Potassium Bichromate Research Articles

Translocation of exogen phenoloids and alkaloids in acceptor plants -histo- and phytochemical characteristics

Phenoloids with allelopathic effect (juglone, ctaechin, tannin, gallic acid t-cinnamic acid, caffeic acid, coumarin, thymol, salicin in 1mM concentration) cannot be detected after the absorption from the acceptor plant (bean) by the applied selective analytical method (TLC densitometry). Their localisation can be determined by histochemical reagens (ferrichloride, potassium bichromate, sodium hydroxide). In the foliage leaves and excised bean plants they are present mainly in the parenchymatuos elements of the vascular tissue already on the 3rd day, at the beginning of wilting. Some substances (tropanes) out of the studied allelopathic alkaloids (atropine, scopolamine, belladonnin, tropine and caffeine) can be detected only in small amounts (7-8%) or only in traces in the leaf. Others (e.g. caffeine) accumulate in substantial amount (almost 200%) in their original form. Alkaloids,as well as phenoloids, can be detected in lesf tissue by histochemical methods (Dragendorff and Meyer reagents).

Controlling crystal surface termination by cleavage direction.

We have investigated the cleaving behavior of potassium bichromate (K(2)Cr(2)O(7)) crystals using atomic force microscopy. This crystal has a double layered AB structure along [001]. We find that, upon cleavage along the [001] plane in the <100> directions, one side is completely A terminated, while the other is B terminated. Moreover, the cleavage plane (between an A and a B layer, or between B and A) depends on the imposed direction of cleavage, i.e., [100] or [*100]. This means that the molecular layer that terminates the crystal surface can be controlled by choosing the macroscopic direction of the cleavage force. One of the two terminations is metastable and partly reconstructs to the stable termination.

A Sulfenic Acid Enzyme Intermediate Is Involved in the Catalytic Mechanism of Peptide Methionine Sulfoxide Reductase fromEscherichia coli

Methionine oxidation into methionine sulfoxide is known to be involved in many pathologies and to exert regulatory effects on proteins. This oxidation can be reversed by a ubiquitous monomeric enzyme, the peptide methionine sulfoxide reductase (MsrA), whose activity in vivo requires the thioredoxin-regenerating system. The proposed chemical mechanism of Escherichia coli MsrA involves three Cys residues (positions 51, 198, and 206). A fourth Cys (position 86) is not important for catalysis. In the absence of a reducing system, 2 mol of methionine are formed per mole of enzyme for wild type and Cys-86 --> Ser mutant MsrA, whereas only 1 mol is formed for mutants in which either Cys-198 or Cys-206 is mutated. Reduction of methionine sulfoxide is shown to proceed through the formation of a sulfenic acid intermediate. This intermediate has been characterized by chemical probes and mass spectrometry analyses. Together, the results support a three-step chemical mechanism in vivo: 1) Cys-51 attacks the sulfur atom of the sulfoxide substrate leading, via a rearrangement, to the formation of a sulfenic acid intermediate on Cys-51 and release of 1 mol of methionine/mol of enzyme; 2) the sulfenic acid is then reduced via a double displacement mechanism involving formation of a disulfide bond between Cys-51 and Cys-198, followed by formation of a disulfide bond between Cys-198 and Cys-206, which liberates Cys-51, and 3) the disulfide bond between Cys-198 and Cys-206 is reduced by thioredoxin-dependent recycling system process.

A thin-layer bichromated gelatin for holography sensitive in the red spectral range

A variant of thin-layer optically sensitive material for holographic applications, based on a bichromated gelatin with glycerol and Methylene Blue dye additives, is suggested. The material is sensitive in the red spectral range, possesses the property of self-development, and provides for the possibility of the realtime reconstruction of holographic images. The bichromated gelatin is prepared using potassium bichromate.

Effectiveness of two devices designed to prevent fluid retraction in a high-speed handpiece

Statement of Problem: Contaminated fluid can be retracted into the turbine air chamber of a high-speed handpiece when it stops rotating. Purpose: This study attempted to evaluate 2 operating systems recently equipped with antiretraction devices installed inside the handpiece (Kavo) or inside the unit (Castellini) and to compare the results with those obtained from an operating system without any antisuction device (Bien Air). Material and Methods: Two test conditions (bur immersed approximately 5 mm into a dye solution or completely immersed in dye solution) were conducted using potassium bichromate dye to simulate a fluid contaminant. Results: During the first procedure dye influx for the Kavo unit was 0.08 ± 0.1 μL, 0.06 ± 0.1 μL for the Castellini unit, and 12.4 ± 5.2 μL for the Bien Air unit (F=28.3; P <.01). During the second procedure, the results of the dye influx were Kavo unit 2.52 ± 1.3 μL, Castellini unit 0.1 ± 0.1 μL, and Bien Air unit 22.22 ± 4.0 μL (F=123; P <.01). Mean values were significantly different between Castellini and Kavo units during the second procedure. Conclusion: Antisuction devices can reduce dye penetration into the air chamber of a high-speed handpiece. Better results may be obtained with devices installed inside the unit and designed to increase the air pressure in the air chamber when the turbine stops running. (J Prosthet Dent 2000;84:225-8.)

Etching and surface termination of K2Cr2O7 {0 0 1} faces observed using in situ atomic force microscopy

The etching behaviour of the double-layered {001) faces of potassium bichromate crystals was studied by using in situ atomic force microscopy (AFM). These crystals were cleaved in air or ethanol along {001}, and the opposite cleavage faces (001) and (001̄) were then etched in ethanol or a water/ethanol mixture. We found that in air an etch resistant layer is formed. Whether this layer can be removed depends on the exposure time to air, on the water content of the etch mixture and on the amount of scanning by the AFM. Under specific conditions this allows us to do lithography on the surface. On the air-cleaved faces, only at some positions expanding etch pits developed, in which layer-by-layer etching took place at freshly etched parts on the flat bottom. Most etch steps were of height d001 as expected for the double-layered structure of K2Cr2O7. However, sometimes split steps of half height d002 were encountered. Both the shapes of the 2D nucleation etch pits and the molecular-resolution images were similar on the (001) and the (001̄) faces, which suggests P1̄ symmetry. Therefore on this molecular scale, the hypomorphism (P1 symmetry in this case) visible on macroscopic K2Cr2O7 crystals appears to be absent. From the orientation of the d002 steps inside the etch pits the stable and the unstable {001} half layers A and B could be identified with respect to the crystal structure. During etching, A was nearly always on top of the crystal surface, proving that this is the most stable layer.

Reducing phosphine after the smoking process using an oxidative treatment.

This article gives a description of the setup in a laboratory of a pilot system to reduce phosphine following the smoking process of foodstuffs. At present, this fumigant is released into the atmosphere and causes serious damage to the environment due to its transformation into aggressive compounds. However, phosphine may prove a good alternative to methyl bromide, which will legally be used as a fumigant until the year 2002, provided it is made inert after the smoking process and transformed into nontoxic and easily disposable substances. Oxidant solutions containing potassium permanganate or potassium bichromate in suitable concentrations proved moderately effective in reducing phosphine. The addition of traces of silver nitrate as a catalyst to the oxidant solutions increased the efficiency in reducing the fumigant, although not completely. Thus it was necessary to use a recycling system to decontaminate air from phosphine, as such an apparatus ensures the complete reduction of phosphine. The mathematical function describing how the concentration of phosphine varies in the smoking chamber also makes it possible to estimate the time necessary to reduce a phosphine concentration from any initial value to a fixed final value.

The structure of coarse crystal surfaces:: the (0 0 1̄) face of K 2Cr 2O 7 crystals grown from aqueous solution as an example

The surface structure of the coarse (0 0 1 ̄ ) face of potassium bichromate (K 2Cr 2O 7) was studied in-situ and ex-situ with the help of optical microscopy, atomic force microscopy and scanning electron microscopy. A multitude of features, like unit cell height steps, bunches, macrosteps of which some are actually small facets, inclusions and spirals were observed. The observations lead to new ideas about the growth mechanisms of this face, in which the combined action of impurity adsorption and volume diffusion plays a key role. These mechanisms may be responsible for the coarse growth on other crystals as well.

Isotachophoretic crystallization of ionogenic substances in electrolyte solutions

Grounds are given for the use of isotachophoresis for the crystallization of ionogenic substances from electrolyte solutions. Regulating function is the basis of this new isotachophoresis trend. A device for isotachophoretic crystallization in capillaries, based on a capillary isotachophoresis instrument is described. The process of sodium chloride crystallization from aqueous solution is described in detail. The applicability of the general rules formulated is confirmed by crystallization of potassium and sodium chlorides, cesium nitrate and potassium perchlorate in cationic isotachophoresis, and potassium bichromate in anionic isotachophoresis.

Three-dimensional model of any shape face disappearance in crystal habit

The formulae to evaluate the length of any edge of a face of any shape and to evaluate critical growth velocity, above which the edge disappears have been derived for a three-dimensional case. These formulae make possible the analysis of the disappearance of any shape face. All theoretical predictions have been verified by computer modeling performed for triclinic potassium bichromate (KBC) crystals.

Three-dimensional model of faces disappearance in crystal habit

The formula to evaluate critical growth velocity, above which a face transforms to an edge or a corner, has been derived for a three-dimensional case. Using computed critical growth velocities for triclinic potassium bichromate (KBC) crystals, it was possible to draw crystal forms showing how a face transforms to an edge or a corner.

Ultrastructural distribution of calcium in cutaneous electroreceptor organs of teleost fish.

The calcium distribution in the ampullary electroreceptor and the type B electroreceptor organ (gymnarchomast) of Gymnarchus niloticus (Glymnarchidae) and in the tuberous organ of Apteronotus leptorhynchus (gymnotidae) was studied. Endogenous calcium appeared as electron-dense precipitates when the cutaneous organs were pre-fixed with phosphate-buffered glutaraldehyde and postfixed with osmium tetroxide plus potassium bichromate. Calcium precipitates were localized in both intracellular compartments of sensory cells, and afferent nerve fibers. In contrast to sensory cells, small amounts of calcium precipitates were found in the cytoplasm of accessory cells. In sensory cells, electron-dense deposits were apparent mainly in synaptic vesicles near synaptic ribbons, inside vacuoles of the endoplasmic reticulum, and between the layers of the nuclear membrane. Very few deposits were found in mitochondria. Precipitates were also observed within the axons of afferent nerves and between the layers of the myelin sheath. The synaptic cleft was devoid of calcium. Calcium deposits have a specific cellular distribution in electroreceptor organs of teleost fish.

Behaviour of steps on the (001) face of K2Cr2O7 crystals

The behaviour of (100) steps, originating from spiral centres, on the (001) face of potassium bichromate (K2Cr2O7) crystals growing from aqueous solutions has been studied by in situ and ex situ optical microscopy as well as by ex situ atomic force microscopy. After considerations concerning the centrosymmetry of K2Cr2O7, the (001) and (001) faces are discriminated and a general view of the (001) surface morphology is given. The bunching, blocking and velocity of the (100) steps as a function of supersaturation have been measured and are discussed in terms of models for step propagation influenced by time-dependent impurity adsorption. Blocking is observed for both growth and dissolution at super (under) saturations below a critical value. By atomic force microscopy steps of half, one and several unit cells height are measured. For the supersaturation region where blocking occurs cusps are found in the steps, which correspond to the sites of the impurities that act as pinning points hindering step propagation. Bunching of lower steps to macrosteps and a proportional dependence of the mutual separation of these steps on their distance from the growth centre is found for supersaturations above the critical value for blocking.

Protective effect of sulfoethylglucan against hexavalent chromium

The effect of pretreatment with sulfoethylglucan (SEG) on the frequency of micronuclei and the liver alkaline phosphatase activity induced by potassium bichromate (Cr(VI)) in mice was evaluated. Simultaneous application of SEG and Cr(VI) decreased the frequency of micronuclei in bone marrow cells ( P < 0.01) and the level of liver alkaline phosphatase activity in comparison to the Cr(VI) group. Pretreatment with SEG 24 h prior to the first Cr(VI) application resulted in a more pronounced decrease in the Cr(VI)-induced frequency of micronuclei. The mechanisms of the protective effects of sulfoethylglucan could be explained either by the formation of Cr ion complexes with sulfoethyl groups of glucan or by the scavenging ability of SEG to trap hydroxyl radicals.

Precision of the nitocra spinipes acute toxicity test and the effect of salinity on toxicity of the reference toxicant potassium bichromate

AbstractThe precision of the 96‐h LC50 test with the eurohaline copepod Nitocra spinipes was evaluated from a data set containing 85 tests with the reference toxicant potassium bichromate conducted at 12 laboratories during a 12‐year period. The overall mean was 30 mg/L as K2Cr2O7 with a coefficient of variation (CV) of 47% (N = 85). Since salinity differed between tests (7–33 o/oo), it explained part of the variation (ca. 25%; Pearson two‐tailed test r = 0.49; p = 0.0000; N = 85). The effect of salinity on Cr(VI) toxicity was confirmed in an experiment with 4 salinities (3.4, 6.8, 14.6, and 27 o/oo) and was explained to 99% by the equation 96‐h LC50 (mg/L) = 2.58 + 1.79 × salinity (o/oo). Intralaboratory CVs for corresponding salinities ranged from 8 to 35% (repeatability). Interlaboratory CVs at two salinities were 42% (N = 11) at 7–9 o/oo and 47% (N = 4) at 15–16 o/oo. © 1993 John Wiley &amp; Sons, Inc.

Evaluation in white mice of the infectivity of eggs of Lagochilascaris minor (Nematoda: Ascarididae), incubated by decortication with sodium hypochlorite (NaOCl).

White mice were used to study the infectivity of the eggs of Lagochilascaris minor Leiper, 1909 after incubation in liquid media, with or without preservative substances. Potassium bichromate (K2Cr2O7) at 1% restrict hatching, while 1% formalin gave a greater larval yield. Incubation of eggs in distilled water, in Roux or Falcon flasks gave a good yield, whether the eggs were obtained from human feces or from experimentally infected cats. Treatment of eggs with Sodium hypochlorite (NaOCl) at 5.25% for 2 min prior to inoculation, produced a notable increment of the larval yield in the infections.

Use of fluorescence induction kinetics of Lemna minor as a tool for chemical stress evaluation

Slow fluorescence induction kinetics have been studied for Lemna minor under exposure to toxic chemicals. The first objective of the study was to find optimal values for condition measurements (dark adaptation time, light intensity, temperature, biomass and CO 2 concentration) to obtain only fluorescence induction due to chemical stress. The second end point was to test three chemical compounds, pentachlorophenol (PCP), simazin wand potassium bichromate. Results of toxicity were expressed as an index derivated from the Lichtentaler Vitality Index. A log-type dose-response curve was obtained for the three chemicals with an I 50 of 1.7 mg·1 −1 for PCP, 2.7 mg·1 −1 for simazin and 45 mg· −1 for potassium bichromate. This index is correlated to the inhibition of growth. The studied signal seems to be a good marker of pertubation of photosynthesis of aquatic plants in respect of the low variability (1–10%), the time scale of the response (1–2 min) and its easiness.

Ibotenic acid-induced calcium deposits in rat substantia nigra. Ultrastructure of their time-dependent formation.

The excitotoxin ibotenic acid (IBO) induces local calcium deposits upon injection into rat substantia nigra. Their formation has been investigated at the ultrastructural level in a time course study from 2 days to 8 weeks survival. Potassium bichromate stain was used to visualize pathological calcium accumulation. Two days after IBO application, reaction product for calcium was observed in mitochondria of degenerating perikarya and dendrites, but not in axons, boutons or glia. Four days after the lesion, calcium stain was found, in addition, in a seemingly free form in a few dendrites, especially those still contacted by intact boutons and not sequestrated by invading glia. Two days later, most of these calcium-accumulating dendrites were separated by astroglia from their synaptic partners. At the border between glia and dendrite a fibrillar matrix was formed which further accumulated calcium. During the following weeks this matrix enlarged stepwise and was infiltrated with calcium, thus giving a picture resembling the annual growth rings of trees. The evolving bodies incorporated smaller deposits in their vicinity, finally representing the large concretions seen at the light microscopic level from the 4th postoperative week onward. Similarities and dissimilarities of these observations with the results from other ultrastructural studies on excitotoxin lesions are detailed. It is suggested that the different outfit of neuronal subpopulations and of glia with ligand-gated and metabotropic glutamate receptors in the single brain region, as well as the local response repertoire of glial cells towards the excitotoxic injury with the subsequent formation of a calcium-accumulating matrix provide the molecular basis for the formation of calcium deposits.

Synthesis and surface activity of sodium salts of branched perfluorocarboxylic acids and their analogs containing one chlorine atom

AbstractIndividual sodium salts of branched perfluorocarboxylic acids, (CF3)2CF(CF2CF2)nCOONa, and their analogs containing one chlorine atom, CF3CF(CF2CI)(CF2CF2)nCOONa, were synthesized by telomerization of 2‐iodoheptafluoropropane and l‐chloro‐2‐iodohexafluoropropane with tetrafluoroethene, the addition of ethylene to both types of iodides considered, HI elimination and the oxidation of perfluoroalkylethylenes with potassium bichromate. The surface tension measurements demonstrated the high surface activity of sodium salts containing 9 and 11 carbon atoms in the hydrophobe. Perfluorocompounds were more surface active than their analogs having one chlorine atom but the differences were not great.

Occurrence of various planes in contact with the bottom of crystallizers during the growth of potassium bichromate crystals from aqueous solutions

Occurrence of various planes in contact with the bottom of crystallizers during the growth of potassium bichromate crystals from aqueous solutions