Adsorption of L-glutamic acid and L-aspartic acid to gamma-Al2O3

作者：Greiner Edward; Kumar Kartik; Sumit Madhuresh; Giuffre Anthony; Zhao Weilong; Pedersen Joel; Sahai Nita^*

来源：Geochimica et Cosmochimica Acta, 2014, 133: 142-155.

DOI：10.1016/j.gca.2014.01.004

The interactions of amino acids with mineral surfaces have potential relevance for processes ranging from pre-biotic chemistry to biomineralization to protein adsorption on biomedical implants in vivo. Here, we report the results of experiments investigating the adsorption of L-glutamic (Glu) and L-aspartic (Asp) acids to gamma-Al2O3. We examined the extent of Glu and Asp coverage as a function of pH and solution concentration (pH edges and isotherms) in solution-depletion experiments and used in situ Attenuated Total Refkectance Fourier Transform Infrared (ATR-FTIR) spectroscopy to estimate the molecular conformations of the adsorbed molecules. Glu and Asp exhibited similar adsorption behavior on gamma-Al2O3 with respect to pH and solution concentration. In general, adsorption decreased as pH increased. At low and high amino acid concentrations, the isotherms exhibited two apparent saturation coverages, which could be interpreted as 1:4 or 1:2 ratios of adsorbed molecule/surface Al sites. Tetradentate tetranuclear and bidentate binuclear species were the dominant conformations inferred independently from FTIR spectra. In these conformations, both carboxylate groups are involved in bonding to either four or to two Al surface atoms, through direct covalent bonds or via H-bonds. An outer sphere species, in which one carboxylate group interacts with a surface Al atom, could not be ruled out based on the FTIR spectra.

• 出版日期2014-5-15