REDUCED HAIR DAMAGE FROM COLORING SYSTEMS 501 ---r� HN H�C � C�H ('" C�H EDDS ( COCH COCH HOOC � N � N) HOOC) EDTA /\t\ / N N H� ) H� HOiC DTPA P03H I N \ CO:zH CO:zH H3C-C-OH P03H HEDP Figure 4. Chemical structures of the four chelants tested. Table III Performance Data for Chelants vs the Cu/Ca Conditional Formation Constant Ratio Chelant (0.05 M) added Ratio of Cu to Ca SEM damage F-IR cysteic to colorant cream conditional formation constant index score acid units No copper control 5.0 100 EDDS 4 X 10 11 6.8 110 DTPA 4.6 X 107 49.8 147 EDTA 1.6 X 106 68.6 165 HEDP 7.7 X 103 61.0 163 as a molecule that can bind a metal via two or more atoms through either a coordination or ionic bond (13 ). Four commonly used chelants were tested to investigate whether the metal-induced radical chemistry could be prevented on hair. The four chelants (Figure 4) were: N ,N' -ethylenediamine disuccinic acid (EDDS) ethylenediaminetetraacetic acid (EDTA) diethylenetriaminepentaacetate (DTPA) and, l-hydroxyethane-1, 1-diphos­ phonic acid (HEDP). These four chelants were formulated into a simple emulsion cream at 0.10 M concen­ tration and mixed with a hydrogen peroxide cream (9% active concentration) in a 1:1 ratio. Five repeat coloring cycles were then performed. At the completion of five cycles, the FT-IR cysteic acid values were measured, the cuticle quality of the fibers was reviewed using SEM, and the semi-quantitative SEM damage index was calculated. The only tested chelant that significantly reduced the fiber damage, and by inference the metal-induced radical formation, was EDDS. We hypothesize that its high efficacy derives from its ability to selectively bind transition metal ions in the high-pH and high-water-hardness ion concentration conditions present during the hair coloring pro­ cess. To compare the metal binding efficiency of the chelants, the conditional formation constants for each with calcium and copper at pH 10 were calculated. The ratio of the

502 JOURNAL OF COSMETIC SCIENCE Figure 5. Gas formation after 10 minutes. Left: no EDDS. Right: with EDDS. conditional formation constant of copper vs that for calcium will give a strong indication of how specific the chelant is to binding copper in the presence of calcium. This is very important in hair because there is a hundred-fold or greater excess of calcium on the hair vs copper (6000-10,000 ppm Ca vs 60-100 ppm Cu). Table III summarizes the FT-IR cysteic acid values, the SEM damage index, and the Cu/Ca conditional formation con­ stant ratio for the four chelants. If the Cu/Ca ratios for the four chelants are compared, EDDS has a very significant advantage in terms of its specificity for binding to copper in the presence of an excess of calcium. This may drive its superiority in preventing the metal-induced radical damage. To directly investigate the role of the chelant on the radical chemistry, an optical microscope was used to compare the gas production from a formulation containing no EDDS chelant (0.1 % EDT A) to one containing EDDS ( 1 % level). The colorant was added to the hair at a 4 g/g dose, and then the gas formation was imaged 10 minutes after application. Figure 5 compares the formulations with and without EDDS and clearly demonstrates the ability of EDDS to reduce the gas formation significantly. CONCLUSIONS The hair of a regular colorant consumer will likely absorb low levels of copper ions (60-200 ppm) from tap water in addition to water hardness ions such as calcium and magnesium. On coloring, the presence of the copper ions can generate the highly reactive hydroxyl radical species that can cause significant damage to the keratin fiber. This fiber damage is measurable as an increase in surface cysteic acid and can be visually observed as a decrease in cuticle quality in the SEM. The addition of a chelant to a hair colorant such as N,N-ethylenediamine disuccinic acid (EDDS) can significantly reduce the formation of the hydroxyl radical by complexing with the copper in the hair. It has been demonstrated that the choice of chelant is crucial. In particular, the chelant must have a high selectivity for complexing to copper, especially relative to other metals that are commonly found in hair such as calcium. REFERENCES (1) M. L. Tate, Y. K. Karnath, S. B. Ruetsch, and H. D. Weigman,]. Soc. Cosmet. Chem., 44, 347-372 (1993).