Chromium Acetate Research Articles

Chemical Properties of Chromium/Polyacrylamide Gels

SUMMARY Experimental studies on aqueous Cr+3/polyacrylamide (HPAAm) gels have led to new insight into their structure and chemical properties. In particular, Cr+3 is shown to form molecular crosslinking complexes with HPAAm, and to display chemical reactivity typical of inorganic coordination complexes. On the basis of ligand-induced de-gelation reactions, a new hypothesis regarding the bonding between HPAAm and Cr+3 is formulated. Comparisons are made between the chemistry of HPAAm gels prepared with chromium acetate complexes and those with inorganic Cr+3.

Immobilisation of β‐galactosidase onto gelatin by glutaraldehyde and chromium(III) acetate

Abstractβ‐Galactosidase (EC 3.2.1.23) was immobilised onto a gelatin carrier system by crosslinking. Glutaraldehyde and chromium(III) acetate were used as crosslinking agents. The effect of pH on enzyme activity, kinetic parameters and reusability of the immobilised enzyme were investigated. To obtain a better relative activity, a method was developed and further modified to increase the surface area of the support system by using polyacrylamide. Relative activity enhancement of 68% was achieved in the gelatin–glutaraldehyde system.

Monitoring of total chromium in rat fluids and lymphocytes following intratracheal administration of soluble trivalent or hexavalent chromium compounds.

1. Intratracheal instillation of sodium dichromate (CrVI) and chromium acetate hydroxide (CrIII) to male Wistar rats gave rise to increased chromium concentrations in whole blood, plasma and urine up to 72 h post exposure; peak concentrations were reached at 6 h after exposure. 2. The ratio of whole blood chromium to plasma chromium concentrations was significantly different for Cr(VI) and Cr(III) treatments. Both blood chromium and plasma chromium assays should therefore be used for the assessment of chromium exposure. 3. Chromium was also detected in peripheral lymphocytes. Cr(VI), but not Cr(III) accumulated significantly in the lymphocytes after treatment. These cells have potential to be used for biomarkers of the assessment of exposure to chromium compounds.

ChemInform Abstract: Synthetic Use of the Organochromium(III) Intermediate in the Reductive Cyclization of δ6,7‐Unsaturated α‐Bromo Esters with Chromium(II) Acetate.

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Pillared Clays Prepared from the Reaction of Chromium Acetate with Montmorillonite

AbstractRefluxing chromium (III) acetate with a Na+-montmorillonite suspension gives rise to the intercalation of linear Cr(III) polyhydroxo-acetate oligomers. Thermally stable chromia pillared mont-morillonite materials are obtained upon calcination under ammonia up to 625°C, and basal expansions up to 6 Å are maintained. The porous materials retain high surface areas (366–464 m2 g−1), a micropore volume of 0.1 cm3 g−1 and narrow pore size distributions centered between 7.5 and 12 Å. The most thermally stable materials in air were those prepared under ammonia at 625°C, containing NH4+ as the exchangeable ion.

A new synthesis of substituted dienes by reductive elimination of allylic nitro derivatives

Tertiary allylic nitro compounds, bearing an acetate or a mesylate in β position smoothly undergo a reductive elimination to give conjugated 1,3 dienes when treated with chromous acetate/ 2,2′-dipyridyl in DMF at 110–120°C.

Influence of acetate ion on the formation reactions of organochromium(III) species. A rapid-scan and high-pressure pulse-radiolysis study

A UV/VIS rapid-scan technique was employed to study the formation of organochromium(III) species that are characterized by absorbance maxima at 321 and 412 nm. The effect of acetate on this formation reaction was studied, and spectral measurements demonstrated that it is mainly the monomeric chromium(II) acetate species that react with the alkyl radical, no involvement of the dimeric species being found. A high-pressure pulse-radiolysis technique was employed to study the effect of pressure on the formation of such complexes. The observed volumes of activation exhibit a decrease from +5.7 to –7.4 cm3 mol–1 on increasing the acetate concentration from 0 to 0.27 mol dm–3. Similar measurements in the presence of phosphate did not indicate any significant effect on the observed volume of activation for the formation of the metal–carbon bond. This difference can be interpreted in terms of the pressure dependence of the dimerization of chromium(II) acetate complexes, which was measured independently and exhibits a reaction volume of +38 ± 4 cm3 mol–1. It is concluded that the mechanism of the formation of chromium-carbon δ bonds is not affected by anions such as acetate and phosphate.

X‐ray attenuation coefficients at 6.46 keV and the validity of the mixture rule for compounds

AbstractX‐ray mass attentuation coefficients for the elements aluminium, copper, molybdenum and tantalum, the materials nylon, PTFE and lucite and the compounds magnesium sulphate, calcium sulphate chromium(III) acetate, cobalt acetate and zinc sulphate were measured using 6.46 keV photons from a 57Co source and adopting a novel method employing a proportional counter spectrometer. For the elements and materials the close agreement of the measured μ/ρ values with the theoretical values indicates the suitability of the proposed method for studying the validity of the mixture rule in the case of compounds. For magnesium sulphate, calcium sulphate, cobalt acetate and zinc sulphate the measured μ/ρ values agree within 1% with the theoretically estimated values, indicating the validity of the mixture rule. However, with chromium(III) acetate, where the chromium K‐edge is less than the incident photon energy by only about 471 eV, the measured μ/ρ value shows a deviation of about – 11%. This is attributed to the effects of EXAFS and to the effects of the chemical environment on the μ/ρ value, which result in an uncertainty in the value of μ/ρ to be used when applying the mixture rule.

Hexavalent chromium produces DNA strand breakage but not unscheduled DNA synthesis at sub-cytotoxic concentrations in hepatocytes

Rat hepatocytes were used to investigate the possible induction of unscheduled DNA synthesis (UDS) and the extent of DNA strand breaks induced by sodium dichromate (a representative chromium(VI) compound) and chromium acetate hydroxide (chromium(III)) in vitro. Cytotoxicity, measured using tetrazolium salts (MTT) reduction assay, was found at a much higher dose of chromium(III), (>50 μM), compared to that of chromium(VI), (>2.5 μM), in cultured hepatocytes over 20 h treatment at 37°C. Chromium(VI), but bot chromium(III), stimulated minimal UDS in hepatocytes at sub-cytotoxic concentrations. A positive UDS response was only observed at cytotoxic concentration. DNA strand breaks in hepatocytes were induced by chromium(VI) following incubation at 37°C for 1 h at doses of 10, 20 and 40 μM sodium dichromate. The subsequent ligation of such strand breaks in hepatocytes treated with 40 μM chromium(VI)_for 1 h at 37°C was demonstrated. The majority of strand breaks was repaired within 30 min following removal of the chromate. In conclusion, chromate-induced DNA strand breakage, possibly involving the formation of oxygen radicals and lack of significant UDS have some analog to those produced by ionizing radiation.

Immobilization of Urease into Carboxymethylcellulose - Gelatine System

Abstract In the present work carboxymethylcellulose (CMC) and CMC-gelatin were used as carrier systems for urease immobilization. Immobilization was based on the formation of insoluble salts of CMC and gelatin with chromium(111) ions. Chromium(111) acetate (CA) and chromium(111) sulfate (CS) were used for this purpose and their effect on urease activity was investigated. The activities of immobilized urease using pure and CMC-gelatin carrier systems were compared. Urease activity was determined by using Berthelot method. Reuse number, pH, enzyme and cross linker concentrations and the incubation period were the factors taken into account in this investigation. Activity of immobilized enzymes were found to be stable for at least 2 months and 16–24 usage. Immobilization percentage obtained under optimum conditions was 40%.

Polyarylenes and poly(arylenevinylene)s Part 10. Reductive polycondensation of a sterically hindered monomer

The synthesis of main-chain bromo-substituted poly(1,4-phenylene-diphenylvinylene)s is possible using 1,4-bis(4-tert,butyl-α,α-dichlorobenzyl)benzene as starting material in a reductive dehalogenation polycondensation with chromium(II) acetate as reducing agent. Some difficulties occur during the coupling reaction, connected with the very low solubility of the starting compound and the formation of substituted benzoquinonebismethides as by-products.

Characterization of Cr/silica ethylene polymerization catalyst by TPO/TPR and FT—IR

A Cr/silica catalyst with a Cr loading of 1 wt.% has been prepared by impregnating an aqueous solution of chromium(III) acetate onto Davison 952 silica. The characterization of the surface chromium species formed during the activation process was performed using TPO/R (temperature-programmed oxidation/reduction) and FT—IR spectroscopy. During activation with dry air, chromium(III) acetate was stabilized on the surface as a hexavalent chromium species. The average oxidation numbers of surface chromium species after activation at 823, 923, 1023, 1123, and 1223 K are found to be 6.0, 5.4, 5.1, 4.2, and 3.7, respectively. The amounts of the Cr(VI) species varied with activation temperature. The fraction of Cr(VI) atoms existing in monochromate form increased with increasing activation temperature, which was a result of the decrease in the fraction of dichromate and/or polychromate. The OH stretching bands of Cr/silica prepared by the reduction of Cr(VI)/silica with CO and the stretching bands of CO adsorbed on it indicate the existence of three distinct types of Cr(II) (Cr A(II), Cr B(II), and Cr C(II)), whose amounts are strongly dependent on the activation temperature.

Induction of DNA strand breaks in peripheral lymphocytes by soluble chromium compounds.

1. Incubation of human lymphocytes with sodium dichromate (CrVI) at 37 degrees C for 3 h resulted in a dose-dependent increase in DNA strand breaks without concurrent cytotoxicity. In contrast, chromium acetate hydroxide (CrIII) failed to induce DNA strand breaks at sub-cytotoxic concentrations. 2. DNA strand breaks were also detected in the peripheral lymphocytes of Wistar rats, 24 h after intratracheal instillation of sodium dichromate (1.3 and 2.5 mg kg-1). Instillation of chromium acetate hydroxide (up to 21.8 mg kg-1) failed to induce DNA strand breaks in peripheral lymphocytes. In accord with previous studies, hexavalent chromium was found to be more readily absorbed from the lungs into the peripheral blood than chromium in its trivalent form. 3. The results of this study indicate that fluorometric analysis of DNA unwinding (FADU) in peripheral lymphocytes might be a convenient method of measuring an important biological effect of chromium in occupationally-exposed workers.

Synthetic Use of the Organochromium(III) Intermediate in the Reductive Cyclization of Δ6,7-Unsaturated α-Bromo Esters with Chromium(II) Acetate

Δ6,7-Unsaturated α-bromo esters 1, 5 and 8 react with chromium(II) acetate to yield the cyclized organochromium(III) compounds. These species can add to benzaldehyde to give the corresponding alcohols 9 and 10, and ketone 11. In the presence of a β-alkoxy substituent, elimination to the olefins 2 and 6 occurs. The intermediate cyclic radical can be trapped with methyl acrylate, to give the adduct 7.

Studies on immobilization of urease in gelatin by cross-linking

Urease enzyme was immobilized in photographic gelatin by chemical cross-linking using formaldehyde, glutaraldehyde and chromium (III) acetate. The effects of enzyme and cross-linker concentrations, temperature, incubation time and pH on urea hydrolysis were investigated. Effect of reuse on the activity of immobilized enzyme was also studied. Glutaraldehyde (0.004 M) was the most suitable cross-linker; relative activities within 2.5 months after 24 reuses were stable (about 78%).

Immobilization of α-amylase into photographic gelatin by chemical cross-linking

α-Amylase was immobilized into photographic gelatin by chemical cross-linking with chromium (III) acetate and chromium (III) sulphate. Cellulose triacetate film strips, enabled simple handling when coated with an α-amylase-gelatin mixture, accomplishing a high degree of durability during consecutive immersions into reaction media. The optimum conditions for pH, substrate concentration, temperature, incubation time and storing conditions of free and immobilized α-amylase were determined. The effect of use number on activity and the effect of resting on reuse number were also determined. Photographic gelatin was found to be a very efficient natural polymer, due to its extraordinary diffusion characteristics for immobilization as a carrier.

Urease immobilization into poly(acrylamide) - gelatin gels

Urease ( EC. 3. 5. 1. 5 ) was immobilized into photographic gelatin-poly(acrylamide) gels by using chromium(III)acetate as crosslinker. The effect of crosslinker concentration , enzyme loading, pH, temperature, supports composition and reuse number on activity were studied. The suitable conditions for an operative and stable system were investigated.

Immobilization of alpha - amylase into gelatin films with various cross - linkers

This article reports the cross linking of α-amulase enzyme to gelatin by using formaldehyde, chromium (III) acetate, chromium (III) sulfate and potassium chromium (III) sulfate as hardeners. The effect of concentration of cross linkers, enzyme and gelatin on the activity of immobilized enzyme were investigated.

Hydrolyzed Polyacrylamide/Chromium(III) Acetate Gel Chemistry

Proton NMR and visible spectroscopy are used to investigate the chemistry of hydrolyzed polyacrylamide/chromium acetate gels. Color changes in conjunction with HNMR are used to monitor chromium acetate hydrolysis, and HNMR is used to characterize Polyacrylamide in solution and to monitor increases of free acetate and decreases of polymer backbone proton and amide proton resonances during gel formation. The data indicate that chromium acetate hydrolysis is halted by polymer coordination. The polymer cross-linking reaction appears to be a simple replacement of chromium(III) coordinated acetate groups on the chromium(III) trimer by polymer carboxylate groups.

Polyester Film Strips Coated with Photographic Gelatin Containing Immobilized Invertase

Abstract Invertase was immobilized into photographic gelatin by chemical crosslinking with formaldehyde and chromium (111) acetate. Polyester film strips were coated with invertase-gelatin mixture which increased durability during consecutive immersions into reaction media. The effect of gelatin, crosslinker and enzyme concentrations on activity were studied. Enzyme leakages from immobilized invertase film strips were controlled by washing with EDTA solutions. The activities of washing solutions were measured spectrophotometrically to determine unbounded enzyme concentration. Effect of use number on activity was also determined. Percent activity of immobilized invertase was lower than that of free enzyme. The activity however retained even after 10 washings (170 minutes) followed by 9 use in 18 weeks.