Photon momentum transfer at water/air interfaces under total internal reflection

The transfer of photon momentum at the water/air interface is important for optical manipulation of minute particles and is at the heart of the Minkowski–Abraham controversy.Weuse photoacoustic (PA) detection of ultrasound waves generated when pulsed laser light meets the water/air interface at 3.9 °C(zero thermal expansion), to distinguish momentum transfer from thermoelastic effects. The PA waves dependence on the angle of incidence reveals that momentum transfer maximizes at the critical angle. Momentum transfer is most efficient when the photons travel in water and remain in water after total reflection at the interface, rather than when they cross the interface between dielectric media

The challenging combination of intense fluorescence and high singlet oxygen quantum yield in photostable chlorins : a contribution to theranostics

High fl uorescence quantum yields, high singlet oxygen quantum yields and intense absorptions in the phototherapeutic window are fundamental properties for compounds intended for fl uorescence diagno- sis and photodynamic therapy. We report on photostable chlorins that combine these properties. The fl uorinated tetraphenylchlorin FCMet has Φ F = 0.396 and Φ Δ = 0.58 ± 0.07, whereas F 2 CMet has Φ F = 0.360 and Φ Δ = 0.54 ± 0.05, and both have molar absorption coe ffi cients larger than 30000 M − 1 cm − 1 above 650 nm. These dual functional agents use nearly all the energy absorbed to perform the desired functions and are appropriate for theranostics applications

A Preuniversity Initiative to Motivate Students to Pursue Chemistry Higher Education

Molecular School (MS) is an extracurricular initiative intended to show relevant and complex concepts of chemical sciences to precollege students. The main goal is to motivate the participants to expand their awareness of chemical sciences and to acknowledge its relevance in everyday life, in order to stimulate the students to engage in chemistry undergraduate degrees. Here, we address the successful case of MS, implemented in Portugal, where recently, the universities have been facing significant difficulties in attracting new students to join chemistry-related courses. We report the first three editions of this free of cost preuniversity school, whose main subject is chemistry. All editions were held in the University of Coimbra, Portugal, and organized by PhD students of the department of chemistry of this institution. The three editions are discussed here, with particular focus on the last edition. Several participants ultimately chose chemistry BSc degrees to continue their education, which substantiates the positive outreach of this initiative. We believe MS can be replicated, adapted, and improved in other contexts and countries to increase the number of students enrolling chemistry university degrees

Antibacterial Photodynamic Inactivation of Antibiotic-Resistant Bacteria and Biofilms with Nanomolar Photosensitizer Concentrations

Gram-negative bacteria and bacteria in biofilms are very difficult to eradicate and are the most antibiotic-resistant bacteria. Therapeutic alternatives less susceptible to mechanisms of resistance are urgently needed to respond to an alarming increase of resistant nosocomial infections. Antibacterial photodynamic inactivation (PDI) generates oxidative stress that triggers multiple cell death mechanisms that are more difficult to counteract by bacteria. We explore PDI of multidrug-resistant bacterial strains collected from patients and show how positive charge distribution in the photosensitizer drug impacts the efficacy of inactivation. We demonstrate the relevance of size for drug diffusion in biofilms. The designed meso-imidazolyl porphyrins of small size with positive charges surrounding the macrocycle enabled the inactivation of bacteria in biofilms by 6.9 log units at 5 nM photosensitizer concentration and 5 J cm-2, which offers new opportunities to treat biofilm infections