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J. Hynek, P. Brázda, J. Rohlíček, M. G. S. Londesborough, J. Demel, Phosphinic Acid Based Linkers: Building Blocks in Metal-Organic Framework Chemistry. Angew.Chem.Int.Ed. 2018, 57, 5016–5019.

Abstract: Metal–organic frameworks (MOFs) are a chemically and topologically diverse family of materials composed of inorganic nodes and organic linkers bound together by coordination bonds. Presented here are two significant innovations in this field. The first is the use of a new coordination group, phenylene1,4bis(methylphosphinic acid) (PBPA), a phosphinic acid analogue of the commonly used terephtalic acid. Use of this new linker group leads to the formation of a hydrothermally stable and permanently porous MOF structure. The second innovation is the application of electrondiffraction tomography, coupled with dynamic refinement of the EDT data, to the elucidation of the structure of the new material, including the localization of hydrogen atoms.

K. Kirakci, P. Kubát, K. Fejfarová, J. Martinčík, M. Nikl, K. Lang, X-ray-Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators. Inorg. Chem. 2016, 5, 803−809.

Abstract: Newly synthesized octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OOC-1-adamantane)6] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O2(1g). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV-Vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O2(1Δg) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV-Vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O2(1g) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O2(1g). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy.

J. Hynek, J. Zelenka, J. Rathouský, P. Kubát, T. Ruml, J. Demel, K. Lang: Designing Porphyrinic Covalent Organic Frameworks for the Photodynamic Inactivation of Bacteria. ACS Appl. Mater. Interfaces 2018, 10, 8527−8535.

Abstract: Microbial colonization of biomedical devices is a recognized complication contributing to healthcare-associated infections. One of the possible approaches to prevent surfaces from the biofilm formation is antimicrobial photodynamic inactivation, based on the cytotoxic effect of singlet oxygen, O2(1g), a short-lived, highly oxidative species, produced by energy transfer between excited photosensitizers and molecular oxygen. We synthesized porphyrin-based covalent organic frameworks (COFs) by the Schiff-base chemistry. These novel COFs have a three-dimensional, diamond-like structure. The detailed analysis of their photophysical and photochemical properties shows that the COFs effectively produce O2(1g) under visible light irradiation and, especially three-dimensional structures, have strong antibacterial effects towards Pseudomonas aeruginosa and Enterococcus faecalis biofilms. The COFs exhibit high photostability and broad spectral efficiency. Hence, the porphyrinic COFs are suitable candidates for the design of antibacterial coating for in-door applications.

L. Cerdán, J. Braborec, I. Garcia-Moreno, A. Costela, M. G. S. Londesborough, A Borane Laser. Nature Commun. 2015, 6, 5958.

Abstract: Emission from electronically excited species forms the basis for an important class of light sources—lasers. So far, commercially available solution-processed blue-emitting laser materials are based on organic compounds or semiconductor nanocrystals that have significant limitations: either low solubility, low chemical- and/or photo-stability and/or uncompetitive prices. Here we report a novel and competitive alternative to these existing laser materials that is based on boron hydrides, inorganic cluster compounds with a rich and diverse chemistry. We demonstrate that solutions of the borane anti-B18H22 show, under pulsed excitation, blue laser emission at 406 nm with an efficiency (ratio of output/input energies) of 9.5%, and a photostability superior to many of the commercially available state-of-the-art blue laser dyes. This demonstration opens the doors for the development of a whole new class of laser materials based on a previously untapped resource for laser technology—the boranes.

M. G. S. Londesborough, D. Hnyk, J. Bould, L. Serrano-Andrés, V. Sauri, J. M. Oliva, P. Kubát, T. Polívka, K. Lang, Distinct Photophysics of the Isomers of B18H22 Explained. Inorg. Chem. 2012, 51 1471−1479.

Abstract: The photophysics of the two isomers of octadecaborane(22), anti- and syn-B18H22, have been studied by UV-vis spectroscopic techniques and theoretical computational methods. In air-saturated hexane, anti-B18H22 shows fluorescence with a high quantum yield, ΦF = 0.97, and singlet oxygen O2(1Δg) production (ΦΔ  0.008). Conversely, isomer syn-B18H22 shows no measurable fluorescence, instead displaying much faster, picosecond nonradiative decay of excited singlet states. Computed potential energy hypersurfaces (PEHs) for both isomers rationalize these data, pointing to a deep S1 minimum for anti-B18H22 and a conical intersection (CI) between its S0 and S1 states that lies 0.51 eV higher in energy. Such an energy barrier to nonradiative relaxation is not present in the PEH of syn-B18H22, and the system therefore has sufficient initial energy on excitation to reach the (S0/S1) CI and to then decay to the ground state without fluorescence. The computational analysis of the geometries at stationary points along the PEH of both isomers shows that the determining factor for the dissimilar photophysics of anti- and syn-B18H22 may be due to the significant differences in the geometrical rearrangements at their respective conical intersections. Thus, the syn isomer shows one very large, B-B elongation of 1.2 Å from 1.8 Å in the ground state to 3.0 Å at the CI, whereas the anti isomer shows smaller elongations (below 1 Å) in several B-B connectivities at its (S0/S1)CI. The absorbed energy in S 1 for the anti-B18H22 is therefore redistributed vibrationally into several regions of the molecule rather than almost completely into a single vibrational mode as in the case for the syn isomer. The consequent prolonged S 1 lifetime for the anti isomer allows for relaxation via fluorescence.

V. Štengl, S. Bakardjieva, N. Murafa, Preparation and Photocatalytic Activity of Rare Earth Doped TiO2 Nanoparticles. Materials Chemistry and Physics 2009, 114, 217-226.

Abstract: A one-step, a one-pot, no post-synthesis calcination and no sol-gel synthesis was used for preparation of rare earth doped visible-light sensitive titania. This method is easy transferable to industrial conditions, is ecologically friendly and makes it possible to produce a low-cost photocatalytic pigment. The products were characterized by all common techniques (X-ray diffraction (XRD), BET and porosity, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), UV/VIS spectra). The photocatalytic activity of the prepared samples was assessed by the photocatalytic decomposition of Orange II dye in aqueous slurry under irradiation of 254, 365 and 400 nm wavelength. The rare earth (La, Ce, Pr, Nd, Sm, Eu, Dy, Gd) for doped titania were used, the best photocatalytic properties in visible light have samples doped with Nd3+ ions (k = 0.0272 min-1 for UV and 0.0143 min-1 for visible light).

T. Baše, Z. Bastl, Z. Plzák, T. Grygar, J. Plešek, M. J. Carr, V. Malina, J. Šubrt, J. Boháček, E. Večerníková, O. Kříž, Carboranethiol-Modified Gold Surfaces. A Study and Comparison of Modified Cluster and Flat Surfaces. Langmuir 2005, 21, 7776-7785.

Abstract: Four different carboranethiol derivatives were used to modify the surfaces of gold nanoparticles and flat gold films. The novel materials engendered from these modifications are extraordinarily stable species with surfaces that support self-assembled monolayers of 1-(HS)-1,2-C2B10H11, 1,2-(HS)2-1,2-C2B10H10, 1,-12-(HS)2-1,12-C2B10H10, and 9,12-(HS)2-1,2-C2B10H10, respectively. Surprisingly, characterization of these materials revealed that a number of molecules of the carboranethiol derivatives are incorporated inside the nanoparticles. This structural feature was studied using a number of techniques, including X-ray photoelectron spectroscopy (XPS), UV-vis, and IR spectroscopies. Thermal desorption experiments show that carborane molecules detach and leave the nanoparticle surface mostly as 1,2-C2B10H10 isotopic clusters, leaving sulfur atoms bound to the gold surface. The surfaces of both the gold nanoparticles and the flat gold films are densely packed with carboranethiolate units. One carborane cluster molecule occupies an area of six to seven surface gold atoms of the nanoparticle and eight surface gold atoms of the flat film. XPS data showed that molecules of 1,12-(HS)2-1,12-C2B10H10 bind to the flat gold surface with only half of the thiol groups due to the steric demands of the icosahedral carborane skeleton. Electrochemical measurements indicate complete coverage of the modified gold surfaces with the carboranethiol molecules.

K. Lang, J. Mosinger, D. M. Wagnerová, Photophysical Properties of Porphyrinoid Sensitizers Noncovalently Bound to Host Molecules; Models for Photodynamic Therapy. Coord. Chem. Rev. 2004, 248, 321-350.

Abstract: The binding of photosensitizers to host molecules is discussed from the perspective of how the confinement in a molecular assembly influences the sensitizer’s photophysical properties. In connection with photodynamic therapy (PDT) of cancer during which the administered sensitizer necessarily interacts with the biological material the problem becomes of utmost importance. This review surveys changes of photophysical behaviour of porphyrins, metalloporphyrins and other porphyrinoid sensitizers induced by their interaction with biopolymers (proteins, nucleic acids), liposomes or synthetic sensitizer carriers (cyclodextrins, calixarenes). The structure, charge, and physicochemical properties of the sensitizer predetermine the type of interaction with the surrounding microenvironment and are manifested by changes in absorption, fluorescence, kinetics of deactivation of the excited states, and generation of singlet oxygen. As follows from the collected data, binding of the sensitizer does not restrict formation of the excited states but influences the kinetics. Various consequences of binding on the form and photophysical parameters of the sensitizers are discussed and general features of the mutual interaction are outlined.

D. Hradil, T. Grygar, T; J. Hradilová, P. Bezdička, Clay and Iron Oxide Pigments in the History of Painting. Appl. Clay Sci. 2003, 22, 223-236.

Abstract: Clay minerals and iron oxides are intimately related in the process of their natural formation. Their mineralogical composition and physical properties correspond to the physical-chemical conditions of weathering, sedimentation and alteration processes by means of which these minerals are associated giving different types of laterites, ferrolites, ochres, and coloured clays and soils. Very early in human history, these and other clay materials were adopted as mineral pigments. Their structural and mineralogical features are directly related with their natural genesis and provenance and help us in the study of historical painting techniques and materials. This paper gives general information about geological sources and their characteristics, the literary evidence of use of different forms of earthy pigments on historical paintings, about analytical methods suitable in their identification within the ground and colour layers of the painting, and handling with the samples of works of art. The examples focused preferentially on the period of European mediaeval and baroque painting.

B. Štíbr, Carboranes other than C2B10H12. Chem. Rev. 1992, 92, 225-250.

The author hopes that not only will boron cluster chemists find in this review, in conjunction with otherreviews of this issue, basic synthetic and structural interrelations intrinsic to carborane species but also some inspiration for their work.

J. Plešek, Potential Applications of the Boron Cluster Compounds. Chem. Rev. 1992, 92, 269-278.

Deltahedral boron derivatives are and always will be quite expensive substances. Any reasonable applications may be expected to occur only in exclusive areas where no other compounds compete. Thus, applications involving only minute quantities of deltahedral species or processes permitting complete recycling will have to be developed. Catalytic effects, BNCT, optical and electrochemical applications, as well as solvent extraction of valuable cations seem to be in accord with this strategy. The author predicts increasing biochemical and medicinal applications using deltahedral clusters even though, with the exception of the impressive BNCT concept, so far no systematic study of their basic biochemical properties has been published – even toxicity studies are scarce. The same is true for biochemically active organic species modified by deltahedral boranes. Fundamental research on deltahedral borane derivatives opened a wide access to specifically tailored substances but now the time is ripe for exploitation of the accumulated knowledge. Hopefully, this review will be the inspiration for scientists to enter this exciting and challenging area of chemistry.