Glass-forming Compounds Research Articles

Chemical model of binary molybdenum phosphate glasses

The influence of molybdenum on the actual chemical composition of phosphate glasses prepared in the range of the batch compositions from ultraphosphate to pyrophosphate was studied. An analysis of the glasses by XRF, ESR and 31P MAS NMR, supplemented by Raman spectroscopy, showed that the chemical composition of the ultraphosphate glass shifted significantly to the metaphosphate region of divalent cations, leading to very stable glass. The chemical composition of the remaining glasses also shifted towards a lower phosphorus content, i.e., to pyrophosphates, but their chemical composition remained in the area between metaphosphates and pyrophosphates of divalent cation. A chemical model was designed for all the glasses, the main glass-forming compounds were determined and the result was successfully confronted with the compositional dependences of both the glass transition temperature and the coefficient of thermal expansion.

Soft Dynamic Confinement of Membrane Proteins by Dehydrated Trehalose Matrices: High-Field EPR and Fast-Laser Studies

In memory of the 85th birthday of Yakov S. Lebedev (Moscow), who died in 1996, we start this Review on soft-glass matrix effects in donor–acceptor complexes with an appreciation of his pioneering work on high-field EPR spectroscopy on tribochemically generated donor–acceptor complexes. The mechanochemical activation of polycrystalline mixtures of porphyrins (and other donors) and quinone acceptors was found to produce large concentrations of triplet donor molecules and donor–acceptor radical pairs with unusual stability. The Review is continued with reporting on W-band high-field EPR and fast-laser studies on disaccharide matrix effects on structure and dynamics of donor–acceptor protein complexes related to photosynthesis, including the non-oxygenic bacterial reaction center (RC) and the oxygenic RCs Photosystem I (PS I) and Photosystem II (PS II, preliminary results). Some organisms can survive complete dehydration and high temperatures by adopting an anhydrobiotic state in which the intracellular medium contains large amounts of disaccharides, in particular trehalose and sucrose. Trehalose is most effective in protecting biostructures, both in vivo and in vitro. To clarify the molecular mechanisms of disaccharide bioprotection, structure and dynamics of sucrose and trehalose matrices at different controlled hydration levels were probed by perdeuterated nitroxide spin labels and native cofactor intermediates in their charge-separated states. Trehalose forms a homogeneous amorphous phase in which the hosted molecules are uniformly distributed. Notably, their rotational mobility at room temperature is dramatically impaired by the trehalose H-bonding network confinement to an extent that in normal protein–matrix systems is only observed at low temperatures around 150 K. From the experimental results, formation of an extended H-bonding network of trehalose with protein molecules is inferred, involving both bulk and local water molecules. The H-bond network extends homogeneously over the whole matrix integrating and immobilizing the hosted protein. Taken together, these observations suggest that in photosystems, such as bacterial RCs and PS I complexes, of different size and complexity regarding subunit composition and oligomeric organization, the molecular configuration of the cofactors involved in the primary processes of charge separation is not significantly distorted by incorporation into trehalose glass, even under extensive dehydration. By means of pulsed W-band high-field multiresonance EPR spectroscopies, such as ELDOR-detected NMR and ENDOR, in conjunction with using isotope labeled water (D2O and H217O), the biologically important issue of sensing and quantification of local water in proteins is addressed. The bacterial RC embedded into the trehalose glass matrix is used as model system. The two native radical cofactor ions of the primary electron donor and acceptor as well as an artificial nitroxide spin label site-specifically attached to the protein surface are studied in the experiments. The three paramagnetic reporter groups probe distinctly different local environments. They sense water molecules via their magnetic hyperfine and quadrupole interactions with either deuterons or 17O nuclei. It is shown that by using oxygen-17 labeled water, quantitative conclusions can be drawn differentiating between local and bulk water. It is concluded that dry trehalose operates as anhydrobiotic protein stabilizer by means of selective changes in the first solvation shell of the protein upon trehalose–matrix dehydration with subsequent changes in the hydrogen-bonding network. Such changes usually have an impact on the global function of a biological system. Finally, preliminary results of optical and W-band EPR experiments on the extremolytes ectoine and its derivative hydroxyectoine are reported; these compounds appear to share several stress-protecting properties with trehalose in terms of stabilizing protein matrices. For instance, they display remarkable stabilizing capabilities towards sensitive proteins and enzymes with respect to freeze-thawing, heat-treatment, and freeze-drying procedures. Moreover, hydroxyectoine is a good glass-forming compound and exhibits a remarkable bioprotective effect against desiccation and heat denaturation of functional protein complexes.

Синтез и колебательные спектры стеклообразующих полупроводниковых соединений TlAsS2 и TlAsSe2

Синтез и колебательные спектры стеклообразующих полупроводниковых соединений TlAsS2 и TlAsSe2

Taking Advantage of Disorder: Small-Molecule Organic Glasses for Radiation Detection and Particle Discrimination.

A series of fluorescent silyl-fluorene molecules were synthesized and studied with respect to their photophysical properties and response toward ionizing neutron and gamma-ray radiation. Optically transparent and stable organic glasses were prepared from these materials using a bulk melt-casting procedure. The prepared organic glass monoliths provided fluorescence quantum yields and radiation detection properties exceeding the highest-performing benchmark materials such as solution-grown trans-stilbene crystals. Co-melts based on blends of two different glass-forming compounds were prepared with the goal of enhancing the stability of the amorphous state. Accelerated aging experiments on co-melt mixtures ranging from 0% to 100% of each component indicated improved resistance to recrystallization in the glass blends, able to remain fully amorphous for >1 month at 60 °C. Secondary dopants comprising singlet fluorophores or iridium organometallic compounds provided further improved detection efficiency, as evaluated by light yield and neutron/gamma particle discrimination measurements. Optimized singlet and triplet doping levels were determined to be 0.05 wt % 1,4-bis(2-methylstyryl)benzene singlet fluorophore and 0.28 wt % Ir3+, respectively.

Photoinduction of spontaneous surface relief gratings on Azo DR1 glass.

Surface relief gratings were spontaneously photoinduced from a collimated Nd:YAG laser beam at 532nm on thin films of a disperse red 1 functionalized glass-forming compound. Pattern formation was studied by measuring the diffraction intensity of a He-Ne laser probe beam at 633nm and by atomic force microscopy (AFM). The dependence of pattern formation on both irradiation time and intensity was studied. The gratings could be erased both optically and thermally. The orientation of the gratings is influenced by the polarization of the writing beam, and it is accompanied by strong diffraction of the incident light into the sample plane, thereby providing a way to couple and trap the light into the substrate. Interestingly, photobleaching upon prolonged irradiation yields transparent gratings, and the process is partially reversible upon thermal erasure.

Neutron diffraction of calcium aluminosilicate glasses and melts

The combination of neutron diffraction with aerodynamic levitation and laser heating, pioneered by Neville Greaves and co-workers about 15years ago, is an important tool for studying the structure of liquid melts. Since the first work on liquid Al2O3 published in 2001, the technique has been largely improved and experiments are now routinely performed at neutron sources, providing interesting structural information on various materials.In this paper, the structure of glass-forming compounds in the system CaO-Al2O3-SiO2 was measured by applying neutron diffraction with aerodynamic levitation. Results obtained in the liquid state above the melting point and from the glass at room temperatures are presented. Various compositions were studied by increasing the silica content and by changing the ratio CaO/Al2O3. As observed using other methods, the main structural changes relate to modification of the Al-O short range order.

Suppressing crystallization in solution-processed thin films of organic semiconductors

Abstract

Design and fabrication of constant-pitch circular surface-relief diffraction gratings on disperse red 1 glass

Circular surface-relief diffraction gratings with a constant pitch were photo-inscribed on thin films of a disperse red 1 functionalized glass-forming compound using a novel holographic technique. Various light-interfering metallic fixtures, which consisted of annular rings with a sloped and polished inner surface, were designed and fabricated. Each of them allowed the inscription of stable and high-quality circular diffraction gratings with pitches ranging from approximately 600-1400 nm and depths up to 250 nm. This was accomplished by exposure to a collimated laser beam with an irradiance of 604 mW/cm2 for 350 s. The resulting gratings had a diameter of 11.4 mm and had the advantage of being produced in a simple single-step procedure with no postprocessing or specialized equipment. The pitch and diameter of these circular gratings were dependent on the fixture geometry, while the depth was related to the exposure time.

Glass-forming property of hydroxyectoine is the cause of its superior function as a desiccation protectant

We were able to demonstrate that hydroxyectoine, in contrast to ectoine, is a good glass-forming compound. Fourier transform infrared and spin label electron spin resonance studies of dry ectoine and hydroxyectoine have shown that the superior glass-forming properties of hydroxyectoine result from stronger intermolecular H-bonds with the OH group of hydroxyectoine. Spin probe experiments have also shown that better molecular immobilization in dry hydroxyectoine provides better redox stability of the molecules embedded in this dry matrix. With a glass transition temperature of 87°C (vs. 47°C for ectoine) hydroxyectoine displays remarkable desiccation protection properties, on a par with sucrose and trehalose. This explains its accumulation in response to increased salinity and elevated temperature by halophiles such as Halomonas elongata and its successful application in ``anhydrobiotic engineering'' of both enzymes and whole cells.

Disperse and disordered: a mexylaminotriazine-substituted azobenzene derivative with superior glass and surface relief grating formation

Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.

Early drug development predictions of glass-forming ability and physical stability of drugs

The purpose of this study was to investigate if rapidly measured physical properties can predict glass-forming ability and glass stability of drug compounds. A series of 50 structurally diverse drug molecules were studied with respect to glass-forming ability and, for glass-formers (n=24), the physical stability upon 1month of storage was determined. Spray-drying and melt-cooling were used to produce the amorphous material and the solid state was analysed by Differential Scanning Calorimetry (DSC) and Powder X-ray Diffraction. Thermal properties and molecular weight (Mw) were used to develop predictive models of (i) glass-forming ability and (ii) physical stability. In total, the glass-forming ability was correctly predicted for 90% of the drugs from their Mw alone. As a rule of thumb, drugs with Mw greater than 300g/mole are expected to be transformed to its amorphous state by using standard process technology. Glass transition temperature and Mw predicted the physical stability upon storage correctly for 78% of the glass-forming compounds. A strong sigmoidal relationship (R2 of 0.96) was identified between crystallization temperature and stability. These findings have the potential to rationalize decisions schemes for utilizing and developing amorphous formulations, through early predictions of glass-forming ability from Mw and physical stability from simple DSC characterization.

Weste products of steel galvanizing processes for obtaining technology of colored glazes

The subject of this research is glass-forming compounds pegmatite-slag of thermal pover plants-waste products of galvanizing processes based on frits. The subject of this research is colored low-melt glazes. The objective of the work is elaboration of compounds and technology obtaining colored glazes using waste products of steel galvanizing processes. Up-to-date methods of investigation (X-ray phase analysis, differential thermal analysis, flame photometry and optical electroscopy) have been used in this work. Peculiarities of the formation of slimes of steel parts galvanizing and their properties have been investigated. The processes of gas formation in the process of thermal treatment of slimes have been studied in the range of temperatures 293…1773 K. Regularities of crystallization of coloring crystal phases α-Fe 2 o 3 , ZnO •Fe 2 o 3 and Feo•Fe 2 o 3 that ensure obtaining colored glazes have been established. Technology of obtaining low-melt glazes of brown and cherry-brown colors based on low-melt frit without adding additional ceramic pigments with firing temperature 1343…1373 K has been elaborated. It was established, that with the increase of slime content from 10 to 30 weight % in the composition of glazes the color of coating changes from brown to cherry-brown and the purity of color increases from 31 % to 47 %. The obtained compositions of such glazes were successfully tested under the manufacturing conditions and confirmed the possibility of producing decorative oven ceramic tiles with improved decorative and maintenance properties.

Spectral Properties of Carbazole- and Phenothiazine-Containing Low-Molecular Compounds for Photonics

Aza-compounds derivatives such as carbazole and phenothiazine are intensively studied as potential components of organic electronics, particularly of OLEDs. The present paper deals with investigations of spectral properties of specific carbazole- and phenothiazine-containing low-molecular glass-forming compounds, i.e., 3-(9-carbazolyl)-9-ethylcarbazole, 3-(9-pheothiazinyl)-9-ethylphenothiazine, 3-(9-pheothiazinyl)-9-ethylcarbazole, and 3-(9-carbazolyl)-9-ethylphenothiazine in different aggregative states (solid samples and solutions) and at different temperatures (77° K, 293° K). The location of the first singlet and triplet energy levels of the investigated compounds has been estimated from the spectral data. The high probability of the intercombinatory transition to the triplet state for the solutions and solid samples of 3-(9-pheothiazinyl)-9-ethylphenothiazine, 3-(9-pheothiazinyl)-9-ethylcarbazole, and 3-(9-carbazolyl)-9-ethylphenothiazine has been stated.

The Brønsted-Lowry Reaction Revisited: Glass-Forming Properties of Salts of 1,5-Dimexylbiguanide

Ionic molecular glasses can be conveniently prepared by reacting 1,5-dimexylbiguanide with a wide variety of carboxylic and sulfonic acids. A library of 51 salts has been prepared and studied by differential scanning calorimetry, 25 of which readily form glassy phases and do not recrystallize upon heating or standing. The crystal structures of 1,5-dimexylbiguanide and six of its salts have been solved and studied, and show extended hydrogen-bonded networks. Curiously, 1,5-dimexylbiguanide, which is extremely stable toward crystallization, crystallized in a close-packed, regular structure, unlike most related glass-forming compounds. This apparent paradox was probed with density functional theory calculations which revealed the presence of two conformers of similar energy, thus contributing to frustrate crystallization.

A Phenomenological Description of the PALS Response in Glass - Forming Systems

A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glass-forming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel – Fulcher – Tamman - Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ3, with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid - like and solid - like domain physical picture of all the three physical states of the disordered phase of the condensed systems.

On the synthesis of Zr-based bulk amorphous alloys from glass-forming compounds and elemental powders

The possibility of producing Zr-based bulk amorphous alloys (Zr65Cu17.5Ni10Al7.5 and Zr57Ti5Cu20Ni8Al10) by mechanical alloying (MA) from either a mixture of elemental powders (EP), or a mixture of glass-forming compounds (GFC), has been investigated. A preliminary study of the crystal structure stability of the GFC-ingredients during mechanical milling was performed. Amorphization was found to be significantly enhanced during MA by using a GFC mixture. A considerable difference in the phase transformations observed on heating the amorphous phase (AP) was noted for alloys obtained from GFC, as compared with those produced by melt quenching (MQ) or milling of a mixture of elemental powders. It is shown that the amorphous phase obtained by MA from GFC has a wider undercooled liquid region between the glass transition temperature Tg and the crystallization temperature Tx than the amorphous phase produced by the conventional MQ technique.

Chalcogenide glasses doped with Tb, Dy and Pr ions

Optically homogeneous As–Se and As–S–Se glasses doped with the ions of rare-earth elements (REE), i.e. praseodymium, dysprosium and terbium up to 9000 wt. ppm were synthesized. A technique for introduction of REE into chalcogenide glasses (CG) is based on solidification of the melt of glass-forming compounds with the dopants of REE iodide and the time–temperature modes minimizing glass crystallization and dopant clustering. Microhomogeneity and absorption of the produced samples of the doped glasses were studied in the middle IR range. A spectral dependence of absorption by REE ions was investigated and the extinction coefficients were determined for the most intensive absorption bands of the ions of praseodymium, dysprosium and terbium. Luminescence properties of CG doped with Tb3+ were investigated at 4–5 μm. The optical fibers based on arsenic selenide doped with terbium were manufactured with optical losses of 1.5 dB/m at 6–9 μm and a bending strength of 0.6 GPa.

Novel hole-transporting carbazole main chain oligomer and its model glass-forming compound

The oligomer containing 9-[2-(9H-carbazol-9-yl)cyclobutyl]-9H-carbazole moiety in the main chain and its model compound were synthesized by Wittig reaction. Both compounds form glasses with glass transition temperatures of 254°C and 135°C respectively. The optical and photoelectrical properties of the compounds were studied. The hole drift mobilities observed in the film of the oligomer by the time of flight technique were in the range of 2.10 -6 - 7.10 -6 cm 2 /(V.s) at an applied electric field ranging from 5.8.10 4 to 2.7.10 5 V/cm.

Photoconductive molecular glasses consisting of twin molecules

Synthesis and properties of photoconductive low-molar-mass glass-forming compounds consisting of twin molecules in which two bulky groups, i.e. 3-(9-carbazolyl)carbazole, 3-( N-diphenylamino)carbazole, 3-(10-phenothiazinyl)carbazole and 3,6-di(9-carbazolyl)carbazole are linked by flexible aliphatic units are reported. These compounds are found to form stable glasses with glass-transition temperatures in the range of 94–179 °C as characterised by differential scanning calorimetry (DSC). The electron photoemission spectra of the molecular glasses synthesised have been recorded and the ionisation potentials have been established. The lowest value of ionisation potential (5.32 eV) was observed for the molecular glass containing 3-( N-diphenylamino)carbazole moieties. The molecular glass containing 3-(9-carbazolyl)carbazole moieties exhibited ionisation potential of 5.80 eV, which is close to that of the polymer containing electronically isolated carbazole chromophores. Hole drift mobilities of the synthesised materials measured by the time of flight method are in the range of 10 −4 to 10 −7 cm 2 V −1 s −1 at an applied electric field of 3.6×10 5 V cm −1.

Glass-Forming Terephthalic Esters with Lateral Phenylthio Groups and their Relaxation Behavior

The esters of 2,5-bis(2-carboxy-phenylthio)terephthalic acid 4a-f were prepared by reaction of 2,5-bis(2-carboxy-phenylthio)terephthalic acid 2 via chloride 3 with alcohols or phenols. These novel glass-forming compounds are of the sulfur ligated “trilling” type. Two structures were established by X-ray analysis as well. The thermal behavior was characterized by DSC. In dependence of the different lateral substituents we found calorimetric glass transition temperatures (Tg ) in the range of −50°C to 85°C. The molecular dynamics were investigated by use of dielectric spectroscopy (10-2Hz-109Hz). The temperature time dependence for the α-relaxation, which is associated with the glass transition, is discussed in the fragility concept of liquids.