Zinc Interactions with Glucosamine-Functionalized Fused Silica/Water Interfaces

The adsorption of Zn2+ to glucosamide-functionalized fused silica/water interfaces is studied using second harmonic generation (SHG). We characterize each step of the surface functionalization using vibrational sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS), where specific vibrational modes in the C-H region and binding energies in the Cls and Nls region are determined to be indicative of glucose covalently tethered to the surface. We employ the SHG chi((3)) technique to track Zn2+ adsorption and desorption directly at the glucosamide-functionalized fused silica/aqueous interface at pH 7 and 10 mM NaCl and determine the electrostatic and thermodynamic binding parameters using standard electrical double layer models to quantify the change in interfacial potential upon zinc adsorption. The results presented here allow for the possibility of 2:1 to 3:1 carbohydrate:metal coordination complexes and suggest the possibility for multivalent interactions which have not been observed with glucose in the bulk aqueous phase, where I:I complexes dominate. These findings suggest that interactions between metal ions and carbohydrate arrays may be much stronger at interfaces as opposed to the bulk phase, with direct implications for controlling and predicting coordination chemistry.