Polypeptide Chain Growth Mechanisms and Secondary Structure Formation in Glycine Gas-Phase Deposition on Silica Surfaces

Prebiotic Peptide Synthesis: How Did Longest Peptide Appear?

The origin of proteins is a fundamental question in the study of the origin of life. Peptides, as the building blocks of proteins, necessarily preceded the first proteins in prebiotic chemical evolution. Prebiotic peptides may have also played crucial roles in early life's evolution, contributing to self-catalysis, interacting with nucleic acids, and stabilizing primitive cell compartments. Longer and more complicated prebiotic peptides often have greater structural flexibility and functional potential to support the emergence and evolution of early life. Since the Miller-Urey experiment demonstrated that amino acids can be synthesized in a prebiotic manner, the prebiotic synthesis route of peptides has garnered increasing attention from researchers. However, it is difficult for amino acids to condense into peptides in aqueous solutions spontaneously. Over the past few decades, researchers have explored various routes of prebiotic peptide synthesis in the plausible prebiotic Earth environment, such as thermal polymerization, clay mineral catalysis, wet-dry cycles, condensing agents, and lipid-mediated. This paper reviews advancements in prebiotic peptide synthesis research and discusses the conditions that may have facilitated the emergence of longer peptides.

Monitoring the aging process in egg-tempera paint films

Tempera painting, a predominant pictorial technique during the Middle Ages, used a variety of aqueous binders, egg yolk being the main one for easel paintings. In an effort to replicate the aging process, multiple mockup paints based on egg yolk tempera, incorporating selected pigments such as lead tin yellow, azurite, and Sienna, were exposed to visible or UVA light for up to 130 days. The chemical transformations within the lipoprotein functional groups of yolk were closely monitored using FTIR spectroscopy throughout the aging process in order to study the reactions leading to the spectra recorded on naturally aged films and historical samples. Lipids and proteins undergo oxidation under complex pathways illustrated by the absorption band evolutions (especially CH2 and Amide I elongations). Notably, in the presence of pigments, the observed chemical changes display a comparable but accelerated pattern. Decomposition of the amide I band of both unpigmented and pigmented tempera paints IR spectra revealed conformational changes in proteins during the aging process. In addition, thermal analysis suggested chain shortening revealed by lower degradation temperatures. This investigation sheds light on the intricate evolution of tempera binder and its components over time.

Effect of cross-linking density on the rheological behavior of ultra-soft chitosan microgels at the oil-water interface

In this paper, microgels with uniform particle size were prepared by physically cross-linking the hydrophobically modified chitosan (h-CS) with sodium phytate (SP). The effects of cross-linking density on the interfacial adsorption kinetics, viscoelasticity, stress relaxation, and micorheological properties of the hydrophobically modified chitosan microgels (h-CSMs) at the oil-water interface were extensively investigated by the dilatational rheology, compressional rheology, and particle tracing microrheology. The results were correlated with the particle size, morphology, and elasticity of the microgels characterized by dynamic light scattering and atomic force microscopy. It was found that with the increase of cross-linking density, the h-CSMs changed from a polymer-like state to ultra-soft fussy spheres with higher elastic modulus. The compression isotherms demonstrated multi-stage increase caused by the interaction between the shells and that between the cores of the microgels successively. As the increase of cross-linking density, the h-CSMs diffused slower to the oil-water interface, but demonstrating faster permeation adsorption and rearrangement at the oil-water interface, finally forming interfacial layers of higher viscoelastic modulus due to the core-core interaction. Both the initial tension relaxation and the microgel rearrangement after interface expansion became faster as the microgel elasticity increased. The interfacial microrheology demonstrated dynamic caging effect caused by neighboring microgels. This article provides a more comprehensive understanding of the behaviors of polysaccharide microgels at the oil-water interface.

Amino Acid Polymerization on Silica Surfaces

The polymerization of unactivated amino acids (AAs) is an important topic because of its applications in various fields including industrial medicinal chemistry and prebiotic chemistry. Silica as a promoter for this reaction, is of great interest owing to its large abundance and low cost. The amide/peptide bond synthesis on silica has been largely demonstrated but suffers from a lack of knowledge regarding its reaction mechanism, the key parameters, and surface features that influence AA adsorption and reactivity, the selectivity of the reaction product, the role of water in the reaction, etc. The present review addresses these problems by summarizing experimental and modeling results from the literature and attempts to rationalize some apparent divergences in published results. After briefly presenting the main types of silica surface sites and other relevant macroscopic features, we discuss the different deposition procedures of AAs, whose importance is often neglected. We address the possible AA adsorption mechanisms including covalent grafting and H-bonding and show that they are highly dependent on silanol types and density. We then consider how the adsorption mechanisms determine the occurrence and outcome of AA condensation (formation of cyclic dimers or of long linear chains), and outline some recent results that suggest significant polymerization selectivity in systems containing several AAs, as well as the formation of specific elements of secondary structure in the growing polypeptide chains.

Controlling Solvent Polarity to Regulate Protein Self-Assembly Morphology and Its Universal Insight for Fibrillation Mechanism

The mechanism of ethanol-induced fibrillation of β-lactoglobulin (β-lg) in the acidic aqueous solution upon heating was investigated using various techniques, mainly thioflavin T fluorescence, atomic force microscopy, nonreducing electrophoresis, mass spectrometry, Fourier transform infrared spectroscopy, and circular dichroism spectroscopy. The results showed that fibrillation occurred with a heating time increase, but high ethanol content slowed down the process. At a low ethanol volume fraction, peptides existed after heating for 2 h, with long and straight fibrils formed after 4-6 h, while at a high ethanol volume fraction, the proteins aggregated with very few peptides appeared at the early stage of heating, and short and curved fibrils formed after heating for 8 h. Ethanol weakened the hydrophobic interactions between proteins in the aqueous solution; therefore the latter could not completely balance the electrostatic repulsion, and thus suppressing the fibrillation process. It is believed that the fibrillation of β-lg in the acidic solution upon heating is mainly dominated by the polypeptide model; however, ethanol inhibited the hydrolysis of proteins, and the self-assembly mechanism changed to the monomer model.

Physico-Chemical Approaches to Investigate Surface Hydroxyls as Determinants of Molecular Initiating Events in Oxide Particle Toxicity

The study of molecular recognition patterns is crucial for understanding the interactions between inorganic (nano)particles and biomolecules. In this review we focus on hydroxyls (OH) exposed at the surface of oxide particles (OxPs) which can play a key role in molecular initiating events leading to OxPs toxicity. We discuss here the main analytical methods available to characterize surface OH from a quantitative and qualitative point of view, covering thermogravimetry, titration, ζ potential measurements, and spectroscopic approaches (NMR, XPS). The importance of modelling techniques (MD, DFT) for an atomistic description of the interactions between membranes/proteins and OxPs surfaces is also discussed. From this background, we distilled a new approach methodology (NAM) based on the combination of IR spectroscopy and bioanalytical assays to investigate the molecular interactions of OxPs with biomolecules and membranes. This NAM has been already successfully applied to SiO₂ particles to identify the OH patterns responsible for the OxPs' toxicity and can be conceivably extended to other surface-hydroxylated oxides.