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At least 271 records · Page 15Linked to original sources
PubMed1991

Analysis of steroids. XLI. Ion-pair high-performance liquid chromatographic separation of quaternary ammonium steroids on silica.

A normal-phase ion-pair chromatographic system has been developed for the high-performance liquid chromatographic investigation of pipecuronium bromide (2 beta,16 beta-bis-(N'-dimethyl-l-piperazinyl)-3 alpha,17 beta-diacetoxy-5 alpha-androstane dibromide) and related quaternary ammonium steroids. The use of silica as the stationary phase and a 96:4 mixture of acetonitrile and water containing 0.1 mol/dm3 sodium perchlorate as the eluent with detection at 213 nm enable the potential impurities as well as the hydrolytic and oxidative degradation products of pipecuronium bromide to be separated and detected down to the 0.01% level. The above system is also applicable to the high-performance liquid chromatographic investigation of other quaternary ammonium steroids (pancuronium bromide, vecuronium bromide).

Chromatography, High Pressure Liquid↗
PubMed2003

Modification of ion chromatographic separations by ionic and nonionic surfactants.

New findings are reported on simple ways to modify an ordinary HPLC column to obtain efficient ion chromatographic (IC) separations. Permanently coating a column with an ionic surfactant is known to produce an effective column for IC. We now show that incorporation of a nonionic surfactant in the coating, or coating in separate layers, results in a dramatic reduction of ion retention times and gives sharper peaks. Dynamic coating by incorporating a small amount of an alcohol, diol or zwitterion in the aqueous mobile phase permits good separations of alkanecarboxylic acids. A mobile phase containing a quaternary ammonium cation and a zwitterion anion provides excellent separations of common anions on a silica C18 column. An aqueous eluent containing a mixture of a zwitterion 4-(2-hydroxyethyl) acid and methanesulfonic acid can be used in conjunction with a standard cation exchange column. After passing through a membrane suppressor, the mobile phase has a slightly acidic pH, permitting divalent transition metal ions (as well as others) to be detected by conductivity.

Anions↗
PubMed2002

Quantitative aspects of inorganic nutrient fluxes in the Gazi Bay (Kenya): implications for coastal ecosystems.

Fluxes of dissolved inorganic nutrients: NH4+, NO2-, NO3-, PO4(3-) and Si(OH)4 from nearshore sediments of Gazi Bay were measured in situ within mangrove, seagrass and coral reef biotopes using benthic flux bell-jar chambers of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, fluvial discharge and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay. The directly measured fluxes ranged from -270 to +148 micromol NH4+-N/m2/h; -60 to +63 micromol NO2(-)-N/m2/h; -79 to +41 micromol NO3(-)-N/m2/h; -79 to +75 micromol PO4(3-)-P/m2/h and +30 to +350 micromol Si(OH)4-Si/m2/h for and respectively. It was established that benthic fluxes are the major sources of dissolved inorganic NH4+, NO2- and Si(OH)4 while fluvial sources are important for NO3- and PO4(3-) into Gazi Bay waters. Seasonal variations had an appreciable effect on the PO4(3-) fluxes, N:Si ratio, river nutrient discharge, plankton productivity and important environmental factors such as salinity and temperature. Tidal and spatial variations had no significant effect on nutrient concentrations and net fluxes within the water column. The results imply that benthic fluxes are largely responsible for the nutrient dynamics of the nearshore coastal ecosystems especially where direct terrestrial inputs do not contribute significantly to the nutrient budget.

Ammonia↗
PubMed2002

Microstructural dependence on relevant physical-mechanical properties on SiO2-Na2O-CaO-P2O5 biological glasses.

Bioactive glasses of the system SiO2-Na2O-CaO-P2O5 have been prepared by the normal melting and annealing technique. The elastic moduli, attenuation, Vickers hardness, fracture toughness and fracture surface energy have been obtained using the known method at room temperature. The temperature dependence of elastic moduli and attenuation measurements have been extended over a wide range of temperature from 150 to 500 K. The SiO2 content dependence of velocities, attenuation, elastic moduli, and other parameters show an interesting observation at 45 wt% of SiO2 by exhibiting an anomalous behaviour. A linear relation is developed for Tg, which explores the influence of Na2O on SiO2-Na2O-CaO-P2O5 bioactive glasses. The measured hardness, fracture toughness and fracture surface energy show a linear relation with Young's modulus. It is also interesting to note that the observed results are functions of polymerisation and the number of non-bridging oxygens (NBO) prevailing in the network with change in SiO2 content. The temperature dependence of velocities, attenuation and elastic moduli show the existence of softening in the glass network structure as temperature increases.

Biocompatible Materials↗
PubMed2002

Direct patterning of modified oligonucleotides on metals and insulators by dip-pen nanolithography.

The use of direct-write dip-pen nanolithography (DPN) to generate covalently anchored, nanoscale patterns of oligonucleotides on both metallic and insulating substrates is described. Modification of DNA with hexanethiol groups allowed patterning on gold, and oligonucleotides bearing 5'-terminal acrylamide groups could be patterned on derivatized silica. Feature sizes ranging from many micrometers to less than 100 nanometers were achieved, and the resulting patterns exhibited the sequence-specific binding properties of the DNA from which they were composed. The patterns can be used to direct the assembly of individual oligonucleotide-modified particles on a surface, and the deposition of multiple DNA sequences in a single array is demonstrated.

Adsorption↗
PubMed2000

[The adsorption on attapulgite and cross-linked agar beads entrapped attapulgite(CAA)].

The adsorption of four drugs with certain toxicity, i.e. chlorpromazine, quinidine, diazepam and phenobarbital on attapulgite and Cross-linked Agar Beads Entrapped Attapulgite(CAA) was determined in this study. The results revealed that attapulgite possessed high adsorption for the cation drugs(chlorpromazine and quinidine), moderate adsorption for diazepam, and slight adsorption for phenobabital. The adsorption in attapulgite was quite quick and came to equilibrium in about 30 min. No significant difference(P > 0.05) of adsorption on attapulgite was observed at 30 min and 60 min. The adsorbent selectivity on CAA was the same as that on attapulgite. The speed of the adsorption was slower on CAA than on attapulgite, but the quantity adsorpted on CAA and that on attapulgite had no marked difference(P > 0.05) after 60 min. CAA preserved the adsorption property of attapulgite fundamentally. CAA overcame the dispersibility of attapulgite distinctly and showed good hemocompatibility and a fair blood flow rate in hemoperfusion. It may play an important role in the separation of blood components and in hemopurification.

Adsorption↗
PubMed1992

[Therapeutic evaluation of Mormoiron attapulgite in acute diarrheas of infants and children. A multicenter study in controlled liberal practice versus placebo in 113 patients].

A placebo-controlled multicenter study was carried out to evaluate the effectiveness and safety of Actapulgite in infants and children with acute diarrhea. One hundred and thirteen patients, with a mean age of 28 months, were enrolled by pediatricians in the office. As recommended during acute diarrhea, the dosage of Actapulgite was doubled during the first three treatment days (2 to 4 packets a day according to the patient's weight), and reduced by half thereafter. The main effectiveness criteria was passage of the first normally formed stool, which denotes normalization of intestinal transit time. The first normally formed stool was recorded after two days of treatment with Actapulgite and was followed, on the next day, by a second normal stool, denoting complete recovery. The greater effectiveness of Actapulgite as compared with the placebo was demonstrated by the fact that both the first and the second normally formed stools were passed one day earlier with the active treatment (p = 0.01 and p = 0.002, respectively). In addition, resumption of a normal diet occurred significantly earlier with Actapulgite (4.4 days) than with the placebo (5.1 days). In addition to being effective, the study drug proved remarkably well tolerated. This study is especially valuable because of its office setting and the use of exclusively clinical criteria with a strict methodology.

Acute Disease↗
PubMed1987

Attapulgite.

Explore the source record for details and available documents.

Animals↗
PubMed1993

[The use of actapulgite for the treatment of acute diarrhea in infants and children. Review of pediatric studies].

Epidemiological data on diarrhea due to Rotavirus are similar enough across different regions of the world to allow the pooling of clinical studies of Actapulgite for the treatment of acute diarrhea in infants and children in France and Africa. A total of 7,616 infants and children were entered into these open or placebo-controlled trials. Most patients were under two years of age, results of the analysis confirmed the antidiarrheal efficacy and safety of Actapulgite.

Acute Disease↗
PubMed1993

Demonstration of silicon in sites of connective-tissue disease in patients with silicone-gel breast implants.

BACKGROUND AND DESIGN: Silica, Silastic, and silicone (any organic compound in which silicon replaces carbon) have been associated with a number of connective-tissue diseases, most commonly systemic sclerosis (scleroderma). Silicone is known to leak from breast implants and spread to surrounding tissues, including lymph nodes, but silicone's role in the origin and pathogenesis of the inflammation and fibrosis related to such conditions remains controversial. Synovial tissue, alveolar macrophages, and skin, each from three different patients with silicone-gel implants, plus the breast implant capsules from each of the three patients, were examined by light microscopy, transmission electron microscopy, and electron probe microanalysis for the presence of silicon-containing material. RESULTS: Silicon was identified within the fibrous breast capsule of each case, associated with a chronic inflammatory cell infiltrate. Silicon was also identified within tissues involved by chronic inflammation and fibrosis, namely, synovium, skin, and alveolar macrophages, in association with clinical, serologic, and histologic evidence of connective tissue disease. All three patients improved after removal of the silicone-gel breast implants. CONCLUSIONS: The presence of silicon-containing material within sites of connective-tissue disease supports a role for silicon in the origin or pathogenesis of such conditions in patients with silicone-gel breast implants. All patients with connective-tissue disease should be questioned about exposure to various forms of silicon. In those patients with known exposure, tissue specimens should be examined carefully for silicon-containing material and, if found, the source should be removed.

Adult↗
PubMed1985

Absence of genotoxic effects of nonasbestos mineral fibers.

The biological activity of natural and synthetic mineral fibers has been examined. Natural attapulgite [(Mg, Al)2Si4O10(OH).4H2O], synthetic xonotlite [Ca3Si3O8(OH)2] and natural sepiolite [Mg2Si3O8.2H2O] were selected. Genotoxic effects were investigated by means of a well established cellular model based upon the measurement of unscheduled DNA synthesis (UDS) in rat hepatocytes in primary culture. The intrinsic capacity of the fibers (1 and 10 micrograms/ml) to induce UDS was first tested. None of the fiber types showed detectable UDS-eliciting activity. Also, the possible modulation of the cellular response to genotoxic agents by the materials was examined by exposing the cells to mixtures of 2-acetylaminofluorene (AAF) (0.05 and 0.25 micrograms/ml) and fibers (1 and 10 micrograms/ml). In these experiments, the UDS response was significantly diminished in the presence of xonotlite. This phenomenon may reflect changes in the uptake and/or metabolism of AAF or may result from an inhibition of DNA repair processes, the latter suggesting a possible cocarcinogenic potential for this synthetic silicate. These results point to the immediate necessity of studying more extensively the biological effects of fibrous materials that can be used as substitutes for asbestos.

Animals↗
PubMedDate not supplied

A comparison of three resin bonding agents to primary tooth dentin.

This study determined the shear bond strength of resin composites to primary dentin using three dentin adhesives and the presence or absence of a hybrid zone. The buccal and lingual surfaces of 40 recently extracted noncarious primary teeth were ground flat with SiC paper ending with the 600 grit. The teeth were divided at randomly into eight groups of five teeth (10 surfaces) each: 1) Unetched dentin, dry dentin, All-Bond 2/Bis-Fil P; 2) Unetched dentin, moist dentin, All-Bond 2/Bis-Fil P; 3) Dentin etched for 15 sec with 10% phosphoric acid, dry dentin, All-Bond 2/Bis-Fil P; 4) Dentin etched for 15 sec with 10% phosphoric acid, moist dentin, All-Bond 2/Bis-Fil P; 5) Dentin etched with 10% maleic acid for 15 sec, dry dentin, Scotchbond Multi-Purpose/Z100; 6) Dentin etched with 10% maleic acid for 15 sec, moist dentin, Scotchbond Multi-Purpose/Z100; 7) Dentin etched with 10 citric acid/3% ferric chloride, dry dentin, Amalgambond Plus/Z100; 8) Dentin etched with 10 citric acid/3% ferric chloride, moist dentin, Amalgambond Plus/Z100. All teeth were thermocycled 1000x (5 and 55 degrees C, 30-sec dwell time), and shear bond strength testing was conducted using an Instron (crosshead speed 0.5 mm/min). Failure sites after debonding were examined with the SEM. For each group, one additional tooth was used to prepare two class V cavities (one facial and one lingual) restored according to the specification in each group, sectioned buccolingually and examined with the SEM. The results, in MPa, were: 1) 12.55 +/- 5.97; 2) 10.41 +/- 6.16; 3) 9.94 +/- 7.26; 4) 12.25 +/- 4.70; 5) 13.02 +/- 8.01; 6) 16.51 +/- 8.62; 7) 12.51 +/- 8.95; 8) 17.93 +/- 6.44. ANOVA and Student-Newman-Keuls tests showed no statistically significant differences. SEM evaluation showed that the smear layer was removed in all groups exposing primary dentin tubules infiltrated by resin. A resin-reinforced hybrid layer was readily seen in all specimens.

Acid Etching, Dental↗
PubMed2002

Long-term durability of the dual-cure resin cement/silicon oxide ceramic bond.

PURPOSE: To determine the effects of using a ceramic primer, ceramic bonding agent, or a combination of primer/bonding agent on the long-term durability of the dual-cure resin cement/silicon oxide ceramic bond. MATERIALS AND METHODS: Ceramic blocks (Vita Celay Blanks), A2M, were cut into 1-, 2-, and 3-mm-thick slices and polished using 600-grit SiC paper. Group 1 consisted of pairs of 1- and 3-mm-thick slices, and Group 2 of pairs of 2- and 3-mm-thick slices. Ceramic surfaces were treated with 40% phosphoric acid and silanated using one of three treatments: (1) Clearfil Liner Bond 2V Primer (2V Pr) and Porcelain Bond Activator (PBA), (2) Liner Bond 2V Primer/PBA and Liner Bond 2V Bond (2V Pr + Bd), and (3) Clearfil Photo Bond/PBA (P Bd). They were then bonded with a dual-cure resin cement (Panavia F) and light-cured for 20 s from each of six directions. After 24 h water storage at 37 degrees C, 0.7-mm-thick slabs were serially sectioned. Immediately thereafter, after one and six weeks, and after one year of water storage, two slabs were randomly selected from each subgroup and sliced into beams for the microtensile bond strength (microTBS) test. Data were evaluated with three-way ANOVA and Fisher's PLSD test (p < 0.05) and failure modes determined using a laser-scanning confocal microscope. RESULTS: After 1 day, there were no significant differences between 2V Pr, 2V Pr + Bd, and P Bd (p > 0.05), whereas after one year, significant differences were found (p < 0.05). For Group 1, the micriTBS of P Bd after one year of water storage was similar to that after one day. In both groups, microTBS of 2V Pr and 2V Pr + Bd significantly decreased over time (p < 0.05), which was accompanied by an increase in the percentage of complete adhesive failures. CONCLUSION: The chemical composition of the multicomponent ceramic primer/bonding agent significantly affects the long-term durability of the dual-cure resin cement/silicon oxide ceramic bond. The presence of water in a ceramic primer has a significant detrimental effect on resin-ceramic bond durability. In addition, the thickness of the ceramic restoration influences dual-cure resin cement/ceramic bond durability.

Analysis of Variance↗