Chromate reactions

They make tubs out if it for laundry, it is not an element that says much to the imagination, it is gray and its salts are colorless, it is not toxic, nor does it produce striking chromatic reactions in short, it is a boring metal. It has been known to humanity for two or three centuries, so it is not a veteran covered with glory, like copper, or even one of those newly minted elements which are still surrounded with the glamour of their discovery. 

Burrows D, ed. 1983. Adverse chromate reactions on the skin. In Burrows D, ed. Chromium Metabolism and toxicity. Boca Raton, EL CRC Press, Inc., 137-163. 

Zinc, Zinck, zinco they make tubs out of it for laundry, it is gray and its salts are colorless, it is not toxic, nor does it produce striking chromatic reactions in short, it is a boring metal. 

If this is the case then the participation of the Crv and CrIV states of oxidation found to be present in other reactions of chromates (119) is possible. These active oxidation states are considered to be responsible for the induced oxidations which occur in certain chromate reactions, for example the oxidation of manganous ion during the chromic acid-arseni-ous acid reaction. 

The results of chromate reduction by the model compounds listed in Table 2, allow us to predict the environment that the SH groups in a protein will require for them to react readily with chromate. The fastest reductants (Table 2) are either neutral (e.g., cysteine, penicillamine) or have a positive charge (cysteamine). However, charge is not the only factor affecting the kinetics, since the cysteine-chromate reaction is faster than the cys-teamine-chromate reaction and the unithiol-chromate reaction is faster than the DTT-chromate reaction. The obvious advantage that cysteine has over cysteamine is its ability to chelate intermediate Gr species after the disulfide bond has been formed, as illustrated in Fig. 3. Such chelation would facilitate the change in coordination number required in going from Cr(VI) to Cr(IV) or Cr(III) (see Sect. 2). 

Postscript. Our continuing kinetic studies of thiol-chromate reactions (see Sect. 7) indicate that the logarithms of the observed rate constants (1M Tris HCl, pH 7.4, 25 °C) show an inverse linear relationship to the microscopic pK, s of the thiols. 

Burgess WA (1981) Potential exposures in industry - their recognition and control. In Clayton GD, Clayton FE (eds) Patty s industrial hygiene and toxicology, 3rd edn, vol 1. John Wiley Sons, New York, pp 1149-221 Burrows D (1983) Adverse chromate reactions on the skin. In Burrows D (ed) Chromium metabolism and toxicity. CRC, Boca Raton, pp 137-163... 

At the beginning of research on EA scientists had the following means for characterizing a product elemental analysis, melting point, characteristic chromatic reactions and measurement of optical rotation. Elemental analyses... 

Diezel (1956, 1957 a) showed that small amounts of brown-metachromatic material were actually components of the normal myelin sheaths. He contrasted cases with accumulation of brown metachromatic material and storage by ganglion cells with others exhibiting yellow myelin breakdown products with an ortho-chromatic reaction and lack of ganglion cell storage. The latter form occurs mainly in adults and does not appear to be a sulfatidosis. 

In Fig. 1.3, the principal ideas of chromate reaction are summarised. Anodic oxidation of iron produces Fe and the cathodic reduction of oxygen gives OH which react to form a passive layer of Fe(OH)2 on the steel substrate, yielding a well adherent oxide layer. In addition, chromates are reported to be attached to the iron oxides and incorporated into the passive layer. In some cases, mixed oxides of Fe(OH)2 and CrOOH are found which can explain the outstanding performance of chromate-based pigments. 

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