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Prismatic Crystals (prismatic + crystal)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Synthesis, Crystal Structure, and Magnetic Properties of Mn2(OH)2SO4: A Novel Layered Hydroxide

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004
Mohsen Ben Salah
Abstract Mn2(OH)2SO4, obtained as pink prismatic crystals by the hydrothermal reaction of MnSO4·H2O and NaOH at 240 °C for 24 h, consists of layers of Mn hydroxide connected to each other through µ6 -sulfate ions. Each layer exhibits vacancies, and each vacant space is capped at the top and bottom by the sulfate groups. The compound is paramagnetic above 50 K (C = 4.36 emu K mol,1, µeff = 5.91 µB, , = ,100 K). Below 45 K, the magnetization increases slightly, indicating canted-antiferromagnetic (TNéel = 42±1 K) behavior consistent with the linear dependence of the magnetization as a function of the field at 2 K, which reaches only 0.4 µB at 50 kOe, and the lack of any imaginary component of the ac-susceptibilities (ac = alternating current). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Guanine-Based Biogenic Photonic-Crystal Arrays in Fish and Spiders

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
Avital Levy-Lior
Abstract Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic-crystal structures using cryo-SEM show that the crystal plates in both fish skin and spider integument are ,20-nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ,230-nm-thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30-nm layers of amorphous guanine, and are stacked with ,200,nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration. [source]

The Pulvinus Endodermal Cells and their Relation to Leaf Movement in Legumes of the Brazilian Cerrado,

PLANT BIOLOGY, Issue 4 2007
T. M. Rodrigues
Abstract: Legume pulvini have a clearly delimited endodermis, whose variable content has been associated with the velocity and type of leaf movement: pulvini in leaves with fast nastic movement contain starch grains; pulvini in leaves with slow nastic movements have calcium oxalate crystals as well as starch grains in the endodermis. However, the studies carried out to date have involved few legume species. This study therefore purported to examine the consistency of this hypothesis in other legumes. Thus, the structure and content of the pulvinus endodermal cells of nine legumes of the Brazilian cerrado, with different types and velocities of leaf movement, were investigated: slow nyctinastic and heliotropic movements (Bauhinia rufa, Copaifera langsdorffii, Senna rugosa - Caesalpinioideae; Andira humilis and Dalbergia miscolobium - Faboideae; Stryphnodendron polyphyllum - Mimosoideae), slow heliotropic movement (Zornia diphylla - Faboideae), and fast seismonastic and slow nyctinastic and heliotropic movements (Mimosa rixosa and Mimosa flexuosa - Mimosoideae). Samples were prepared following standard plant anatomy and ultrastructure techniques. The endodermis of all the species contains starch grains. In the species displaying only slow movements, calcium oxalate prismatic crystals were observed in addition to starch grains, except in Zornia diphylla. In conclusion, oxalate crystals occur only in endodermal cells of pulvini that display slow movements, while starch grains are always present in pulvinus endodermal cells of plants with any kind of movement. [source]

Dimorphic forms of 3,6-dinitrodurene in a single space group

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009
José Alberto Galicia Aguilar
3,6-Dinitrodurene (1,2,4,5-tetramethyl-3,6-dinitrobenzene), C10H12N2O4, has been crystallized in two polymorphic forms which may be distinguished by their colours in the solid state. Polymorph I gives clear colourless prismatic crystals, while polymorph II crystallizes in the dark and under an inert atmosphere as irregular purple blocks. Both forms belong to the space group C2/c, with both asymmetric units containing two half-molecules. One molecule is located on an inversion centre and the other lies on a twofold axis. The polymorphism arises from different orientations of the twofold axis: in form I, this axis passes through the mid-points of two C,C bonds of the benzene ring and, as a consequence, all atoms in the asymmetric unit are in general positions. In form II, the N atoms of the nitro groups and the Cipso atoms are located on the binary axis. Comparing phases I and II, slightly different conformations are observed for the nitro substituents, while the stacking structures are very similar. [source]