Search

Calcium phosphate based biomaterials are extensively used in the context of tissue engineering: small changes in composition can lead to significant changes in properties allowing their use in a wide range of applications. Samples of composition (Al(2)O(3))(x)(Na(2)O)(0.11-x)(CaO)(0.445)(P(2)O(5))(0.445), where x = 0, 0.03, 0.05, and 0.08, were prepared by melt quenching. The atomic-scale structure has been studied using neutron diffraction and solid state (27)Al MAS NMR, and these data have been rationalised with the determined density of the final glass product. With increasing aluminium concentration the density increases initially, but beyond about 3 mol. % Al(2)O(3) the density starts to decrease. Neutron diffraction data show a concomitant change in the aluminium speciation, which is confirmed by (27)Al MAS NMR studies. The NMR data reveal that aluminium is present in 4, 5, and 6-fold coordination and that the relative concentrations of these environments change with increasing aluminium concentration. Materials containing aluminium in 6-fold coordination tend to have higher densities than analogous materials with the aluminium found in 4-fold coordination. Thus, the density changes may readily be explained in terms of an increase in the relative concentration of 4-coordinated aluminium at the expense of 6-fold aluminium as the Al(2)O(3) content is increased beyond 3 mol. %.

Neutron diffraction studies have been made on the newly discovered amorphous transition metal sulfides, MoS4.65, and WS5, and the amorphous selenide, CrSe3. Structure factor data have been transformed to yield the total correlation function T(r). The first four peaks in the T(r) data for the sulfides, MoS4.65 and WS5, at around 2.0 A, 2.4 A, 2.9 A and 3.4 A, are ascribed to the S-S bond length in disulfide (S22-1) groups, the metal-sulfur bond, a metal-metal bond and the first non-bonded S-S distance, respectively. Over a similar range of T(r), the chromium selenide, CrSe3, shows only two peaks at 2.46 A and 3.64 A. In this case, the first peak is made up of a contribution from both the Se-Se distance in diselenide (Se22-) groups and the metal to selenium bond distance. The second peak corresponds to the first non-bonded Se-Se distances. We conclude that the basic structural unit in all these compounds is the octahedral MX6 group (X = S or Se), and that all the sulfur is found is found in S22- groups. CrSe3 is more complicated containing both Se2- and Se22- groups.

The short range structure of (CaO)(0.5)(P2O5)(0.5) glass has been studied using x-ray and neutron diffraction and modelled using the reverse Monte Carlo method. Using this combination of techniques has allowed six interatomic correlations to be distinguished and fitted to obtain a set of bond lengths and coordination numbers that describe the structure of the glass. The glass consists of metaphosphate chains of phosphate tetrahedra and each phosphate unit has two non-bridging oxygen atoms available for coordination with Ca. The Ca-O correlation was fitted with two peaks at 2.35 and 2.86 angstrom, representing a broad distribution of bond lengths. The total Ca-O coordination is 6.9 and is consistent with distorted polyhedral units such as capped octahedra or capped trigonal prisms. It is found that most non-bridging oxygen atoms are bonded to two calcium atoms. All of these observations are consistent with Hoppe's model for phosphate glasses. Furthermore, the medium range order is revealed to consist of phosphate chains intertwined with apparently elongated clusters of Ca ions, and the Ca-O and Ca-P correlations contributed significantly to the first sharp diffraction peak in x-ray diffraction.

Extended X-ray absorption fine structure (EXAFS) studies of the amorphous chromium sulfide, CrS3, the amorphous chromium selenide, CrSe3, and the crystalline vanadium sulfide model compound, VS4, have been carried out at both the metal and chalcogen K edges. Structural models based on the distances and coordination numbers obtained from the analysis of these data are presented for CrS3 and CrSe3. In CrS3, chromium is surrounded by an average of six sulfurs at 2.35 A. The sulfur-edge data can be fitted by two shells containing two chromium neighbours at 2.34 A and one sulfur neighbour at 2.03 A. The results of sulfur K-edge absorption spectroscopy of CrS3, Cr2S3, VS4 and α-S suggest that all sulfur is found in one oxidation state, S–1, and we formulate CrS3 as CrIII(S–12)1.5. The edge shift, ΔE, of the chromium K edge of CrS3(ΔE= 6.37 eV) relative to chromium metal, is close to that of Cr2S3(ΔE= 6.88 eV), supporting the assignment of the oxidation state of chromium as III. In CrSe3, chromium is surrounded by an average of six seleniums at a distance of 2.50 A. Each selenium has an average of two chromium neighbours at 2.45 A, and 0.67 of a selenium neighbour at 2.34 A. We formulate CrSe3 as CrIV(Se–12)Se–II. The chromium K-edge shift of CrSe3(ΔE= 5.79 eV) is large for a chromium selenide and provides further evidence for the assignment of the oxidation state of chromium in CrSe3 as IV. The magnetic moments per chromium measured at room temperature were 1.74(3)µB for CrS3 and 2.62(3)µB for CrSe3, supporting the assignment of different oxidation states to chromium in the two materials.

Extended X-ray absorption fine structure (EXAFS) and S K-edge absorption studies of the amorphous tungsten sulfide, WS5, and EXAFS studies of the amorphous tungsten selenide, WSe5, suggest these compounds can be formulated as WV(S22–) and WV(Se22–)2.5. The observed metal–metal distances of ca. 2.75 A are consistent with the formation of a metal–metal bond between these d1 metal centres; the metal–metal bond would explain the observed diamagnetism of these compounds. The Se—Se bond length of 2.34 A, determined from the Se K-edge EXAFS studies, is typical of a diselenide group. Comparison of the S K-edge absorption spectrum for WS5 with spectra from related compounds suggests that the sulfur is in the –1 oxidation state. This is in agreement with the observed absorption in the infrared at 518 cm–1 which we assign to an S–S stretch in a disulfide group. The S K-edge absorption spectrum of WS3 suggests that this compound contains both S–I and S–II. W LIII-edge EXAFS studies of WS3 show much greater disorder in the W—S bonding than in WS5, which can be attributed to the presence of sulfur in two oxidation states. Models based on two possible formulations, WV(S2–)2(S22–)0.5 and WIV(S2–)(S22–), give almost equally good fits to the experimental data. The observed diamagnetism of WS3 can be explained by the formation of W—W bonds of ca. 2.75 A, which are found in the EXAFS studies. Possible structural models for WS5 and WSe5 are presented.

Despite the numerous studies of bone mineral, there are still many questions regarding the exact structure and composition of the mineral phase, and how the mineral crystals become organised with respect to each other and the collagen matrix. Bone mineral is commonly formulated as hydroxyapatite, albeit with numerous substitutions, and has previously been studied by (31)P and (1)H NMR, which has given considerable insight into the complexity of the mineral structure. However, to date, there has been no report of an NMR investigation of the other major component of bone mineral, calcium, nor of common minority cations like sodium. Here, direct analysis of the local environment of calcium in two biological apatites, equine bone (HB) and bovine tooth (CT), was carried out using both (43)Ca solid state NMR and Ca K-edge X-ray absorption spectroscopy, revealing important structural information about the calcium coordination shell. The (43)Ca delta(iso) in HB and CT is found to correlate with the average Ca-O bond distance measured by Ca K-edge EXAFS, and the (43)Ca NMR linewidths show that there is a greater distribution in chemical bonding around calcium in HB and CT, compared to synthetic apatites. In the case of sodium, (23)Na MAS NMR, high resolution 3Q-MAS NMR, as well as (23)Na{(31)P} REDOR and (1)H{(23)Na} R(3)-HMQC correlation experiments give the first direct evidence that some sodium is located inside the apatite phase in HB and CT, but with a greater distribution of environments compared to a synthetic sodium substituted apatite (Na-HA).

This study investigates the effect of doping a high calcium oxide containing metaphosphate glass series (CaO)(40)(Na2O)(10)(P2O5)(50) with TiO2 (1, 3, and 5 mol%). TiO2 incorporation increased the density and glass transition temperature while reduced the degradation rate (5 mol% in particular) by twofold compared with (CaO)30 system reported previously. This has been confirmed by ion release and the minimal pH changes. TiP2O7, NaCa(PO3)(3) and CaP2O6 phases were detected for all TiO2-containing ceramics. XPS showed that the surface is composed of Ca, h, and Ti. Ti was recognized mainly as TiO2, but its total amount was lower than theoretical values. P-31 magic angle spinning (MAS) NMR showed a downfield shift of the P-31 lineshape with increasing TiO2, interpreted as an effect of the titanium cation rather than an increase in the phosphate network connectivity. FTIR showed that incorporation of TiO2 increased the strength of the phosphate chains, and the O/P ratio while introducing more Q(1) units into the structure at the expense of the Q(2) units. There were no differences, however, in surface topography roughness and free energies between these glasses. These results suggested that TiO2 and CaO were acting synergistically in producing glasses with controllable bulk and structural properties.

A sol-gel preparation of Ga-doped phosphate-based glass with potential application in antimicrobial devices has been developed. Samples of composition (CaO)(0.30)(Na2O)(0.20-x) (Ga2O3) (x) (P2O5)(0.50) where x = 0 and 0.03 were prepared, and the structure and properties of the gallium-doped sample compared with those of the sample containing no gallium. Analysis of the P-31 MAS NMR data demonstrated that addition of gallium to the sol-gel reaction increases the connectivity of the phosphate network at the expense of hydroxyl groups. This premise is supported by the results of the elemental analysis, which showed that the gallium-free sample contains significantly more hydrogen and by FTIR spectroscopy, which revealed a higher concentration of -OH groups in that sample. Ga K-edge extended X-ray absorption fine structure and X-ray absorption near-edge structure data revealed that the gallium ions are coordinated by six oxygen atoms. In agreement with the X-ray absorption data, the high-energy XRD results also suggest that the Ga3+ ions are octahedrally coordinated with respect to oxygen. Antimicrobial studies demonstrated that the sample containing Ga3+ ions had significant activity against Staphylococcus aureus compared to the control.

Antimicrobial gallium-doped phosphate-based glasses of general composition (P(2)O(5))(0.45)(CaO)(0.16)(Na(2)O)(0.39-x)(Ga(2)O(3))(x) (where x=0, 0.01, 0.03, and 0.05) have been studied using the advanced synchrotron-based techniques of Ga K-edge x-ray absorption spectroscopy and high-energy x-ray diffraction to provide a structural insight into their unique properties. The results show that the Ga(3+) ions are octahedrally coordinated. Furthermore, substitution of Na(2)O by Ga(2)O(3) strengthens the phosphate network structure because the presence of GaO(6) octahedra inhibits the migration of the remaining Na(+) ions. The results are discussed in terms of the use of Na(2)O-CaO-P(2)O(5) glasses as controlled-delivery devices for antimicrobial Ga(3+) ions in biomedical applications. We are thereby able to relate the atomic-scale environment of the Ga(3+) ions beneficially to the glass dissolution, and thus to their ability to disrupt bacterial cell activity by usurping the role of iron.

The general trend in biomaterials is to use and employ materials that play an active role in tissue regeneration rather than passive and inert materials. Therefore, understanding how a material interacts with the surrounding environments, including cells and tissue fluid, allows material design to be tailored so that implants can be constructed to promote a specific biological response, helping them better perform their function. This class of materials has been described as the "Third Generation" of biomaterials. Phosphate based glasses fall into this category and it has been shown that the properties of these glasses can be tuned via their composition according to the desired end application. These glasses can be prepared as melt-quenched or sol-gel bulk form suitable for potential hard tissue engineering applications and as vehicles for antimicrobial agents. They can also be prepared as fibres suitable for soft tissue engineering applications such as those involving muscle, ligaments, and tendon, where, like the fibres, the tissue has a high degree of anisotropy.

Neutron diffraction with isotopic substitution has been used to probe the local environment of silver in a melt-quench derived bioresorbable phosphate glass. Samples enriched with Ag-107 and Ag-109 were prepared and neutron diffraction data collected. A first-order difference was taken between the data sets to give detailed information about the silver environment in the glass matrix. The measured Ag-O correlation has three components in the first coordination shell at 2.28 angstrom, 2.51 angstrom, and 2.58 angstrom with coordination numbers of 2.1,23, and 1.1, respectively, consistent with silver occupying a distorted octahedral environment. These results have been correlated with those from Ag K-edge X-ray absorption near-edge spectroscopy measurements. The results suggest that the addition of silver to the (CaO)(0.3)(Na2O)(0.2)(P2O5)(0.5) system has a significant effect on the host phosphate network, with shorter and more branched chains replacing the long chains and rings normally associated with the metaphosphate composition.

The HfO2-SiO2 system is attracting interest as a possible new dielectric material in semiconductor devices. Knowledge of the location of hafnium within the silica network and the effect hafnium has on the structure will be central to the successful use of this material system in this application. Here, sol-gel techniques have been used to manufacture (HfO2)(x)(SiO2)(1-x) samples (x = 0.1, 0.2 and 0.4, each heat treated at 250, 500 and 750 degrees C) and these have been characterised by magic angle spinning (MAS) NMR (H-1, C-13, O-17, Si-29), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. 29Si MAS NMR showed that increasing the hafnia content decreases the connectivity of the silicate network, i.e. increases the range of differently connected SiO4 (Q(n)) units with more having increased numbers of non-bridging oxygens (i.e. lower n). FTIR and O-17 MAS NMR showed unequivocally that the x = 0.4 sample phase-separated at higher temperatures, while in the x = 0.1 sample the hafnium was homogeneously mixed into the SiO2 phase without any phase separation. (C) 2007 Elsevier Inc. All rights reserved.

An improved method for the sol-gel synthesis of binary (TiO2)(0.5)(P2O5)(0.5) glasses has been developed. Elemental analysis of the products showed that the loss of phosphorous upon drying and heat treatment is low. The structure of the heat-treated glasses was studied using neutron diffraction and high-energy X-ray diffraction, analysis of which revealed a structure consisting Of PO4 tetrahedra and TiO6 octahedra sharing corners in a three-dimensional amorphous network. The Reverse Monte Carlo method was used to produce a structural model which illustrated that the structure of the glass is, at the near-neighbour level, closely analogous to the superstructure of crystalline TiP2O7. No significant atomic-scale structural differences were observed between glasses prepared by acid- or base-catalysed sol-gel reactions. (c) 2007 Elsevier Ltd. All rights reserved.

Staphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 μg·mm −2 ·h −1 ) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (∼20 μm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31 P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections.

An undoped and two silver-doped (0, 3 and 5 mol% Ag) phosphate glass compositions were investigated for their structure and properties. These compositions had in a previous study been investigated for their antimicrobial properties, and were found to be extremely potent at inhibiting the micro-organisms tested. Thermal, X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and X-ray absorption Near Edge Structure (XANES) studies were used to elucidate the structure of the compositions investigated, whilst degradation and ion release studies were conducted to investigate their properties. No significant differences were found between the T (g) values of the silver containing glasses, while XRD analysis revealed the presence of a NaCa(PO3)(3) phase. NMR showed the dominance of Q(2) species, and XANES studies revealed the oxidation state of silver to be in the +1 form. No correlation was seen between the degradation and cation release profiles observed, and the P3O93 anion was the highest released anionic species, which correlated well with the XRD and NMR studies. Overall, it was ascertained that using Ag2SO4 as a precursor, and producing compositions containing 3 and 5 mol% Ag, the levels of silver ions released were within the acceptable cyto/biocompatible range.

Neutron diffraction and P-31 nuclear magnetic resonance spectroscopy were used to probe the structure of phosphate glass biomaterials of general composition (CaO)(0.5-x) (Na2O)(x) (P2O5)(0.5) (x = 0, 0.1 and 0.5). The results suggest that all three glasses have structures based on chains of Q(2) phosphate groups. Clear structural differences are observed between the glasses containing Na2O and CaO. The P-O bonds to bridging and non-bridging oxygens are less well resolved in the neutron data from the samples containing CaO, suggesting a change in the nature of the bonding as the field strength of the cation increases Na+ -> Ca2(+). In the (CaO)(0.5)(P2O5)(0.5) glass most of the Ca2+ ions are present in isolated CaOx polyhedra whereas in the (Na2O)(0.5) (P2O5)(0.5) glass the NaOx polyhedra share edges leading to a Na-Na correlation. The results of the structural study are related to the properties of the (CaO)(0.4) (Na2O)(0.1) (P2O5)(0.5) biomaterial.

Phosphate-based glasses have recently attracted much interest as a new generation of biomaterials because of their ability to react and dissolve in the physiological environment and eventually to be replaced by regenerated hard or soft tissue. A series of phosphate-based glasses containing 45 mol% P2O5 and various amounts of CaO and Na2O were synthesized by sol–gel and melt-quenching techniques. A comparison between the structure of the sol–gel glass and the structure of the analogous melt-quenched glasses has been undertaken. A broad-based characterization approach combining different techniques has been used to investigate the short-range structure of the glasses and the effect of adding modifier oxides to the network structure (conventional and high energy X-ray diffraction, infra-red spectroscopy, 31P solid state magic angle spinning NMR spectroscopy). Sol–gel and melt-quenched glasses appear to have a similar structure, showing similar Qn distributions and atomic correlations.

Bioactive sol-gel derived glass scaffolds bond to bone and their dissolution products stimulate new bone growth in vitro and in vivo; they may therefore be used to regenerate diseased or damaged bone to its original state and function in bone tissue engineering applications. We seek herein to cast light upon these reaction mechanisms by attempting to quantify changes in the atomic-scale structure of the glass scaffold as a result of in vitro reaction with simulated body fluid (SBF). We report the results of a study using neutron diffraction with isotopic substitution (NDIS) to gain new insights into the nature of the atomic scale calcium environment in bioactive sol-gel glasses. This is augmented by high-energy X-ray total diffraction. We have thereby begun to explore the nature of the principal stages to the generation of hydroxyapatite (i.e. the mineral 'building block' of bone) on the bioactive glass surface. The data are examined in light of our complementary solid-state NMR and computer modelling studies. The results reveal that the Ca-O environment in an SBF exposed (CaO)(0.3)(SiO2)(0.7) sol-gel glass, which initially comprises three distinct but partially overlapping correlation shells centered at 2.3 angstrom, 2.5 angstrom and 2.75 angstrom, preferentially loses the shortest length correlation. A (CaH)-H-... correlation appears at 2.95 angstrom. The surface deposited (CaP)-P-... environment consists of three partially overlapping, but nonetheless distinct, correlation shells, at 3.15 angstrom, 3.40 angstrom and 3.70 angstrom. (c) 2007 Elsevier B.V. All rights reserved.

Nanocrystalline samples of Ba1-xCaxF2 prepared by high-energy milling show an unusually high F? ion conductivity, which exhibit a maximum in the magnitude and a minimum in the activation energy at x = 0.5. Here, we report an X-ray absorption spectroscopy (XAS) at the Ca and Sr K edges and the Ba L3 edge and a molecular dynamics (MD) simulation study of the pure and mixed fluorides. The XAS measurements on the pure binary fluorides, CaF2, SrF2 and BaF2 show that high-energy ball-milling produces very little amorphous material, in contrast to the results for ball milled oxides. XAS measurements of Ba1-xCaxF2 reveal that for 0 < x

Phosphate-based glasses of the general formula Na2O-CaO-P2O5 are degradable in an aqueous environment, and therefore can act as antibacterial materials through the inclusion of ions such as copper. In this study, CuO and Cu2O were added to Na2O-CaO-P2O5 glasses (1-20 mol% Cu) and X-ray absorption spectroscopy (XAS) and high-energy X-ray diffraction (HEXRD) used to probe the local environment of the copper ions. Copper K-edge X-ray absorption near-edge structure (XANES) spectra confirm the oxidation state of copper to be predominantly 2+ in all samples regardless of which copper oxide was used in the preparation. The XANES results suggest the structural environment of copper to be octahedral with respect to oxygen in all samples. The HEXRD results yield a Cu-O nearest-neighbour distance of 1.98 angstrom and associated coordination number of approximately six, both consistent with octahedral coordination. Analysis of the extended X-ray absorption fine structure (EXAFS) data also yields structural parameters consistent with copper in an octahedral environment. The HEXRD and EXAFS results reveal a Cu-P distance of 3.13 angstrom, which confirms that the copper ions are coordinated within the phosphate glass network and not phase-separated in domains of copper oxide. (c) 2006 Elsevier B.V. All rights reserved.

To understand amorphous and structurally disordered materials requires the application of a wide-range of advanced physical probe techniques and herein a combined methodology is outlined. The relatively short-range structural sensitivity of solid state NMR means that it is a core probe technique for characterizing such materials. The aspects of the solid state NMR contribution are emphasized here with examples given from a number of systems, with especial emphasis on the information available from 17O NMR in oxygen-containing materials. 17O NMR data for crystallization of pure sol-gel prepared oxides is compared, with new data presented from In2O3 and Sc2O3. Sol-gel formed oxide mixtures containing silica have been widely studied, but again the role and effect of the other added oxide varies widely. In a ternary ZrO2-TiO2-SiO2 silicate sol-gel the level of Q4 formation is dependent not only on the composition, as expected, but also the nature of the second added oxide. Sol-gel formed phosphates have been much less widely studied than silicates and some 31P NMR data from xerogel, sonogel and melt-quench glasses of the same composition are compared. The effect of small amounts of added antibacterial copper on phosphate glass networks is also explored.

Sol-gel derived calcium silicate glasses may be useful for the regeneration of damaged bone. The mechanism of bioactivity is as yet only partially understood but has been strongly linked to calcium dissolution from the glass matrix. In addition to the usual laboratory-based characterisation methods, we have used neutron diffraction with isotopic substitution to gain new insights into the nature of the atomic-scale calcium environment in bioactive sol-gel glasses, and have also used high energy X-ray total diffraction to probe the nature of the processes initiated when bioactive glass is immersed in vitro in simulated body fluid. The data obtained point to a complex calcium environment in which calcium is loosely bound within the glass network and may therefore be regarded as facile. Complex multi-stage dissolution and mineral growth phases were observed as a function of reaction time between 1 min and 30 days, leading eventually, via octacalcium phosphate, to the formation of a disordered hydroxyapatite (HA) layer on the glass surface. This methodology provides insight into the structure of key sites in these materials and key stages involved in their reactions, and thereby more generally into the behaviour of bone-regenerative materials that may facilitate improvements in tissue engineering applications.

The formation of a carbonate-containing hydroxyapatite, HCAp, layer on bioactive calcium silicate sol-gel glass of the formula (CaO)0.3(SiO2)0.7 has been studied in-vitro in Simulated Body Fluid (SBF). Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR) measurements have been performed with results showing the formation of a significantly amorphous HCAp layer after less than 5 hours in solution.

A range of nitrogen-doped amorphous hydrogenated carbon samples (a-C:Nx:H, where x = 3 at.% and x = 7 at.%) have been studied using neutron diffraction, inelastic neutron scattering (INS) and Fourier transform infra-red (FTIR) spectroscopy to obtain detailed information about their atomic-scale structure, particularly the bonding environment of the hydrogen. The results show that the overall atomic scale network structure of the two samples is very similar; however, the hydrogen-bonding sites alter subtly as the nitrogen content of the samples is increased.

Neutron diffraction with 46Ti and 48Ti stable isotopes and isotope-enriched 17O and 49Ti MAS NMR have been used to characterize the structure of (TiO2)x(SiO2)1-x sol−gel glass as a function of composition (x = 0.08, 0.18, and 0.41) and calcination temperature (T = 250, 500, and 750 °C). The results reveal the first direct observation of two Ti−O distances in a homogeneous (TiO2)0.18(SiO2)0.82 sol−gel derived glass. In the sample heat treated at 250 °C, the Ti occupies a distorted octahedral environment similar to that found in the mineral ramsayite with four Ti−O bond lengths of around 1.89 A and two close to 2.11 A. After heating to 750 °C, two shorter bond distances are observed: a short distance at 1.81 A due to tetrahedrally coordinated Ti and a longer distance of 1.94 A due to a minority species of octahedrally coordinated Ti. The (TiO2)0.08(SiO2)0.92 sample exhibits similar behavior. After heating to 250 °C, two Ti−O distances are observed at 1.84 and 2.10 A consistent with the presence of both tet...

A new synthetic method has been developed and demonstrated for the utilization of commercially cheap MnO2 for the production of nanoparticles of LiMn2O4 spinel as a cathode material for Li-ion batteries. The process involves the insertion of lithium into electrolytic manganese dioxide (EMD) in an aqueous medium with glucose as a mild reductant in open air. The material resulting from calcination is pure, spinel-structured Li0.96Mn2O4 particles of sub-micrometric and nanometric size that exhibit promising electrochemical behavior in nonaqueous Li-salt solutions. Further development of this process may be interesting for the commercial production of LiMn2O4 for Li-ion batteries.

Amorphous (TiO2) x (SiO2)1−x (x = 0.08, 0.18, and 0.41) sol-gel formed materials have been characterised by a combination of X-ray and neutron diffraction, infra-red and 29Si and 17O magic angle spinning NMR spectroscopy. This combination allows new insight into the fundamental structural role titanium additions play in silica, entering the network at x = 0.08 but largely phase separating at x = 0.41. At an intermediate value of x = 0.18 there is complex coordination behaviour with initially some Ti—O—Ti linkages forming and both TiO4 and TiO6 coordinations present. It appears that at 500°C for the x = 0.18 sample all titanium is present in Ti—O—Si linkages but that this situation is unstable on further calcination. The new information presented here is amalgamated with that from our previous EXAFS, XANES and SAXS on the same samples to produce the most complete view to date of the local and mesoscopic structural behaviour of the (TiO2) x (SiO2)1−x system produced by the sol-gel method.

Extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure, X-ray fluorescence spectroscopy, and X-ray powder diffraction have been used to study the local calcium environment in four sol–gel-derived bioactive calcium silicate glasses of the general formula (CaO)x(SiO2)1−x. The formation of a hydroxyapatite layer on the composition with the highest bioactivity (x = 0.3) with time has been studied, in an in vitro environment, by immersion in simulated body fluid (SBF) at 37°C. The calcium oxygen environment in the four compositions has been shown to be six-coordinate in character. Both the extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure show a gradual increase in coordination number and CaO bond distance with longer exposure to SBF. X-ray fluorescence show that calcium is quickly lost from the samples on exposure to SBF and the calcium concentration then recovers with time. There is clear evidence that the recovery of calcium content is due to the formation of a CaO-P2O5-rich layer. Annealing of samples at 650°C shows the presence of what, on the length scales probed by X-ray diffraction, appears to be noncrystalline calcium phosphate after 1 h of exposure to an SBF solution, which becomes more crystalline on longer exposure. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 354–360, 2004

The X-ray absorption near edge structure (XANES) at the calcium K-edge is rich in information, but complex and difficult to interpret fully. We present here a systematic study of a range of calcium/oxygen containing compounds and minerals and show that the XANES may be used to obtain qualitative information on the calcium coordination environment.

The effects of different heat treatment schemes (i.e. successively or directly heated to particular temperatures) and atmospheres (air or nitrogen) on the solid-state NMR spectra obtained from (TiO2)(0.15)(ZrO2)(0.05)(SiO2)(0.80) sol-gel materials are investigated. A combination of H-1, C-13, O-17 and Si-29 NMR is used. Si-29 MAS NMR indicates that the extent of condensation of the silica-based network strongly depends on the maximum temperature the sample has experienced, but the condensation is largely independent of the details of the heat treatment scheme and atmosphere used. For sol-gel produced silicate-based materials the results show that the equilibrium structure at each temperature is reached rapidly compared to the time (2 h) spent at that temperature. The O-17 NMR results confirm that a nitrogen atmosphere does significantly reduce loss of O-17 from the structure but care must be taken since there could be differential loss of O-17 from the regions having different local structural characteristics. (C) 2003 Elsevier Science (USA). All rights reserved.

Sonolysis of diphenylmethane (DPhM) has been studied under the effect of 20 kHz ultrasound (absorbed acoustic power 0.45 W/ml, surface area of sonotrode 1 cm2, volume of sonicated solution 100 ml) under argon at 60 °C. The solid product of the sonolysis was characterized by elemental analysis, FTIR, 13C MAS NMR, TGA/DSC, XRD and TEM techniques. It was found that the sonolysis of DPhM causes formation of the polymer with the composition similar to crosslinked polystyrene. Assumed mechanism of DPhM sonolysis consists of DPhM molecules dissociation inside the cavitating bubble. Secondary radical scavenging and radical recombination processes yields the sonopolymer in the liquid phase. The breakdown of the aromatic ring during DPhM sonolysis confirms that a very high temperature established in the cavitating bubble.

A combination of Si-29 and O-17 MAS NMR, EXAFS and FT-IR spectroscopy has been used to study the atomic structure of (Ta2O5)(x)(SiO2)(1 - x) (x = 0.05, 0.11, 0.18 and 0.25) xerogels prepared by reacting partially-hydrolysed tetraethyl orthosilicate with tantalum(V) ethoxide. Amorphous tantala, a-Ta2O5, xerogels have also been prepared and their structures studied in detail for the first time. Results have shown that in all these materials, Ta adopts predominantly 5-fold coordination with respect to oxygen. For the mixed oxide xerogels, partial phase separation of the two component oxides occurs for x > 0.11.

The height and position of the pre-edge peak in Ti K-edge X-ray absorption near-edge structure (XANES) is a sensitive indicator of the coordination of Ti. This method is used in situ to investigate Ti coordination in titania–silica xerogels with low TiO 2 content. Unheated xerogels contain Ti with isolated, distorted 6-fold coordination ( [6] Ti ). Initial heating causes [6] Ti to be rapidly converted into 4-fold coordinated Ti( [4] Ti ), which upon cooling reverts to [6] Ti . Increased heat treatment creates more stable [4] Ti , which remains after cooling. Thus, the coordination of Ti depends on ambient conditions in addition to heat treatment. In-situ XANES is important for distinguishing different kinds of [4] Ti , and hence for understanding catalytic properties.

A combination of Si-29 and O-17 MAS NMR, EXAFS and FTIR spectroscopy has been used to study the atomic structure of(ZrO2)(x)(SiO2)(1-x) (x = 0.1, 0.2, 0.3 and 0.4) xerogels prepared by reacting partially hydrolysed tetraethyl orthosilicate with zirconium(rv) propoxide. Results from (ZrO2)(0.1)(SiO2)(0.9) samples reveal the oxides to be atomically mixed with no evidence of phase separation. In these samples, the nearest neighbour environment of zirconium is similar to that found in cubic zirconia. In the (ZrO2)(0.4)(SiO2)(0.6) samples, phase separation occurs with a significant proportion of the zirconium present as amorphous ZrO2 with a local structure similar to that of monoclinic zirconia. O-17 MAS NMR and EXAFS have proven valuable techniques for gauging the level of atomic mixing in these materials.

The synthesis of high surface area (TiO2)0.18(SiO2)0.82xerogels has been achieved using the sol-gel route. Heptane washing was used before the drying stage to minimise capillary pressure and hence preserve pore structure and maximise the surface area. The as-prepared xerogels were tested for their catalytic activity using the epoxidation of cyclohexene with tert-butyl hydrogen peroxide (TBHP) as a test reaction. Surface areas up to 450 m2g-1 were achieved with excellent selectivities and reasonable percent conversions. SAXS data has identified that heptane washing during drying, in general, results in a preservation of the pore structure, and produces more effective catalysts with higher surface areas and larger pore diameters. Fr-IR spectroscopy has revealed that the catalytic activity is dependant upon the number of Si-O-Ti linkages, inferring intimate mixing of the precursors at the atomic level. XANES data reveals the presence of reversible 4/6-fold Ti sites that are thought to be ‘active’ catalytic sites. The most effective catalyst was produced with a calcination temperature of 500°C, and a heating rate of 5 °Cmin-l

Previous structural studies on titania- and zirconia-silica xerogels have shown the occurrence of homogeneous mixing at low metal content, and phase separation at high metal content. The use of additional, complementary, synchrotron-based methods can contribute to a fuller structural description of these materials. We present new x-ray absorption near edge structure (XANES) and SAXS results for (ZrO2)x(SiO2)1-x, xerogels and compare them with previous results for (TiO2)x(SiO2)1-x xerogels. Significant differences between (TiO2)x(SiO2)1. and (ZrO2)X(SiO2)1-x xerogels are observed in the affects of heat treatment on the coordination of homogeneously mixed metal atoms, and in the development of phase separated metal oxide regions.

Sol-gel produced mixed oxide materials have been extensively studied using conventional, ex situ structural techniques. Because the structure of these materials is complex and dependent on preparation conditions, there is much to be gained from in situ techniques: the high brightness of synchrotron x-ray sources makes it possible to probe atomic structure on a short timescale, and hence in situ. Here we report recent results for mixed titania- (and some zirconia-) silica gels and xerogels. Titania contents were in the range 8–18 mol%, and heat treatments up to 500°C were applied. The results have been obtained from intrinsically rapid synchrotron x-ray experiments: i) time-resolved small angle scattering, using a quadrant detector, to follow the initial stages of aggregation between the sol and the gel; ii) the use of a curved image plate detector in diffraction, which allowed the simultaneous collection of data across a wide range of scattering at high count rate, to study heat treatments; and iii) x-ray absorption spectroscopy to explore the effects of ambient moisture on transition metal sites.

An improved sol-gel synthesis of (CaO)(0.3)(Na2O)(0.2)(P2O5)(0.5) bioresorbable glass has been developed. The structures of both the dried gel and the stabilised sol-gel glass have been characterised using high-energy XRD, P-31 MAS NMR and FT-IR spectroscopy. The structure of the analogous melt-quench prepared glass has also been studied for comparison. The results show that the dried gel has a structure consisting of mainly Q(0) and Q(1) phosphate units, whereas that of the stabilised sol-gel glass comprises predominantly Q(1) and Q(2) units. Furthermore, it is demonstrated that the structure of the sol-gel glass is similar to that of its melt-quenched counterpart except for the presence of hydroxyl groups which terminate the phosphate chains, reducing the connectivity of the network.

A series of phosphate-based sol-gel glasses in the system P2O5-CaO-Na2O-SiO2 were synthesised using PO(OH)(3-x)(OC2H5)(x) (x = 1, 2) as a phosphorus precursor and alkoxides of sodium, calcium and silicon in an ethylene glycol solution. It has been found that the upper limit for gel formation is about 22 mol% phosphorus and that the gelation time increases with increasing phosphorus content of the sol. X-ray diffraction (XRD) along with X-ray fluorescence chemical analysis (XRF) have been performed on samples containing 45 mol% of P2O5 and 0, 10, 15 and 25 mol% of SiO2 with varying amount of modifier oxides (CaO, Na2O). All the samples are predominantly amorphous up to 400 degrees C and some of them, depending on the composition, retain their amorphous structure up to 600 and 800 degrees C. To the knowledge of the authors, this is the first time that phosphate-based glasses having these compositions have successfully been synthesised via the sol-gel method.

Extended X-ray absorption fine structure (EXAFS) and S K-edge absorption studies of the amorphous tungsten sulfide, WS5, and EXAFS studies of the amorphous tungsten selenide, WSe5, suggest these compounds can be formulated as WV(S22–) and WV(Se22–)2.5. The observed metal–metal distances of ca. 2.75 A are consistent with the formation of a metal–metal bond between these d1 metal centres; the metal–metal bond would explain the observed diamagnetism of these compounds. The Se—Se bond length of 2.34 A, determined from the Se K-edge EXAFS studies, is typical of a diselenide group. Comparison of the S K-edge absorption spectrum for WS5 with spectra from related compounds suggests that the sulfur is in the –1 oxidation state. This is in agreement with the observed absorption in the infrared at 518 cm–1 which we assign to an S–S stretch in a disulfide group. The S K-edge absorption spectrum of WS3 suggests that this compound contains both S–I and S–II. W LIII-edge EXAFS studies of WS3 show much greater disorder in the W—S bonding than in WS5, which can be attributed to the presence of sulfur in two oxidation states. Models based on two possible formulations, WV(S2–)2(S22–)0.5 and WIV(S2–)(S22–), give almost equally good fits to the experimental data. The observed diamagnetism of WS3 can be explained by the formation of W—W bonds of ca. 2.75 A, which are found in the EXAFS studies. Possible structural models for WS5 and WSe5 are presented.

Extended X-ray absorption fine structure (EXAFS) studies of the amorphous chromium sulfide, CrS3, the amorphous chromium selenide, CrSe3, and the crystalline vanadium sulfide model compound, VS4, have been carried out at both the metal and chalcogen K edges. Structural models based on the distances and coordination numbers obtained from the analysis of these data are presented for CrS3 and CrSe3. In CrS3, chromium is surrounded by an average of six sulfurs at 2.35 A. The sulfur-edge data can be fitted by two shells containing two chromium neighbours at 2.34 A and one sulfur neighbour at 2.03 A. The results of sulfur K-edge absorption spectroscopy of CrS3, Cr2S3, VS4 and α-S suggest that all sulfur is found in one oxidation state, S–1, and we formulate CrS3 as CrIII(S–12)1.5. The edge shift, ΔE, of the chromium K edge of CrS3(ΔE= 6.37 eV) relative to chromium metal, is close to that of Cr2S3(ΔE= 6.88 eV), supporting the assignment of the oxidation state of chromium as III. In CrSe3, chromium is surrounded by an average of six seleniums at a distance of 2.50 A. Each selenium has an average of two chromium neighbours at 2.45 A, and 0.67 of a selenium neighbour at 2.34 A. We formulate CrSe3 as CrIV(Se–12)Se–II. The chromium K-edge shift of CrSe3(ΔE= 5.79 eV) is large for a chromium selenide and provides further evidence for the assignment of the oxidation state of chromium in CrSe3 as IV. The magnetic moments per chromium measured at room temperature were 1.74(3)µB for CrS3 and 2.62(3)µB for CrSe3, supporting the assignment of different oxidation states to chromium in the two materials.

Novel quaternary gallium-doped phosphate-based glasses (1, 3, and 5 mol % Ga2O3) were synthesized using a conventional melt quenching technique. The bactericidal activities of the glasses were tested against both Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Clostridium difficile) bacteria. Results of the solubility and ion release studies showed that these glass systems are unique for controlled delivery of Ga3+.Ga-71 NMR measurements showed that the gallium is mostly octahedrally coordinated by oxygen atoms, whilst FTIR spectroscopy provided evidence for the presence of a small proportion of tetrahedral gallium in the samples with the highest gallium content. FTIR and Raman spectra also afford an insight into the correlation between the structure and the observed dissolution behavior via an understanding of the atomic-scale network bonding characteristics. The results confirmed that the net bactericidal effect was due to Ga3+, and a concentration as low as 1 mol % Ga2O3 was sufficient to mount a potent antibacterial effect. The dearth of new antibiotics in development makes Ga3+ a potentially promising new therapeutic agent for pathogenic bacteria including MRSA and C. difficile.

Gallium-doped phosphate-based glasses (PBGs) have been recently shown to have antibacterial activity. However, the delivery of gallium ions from these glasses can be improved by altering the calcium ion concentration to control the degradation rate of the glasses. In the present study, the effect of increasing calcium content in novel gallium (Ga2O3)-doped PBGs on the susceptibility of Pseudomonas aeruginosa is examined. The lack of new antibiotics in development makes gallium-doped PBG potentially a highly promising new therapeutic agent. The results show that an increase in calcium content (14, 15 and 16 mol.% CaO) cause a decrease in degradation rate (17.6, 13.5 and 7.3 microg mm(-2) h(-1)), gallium ion release and antimicrobial activity against planktonic P. aeruginosa. The most potent glass composition (containing 14 mol.% CaO) was then evaluated for its ability to prevent the growth of biofilms of P. aeruginosa. Gallium release was found to reduce biofilm growth of P. aeruginosa with a maximum effect (0.86 log(10) CFU reduction compared to Ga2O3-free glasses) after 48 h. Analysis of the biofilms by confocal microscopy confirmed the anti-biofilm effect of these glasses as it showed both viable and non-viable bacteria on the glass surface. Results of the solubility and ion release studies show that this glass system is suitable for controlled delivery of Ga3+. 71Ga NMR and Ga K-edge XANES measurements indicate that the gallium is octahedrally coordinated by oxygen atoms in all samples. The results presented here suggest that PBGs may be useful in controlled drug delivery applications, to deliver gallium ions in order to prevent infections due to P. aeruginosa biofilms.