Chromium crosslinking

Chromium crosslinked gels prepared from a 3 1 blend of partially hydrolyzed polyacrylamide and guar gum have been found to have a higher strength and stability than gels prepared from the partially hydrolyzed polyacrylamide alone (222). 

Davidson(248) has also adapted chromium crosslinked gels. 

IMC also affects the timing of gelation and the properties of the developed gel. It consumes the chromium crosslinker that would otherwise be available for formation of intermolecular crosslinks, and thereby delays the development of the gel network. It is also suspected that IMC may be the primary factor in preventing a mechanically degraded Cr(III)-PAAM gel from reforming, as observed in our laboratory. 

N. A. Mumallah. Chromium (iii) propionate a crosslinking agent for water-soluble polymers in real oilfield waters. In Proceedings Volume. SPE Oilfield Chem Int Symp (San Antonio, TX, 2/4—2/6), 1987. 

Occasionally it may be desirable to have a rapid crosslinking take place. Blends of chromium triacetate and hydrochloric acid have been used in this situation (212). Gelation time decreases substantially as applied shear increases (213,214). Thus, static laboratory gelation time experiments should not be used to predict gelation time in actual well treatments. 

Crosslinked xanthan gums have also been used to reduce the permeability of thief zones. Trivalent chromium and aluminum have been used as crosslinkers (223,224). While crosslinker effectiveness is reduced at high salinity, Cr(III) has been used in the field at... 

The use of other crosslinking metals developed simultaneously with the use of antimony, chromium, and boron(borate). Tiner, et al.(242) introduced titanium (IV) crosslinkers in 1975 as ammonium tetralactonate or bis(triethanolamine)bis(isopropyl)titanium(IV). Upon contact with water soluble titanium (IV) derivatives ordinarily form orthotitanic acid, Ti(0H)4, which rapidly forms oligimeric metatitanic acid, [Ti(0H)2] and titanium dioxide. Electron donors such as the hydroxyl groupsxof polysaccharides, if properly oriented, can participate in the sequence of titania reactions and a crosslinked gel network results. Various titanium metal crosslinkers remain in common use today. More will be said about titanium crosslinked gels later. 

Chromium(III) is a commonly-used crosslinker for preparing profile control gels with polymers having carboxylate and amide functionalities (la,b). Cr(III) is applied in many forms. For example, it can be used in the form of simple chromic salts of chloride and sulfate, or as complexed Cr(III) used in leather tanning (2), or as in situ generated Cr(III) from the redox reaction of dichromate and bisulfite or thiourea. The gelation rate and gel quality depend on which form of Cr(III) is used. 

None of the Cr(III) products from Equations 6 or 7 are effective crosslinkers since a chromic aqua ion must be hydrolyzed first to form olated Cr to become reactive. Colloidal and solid chromium hydroxides react very slowly with ligands. In many gelation studies, this critical condition was not controlled. Therefore, both slow gelation times and low Cr(VI) Cr(III) conversion at high chromate and reductant concentrations were reported (9,10). 

The absorbed chromium (VI) is gradually reduced to chromium (III) as a result of participation in the oxidative decomposition of cystine crosslinks as represented by Scheme 5.18. 

The application of lignosulfonate-chromium derivatives in oil well drilling mud has already been mentioned as a typical example of the above effects in combination with crosslinking. The use of lignosulfonates as active extenders in concretes is a further example of the applicability of the above effects (61). Another is the use of lignins as extenders for asphalt cement (70). 

However, an increase in DNA-protein crosslinking was found in the livers of rats exposed to potassium chromate in the drinking water at 6 mg chromium(VI)/kg/day for 3 or 6 weeks (Coogan et al. 1991a). 

Inhalation exposure of rats to fumes of chromium(O) (1.84 or 0.55 mg chromium(0)/m3) for 1 week or 2 months induced increased chromosomal aberrations and sister chromatid exchanges in peripheral lymphocytes, but not in bone marrow cells (Koshi et al. 1987). An increase in DNA-protein crosslinking... 

Rat liver and kidney nuclei (intraperitoneal exposure) DNA crosslinks, DNA-protein crosslinks, DNA strain breaks Cupo and Wetterhahn 1985 (III) Chromium oxide... 

Escherichia coli DNA DNA-protein crosslinks No data + Fornance et al. 1981 Chromium trichloride... 

Chick embryos DNA damage (crosslinks, strand breaks) No data Tsapakos et al. 1983a Chromium nitrate... 

Exposure to chromium(VI) can result in DNA-protein complexes, the identification of which may be useful as biomarkers of exposure to chromates (Costa 1991). Gel electrophoresis and immunochemical techniques were used to identify actin as the protein in a DNA-protein complex induced by potassium chromate in cultured Chinese hamster ovary cells. While the DNA-protein complexes induced by formaldehyde and ultraviolet light were different from those induced by chromate, actin was also identified as the protein in the complex induced by cis-platinum, indicating that the DNA-actin complex is not specific for chromium. However, an experiment in a group of four volunteers did not demonstrate an increase in DNA-protein crosslinks in leukocytes over a 240 minute period following the ingestion of 5 mg chromium(VI) as potassium dichromate in a 10 mg chromium/L solution or the same amount added to 300 mL of orange juice (presumably reducing chromium(VI) to chromium(III)) and diluted to 500 mL with deionized water (Kuykendall et al. 1996). Chromium levels in red cells, plasma and urine were increased. In a separate experiment in this study, a threshold dose of 52 pg chromium(VI)/L was determined for crosslink formation in cultured lymphoma cells. 

Patierno SR George Washington University DNA crosslinking in chromium toxicity and carcinogenesis NIEHS... 

Bridgewater LC, Manning FCR, Patierno SR. 1994a. Base-specific arrest of in vitro DNA replication by carcinogenic chromium relationship to DNA interstrand crosslinking. Carcinogenesis 15(11) 2421-2427. 

Izzotti A, Bagnasco M, Camoirano A, et al. 1998. DNA fragmentation, DNA-protein crosslinks, 32P postlabeled nucleotide modifications, and 8-hydroxy-2 -deoxyguanosine in the lung but not in the fiver of rats receiving intratracheal instillations of chromium(VI). Chemoprevention by oral N-acetylcysteine. Mutat Res 400 233-244. 

Lin X, Zhuang Z, Costa M. 1992. Analysis of residual amino acid-DNA crosslinks induced in intact cells by nickel and chromium compounds. Carcinogenesis 3(10) 1763-1768. 

Taioli E, Zhitkovich A, Kinney P, et al. 1995. Increased DNA-protein crosslinks in lymphocytes of residents living in chromium-contaminated areas. Biol Trace Elem Res 50 175-180. 

When 8-hydroxyquinoline and derivatives of bis(8-hydroxy-quinoline) react with metal ions, coordination complexes and polymers are formed, respectively, which exhibit improved thermal stability. This paper reviews the reaction of first-row transition metal ions with such ligands and their effect on the stabilization of these organic molecules. For the polymers containing divalent Mn, Co, Ni, Cu, or Zn the decomposition temperature is related to the periodic properties of the metal as well as the composition of the ligand to which the metal is coordinated. Trivalent chromium produces a crosslinked polymer when it reacts with bis(8-hydroxy-5-quinolyl)methane, and the thermogram for this polymer is also reported. 

The use of static SIMS for the characterization of surfaces of polypropylene (PP), PTFE and a PMDA-ODA type poly-imide is described. Interfaces between evaporated copper or chromium films onto PTFE and polyimide were also analyzed. Some of the polymer substrates were modified by ion beams, corona discharge in air or plasma treatments in air, At and H2. It is demonstrated that SIMS is highly complementary to XPS for the analysis of such modified surfaces, in that effects such as crosslinking, unsaturation and formation of low-molecular weight material at surfaces can be detected. 

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