The adsorption of amino acids and cations onto goethite: a prebiotic chemistry experiment

Insight on the heterogeneously activated H2O2 with goethite under visible light for cefradine degradation: pH dependence and photoassisted effect

The iron mineral-catalyzed degradation of cephalosporin antibiotics with H₂O₂ occurs ubiquitously in nature. Despite numerous studies, the effects of environmental conditions on reactive species production and degradation processes of cephalosporins remain unclear. Here, we report the iron mineral of goethite as the efficient and heterogenous catalyst for the degradation of cefradine (CRD) via H₂O₂ activation under different conditions involving pH and visible light irradiation. Results show that the CRD removal rate is highly dependent on pH and visible light irradiation. Interestingly, when the pH ranges from 4.0 to 7.0, the degradation intermediates of CRD under dark are the same as under visible light conditions in the goethite/H₂O₂ system. And, the ratio of CRD degradation rate constant (k_Light/k_Dark) reaches a maximum at pH 5.0, suggesting that CRD existing as zwitterion species is preferable for its removal with photoassistance. The mechanism investigation reveals that both •OH and ≡[Fe^IVO]²⁺ oxidants are generated during the reaction process, and •OH is the major oxidant at acidic pH, while ≡[Fe^IVO]²⁺ is more likely to be formed with photoassistance at near-neutral pH. According to UPLC-MS/MS analysis, CRD degradation likely happens via hydrogen atom abstraction from cyclohexadienyl by •OH, thioether and olefin oxidation by ≡[Fe^IVO]²⁺, and Fe^III-catalyzed hydrolytic cleavage of β-lactam ring. These findings highlight the vital roles of pH and photoassistance in the heterogeneously activated H₂O₂ with goethite for CRD degradation.

A comparative study on aggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles in synthetic and natural waters based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and molecular dynamics simulations

Natural iron oxides nanomaterials have important roles in biogeochemical processes. In this study, the effects of pH, natural organic matter, and cations on aggregation and sedimentation of natural goethite and artificial Fe₃O₄ nanoparticles in water were investigated to learn more about the environmental behaviors of engineered and natural nanomaterials and how they differ. In addition, a novel extended DLVO theory that considered steric, gravitational, and magnetic attraction forces concurrently was specifically developed to provide mechanisms explanations. Specifically, Fe₃O₄ NPs were more likely than bulk goethite to aggregate (because of magnetic attraction interactions) at low HA concentrations and disperse at high HA concentrations. Besides, goethite was less prone to settle with the same concentration of NaCl than Fe₃O₄ NPs, but the opposite trend was found for the same concentration of CaCl₂ because of the difference in maximum net energy (barrier) and strong Ca²⁺ bridging effectiveness of goethite in CaCl₂ solution. Statistical models were established to evaluate colloidal stability of the particles. XPS and molecular dynamics simulation results suggested that ions were adsorbed onto particles via ionic polarization and that the binding free energies at high coverage followed the order Ca²⁺ > Na⁺ > Cl^- and presence of cation bridging between particles.

A Few Experimental Suggestions Using Minerals to Obtain Peptides with a High Concentration of L-Amino Acids and Protein Amino Acids

The peptides/proteins of all living beings on our planet are mostly made up of 19 L-amino acids and glycine, an achiral amino acid. Arising from endogenous and exogenous sources, the seas of the prebiotic Earth could have contained a huge diversity of biomolecules (including amino acids), and precursors of biomolecules. Thus, how were these amino acids selected from the huge number of available amino acids and other molecules? What were the peptides of prebiotic Earth made up of? How were these peptides synthesized? Minerals have been considered for this task, since they can preconcentrate amino acids from dilute solutions, catalyze their polymerization, and even make the chiral selection of them. However, until now, this problem has only been studied in compartmentalized experiments. There are separate experiments showing that minerals preconcentrate amino acids by adsorption or catalyze their polymerization, or separate L-amino acids from D-amino acids. Based on the [GADV]-protein world hypothesis, as well as the relative abundance of amino acids on prebiotic Earth obtained by Zaia, several experiments are suggested. The main goal of these experiments is to show that using minerals it is possible, at least, to obtain peptides whose composition includes a high quantity of L-amino acids and protein amino acids (PAAs). These experiments should be performed using hydrothermal environments and wet/dry cycles. In addition, for hydrothermal environment experiments, it is very important to use one of the suggested artificial seawaters, and for wet/dry environments, it is important to perform the experiments in distilled water and diluted salt solutions. Finally, from these experiments, we suggest that, without an RNA world or even a pre genetic world, a small peptide set could emerge that better resembles modern proteins.

Nitrogen-Doped Hollow Copolymer Tube via Template-Free Asynchronous Polymerization with Highly Selective Separation of Hydrophilic Dipeptide for Enhancing Inhibitory Activity of Angiotensin Converting Enzyme

A N-doped hollow copolymer tube (NHCT) was fabricated via template-free one-pot asynchronous polymerization strategy. Discrepancies of monomer polymerization speed and their hydrophilic-hydrophobic interaction resulted in the assembly of a hollow tube having inner diameter and double wall thickness of ∼230 and 40 nm, respectively. The formation and growth mechanism of NHCT analyzed via advanced characterization revealed that the unique growth processes tuned a demarcating surface layer between inner (hydrophilic) and outer (hydrophobic) layers. The screening and recognition ability of NHCT were determined for two specific dipeptides (WW and RR) possessing great discrepancies in hydrophilicity and angiotensin converting enzyme inhibitory (ACE-I) activity. NHCT realized high adsorption capacity (1.57 mmol/g) and selectivity (∼1274) for hydrophilic dipeptide RR (low ACE-I activity) from the mixture of RR/WW. As a result, ACE-I activity for residual solution were enhanced about 4.1 times as compared to original solution from natural silkworm pupae protein hydrolysate. Awarding to these results and its facile and discerning ability, NHCT can be envisioned to be of great value for the separation of small functional peptides from a natural edible source.

Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems

Iron oxyhydroxide minerals, known to be chemically reactive and significant for elemental cycling, are thought to have been abundant in early-Earth seawater, sediments, and hydrothermal systems. In the anoxic Fe²⁺-rich early oceans, these minerals would have been only partially oxidized and thus redox-active, perhaps able to promote prebiotic chemical reactions. We show that pyruvate, a simple organic molecule that can form in hydrothermal systems, can undergo reductive amination in the presence of mixed-valence iron oxyhydroxides to form the amino acid alanine, as well as the reduced product lactate. Furthermore, geochemical gradients of pH, redox, and temperature in iron oxyhydroxide systems affect product selectivity. The maximum yield of alanine was observed when the iron oxyhydroxide mineral contained 1:1 Fe(II):Fe(III), under alkaline conditions, and at moderately warm temperatures. These represent conditions that may be found, for example, in iron-containing sediments near an alkaline hydrothermal vent system. The partially oxidized state of the precipitate was significant in promoting amino acid formation: Purely ferrous hydroxides did not drive reductive amination but instead promoted pyruvate reduction to lactate, and ferric hydroxides did not result in any reaction. Prebiotic chemistry driven by redox-active iron hydroxide minerals on the early Earth would therefore be strongly affected by geochemical gradients of E_h, pH, and temperature, and liquid-phase products would be able to diffuse to other conditions within the sediment column to participate in further reactions.

Enhancement and Inhibitory Activities of Minerals for Alanine Oligopeptide Elongation Under Hydrothermal Conditions

In a previous study, we have showed that the elongation of an alanine oligopeptide [L-alanyl-L-alanyl-L-alanyl-L-alanine ((Ala)₄)] to higher oligopeptides is enhanced by calcite and dolomite at 275°C, using a mineral-mediated hydrothermal flow reactor system. However, a problem during the use of hydrothermal flow reactor system was that some of the minerals, such as clay, could not be tested due to their clogging in the reactor. In this article, we attempted to analyze the scope of enhancement for the formation of L-alanyl-L-alanyl-L-alanyl-L-alanyl-L-alanine ((Ala)₅) and higher oligopeptides with different minerals including clay minerals for the elongation of alanine oligopeptide at 175°C. First, carbonate minerals and some clay minerals showed an enhancement of the formation of (Ala)₅ from (Ala)₄. On the contrary, volcanic products showed strong inhibitory activities. According to the pH dependence on the (Ala)₄ elongations, we confirmed that most enhancement and inhibitory activities are due to the pH influence on the elongation of (Ala)₄. However, the enhancement of montmorillonite (Tsukinuno), sphalerite, apatite, tourmaline, calcite (Nitto Funka), and the inhibitory activities by volcanic ash (Shinmoedake), volcanic ash (Sakurajima), dickite, and pyrophillite are not simply due to the pH change in the presence of these minerals. The difference found between the previous and present studies suggests that the interaction kinetics of the aqueous phase with the mineral phase is also an important factor for the elongation of (Ala)₄. These data imply that the environments with pH near neutral to weak alkaline and with minerals might have been useful for the accumulation of oligopeptides in hydrothermal conditions.