Vibrational Spectroscopic Investigation of Glycine Binding in a Zirconium—Aluminum—Glycine Antiperspirant Material

Abstract

Through use of Raman and infrared spectroscopy, we have determined the mode of incorporation of glycine, a gelation inhibitor, in a complex antiperspirant material (ZAG) containing zirconium and aluminum hydroxy chlorides. Most of the vibrational modes of glycine are affected upon inclusion of this component in ZAG. Our spectral analysis indicates that the glycine in ZAG exists as the dipolar ion, coordinated to metal ions through the COO⁻ end and hydrogen bonded to various constituents through the NH₃⁺ end. Almost all of the glycine in solid ZAG is bound in this fashion, as is more than half of the glycine in a 50% (by wt.) aqueous ZAG solution. This binding could well contribute to the gelation-inhibiting property of the glycine in aqueous ZAG by interfering with the extended hydroxy and oxy bridging that commonly exists in solutions containing Zr(IV) and Al(III). Several spectral features of the bound glycine dipolar ion, most especially a prominent Raman and infrared band near 1475 cm⁻¹, are discussed in detail for the first time.