Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer

For many biological and biomedical studies, it is essential to detect the production of O-1(2) and quantify its production yield. Among the available methods, detection of the characteristic 1270-nm phosphorescence of singlet oxygen by time-resolved near-infrared (TRNIR) emission constitutes the most direct and unambiguous approach. An alternative indirect method is electron paramagnetic resonance (EPR) in combination with a singlet oxygen probe. This is based on the detection of the TEMPO free radical formed after oxidation of TEMP (2,2,6,6-tetramethylpiperidine) by singlet oxygen. Although the TEMPO/EPR method has been widely employed, it can produce misleading data. This is demonstrated by the present study, in which the quantum yields of singlet oxygen formation obtained by TRNIR emission and by the TEMPO/EPR method are compared for a set of well-known photosensitizers. The results reveal that the TEMPO/EPR method leads to significant overestimation of singlet oxygen yield when the singlet or triplet excited state of the photosensitizer is efficiently quenched by TEMP, acting as electron donor. In such case, generation of the TEMP+(center dot) radical cation, followed by deprotonation and reaction with molecular oxygen, gives rise to an EPR-detectable TEMPO signal that is not associated with singlet oxygen production. This knowledge is essential for an appropriate and error-free application of the TEMPO/EPR method in chemical, biological, and medical studies.The Spanish government (CTQ2012-32621, RyC-2007-00476, PFIS FI09/00312, Severo Ochoa Program SEV-2012-0267), the Carlos III Institute of Health (Grant RIRAAF, RETICS Program RD12/0013/0009), and the Generalitat Valenciana (Prometeo II/2013/005) are gratefully acknowledged for financial support. Dr. A. Vidal-Moya is acknowledged for his help with the EPR measurements.Nardi, G.; Manet, I.; Monti, S.; Miranda Alonso, MÁ.; Lhiaubet-Vallet, V. (2014). Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer. Free Radical Biology and Medicine. 77:64-70. https://doi.org/10.1016/j.freeradbiomed.2014.08.020S64707

Polymorph Separation by Ordered Patterning

We herein address the problem of polymorph selection by introducing a general and straightforward concept based on their ordering. We demonstrated the concept by the ordered patterning of four compounds capable of forming different polymorphs when deposited on technologically relevant surfaces. Our approach exploits the fact that, when the growth of a crystalline material is confined within sufficiently small cavities, only one of the possible polymorphs is generated. We verify our method by utilizing several model compounds to fabricate micrometric "logic patterns" in which each of the printed pixels is easily identifiable as comprising only one polymorph and can be individually accessed for further operations

Control of polymorphism in thiophene derivatives by sublimation-aided nanostructuring

Here we applied the concept of "sublimation-aided nanostructuring" to control the polymorphism of a model material

Cellulose Acetate Fabrics Loaded with Rhodamine B Hydrazide for Optical Detection of Cu(II)

In this work, different materials were fabricated from cellulose acetate, loaded with rhodamine B hydrazide and tested as Cu(II) optical sensor. We prepared membranes displaying a sub-micron porous structure using the phase inversion technique, clusters of fibers with varying diameter depending on the preparation procedure using electrospinning, and casted films presenting a smooth non porous structure. Loading of rhodamine B hydrazide on the fabrics after their production was found to be the best procedure to ensure the stability of the dye in the polymeric materials. Absorption and emission analysis of the solid substrates revealed the presence of the dye on the porous fabrics and allowed to choose the most suited materials and loading conditions to test their response towards Cu(II) ions. Reaction of the loaded rhodamine B hydrazide with Cu(II) was confirmed by absorption and emission spectroscopies and by confocal fluorescence imaging, through detection of the product rhodamine B. The results point to promising sensing applications of the prepared composite materials

Water-Soluble Naphthalene Diimides as Singlet Oxygen Sensitizers

Bromo- and alkylamino-substituted and hydrosoluble naphthalene diimides (NDIs) were synthesized to study their multimodal photophysical and photochemical properties. Bromine-containing NDIs (i.e., 11) behaved as both singlet oxygen photosensitizers and fluorescent molecules upon irradiation at 532 nm. Among the NDIs not containing Br, only 12 exhibited photophysical properties similar to those of Br-NDIs, by irradiation above 610 nm, suggesting that for these NDIs both singlet and triplet excited-state properties are strongly affected by length, structure of the solubilizing moieties, and pH of the solution. Laser flash photolysis confirmed that the NDI lowest triplet excited state was efficiently populated, upon excitation at both 355 and 532 nm, and that free amine moieties quenched both the singlet and triplet excited states by intramolecular electron transfer, with generation of detectable radical anions. Time-resolved experiments, monitoring the 1270 nm 1O2 phosphorescence decay generated upon laser irradiation at 532 nm, allowed a ranking of the NDIs as sensitizers, based on their sinlet oxygen quantum yields (ΦΔ). The tetrafunctionalized NDI 12, exhibiting a long-lived triplet state (τ 32 μs) and the most promising absorptivity for photodynamic therapy application, was tested as efficient photosensitizers in the photo-oxidations of 1,5-dihydroxynaphthalene and 9,10-anthracenedipropionic acid in acetonitrile and water

PHEEL: photonics in biological and environmental applications

<p>In 2023, the Italian National Research Council (<strong>CNR</strong>) celebrated 100 years from its fundation (website: https://centenario.cnr.it/evento/porte-aperte-allarea-della-ricerca-di-bologna/). On October 27th, at the Research Area of Bologna, an event open to general public took place in order to present the main CNR activities (program: https://area-new.bo.cnr.it/wp-content/uploads/2023/10/Programma-100-CNR-Bologna.pdf).</p><p>The "<i>Photonics for Health, Energy & Environmental Laboratory</i>" (<strong>PHEEL</strong>) group of the Institute of Organic Synthesis and Photoreactivity (<strong>ISOF</strong>),  proposed a series of activities and materials in order to present their main research topics and focus, especially the most recent Europe-funded projects.</p><p> </p><p> </p&gt

Photosensitized oxidation of sulfides: discriminating between the singlet-oxygen mechanism and electron transfer involving superoxide anion or molecular oxygen

The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ+), and triphenylpyrylium tetrafluoroborate (TPP+) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroethane

PHEEL: photonics in biological and enviromental applications

<p>In 2023, the Italian National Research Council (<strong>CNR</strong>) celebrated 100 years from its fundation (website: https://centenario.cnr.it/evento/porte-aperte-allarea-della-ricerca-di-bologna/). On October 27th, at the Research Area of Bologna, an event open to general public took place in order to present the main CNR activities (program: https://area-new.bo.cnr.it/wp-content/uploads/2023/10/Programma-100-CNR-Bologna.pdf).</p><p>The "<i>Photonics for Health, Energy & Environmental Laboratory</i>" (<strong>PHEEL</strong>) group of the Institute of Organic Synthesis and Photoreactivity (<strong>ISOF</strong>),  proposed a series of activities and materials in order to present their main research topics and focus, especially the most recent Europe-funded projects.</p><p> </p><p> </p&gt