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PubMed1991

Elemental composition of pyroantimonate precipitates analysed by electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) in vitellogenic ovarian follicles of Drosophila.

Ca2+ was precipitated with potassium antimonate in vitellogenic follicles of the fruit fly Drosophila melanogaster and the distribution of the precipitates formed was studied by electron microscopy. The microvilli of the oolemma in mid- and late vitellogenic follicles were lined with precipitates. The chemical composition of the precipitates was analysed by electron spectroscopic imaging (ESI). The images produced by inelastically scattered electrons at specific ionization edges were compared, and the non-specific background signals were subtracted by an image processing system. The presence of Ca2+, antimony and oxygen in the precipitates formed could be demonstrated. The elemental composition of the precipitates and of yolk spheres was also analysed by electron energy-loss spectroscopy (EELS). With respect to the precipitates, signals at the calcium L2,3-edge, the oxygen K-edge and the antimony M4,5-edge were recorded without deconvolution and background subtraction. The yolk spheres, which were free of precipitates, gave the characteristic signal of the nitrogen K-edge. The applied techniques combine good ultrastructural resolution with the possibility of analysing the elemental composition of histochemical reaction products and cellular structures.

Animals↗
PubMed1995

Backscattered electron imaging of the undersurface of resin-embedded cells by field-emission scanning electron microscopy.

In this study backscattered electron (BSE) imaging was used to display cellular structures stained with heavy metals within an unstained resin by atomic number contrast in successively deeper layers. Balb/c 3T3 fibroblasts were cultured on either 13-mm discs of plastic Thermanox, commercially pure titanium or steel. The cells were fixed, stained and embedded in resin and the disc removed. The resin block containing the cells was sputter coated and examined in a field-emission scanning electron microscope. The technique allowed for the direct visualization of the cell undersurface and immediately overlying areas of cytoplasm through the surrounding embedding resin, with good resolution and contrast to a significant depth of about 2 microm, without the requirement for cutting sections. The fixation protocol was optimized in order to increase heavy metal staining for maximal backscattered electron production. The operation of the microscope was optimized to maximize the number of backscattered electrons produced and to minimize the spot size. BSE images were collected over a wide range of accelerating voltages (keV), from low values to high values to give 'sections' of information from increasing depths within the sample. At 3-4 keV only structures a very short distance into the material were observed, essentially the areas of cell attachment to the removed substrate. At higher accelerating voltages information on cell morphology, including in particular stress fibres and cell nuclei, where heavy metals were intensely bound became more evident. The technique allowed stepwise 'sectional' information to be acquired. The technique should be useful for studies on cell morphology, cycle and adhesion with greater resolution than can be obtained with any light-microscope-based system.

3T3 Cells↗
PubMed1995

The function of Wolinella succinogenes psr genes in electron transport with polysulphide as the terminal electron acceptor.

The membrane-integrated polysulphide reductase (Psr) of Wolinella succinogenes is part of the electron transport chain catalyzing polysulphide reduction by formate or hydrogen. The isolated enzyme catalyzes sulphide oxidation by dimethylnaphthoquinone. The two hydrophilic subunits, PsrA and PsrB of the enzyme, are encoded by genes that form an apparent operon psrABC together with a third gene. Using homologous recombination, three deletion mutants of W. succinogenes were constructed that lack psrC, psrBC or the whole psr operon. The mutants grown with formate and fumarate were fractionated, and the cell fractions were analyzed for the presence of PsrA and enzyme activity. It was concluded that: (a) polysulphide reductase is a constituent of the wild-type chain catalyzing electron transport from formate to polysulphide; (b) the gene psrC encodes a subunit that anchors the enzyme in the membrane and is required for electron transport; (c) PsrA which probably carries the substrate site, is exposed to the bacterial periplasm; (d) PsrA and PsrB are required for the activity of sulphide oxidation with 2,3-dimethyl-1,4-naphthoquinone. Surprisingly, the delta psrABC mutant could grow with formate and polysulphide. The membrane fraction of the mutant grown under these conditions contained an enzyme that replaced polysulphide reductase in electron transport, and catalyzed sulphide oxidation with 2,3-dimethyl-1,4-naphthoquinone.

Electron Transport↗
PubMed1982

Rhein as an electron acceptor for various flavoproteins and for electron transport particles.

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) which has been previously employed as an inhibitor for electron transport particles, NADH dehydrogenase, and other flavoproteins is reducible under physiological conditions. Soluble hydrogenase from Alcaligenes eutrophus H 16, several flavoproteins, and electron transport particles from baker's yeast and from beef heart were found to catalyse NADH oxidation with 9 micrometers to 2mM rhein as the electron acceptor. Dithionite or enzymatically reduced rhein (lambda max = 408 nm) is immediately reoxidized to rhein lambda max = 437 nm) by oxygen. Cyclovoltagrams reveal the midpoint redox potentials --0.240 V, -0.270 V, -0.280 V, -0.335 V at pH 6.0, 7.0, 7.7, 9.2, respectively. Due to its redox behaviour, caution should be exercised using rhein as a flavin-site-directed inhibitor for biological electron transfer systems.

Alcaligenes↗
PubMed1992

Transmission electron microscopic and high voltage electron microscopic observations of the bone and osteocyte activity adjacent to unloaded dental implants placed in dogs.

The purpose of this report is to describe ultrastructural observations of the bone and associated tissues supporting 24 unloaded endosteal dental implants placed in mongrel dogs (canis familiaris). The following 3 specific areas of the supporting tissues were targeted: 1) the osteocyte populations; 2) the mineralized collagen fiber matrix of the bone; and 3) an electron dense interfacial deposit. To investigate these areas, transmission electron microscopy and high voltage electron microscopic (HVEM) protocols were emphasized. HVEM permitted stereologic observations. Further, all observations were obtained from undecalcified tissues obtained from animals with commercially available implants placed into the mandible. From the study we observed a mineralization pattern of the implant supporting bone that was similar to those events occurring naturally within the mandibular bone. Osteocyte morphology was similar whether the osteocytes were found well below the implant interface or close to the interface. Osteocytes within lacunae were routinely found close to the implant interface, often extending cellular processes through canaliculi to the bone-implant interface. At the interface, an electron dense deposit approximately 50 nm in thickness was often observed. In interfacial regions, densely mineralized collagen fibers were observed running primarily parallel to the implant surface. This dense mineralized tissue was separated from the interface by a mineralized, but finely fibrillar matrix of approximately 200 nm in thickness.

Animals↗
PubMed2001

The application of electron microscopic morphometry as a helpful method in the diagnosis of focal segmental glomerulosclerosis (FSGS) early phase. II. Clinical usefulness of electron microscopic morphometric studies in cases of minimal change disease (MCD) and mesangioproliferative glomerulonephritis (GNMES) with suspicion of progression into focal segmental glomerulosclerosis (FSGS).

Clinical and morphological analysis (including morphometric studies of electron microscopic material) was made in 15 children with MCD and 15 children with GNMES. In both groups, an early phase of FSGS was suspected on the basis of electron microscopic studies. Moreover, analysis included the results obtained in 13 children with the diagnosis of FSGS and in whom repeated biopsies were performed. In most of them, MCD or GNMES was diagnosed from the first biopsy. In most children in whom electron microscopic studies revealed an increase in matrix area in some mesangial regions, thereby suggesting an early stage of glomerular sclerosis, the results of morphometric studies resembled or were identical to the results obtained from a control group with the established diagnosis of FSGS. These findings indicate that morphometric studies of electron microscopic material are significant. The results, when compared with the clinical data, confirm the usefulness of such a diagnostic procedure.

Child, Preschool↗
PubMed1979

Ionic effects on adrenal steroidogenic electron transport. The role of adrenodoxin as an electron shuttle.

We have shown (Seybert, D., Lambeth, D., and Kamin, H. (1978), J. Biol. Chem. 253, 8355-8358) that, whereas the 1:1 complex between adrenodoxin reductase and adrenodoxin is the active species for cytochrome c reduction, the complex is not sufficient to allow cytochrome P-45011 beta-mediated hydroxylations;adrenodoxin in excess of reductase is required. In the present studies, reduction by NADPH of excess adrenodoxin is shown to occur at a rate sufficient to support both cytochrome P-450 11 beta-mediated hydroxylation of deoxycorticosterone, and cytochrome P-450sec-mediated side chain cleavage of cholesterol. Oxidation-reduction potential and ion effect studies indicate that the mechanism of steroidogenic electron transport involves an adrenodoxin electron "shuttle" rather than a macromolecular complex of reductase, adrenodoxin, and cytochrome. The oxidation-reduction potential of adrenodoxin is shifted about -100 mV when bound to reductase, and reduction of the iron-sulfur protein thus promotes dissociation of the complex. The rate of adrenodoxin reduction is first stimulated, then inhibited by increasing salt; the effect is ion-specific, with Ca2+ approximately Mg2+ greater than Na+ greater than NH/+. Similar ion-specific rate effects are observed for both of the cytochrome P-450-mediated hydroxylations, indicating that the same reduction mechanism is required for these reactions. Increasing salt concentrations caused dissociation of the complex; dissociation of the form of the complex containing reduced adrenodoxin occurred at lower salt concentrations than that containing oxidized adrenodoxin. The order of effectiveness of ions in causing dissociation is the same as the order for stimulation of adrenodoxin reduction, suggesting a dissociation step in the mechanism. This proposed model, together with dissociation constants for the form of the complex containing either oxidized or reduced adrenodoxin, allows accurate prediction of the salt rate effects curve. For all ions, an activity maximum is seen at the ion concentration which produces the largest molar difference between associated-oxidized and dissociated-reduced states, and the model predicts the positions of the maxima for adrenodoxin reduction, 11 beta-hydroxylation, and side chain cleavage. Thus reduction-induced dissociation of adrenodoxin from adrenodoxin reductase appears to be a required step in steroidogenic electron transport by this system, and a role for adrenodoxin as a mobile electron shuttle is proposed.

Adrenal Cortex↗
PubMed1990

Electron backscattering. Implication to electron dosimetry.

Plane-parallel electron chambers have structures made of plastic materials of low atomic number which do not provide the same scattering into the sensitive volume as water and suitable correction factors are therefore required to allow for this effect. Hunt et al. (1988) measured electron backscatter in low atomic number materials and this data was, in this work, analyzed together with the experimental data obtained for higher atomic number materials published earlier (Klevenhagen et al., 1982). It was found that both sets of data correlate well and fit to an empirical exponential expression for which the necessary calculation parameters were derived. This expression enables suitable backscatter correction factors to be calculated for materials of atomic numbers between 4 and 82, including plastics, and electron energies between 3 and 35 MeV. The deficiency of backscatter was evaluated for the most popular materials used in the construction of electron chambers and this data may be used for corrections.

Electrons↗
PubMed1988

[Scanning electron microscopy of intracellular structures in the hair cells of the guinea pig cochlea using backscatter electrons].

Guinea pig cochleae were prepared for scanning electron microscopy (SEM). The lateral surface of the outer hair cells was studied first with secondary electrons. It was possible to find a network of tubular cisterns and long mitochondria stained by osmium immediately under the plasma membrane detected by backscattered electrons. The lateral arrangement of the mitochondria and the tubular cisterns was confirmed by observing the embedded SEM tissues by transmission electron microscopy.

Animals↗
PubMedDate not supplied

[Electron spectroscopy and the electron structure of molecules].

The experimental-theoretical approach to the study of physico-chemical, in particular, spectroscopic and photochemical properties of groups of related molecules is considered. The problem of physically correct spectral decompositions of complex electronic spectra into bands corresponding to separate electronic transitions and of the information obtained therefrom is discussed. Concrete examples of revealing photo- and enzymatic reaction mechanisms by combined spectroscopic and theoretical studies of molecular electronic structure and spectra are given. Special attention is paid to the connection of electronic structure of molecules with their physico-chemical, in particular, spectroscopic properties.

Electrons↗
PubMed1995

Electron energy-loss spectroscopy study of amorphization process of graphite bombarded with hydrogen ions and energetic electrons at low temperatures.

Structural change of graphite bombarded with hydrogen ions as well as energetic electrons is investigated mainly by the EELS (electron energy-loss spectroscopy) technique, with a focus on the formation of diamond-like amorphous (DLA) phase at low temperatures. The chemical effects of hydrogen ions on the amorphization process are examined by comparing the results obtained by hydrogen-ion bombardment with those obtained by electron bombardment. The critical temperatures for the formation of DLA phase during hydrogen-ion and electron bombardments are determined. Finally, a model of the amorphization process of graphite during ion-bombardment is presented.

Electrons↗
PubMedDate not supplied

The effect of fast secondary electrons on x-ray microanalysis in the scanning electron microscope.

In this paper, the effect of fast secondary electrons (FSE), which result from inelastic scattering of incident electrons, on the characterization of materials in the scanning electron microscope are investigated with the aid of Monte Carlo simulations. The effect of FSE on x-ray microanalysis of light elements is investigated. A full description of the Monte Carlo simulations of FSE in solids is given.

Boron↗
PubMed1976

A combined scanning and transmission electron microscopic study and electron probe microanalysis of human pineal acervuli.

Untreated, decalcified and trypsinized acervuli from human pineal bodies were studied with the scanning and transmission electron microscope as well as by electron probe microanalysis. The mulberry-like acervuli are composed of a various number of spherical lobes (135-800 mum) between which clustered groups of globuli (4--14 mum in diameter) are observed. The acervular lobes are very probably formed by an aggregation of these globuli. Small round particles 125--500 A in diameter are observed on the surface of the pineal concretions. These are not influenced by either decalcification or trypsin treatment. The acervular mineral corresponds morphologically to hydroxyapatite. The electron probe microanalysis reveals the existence of calcium and phosphorus as main components of the acervuli. Small quantities of magnesium and strontium were also detected.

Aged↗
PubMed2005

Some effects of electron channeling on electron energy loss spectroscopy.

As an electron beam (of order 100 keV) travels through a crystalline solid it can be channeled down a zone axis of the crystal to form a channeling peak centered on the atomic columns. The channeling peak can be similar in size to the outer atomic orbitals. Electron energy loss spectroscopy (EELS) measures the losses that the electron experiences as it passes through the solid yielding information about the unoccupied density of states in the solid. The interaction matrix element for this process typically produces dipole selection rules for small angle scattering. In this paper, a theoretical calculation of the EELS cross section in the presence of strong channeling is performed for the silicon L23 edge. The presence of channeling is found to alter both the intensity and selection rules for this EELS signal as a function of depth in the solid. At some depths in the specimen small but significant non-dipole transition components can be produced, which may influence measurements of the density of states in solids.

Algorithms↗
PubMed2000

Continuous electronic heart rate monitoring for fetal assessment during labor.

BACKGROUND: Electronic fetal monitoring (EFM) has been widely adopted. There is debate about its overall effectiveness as well as the relative merits of routine application versus use for high-risk pregnancies only. OBJECTIVES: The objective of this review was to assess the effects of routine continuous electronic fetal monitoring during labour compared with intermittent auscultation. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register, Medline (1966 to 1994), and reference list of relevant articles. We also contacted experts in the field. SELECTION CRITERIA: Randomised trials comparing routine continuous electronic fetal monitoring with intermittent auscultation. DATA COLLECTION AND ANALYSIS: Data were extracted by one reviewer, and their accuracy was confirmed independently by a second person. A single reviewer assessed study quality based on criteria developed by others for randomised controlled trials. Data reported from similar studies were used to calculate a combined risk estimate for each of eight outcomes. MAIN RESULTS: Nine studies involving 18,561 women and their 18,695 infants were included. The trials were of variable quality. A statistically significant decrease was associated with routine continuous EFM for neonatal seizures (relative risk (RR) = 0. 51, confidence interval (CI) = 0.32,0.82). The protective effect for neonatal seizures was only evident in studies with high-quality scores. No significant differences were observed in 1-minute Apgar scores below 4, 1-minute Apgar scores below 7, rate of admissions to neonatal intensive care units, and perinatal death. An increase associated with the use of EFM was observed in the rate of cesarean delivery (RR = 1.41, CI = 1.23,1.61) and operative vaginal delivery (RR = 1.20, CI = 1.11,1.30). REVIEWER'S CONCLUSIONS: The only clinically significant benefit from the use of routine continuous EFM was in the reduction of neonatal seizures. In view of the increase in cesarean and operative vaginal deliveries, the long-term benefit of this reduction must be evaluated in the decision reached jointly by the pregnant woman and her clinician to use continuous EFM or intermittent auscultation during labor.

Cardiotocography↗
PubMed2005

High-electron-density C6H6 units: stable ten-pi-electron benzene complexes.

The first stable benzene molecule with ten pi electrons is predicted. Stability is achieved through barium atoms acting as an electron-donating "matrix" to C6H6 in the inverted sandwich complex [Ba2(C6H6)]. The bis(barium)benzene complex has been computed at the density functional level of theory by using the hybrid functional mPW1PW91. Ab initio calculations were performed by using the coupled-cluster expansion, CCSD(T). Nucleus independent chemical shift (NICS) indices imply distinct aromatic character in the benzene ring of bis(barium)benzene. The D6h-symmetric structure with a 1A(1g) electronic ground state represents a thermochemically stable, aromatic benzene molecule with four excess pi electrons, stabilised by two barium ions. A possible molecular wire, built up from Ba end-capped thorium-benzene "sandwiches", is discussed.

Journal Article↗
PubMed2005

Charge-shift bonding--a class of electron-pair bonds that emerges from valence bond theory and is supported by the electron localization function approach.

This paper deals with a central paradigm of chemistry, the electron-pair bond. Valence bond (VB) theory and electron-localization function (ELF) calculations of 21 single bonds demonstrate that along the two classical bond families of covalent and ionic bonds, there exists a class of charge-shift bonds (CS bonds) in which the fluctuation of the electron pair density plays a dominant role. In VB theory, CS bonding manifests by way of a large covalent-ionic resonance energy, RE(CS), and in ELF by a depleted basin population with large variances (fluctuations). CS bonding is shown to be a fundamental mechanism that is necessary to satisfy the equilibrium condition, namely the virial ratio of the kinetic and potential energy contributions to the bond energy. The paper defines the atomic propensity and territory for CS bonding: Atoms (fragments) that are prone to CS bonding are compact electronegative and/or lone-pair-rich species. As such, the territory of CS bonding transcends considerations of static charge distribution, and involves: a) homopolar bonds of heteroatoms with zero static ionicity, b) heteropolar sigma and pi bonds of the electronegative and/or electron-pair-rich elements among themselves and to other atoms (e.g., the higher metalloids, Si, Ge, Sn, etc), c) all hypercoordinate molecules. Several experimental manifestations of charge-shift bonding are discussed, such as depleted bonding density, the rarity of ionic chemistry of silicon in condensed phases, and the high barriers of halogen-transfer reactions as compared to hydrogen-transfers.

Journal Article↗
PubMed2005

Electron pairing and chemical bonds. Electron fluctuation and pair localization in ELF domains.

This article reports the numerical comparison of the quantities characterizing the extent of electron fluctuation and pair localization in the domains determined by the direct minimization of electron fluctuation with the domains resulting from the partitioning of the molecules based on the topological analysis of the so-called electron localization function (ELF). Such a comparison demonstrates that the ELF partitioning can be regarded as a feasible alternative to computationally much more demanding direct optimization of minimum fluctuation domains. This opened the possibility of the systematic scrutiny of the electron pair model of the chemical bond, and as it was demonstrated, the previous pessimistic claims about the applicability of this model are not completely justified.

Journal Article↗