Pedro M. Aguiar

Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: I. Crystal chemistry by SREF, EMPA, MAS NMR and Mössbauer spectroscopy

Abstract Tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, shows a variety of habits that resemble mushrooms, and it is commonly referred to as ‘mushroom tourmaline’. The structure of nine single crystals of elbaite, ranging in colour from pink to white to black and purple, extracted from two samples of mushroom tourmaline from Mogok, have been refined (SREF) to R indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation. 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy shows the presence of [4]B and the absence of [4]Al in samples with transition-metal content low enough to prevent paramagnetic quenching of the signal. Site populations were assigned from refined site-scattering values and unit formulae derived from electron-microprobe analyses of the crystals used for X-ray data collection. 57Fe Mössbauer spectroscopy shows that both Fe2+ and Fe3+ are present, and the site populations derived by structure refinement show that there is no Fe at the Z site; hence all Fe2+ and Fe3+ occurs at the Y site. The 57Fe Mössbauer spectra also show peaks due to intervalence charge-transfer involving Fe2+ and Fe3+ at adjacent Y sites. Calculation of the probability of the total amount of Fe occurring as Fe2+–Fe3+ pairs for a random short-range distribution is in close accord with the observed amount of Fe involved in Fe2+-Fe3+, indicating that there is no short-range order involving Fe2+ and Fe3+ in these tourmalines.

The occurrence of tetrahedrally coordinated Al and B in tourmaline: An 11B and 27Al MAS NMR study

Abstract Considerable uncertainty has surrounded the occurrence of tetrahedrally coordinated Al and B at the T site in tourmaline. Although previously detected in several tourmaline specimens, the frequency of these substitutions in nature, as well as the extent to which they occur in the tourmaline structure, is not known. Using 11B and 27Al MAS NMR spectroscopy, we have investigated the presence of B and Al at the T site in 50 inclusion-free tourmaline specimens of low transition-metal content and different species (elbaite, “fluor-elbaite” , liddicoatite, dravite, uvite, olenite, and magnesiofoitite) from different localities worldwide. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well resolved, allowing detection of even small amounts of T-site constituents. In the observed spectra, [4]B and [3]B peaks are located at 0 and 18-20 ppm, respectively, with the greatest intensity corresponding to [3]B (=3 apfu). In 27Al spectra, [4]Al and [6]Al bands are located at 68-72 and 0 ppm, respectively, with the greater intensity corresponding to [6]Al. However, inadequate separation of YAl and ZAl precludes resolution of these two bands. Simulation of 11B MAS NMR spectra shows that tetrahedrally and trigonally coordinated B can be readily distinguished at 14.1 T and that a [4]B content of 0.0-0.5 apfu is common in tourmaline containing low amounts of paramagnetic species. 27Al MAS NMR spectra show that Al is also a common constituent of the T site in tourmaline. Determination of [4]Al content by peak-area integration commonly shows values of 0.0-0.5 apfu. Furthermore, the chemical shift of the 27Al tetrahedral peak is sensitive to local order at the adjacent Y and Z octahedra, where [4]Al-YMg3 and [4]Al-Y(Al,Li)3 arrangements result in peaks located at ~65 and ~75 ppm, respectively. Both 11B MAS NMR and 27Al MAS NMR spectra show peak broadening as a function of transition-metal content (i.e., Mn2+ + Fe2+ = 0.01-0.30 apfu) in the host tourmaline. In 11B spectra, broadening and loss of intensity of the [3]B signal ultimately obscures the signal corresponding to [4]B, increasing the limit of detection of [4]B in tourmaline. Our results clearly show that all combinations of Si, Al, and B: T = (Al, Si)6, T = (B, Si)6, T = (Al, B, Si)6, and T = Si6 apfu, are common in natural tourmalines.

Elbaite-liddicoatite from Black Rapids glacier, Alaska

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 57-73 - DOI: 10.2451/2011PM0005 Special Issue in memory of Sergio Lucchesi Elbaite-liddicoatite from Black Rapids glacier, Alaska Aaron J. Lussier 1 , Frank C. Hawthorne 1,* , Vladimir K. Michaelis 2 , Pedro M. Aguiar 2 and Scott Kroeker 2 1 Department of Geological Sciences, University of Manitoba, Winnipeg, Canada 2 Department of Chemistry, University of Manitoba, Winnipeg, Canada *Corresponding author: frank_hawthorne@umanitoba.ca Abstract Liddicoatite, ideally Ca(AlLi 2 )Al 6 (SiO 6 )(BO 3 ) 3 (OH) 3 F, is an extremely rare species of tourmaline, found in very few localities worldwide. A large (~ 2 cm in cross section), euhedral sample of tourmaline retrieved from atop the Black Rapids glacier, Alaska, is shown to vary from a light pink elbaite in the core region, average composition (Na 0.4 Ca 0.3□0.3 )(Al 1.75 Li 1.25 ) Al 6 (BO 3 ) 3 (Si 6 O 18 )F 0.4 (OH) 3.6 , to a pale green liddicoatite at the edge of the crystal, (Na 0.3 Ca 0.6 □ 0.1 )(Al 1.0 Li 1.6 Fe 0.2 Mn 0.2 )Al 6 (BO 3 ) 3 (Si 6 O 18 )F 1.0 (OH) 3.0 . Detailed electron-microprobe analysis and 11 B and 27 Al Magic-Angle-Spinning Nuclear Magnetic Resonance spectroscopy show that several substitutions were active during growth, with X □ + Y Al → X Ca + Y Li (liddicoatite-rossmanite solid-solution) and 2 Y Al + X □ → 2 Y M* + X Ca accounting for most of the compositional variation. Throughout the tourmaline, there are instances of reversals in the trends of all major constituents, although few compositional gaps are observed. Most notably, a sharp decline in Ca content from ~ 0.35 to ~ 0.05 apfu (atoms per formula unit) with increasing distance from the core at ~ 2 mm from the crystal edge is followed by a sharp rise in Ca content (to 0.55 apfu), along with (Fe + Mn) content (from 0.01 to 0.35 apfu). In the core region, the origin of the Ca in the tourmaline is not clear; the correlation of Ca and F is consistent with both (1) a melt in which Ca was held as complexes with F, or (2) earlier contamination of the melt by a (Ca, F)-rich fluid. Close to the rim, a dramatic increase in Ca, F, Mn and Fe is probably due to late-stage contamination by fluids that have removed these components from adjacent wallrocks. Key words: liddicoatite; elbaite; tourmaline; late-stage Ca enrichment; pegmatite; zoning; electron-microprobe analysis; Black Rapids glacier, Alaska; 11 B MAS NMR; 27 Al MAS NMR.

Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: II. Zoning and crystal growth

Abstract A variety of mushroom tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, consists of a black-to-grey single-crystal core from which a single prismatic crystal reaches to the edge of the mushroom, forming a slight protuberance. The rest of the mushroom (~50% by volume) consists of extremely acicular sub-parallel crystals that diverge toward the edge of the mushroom. The acicular crystals are dominantly colourless to white, with a continuous black zone (2 mm across) near the edge, and pale pink outside the black zone. The composition varies from ~Na0.75Ca0.05(Li0.80Al0.70Fe1.10Mn0.30Ti0.10) Al6Si6(BO3)3O18(OH)3(OH,F) at the base of the mushroom to ~Na0.60Ca0.06(Li1.00Al1.98Fe0.02)Al6(Si5.35 B0.65)(BO3)3O18(OH)3(OH,F) close to the edge at the top of the mushroom. The principal substitutions are: (1) YLi + YAl → YFe* + YFe* and (2) TB + YAl → Si + YFe*, but there are five other minor substitutions that are also operative. There are six significant compositional discontinuities at textural boundaries in the mushroom, suggesting that the changes in habit are driven in part by changes in external variables such as T and P, plus possible involvement of new fluid phases.

The crystal chemistry of ‘wheatsheaf’ tourmaline from Mogok, Myanmar

Abstract Tourmalines of unusual (mushroom) habit are common in granitic pegmatites of Momeik, northeast of Mogok, Myanmar. Here, we examine a sample of elbaite of significantly different habit, consisting of a series of diverging crystals, resembling a sheaf of wheat and ranging in colour from light purplish-red at the base to dark purplish-red at the tip with a thin green cap at the termination. The crystal structures of eight crystals are refined to R1-indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation; the same crystals were analysed by electron microprobe. 11B and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra were collected on four regions of the wheatsheaf crystal, and show ~0.3 a.p.f.u. [4]B and <0.1 a.p.f.u. [4]Al in the structure. 57Fe Mössbauer spectroscopy was done on the dark green rim at the termination of the crystal, showing all Fe in this region (~0.6 a.p.f.u.) to be Fe2+. Detailed electron-microprobe traverses show that the principal compositional variation involves the substitutions [4]B + YAl → Si + YFe*, where transition metals are present, and [4]B2 + YAl → Si2 + YLi, where transition metals are not present, although several other minor substitutions also affect crystal composition. Successive microscopic bifurcation of crystallites causes divergence of growth directions along the c axis, imparting the overall ‘wheatsheaf’ shape to the crystal aggregate. We suggest that such bifurcation is common in pegmatitic elbaite crystals, resulting in their common divergent habit.

DNA recognition for virus assembly through multiple sequence-independent interactions with a helix-turn-helix motif

The helix-turn-helix (HTH) motif features frequently in protein DNA-binding assemblies. Viral pac site-targeting small terminase proteins possess an unusual architecture in which the HTH motifs are displayed in a ring, distinct from the classical HTH dimer. Here we investigate how such a circular array of HTH motifs enables specific recognition of the viral genome for initiation of DNA packaging during virus assembly. We found, by surface plasmon resonance and analytical ultracentrifugation, that individual HTH motifs of the Bacillus phage SF6 small terminase bind the packaging regions of SF6 and related SPP1 genome weakly, with little local sequence specificity. Nuclear magnetic resonance chemical shift perturbation studies with an arbitrary single-site substrate suggest that the HTH motif contacts DNA similarly to how certain HTH proteins contact DNA non-specifically. Our observations support a model where specificity is generated through conformational selection of an intrinsically bent DNA segment by a ring of HTHs which bind weakly but cooperatively. Such a system would enable viral gene regulation and control of the viral life cycle, with a minimal genome, conferring a major evolutionary advantage for SPP1-like viruses.

Field Stabilization of the Iseult/Inumac Magnet Operating in Driven Mode

A neuroscience research center with very high field MRI equipments was opened in November 2006 by the CEA life sciences division. Three MRI systems operating at 3, 7 and 17 T have been already installed. One of the imaging systems will require a 11.75 T magnet with a 900 mm warm bore. The large aperture and high field strength of this magnet provide a substantial engineering challenge compared to the largest MRI systems ever built. This magnet is being developed within an ambitious R&D program, Iseult, whose focus is high field MRI. Traditional MRI magnet design principles are not readily applicable and thus concepts taken from high energy physics or fusion experiments, namely the Tore Supra tokamak magnet system, will be used. The coil will be made of a niobium-titanium conductor cooled by a He II bath at 1.8 K, permanently connected to a cryoplant. Due to its design the magnet will be operated in a non-persistent mode. As the field stability needed for MRI imaging requires a field drift of less than 0.05 ppm/h, it is hardly feasible to directly transpose these requirements in the power supply specification. Two existing solutions developed for other applications have been selected: one using a semi-persistent mode, and the other using a short-circuited superconducting coil in the inner bore. In order to make a decision on experimental basis, an ambitious R&D field stability program has been set-up based on magnet prototypes, high field test facility (Seht, a 44 H and 8 T magnet with a warm bore to 600 mm). We will present development and experimental results of the two stabilization solutions. In conclusion, the stability solution selected for the Iseult magnet is given.

A paramagnetic Cu(I)/Cu(II)/Zn(II) coordination polymer with multiple CN-binding modes and its solid-state NMR characterization

A Cu(I)/Cu(II)/Zn(II) mixed-valent [Cu(en)2][Zn(NC)4(CuCN)2] polymer, which has a 2-D layer structure with six structurally inequivalent cyanides in four distinct bonding modes, has been prepared; structurally informative 13C and 15N MAS NMR spectra of this paramagnetic system are readily observable.

Capacitance-Assisted Sustainable Electrochemical Carbon Dioxide Mineralisation

Abstract An electrochemical cell comprising a novel dual‐component graphite and Earth‐crust abundant metal anode, a hydrogen producing cathode and an aqueous sodium chloride electrolyte was constructed and used for carbon dioxide mineralisation. Under an atmosphere of 5 % carbon dioxide in nitrogen, the cell exhibited both capacitive and oxidative electrochemistry at the anode. The graphite acted as a supercapacitive reagent concentrator, pumping carbon dioxide into aqueous solution as hydrogen carbonate. Simultaneous oxidation of the anodic metal generated cations, which reacted with the hydrogen carbonate to give mineralised carbon dioxide. Whilst conventional electrochemical carbon dioxide reduction requires hydrogen, this cell generates hydrogen at the cathode. Carbon capture can be achieved in a highly sustainable manner using scrap metal within the anode, seawater as the electrolyte, an industrially relevant gas stream and a solar panel as an effective zero‐carbon energy source.

1H high resolution magic-angle coil spinning (HR-MACS) μNMR metabolic profiling of whole Saccharomyces cervisiae cells: a demonstrative study

The low sensitivity and thus need for large sample volume is one of the major drawbacks of Nuclear Magnetic Resonance (NMR) spectroscopy. This is especially problematic for performing rich metabolic profiling of scarce samples such as whole cells or living organisms. This study evaluates a 1H HR-MAS approach for metabolic profiling of small volumes (250 nl) of whole cells. We have applied an emerging micro-NMR technology, high-resolution magic-angle coil spinning (HR-MACS), to study whole Saccharomyces cervisiae cells. We find that high-resolution high-sensitivity spectra can be obtained with only 19 million cells and, as a demonstration of the metabolic profiling potential, we perform two independent metabolomics studies identifying the significant metabolites associated with osmotic stress and aging.