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Copyright © Tarek Kakhia. All rights reserved. http://tarek.kakhia.org 4 . 1 . 1 . Reaction with protein sulfhydryl groups Knox et al . first noted that HClO is a sulfhydryl inhibitor that, in sufficient quantity, could completely inactivate proteins containing sulfhydryl groups. This is because HClO oxidises sulfhydryl groups, leading to the formation of disulfide bonds[23] that can result in crosslinking of proteins. The HClO mechanism of sulfhydryl oxidation is similar to that of chloramine, and may only be bacteriostatic, because, once the residual chlorine is dissipated, some sulfhydryl function can be restored . One sulfhydryl-containing amino acid can scavenge up to four molecules of HOCl . Consistent with this, it has been proposed that sulfhydryl groups of sulfur-containing amino acids can be oxidized a total of three times by three HClO molecules, with the fourth reacting with the α-amino group. The first reaction yields sulfenic acid ( R - SOH ) then sulfinic acid (R-SO2H) and finally R - SO3H. Each of those intermediates can also condense with another sulfhydryl group, causing cross-linking and aggregation of proteins. Sulfinic acid and R - SO3H derivatives are produced only at high molar excesses of HClO , and disulfides are formed primarily at bacteriocidal levels . Disulfide bonds can also be oxidized by HClO to sulfinic acid . Because the oxidation of sulfhydryls and disulfides evolves hydrochloric acid, this process results in the depletion HClO. 4 . 1 . 2 . Reaction with protein amino groups Hypo chlorous acid reacts readily with amino acids that have amino group side - chains, with the chlorine from HClO displacing a hydrogen, resulting in an organic chloramine . Chlorinated amino acids rapidly decompose, but protein chloramines are longer-lived and retain some oxidative capacity. Thomas et al . concluded from their results that most organic chloramines decayed by internal rearrangement and that fewer available NH2 groups promoted attack on the peptide bond, resulting in cleavage of the protein. McKenna and Davies found that 10 mM or greater H ClO is necessary to fragment proteins in vivo. Consistent with these results, it was later proposed that the chloramine undergoes a molecular rearrangement, releasing HCl and ammonia to form an amide . The amide group can 36PDF Image | Chlorine Characteristics
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