Periodic Reporting for period 4 - A-LIFE (The asymmetry of life: towards a unified view of the emergence of biological homochirality)
Reporting period: 2023-10-01 to 2024-09-30
The ERC ALIFE project investigated the origin of biological homochirality, life’s exclusive use of one enantiomer for chiral building blocks like amino acids and sugars. This fundamental property of life is central to the molecular machinery of living systems, yet its origin remains unresolved. Therefore, the project explored the initial asymmetry of life’s molecules, hypothesizing it began in interstellar space where circularly polarized light (CPL) caused chiral biases. This hypothesis aligns with observations of CPL in molecular clouds and amino acids in meteorites that are enriched in the biological L-enantiomer.
The project had implications for astrobiology and the detection of life beyond Earth, the philosophical understanding of the uniqueness of life, and interdisciplinary progress in chemistry, physics and biology.
To uncover the origins of biomolecular homochirality and determine how and where the first chiral biomolecules were formed, as well as the mechanisms behind the selection of their specific handedness, we sought to explore the possibility of a unified asymmetric formation pathway for the chiral subunits of the genome, proteome, and lipidome, i.e. sugars, amino acids, and glycerophospholipids, respectively.
Key objectives were:
1. Investigating the formation of chiral precursors in interstellar/cometary materials.
2. Demonstrating CPL’s stereoselective effects through laser- and synchrotron irradiation experiments in combination with enantioenriched detection in meteorite and asteroid samples.
3. Synthesizing and amplifying chiral subunits of life’s biopolymers under prebiotic conditions.
The project had implications for astrobiology and the detection of life beyond Earth, the philosophical understanding of the uniqueness of life, and interdisciplinary progress in chemistry, physics and biology.
To uncover the origins of biomolecular homochirality and determine how and where the first chiral biomolecules were formed, as well as the mechanisms behind the selection of their specific handedness, we sought to explore the possibility of a unified asymmetric formation pathway for the chiral subunits of the genome, proteome, and lipidome, i.e. sugars, amino acids, and glycerophospholipids, respectively.
Key objectives were:
1. Investigating the formation of chiral precursors in interstellar/cometary materials.
2. Demonstrating CPL’s stereoselective effects through laser- and synchrotron irradiation experiments in combination with enantioenriched detection in meteorite and asteroid samples.
3. Synthesizing and amplifying chiral subunits of life’s biopolymers under prebiotic conditions.
WP1. We collaborated with Prof. R. Kaiser’s team from the University Hawaii to study interstellar ices, detecting key molecules like glycerol, carboxylic acids, and phosphorus- and sulfur-containing compounds, vital to prebiotic evolution. Our experiments provided evidence for the abiotic formation of these molecules in interstellar environments and despite phosphorus’s vital role in biochemical reactions and phosphate-containing molecules like ATP, no experiments have been conducted in such settings.
WP2. To explore asymmetric photochemistry, we used chiroptical spectroscopy at the synchrotron radiation CD facility at ASTRID2, Aarhus University, to predict enantiomeric excesses (ee) inducible by CPL. Experiments with amino acids, sugars, and lipids demonstrated that helicity-dependent enantioselectivity is highly sensitive to the environmental conditions (solution, solid, or gas phase). Notably, sugars exhibited the highest enantioselectivity toward CPL, followed by amino acids, while lipids showed minimal selectivity.
We demonstrated CPL’s effective enantioselectivity on isovaline, a non-proteinogenic amino acid found with L-excesses in meteorites. Enabled by a UV-tunable laser developed under my ERC Starting Grant, this work suggests that small yet consistent L-biases from stellar CPL were likely amplified during aqueous alteration on meteorite parent bodies, potentially influencing Earth’s prebiotic inventory toward left-handed proteome precursors.
WP3. Our recent investigations into the evolution of chiral complexity have yielded highly promising results, particularly through the interplay of chiral sugar molecules and amino acids. A key aspect of this work was the role of mineral surfaces, which influence both aqueous alteration on meteorite parent bodies and the chemical evolution of organic matter on early Earth. Notably, research on mineral-surface catalysis has demonstrated olivine’s ability to facilitate sugar formation directly from formaldehyde—an abundant molecule in both interstellar and prebiotic environments—providing a crucial link between interstellar chemistry and prebiotic Earth processes.
Our research has resulted in a total of 17 scientific publications across three main objectives: Key findings on chiral molecule formation in interstellar and Solar System ices, as well as advancements in analytical workflows for meteorite and asteroid sample analysis, have been published in PNAS (2024) and Nature Communications (2024), among others. Investigations into the enantioselective interaction of chiral photons with biomolecules, including the first chiroptical gas phase spectra measurements, have been published in Nature Communications (2023) and Science Advances (2022). Experimental results on the role of mineral surfaces in the evolution of chiral complexity have appeared in ACS Earth and Space Chemistry (2024) and Earth and Planetary Science Letters (2024). Additionally, our critical reviews on the plausibility of stellar CPL as the original trigger for lipid homochirality was published in Nature Reviews Chemistry (2024).
All publications stem from experimental and theoretical work by both permanent and non-permanent team members, including doctoral and postdoctoral researchers. Many were accompanied by press releases, attracting attention from national and international media and leading to radio interviews. Our team has actively participated in scientific conferences and happily engaged in public outreach activities.
WP2. To explore asymmetric photochemistry, we used chiroptical spectroscopy at the synchrotron radiation CD facility at ASTRID2, Aarhus University, to predict enantiomeric excesses (ee) inducible by CPL. Experiments with amino acids, sugars, and lipids demonstrated that helicity-dependent enantioselectivity is highly sensitive to the environmental conditions (solution, solid, or gas phase). Notably, sugars exhibited the highest enantioselectivity toward CPL, followed by amino acids, while lipids showed minimal selectivity.
We demonstrated CPL’s effective enantioselectivity on isovaline, a non-proteinogenic amino acid found with L-excesses in meteorites. Enabled by a UV-tunable laser developed under my ERC Starting Grant, this work suggests that small yet consistent L-biases from stellar CPL were likely amplified during aqueous alteration on meteorite parent bodies, potentially influencing Earth’s prebiotic inventory toward left-handed proteome precursors.
WP3. Our recent investigations into the evolution of chiral complexity have yielded highly promising results, particularly through the interplay of chiral sugar molecules and amino acids. A key aspect of this work was the role of mineral surfaces, which influence both aqueous alteration on meteorite parent bodies and the chemical evolution of organic matter on early Earth. Notably, research on mineral-surface catalysis has demonstrated olivine’s ability to facilitate sugar formation directly from formaldehyde—an abundant molecule in both interstellar and prebiotic environments—providing a crucial link between interstellar chemistry and prebiotic Earth processes.
Our research has resulted in a total of 17 scientific publications across three main objectives: Key findings on chiral molecule formation in interstellar and Solar System ices, as well as advancements in analytical workflows for meteorite and asteroid sample analysis, have been published in PNAS (2024) and Nature Communications (2024), among others. Investigations into the enantioselective interaction of chiral photons with biomolecules, including the first chiroptical gas phase spectra measurements, have been published in Nature Communications (2023) and Science Advances (2022). Experimental results on the role of mineral surfaces in the evolution of chiral complexity have appeared in ACS Earth and Space Chemistry (2024) and Earth and Planetary Science Letters (2024). Additionally, our critical reviews on the plausibility of stellar CPL as the original trigger for lipid homochirality was published in Nature Reviews Chemistry (2024).
All publications stem from experimental and theoretical work by both permanent and non-permanent team members, including doctoral and postdoctoral researchers. Many were accompanied by press releases, attracting attention from national and international media and leading to radio interviews. Our team has actively participated in scientific conferences and happily engaged in public outreach activities.
Our studies on phosphorus and sulfur organic compounds in interstellar ices revealed alternative extraterrestrial sources for these elements, crucial for life’s precursors. This discovery addressed a key challenge in prebiotic chemistry: geochemically linking insoluble abiotic P- and S-sources, often trapped in terrestrial minerals, with the emergence of life’s molecular precursors on early Earth.
Moreover, our work expanded the known inventory of prebiotic molecules by identifying lipid precursors under interstellar conditions, bridging a gap in understanding biological membranes’ origins. Among those lipid precursors are amphiphilic molecules, which are key to the self-assembly of protocellular structures, thereby completing the set of chiral biological building blocks required for life as we know it. These findings highlight the potential of interstellar chemistry to contribute more comprehensively to the molecular inventory of early Earth.
Driven by our core question on life’s homochirality, we explored the distinct lipid chirality of archaea versus bacteria and eukarya—the "chiral lipid divide." Initially, we hypothesized that the biological enantiomers of all homochiral biopolymers were selected by a common physical process. However, our experimental findings challenge this view, suggesting that phospholipid chirality arose from localized interactions in primitive vesicles rather than direct asymmetric effects of circularly polarized light in interstellar environments.
Advanced experiments in gas, amorphous solid and solution phases simulated different stages and locations of UV-illuminated interstellar ices within dense molecular clouds and protoplanetary disks and the associated morphological changes. Those experiments improved our understanding of a more realistic astrophysical scenario and demonstrated CPL’s role in inducing small enantiomeric excesses through asymmetric photolysis of interstellar ices intimately connected with the surrounding gas and dust. We proposed a two-step process for biomolecular homochirality: initial symmetry-breaking in interstellar gas and dust, followed by Earth-based nonequilibrium reactions driving prebiotic molecular systems toward a homochiral state.
Moreover, our work expanded the known inventory of prebiotic molecules by identifying lipid precursors under interstellar conditions, bridging a gap in understanding biological membranes’ origins. Among those lipid precursors are amphiphilic molecules, which are key to the self-assembly of protocellular structures, thereby completing the set of chiral biological building blocks required for life as we know it. These findings highlight the potential of interstellar chemistry to contribute more comprehensively to the molecular inventory of early Earth.
Driven by our core question on life’s homochirality, we explored the distinct lipid chirality of archaea versus bacteria and eukarya—the "chiral lipid divide." Initially, we hypothesized that the biological enantiomers of all homochiral biopolymers were selected by a common physical process. However, our experimental findings challenge this view, suggesting that phospholipid chirality arose from localized interactions in primitive vesicles rather than direct asymmetric effects of circularly polarized light in interstellar environments.
Advanced experiments in gas, amorphous solid and solution phases simulated different stages and locations of UV-illuminated interstellar ices within dense molecular clouds and protoplanetary disks and the associated morphological changes. Those experiments improved our understanding of a more realistic astrophysical scenario and demonstrated CPL’s role in inducing small enantiomeric excesses through asymmetric photolysis of interstellar ices intimately connected with the surrounding gas and dust. We proposed a two-step process for biomolecular homochirality: initial symmetry-breaking in interstellar gas and dust, followed by Earth-based nonequilibrium reactions driving prebiotic molecular systems toward a homochiral state.