Adsorption of Copper-Amino Acid Complexes on the Surface of Highly Dispersed Silica

Glutamate surface speciation on amorphous titanium dioxide and hydrous ferric oxide

Hydrous ferric oxide (HFO) and titanium dioxide exhibit similar strong attachment of many adsorbates including biomolecules. Using surface complexation modeling, we have integrated published adsorption data for glutamate on HFO over a range of pH and surface coverage with published in situ ATR-FTIR studies of glutamate speciation on amorphous titanium dioxide. The results indicate that glutamate adsorbs on HFO as a deprotonated divalent anion at pH 3-5 and 0.2 micromol x m(-2) in the form of chelating-monodentate and bridging-bidentate species attached to the surface through three or four of the carboxylate oxygens, respectively. The amine group may interact weakly with the surface. However, at similar pH values and higher surface coverages, glutamate adsorbs mainly as a monovalent or divalent anion chelated to the surface by the gamma-carboxylate group. In this configuration the alpha-carboxylate and amine groups might be free to interact above the surface with the free ends of adjacent glutamates, suggesting a possible mechanism for chiral self-organization and peptide bond formation.

Adsorption and polymerization of amino acids on mineral surfaces: a review

The present paper offers a review of recent (post-1980) work on amino acid adsorption and thermal reactivity on oxide and sulfide minerals. This review is performed in the general frame of evaluating Bernal's hypothesis of prebiotic polymerization in the adsorbed state, but written from a surface scientist's point of view. After a general discussion of the thermodynamics of the problem and exactly what effects surfaces should have to make adsorbed-state polymerization a viable scenario, we examine some practical difficulties in experimental design and their bearing on the conclusions that can be drawn from extant works, including the relevance of the various available characterization techniques. We then present the state of the art concerning the mechanisms of the interactions of amino acids with mineral surfaces, including results from prebiotic chemistry-oriented studies, but also from several different fields of application, and discuss the likely consequences for adsorption selectivities. Finally, we briefly summarize the data concerning thermally activated amide bond formation of adsorbed amino acids without activating agents. The reality of the phenomenon is established beyond any doubt, but our understanding of its mechanism and therefore of its prebiotic potential is very fragmentary. The review concludes with a discussion of future work needed to fill the most conspicuous gaps in our knowledge of amino acids/mineral surfaces systems and their reactivity.