Cu(II) catalyzed reaction between phenyl hydrazine and toluidine blue?dual role of acid

Abstract

The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB ϩ ) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions are the main products of the reaction. The diazonium ion further decomposes to phenol (PhOH) and nitrogen. At low concentrations of acid, H ϩ ion autocatalyzes the uncatalyzed reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, H ϩ hinders both the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to the uncatalyzed reaction, Cu(II) catalyzed2 2 reaction occurs possibly through ternary complex formation between the unprotonated toluidine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed reaction is A detailed 13-step mechanistic scheme for the Cu(II) catalyzed 4 Ϫ2 Ϫ12.1 ϫ 10 M s . reaction is proposed, which is supported by simulations.

Chemoselective Copper-Mediated Modification of Selenocysteines in Peptides and Proteins

“…In light of the above results, we propose the mechanism shown in Scheme . R-NHNH 2 ( 2 ) is oxidized to R • by Cu 2+ , which binds to the Se of Sec in the peptide. − , The formed R • reacts with diselenide (or selenylsulfide) to generate the intermediate trivalent selenium radical ( 3 ), , which converts to the final product ( 4 ) and another Cys peptide ( 3-II ) or another Sec radical ( 3-I ), which could in turn form dimer ( 1 ) for the next reaction.…”

“…Here, we report a previously unexplored, chemoselective Sec modification with a series of hydrazine compounds in the presence of copper ions. This strategy exploits the efficient generation of an aryl/alkyl radical from hydrazine substrates in the presence of Cu­(II), − which readily reacts with Sec in peptides and proteins to provide the desired corresponding conjugates (Figure c).…”

Chemoselective Copper-Mediated Radical Modification of Selenocysteines in Peptides and Proteins

“…42,43 Here, we report a previously unexplored, chemoselective Sec-modification with a series of hydrazine compounds in the presence of copper ions. This strategy exploits the efficient generation of alkyl/aryl radical from hydrazine substrates in the presence of Cu(II), [44][45][46][47] which readily reacts with Sec in peptides and proteins to provide the desired corresponding conjugates (Fig. 1c).…”