scholarly journals Planar-Chiral P and N-bridged Diferrocenes

Molbank ◽  
10.3390/m1130 ◽  
2020 ◽  
Vol 2020 (2) ◽  
pp. M1130
Author(s):  
Philipp Honegger ◽  
Lukas Scheibelberger ◽  
Michael Widhalm
Keyword(s):  
Complex Structures ◽  
New Family ◽  
Asymmetric Catalyst

We describe the synthesis of planar-chiral diferrocene compounds 4, 7 and 12, intended as key precursors for a new family of asymmetric catalyst ligands with less complex structures than their popular equivalents. In contrast to conventional 1,2-disubstituted ferrocenes containing center-chiral and planar-chiral elements, these compounds are purely planar-chiral due to the absence of α-substiuted ethyl groups. The title compounds 4, 7 and 12 were obtained from known precursors in 87%, 59% and 60% yields, respectively.

Lacantunia enigmatica (Teleostei: Siluriformes) a new and phylogenetically puzzling freshwater fish from Mesoamerica

Zootaxa ◽  
2005 ◽  
Vol 1000 (1) ◽  
pp. 1 ◽  
Author(s):  
ROCÍO RODILES-HERNÁNDEZ ◽  
DEAN A. HENDRICKSON ◽  
JOHN G. LUNDBERG ◽  
JULIAN M. HUMPHRIES
Keyword(s):  
Freshwater Fish ◽  
Uncinate Process ◽  
Lateral Margin ◽  
Complex Structures ◽  
The Third ◽  
Skull Roof ◽  
New Family ◽  
Early Tertiary ◽  
Gas Bladder ◽  
Lateral Ethmoid

A new family (Lacantuniidae), genus and species of catfish, Lacantunia enigmatica, is described from the Río Usumacinta basin of Chiapas, México. This odd siluriform is diagnosed by five distinctively autapomorphic and anatomically complex structures. The fifth (last) infraorbital bone is relatively large, anteriorly convex and remote from a prominent sphenotic process. The lateral margin of the frontal, lateral ethmoid and sphenotic bones are thick at the origins of much enlarged adductor mandibulae and levator arcus palatini muscles; otherwise the skull roof is constricted and flat. One pair of cone-shaped "pseudo-pharyngobranchial" bones is present at the anterior tips of enlarged cartilages medial to the first epibranchial. A hypertrophied, axe-shaped uncinate process emerges dorsally from the third epibranchial. The gas bladder has paired spherical, unencapsulated diverticulae protruding from its anterodorsal wall. Lacantunia enigmatica cannot be placed within or as a basal sister lineage to any known catfish family or multifamily clade except Siluroidei. This species may represent an ancient group, perhaps of early Tertiary age or older, and it adds another biogeographic puzzle to the historically complex Mesoamerican biota.

Cell morphology, volume, and surface area determinations from multilevel contouring within HVEM micrographs of serial sections and whole-cell mounts

1987 ◽  
Vol 45 ◽  
pp. 588-589
Author(s):  
M. Marko ◽  
A. Leith ◽  
D. Parsons
Keyword(s):  
Surface Area ◽  
Electron Micrographs ◽  
Cell Morphology ◽  
Individual Variation ◽  
Serial Section ◽  
Stereo Pair ◽  
Complex Structures ◽  
Serial Sections ◽  
Surface Areas ◽  
Computer Based

The use of serial sections and computer-based 3-D reconstruction techniques affords an opportunity not only to visualize the shape and distribution of the structures being studied, but also to determine their volumes and surface areas. Up until now, this has been done using serial ultrathin sections.The serial-section approach differs from the stereo logical methods of Weibel in that it is based on the Information from a set of single, complete cells (or organelles) rather than on a random 2-dimensional sampling of a population of cells. Because of this, it can more easily provide absolute values of volume and surface area, especially for highly-complex structures. It also allows study of individual variation among the cells, and study of structures which occur only infrequently.We have developed a system for 3-D reconstruction of objects from stereo-pair electron micrographs of thick specimens.

Stereo modeling of HVEM specimens by serial tilting and computer graphics

1986 ◽  
Vol 44 ◽  
pp. 34-35
Author(s):  
J.R. McIntosh ◽  
D.L. Stemple ◽  
William Bishop ◽  
G.W. Hannaway
Keyword(s):  
Computer Graphics ◽  
Analytical Methods ◽  
Photographic Film ◽  
Complex Structures ◽  
Multiple Objects ◽  
Multiple Images ◽  
3 Dimensional

EM specimens often contain 3-dimensional information that is lost during micrography on a single photographic film. Two images of one specimen at appropriate orientations give a stereo view, but complex structures composed of multiple objects of graded density that superimpose in each projection are often difficult to decipher in stereo. Several analytical methods for 3-D reconstruction from multiple images of a serially tilted specimen are available, but they are all time-consuming and computationally intense.

EXELFS Studies of Carbon Fibers

1990 ◽  
Vol 48 (2) ◽  
pp. 72-73
Author(s):  
V. Serin ◽  
K. Hssein ◽  
G. Zanchi ◽  
J. Sévely
Keyword(s):  
Carbon Fibers ◽  
Energy Analysis ◽  
Electron Excitation ◽  
Complex Structures ◽  
High Modulus ◽  
Promising Technique ◽  
X Ray ◽  
Fine Structures ◽  
X Ray Absorption

The present developments of electron energy analysis in the microscopes by E.E.L.S. allow an accurate recording of the spectra and of their different complex structures associated with the inner shell electron excitation by the incident electrons (1). Among these structures, the Extended Energy Loss Fine Structures (EXELFS) are of particular interest. They are equivalent to the well known EXAFS oscillations in X-ray absorption spectroscopy. Due to the EELS characteristic, the Fourier analysis of EXELFS oscillations appears as a promising technique for the characterization of composite materials, the major constituents of which are low Z elements. Using EXELFS, we have developed a microstructural study of carbon fibers. This analysis concerns the carbon K edge, which appears in the spectra at 285 eV. The purpose of the paper is to compare the local short range order, determined by this way in the case of Courtauld HTS and P100 ex-polyacrylonitrile carbon fibers, which are high tensile strength (HTS) and high modulus (HM) fibers respectively.

Microstructure and crystal symmetry of Pb2Sr2(Y/Ca)Cu3O9−δ

1990 ◽  
Vol 48 (4) ◽  
pp. 64-65
Author(s):  
Y. P. Lin ◽  
J. S. Xue ◽  
J. E. Greedan
Keyword(s):  
Electron Diffraction ◽  
High Temperature Superconductors ◽  
Carbon Film ◽  
Basic Structure ◽  
Crystal Symmetry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Space Groups ◽  
New Family ◽  
Convergent Beam

A new family of high temperature superconductors based on Pb2Sr2YCu3O9−δ has recently been reported. One method of improving Tc has been to replace Y partially with Ca. Although the basic structure of this type of superconductors is known, the detailed structure is still unclear, and various space groups has been proposed. In our work, crystals of Pb2Sr2YCu3O9−δ with dimensions up to 1 × 1 × 0.25.mm and with Tc of 84 K have been grown and their superconducting properties described. The defects and crystal symmetry have been investigated using electron microscopy performed on crushed crystals supported on a holey carbon film.Electron diffraction confirmed x-ray diffraction results which showed that the crystals are primitive orthorhombic with a=0.5383, b=0.5423 and c=1.5765 nm. Convergent Beam Electron Diffraction (CBED) patterns for the and axes are shown in Figs. 1 and 2 respectively.

A new family of fluorescent calcium indicators designed to resist leakage or for measuring calcium near membranes

1994 ◽  
Vol 52 ◽  
pp. 168-169
Author(s):  
Martin Poenie ◽  
Akwasi Minta ◽  
Charles Vorndran
Keyword(s):  
Metal Binding ◽  
Acetoxymethyl Ester ◽  
Binding Properties ◽  
Fura 2 ◽  
New Family ◽  
Anion Transporter ◽  
Calcium Indicator ◽  
Calcium Indicators ◽  
High Calcium ◽  
Intracellular Compartmentalization

The use of fura-2 as an intracellular calcium indicator is complicated by problems of rapid dye leakage and intracellular compartmentalization which is due to a probenecid sensitive anion transporter. In addition there is increasing evidence for localized microdomains of high calcium signals which may not be faithfully reported by fura-2.We have developed a new family of fura-2 analogs aimed at addressing some of these problems. These new indicators are based on a modified bapta which can be readily derivatized to produce fura-2 analogs with a variety of new properties. The modifications do not affect the chromophore and have little impact on the spectral and metal binding properties of the indicator. One of these new derivatives known as FPE3 is a zwitterionic analog of fura-2 that can be loaded into cells as an acetoxymethyl ester and whose retention in cells is much improved. The improved retention of FPE3 is important for both cuvettebased measurements of cell suspensions and for calcium imaging.

Scanning tunneling microscopy and atomic force microscopy: New tools for biology

1989 ◽  
Vol 47 ◽  
pp. 778-779
Author(s):  
CE Bracker ◽  
P. K. Hansma
Keyword(s):  
Physical Property ◽  
Scanning Probe ◽  
Scanning Tunneling ◽  
Small Scale ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
New Family ◽  
Small Probe ◽  
Atomic Force ◽  
Transmission Electron

A new family of scanning probe microscopes has emerged that is opening new horizons for investigating the fine structure of matter. The earliest and best known of these instruments is the scanning tunneling microscope (STM). First published in 1982, the STM earned the 1986 Nobel Prize in Physics for two of its inventors, G. Binnig and H. Rohrer. They shared the prize with E. Ruska for his work that had led to the development of the transmission electron microscope half a century earlier. It seems appropriate that the award embodied this particular blend of the old and the new because it demonstrated to the world a long overdue respect for the enormous contributions electron microscopy has made to the understanding of matter, and at the same time it signalled the dawn of a new age in microscopy. What we are seeing is a revolution in microscopy and a redefinition of the concept of a microscope.Several kinds of scanning probe microscopes now exist, and the number is increasing. What they share in common is a small probe that is scanned over the surface of a specimen and measures a physical property on a very small scale, at or near the surface. Scanning probes can measure temperature, magnetic fields, tunneling currents, voltage, force, and ion currents, among others.

Silicification of wood-cell walls

1994 ◽  
Vol 52 ◽  
pp. 428-429
Author(s):  
S. E. Keckler ◽  
D. M. Dabbs ◽  
N. Yao ◽  
I. A. Aksay
Keyword(s):  
Electron Microscopy ◽  
Cell Wall ◽  
Cell Walls ◽  
Lignin Content ◽  
Resin Composite ◽  
Middle Lamella ◽  
Cellulose Fibers ◽  
Complex Structures ◽  
Rich Region ◽  
Inorganic Precursors

Cellular organic structures such as wood can be used as scaffolds for the synthesis of complex structures of organic/ceramic nanocomposites. The wood cell is a fiber-reinforced resin composite of cellulose fibers in a lignin matrix. A single cell wall, containing several layers of different fiber orientations and lignin content, is separated from its neighboring wall by the middle lamella, a lignin-rich region. In order to achieve total mineralization, deposition on and in the cell wall must be achieved. Geological fossilization of wood occurs as permineralization (filling the void spaces with mineral) and petrifaction (mineralizing the cell wall as the organic component decays) through infiltration of wood with inorganics after growth. Conversely, living plants can incorporate inorganics into their cells and in some cases into the cell walls during growth. In a recent study, we mimicked geological fossilization by infiltrating inorganic precursors into wood cells in order to enhance the properties of wood. In the current work, we use electron microscopy to examine the structure of silica formed in the cell walls after infiltration of tetraethoxysilane (TEOS).

Lipid Polymorphism and Virus-Membrane Fusion as Observed in Vitrified Thin Films by Cryo-Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 492-493
Author(s):  
P.M. Frederik ◽  
K.N.J. Burger ◽  
M.C.A. Stuart ◽  
A.J. Verkleij
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Membrane Fusion ◽  
Film Formation ◽  
Molar Ratio ◽  
Influenza B ◽  
Complex Structures ◽  
Type Ii ◽  
Suspended Material ◽  
Cryo Electron Microscopy

Cellular membranes are often composed of phospholipid mixtures in which one or more components have a tendency to adopt a type II non-bilayer lipid structure such as the inverted hexagonal (H||) phase. The formation of a type II non-bilayer intermediate, the inverted lipid micel is proposed as the initial step in membrane fusion (Verkleij 1984, Siegel, 1986). In the various forms of cellular transport mediated by carrier vesicles (e.g. exocytosis, endocytosis) the regulation of membrane fusion, and hence of inverted lipid micel formation, is of vital importance.We studied the phase behaviour of simple and complex lipid mixtures by cryo-electron microscopy to gain more insight in the ultrastructure of different lipid phases (e.g. Pβ’, Lα, H||) and in the complex membrane structures arising after Lα < - > H|| phase changes (e.g. isotropic, cubic). To prepare hydrated thin films a 700 mesh hexagonal grid (without supporting film) was dipped into and withdrawn from a liposome suspension. The excess fluid was blotted against filter paper and the thin films that form between the bars of the specimen grid were immediately (within 1 second) vitrified by plunging of the carrier grids into ethane cooled to its melting point by liquid nitrogen (Dubochet et al., 1982). Surface active molecules such as phospholipids play an important role in the formation and thinning of these aqueous thin films (Frederik et al., 1989). The formation of two interfacial layers at the air-water interfaces requires transport of surface molecules from the suspension as well as the orientation of these molecules at the interfaces. During the spontaneous thinning of the film the interfaces approach each other, initially driven by capillary forces later by Van der Waals attraction. The process of thinning results in the sorting by size of the suspended material and is also accompanied by a loss of water from the thinner parts of the film. This loss of water may result in the concentration and eventually in partial dehydration of suspended material even if thin films are vitrified within 1 sec after their formation. Film formation and vitrification were initiated at temperatures between 20-60°C by placing die equipment in an incubator provided widi port holes for the necessary manipulations. Unilamellar vesicles were made from dipalmitoyl phosphatidyl choline (DPPC) by an extrusion method and showed a smooth (Lα) or a rippled (PB’.) structure depending on the temperature of the suspensions and the temperature of film formation (50°C resp. 39°C) prior to vitrification. The thermotropic phases of hydrated phospholipids are thus faithfully preserved in vitrified thin films (fig. a,b). Complex structures arose when mixtures of dioleoylphosphatidylethanol-amine (DOPE), dioleoylphosphatidylcholine (DOPC) and cholesterol (molar ratio 3/1/2) are heated and used for thin film formation. The tendency of DOPE to adopt the H|| phase is responsible for the formation of complex structures in this lipid mixture. Isotropic and cubic areas (fig. c,d) having a bilayer structure are found in coexistence with H|| cylinders (fig. e). The formation of interlamellar attachments (ILA’s) as observed in isotropic and cubic structures is also thought to be of importance in biological fusion events. Therefore the study of the fusion activity of influenza B virus with liposomes (DOPE/DOPC/cholesterol/ganglioside in a molar ratio 1/1/2/0.2) was initiated. At neutral pH only adsorption of virus to liposomes was observed whereas 2 minutes after a drop in pH (7.4 - > 5.4) fusion between virus and liposome membranes was demonstrated (fig. f). The micrographs illustrate the exciting potential of cryo-electron microscopy to study lipid-lipid and lipid-protein interactions in hydrated specimens.

Sign in / Sign up

Export Citation Format

Share Document