The Oligomerization of Glucose Under Plausible Prebiotic Conditions

Abiotic formation of hexoses and disaccharides in aqueous microdroplets

Understanding the chemical reactions that led to the origin of life is a fundamental challenge of chemistry. The formose reaction, an abiotic pathway to monosaccharides, provides a mechanism of sugar formation from simple aldehydes and ketones. However, the reaction requires the addition of base, metal catalysts, and is prone to side reactions, leaving questions about how such processes could have occurred on a primitive Earth. The abiotic formation of more complex sugars, such as disaccharides also require catalysts, and remains underexplored compared to other classes of biomolecules. This study investigates the role of microdroplets in the formation of hexoses and their subsequent condensation reactions to produce disaccharides, without the need for catalysts. The microdroplet-mediated synthesis of fructose and sorbose from glyceraldehyde or dihydroxyacetone, as well as that of disaccharides from various pentoses or hexoses, was monitored via mass spectrometery. Products were confirmed by high resolution mass spectrometry and tandem mass spectrometry. The product distribution of glucose disaccharides was determined by matching the relative intensities of product ions to a mixture of six disaccharide and showed a maximum yield of 9.4% or 1.7 µg min-1 emitter. This study demonstrates the abiotic formation of monosaccharides and disaccharides, such as xylobiose and maltose, providing a possible link between prebiotic sugar synthesis and extant carbohydrate biochemistry. Hexose formation and disaccharide synthesis are driven by the unique air water interface of microdroplets, where partial solvation, pH extremes, and fast mass transfer kinetics enable abiotic transformations.

Evolution of complex chemical mixtures reveals combinatorial compression and population synchronicity

Many open questions about the origins of life are centred on the generation of complex chemical species. Past work has characterized specific chemical reactions that might lead to biological molecules. Here we establish an experimental model of chemical evolution to investigate general processes by which chemical systems continuously change. We used water as a chemical reactant, product and medium. We leveraged oscillating water activity at near-ambient temperatures to cause ratcheting of near-equilibrium reactions in mixtures of organic molecules containing carboxylic acids, amines, thiols and hydroxyl groups. Our system (1) undergoes continuous change with transitions to new chemical spaces while not converging throughout the experiment; (2) demonstrates combinatorial compression with stringent chemical selection; and (3) displays synchronicity of molecular populations. Our results suggest that chemical evolution and selection can be observed in organic mixtures and might ultimately be adapted to produce a broad array of molecules with novel structures and functions.

Stem Life: A Framework for Understanding the Prebiotic-Biotic Transition

Abiogenesis is frequently envisioned as a linear, ladder-like progression of increasingly complex chemical systems, eventually leading to the ancestors of extant cellular life. This "pre-cladistics" view is in stark contrast to the well-accepted principles of organismal evolutionary biology, as informed by paleontology and phylogenetics. Applying this perspective to origins, I explore the paradigm of "Stem Life," which embeds abiogenesis within a broader continuity of diversification and extinction of both hereditary lineages and chemical systems. In this new paradigm, extant life's ancestral lineage emerged alongside and was dependent upon many other complex prebiotic chemical systems, as part of a diverse and fecund prebiosphere. Drawing from several natural history analogies, I show how this shift in perspective enriches our understanding of Origins and directly informs debates on defining Life, the emergence of the Last Universal Common Ancestor (LUCA), and the implications of prebiotic chemical experiments.

Cross-linking impacts the physical properties of mycelium leather alternatives by targeting hydroxyl groups of polysaccharides and amino groups of proteins

Cross-linking, also called tanning, improves mechanical properties of leather and also increases its enzymatic and thermal stability. As a final product, leather has an ultimate tensile strength (σ) of 8-25 MPa and an elongation at break (ε) of >30 %. Mycelium-based materials are a sustainable alternative to leather. Here, the effect of cross-linkers was assessed on mechanical properties of Schizophyllum commune mycelium sheets. To this end, glutaraldehyde and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) were used as well as extracts of Ligustrum vulgare leaves, and bark of Acacia mearnsii and Caesalpinia spinosa. Untanned sheets had a σ of 7.8 MPa and an ε of 15.2 %, while the best overall combination of strength and elasticity was obtained with 0.1 % glutaraldehyde with a σ of 11.1 MPa and an ε of 14.6 %. Cross-linking also increased enzymatic stability and reduced mycelial water absorption but did not result in increased thermal stability. Fourier transform infrared spectroscopy (FTIR), 1D nuclear magnetic resonance spectroscopy (NMR), and amino acid analysis showed that glutaraldehyde bound both protein amino groups and polysaccharide hydroxyl groups by forming Schiff bases and acetals, respectively. Together, synthetic and vegetable cross-linkers can be used to obtain mycelium materials with leather-like tensile strength.

Qualitative Monitoring of Proto-Peptide Condensation by Differential FTIR Spectroscopy

Condensation processes such as wet-dry cycling are thought to have played significant roles in the emergence of proto-peptides. Here, we describe a simple and low-cost method, differential Fourier transform infrared (FTIR) spectroscopy, for qualitative analysis of peptide condensation products in model primordial reactions. We optimize differential FTIR for depsipeptides and apply this method to investigate their polymerization in the presence of extraterrestrial dust simulants.

Differential Oligomerization of Alpha versus Beta Amino Acids and Hydroxy Acids in Abiotic Proto-Peptide Synthesis Reactions

The origin of biopolymers is a central question in origins of life research. In extant life, proteins are coded linear polymers made of a fixed set of twenty alpha-L-amino acids. It is likely that the prebiotic forerunners of proteins, or protopeptides, were more heterogenous polymers with a greater diversity of building blocks and linkage stereochemistry. To investigate a possible chemical selection for alpha versus beta amino acids in abiotic polymerization reactions, we subjected mixtures of alpha and beta hydroxy and amino acids to single-step dry-down or wet-dry cycling conditions. The resulting model protopeptide mixtures were analyzed by a variety of analytical techniques, including mass spectrometry and NMR spectroscopy. We observed that amino acids typically exhibited a higher extent of polymerization in reactions that also contained alpha hydroxy acids over beta hydroxy acids, whereas the extent of polymerization by beta amino acids was higher compared to their alpha amino acid analogs. Our results suggest that a variety of heterogenous protopeptide backbones existed during the prebiotic epoch, and that selection towards alpha backbones occurred later as a result of polymer evolution.

Separations of Carbohydrates with Noncovalent Shift Reagents by Frequency-Modulated Ion Mobility-Orbitrap Mass Spectrometry

An increased focus on characterizing the structural heterogeneity of carbohydrates has been driven by their many significant roles in extant life and potential roles in chemical evolution and the origin of life. In this work, multiplexed drift tube ion mobility-Orbitrap mass spectrometry methods were developed to analyze mixtures of disaccharides modified with noncovalent shift reagents. Since traditional coupling of atmospheric pressure drift tube ion mobility cells with Orbitrap mass analyzers suffers from low duty cycles (<0.1%), a frequency modulation scheme was applied to improve the signal-to-noise ratios (SNR). Several parameters such as the resolution setting and maximum injection time of the Orbitrap analyzer and the magnitude and duration of the frequency sweep were investigated for their impact on the sensitivity gains and resolution of disaccharide-shift reagent adducts. The sweep time and disaccharide concentration had a positive correlation with SNR. The magnitude of the frequency sweep had a negative correlation with SNR. However, increasing the frequency sweep improved the resolution of mixtures of disaccharide analytes. Application of frequency-modulated ion mobility-Orbitrap mass spectrometry to four noncovalently modified glucose dimers allowed for the differentiation of three out of these four analytes.

Prebiotic Peptides: Molecular Hubs in the Origin of Life

The fundamental roles that peptides and proteins play in today's biology makes it almost indisputable that peptides were key players in the origin of life. Insofar as it is appropriate to extrapolate back from extant biology to the prebiotic world, one must acknowledge the critical importance that interconnected molecular networks, likely with peptides as key components, would have played in life's origin. In this review, we summarize chemical processes involving peptides that could have contributed to early chemical evolution, with an emphasis on molecular interactions between peptides and other classes of organic molecules. We first summarize mechanisms by which amino acids and similar building blocks could have been produced and elaborated into proto-peptides. Next, non-covalent interactions of peptides with other peptides as well as with nucleic acids, lipids, carbohydrates, metal ions, and aromatic molecules are discussed in relation to the possible roles of such interactions in chemical evolution of structure and function. Finally, we describe research involving structural alternatives to peptides and covalent adducts between amino acids/peptides and other classes of molecules. We propose that ample future breakthroughs in origin-of-life chemistry will stem from investigations of interconnected chemical systems in which synergistic interactions between different classes of molecules emerge.

Organic acid shift reagents for the discrimination of carbohydrate isobars by ion mobility-mass spectrometry

Traveling wave and drift tube ion mobility were utilized to separate isomeric disaccharides. Organic acid shift reagents were necessary to increase the resolution of these separations for mixture analysis.