Techniques for the Microanalysis of Higher Plants with Particular Reference to Silicon in Cryofixed Wheat Tissues

The applications of x-ray microanalysis in research into silicon in higher plants are reviewed, recent developments are assessed, and new data are presented. Conventionally prepared material [air or freeze drying for scanning electron microscopy (SEM), and glutaraldehyde/osmium tetroxide fixation for transmission electron microscopy (TEM)) has been studied using both wavelength and energy dispersive microanalysis. These techniques are reliable provided that the deposited form of silica is the major focus of investigation. Recently, studies concerning the soluble, mobile forms of silica, and the ionic environment at deposition sites have been initiated. In these investigations x -ray microanalysis has been carried out on the cold stage of an SEM, or after freeze substitution on sections in TEM. Two other developments which are considered are the use of proton induced x-ray emission, and electron energy loss spectroscopy. To illustrate the most recent developments in this field we present new observations on mineral distribution in the culm and awn of wheat using microanalysis of frozen hydrated material in SEM, and in the wheat leaf using freeze substitution and TE M and scanning transmission electron microscopy

Magmatic Cu-Ni-PGE-Au sulfide mineralisation in alkaline igneous systems: An example from the Sron Garbh intrusion, Tyndrum, Scotland

Magmatic sulfide deposits typically occur in ultramafic-mafic systems, however, mineralisation can occur in more intermediate and alkaline magmas. Sron Garbh is an appinite-diorite intrusion emplaced into Dalradian metasediments in the Tyndrum area of Scotland that hosts magmatic Cu-Ni-PGE-Au sulfide mineralisation in the appinitic portion. It is thus an example of magmatic sulfide mineralisation hosted by alkaline rocks, and is the most significantly mineralised appinitic intrusion known in the British Isles. The intrusion is irregularly shaped, with an appinite rim, comprising amphibole cumulates classed as vogesites. The central portion of the intrusion is comprised of unmineralised, but pyrite-bearing, diorites. Both appinites and diorites have similar trace element geochemistry that suggests the diorite is a more fractionated differentiate of the appinite from a common source that can be classed with the high Ba-Sr intrusions of the Scottish Caledonides. Mineralisation is present as a disseminated, primary chalcopyrite-pyrite-PGM assemblage and a blebby, pyrite-chalcopyrite assemblage with significant Co-As-rich pyrite. Both assemblages contain minor millerite and Ni-Co-As-sulfides. The mineralisation is Cu-, PPGE-, and Au-rich and IPGE-poor and the platinum group mineral assemblage is overwhelmingly dominated by Pd minerals; however, the bulk rock Pt/Pd ratio is around 0.8. Laser ablation analysis of the sulfides reveals that pyrite and the Ni-Co-sulfides are the primary host for Pt, which is present in solid solution in concentrations of up to 22 ppm in pyrite. Good correlations between all base and precious metals indicate very little hydrothermal remobilisation of metals despite some evidence of secondary pyrite and PGM. Sulfur isotope data indicate some crustal S in the magmatic sulfide assemblages. The source of this is unlikely to have been the local quartzites, but S-rich Dalradian sediments present at depth. The generation of magmatic Cu-Ni-PGE-Au mineralisation at Sron Garbh can be attributed to post-collisional slab drop off that allowed hydrous, low-degree partial melting to take place that produced a Cu-PPGE-Au-enriched melt, which ascended through the crust, assimilating crustal S from the Dalradian sediments. The presence of a number of PGE-enriched sulfide occurrences in appinitic intrusions across the Scottish Caledonides indicates that the region contains certain features that make it more prospective than other alkaline provinces worldwide, which may be linked the post-Caledonian slab drop off event. We propose that the incongruent melting of pre-existing magmatic sulfides or ‘refertilised’ mantle in low-degree partial melts can produce characteristically fractionated, Cu-PPGE-Au-semi metal bearing, hydrous, alkali melts, which, if they undergo sulfide saturation, have the potential to produce alkaline-hosted magmatic sulfide deposits

Generation of Intrinsic Vibrational Gap Modes in Three-Dimensional Ionic Crystals

The existence of anharmonic localization of lattice vibrations in a perfect 3-D diatomic ionic crystal is established for the rigid-ion model by molecular dynamics simulations. For a realistic set of NaI potential parameters, an intrinsic localized gap mode vibrating in the [111] direction is observed for fcc and zinc blende lattices. An axial elastic distortion is an integral feature of this mode which forms more readily for the zinc blende than for the fcc structure. Molecular dynamics simulations verify that in each structure this localized mode may be stable for at least 200 cycles.Comment: 5 pages, 4 figures, RevTeX, using epsf.sty. To be published in Phys. Rev. B. Also available at http://www.msc.cornell.edu/~kiselev

U-Pb geochronology of the Lime Hill gneissic complex, Cape Breton Island, Nova Scotia

Low-grade metasedimentary rocks of Late Proterozoic age in the Bras d'Or Terrane of Cape Breton Island contain small areas of gneissic rocks which were previously undated. New U-Pb data indicate that the Lime Hill gneissic complex is the product of an Early Cambrian intrusive/metamorphic event Two intrusions at Lime Hill give similar ages which indicate that emplacement and deformation of foliated tonalitic orthogneiss were followed very quickly by intrusion of massive granitic dykes at about 540 to S4S Ma. U-Pb analyses of metamorphic monazite from the Lime Hill paragneiss indicate that these rocks last cooled through the closure temperature of the U-Pb system for monazite (650-700°C) at about 549 Ma. All zircon fractions analyzed from the tonalitic orthogneiss and granitic dyke contain older inherited zircons which yield an apparent age range of at least 1.4 to 23 Ga. The presence of an inherited monazite component may suggest that the rocks have been affected by an older metamorphic event and are in fact older than the Malagawatch Formation, as suggested by published ore lead isotopic values. RÉSUMÉ Des roches métasédimentaires faiblement meétamorphisees d'âge protérozolque tardif et faisant partie de la Lanière de Bras d'Or (ile du Cap Breton), renferment des Hots de roches gneissiques dont l'âge n'avait pas encore été déterminé. De nouvelles données U-Pb indiquent que le complexe gneissique de Lime Hill est le résultat d'un épisode intrusif ou métamorphique datant du deimt du Cambrien. A Lime Hill, deux intrusions ont produit des âges semblables qui montrent que l'emplacement et la déformation d'un orthogneiss tonalitique furent suivis très rapidement par l'intrusion de dykes granitiques massifs, il y a environ 540 à 545 Ma. Des analyses U-Pb d'une monazite métamoiphique provenant du paragneiss de Lime Hill indiquent que le demier réfroidissement de ces roches en deca de la température de clôture du système U-Pb pour la monazite, i.e. de 650 à 700°C, eût lieu vers 549 Ma. Toutes les portions de zircons extraites de l'orthogneiss tonalitique et du dyke granitique comprennent des zircons remaniés qui donnent un âge apparent dont la gamme s'étend de 1.4 à 2.3 Ga. La présence d'une composante de monazite remaniée semble suggèrer que les roches ont subi un épisode antérieur de métamorphisme, et indiquer que les roches sont en réalité plus vieilles que la Formation de Malagawatch, tel que suggèré par les valeurs publiées des isotopes du plomb du minéral. [Traduit par le journal

Histone deacetylase inhibitors: A new mode for inhibition of cholesterol metabolism

<p>Abstract</p> <p>Background</p> <p>Eukaryotic gene expression is a complex process involving multiple cis and trans activating molecules to either facilitate or inhibit transcription. In recent years, many studies have focused on the role of acetylation of histone proteins in modulating transcription, whereas deacetylation of these same proteins is associated with inactivation or repression of gene expression. This study explores gene expression in HepG2 and F9 cell lines treated with Trichostatin A (TSA), a potent histone deacetylase inhibitor.</p> <p>Results</p> <p>These experiments show that TSA treatment results in clear repression of genes involved in the cholesterol biosynthetic pathway as well as other associated pathways including fatty acid biosynthesis and glycolysis. TSA down regulates 9 of 15 genes in this pathway in the F9 embryonal carcinoma model and 11 of 15 pathway genes in the HepG2 cell line. A time course study on the effect of TSA on gene expression of various enzymes and transcription factors involved in these pathways suggests that down regulation of <it>Srebf2 </it>may be the triggering factor for down regulation of the cholesterol biosynthesis pathway.</p> <p>Conclusion</p> <p>Our results provide new insights in the effects of histone deacetylases on genes involved in primary metabolism. This observation suggests that TSA, and other related histone deacetylase inhibitors, may be useful as potential therapeutic entities for the control of cholesterol levels in humans.</p

New Trends and Future Opportunities in the Enzymatic Formation of C-C, C-N, and C-O bonds

Organic chemistry provides society with fundamental products we use daily. Concerns about the impact that the chemical industry has over the environment is propelling major changes in the way we manufacture chemicals. Biocatalysis offers an alternative to other synthetic approaches as it employs enzymes, Nature''s catalysts, to carry out chemical transformations. Enzymes are biodegradable, come from renewable sources, operate under mild reaction conditions, and display high selectivities in the processes they catalyse. As a highly multidisciplinary field, biocatalysis benefits from advances in different areas, and developments in the fields of molecular biology, bioinformatics, and chemical engineering have accelerated the extension of the range of available transformations (E. L. Bell et al., Nat. Rev. Meth. Prim. 2021, 1, 1–21). Recently, we surveyed advances in the expansion of the scope of biocatalysis via enzyme discovery and protein engineering (J. R. Marshall et al., Tetrahedron 2021, 82, 131926). Herein, we focus on novel enzymes currently available to the broad synthetic community for the construction of new C-C, C-N and C-O bonds, with the purpose of providing the non-specialist with new and alternative tools for chiral and sustainable chemical synthesis. © 2021 The Authors. ChemBioChem published by Wiley-VCH GmbH