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PubMed2002

Siting of antimony dopants and gallium in Ba(8)Ga(16)Ge(30) clathrates grown from gallium flux.

A series of antimony-doped Ba(8)Ga(16)Ge(30) clathrates was grown as large crystals from gallium flux. These compounds form in the cubic space group Pm(-)3n, with the unit cell parameter varying from 10.784(5) to 10.9008(6) A as the amount of GaSb substituting for germanium atoms in the framework is increased. It was found that more antimony than extra gallium was incorporated into the material and that a specific site (the 24k Wyckoff site) was favored by this element. (71)Ga NMR was carried out to determine the siting of gallium; it fills the 6c site preferentially.

Journal Article↗
PubMed2005

Reactions of a gallium(II)-diazabutadiene dimer, [{{[(H)C(Bu(t))N]2}GaI}2], with [ME(SiMe3)2] (M = Li or Na; E = N, P, or As): structural, EPR, and ENDOR characterization of paramagnetic gallium(III) pnictide complexes.

The reactions of the paramagnetic gallium(II) complex [{(Bu(t)-DAB)GaI}2] (Bu(t)-DAB = {(Bu(t))NC(H)}2) with the alkali metal pnictides [ME(SiMe3)2] (M = Li or Na; E = N, P, or As) have been carried out under a range of stoichiometries. The 1:2 reactions have led to a series of paramagnetic gallium(III)-pnictide complexes, [(Bu(t)-DAB)Ga{E(SiMe3)2}I] (E = N, P, or As), while two of the 1:4 reactions afforded [(Bu(t)-DAB)Ga{E(SiMe3)2}2] (E = P or As). In contrast, treatment of [{(Bu(t)-DAB)GaI}2] with 4 equiv of [NaN(SiMe3)2] resulted in a novel gallium heterocycle coupling reaction and the formation of the diradical species [(Bu(t)-DAB)Ga{N(SiMe3)2}{[CC(H)N2(Bu(t))2]Ga[N(SiMe3)2]CH3}]. The mechanism of this unusual reaction has been explored, and evidence suggests it involves an intramolecular transmethylation reaction. The X-ray crystal structures of all prepared complexes are reported, and all have been characterized by EPR and ENDOR spectroscopies. The observed spin Hamiltonian parameters provide a detailed picture of the distribution of the unpaired spin density over the molecular frameworks of the complexes.

Journal Article↗
PubMed2003

What should be impossible: resolution of the mononuclear gallium coordination complex, Tris(benzohydroxamato)gallium(III).

Complexes of Ga3+, a d10 metal ion which lacks ligand-field-stabilization energy, are considered labile. In fact, hexaaquagallium(III) has a ligand exchange rate of 403 s-1, 2.5 times that of the analagous Fe3+ complex (Hugi-Cleary, D.; Helm, L.; Merbach, A. E. J. Am. Chem. Soc. 1987, 109, 4444-4450). Given this lability, resolution of Ga3+ complexes should be impossible. Despite this, we report the resolution of the Lambda and Delta isomers of tris(benzohydroxamate)gallium (III) (1), the first resolution of a mononuclear gallium complex. Not only is resolution possible, but these resolved complexes show remarkable resistance to racemization in aprotic solvents. The unprecedented stability of Lambda- and Delta-1 is a surprise, and as such, alters our understanding of classical coordination chemistry.

Circular Dichroism↗
PubMed2002

Two chain gallium fluorodiphosphates: synthesis, structure solution, and their transient presence during the hydrothermal crystallisation of a microporous gallium fluorophosphate.

Two novel gallium fluorodiphosphates have been isolated and their structures solved ab initio from powder X-ray diffraction data; the materials readily interconvert under hydrothermal conditions, and are metastable with respect to an open-framework zeolitic gallium fluorophosphate, during the synthesis of which they are present as transient intermediates.

Crystallography↗
PubMed1991

Targeting iron-dependent DNA synthesis with gallium and transferrin-gallium.

While iron is essential for numerous intracellular processes, its critical role in DNA synthesis relates to the activity of the iron-containing M2 subunit of ribonucleotide reductase, the enzyme responsible for the synthesis of deoxyribonucleotides. Gallium, a metal which resembles iron with respect to transferrin (Tf) binding, cellular uptake by the Tf receptor and incorporation into ferritin, blocks the cellular uptake of iron and inhibits cell growth. Exposure of HL60 cells to Tf-gallium (Ga) results in decreased deoxyribonucleotide synthesis and a diminution in the electron spin resonance (ESR) spectroscopy signal of ribonucleotide reductase, findings consistent with inhibition of this enzyme. In the present study, Ga nitrate blocked the uptake of 59Fe by L1210 cells and inhibited their proliferation. The ribonucleotide reductase M2 subunit ESR signal in cell cytoplasmic extracts was markedly inhibited in Ga-treated cells; however, the signal was restored to normal within 10 min of exposure of these cytoplasmic extracts to ferrous ammonium sulfate. These results confirm that Ga inhibits DNA synthesis by specifically limiting the amount of intracellular iron needed for the activity of the M2 subunit of ribonucleotide reductase. Further studies utilizing HL60 cells made resistant to Ga showed that these cells were also more resistant to growth inhibition by an anti-Tf receptor monoclonal antibody and deferoxamine. Ga blocks cell growth through inhibition of iron-dependent DNA synthesis. Cells appear to overcome the effects of Ga through compensatory mechanisms involving cellular iron metabolism.

Animals↗
PubMed1997

Reactions of Transition Metal Carbonyl Dianions with (Organo)gallium Chlorides: Anionic Gallium Complexes of Chromium, Iron, and Manganese. Structure of [PPN](2){[(CO)(4)Fe-Ga(CH(3))-Fe(CO)(4)]}

Salt elimination reactions between the divalent transition carbonyl metalates [L(CO)(n)()M](2)(-) (M = Cr, Mn, Fe; L = CO, NO; n = 3, 4) and the (organo)gallium halides Cl(a)()GaR(3)(-)(a)() (R = CH(3), CH(2)CH(3); a = 1, 2, 3) as well as the intramolecularly donor stabilized species ClGa[(CH(2))(3)NMe(2)](R) (R = Cl, Me, (t)Bu) have been studied in some detail. Novel stable anionic (organo)gallium and chlorogallium metal complexes of the types {[L(CO)(n)()M]Ga[(CH(2))(3)NMe(2)](R)}(-) (1-6), {[L(CO)(n)()M]GaCl(2)}(-) (7, 8), {[L(CO)(n)()M]Ga(Cl)(R)}(-) (9, 10), and {[L(CO)(n)()M](2)Ga(CH(3))}(2)(-) (11-13) have been prepared in high yields and were fully characterized by means of elemental analysis, infrared nu(CO) data, and NMR spectroscopy. The effect of substituents at the Ga center on the Lewis acidity was studied by temperature-dependent NMR (inversion at the N atom of the alkylamine ligand) using the compounds 1-6. The compounds 7-10 are supposed to be dimeric. The dianionic complex [PPN](2){[(CO)(4)Fe-Ga(CH(3))-Fe(CO)(4)]} (11a) was also characterized by single-crystal X-ray diffraction: monoclinic, C2/c, a = 2699.1(3) pm, b = 1411.2(2) pm, c = 2392.8(3) pm, beta = 127.45(1) degrees, V = 7236 x 10(6) pm(3), Z = 4, and R = 0.038 (R(w) = 0.097). The diminished Lewis acidity of the compounds 1-13 is explained by an electrostatic effect, which also stabilizes low-coordinate Ga centers without steric shielding.

Journal Article↗
PubMed2000

Large disparity between gallium and antimony self-diffusion in gallium antimonide.

The most fundamental mass transport process in solids is self-diffusion. The motion of host-lattice ('self-') atoms in solids is mediated by point defects such as vacancies or interstitial atoms, whose formation and migration enthalpies determine the kinetics of this thermally activated process. Self-diffusion studies also contribute to the understanding of the diffusion of impurities, and a quantitative understanding of self- and foreign-atom diffusion in semiconductors is central to the development of advanced electronic devices. In the past few years, self-diffusion studies have been performed successfully with isotopically controlled semiconductor heterostructures of germanium, silicon, gallium arsenide and gallium phosphide. Self-diffusion studies with isotopically controlled GaAs and GaP have been restricted to Ga self-diffusion, as only Ga has two stable isotopes, 69Ga and 71Ga. Here we report self-diffusion studies with an isotopically controlled multilayer structure of crystalline GaSb. Two stable isotopes exist for both Ga and Sb, allowing the simultaneous study of diffusion on both sublattices. Our experiments show that near the melting temperature, Ga diffuses more rapidly than Sb by over three orders of magnitude. This surprisingly large difference in atomic mobility requires a physical explanation going beyond standard diffusion models. Combining our data for Ga and Sb diffusion with related results for foreign-atom diffusion in GaSb (refs 8, 9), we conclude that the unusually slow Sb diffusion in GaSb is a consequence of reactions between defects on the Ga and Sb sublattices, which suppress the defects that are required for Sb diffusion.

Journal Article↗
PubMed2003

Bone tissue incorporates in vitro gallium with a local structure similar to gallium-doped brushite.

During mineral growth in rat bone-marrow stromal cell cultures, gallium follows calcium pathways. The dominant phase of the cell culture mineral constitutes the poorly crystalline hydroxyapatite (HAP). This model system mimics bone mineralization in vivo. The structural characterization of the Ga environment was performed by X-ray absorption spectroscopy at the Ga K-edge. These data were compared with Ga-doped synthetic compounds (poorly crystalline hydroxyapatite, amorphous calcium phosphate and brushite) and with strontium-treated bone tissue, obtained from the same culture model. It was found that Sr(2+) substitutes for Ca(2+) in the HAP crystal lattice. In contrast, the replacement by Ga(3+) yielded a much more disordered local environment of the probe atom in all investigated cell culture samples. The coordination of Ga ions in the cell culture minerals was similar to that of Ga(3+), substituted for Ca(2+), in the Ga-doped synthetic brushite (Ga-DCPD). The Ga atoms in the Ga-DCPD were coordinated by four oxygen atoms (1.90 A) of the four phosphate groups and two oxygen atoms at 2.02 A. Interestingly, the local environment of Ga in the cell culture minerals was not dependent on the onset of Ga treatment, the Ga concentration in the medium or the age of the mineral. Thus, it was concluded that Ga ions were incorporated into the precursor phase to the HAP mineral. Substitution for Ca(2+ )with Ga(3+) distorted locally this brushite-like environment, which prevented the transformation of the initially deposited phase into the poorly crystalline HAP.

Animals↗
PubMed2006

Synthesis, characterization, and X-ray crystal structure of a gallium monohydroxide and a hetero-bimetallic gallium zirconium oxide.

A monomeric hydroxide of gallium, LGa(Me)OH, containing terminal hydroxide and methyl groups was prepared by the hydrolysis of LGa(Me)Cl in the presence of N-heterocyclic carbene and water [L = HC{(CMe)(2,6-i-Pr2C6H3N)}2] in high yield and in a pure form. LGa(Me)OH was used as a synthon to assemble the first hetero-bimetallic compound with a Ga-O-Zr core, [(LGaMe)(Cp2ZrMe)](mu-O).

Crystallography, X-Ray↗
PubMedDate not supplied

Inhibitory effects of gallium chloride and tris (8-quinolinolato) gallium III on A549 human malignant cell line.

The effects of two gallium (Ga) compounds, Ga chloride (GaCl3) and tris(8-quinolinolato)Ga (III) on the viability of A549 human malignant lung adenocarcinoma cells were investigated. The results demonstrated that both drugs reduced the viability of A549 cells but to different extents. The inhibitory effects of tris(8-quinolinolato)Ga (III) were 10 times more profound than those produced by GaCl3. The IC50 was obtained with 2.5 microM of tris(8-quinolinolato)Ga (III) and 25 microM GaCl3 after an exposure time of 48 hours. Further, whereas the inhibitory effects of GaCl3 were both dose and time-dependent those of tris(8-quinolinolato)Ga (III) appeared to be only dose-dependent, indicating differences in their mechanism of action. Comparison with data drawn from the literature suggests that GaCl3 seems to be in the same range of activity as Ga nitrate or Ga-pyridoxal isocotinoyl hydrazone. Tris(8-quinolinolato)Ga (III) could be as effective as transferrin-Ga, but with the advantage of oral administration and a greater bioavailability of the tris(8-quinolinolato)Ga (III) compound.

Adenocarcinoma↗
PubMed1992

Gallium-67 distribution in a man with a decrease in both transferrin and hepatic gallium-67 concentration.

A patient with reduced transferrin concentration had a 67Ga scintigram that showed uptake in a peritoneal abscess, pericarditis and pleural effusion but only faint liver uptake. Gallium-67 activity was measured in liver, lung, muscle and plasma samples obtained at autopsy. The percent injected dose/kg for liver and plasma samples was considerably lower than previously reported while that in muscle and lung tissues values were comparable to prior data. In this patient, sites on transferrin available to bind 67Ga were reduced from the normal 40 microM to 5.2 microM; this in turn increased the concentration of radiogallate from 1% to 7%. This elevated free activity increased 67Ga excretion and reduced the amount of 67Ga*transferrin species. These results and those of previous studies suggest that liver uptake is slower than abscess uptake and more sensitive to concentration of 67Ga*transferrin. Iron status is an important facet of the interpretation of 67Ga scintigrams.

Abscess↗
PubMed1990

Gallium-67/stable gadolinium antagonism: MRI contrast agent markedly alters the normal biodistribution of gallium-67.

An 11-yr-old patient was scanned 96 hr after the administration of gallium-67 (67Ga). The scan emulated the biodistribution of a typical bone-seeking radipharmaceutical-rather than that of 67Ga. None of the factors previously identified with alteration of the biodistribution of 67Ga were found. However, the patient had been injected with gadopentetate in conjunction with magnetic resonance imaging 4 hr before receiving the 67Ga. Gadolinium appears to cause a strong carrier-like effect in 67Ga scans.

Burkitt Lymphoma↗
PubMed1990

[Studies on gallium alloys for dental restorations. 2. Electron probe microanalysis for hardened gallium alloys].

Hardened gallium alloys were analyzed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The cores, matrix and white irregular shape phases were visible with SEM. The round or irregular shape cores contained Ag, Pd, Cu and Zn but did not contain Ga and In. The dark irregular shape matrix, which surrounded the core, consisted of Ga-Ag, Ga-Pd, Ga-Cu and Ga-Sn phases. However, the amount of Ga-Sn phase was very low. The white phase in the matrix was Ag-In phase.

Dental Alloys↗
PubMed1978

Studies on gallium accumulation in inflammatory lesions: I. Gallium uptake by human polymorphonuclear leukocytes.

The mechanism of ionic gallium-67 localization in inflammatory lesions was studied. Human polymorphonuclear leukocytes (PMN) had higher Ga-67 uptake than lymphocytes, whereas red blood cells had no affinity for Ga-67. Uptake by PMN showed temperature dependence, was independent of Ga-67 concentrations, and was not inhibited by metabolic inhibitors. However, its binding to PMN could be removed by trypsin but not by neuraminidase. These results are consistent with the hypothesis that the plasma membrane serves as a diffusion barrier and Ga-67 only binds to the surface of the PMN plasma membrane. When this membrane's permeability barrier was disrupted, as in heat-killed PMN, Ga-67 uptake increased markedly. Experimental abscesses were induced with E. coli or turpentine in rabbits. Twenty-four hours after i.v. injection, only 20% of Ga-67 in abscesses was in fractions containing intact PMN, cell debris or bacteria; the remainder was in a soluble, non-cellular fraction (2,500-g supernatant).

Abscess↗
PubMed1993

Potential gallium-68 tracers for imaging the heart with PET: evaluation of four gallium complexes with functionalized tripodal tris(salicylaldimine) ligands.

Gallium-67 and 68Ga complexes have been synthesized with tripodal hexadentate salicylaldimine ligands derived from 1,1,1-tris(salicylaldiminomethyl)ethane, sal3tame. The four ligands evaluated contained alkoxy substituents (n-BuO-, iso-BuO-, sec-BuO-, and n-PrO-) on the terminal ethane carbon of the ligand backbone. In the case of the n-PrO-derivative, the tris(salicylaldimine) ligand was additionally substituted with methoxy groups in the 5-position of the aromatic rings. The 67Ga and 68Ga-complexes of these ligands were prepared by ligand exchange from 67Ga- or 68Ga-acetylacetonate in ethanol. The nonradioactive Ga[(sal)3tame-O-iso-Bu] complex was similarly prepared and shown by x-ray crystallography to exhibit the expected pseudo-octahedral N3O3(3-) coordination sphere about the Ga3+ center. These Ga-radiotracers are highly lipophilic, as demonstrated by their octanol/water partition coefficients. Log P values of 3.1, 3.1, 2.6, and 2.5 were found for the [(sal)3tame-O-iso-Bu], [(sal)3tame-O-n-Bu], [(sal)3tame-O-sec-Bu], and [(5-MeOsal)3tame-O-n-Pr] complexes, respectively. Following intravenous injection into rats, these complexes are rapidly cleared from the blood and exhibit significant myocardial uptake. At 1 min postinjection, 2.4%, 2.0%, 2.1% and 1.1% of the injected dose was found in the heart for the iso-BuO, n-BuO, sec-BuO, and n-PrO complexes, respectively, dropping to 1.0%, 0.8%, 0.8%, and 0.7% at 5 min. The corresponding heart-to-blood ratios are quite high: 17 +/- 3, 14 +/- 2, 12 +/- 2 and 3.5 +/- 0.4 at 1 min and 14 +/- 4, 10 +/- 1, 10 +/- 1 and 3.2 +/- 0.1 at 5 min postinjection. High quality myocardial images were obtained with PET in a normal dog using data collected from 2 to 10 min following intravenous injection of 68Ga[(sal)3tame-O-iso-Bu].

Animals↗