harmless visible light. This paper reports physicochemical properties, cell uptake, localisation as well as photodynamic efficiency of two novel lipophilic porphyrin derivatives, suitable for use as PDT sensitisers. Both compounds are characterised by high quantum yield of singlet oxygen generation which was measured by time-resolved phosphorescence. Photodynamic in vitro studies were conducted on three cancer cell lines. Results of cell survival tests showed negligible dark cytotoxicity but high phototoxicity. The results also indicate that cell death is dependent on energy dose and time following light exposure. Using confocal laser scanning microscopy both compounds were found to localise in the cytoplasm around the nucleus of the tumour cells. The mode of cell death was evaluated based on the morphological changes after differential staining. In summary, good photostability, high quantum yield of singlet oxygen and biological effectiveness indicate that the examined lipophilic porphyrin derivatives offer quite interesting prospects of photodynamic therapy application.

Argilas como catalisadores verdes na esterificação do colesterol: caracterização espectroscópica e identificação de polimorfos por métodos de análise térmica. Uma proposta laboratorial interdisciplinar para o 1º ciclo universitário

A laboratory experiment that enables the professor to introduce the problematic of sustainable development in pharmaceutical chemistry to undergraduate students is proposed, using a simple synthetic procedure. Cholesteryl acetate is prepared by the esterification of cholesterol using Montmorillonite K10 as heterogeneous catalyst. Cholesterol and cholesteryl acetate are characterized by spectroscopic (1H RMN, 13C RMN, FTIR) and thermal analysis techniques. The thermal methods are used to introduce the concepts of polymorphism and the nature of mesophases.