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At least 559 records · Page 31Linked to original sources
PubMed2001

New pillared layered gallium phosphonates in the gallium/1,2-ethylenediphosphonic acid system.

1,2-Ethylenediphosphonic acid reacts with gallium nitrate in water to give new pillared layered gallium phosphonates, the structure of which depends on the experimental conditions used for their preparation. Thus, Ga(4)(O(3)PC(2)H(4)PO(3))(3) (1) and Ga(2)(OH)(2)(O(3)PC(2)H(4)PO(3)) (2) were isolated and the structure of 1 was solved by single-crystal X-ray diffraction, while 2 was shown to have the same metal/PO(3) arrangement as the previously described Ga(OH)(O(3)PCH(3)). Ga(4)(O(3)PC(2)H(4)PO(3))(3) (1) is triclinic, with space group P1 with Z = 2, a = 5.1480(4), b = 8.0354(7), and c = 12.383(1) A; alpha = 91.34(1), beta = 101.40(1), and gamma = 90.86(1) degrees; V = 501.9(1) A(3). The structure of 1 is unusual with (i) mixed GaO(4) and GaO(5) sites while a 6-fold coordination is observed for gallium in (2) and (ii) the presence of the organic moiety within both the layers and the interlayer space. The two compounds were fully characterized using (31)P and (71)Ga solid-state NMR.

Journal Article↗
PubMed2002

Lewis acidity of gallium halides.

The Lewis acidity of GaF(3), GaF(2)Cl, GaFCl(2), and GaCl(3) in acid-base interactions has been studied by taking ammonia as their electron-donating counterpart. We have derived an unoccupied reactive orbital that shows the maximum localization on the Ga atomic center for each species. The orbital is located lower in energy compared to those in the corresponding boron and aluminum halides. In contrast to boron halides, the unoccupied reactive orbital of the acid site tends to be delocalized considerably on the halogens as the fluorines are substituted by chlorines in gallium halides. The trend observed in the effects of fluorine and chlorine on the acidity of the gallium halides is opposite to those found in the boron halides. This cannot be interpreted solely in terms of the electron-accepting strength of the gallium center, but can be understood by including electrostatic interactions and closed-shell repulsion with ammonia in the adducts. The origin of the difference in Lewis acidity of BCl(3), AlCl(3), and GaCl(3) has been clarified.

Journal Article↗
PubMed2001

Trapping of an activated HF molecule inside a double four-ring unit: a quantum chemical model of the microporous fluorinated gallium phosphate ULM-18.

The penetration of a proton into the prenucleation building unit of a microporous gallophosphate and its interaction with an encapsulated fluorine anion have been investigated by means of DFT calculations. The inorganic part of the fluorinated gallophosphate ULM-18 has been modeled by a neutral, double four-ring (D4R) unit of formula [(GaOH)4(HPO4)4-H2O] encapsulating the fluorine ion. Assuming the cage to be rigid and to retain throughout the calculations the geometry determined from X-ray diffraction (XRD), the position of F(-) has been optimized, either as an isolated guest species or in the presence of an incoming proton. In agreement with the XRD structure, the fluorine atom has been shown to occupy in both cases a nonsymmetric position in the cage, being attached to three gallium atoms out of four. The distribution of the molecular electrostatic potential inside and outside the (F(-))@[(GaOH)4(HPO4)4-H2O] system has provided indications concerning the pathways that could be used by an incoming proton to penetrate the D4R unit and to approach the fluorine anion. The migration of a proton from an external site of fixation to the interior of the D4R unit has been found possible through two faces out of six. In both cases, the process has been found exothermic by approximately 0.17 eV and the energy barrier was estimated to approximately 0.8 eV. Inside the gallophosphate cage, the proton first adopts a position typical of a strong F...H...O bond made possible through an important shift of the fluorine anion away from the tripod of bonded gallium atoms. Then, the F(-)...H(+) system can easily evolve back and forth on a flat potential curve between one of the F...H...O bonded conformations and a situation characterized by the cleavage of the H...O link and the formation of a moderately activated F-H molecule, with the fluorine still attached to three gallium atoms.

Journal Article↗
PubMed2002

Molten gallium as a catalyst for the large-scale growth of highly aligned silica nanowires.

The vapor-liquid-solid (VLS) process is a fundamental mechanism for the growth of nanowires, in which a small size (5-100 nm in diameter), high melting point metal (such as gold and iron) catalyst particle directs the nanowire's growth direction and defines the diameter of the crystalline nanowire. In this article, we show that the large size (5-50 microm in diameter), low melting point gallium droplets can be used as an effective catalyst for the large-scale growth of highly aligned, closely packed silica nanowire bunches. Unlike any previously observed results using gold or iron as catalyst, the gallium-catalyzed VLS growth exhibits many amazing growth phenomena. The silica nanowires tend to grow batch by batch. For each batch, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. The force between the batches periodically lifts the gallium catalyst upward, forming two different kinds of products on a silicon wafer and alumina substrate. On the silicon wafer, carrot-shaped tubes whose walls are composed of highly aligned silica nanowires with diameters of 15-30 nm and length of 10-40 microm were obtained. On the alumina substrate, cometlike structures composed of highly oriented silica nanowires with diameters of 50-100 nm and length of 10-50 microm were formed. A growth model was proposed. The experimental results expand the VLS mechanism to a broader range.

Journal Article↗
PubMed2005

Influence of oxygen on the crystalline-amorphous transition in gallium nitride films.

Oxygen is a common impurity in nitride-based materials that affects the properties of technologically important materials such as gallium nitride semiconductors. In this work, the influence of oxygen on the structural evolution of GaN films is investigated using near-edge X-ray absorption fine structure (NEXAFS). The combined spectra of Ga L3-edge, N K-edge, and O K-edge indicate that the gallium coordination, formed by a mixture of oxide and nitride bonds, is directly dependent on the concentration of oxygen in the films. Below 24 atom % oxygen, gallium atoms are tetrahedrally coordinated within the films, while at higher concentrations the octahedral environment persists.

Journal Article↗
PubMed2005

Solvent-dependent assembly of terphenyl- and quaterphenyldithiol on gold and gallium arsenide.

The assembly of terphenyldithiol (TPDT) and quaterphenyldithiol (QPDT) on gold and gallium arsenide from ethanol (EtOH), tetrahydrofuran (THF), and solutions consisting of both solvents has been characterized by near-edge X-ray absorption fine structure spectroscopy. The surface coverage and the average orientation of both TPDT and QPDT on gold are solvent-independent. These molecules readily form monolayers on gold with an ensemble-average backbone tilt of 30 degrees +/- 3 degrees from the substrate normal. In sharp contrast, the assembly of TPDT and QPDT on gallium arsenide is extremely solvent-sensitive. At high ethanol fractions, both molecules form monolayers with an ensemble-average orientation that is indistinguishable from those on gold substrates. At low ethanol fractions and in pure THF, however, these molecules are disordered on gallium arsenide and the surface coverage is poor.

Journal Article↗
PubMed2002

Carbon nanothermometer containing gallium.

Many applications have been found for carbon nanotubes, and we can now add a role as a 'nanothermometer' to this list. We describe how the height of a continuous, unidimensional column of liquid gallium inside a carbon nanotube (up to about 10 micrometres long and about 75 nanometres in diameter) varies linearly and reproducibly in the temperature range 50-500 degrees C, with an expansion coefficient that is the same as for gallium in the macroscopic state. We chose gallium as our thermal indicator because it has one of the greatest liquid ranges of any metal (29.78-2,403 degrees C) and a low vapour pressure even at high temperatures. This nanothermometer should be suitable for use in a wide variety of microenvironments.

Journal Article↗
PubMed2006

A gallium nitride single-photon source operating at 200 K.

Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III-V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.

Journal Article↗
PubMed2005

Axially modified gallium phthalocyanines and naphthalocyanines for optical limiting.

Phthalocyanines (Pcs) offer a high architectural flexibility in structure, which facilitates the tailoring of their physical, optoelectronic and chemical parameters over a very broad range. This tutorial review describes the recent advances in the synthesis of soluble axially substituted or bridged gallium phthalo- and naphthalocyanine compounds, and their photophysical and nonlinear optical properties. The exploitation of the chemical reactivity of the Ga-Cl bond can allow the preparation of a series of highly soluble axially substituted and bridged Pc complexes. Axial substituents in Pcs influence favourably nonlinear optical absorption for the presence of a dipole moment perpendicular to the macrocycle in the axially substituted phthalocyanines. All Z-scans performed exhibit a decrease of transmittance about the focus typical of an induced positive nonlinear absorption of incident light. Substitution and dimerization of the phthalocyanine monomer resulted in significant reductions in the saturation energy density of the material displaying clear evidence of the usefulness of structurally modifying the gallium phthalocyanine unit. Similar to indium phthalocyanines, gallium phthalocyanines are also among the most promising materials that have been investigated as limiters of intense light and the current series presents a selection of structural modifications useful for varying their nonlinear optical properties.

Journal Article↗
PubMed1992

Bone and gallium scintigraphy in sacral chordoma. Report of four cases.

Bone scintigraphy with Tc-99m HMDP and gallium scintigraphy were evaluated in four patients with a primary sacrococcygeal chordoma. All lesions showed a photon-deficient or cold lesion corresponding to the tumor on bone scintigraphy, with no abnormal accumulation clearly observed on gallium scintigraphy. These findings led the authors to conclude that a midline sacrococcygeal tumor showing reduced uptake or a cold lesion on bone scintigraphy and no increased accumulation on gallium scintigraphy could be a chordoma rather than the malignant neoplasm suspected in this region.

Adult↗
PubMed2002

Spin-lattice relaxation enhancement in liquid gallium confined within nanoporous matrices.

Nuclear spin relaxation for liquid gallium embedded into nanoporous matrices was found to accelerate remarkably compared to the bulk melt. NMR measurements on two gallium isotopes showed that the dominant mechanism of relaxation was changed from magnetic to quadrupolar and the relation rate depended on the Larmor frequency. The correlation time of electric field gradient fluctuations was estimated using data for quadrupolar relaxation contribution and was found to increase drastically compared to bulk, which corresponded to slowing down mobility in confined liquid gallium.

Journal Article↗
PubMed2003

Hot and solid gallium clusters: too small to melt.

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for Ga(+)(n) (n=17 39, and 40) over a 90-720 K temperature range. For Ga+39 and Ga+40 a broad maximum in the heat capacity-a signature of a melting transition for a small cluster-occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for Ga+17.

Journal Article↗
PubMed1996

Diagnosis of alveolitis in interstitial lung manifestation in connective tissue diseases: importance of late inspiratory crackles, 67 gallium scan and bronchoalveolar lavage.

The diagnostic relevance of bronchoalveolar lavage (BAL) and associated non-invasive findings in connective tissue diseases (CTD) has not been established regarding alveolitis so far. The goal of the study was to determine the relations between BAL cell differential count and findings of non-invasive diagnostic procedures for alveolitis to predict the clinical value of BAL in CTD. One hundred-five patients (92 non-smokers; 13 smokers) with CTD (73 patients with systemic sclerosis, 19 with systemic lupus erythematosus, 13 with primary Sjögren's syndrome) had symptoms or signs of lung involvement and were further examined (lung function test, chest radiography, thoracic computed tomography, 67 gallium scintigraphy and BAL). The relations between BAL in middle lobe and cell count differentiation to non-invasive investigations were analyzed by logistic regression. In all CTD patients investigated a pulmonal involvement occurred based on non-invasive methods. Regarding non-invasive methods, alveolitis determined by BAL cell differential count was significantly associated with an increased 67-gallium uptake and late inspiratory crackles (P < 0.01), and to a lesser extent with an abnormal interstitial pattern in CT (P < 0.055). Parameters of lung function and laboratory parameters were related to alveolitis using multivariate testing. Considering the alveolitis subtype (granulo- or lymphocytosis), only a reduced FEV1 showed a relationship to granulocytic alveolitis (P < 0.01). Late inspiratory crackles and increased 67 gallium uptake as non-invasive diagnostic findings point out alveolitis in CTD remarkably. Therapeutic and prognostic aspects necessitate BAL to specify the type of alveolitis (lymphocytosis or granulocytosis or mixed forms) in CTD patients with lung manifestation. Non-invasive diagnostic procedures cannot predict the type of alveolitis sufficiently.

Adult↗
PubMed1998

[A comparative study between gallium alloy and amalgan for the creep and clinical handing]

OBJECTIVE: This study showed that the creep value of gallium alloy is higher than that of amalgam,but it was within the limits permitted by ISO.It was suggested that the poor handing characteristics of gallium alloy may make it difficult to use in clinic.So,if gallium alloy could use in the clinic or not,according to it's clinical handling characteristic.

Journal Article↗
PubMed1997

[Comparative study of grind-resistance,corrosion,and adhesion of dental plaque on gallium and amalgam alloy's filling]

The adhesion of plaque on dental restorative between gallium alloy and amalgam alloy were compared.The results showed that plaque index and plaque account of gallium alloy was higher than those of amalgam,there was statistically significance(P<0.01).It was possible that secondary caries of gallium alloy's restorative may be higher than those of amalgam.One the other hand,the surface of restorative polished was necessary to improve the adhesion of plaque and to prevent the secondary caries.

Journal Article↗
PubMed2006

[Precipitation trapping with phenylfluorone and determination of trace gallium, germanium, molybdenum and indium by GFAAS].

The preconcentration of trace gallium, germanium, molybdenum and indium by trapping with precipitation of phenylfluorone (PF), and the determination of the elements by GFAAS were developed. The effects such as those of acidity, amounts of PF, aging time, volume of test solution, and the coexistent ions on the preconcentration of the trace elements were examined in detail. The optimum conditions of preconcentration for Ga(III) were pH approximately 2 test solution 500 mL with added 10.00 mg x mL(-1) PF (2.00 mL) and aging for 4 h, those for Ge(IV) were pH approximately 2 test solution 500 mL with added 10.00 mg x mL(-1) PF (4.00 mL) and aging for 10 h, those for Mo(V) were pH approximately 3 test solution 1 000 mL with added 10.00 mg x mL(-1) PF (3.00 mL) and aging for 6 h, and those for In(III) were pH approximately 5 test solution 100 mL with added 10.00 mg x mL(-1) PF (3.00 mL) and aging for 10 h. The experiment results showed that the main contribution to trapping trace gallium, germanium, molybdenum and indium with PF precipitation was post-precipitation instead of coprecipitation. The detection limits (3s) were 0.12 ng x mL(-1) for gallium, 0.30 ng x mL(-1) for germanium, 0.046 ng x mL(-1) for molybdenum and 2.7 ng x mL(-1) for indium. The developed methods were successfully applied to the determination of trace amount of the elements in water samples, geological standard reference materials, and zinc concentrate samples by graphite furnace atomic absorption spectrometry.

English Abstract↗
PubMed2000

Agreement rates among single photon emission computed tomography using gallium-67, computed axial tomography and lymphangiography for Hodgkin disease and correlation of image findings with clinical outcome.

BACKGROUND: This study was undertaken to systematically evaluate the agreement rates among single photon emission computed tomography using gallium-67 (Ga-67 SPECT), lymphangiography (LAG), and computed axial tomography (CT) scan findings for Hodgkin disease and to correlate radiologic findings with clinical outcome. METHODS: One hundred three previously untreated patients with Hodgkin disease who had Ga-67 SPECT scan between August 1992 and December 1994 at our institution form the basis of this study. The agreement rates among Ga-67 SPECT, LAG, and CT scan findings were calculated by sites from the pretreatment evaluation throughout the courses of chemotherapy. The probabilities of recurrence or progression by sites were correlated with the radiologic findings. RESULTS: The median follow-up was 3 years. The pretreatment agreement ranged from 75% to 100% between Ga-67 SPECT and CT scans, 85-100% between CT scan and LAG, and 74-99% between Ga-67 SPECT and LAG. A greater variation in agreement was observed once chemotherapy was started, the site with the least agreement being the mediastinum. The most common site of the recurrence or progression was also the mediastinum. When the CT scan showed persistent abnormality even after Ga-67 SPECT turned negative after chemotherapy, the chances of mediastinal recurrence or progression were 3 in 34 and 3 in 18 after 1-3 cycles and 4-6 cycles, respectively. CONCLUSIONS: Although there was a relatively high correlation between Ga-67 SPECT and the other modalities, the intrinsic limitation of planar Ga-67 was still observed in Ga-67 SPECT especially in the mediastinum. There was still a moderate risk of mediastinal recurrence or progression even after residual CT scan abnormality lost gallium avidity from chemotherapy.

Adolescent↗
PubMed1992

Absolute quantitation of gallium-67 citrate accumulation in the lungs and its importance for the evaluation of disease activity in pulmonary sarcoidosis.

Our modification of a method for the absolute quantification of gallium-67 uptake in lungs with a scintillation camera and computer is described. The uptake of 67Ga in lungs, expressed in percentage of administered radioactivity, was determined by the transmission-emission method. We proved theoretically and experimentally that a 67Ga planar source could be replaced with a 57Co planar source. The performance of lung perfusion scans allows a more accurate delineation of the regions of interest on gallium scans. The method was applied to control subjects (n = 27) and to patients (n = 114) suffering from biopsy-proven pulmonary sarcoidosis (28 with inactive and 86 with active disease). The obtained results were compared with chest X-ray findings, the percentage of lymphocytes in the bronchoalveolar fluid (BAF-ly%), and serum angiotensin-converting enzyme (SACE) values. The method seems suitable for the assessment of disease activity in sarcoidosis. It is more accurate in detecting parenchymal involvement in lung sarcoidosis than the commonly used X-ray criteria. No correlation was found between 67Ga uptake and the BAF-ly% and SACE values.

Bronchoalveolar Lavage Fluid↗