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Binding of Mg2+ to Palmitic Acid and Deprotonation of the COOH Headgroup

Summary: Binding of Mg2+
and Ca2+
to Palmitic Acid and Deprotonation of the COOH Headgroup
Studied by Vibrational Sum Frequency Generation Spectroscopy
Cheng Y. Tang, Zishuai Huang, and Heather C. Allen*
Department of Chemistry, The Ohio State UniVersity, 100 West 18th AVenue, Columbus, Ohio 43210, United States
ReceiVed: June 14, 2010; ReVised Manuscript ReceiVed: October 13, 2010
At the air/liquid interface, cation binding specificity of alkaline earth cations, Mg2+
and Ca2+
, with the
biologically relevant ligand carboxylate (COO-
) using vibrational sum frequency generation spectroscopy is
reported. The empirical evidence strongly supports that the ionic binding strength is much stronger for Ca2+
to COO-
than that for Mg2+
. We conclude that at a near-neutral pH, the mechanism that governs Ca2+
to COO-
is accompanied by commensurate deprotonation of the carboxyl headgroup. In addition, surface
molecular structure and ion concentration influence the cation binding behavior at the air/liquid interface. In


Source: Allen, Heather C.- Department of Chemistry, Ohio State University


Collections: Chemistry