Adsorption and Mechanism of Glycine on the Anatase with Exposed (001) and (101) Facets

Abstract

As a widely existing mineral types on Earth, semiconductor minerals play an important role in the origin of life and the material geochemical cycle. The first step of peptide formation is amino acid adsorption on the mineral surface, but the role and mechanism of different crystal facets of semiconductor minerals are not well understood. Anatase (TiO2) with exposed (001) facets was synthesized by a hydrothermal method, and then analyzed and compared with the purchased ordinary anatase (TiO2) for the adsorption of glycine, the simplest amino acid. XRD, SEM and TEM results show that the hydrothermally synthesized anatase (TiO2) has a good anatase crystal form, which is micro-nano-scale flake particles and mainly composed of (001) facets. The results of HPLC used in the adsorption experiment showed that under optimal conditions (pH 5 to 6, an adsorption time of 24 h, and an initial concentration of 0.09 mol/L), the adsorption quantity of glycine on anatase (TiO2) with exposed (001) facets may reach 10 mg/m2, which is larger than that for ordinary anatase (TiO2) with exposed (101) facets. Based on a combination of various characterizations and simulation calculations, the results proved that anatase can activate thermodynamically stable γ-glycine to β-glycine. The adsorption of glycine on anatase (TiO2) has two forms, one is the zwitterionic form in which the carboxyl group forms a bridge structure with two Ti atoms connected by surface bridging oxygen, and the dissociated form is in which the amino group forms a bond with the surface Ti atom. Among these, glycine is mainly adsorbed to anatase by dissociative molecules on the anatase (TiO2) with exposed (001) facets and by zwitterion adsorption on the anatase (TiO2) with exposed (101) facets. This research elucidates the conditions and mechanism of amino acid adsorption by semiconductor minerals in weak acidic environment, which is similar to the environmental pH that was beneficial to the formation of life on the early Earth. Therefore, these can provide a reference for the further study of the role of semiconductor minerals in the adsorption and polymerization of small biomolecules in the origin of life.

Adsorption of Glycine on TiO2 in Water from On-the-fly Free-Energy Calculations and In Situ Electrochemical Impedance Spectroscopy

“…The low adsorption free-energy value and the rotational mobility of water molecules linked to the O br sites prevent us from identifying a unique adsorption configuration for the M 2 mode (see Supporting Information). We note that this mode might be more dominant by lowering the pH of the solution, as reported in IR adsorption studies. , Overall the low adsorption free energy for this mode is in line with the observation that negatively charged amino acids, at neutral pH, do not guide the peptide adhesion on oxide surfaces in the presence of water ,,,,,, (while it is the contrary for dry conditions).…”

“…We note that this mode might be more dominant by lowering the pH of the solution, as reported in IR adsorption studies. 61 , 62 Overall the low adsorption free energy for this mode is in line with the observation that negatively charged amino acids, at neutral pH, do not guide the peptide adhesion on oxide surfaces in the presence of water 15 , 16 , 20 , 22 , 25 , 63 , 64 (while it is the contrary for dry conditions).…”

Synthesis of Peptides from Glycine on Anatases with Different Crystal Facets

“…Since Bernal [6] and Goldschmidt [7] proposed the conclusion that "minerals are an important material basis in the origin of life", a large number of scholars have put forward general principles and assumptions in terms of mineral-assisted biosynthesis, and clay minerals are the most common in the specific mineral groups that are cited [3]. Many scholars have used the interaction between clay minerals and amino acids to explore the evolution of early biological macromolecules, but the mechanism is still not fully explained [8]. Hu et al [3] used orthoclase to study the reaction mechanism of amino acid condensation to generate peptide bonds based on density functional theory, analyzed the role of metal ions, surface of orthoclase and amino acid side chains, and concluded that metal ions could catalyze the polymerization of amino acid molecules to generate peptide bonds, amino acid side chains can affect the formation of peptide bonds and the catalytic properties of different ionic systems are significantly different.…”

“…In general, the ordinary anatase is composed of a (101) crystal face with a higher surface energy, while a (001) crystal face with a higher reactivity is almost non-existent due to its low surface energy. Liu et al [8] studied the adsorption and mechanism of glycine on anatase with exposed (001) and (101) facets. Pantaleone et al [20] studied the interaction of 11 amino acids with the TiO 2 (101) anatase surface by means of PBE-D2* periodic simulations, both from a static and dynamic point of view.…”

La3+’s Effect on the Surface (101) of Anatase for Methylene Blue Dye Removal, a DFT Study

“…The most stable and most commonly occurring anatase crystallographic surface is (101) [ 21 ]. In general, ordinary anatase is composed of crystal surfaces (101) with higher surface energy, while crystal surfaces (001) with higher reactivity are almost non-existent due to their low surface energy [ 28 ].…”