SEARCH · PubMed Health

Results for “Transition Elements”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources

PubMed2004

Exhaled breath condensate as a suitable matrix to assess lung dose and effects in workers exposed to cobalt and tungsten.

The aim of the present study was to investigate whether exhaled breath condensate (EBC), a fluid formed by cooling exhaled air, can be used as a suitable matrix to assess target tissue dose and effects of inhaled cobalt and tungsten, using EBC malondialdehyde (MDA) as a biomarker of pulmonary oxidative stress. Thirty-three workers exposed to Co and W in workshops producing either diamond tools or hard-metal mechanical parts participated in this study. Two EBC and urinary samples were collected: one before and one at the end of the work shift. Controls were selected among nonexposed workers. Co, W, and MDA in EBC were analyzed with analytical methods based on mass spectrometric reference techniques. In the EBC from controls, Co was detectable at ultratrace levels, whereas W was undetectable. In exposed workers, EBC Co ranged from a few to several hundred nanomoles per liter. Corresponding W levels ranged from undetectable to several tens of nanomoles per liter. A parallel trend was observed for much higher urinary levels. Both Co and W in biological media were higher at the end of the work shift in comparison with preexposure values. In EBC, MDA levels were increased depending on Co concentration and were enhanced by coexposure to W. Such a correlation between EBC MDA and both Co and W levels was not observed with urinary concentration of either element. These results suggest the potential usefulness of EBC to complete and integrate biomonitoring and health surveillance procedures among workers exposed to mixtures of transition elements and hard metals. Key words: cobalt, exhaled breath condensate, hard metals, lung, malondialdehyde, oxidative stress, tungsten.

Adult↗

PubMed1965

The fine structure of Brunner's glands in the mouse.

Examined with the electron microscope, the secretory cells of the submucosal glands of Brunner in the mouse present a curious combination of the fine-structural features of both serous and mucus-secreting cells. The cells have numerous mitochondria, abundant basal ergastoplasm, dense secretory granules that bear a superficial resemblance to pancreatic zymogen granules, and an unusually extensive Golgi apparatus. The prominence of the lamellar, vesicular, and vacuolar elements of the Golgi complex facilitates detailed observation of these components. More evident than in other glandular cells, aggregates of small vesicles appear to represent the transitional elements and are vehicles for transport of the product between the ergastoplasm and the Golgi complex. The numerous vesicular evaginations of smooth-surfaced regions on cisternae of the rough-surfaced endoplasmic reticulum and accumulations of innumerable vesicles of similar size in the area between the nearest profiles of the ergastoplasm and the Golgi complex support this contention. The cytological characteristics and physiologic properties of Brunner's glands in various species are discussed briefly. It is concluded that the submucosal glands of the mouse are excellent material for exploration of the ultrastructural correlates of both protein and carbohydrate secretion, and it is suggested that their secretion may have functions other than those generally attributed to them, namely, chemical and mechanical protection of the duodenal surface epithelium.

Animals↗

PubMed2005

Hydrogenation-induced insulating state in the intermetallic compound LaMg2Ni.

Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations.

Journal Article↗

PubMed2003

Experimental and mechanism studies on seawater flue gas desulfurization.

Seawater flue gas desulfurization (Seawater FGD) process has a number of advantages, but the study on mechanism of seawater FGD is little. The effects of absorbing efficiency of SO2 by the constant component and part of trace transition elements in seawater are studied by the experiment. The results indicate that the effect factors of absorption of SO% by seawater are alkaline, ion intensity, catalysis of Cl- and transition metal ions Fe2+ Mn(2+). The degree of effect is alkaline > the catalysis of Cl-, Fe2+ and Mn2+ > ion intensity. The mechanisms of catalysis oxidation for S( IV) by Cl -, Fe2+ and Mn2 are discussed. According to the results, some measures can be used to improve the capability of desulfurization.

Absorption↗

PubMed2001

Multielemental analysis of purpleback flying squad using high resolution inductively coupled plasma-mass spectrometry (HR ICP-MS).

Forty-four elements were analyzed in 21 tissues of purpleback flying squid, Sthenoteuthis oualaniensis, by high resolution inductively coupled plasma-mass spectrometry (HR ICP-MS) and inductively coupled plasma atomic emission spectrophotometry (ICP-AES). Greater concentrations of V, Fe, Co, Ni, Cu, Ag, Cd, Pb, and Bi were found in liver, pancreas, and ink sac than in other tissues. Ink sac concentrated remarkable levels of Ca and Sr in addition to the above-mentioned elements. Several alkalis, alkaline earth, and rare earth elements preferentially accumulated in muscle. Among the hard tissues, accumulation of V and U in beak, Ni, Zn, and Cd in gladius and Cr in skin was prominent. K, Rb, Cs, Pb, Bi and some transition elements (V, Co, Cu, Zn, Ag, Cd) were significantly (p < 0.05) higher in the livers of adult than in juvenile squids. Sodium, alkaline earth, and rare earth elements were higher in the livers of juveniles than in adult squids.

Age Factors↗

PubMed2002

Evaluation and optimization of two complementary cross-flow ultrafiltration systems toward isolation of coastal surface water colloids.

While colloidal phases in natural waters are important to the speciation and bioavailability of trace metals and organic compounds, accurate isolation of these submicron entities from their lower molecular-weight counterparts has proved challenging. Here, both laboratory and field experiments have been conducted to constrain integrity aspects of two different cross-flow filtration (CFF) systems. We tested both a commonly applied 5000 cm2 CFF system (Pellicon2, Millipore; manufacturer-specified 1 and 3 kDa cutoff) and a less studied mini-CFF system with a 50 cm2 membrane area (Pellicon Lab Scale XL, Millipore; with 5, 10, 100, and 1000 kDa cutoff). A natural water matrix amended with a series of fluorescently tagged colloidal probes was employed to demonstrate that a cross-flow ratio (CFR; retentate-to-permeate flux) > 15 was required for both of these systems to obtain high recoveries of colloids. Contrary to previous calibrations of CFF, also at colloid concentrations characteristic of natural waters, the established retention profiles for the colloid probes on these systems, when operated under CFR > 15, affirmed the manufacturer-specified cutoff values (in parentheses): 2.4 kDa (1 kDa), 3.3 kDa (3 kDa), 6.1 kDa (5 kDa) and 8.7 kD (10 kDa). A concentration factor (cf) > 10 was found necessary for the reliable determination of the colloidal pool of several elements in the surface waters of the open Baltic Sea. Application of CFR > 15 and cf > 10 returned recoveries around 100% for the studied organic carbon, Ca, Mo, Fe, Cu, and Ni on both systems. Furthermore, the trend of colloid association for the transition elements in the offshore Baltic surface waters followed expectations from their Irving-Williams series of coordination chemistry.

Biological Availability↗

PubMed1989

Dimethylnitrosamine-induced cirrhosis. Evidence for an immunological mechanism.

The present study is concerned with the early events associated with the development of cirrhosis induced by dimethylnitrosamine (DMN). The antigenic expression of MHC class II components (Ia) and of some intermediate filament proteins (vimentin and desmin) have been studied by immunohistochemistry and the findings correlated with ultrastructural data. Micronodular cirrhosis developed after 3 weeks of treatment with DMN but enhanced expression of Ia antigen on macrophages and on infiltrating lymphocytes was observed after 1 week, before the formation of septa, suggesting that immune-mediated mechanisms are involved in the response to DMN-induced liver injury. The expression of vimentin and of desmin also increased at an early stage and at 3 weeks the septa were outlined by cellular elements showing positivity for both intermediate filament proteins. In keeping with these observations, ultrastructural data showed active division of macrophages in situ, infiltration of the parenchyma by T and B lymphocytes, activation of lipocytes (Ito cells) showing evidence of mitosis, and the presence of transitional elements between lipocytes, myofibroblasts and fibroblasts. This experimental model may be helpful in understanding the relationship between immune-mediated response to liver injury and development of hepatic fibrosis.

Animals↗

PubMed1986

The functional and structural borders between the CSF- and blood-dominated milieus in the choroid plexuses and the area postrema of the rat.

In the borderline area between the hemal milieu of the choroid plexuses (PC) and the interstitial cerebrospinal-fluid (CSF) compartment, ground substances displaying increased amounts of basal lamina-like material and containing negatively charged sulfated glycosaminoglycans appear to be endowed with selective properties. They may function as a sieve or filtration barrier gradually controlling the passage of substances between the two milieus, depending on their charge and molecular weight. Special structural features and functional properties of ependymal cells are associated with such bordering structures. These ependymal cells are transitional elements between choroid epithelium and ciliated ependymal cells. As judged from experiments with horseradish peroxidase and conventional electron microscopy, occluding junctions at the basal pole of these cells prevent a rapid alteration in the milieu conditions, enabling gradual change from hemal to CSF composition near the bases of these transitional ependymal cells. The borderline structures between the hemal milieu of the PC and the area postrema are established by leptomeningeal cells which face a hemal milieu, are endowed with conspicuous tight junctions, and produce a flocculent substance, the light-microscopic equivalent of which is PAS positive. These structures probably establish an effective barrier between the two milieus of different composition. The functional characteristics and the morphology of the meningeal cells facing the hemal milieu of neurohemal regions resemble closely the neurothelial cells, which are interposed between the CSF milieu and the hemal milieu in the dura mater. The present results suggest that the location between the hemal and the CSF milieu is decisive for the transformation of leptomeningeal cells into "neurothelial" elements.

Animals↗

PubMed1986

Immunolocalization of the oligosaccharide trimming enzyme glucosidase II.

We used immunoelectron microscopy to localize glucosidase II in pig hepatocytes. The enzyme trims the two inner alpha 1,3-linked glucoses from N-linked oligosaccharide precursor chains of glycoproteins. Immunoreactive enzyme was concentrated in rough (RER) and smooth (SER) endoplasmic reticulum but not detectable in Golgi apparatus cisternae. Transitional elements of RER and smooth membraned structures close to Golgi apparatus cisternae contained labeling for glucosidase II. Specific labeling was also found in autophagosomes. These results indicate strongly that glucosidase II acts on glycoproteins before their transport to, and processing in Golgi apparatus cisternae, and suggest that an important transitional region for glucosidase II exists between RER and Golgi apparatus cisternae. Degradation in autophagolysosomes could form a normal catabolic pathway for glucosidase II.

Animals↗

PubMed2006

A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions.

We present a new local density functional, called M06-L, for main-group and transition element thermochemistry, thermochemical kinetics, and noncovalent interactions. The functional is designed to capture the main dependence of the exchange-correlation energy on local spin density, spin density gradient, and spin kinetic energy density, and it is parametrized to satisfy the uniform-electron-gas limit and to have good performance for both main-group chemistry and transition metal chemistry. The M06-L functional and 14 other functionals have been comparatively assessed against 22 energetic databases. Among the tested functionals, which include the popular B3LYP, BLYP, and BP86 functionals as well as our previous M05 functional, the M06-L functional gives the best overall performance for a combination of main-group thermochemistry, thermochemical kinetics, and organometallic, inorganometallic, biological, and noncovalent interactions. It also does very well for predicting geometries and vibrational frequencies. Because of the computational advantages of local functionals, the present functional should be very useful for many applications in chemistry, especially for simulations on moderate-sized and large systems and when long time scales must be addressed.

Journal Article↗

PubMed1978

Radioautographic investigation of gliogenesis in the corpus callosum of young rats. II. Origin of microglial cells.

Microglial cells are absent from the corpus callosum of newborn rats. In the hope of finding out when and how microglial cells appear with age, 3H-thymidine was given intraperitoneally as single or three shortly spaced injections to 5-day-old rats weighing about 15 g; and these animals were sacrificed at various time intervals from 2 hours to 35 days later. Pieces of corpus callosum were taken near the superior lateral angle of the lateral ventricles; and semithin sections were radioautographed and stained with toluidine blue. The corpus callosum of 5-day-old rats is composed of loosely arranged unmyelinated fibers and scattered cells. Among these cells, microglia are rare; there are a few astrocytes, many immature glial cells, rare pericytes, and 6--7% of phagocytic "ameboid cells" consisting of a few monocytes and many macrophages. In the animals sacrificed two hours after 3H-thymidine administration, label is present only in immature cells and "ameboid cells." As time elapses and the fibers of corpus callosum become myelinated, oligodendrocytes and, later, microglial cells appear. At the age of 12 days, microglial cells are present in substantial number; and by 19 days, the number doubles to reach a plateau. Many of the new microglial cells are labeled, e.g., 78.1% in 12-day-old animals (7 days after 3H-thymidine administration). The labeled microglial cells must have come from the transformation of cells that acquired label early, that is, from the immature cells or the "ameboid cells." The height of the peaks of labeling--59.8% at nine days for immature cells and 77.8% at 12 days for "ameboid cells"--points to the latter as precursors of the highly labeled microglial cells. Furthermore, the "ameboid cells" disappear as microglial cells appear and there are transitional elements between these two cell types. Cell counts suggest that about a third of the "ameboid cells" transform into microglial cells, while the others degenerate and die. Thus, the microglial cells which appear in the corpus callosum during the first three weeks of life result from transformation of the "ameboid cells"--a group of macrophages showing various stages of transition from monocytes. As for the occasional microglial cell appearing after the third week or in the adult, they presumably come directly from monocytes. In either case, monocytes would be the initial precursors.

Aging↗

PubMed1990

Retinoid modulation of cell-free membrane transfer between endoplasmic reticulum and Golgi apparatus.

Cell-free transfer of radiolabeled membrane proteins from part-rough, part-smooth transitional elements of the endoplasmic reticulum to Golgi apparatus immobilized to nitrocellulose in the presence of nucleoside triphosphate, an ATP-regenerating system and a cytosol fraction was promoted by retinol. At an optimum concentration of 1 microgram/ml, the rate and amount of transfer was approximately doubled over 1 to 2 h of incubation in the cell-free system. The transition vesicles induced to form in the cell-free system were concentrated by preparative free-flow electrophoresis in order to study separately the steps of vesicle formation from transitional endoplasmic reticulum and the steps of vesicle fusion with Golgi apparatus. The retinol effect was on vesicle formation as evidenced by an approx. 2-fold increase in transition vesicle numbers, as determined by electron microscope morphometry, and amount from protein determinations on the isolated fractions enriched in transition vesicles. The retinol response in the complete transfer could be eliminated by addition of concentrated cytosol, including cytosol depleted of retinol. An interaction of retinol with some component of the vesicle formation process, possibly involving guanine nucleotides, is indicated.

Adenosine Triphosphate↗

PubMed2001

The Sar1 GTPase coordinates biosynthetic cargo selection with endoplasmic reticulum export site assembly.

Cargo selection and export from the endoplasmic reticulum is mediated by the COPII coat machinery that includes the small GTPase Sar1 and the Sec23/24 and Sec13/31 complexes. We have analyzed the sequential events regulated by purified Sar1 and COPII coat complexes during synchronized export of cargo from the ER in vitro. We find that activation of Sar1 alone, in the absence of other cytosolic components, leads to the formation of ER-derived tubular domains that resemble ER transitional elements that initiate cargo selection. These Sar1-generated tubular domains were shown to be transient, functional intermediates in ER to Golgi transport in vitro. By following cargo export in live cells, we show that ER export in vivo is also characterized by the formation of dynamic tubular structures. Our results demonstrate an unanticipated and novel role for Sar1 in linking cargo selection with ER morphogenesis through the generation of transitional tubular ER export sites.

Animals↗

PubMed2000

Highly Polar Metal-Metal Bonds in "Early-Late" Heterodimetallic Complexes.

Metal-metal bond polarity in its extreme form involving transition elements is found in di- or polynuclear complexes in which molecular fragments containing metal atoms from the two ends of the d block in the periodic table are combined. This linkage by direct metal-metal bonds of metal centers having very different oxidation states has been a challenge to the synthetic chemist. The suppression of degradative reaction channels caused by intramolecular single-electron transfer and the protection of the highly Lewis acidic early transition metal center by an appropriately designed ligand shell have opened up the systematic investigation of such systems. Concomitant with this development, advances in the conceptual framework for the quantitative description of bond polarity have led to a refined understanding of the nature of this type of metal-metal bonding. The greatest stimulus for the development of this field of research is the investigation of the cooperative reactivity of two or more coordination centers in their interaction with and transformation of organic substrates. This cooperativity, which is characterized by the different functions adopted by the metal centers in these conversions offers attractive perspectives in stoichiometric or even catalytic transformations.

Journal Article↗

PubMed2002

Gallium nitrate accelerates partial thickness wound repair and alters keratinocyte integrin expression to favor a motile phenotype.

The nitrate form of the Group III transitional element gallium (GN) increases expression of specific structural components of the provisional wound matrix (i.e., collagen type I, fibronectin) in human dermal fibroblasts. To evaluate the potential of GN as a therapeutic option in management of cutaneous trauma, GN-treated partial thickness porcine wounds and experimentally "injured" human keratinocyte (NHK) monolayer cultures were compared with mirror image control (i.e., saline-treated) sites. GN suppressed cell proliferation in both models, as determined by reduced Ki-67 reactivity and significant lengthening of keratinocyte cell cycle transit times, while effectively promoting reepithelialization. The primary effect of GN was apparently to promote cell migration, as neither epidermal thickness nor epidermal differentiation was altered as a result of GN exposure in vivo or in vitro. Significantly enhanced epidermal reepithelialization was associated with alterations in expression of several keratinocyte integrin subunits. GN induced a significant increase in alpha5 expression. alpha5beta1 switching is a characteristic of the motile phenotype in the setting of cutaneous injury. Concomitantly, GN treatment also induced a dramatic (70%) decrease in the expression of the alpha3 subunit; alpha3beta1 binds laminin 5 and is associated with hemidesmosome formation and reestablishment of a nonmotile phenotype. Taken together, the GN-induced changes in integrin expression favor acellular migration. While the molecular mechanism of GN action on resident cells of the skin remains to be defined, these data suggest that GN administration which represses MMP activity in the wound and increases matrix synthesis also accelerates NHK motility and, thereby, may be a useful therapeutic agent for wound repair.

Animals↗

PubMed2001

New delta (distorted-bcc) titanium to 220 GPa.

Structural phase transitions of a 3d transition element, titanium, have been investigated at pressures up to 220 GPa at room temperature using a monochromatic synchrotron x-ray diffraction technique. At 140 GPa, the hexagonal (omega) phase was transformed into an orthorhombic (delta) phase with a distorted bcc structure via an intermediate (gamma) phase, which has recently been proposed by Vohra and Spencer [Phys. Rev. Lett. 86, 3068 (2001)]. Both the delta and the gamma phases had a unique zigzag-chain-like structure, which resulted from an orthorhombic distortion. The delta-gamma transition could be explained as a rearrangement of the packing between the zigzag chains.

Journal Article↗

PubMed1991

Trafficking of lipids from the endoplasmic reticulum to the Golgi apparatus in a cell-free system from rat liver.

Trafficking and sorting of lipids during transport from the endoplasmic reticulum to the Golgi apparatus was studied using a cell-free system from rat liver. Transitional elements of the endoplasmic reticulum were prepared from liver slices prelabeled with [14C]- or [3H]acetate as the donor fraction. Non-radioactive Golgi apparatus were immobilized on nitrocellulose as the acceptor. When reconstituted, the radiolabeled donor retained a capacity to transfer labeled lipids to the non-radioactive Golgi apparatus acceptor. Transfer exhibited two kinetically different components. One was stimulated by ATP, facilitated by cytosol and inhibited by guanosine 5'-O-(thiotriphosphate) and N-ethylmaleimide. In parallel with protein transport, the ATP-dependent lipid transfer occurred with a temperature transition at about 20 degrees C. The other was not stimulated by ATP, did not require cytosol, was acceptor unspecific, was unaffected by inhibitors and, while temperature dependent, did not exhibit a sharp temperature transition. The ATP-independent transfer was non-vesicular. In contrast, the ATP-dependent transfer was vesicular. Transition vesicles isolated by preparative free-flow electrophoresis, when used as the donor fraction, transferred lipids to Golgi apparatus acceptor with a 5-6-fold greater efficiency than that exhibited by the unfractionated transitional endoplasmic reticulum. Formation of transition vesicles was ATP-dependent. Transferred lipids were chiefly phosphatidylcholine and cholesterol. Membrane triglycerides, major constituents of the transitional endoplasmic reticulum membranes, were both depleted in the transition vesicle-enriched fractions and not transferred to Golgi apparatus suggestive of lipid sorting prior to or during transition vesicle formation. The characteristics of the ATP plus cytosol-dependent transfer were similar to those for protein transfer mediated by transition vesicles. Thus, the 50-70-nm vesicles derived from transitional endoplasmic reticulum appear to function in the trafficking of both newly synthesized proteins and lipids from the endoplasmic reticulum to the Golgi apparatus.

Adenosine Triphosphate↗

PubMed1994

Control theory of one enzyme.

The analogue of metabolic control theory is developed for the control of reactions catalyzed by single enzymes. The control exerted by any of the elemental transitions of enzyme catalytic cycles on reaction rate and on concentrations (probabilities) of enzyme states is quantified in line with the principle of detailed balance. For enzyme reactions with arbitrary kinetic schemes, e.g., with several enzyme cycles, reflecting coupling and slipping of reactions, it is derived what the various sums of the control coefficients are equal to (cycle summation theorems). Total control on flux, state probability and ratios of branch fluxes are 1, 0 and 0, respectively. The general connectivity theorems are derived which indicate how control is determined by the kinetics of the elemental steps. In addition, for enzymes catalyzing single (or completely coupled) processes the control coefficients are expressed in terms of actual and standard free energy differences across the steps. The prevalent qualitative contention that the step with the smallest forward rate constant, or with the largest free energy drop is the step limiting the performance of the enzyme is shown to fail. The new theory should allow subtle analysis of the control of an enzyme catalyzed reaction.

Enzymes↗