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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cryo-TEM was carried out on samples containing polyelectrolyte-micelle complexes, formed by combining poly(diallyldimethylammonium chloride) (PDADMAC), a strong cationic polyelectrolye, with oppositely charged mixed micelles of sodium dodecyl sulfate (SDS) and nonionic Triton X-100 (TX100), in 0.40 M NaCl. Complexation appears to involve the formation of micelle-rich regions, presumably within the domains of polymer chains, without any particular organization or restructuring of the micelles. At polymer concentrations (CP) </= 0.4 g/L, the observation of such clusters with dimensions as low as 50 nm suggests that intrapolymer complexes may exist at low CP. With increasing polymer concentration, aggregates grow in size, with dimensions that indicate the involvement of many polymer chains. Upon increase in the ratio of SDS:TX100, the system coacervates, and the micelle/polymer-rich phase forms a continuous matrix.
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PMID:Cryo-TEM of Polyelectrolyte-Micelle Complexes 905 71

The development of acinar and ductal cells of the mouse submandibular gland was studied using field emission SEM, conventional TEM and HVTEM methods. The specimens, at 15 and 18 days of gestation and 1, 3, 7, 14, 21, 30, 90 and 180 postnatal days were fixed in 2.5% glutaraldehyde solution in 0.1 M sodium phosphate buffer (pH 7.3). At 15 and 18 days of gestation, the structure of mouse submandibular gland contains acinar and ductal cells in proliferation. The cytoplasmic organelles such as mitochondria, granular endoplasmic reticulum and Golgi apparatuses are scattered in the cytoplasm. At 18 prenatal days only several acinar cells present immature secretory granules in the apical portion. In this stage the acinar and ductal cells are enveloped by bundles of fine collagen fibrils disposed in several directions. There are also numerous capillaries located closely to the acinar cell membranes. In the aging stages of 1, 3, 7, 14, 21, and 30 postnatal days, the histo-differentiation of acinar, intercalated and ductal cell components are observed. At newborn day one the cytoplasmic organelles start to place themselves around the nucleus. Several immature secretory granules are observed at day one, however, they increase in the aging days. At postnatal day 30, the cytoplasms of acinar and ductal cells are filled with a large number of secretory granules of different sizes. The stacks of granular endoplasmic reticulum and Golgi apparatus and some vesicles and free ribosomes are noted. The intercellular membranes are attached by desmosomes and cytoplasmic interdigitations. The luminal surface shows several small projections of microvilli. An electron-dense line of basement membranes followed by fine collagen fibrils are recognized. Delicate capillaries are found in the outer surface of acinar cells. At postnatal day 90 and 180 the acinar, intercalated and striated ductal cells reveal numerous secretory granules in the apical portion. The acinar cells showed basal nuclei and the parallel arrangement of granular endoplasmic reticulum. The mitochondria are located at the base of ductal cells showing a typical pattern of cristae. In these stages the intercellular digitations of cytoplasmic protrusions and desmosomes are also noted. The cytoplasm of myoepithelial cells are seen along the cell membranes. The spongy-like structures constituting the basement membrane are followed by bundles of fine collagen fibers.
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PMID:Field emission SEM, conventional TEM and HVTEM study of submandibular gland in prenatal and postnatal aging mouse. 915 Nov 34

The objective of this study was to determine whether cells of the secretory- and maturation-stage enamel organ of rats contain anion translocation mechanisms similar to those found in other ion-regulating epithelia. Sodium bromide (Br) was used to localize the distribution of anions in the enamel organ. Furosemide, an inhibitor of the Na-K-2Cl co-transporter and other anion transporters, was administered with NaBr or sodium fluoride (F) to investigate if halogens other than Cl can use these transport mechanisms. We obtained the data by using freeze-fracture and freeze-drying methodology in conjunction with scanning and transmission electron microscopy (SEM, TEM) and energy-dispersive x-ray spectroscopy (EDS). The secretory- and maturation-stage enamel organ prevented Br from entering the enamel matrix. Br was localized in the Tomes' processes, but not in the enamel matrix, strongly suggesting that the distal intercellular junctions of ameloblasts are "tight". Furosemide disrupted anion transport to allow not only Cl but also Br to enter the forming enamel matrix. Periodic administration of high F doses promoted the formation of bands of disrupted enamel, reflecting the periodicity of F administration. The same concentration of F administered with furosemide increased the severity of disrupted enamel, resulting in "blisters" and pits in the maturing enamel. The enamel "blisters" contained pools of small, disorganized enamel crystallites. The group receiving furosemide only displayed normal enamel structure but had increased Cl in the enamel matrix. This study provides evidence that anion transporters, possibly the Na-K-2Cl co-transporter, function to regulate anion translocation, including F, to the enamel matrix in secretory- and maturation-stage enamel organ. These mechanisms may explain why the ionic composition on the cellular side of the anion barrier is different from that of the enamel matrix.
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PMID:Anion translocation through the enamel organ. 920 43

This study examined the effects of tetracycline hydrochloride (TCN) and chlorhexidine gluconate (CHX) on the growth and viability of Candida albicans. Subcultures of Candida albicans on Sabouraud's agar, were divided into 5 treatment groups: group 1, untreated control; group 2, 0.12% CHX; group 3, 3.0 mg/ml TCN adjusted to pH 4.5; groups 4 and 5, sodium azide free Tris buffer adjusted to pH 4.5 and pH 7.4, respectively. All groups were incubated for 10 days, and sampled and subcultured daily to determine the viability of each group. Additional samples from group 2 (day 4), group 4 (day 7) and all groups at day 10 were selected for SEM and TEM examination. Visual, SEM and TEM results showed that for groups 1, 3, 4, and 5 there was a heavy and constant uniform growth of Candida albicans throughout the period of the study. However, group 2 (CHX), showed decreasing viability and attachment from day 3 to day 10, with SEM and TEM revealing decreased blastospores and profound changes in the ultrastructural morphology, indicating inhibition of normal cell growth and replication. These results show that TCN even when used at high concentrations, in vitro, will allow uninhibited growth of Candida albicans whereas CHX inhibits cell growth and replication.
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PMID:Effects of tetracycline hydrochloride and chlorhexidine gluconate on Candida albicans. An in vitro study. 935 May 60

Block copolymers consisting of poly(gamma-benzyl L-glutamate) (PBLG) as the hydrophobic block and poly(ethylene oxide) (PEO) as the hydrophilic block were synthesized and characterized. Core-shell type nanoparticles of the block copolymers (abbreviated as GE) were prepared by the diafiltration method. The particle size diameter obtained by dynamic light scattering of GE-1 (PBLG content: 60.5 mol%), GE-2 (PBLG content: 40.0 mol %), GE-3 (PBLG content: 124.4 mol %) copolymer was 309.9 +/- 160.9, 251.9 +/- 220.6 and 200.5 +/- 177.1nm, respectively. The shape of the nanoparticles by SEM or TEM was almost spherical. The critical micelle concentration of the block copolymers obtained by fluorescence spectroscopy was dependent on the chain length of hydrophobic PBLG. The micelle structure of the copolymers nanoparticle was very stable against sodium dodecyl sulfate. Clonazepam (CZ) was loaded onto the core part of the nanoparticle as the crystalline state. Release of CZ from the nanoparticles in vitro was dependent on the drug loading contents and PBLG chain length.
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PMID:Clonazepam release from core-shell type nanoparticles in vitro. 968 14

Admixture of aluminum nitrate, sodium polyphosphate, and ammonium hydroxide solutions yields stable dispersions of hydrated aluminum polyphosphate particles within a broad reagent concentration range. These particles are formed by liquid-liquid phase separation, for which a phase diagram was calculated using suitable models for concentrated electrolyte solutions. Particle effective diameters range from a few nanometers to many hundreds and are fractionated by centrifugation. Particle electrophoretic mobility is very low and the hydration degree is high ( approximately 80% v/v). Dry nanoparticles (1- to 15-nm diameter as observed by TEM) as well as particle aggregates are obtained by lyophilization. Element (P, Al, and Na) mapping by ESI-TEM shows that particle aggregates have a core-and-shell morphology, with a higher content of P in the aggregate core and a higher Na content at the outer shell. Copyright 1999 Academic Press.
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PMID:Aluminum Polyphosphate Nanoparticles: Preparation, Particle Size Determination, and Microchemistry. 1046 32

Oppositely charged globular protein and surfactant systems, such as lysozyme-sodium dodecyl sulfate (SDS) and ovalbumin-dodecyltrimethylammonium chloride (DOTAC) form precipitate, gel, and colorless solution in water over a wide concentration range. Bluish solutions are also recognized in connection with the redissolution of precipitate as well as prior to the gel formation. For the lysozyme-SDS system the bluish solution has been suggested to consist of finely dispersed gel particles in solution. The oppositely charged bovine serum albumin (BSA)-DOTAC-water system forms only a large, clear solution phase and a narrow, bluish solution region within a very limited surfactant concentration range. In the lysozyme-SDS system the formation of protein-surfactant aggregates and their growth and breakdown are studied in detail by cryogenic-transmission electron microscopy (cryo-TEM) method. In particular a series of samples with an increased surfactant concentration at fixed 4 wt% of lysozyme is studied. Imaging of the bluish solution at different protein concentrations exhibits large aggregates in the form of rod-like, sheet-like, and star-like objects which are attributed to the gel. At excess amounts of SDS, in the colorless solution, only small objects are detected. In the ovalbumin-DOTAC-water and BSA-DOTAC-water systems large aggregates are also observed in the bluish solutions. Colorless solutions for these two systems show the presence of small objects in the cryo-TEM micrographs. Ultrathin sections of the lysozyme and ovalbumin gels fixed with OsO(4) also show the presence of aggregated structures as judged from the transmission electron microscopy observations. Copyright 2000 Academic Press.
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PMID:A Cryo-TEM Study of Protein-Surfactant Gels and Solutions. 1066 12

Octacalcium phosphate (OCP) hydrolysis into hydroxyapatite (HA) has been investigated in aqueous solutions at different concentrations of sodium polyacrylate (NaPA). In the absence of the polyelectrolyte, OCP undergoes a complete transformation into HA in 48 h. The hydrolysis is inhibited by the polymer, which is significantly adsorbed on the crystals, up to about 22 wt.%. A polymer concentration of 10(-2) mM is sufficient to cause a partial inhibition of OCP to HA transformation, which is completely hindered at higher concentrations. The small platelet-like crystals in the TEM images of partially converted OCP can display electron diffraction patterns characteristic either of OCP single crystals or of polycrystalline HA, whereas the much bigger plate-like crystals exhibit diffraction patterns characteristic of OCP single crystals. The polyelectrolyte adsorption on OCP crystals is accompanied by an increase of their mean length and by a significant reduction of the coherence length of the perfect crystalline domains along the c-axis direction. It is suggested that the carboxylate-rich polyelectrolyte is adsorbed on the hydrated layer of the OCP (100) face, thus inhibiting its in situ hydrolysis into HA.
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PMID:Effect of sodium polyacrylate on the hydrolysis of octacalcium phosphate. 1080 79

An expression system has been developed that allows high levels of production of TEM-1 beta-lactamase with ease of biosynthetic incorporation of nuclear isotopes. The gene for mature TEM-1 beta-lactamase fused to the leader sequence of the ompA protein was subcloned into the pET-24a(+) vector by introduction of an NdeI restriction site at the first codon of the fused genes and transformed into Escherichia coli BL21 (DE3) cells. With protein induction at 25 degrees C supported by LB medium supplemented with osmolytes (300 mM sucrose and 2.5 mM betaine), the extracellular, mature form of wild-type TEM-1 beta-lactamase was recovered at a level of 140 mg/L. The production level of E166N, E240C, E104C, and M272C mutants depended on the mutation but was invariably higher than reported by others for expression systems of the wild-type enzyme. Comparison of different carbon sources on the efficiency of biosynthetic incorporation of covalent deuterium showed maximal (90%) incorporation with minimal medium containing 99% (2)H(2)O and sodium d(3)-acetate (99 atom% (2)H). The yield of deuterium-enriched wild-type enzyme was 80 mg/L with yields for mutants proportionally reduced. The high level of protein deuteration achieved with this system allowed detection of the hyperfine coupling between the paramagnetic nitroxyl group of a spin-labeled penicillin substrate and hydrogens on the penicillin moiety in a cryokinetically isolated acylenzyme reaction intermediate because of the decrease in overlapping resonances of active site residues. The overexpression system is readily adaptable for other target proteins and facilitates studies requiring large quantities of protein in isotopically enriched forms.
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PMID:Overexpression and biosynthetic deuterium enrichment of TEM-1 beta-lactamase for structural characterization by magnetic resonance methods. 1087 36

The influence of concentration on rheological properties, including shear viscosity, shear instability, transient stress start-up and relaxation, apparent extensional viscosity, viscoelastic behavior, and microstructure by cryo-TEM, were studied with surfactant Ethoquad O/12, commercialized oleyl methyl bishydroxyethyl chloride, with counterion sodium salicylate. Counterion to surfactant molar ratios, xi, were 1.0 and 2.5. Concentrations for the xi=1 series are 5 mM/5 mM, 10 mM/10 mM, 50 mM/50 mM, 100 mM/100 mM, and 200 mM/200 mM (surfactant/counterion); those for the xi=2.5 series are 5 mM/12.5 mM, 10 mM/25 mM, 50 mM/125 mM, 100 mM/250 mM, and 200 mM/500 mM. The experimental results showed complicated rheological behavior with concentration changes. Shear viscosity decreases with increases in concentration for the xi=1 series. At xi=2.5 apparent viscosity increases with concentration above 10 mM. Viscoelasticity of the solutions also decreases with increases in surfactant concentration. At high concentration, a high shear rate is needed to induce viscoelasticity. A high extensional rate induces supermicellar structures. Gelation was observed during shear for the 100 mM/250 mM and 200 mM/500 mM solution in the cone-and-plate geometry. Cryo-TEM results revealed that all of the solutions examined had wormlike network micelle microstructures. Copyright 2001 Academic Press.
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PMID:Influence of Surfactant Concentration and Counterion to Surfactant Ratio on Rheology of Wormlike Micelles. 1142 22


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