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Oral History Interview: Eldor Marten (576)
No full textEducation; Department of Chemistry; Social activities; Research areas
Mineralogy, petrology, petrogenesis, paragenesis and geochemistry of the Eldor carbonatite complex, Labrador Trough, Quebec, Canada
No full textThe Eldor carbonatite complex, located in the Labrador Trough region of Quebec, Canada, is a relatively unstudied deposit. The complex has a ubiquitos distribution of pyrochlore throughout the units, contains REE mineralization in the form of monazite and contains several minerals which would be economically viable as a by-product of pyrochlore mining.
The units identified in this study, at the Eldor complex, consist of early stage 2 calcite and dolomitized carbonatites and late-stage VeInIng calcite carbonatite. Fenitization is apparent in many of the units.
Cathodoluminescence mIcroscopy was used extensively to identify the extent of fenitization, characterize the type and stage of carbonate and apatite present as well as identifiy other constituents.
Pyrochlore mineralization is concentrated in the glimmerite units of the complex. Several types, alterations and generations of pyrochlore exist in the units at Eldor. Pyrochlore composition is highly variable within each specimen as well as each unit. Pyrochlore in the Ankeritic-Carbonatitic Unit is characterized by notable enrichment of uranium.
Hydrothermal fluids deposited the pyrochlore in the Glimmerite unit at Eldor. A Ta/Nb versus Fe/Nb ratio plot indicates fenitizing fluids did not produce the Glimmerite pyrochlore. An elevated Ce/Ce* ratio for the Glimmerites indicates high fluid flow, complexting and oxidation during formation.
Monazite is the independent REE mineral identified the complex. It is present as discrete grains in several types of units and it is especially concentrated in the Ankeritic-Carbonatitic Unit. This monazite formed during secondary alteration of the unit when the LREE\u27s were released from apatite and formed in the presence of abundant phosphorus.
The Ta/Nb ratio in the carbonatite-related Eldor units IS elevated to values as high as six which is unusual for most carbonatite complexes. A compilation of data indicates there are several are complexes (Nachendaz, Mt Weld, Jacupirangi and Kola) with similar values. Ta/Nb values greater than unity indicates a possible geochemical link between dissimilar carbonatite complexes --Abstract, pages iii-iv
Two-dimensional ELDOR in the study of model and biological membranes
No full text[[abstract]]Recent studies on model and biological membranes by two-dimensional (2-D) electronelectron double resonance (ELDOR) are reviewed and discussed. The studies include (1) the phase behavior of dispersions of phospholipid-cholesterol membrane vesicles; (2) the effect of the ion-channel-forming peptide gramicidin A on the lipid membrane; and (3) the effects of stimulation by antigen of the immunoglobulin E receptors in plasma membrane vesicles upon the lipid structure. In the first studies it is shown that the 2-D ELDOR spectra enable clear distinctions amongst the different phases, and this leads to a reliable temperature and composition-dependent phase diagram. In the second studies it is possible to distinguish bulk and boundary lipids and to describe their different dynamic structures. In the third studies we could distinguish both liquid-ordered and liquid-disordered spectral components, and one finds that the fraction of the latter increases as a result of stimulation. Emphasis is placed on the new "full Sc- method" of processing the 2-D ELDOR data to significantly enhance spectral resolution, which is particularly important in studying the spectra from coexisting phases or components. In the full Sc- method, one utilizes both the real and imaginary parts of the signal, instead of their magnitude; the needed phase corrections are obtained as part of the nonlinear least-squares fitting of the 2-D ELDOR data.[[fileno]]2010320010005[[department]]化學
Dynamic Molecular Structure and Phase Diagram of DPPC−Cholesterol Binary Mixtures: A 2D-ELDOR Study
No full textThis paper is an application of 2D electron−electron double resonance (2D-ELDOR) with the “full Sc−
method” to study model membranes. We obtain and confirm the phase diagram of 1,2-dipalmitoyl-sn-glycerophosphatidylcholine (DPPC)−cholesterol binary mixtures versus temperature and provide quantitative
descriptions for its dynamic molecular structure using 2D-ELDOR at the Ku band. The spectra from the
end-chain 16-PC spin label in multilamellar phospholipid vesicles are obtained for cholesterol molar
concentrations ranging from 0 to 50% and from 25 to 60 °C. This phase diagram consists of liquid-ordered,
liquid-disordered, and gel phases and phase coexistence regions. The phase diagram is carefully examined
according to the spectroscopic evidence, and the rigorous interpretation for the line shape changes. We show
that the 2D-ELDOR spectra differ markedly with variation in the composition. The extensive line shape
changes in the 2D-plus-mixing-time representation provide useful information to define and characterize the
membrane phases with respect to their dynamic molecular structures and to determine the phase boundaries.
The homogeneous T2's are extracted from the pure absorption spectra and are used to further distinguish the
membrane phases. These results show 2D-ELDOR to be naturally suitable for probing and reporting the
dynamic structures of microdomains in model membrane systems and, moreover, providing a very detailed
picture of their molecular dynamic structure, especially with the aid of the “full Sc− method”
ELDOR studies of nitroxide radicals: Discrimination between rotational and translational correlation times in liquids
No full textA new ELDOR spectrometer linked with a computer was constructed which permits one to scan the magnetic field, the pumping frequency, or both simultaneously, the latter being equivalent to scanning the observing frequency. The advantages of this last method are discussed. Using this spectrometer we have investigated the intra- and intermolecular ELDOR effect as a function of the rotational correlation time τrot using mixtures of nitroxide radicals which contain the nitrogen isotopes 14N and 15N. The variation of rrot was achieved either by varying the temperature or by selecting solvents of different viscosity at constant temperature. It can be shown theoretically that the intermolecular part of the ELDOR reduction factor due to exchange interactions is a function of the exchange frequency ωex, while the intramolecular part due to dipolar interactions depends as well on the nuclear relaxation rates Wn and Wn′. Since the former always contributes to the ELDOR reduction and the latter only if the pumped and the observed hyperfine lines belong to the same nitrogen isotope, it is possible to differentiate between the rotational correlation time τrot and the translational correlation time τrans if one takes into account the fact that Wn and Wn′ depend on τrot while τtrans is inversely proportional to the exchange frequency ωex
ELDOR-detected NMR at Q-Band
No full textIn recent years, electron–electron double resonance detected nuclear magnetic resonance (EDNMR) has gained considerable attention as a pulsed electron paramagnetic resonance technique to probe hyperfine interactions. Most experiments published so far were performed at W-band frequencies or higher, as at lower frequencies detection of weakly coupled low-γ nuclei is hampered by the presence of a central blind spot, which occurs at zero frequency. In this article we show that EDNMR measurements and a meaningful data analysis is indeed possible at intermediate microwave frequencies (Q-band, 34 GHz), once experimental parameters have been optimized. With highly selective detection pulses and Gaussian shaped electron–electron double resonance (ELDOR) pulses it is possible to detect low-γ nuclei coupled to paramagnetic Mn2+. Weakly coupled 14N resonances, which are separated from the zero frequency by only 2.8 MHz, were readily detected. In systems where different spin active nuclei are coupled to the electron spin, particular care has to be taken when using higher powered ELDOR pulses, as combination frequencies from the two nuclei (∆mS = ±1, ∆mI,1 = ±1, ∆mI,2 = ±1) can lead to severe line broadening and complicated EDNMR spectra. We also compare the EDNMR spectra of 13C-labeled Mn–DOTA to 13C-Mims electron–nuclear double resonance to get a better insight into the similarities and differences in the results of the two techniques for 13C hyperfine coupling
2D-ELDOR Study of Heterogeneity and Domain Structure Changes in Plasma Membrane Vesicles upon Cross-Linking of Receptors
No full text2D electron–electron double resonance (2D-ELDOR) with the “full Sc–” method of analysis is applied to the study of plasma membrane vesicles. Membrane structural changes upon antigen cross-linking of IgE receptors (IgE-FcεRI) in plasma membrane vesicles (PMVs) isolated from RBL-2H3 mast cells are investigated, for the first time, by means of these 2D-ELDOR techniques. Spectra of 1-palmitoyl-2-(16-doxyl stearoyl) phosphatidylcholine (16-PC) from PMVs before and after this stimulation at several temperatures are reported. The results demonstrate a coexistence of liquid-ordered (Lo) and liquid-disordered (Ld) components. We find that upon cross-linking, the membrane environment is remodeled to become more disordered, as shown by a moderate increase in the population of the Ld component. This change in the relative amount of the Lo versus Ld components upon cross-linking is consistent with a model wherein the IgE receptors, which when clustered by antigen to cause cell stimulation, lead to more disordered lipids, and their dynamic and structural properties are slightly altered. This study demonstrates that 2D-ELDOR, analyzed by the full Sc– method, is a powerful approach for capturing the molecular dynamics in biological membranes. This is a particular case showing how 2D-ELDOR can be applied to study physical processes in complex systems that yield subtle changes
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