Residence time of singlet oxygen in membranes

Photodynamic therapy uses photosensitizers (PS) to kill cancer cells by generating reactive oxygen species like singlet oxygen (SO) - upon illumination with visible light. PS membrane anchoring augments local SO concentration, which in turn increases photodynamic efficiency. The latter may suffer from SOs escape into the aqueous solution or premature quenching. Here we determined the time constants of SO escape and quenching by target molecules to be in the nanosecond range, the former being threefold longer. We confined PS and dipolar target molecules either to different membrane monolayers or to the same leaflet and assessed their abundance by fluorescence correlation spectroscopy or membrane surface potential measurements. The rate at which the contribution of the dipolar target molecules to membrane dipole potential vanished, served as a measure of the photo-oxidation rate. The solution of the reactiondiffusion equations did not indicate diffusional rate limitations. Nevertheless, reducing the PS-target distance increased photodynamic efficiency by preventing other SO susceptible moieties from protecting the target. Importantly, our analytical model revealed a fourfold difference between SO generation rates per molecule of the two used PSs. Such analysis of PS quantum yield in a membrane environment may help in designing better PSs.14-13-01373P(VLID)341513

Heteroleptic Crown-Substituted Tris(phthalocyaninates) as Dynamic Supramolecular Scaffolds with Switchable Rotational States and Tunable Magnetic Properties

Herein we report single-crystal X-ray diffraction characterization and complementary solution studies of supramolecular interaction between potassium salts and heteroleptic homo- and heteronuclear triple-decker crown phthalocyaninates [(15C5)4Pc]M*[(15C5)4Pc]M(Pc) or [M*,M], where M∗ and M = Y and/or Tb. Our results evidence that, in contrast to the previously studied crown-substituted phthalocyanines, the interaction of K+ cations with [M*,M] does not induce their intermolecular aggregation. Instead, the cations reversibly intercalate between the crown-substituted phthalocyanine ligands, resulting in switching of the coordination polyhedron of the metal center M∗ from square-antiprismatic to square-prismatic. In the case of terbium(III) complexes, such a switching alters their magnetic properties, which can be read-out by 1H NMR spectroscopy. For [Tb*,Y], such a switching causes an almost 25% increase in the axial component of the magnetic susceptibility tensor. Even though the polyhedron of the paramagnetic center in [Y*,Tb] is not switched, minor structural perturbations associated with the overall reorganization of the receptor also cause smaller, but nevertheless appreciable, growth of the axial anisotropy. The observed effects render the studied complexes as molecular switches with tunable magnetic properties.

Functional supramolecular systems: Design and applications

The interest in functional supramolecular systems for the design of innovative materials and technologies, able to fundamentally change the world, is growing at a high pace. The huge array of publications that appeared in recent years in the global literature calls for systematization of the structural trends inherent in the formation of these systems revealed at different molecular platforms and practically useful properties they exhibit. The attention is concentrated on the topics related to functional supramolecular systems that are actively explored in institutes and universities of Russia in the last 10-15 years, such as the chemistry of host-guest complexes, crystal engineering, self-assembly and self-organization in solutions and at interfaces, biomimetics and molecular machines and devices