Surface functional group contributions to biosorption of strontium ions by Saccharomyces cerevisiae as well as interface interactions were elucidated.

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.

Semiconductor minerals are widely present on the surface of Earth, but their roles in the process of peptide formation from amino acids are less studied, especially the role of different crystal facets in the origin of life. In this research, High Performance Liquid Chromatography (HPLC), thermogravimetric analysis (TA/DTA), Nuclear Magnetic Resonance (NMR) and simulation calculations were used to study the condensation of glycine on the surface of anatase with (001) crystal facets and ordinary anatase as well as the reaction mechanism. Combined with TA/DTA and heating experiments (80–130 °C), it was found that anatase with (001) crystal facets and ordinary anatase could both catalyze the condensation of glycine to form corresponding oligopeptides (mainly DKP, Gly2 and Gly3). Anatase with (001) crystal facets shows better catalytic effect, which can reduce the condensation temperature of glycine to 90 °C. With the increase in temperature, the condensation efficiency of anatase with (001) crystal facets for Gly2 is relatively higher, and the maximum yield is about 0.20 mg/m2. The condensation efficiency of ordinary anatase for Gly3 is relatively higher, and the maximum yield is about 0.28 mg/m2. The results of FTIR and simulation calculation show that the electron density of the carboxyl group changes after glycine is adsorbed on the surface of anatase, which is easily subject to the nucleophilic attack of amino groups to promote the condensation reaction. These results can provide reference for the research of condensation of small biomolecules on semiconductor mineral surfaces in the origin of life.