Synthesis, Crystal Structure, and Broadband Emission of (CH3)3SSnCl3.

We report here on the synthesis, crystal structure, optoelectronic and vibrational properties, as well as the DFT calculations of the novel trimethylsulfonium tin trichloride (CH3)3SSnCl3. The air-stable compound is prepared by reacting the (CH3)3SCl and SnCl2 solid precursors in evacuated silica tubes at 100 °C. According to powder X-ray diffraction and Rietveld refinement, it crystallizes at room temperature in the orthorhombic space group Pbca (No. 61) with isolated pyramids of [SnCl3]- and (CH3)3S+ units. UV-vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 3.85 eV, accompanied by a broad Stokes-shifted luminescence signal. Photoexcitation of the compound at room temperature and at -196 °C results in broadband luminescence with weak magenta emission centered at 400 nm using an excitation at 250 nm. First principal calculations provide insight into the physical properties through the electron and phonon density of states. Multitemperature Raman spectroscopy and differential scanning calorimetry reveal a reversible phase transition at ca. 70 °C that affects the vibrational modes of the [SnCl3]-. By dissolving (CH3)3SSnCl3 in dimethylformamide in ambient air for a week, oxidation of tin occurs in the "defect" perovskite ((CH3)3S)2SnCl6. The crystal structure of ((CH3)3S)2SnCl6 is also determined with high accuracy via single-crystal X-ray diffraction (cubic space group Pa-3 (No. 205)) and compared with (CH3)3SSnCl3 via Hirshfeld surface analysis.

Trimethylsulfonium Lead Triiodide: An Air-Stable Hybrid Halide Perovskite.

We report on the synthesis, characterization, and optoelectronic properties of the novel trimethylsulfonium lead triiodide perovskite, (CH3)3SPbI3. At room temperature, the air-stable compound adopts a hexagonal crystal structure with a 1D network of face-sharing [PbI6] octahedra along the c axis. UV-vis reflectance spectroscopy on a pressed pellet revealed a band gap of 3.1 eV, in agreement with first-principles calculations, which show a small separation between direct and indirect band gaps. Electrical resistivity measurements on single crystals indicated that the compound behaves as a semiconductor. According to multi-temperature single-crystal X-ray diffraction, synchrotron powder X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry, two fully reversible structural phase transitions occur at -5 and ca. -100 °C with reduction of the unit cell symmetry to monoclinic as temperature decreases. The role of the trimethylsulfonium cation regarding the chemical stability and optoelectronic properties of the new compound is discussed in comparison with APbI3 (A = Cs, methylammonium, and formamidinium cation), which are most commonly used in perovskite solar cells.

Mechanisms of diphylline release from dual-solute loaded poly(vinyl alcohol) matrices.

The release kinetics of the model hydrophilic drug, diphylline (DPL), from physically crosslinked poly(vinyl alcohol) (PVA) matrices, is studied in relation to the drug load and the presence of a second solute incorporated in the matrix. The second solute, a gadolinium (III) complex (Gd-DTPA), is a commonly used MRI contrast agent. The water uptake kinetics by the glassy PVA matrix was found to deviate from t(1/2) law and to occur on time scales comparable to those of diphylline release. The corresponding rate of diphylline release was found to be substantially stabilized as compared to a purely diffusion-controlled release process, in line with theoretical predictions under conditions of relaxation-controlled water uptake kinetics. The release rate of DPL was found (i) to increase with increasing DPL load and (ii) for a particular DPL load, to increase in the presence of Gd-DTPA, incorporated in the matrix. The results were interpreted on the basis of the diphylline-induced plasticization of the polymer (evidenced by the depression of Tg) and of the excess hydration of the matrix at high solute loads. The latter effect was found to be additive in the case of dual-solute loaded matrices.

Hydrophilic modification of silicone elastomer films: thermal, mechanical and theophylline permeability properties.

The improvement of the hydrophilicity of silicone rubber (SR) is sought in many biomedical applications. In the present work, we have prepared neat films coming from condensation-type SR, modified either through blending or end-linking reaction with low molecular weight poly(ethylene glycol) (PEG). The films were studied with respect to their water uptake capacity, stability of embedment of ethylenoxy moieties, and mechanical and thermal properties. Subsequently, we prepared drug-loaded films with theophylline, a relatively hydrophilic model drug, and studied the release performance of these systems. Results on neat films showed that blending increases significantly the overall water uptake of the films and, at the same time, has a limited detrimental effect on their mechanical properties. On the other hand, end-linked films loaded with theophylline exhibited better rate-controlling properties in vitro, due to better dispersion of the sorbed water.

Device and materials for in vitro evaluation of forces developed to teeth and periodontal structures during dental practices.

This study aimed at providing a gauge device (Ekontak et al Gauge K-Device) in order to analyze the forces applied to teeth and periodontal tissues during dental practices in vitro. This force gauge device can be used in the investigation of the possible defect generation to tooth structures when overloaded forces are applied during dental procedures in vitro. Ekontak et al Gauge K-Device consists of three units: the specimen's holder, a high-performance digital force gauge, and the support frame. The holder was fabricated by an Al alloy providing a steady detachable attachment between the specimens and the force gauge's pin connector. The clinical simulation was achieved with the use of a proper silicone material, selected to provide similar elastic behavior with the human periodontal ligament and to join the teeth inside a solid matrix of an acrylic resin. The digital force gauge is a high-speed collection and recording (1000 Hz) product coupled with data recording software. The forces developed to 15 specimens' root canals during lateral condensation and vertical compaction of cold gutta-percha obturation procedures were monitored, saved as graphs, CSV, and excel files and presented over time. The forces developed during vertical compaction (mean maximum force per obturation circle = 13.22 N) were more excessive than those during lateral condensation (mean maximum force per obturation circle = 10.14 N). In conclusion, Ekontak et al Gauge K-Device is provided as a modern gauge device, capable of performing clinical simulation in vitro, under the terms of its protocol.

Proxyphylline release kinetics from symmetrical three-layer silicone rubber matrices: effect of different excipients in the outer rate-controlling layers.

In this work we present results on the release kinetics of a water-soluble model drug (proxyphylline) from symmetrical three-layer ABA matrices made from silicone rubber. The ABA matrices, consisting of an inner drug-containing layer, loaded at concentration near the percolation threshold, and two drug-free outer layers, were studied with respect to (a) the varying permeability properties of the outer layers achieved by the incorporation of either poly(ethylene glycol), a hydrophilic polymeric excipient, or NaCl, an inorganic salt with high osmotic action, and (b) the relative thickness of the inner to outer layers. In all cases, substantial uniformity of release rate was achieved and the initial burst effect, characterizing the corresponding single-layer system, was suppressed. The results are interpreted on the basis of the permeation mechanisms operating in each individual inner and outer layer. Thus, we have demonstrated that by judicious choice of the composition and relative thickness parameters the release rate can be adjusted to any desired level. Finally, the case of the NaCl excipient, released parallel to proxyphylline, serves as an example of a dual-drug releasing system.

Higuchi's equation and beyond: overview of the formulation and application of a generalized model of drug release from polymeric matrices.

An account is presented of modeling and experimental work, which complements, in many useful ways, the excellent coverage, afforded by a recent dedicated issue edited by Siepmann and Peppas (Int. J. Pharm. 2011, 418(1)), of the theoretical background and many ramifications, as well as practical applications, of the Higuchi equation. The main notable feature of the said modeling work is formulation and successful practical application, of an ab initio generalized approach, based on solving the fundamental transport equations applicable to the operation of typical matrix-controlled release (MCR) devices. This approach (i) reduces to the Higuchi equation under the pertinent restrictive conditions but can duly handle most of its more complex ramifications and (ii) can be parameterized (by the use of appropriate data from the literature or from independent experiments) to adapt itself to the physics of the particular matrix-solvent-solute system under consideration; as demonstrated here with examples from our laboratory or from the literature. A distinctive feature of the experimental work is the extensive use of simpler "model" MCR systems, chosen so as to promote better understanding of the effect of various physicochemical parameters and mechanisms on drug MCR rate and kinetics. A concept of MCR device efficiency is also discussed.

Regulation of proxyphylline's release from silicone rubber matrices by the use of osmotically active excipients and a multi-layer system.

In this work we present results on the modification of the release kinetics of a water-soluble model drug (proxyphylline) from silicone rubber (SR) matrices by either: (i) the incorporation of inorganic salts acting as osmotically active excipients in single-layer matrices, containing a uniform concentration of proxyphylline or (ii) by the use of three-layer matrices with distributed proxyphylline load. In relation to (i) our data show that the incorporation of inorganic salts, of varying water solubilities and in different initial loads, accelerated the release of proxyphylline and helped to the stabilization of its declining release rate. Drug release kinetics is supplemented by measurements of concurrent water uptake, and salt release, kinetics. In addition, in order to further investigate the release mechanisms of the drug and the salts, we studied the diffusion and sorption properties of the depleted polymeric matrix along with the morphology and the mechanical properties of the matrices either in the presence or after the depletion of the solutes. The combined information, derived from these techniques, supports a drug release mechanism occurring through an excessively swollen polymer matrix and accelerated by the formation of microscopic cracks generated by the osmotically active excipients. In relation to (ii) we studied a multi-layer device with proxyphylline-loaded inner layer and drug-free outer layers which practically diminished the initial burst effect and allowed the release of about 60% of the drug at a constant rate.

Study of leaching mechanisms of caesium ions incorporated in Ordinary Portland Cement.

In this work, a study of the leaching kinetics of Cs(+) ions from cement paste solids, containing inactive Cs(2)SO(4), is presented, involving (i) the parallel performance of leaching experiments at two temperatures (30 degrees C and 70 degrees C); (ii) the performance of leaching tests with intermediate changes in temperature between 30 degrees C and 70 degrees C; (iii) the use of specimens of two different thicknesses and (iv) the determination of the distribution of Cs(+) in the cement specimen at various stages of the leaching test. The results of leaching studies at 30 degrees C with cement solids simulating the composition of real radioactive wastes, containing NaNO(3), small amounts of inactive CsNO(3) and traces of (137)Cs(+) are also reported. Concentration profiles of Cs(+) in inactive specimens showed that part of the Cs(+) (20-30%) tends to be immobilized in the matrix, while elution of the readily leachable portion follows Fick's law reasonably well. No immobilized Cs(+) was detected in the samples containing considerable amounts of NaNO(3). Long-term leaching experiments (up to 8 years) revealed acceleration of the elution process (not detectable in short-term tests), attributable to increase in porosity caused by erosion of the cement matrix. Sorption experiments of Cs(+) ions by cement granules indicated that adsorption on cement pore surfaces is not significant. On the other hand, the leaching tests at two different temperatures or with intermediate changes in temperature between 30 degrees C and 70 degrees C, yielded activation energies that indicated a more complicated kinetic behavior.