138 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS RESULTS PRELIMINARY STUDY: KINETICS OF BINDING OF Zn-GLY TO HAIR Before undertaking quantitative substantivity studies, it was necessary to establish the time scale of binding of Zn to the substrate. Figure 2 shows that for Zn concentration exceeding 1 mM, binding is near equilibrium after an hour and that hair can hold at least 10 Ixmol of Zn-GLY/g. Subsequent experiments were conducted using overnight incubation of Zn-GLY with substrate. SUBSTANTIVITY OF Zn-GLY TO HAIR: EFFECT OF GLYCINE The effect of complexation of the Zn ion on its substantivity to hair was investigated by measuring the binding of Zn from zinc chloride in the presence and absence of glycine. Figure 3 shows that Zn is bound to hair more efficiently when glycine is present. Apparently, Zn-GLY binds to keratin with somewhat higher affinity than Zn chloride. 7O 6O 5O 4O 3O 2O 10 Zn GLY 0 1 -4 -3 -2 Zn Chloride log Zn GLY concentration, M. Figure 3. Binding of zinc glycinate to hair, concentration dependence.

ODOR INHIBITION 139 Table 1 Deposition of Zn-GLY Onto Stratum Corneum •mol Zn-GLY/g stratum corneum [Zn-GLY] Trial 1 Trial 2 Average 0.01 mM 0.3 0.3 0.3 50.0 mM 82.0 108.0 95.0 This study indicates that the formation of Zn-GLY is proceeding in the solution and that the Zn from Zn-GLY binds appreciably to hair from solutions where Zn-GLY concen- tration exceeds approximately 1 raM. When Zn-GLY expressed as [Zn] exceeds about 10 mM in solution, binding is about 50 I.•mol/g. SUBSTANTIVITY OF Zn-GLY TO SKIN Table 1 shows that stratum corneum exposed to 50 mM Zn-GLY binds approximately 90 I.•mol Zn/g. Exposure to 0.01 mM Zn-GLY produces binding of less than 1 I.•mol/g. 6O 50 lO o. oo mM Zn • 0.85 mM Zn 3.4 mM Zn 10 20 30 40 50 60 time, min. Figure 4. Beta-G reactions in the presence of hair treated with Zn-GLY. 7O