Showing papers on "Chemical binding published in 2007"

Sources and bioavailability of phosphorus fractions in freshwaters: a British perspective

Abstract: This paper seeks a perspective on the forms of phosphorus which promote aquatic eutrophication, with the particular quest of establishing their sources. A short background traces the development of understanding of nutrient enrichment and the suppositions about the relative contributions of agriculture, sewage and detergent residues. Most aquatic systems, and their primary producers, are naturally deficient in biologically-available phosphorus. Aquatic plants have evolved very efficient phosphorus uptake mechanisms. The biomass responses to an increase in the supply of phosphorus are stoichiometrically predictable. The most bioavailable forms of phosphorus are in solution, as orthophosphate ions, or are readily soluble or elutable from loose combinations. Ready bioavailability coincides well with what is measurable as molybdate-reactive (MRP) or soluble-reactive phosphorus (SRP). Most other forms, including phosphates of the alkaline earth metals, aluminium and iron are scarcely available at all. Orthophosphate ions sorbed to metal oxides and hydroxides are normally not biologically available either, except through weak dissociation ('desorption'). The production of alkaline phosphatase provides organisms with an additional mechanism for accelerating the sequestration of phosphate from organic compounds. Bioavailable phosphate is liberated when redox- or alkali-sensitive metal hydroxides dissolve but these processes are minor contributors to the biological responses to nutrient enrichment. Most of the familiar eutrophication is attributable to the widespread application of secondary sewage treatment methods to the wastes emanating from a burgeoning and increasingly urbanised human population. The use of polyphosphate-based detergents, now in decline, has contributed to the problem. In aquatic systems, the additional phosphorus raises the biological supportive capacity, sometimes to the capacity of the next limiting factor (carbon, light, hydraulic retention or of another nutrient). At high orthophosphate loadings, the straight stoichiometric yield relationship between biomass yield and phosphorus a vailability is lost. Movements of phosphorus and its recycling within aquatic systems do not prevent the slow gravitation of phosphorus to the bottom substrata. The phosphorus retentivity of sediments depends upon their chemical composition. While oxide-hydroxide binding capacity in the surface sediments persists, they act as a sink for phosphorus and a control on further cycling. Iron-rich and clay-rich sediments perform best in these conditions; calcareous sediments least so. Eutrophication may lead to the exhaustion of sediment P-binding capacity. Non-sorbed phosphate is readily recyclable if primary producers have access to it. Recycling is most rapid in shallow waters (where sediment disturbance, by flow, by wind action and through bioturbation, is frequent and least in deep ventilated sediments. The contributions of phosphorus from catchments are assessed. The slow rate of weathering of (mostly apatitic) minerals, the role of chemical binding in soils and the incorporation and retentivity bv forested terrestrial ecosystems each contribute to the minimisation of phosphorus leakage to drainage waters. Palaeolimnological and experimental evidence confirms that clearance of land and ploughing its surface weakens the phosphorus retentivity of catchments. The phosphorus transferred from arable land to drainage remains dominated by sorbed fractions which are scarcely bioavailable. Some forms of intensive market gardening or concentrated stock rearing may mobilise phosphates to drainage but it is deduced that drainage from agricultural land is not commonly a major source of readily bioavailable phosphorus in water. Careful budgeting of the phosphates in run-off from over-fertilised soils may nevertheless show that a proportionately small loss of bioavailable phosphorus can still be highly significant in promoting aquatic plant production. The bioavailable-phosphorus (BAP) load achieving the OECD threshold of lake eutrophy (35 mg P m(-3)) is calculated to be equivalent to a terrestrial loss rate of approximately 17.5 kg BAP km(-2) year(-1)), or only 1-2% of a typical fertiliser application. The output is shown to be comparable with the P yield from secondary treatment of the sewage produced by a resident population of 30-44 persons km(-2). With tertiary treatment, the equivalence is with approximately 200 persons km(-2).

Synthesis and Characterization of Antibacterial Ag−SiO2 Nanocomposite

Abstract: In order to increase antibacterial abilities and avoid aggregation of Ag nanoparticles, Ag−SiO2 nanocomposites were studied to achieve hybrid structure. SiO2 nanoparticles synthesized by the Stober method served as seeds for immobilization of Ag. The chemical binding structure and morphology of Ag−SiO2 nanocomposites and SiO2 nanoparticles were investigated with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The antibacterial properties of Ag−SiO2 nanocomposites were examined with disk diffusion assay and minimum inhibitory concentration (MIC). Results showed that Ag nanoparticles are homogeneously formed on the surface of SiO2 nanoparticles without aggregation and showed excellent antibacterial abilities.

Controlled Growth and Characterization of Tungsten Oxide Nanowires Using Thermal Evaporation of WO3 Powder

Abstract: Tungsten oxide (WO3) nanowires were prepared on a tungsten (W) substrate by thermal evaporation of WO3 powder at elevated temperature in a tube furnace. The morphology, structure, composition, and chemical state of the prepared nanowires were characterized by SEM, EDX, TEM, XRD, Raman spectroscopic, and XPS measurements. The nanowires grown using WO3 powder were found to have uniform morphology with a high density and a crystalline structure consistent with monoclinic WO3. The field-emission measurements showed that the prepared nanowires have a turn-on field of 4.8 V/μm. The role of WO3 powder in the growth of high-density nanowires has been discussed by comparing the above results with those of nanowires grown without using WO3 powder and also on a different substrate. Also, the effects of growth temperature on the chemical binding states and product morphology of the nanowires were investigated.

Study on the ablation threshold induced by pulsed lasers at different wavelengths

Abstract: A study of the effects induced by pulsed laser ablation on different materials as a function of the laser wavelength is presented. In particular the ablation at low laser fluence, of the order of 10 8 –10 10 W/cm 2 with ns pulse width, is investigated experimentally on different metals, semiconductors and polymers. Two theoretical models, explain the experimental results about the fluence threshold value measurements, as depending on the laser wavelength are discussed. The photothermal process is valid for the estimation of the threshold fluence for IR and visible radiation, both inducing thermal heating in metals and semiconductors through the photon-free electron energy transfer. This model is not valid for polymers. The photochemical process is valid for the estimation of the threshold fluence for UV radiation, which photon energy is higher with respect to the chemical binding energy. This radiation induces chemical bond breaking in insulators and scission and cross linking effects can be produced. This last model is not valid for metals and semiconductors.

Physiochemical microparticle sensors based on nonlinear magnetic oscillations

Abstract: Recently, the nonlinear rotation of single magnetic particles has emerged as a tool to measure physical parameters on the micro-scale. In this paper, detailed theoretical analyses are carried out for tailored microprobes that measure (1) local magnetic fields, (2) magnetic particle characteristics, (3) viscosity and (4) chemical binding, along with their corresponding experimental demonstrations. Such new physical measurement methods, using single micro- or nano-particles, in combination with previous chemical nanoparticle sensing methods, lead to a new class of physiochemical micro- and nano-particle sensors that may be of significant biomedical and technological interest.

Direct synthesis of W18O49 nanorods from W2N film by thermal annealing

Abstract: Tungsten oxide nanorods were prepared from W2N film by a simple annealing method. W2N film was deposited on a Si(100) substrate by chemical vapour deposition (CVD) at 450 °C, and then heating of the film at 600–700 °C produces a high density of tungsten oxide nanorods. The morphology, structure, composition and chemical binding states of the prepared nanorods were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) and transmission electron microscopy (TEM) measurements. XRD and TEM analysis showed that the grown nanorods were single-crystalline W18O49. According to XPS analysis, the W18O49 nanorods contained ~62% of W6+, ~28% of W5+, and ~10% of W4+. Field-emission measurements showed a low turn-on field of 9.5 V µm−1 for the W18O49 nanorods, indicating that they can be used as potential field emitters. Also, a synthesis reaction mechanism based on thermodynamics is proposed for the growth of tungsten oxide nanorods from W2N.

Direct Observation of Dipolar Couplings and Hydrogen Bonds across a β-Hairpin in 8 M Urea

Abstract: A detailed, quantitative description of the unfolded states of proteins at atomic resolution has been elusive due to enormous experimental and theoretical problems resulting from the huge number of degrees of freedom of an unfolded structural ensemble. In particular, direct long-range information has been extremely sparse. Here we show that such long-range information can be obtained by NMR with high sensitivity and precision from HN−HN residual dipolar couplings (RDCs) and hydrogen bond (H-bonds) scalar couplings for an unfolded, perdeuterated (amide protonated) protein (urea-denatured ubiquitin at pH 2.5). Besides numerous sequential contacts, the RDCs reveal the persistence of native-like structure in ubiquitin's first β-hairpin. This native-like structure is confirmed by the direct detection of H-bonds via h3JNC‘ H-bond scalar couplings as well as by chemical shifts, 3JHNHA couplings, and relaxation rates. A quantitative analysis suggests that despite 25% native backbone torsion angles indicated by th...

Atomic Layer Deposition and Electrical Properties of SrTiO3 Thin Films Grown Using Sr ( C11H19O2 ) 2, Ti ( Oi-C3H7 ) 4, and H2O

Abstract: Atomic layer deposited SrTiO 3 (STO) thin films were grown using Sr(C 11 H 19 O 2 ) 2 and Ti(Oi-C 3 H 7 ) 4 with a remote plasma activated or thermal H 2 O vapor as oxidant at growth temperatures ranging from 190 to 270°C. The as-grown films were amorphous and showed a low effective dielectric constant of -20 with a low leakage current density (< 10 -7 A/cm 2 at 1 V). The chemical binding status of the Sr ions varied with the degree of crystallization of the STO film. A reasonable film growth rate and stoichiometric cation composition were obtained when the vaporization temperature of Sr-precursor was <200°C with the thermal H 2 O vapor. The low density of the as-grown film induced a large shrinkage in the film thickness which caused microcracking of the crystallized films during postannealing, even with the increased H 2 O supply. Adoption of thin (∼5 nm) crystallized seed layer before the main layer STO growth improved the microstructure after the crystallization and the leakage current performance. As a result of the process optimization, the best electrical properties of an STO film grown on a Ru electrode were 0.45 nm for the equivalent oxide thickness and 1 X 10 -3 A/cm 2 for the leakage current density at 1 V.

Theoretical Study of C2H2 Adsorbed on Low-Index Cu Surfaces

Abstract: Ab initio density functional theory was used to determine the adsorption systems of C2H2 on Cu (100), (111), and (110) surfaces. Infinitely large models with three-dimensional periodic boundary conditions are implemented in these adsorption systems. The results show that the Cu(100) surface was modified from “square” to “rhombus” through the charge redistribution caused by adsorbing the C2H2 molecules. This reveals that the interaction energy dominates the adsorption system rather than the adsorption energy, which involves large deformation. The interaction energy values of C2H2/Cu systems on different surfaces have a sequence of C2H2/Cu(110) < C2H2/Cu(100) < C2H2/Cu(111). The tilting angle of the H atom is proportional to chemical binding of the systems.

Significant increase in the stability of rare gas hydrides on insertion of beryllium atom

Abstract: Chemical binding between a rare gas atom with other elements leading to the formation of stable chemical compounds has received considerable attention in recent years. With an intention to predict highly stable novel rare gas compounds, the process of insertion of beryllium atom into rare gas hydrides (HRgF with Rg = Ar , Kr, and Xe) has been investigated, which leads to the prediction of HBeRgF species. The structures, energetic, and charge distributions have been obtained using MP2, density functional theory, and CCSD(T) methods. Analogous to the well-known rare gas hydrides, HBeRgF species are found to be metastable in nature; however, the stabilization energy of the newly predicted species has been calculated to be significantly higher than that of HRgF species. Particularly, for HBeArF molecule, it has been found to be an order of magnitude higher. Strong chemical binding between beryllium and rare gas atom has also been found in the HBeArF, HBeKrF, and HBXeF molecules. In fact, the basis set superposition error and zero-point energy corrected Be–Ar bond energy calculated using CCSD(T) method has been found to be 112 kJ ∕ mol , which is the highest bond energy ever achieved for a bond involving an argon atom in any chemically bound neutral species. Vibrational analysis reveals a large blueshift ( ∼ 200 cm − 1 ) of the H–Be stretching frequency in HBeRgF with respect to that in BeH and HBeF species. This feature may be used to characterize these species after their preparation by the laser ablation of Be metal along with the photolysis of HF precursor in a suitable rare gas matrix. An analysis of the nature of interactions involved in the present systems has been performed using theory of atoms in molecules (AIM). Geometric as well as energetic considerations along with the AIM results suggest a substantial covalent nature of Be–Rg bond in these systems. Thus, insertion of a suitable metal atom into rare gas hydrides is a promising way to energetically stabilize the HRgX species, which eventually leads to the formation of a new class of insertion compounds, viz., rare gas metallohydrides.

Label-free sensing of binding to microarrays using Brewster angle straddle interferometry.

Abstract: We report an interferometric method to detect chemical binding at an interface. The interference layer consists of the thin native oxide on silicon, and we utilize nearly opposite phase shifts of light at the oxide/water and oxide/silicon interfaces to achieve near-complete destructive interference. We measure selective binding of thrombin in solution to DNA aptamers covalently bound to the oxide. The technique can be used to detect and quantify surface binding of less than 1 A of material, sensitivity similar to that of surface plasmon resonance imaging or arrayed imaging reflectometry. Results are in quantitative agreement with what is predicted theoretically. The method is very convenient to implement since it utilizes unmodified silicon wafers as substrates and is extremely insensitive to both probe light bandwidth and collimation.

The insertion of the antimicrobial peptide dicynthaurin monomer in model membranes: thermodynamics and structural characterization.

Abstract: This paper is focused on the thermodynamics and the structural investigation of the interaction of the antimicrobial peptide dicynthaurin monomer with model lipid membranes composed of mixtures of 1-palmitoyl-2-oleyl-glycerophosphocholine and -glycerophosphoglycerol. The thermodynamic binding parameters as obtained by isothermal titration calorimetry reveal strong binding toward the lipid model system dominated by large chemical binding constants which exceeds the electrostatic binding effects and thus suggests insertion of the amphipathic alpha-helical peptide into the hydrophobic membrane core. Circular dichroism study shows that the peptide exhibits trans-membrane alpha-helix secondary structure. Neutron diffraction measurements using partially deuterated sequences were successfully applied to determine the orientation of the peptide thus proving insertion into the hydrophobic membrane core. This insertion and the formation of higher order porelike aggregates is assumed to be the most relevant event in microbial membrane perturbation that in vivo finally leads to bacterial cell death on a fast time scale.

Chemical and Potential Bending Characteristics of SiNx/AlGaN Interfaces Prepared by In situ Metal-Organic Chemical Vapor Deposition

Abstract: We investigate the chemical and potential-bending characteristics of in situ SiNx/AlGaN interfaces prepared by metal-organic chemical vapor deposition. X-ray photoelectron spectroscopy showed that the in situ SiNx layer had typical chemical binding energies corresponding to the Si–N bonds. The in situ SiNx deposition brought no chemical degradation on the AlGaN surface at the SiNx/AlGaN interface, whereas the ex situ deposition of SiNx by a plasma process induced chemical disorder on the AlGaN surface including a composition change and the formation of interfacial oxides. A significant reduction in the surface band bending was observed on the AlGaN surface after the in situ SiNx passivation, probably due to a decrease in the surface state density.

QSAR and mechanistic interpretation of estrogen receptor binding.

Abstract: A multi-dimensional formulation of the COmmon REactivity PAttern (COREPA) modeling approach has been used to investigate chemical binding to the human estrogen receptor (hER). A training set of 645 chemicals included 497 steroid and environmental chemicals (database of the Chemical Evaluation and Research Institute, Japan - CERI) and 148 chemicals to further explore hER-structure interactions (selected J. Katzenellenbogen references). Upgrades of modeling approaches were introduced for multivariate COREPA analysis, optimal conformational generation and description of the local hydrophobicity of chemicals. Analysis of reactivity patterns based on the distance between nucleophilic sites resulted in identification of distinct interaction types: a steroid-like A-B type described by frontier orbital energies and distance between nucleophilic sites with specific charge requirements; an A-C type where local hydrophobic effects are combined with electronic interactions to modulate binding; and mixed A-B-C (AD) type. Chemicals were grouped by type, then COREPA models were developed for within specific relative binding affinity ranges of >10%, 10 > RBA > or = 0.1%, and 0.1 > RBA > 0.0%. The derived models for each interaction type and affinity range combined specific prefiltering requirements (interatomic distances) and a COREPA classification node using no more than 2 discriminating parameters. The interaction types are becoming less distinct in the lowest activity range for each chemicals of each type; here, the modeling was performed within chemical classes (phenols, phthalates, etc.). The ultimate model was organized as a battery of local models associated to interaction type and mechanism.

Specific capture of phosphopeptides on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry targets modified by magnetic affinity nanoparticles

Abstract: Specific capture of phosphopeptides from protein digests is a critical step for identification of phosphoproteins by mass spectrometry. In this study, we report a novel phosphopeptide-capture approach based on the specific interaction of phosphopeptides with a stainless steel target modified with magnetic affinity nanoparticles. The modification which was carried out by loading the suspension of nanoparticles into sample wells of the target did not require any pretreatment procedure to the target and did not involve chemical binding reactions. To isolate phosphopeptides, digests were loaded into the wells of the modified target for 10 min incubation, followed by rinsing with washing buffer to remove unbound species; matrix was then added to the captured phosphopeptides prior to analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Capturing the phosphopeptides on the modified target simplified significantly analytical operations and reduced sample loss. This approach has been applied to solution digests of α-casein, β-casein, and a mixture of five proteins; a number of phosphopeptides were confidently detected. Phosphopeptides from digests of 10 fmol β-casein could be isolated and detected by MALDI-TOFMS with this method. In addition, this approach has been applied successfully to the isolation of phosphopeptides from in-gel digestive products of sub-pmol phosphoproteins after separation by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE). Copyright © 2007 John Wiley & Sons, Ltd.

Sorption Removal of Pb(II) from Solution by Uncalcined and Calcined MgAl‐Layered Double Hydroxides

Abstract: Layered double hydroxide (LDH) with a Mg/Al molar ratio of 1:1 was synthesized by using a co-precipitation method and its calcined product (CLDH) was obtained by calcination of the MgAl-LDH at 500 °C. The sorption removal of Pb2+ from solution was investigated, finding that both LDH and CLDH show good sorption ability and they could be used as a new type of environmental sorbent for the removal of Pb2+ from water. The sorption kinetics and the sorption isotherms of Pb2+ on both LDH and CLDH can be described by the pseudo-second order kinetics and Freundlich isotherm, respectively, under the studied conditions. The sorption amounts of Pb2+ on LDH and CLDH are independent of pH in a pH range of about 3–10. The presence of NaNO3 may inhibit the sorption ofPb2+ on LDH while hardly affect that on CLDH. The sorption mechanism of Pb2+ on LDH and CLDH may be attributed to the surface precipitation and the surface complex adsorption. The surface complex adsorption may be further distinguished to the chemical binding adsorption forming the inner-sphere surface complexes and the electrostatic binding adsorption forming the outer-sphere surface complexes. The sorption mechanism of Pb2+ on LDH may be attributed to the surface precipitation and the electrostatic binding adsorption, while that on CLDH may be attributed to the surface precipitation and the chemical binding adsorption.

Binding, tuning and mechanical function of the 4-hydroxy-cinnamic acid chromophore in photoactive yellow protein.

Abstract: The bacterial photoreceptor protein photoactive yellow protein (PYP) covalently binds the chromophore 4-hydroxy coumaric acid, tuning (spectral) characteristics of this cofactor. Here, we study this binding and tuning using a combination of pointmutations and chromophore analogs. In all photosensor proteins studied to date the covalent linkage of the chromophore to the apoprotein is dispensable for light-induced catalytic activation. We analyzed the functional importance of the covalent linkage using an isosteric chromophore-protein variant in which the cysteine is replaced by a glycine residue and the chromophore by thiomethyl-p-coumaric acid (TMpCA). The model compound TMpCA is shown to weakly complex with the C69G protein. This non-covalent binding results in considerable tuning of both the pKa and the color of the chromophore. The photoactivity of this system, however, was strongly impaired, making PYP the first known photosensor protein in which the covalent linkage of the chromophore is of paramount importance for the functional activity of the protein in vitro. We also studied the influence of chromophore analogs on the color and photocycle of PYP, not only in WT, but especially in the E46Q mutant, to test if effects from both chromophore and protein modifications are additive. When the E46Q protein binds the sinapinic acid chromophore, the color of the protein is effectively changed from yellow to orange. The altered charge distribution in this protein also results in a changed pKa value for chromophore protonation, and a strongly impaired photocycle. Both findings extend our knowledge of the photochemistry of PYP for signal generation.

Heat treatment induced structural and optical properties of rf magnetron sputtered tantalum oxide films

Abstract: Rf magnetron sputtering technique was employed for preparation of tantalum oxide films on quartz and crystalline silicon (111) substrates held at room temperature by sputtering of tantalum in an oxygen partial pressure of 1x10-4 mbar. The films were annealed in air for an hour in the temperature range 573 – 993 K. The effect of annealing on the chemical binding configuration, structure and optical absorption of tantalum oxide films was systematically studied. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Haptic Manipulation of Microspheres Using Optical Tweezers Under the Guidance of Artificial Force Fields

Abstract: Using optical tweezers and a haptic device, microspheres having diameters ranging from 3 to 4 um (floating in a fluid solution) are manipulated in order to form patterns of coupled optical microresonators by assembling the spheres via chemical binding. For this purpose, biotin-coated microspheres trapped by a laser beam are steered and chemically attached to an immobilized streptavidin-coated sphere (i.e. anchor sphere) one by one using an XYZ piezo scanner controlled by a haptic device. The positions of all spheres in the scene are detected using a CCD camera and a collision-free path for each manipulated sphere is generated using the potential field approach. The forces acting on the manipulated particle due to the viscosity of the fluid and the artificial potential field are scaled and displayed to the user through the haptic device for better guidance and control during steering. In addition, a virtual fixture is implemented such that the desired angle of approach and strength are achieved during the binding phase. Our experimental studies in virtual and real environments with 8 human subjects show that haptic feedback significantly improves the user performance by reducing the task completion time, the number of undesired collisions during steering, and the positional errors during binding. To our knowledge, this is the first time that a haptic device is coupled with OT to guide the user during an optical manipulation task involving steering and assembly of microspheres to construct a coupled microresonator.

Structural Characterization and Thermal Decomposition Behavior of Microsized and Nanosized CaCO_3

Abstract: The surface organic modification of nanosized CaCO_3 with palmitic acid was carried out The prepared samples were characterized by SEM, TEM, XRD, FTIR, and TG-DTG techniques A comparative study on the crystal structure and thermal decomposition characteristics of nanosized CaCO_3, modified nanosized CaCO_3, and microsized CaCO_3 was made According to the spectra of FTIR, it was inferred that the chemical binding and the physical adsorption between palmitic acid and nanosized CaCO_3 have happened during the modification reaction The results also revealed that the infrared absorption peaks of C-O bond of modified and unmodified nanosized CaCO_3 shifted to a higher frequency by 35 cm~(-1) compared with that of microsized CaCO_3 The mechanism of blue shift in nanosized CaCO_3 was discussed, and it was believed that crystalline electric field effect and size effect influenced their infrared spectra TG-DTG analysis showed that nanosized CaCO_3, modified nanosized CaCO_3, and microsized CaCO_3 decomposed at 7350, 7647, and 7756 ℃, respectively The decrease of the decomposition temperature was supposed to be related to the lattice expansion and crystallographic deformation of nanosized CaCO_3

LOW-TEMPERATURE SYNTHESIZED ZnO NANONEEDLES: XPS AND PL ANALYSIS

Abstract: Evolution of morphology change was investigated for ZnO nanoneedle array grown by low-temperature MOCVD. Well-aligned ZnO nanoneedle array was deposited on the ZnO buffer-film/Si substrate at temperatures below 500°C. A rod-shaped ZnO nanowire in the initial growth stage changed into needle-shaped as the deposition proceeds. ZnO nanoneedle array deposited on the annealed buffer-film showed better alignment compared to that deposited on the as-grown film. XPS analysis showed that Zn 2p peak has a single binding energy state of a stoichiometric Zn–O bond while O 1 s peak has three different chemical binding states. Highly crystalline ZnO nanoneedle array showed a strong bandedge emission at 380 nm in photoluminescence measurements.