The role of chelants in controlling Cu(II)‐induced radical chemistry in oxidative hair colouring products

Abstract

The catalytic formation of hydroxyl radicals in oxidative hair colourant systems in the presence of added copper ions was measured and quantified using a colorimetric probe N,N'-(5-nitro-1,3-phenylene)bisglutaramide. Also monitored in the same experiments was the decomposition of hydrogen peroxide. The first set of experiments was performed using aqueous model solutions containing the key oxidant actives in a hair colourant, ammonium hydroxide and hydrogen peroxide at pH 10, with added copper and calcium ions. The second set of experiments was performed in the presence of hair containing different levels of copper in conditions very close to those found during hair colouring. Both sets of experiments demonstrate the ability of copper ions to trigger the formation of hydroxyl radicals and catalyse the decomposition of hydrogen peroxide. The ability of chelants ethylenediamine tetraacetic acid (EDTA) and N,N'-ethylenediamine disuccinic acid (EDDS) to moderate the flux of hydroxyl radicals formed in solution systems was demonstrated in the presence of copper ions alone. However, only EDDS was successful in the presence of both calcium and copper ions. This was confirmed in the hair experiments where again only EDDS was successful at preventing hydroxyl radical formation where hair is added as the source of copper and calcium ions. These results are explained using metal speciation modelling and demonstrate the importance of the chelant to be able to specifically bind and prevent the one-electron redox chemistry of copper in the presence of high levels of calcium ions as found in hair. The formation of hydroxyl radicals during the colouring process was shown to lead to hair structure damage as measured by protein loss. EDDS was demonstrated to significantly reduce cuticle damage by suppressing the formation of the hydroxyl radicals in systems with realistic concentrations of calcium and copper.

Oxidative Modification in Human Hair: The Effect of the Levels of Cu (II) Ions, UV Exposure and Hair Pigmentation

“…Environmental factors that impact human hair include exposure to UV and visible light , effects from bound metals and chemical agents used in hair care . The presence of Cu (II) ions in human hair (a common phenomenon, since copper from tap water is deposited in hair during routine washing) was here investigated for its suspected role in exacerbating hair damage in concert with exposure to UV light .…”

Role of copper in photochemical damage to hair

“…The presence of copper is important because it is can catalytically participate in oxidative chemistry via one electron oxidation and reduction steps. For example, it has also been shown that the presence of copper can cause protein degradation via a Cu (II)‐induced radical process in the presence of colourants where hydrogen peroxide at high pH is the oxidant . The likely source of the exogenous copper (i.e.…”

The coordination environment of copper in hair can be altered by treatment products

“…However, as copper is also involved in certain types of cancer [20,21] and the pathogenesis of neurological disorders such as Alzheimer's disease [22], motor neuron diseases [23] and prion diseases [24], it is plausible that the chemical forms rather than the total amounts of copper in the hair could be markers of various health conditions. In addition, as shown recently by Naqvi et al [25], the chemical forms of copper influence the free radical chemistry in hair that can produce structural damage during colouring processes.…”

“…In addition, as shown recently by Naqvi et al . , the chemical forms of copper influence the free radical chemistry in hair that can produce structural damage during colouring processes.…”