Chromium oxalate

Presumably, for DNA damage to occur, chromium must enter the cell. The second set of results (excerpt 4D) addresses this issue. The authors look for chromium uptake inside E. coli cells using a technique known as flame atomic absorption spectroscopy (FAAS). These results build on the authors first set of results, providing additional evidence that chromium oxalate is somehow different than the other chromium compounds studied. 

In the third set of results (not included in excerpt 4D), the authors examine how Cr + affects gyrase, an enzyme that regulates the ability of supercoiled DNA to relax. Results, however, are reported only for chromium chloride, not for chromium oxalate or chromium nitrate. By omitting these latter two compounds, the authors illustrate what we call a broad-to-narrow approach. At the start of a research project, there are typically many variables however, as knowledge is gained, some of these variables can be eliminated. In this case, chromium oxalate... 

Before moving on to excerpt 4E, we call your attention to two ways in which the concept of zero is addressed in excerpt 4D. First, we consider the concept of zero in measured concentrations (i.e., the concentrations reported in the last column of Table 1). Recall that no chromium oxalate was detected in the cells however, the authors do not report this with a zero. Rather, they use the phrase below the detection limit in the text and the less-than symbol (e.g., <0.025 mg/g) in Table 1, which puts an upper limit on the amount of chromium oxalate present. Novice writers might (incorrectly) suggest that no chromium was present in the text and use a zero in the table (0 mg/g). Such uses of zero, however, are incorrect, because (for measured concentrations) zero varies with the sensitivity of the detecting instrument. For example, on one instrument, zero will be less than one part per million on a more sensitive instrument, zero will be less than one part per billion. Instead of reporting zero, authors report that the measurement was below the detection limit for that instrument. Some common ways to express this concept in the text and table are as follows ... 

Alternatively, it is correct to use zero to indicate added amounts of compounds. You may say that no chromium oxalate was added and use a 0 to indicate this in a table. For example, the second column of Table 1 includes three zeroes, indicating that no chromium compounds were added to the cells in these three experiments. 

P3 When E. coli test strains were treated with chromium nitrate, the induction profile obtained was very similar to chromium chloride profile (data not shown). The promoters that were induced indicate that the action of Cr + was on DNA. However, none of the 13 stress promoters responded to chromium oxalate at any of the concentrations... 

Let s imagine that several studies (7-9) suggest that chromium oxalate cannot enter bacteria cells because of its size. (It is too big the oxalate anion is -OOC-COO , significantly larger than either NOj or Cl .) Add a sentence or two to the end of the second paragraph (P3) to relate the current work to these studies. 

The lack oflacZ induction in the case of chromium oxalate is possibly due to the inability of that compound to enter the bacterial cells. 

The bromide, [Cr(XH3)4(C204)]Br. H20, and the chloride, [Cr(NH3)4 (C204)]C1, are obtained from the nitrate by treating with concentrated hydrobromic and hydrochloric acid respectively. They crystallise in orange-coloured leaflets. If chloro-aquo-tetraminino-chromic chloride be treated with ammonium oxalate and hydrobromic acid successively, Cleve s triammino-chromium oxalate is formed and not oxalato-tetram-mino-salt.2... 

The second aliquot was passed onto another cation exchange resin and eluted as before, the effluent solution was passed onto a second cation exchange column, and the elution process was repeated. No dark band was left on the second column, and analysis of a portion of the new effluent solution showed that there had been no further loss of chromium on passage through the second column. Two additional portions of the last-mentioned solution were withdrawn for examination. The first portion was analyzed for oxalate, as before, and chromium-oxalate ratios of 1.00 to 1.02 were obtained. The spectrum of the second portion was measured through the visible range and found to agree well with the spectrum of the mono-oxalatotetraaquochromium (III) ion at the same chromium concentration. 

Chlorides or sulphates occur in gall or logwood inks prepared with iron or chromium chlorides or sulphates and in copying inks containing calcium chloride. Oxalates occur especially in logwood inks prepared with chromium oxalate. 

Two methods for preparation of ordered macroporous crystalline Ct203 have been reported. Chromium oxalate is soluble in H2O-EtOH solution, and the chromium oxalate solution infiltrates the voids of the templates. Solvents are removed by heating, and solid chromium oxalate is deposited in the voids and can be converted to Ct203 without melting. Another method is an in situ method. Cr(N03)3 is dissolved in EG-MeOH mixed solution, and the solution infiltrates the voids of the templates. By heating, EG reacts with Cr(N03)3 to form chromium oxalate derivatives in the voids by nitrate oxidation, and the chromium oxalate derivatives can be converted to Ct203 without melting. ... 

Fig. 5.11. The EPR spectra of spin label TEMPOamine in chloroplast suspension (a) without broadening agents and (b) in the presence of 80 mM chromium oxalate (after [78]).

Fig. 5.12. The light-induced uptake of spin label TEMPOamine by the thylakoids revealed as the increase in the magnitude of the high field component of the EPR signal from TEMPOamine in a chloroplast suspension containing 16 mM chromium oxalate, the lower curve is in the presence of 20 /xM gramicidin D (after [78]).

---