Reaction of rat connective tissue to implanted dentin tubes filled with mineral trioxide aggregate or calcium hydroxide

This study was conducted to observe the rat subcutaneous connective tissue reaction to the implanted dentin tubes filled with calcium hydroxide or mineral trioxide aggregate. The animals were sacrificed after 7 and 30 days, and the specimens were prepared for morphological study. Some undecalcified specimens were prepared for histological analysis with polarized light and Von Kossa technique for calcium. The results were similar for both studied materials. At the tube openings, there were Von Kossa-positive granules that were birefringent to polarized light. Next to these granulations, there was an irregular tissue like a bridge that was Von Kossa-positive. The dentin walls of the tubes exhibited in the tubules a structure highly birefringent to polarized light, usually like a layer and at different depths. It is possible that the mechanism of action of both materials has some similarity. Copyright © 1999 by The American Association of Endodontists.

Reaction of dogs' teeth to root canal filling with mineral trioxide aggregate or a glass ionomer sealer

This study was conducted to observe the reaction of apical tissues of dogs' teeth after root canal filling with gutta-percha and mineral trioxide aggregate (MTA) or a glass ionomer (Ketac-Endo) as a sealer. The root canals were instrumented and filled by the lateral condensation technique with the sealers studied. Animals were killed 6 months later, and the specimens were removed and prepared for histological analysis. Results showed no inflammatory reaction of apical tissue and total closure of the apical foramen of all the teeth sealed with MTA. The teeth sealed with Ketac-Endo showed two cases of partial closure and different degrees of chronic inflammatory reaction. In conclusion, MTA exhibited better biological properties than Ketac-Endo. Copyright © 1999 by The American Association of Endodontists.

Reaction of rat connective tissue to implanted dentin tube filled with mineral trioxide aggregate, Portland cement or calcium hydroxide.

The subject of this study was to observe the rat subcutaneous connective tissue reaction to implanted dentin tubes filled with mineral trioxide aggregate, Portland cement or calcium hydroxide. The animals were sacrificed after 7 or 30 days and the undecalcified specimens were prepared for histological analysis with polarized light and Von Kossa technique for mineralized tissues. The results were similar for the studied materials. At the tube openings, there were Von Kossa-positive granules that were birefringent to polarized light. Next to these granulations, there was an irregular tissue like a bridge that was Von Kossa-positive. The dentin walls of the tubes exhibited in the tubules a structure highly birefringent to polarized light, usually like a layer and at different depths. The mechanism of action of the studied materials has some similarity.

Reaction of rat connective tissue to implanted dentin tubes filled with a white mineral trioxide aggregate.

The purpose of this paper was to study the reaction of rat subcutaneous connective tissue to the implantation of dentin tubes filled with white mineral trioxide aggregate (MTA), a material that will be marketed. The tubes were implanted into rat subcutaneous tissue and the animals were sacrificed after 7 and 30 days. The undecalcified pieces were prepared for histological analysis with polarized light and von Kossa technique for mineralized tissues. Granulations birefringent to polarized light and an irregular structure like a bridge were observed next to the material; both were von Kossa positive. Also, in the dentin wall tubules a layer of birefringent granulations was observed. The results were similar to those reported for gray MTA, indicating that the mechanisms of action of the white and gray MTA are similar.

Use of a zeolite synthesised from alkali treated kaolin as a K fertiliser : glasshouse experiments on leaching and uptake of K by wheat plants in sandy soil

Zeolite N, a zeolite referred to in earlier publications as MesoLite, is made by caustic reaction of kaolin at temperatures between 80 °C and 95 °C. This material has a very high cation exchange capacity (CEC ≈ 500 meq/100 g). Soil column leaching experiments have shown that K-zeolite N additions greatly reduce leaching of NH4+ fertilisers but the agronomic effectiveness of the retained K+ and NH4+ is unknown. To measure the bioavailability of K in this zeolite, wheat was grown in a glasshouse with K-zeolite N as the K fertiliser in highly-leached and non-leached pots for four weeks and compared with a soluble K fertiliser (KCl). The plants grown in non-leached pots and fertilised with K-zeolite N were slightly larger than those grown with KCl. The elemental compositions in the plants were similar except for Si being significantly more concentrated in the plants supplied with K-zeolite N. Thus K-zeolite N may be an effective K-fertiliser. Plants grown in highly-leached pots were significantly smaller than those grown in non-leached pots. Plants grown in highly-leached pots were severely K deficient as half of the K from both KCl and K-zeolite N was leached from the pots within three days.

Enhancement of 1,2-dehydration of alcohols by alkali cations and protons : a model for dehydration of carbohydrates

We have used electronic structure calculations to investigate the 1,2-dehydration of alcohols as a model for water loss during the pyrolysis of carbohydrates found in biomass. Reaction enthalpies and energy barriers have been calculated for neat alcohols, protonated alcohols and alcohols complexed to alkali metal ions (Li + and Na +). We have estimated pre-exponential A factors in order to obtain gas phase rate constants. For neat alcohols, the barrier to 1,2-dehydration is about 67 kcal mol -1, which is consistent with the limited experimental data. Protonation and metal complexation significantly reduce this activation barrier and thus, facilitate more rapid reaction. With the addition of alkali metals, the rate of dehydration can increase by a factor of 10 8 while addition of a proton can lead to an increase of a factor of 10 23.

Nanoporous Pt with High Surface Area by Reaction-Limited Aggregation of Nanoparticles

Nanoporous structures with high active surface areas are critical for a variety of applications. Here, we present a general templateless strategy to produce such porous structures by controlled aggregation of nanostructured subunits and apply the principles for synthesizing nanoporous Pt for electrocatalytic oxidation of methanol. The nature of the aggregate produced is controlled by tuning the electrostatic interaction between surfactant-free nanoparticles in the solution phase. When the repulsive force between the particles is very large, the particles are stabilized in the solution while instantaneous aggregation leading to fractal-like structures results when the repulsive force is very low. Controlling the repulsive interaction to an optimum, intermediate value results in the formation of compact structures with very large surface areas. In the case of Pt, nanoporous clusters with an extremely high specific surface area (39 m(2)/g) and high activity for methanol oxidation have been produced. Preliminary investigations indicate that the method is general and can be easily extended to produce nanoporous structures of many inorganic materials.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfied linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc - Cys - Pro - Leu - Cys - NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of (CH)-H-alpha or (CH)-H-beta protons of Cys residues, with Subsequent elimination of H2S or H2S2. The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S-2. (J Am Soc Mass Spectrom 2009, 20, 783-791) (C) 2009 American Society for Mass Spectrometry.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfied linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc - Cys - Pro - Leu - Cys - NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of (CH)-H-alpha or (CH)-H-beta protons of Cys residues, with Subsequent elimination of H2S or H2S2. The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S-2. (J Am Soc Mass Spectrom 2009, 20, 783-791) (C) 2009 American Society for Mass Spectrometry.

A Novel Synthetic Route For The Preparation Of Ammonium And Alkali-Metal Tetrafluoroborates And Alkyl Substituted Ammonium Tetrafluoroborates Using Pyridinium Tetrafluoroborate As The Precursor

Ammonium and alkali metal tetrafluoroborates have been prepared by the cation exchange reaction of pyridinium tetrafluoroborate with the corresponding hydroxides/halides. The reaction of pyridinium tetrafluoroborate with primary, secondary and tertiary alkyl amines at room temperature gives rise to mono-, di- and tri-alkylammonium tetrafluoroborates, respectively. The yields are good and the samples are of high purity. The products have been characterised by elemental analysis, IR and PMR spectroscopy. The spectral data for most of the compounds are reported for the first time.

Low-temperature synthesis of novel layered alkali metal-MoO3 bronzes and hexagonal bronzes of the type KyW1−xMoxO3

A new class of layered alkali metal-MoO3 bronzes,AxMoO3 (A =Li, Na, K, Rb), with nearly the same unit cell parameters as the host oxide has been synthesized by the solid-state reaction of MoO3 with alkali metal iodides around 575 K; LixMoO3 absorbs H2O causing an increase in theb parameter of the unit cell. Hexagonal potassium bronzes of W1−xMoxO3 are synthesized for the first time.

Growth Kinetics of ZnO Nanocrystals in the Presence of a Base: Effect of the Size of the Alkali Cation

Following an earlier study (J. Am. Chem Soc. 2007, 129, 4470) describing a very unusual growth kinetics of ZnO nanoparticles, we critically evaluate here the proposed mechanism involving a crucial role of the alkali base ion in controlling the growth of ZnO nanoparticles using other alkali bases, namely, LiOH and KOH. While confirming the earlier conclusion of the growth of ZnO nanoparticles being hindered by an effective passivating layer of cations present in the reaction mixture and thereby generalizing this phenomenon, present experimental data reveal an intriguing nonmonotonic dependence of the passivation efficacy on the ionic size of the alkali base ion. This unexpected behavior is rationalized on the basis of two opposing factors: (a) solvated cationic radii and (b) dissociation constant of the base.

High-temperature reactions of alkali and plagioclase feldspars with alkali and alkaline-earth chlorides-formation of celsian

High-temperature reactions (Ca 900-degrees-C) involving albite, K-feldspar or plagioclase and K, Ba-or K, Sr chlorides were experimentally studied. These experiments reveal that the reaction between K-exchanged albite, potash feldspar, or plagioclase and Ba-chloride/Ba-K chloride results in the formation of celsian by the breakdown of the starting feldspar structure above 800-degrees-C. Sr-feldspar does not form under similar conditions. A size-effect of the large M-site cation appears to be responsible for the formation of celsian. The reaction between K-feldspar and barium chloride may be used as a method for synthesizing celsian.

Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction

Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu M, M=Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process.

Chemisorption and reaction characteristics of methyl radicals on Cu(110)

Methyl radicals are generated by pyrolysis of azomethane, and the condition for achieving neat adsorption on Cu(110) is described for studying their chemisorption and reaction characteristics. The radical-surface system is examined by X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, temperature-programmed desorption, low-energy electron diffraction (LEED), and high-resolution electron energy loss spectroscopy under ultrahigh vacuum conditions. It is observed that a small fraction of impinging CH3 radicals decompose into methylene possibly on surface defect sites. This type of CH2 radical has no apparent effect on CH3(ads) surface chemistry initiated by dehydrogenation to form active CH2(ads) followed by chain reactions to yield high-mass alkyl products. All thermal desorption products, such as H-2, CH4, C2H4, C2H6, and C3H6, are detected with a single desorption peak near 475 K. The product yields increase with surface coverage until saturation corresponding to 0.50 monolayer of CH3(ads). The mass distribution is, however, invariant with initial CH3(ads) coverage, and all desorbed species exhibit first-order reaction kinetics. LEED measurement reveals a c(2 x 2) adsorbate structure independent of the amount of gaseous exposure. This strongly suggests that the radicals aggregate into close-packed two-dimensional islands at any exposure. The islanding behavior can be correlated with the reaction kinetics and is deemed to be essential for the chain propagation reactions. Some relevant aspects of the CH3/Cu(111) system are also presented. The new results are compared with those of prior studies employing methyl halides as radical sources. Major differences are found in the product distribution and desorption kinetics, and these are attributed to the influence of surface halogen atoms present in those earlier investigations.