Mineral-mediated carbohydrate synthesis by mechanical forces in a primordial geochemical setting

Prebiotic chemistry seeks plausible routes to biomolecule precursors under the harsh, variable conditions of early Earth. Sugars are central to metabolism and genetic polymers, and the formose reaction—first reported by Butlerow in 1861—provides a pathway from formaldehyde to a network of monosaccharides, typically catalyzed by bases such as calcium hydroxide and potentially by minerals. In aqueous solution, sugar formation competes with degradation (e.g., Cannizzaro, β-elimination, polymerization), and product instability hampers selectivity and yield. Prior work showed that solvent-free, mechanochemical conditions can accelerate and alter product formation with improved selectivity relative to aqueous media. Yet, the roles of different mineral catalysts and the impact of atmospheric composition on the solid-state formose reaction were unclear. This study investigates whether mechanochemical sugar synthesis is broadly catalyzed by diverse minerals, how catalysts influence product distributions, whether adsorbed formaldehyde can be incorporated, and how different gas atmospheres relevant to early Earth affect the reaction.

The formose reaction has long been studied as a route from formaldehyde to carbohydrates, commonly using Ca(OH)2, with proposed relevance to prebiotic chemistry and supported by sugar detections in meteorites. Alternative glyoxylate scenarios and photochemical processes have also been explored. In solution, reaction outcome depends on base strength and coordinating metal ions, and undesired pathways (Cannizzaro reactions, β-elimination, retro-aldol processes) degrade sugars or divert carbon into side products. Thiazolium salts (vitamin B1 analogs) can catalyze umpolung steps to initiate sugar formation from formaldehyde. Previous work indicated mechanochemical conditions can enhance selectivity and reduce decomposition compared to aqueous systems, and that specific meteoritic minerals like schreibersite can act as catalysts. However, comprehensive screening across mineral classes and systematic assessment of atmospheric effects on solid-state formose chemistry had been lacking.

• Catalysts and minerals: A broad set of minerals representing hydroxides (e.g., portlandite, brucite), carbonates (calcite, magnesite), sulfates (anhydrite), silicates (quartz, talc, olivines), micas (muscovite, fuchsite), zeolites (clinoptilolite, chabazite, analcime), clays (montmorillonite variants), phosphates (apatite), phosphides (schreibersite), and borates (colemanite) were tested.
• Mechanochemical screening with glycolaldehyde: Glycolaldehyde dimer (0.5 eq.) and mineral (0.2 eq.; 20 mol%) were milled in an oscillatory ball mill (5 mL stainless steel jar, one 7 mm ball) at 30 Hz for 90 min at room temperature or under intermittent liquid nitrogen cooling. Total mass per run was kept constant (~155 mg).
• Formaldehyde adsorption and incorporation: Paraformaldehyde was dried, depolymerized at 150 °C under N2, and the gas was passed through dried minerals or 4 Å molecular sieves to load adsorbed formaldehyde; adsorption quantified by weight gain. Reactions with adsorbed formaldehyde (1.0 eq.) and glycolaldehyde dimer (0.5 eq.) were performed in a planetary ball mill (20 mL bowls, ten 10 mm balls) at 400 rpm for 90 min using minerals (zeolites, sheet silicates) as both supports and catalysts. Addition of Ca(OH)2 was also tested.
• Umpolung catalysts: Tested 2-hydroxy-1-phenylethan-1-one (enolizable catalyst) and thiazolium salts (3-ethylbenzothiazolium bromide, 3-ethylthiazolium bromide, 3-methylbenzothiazolium iodide) with adsorbed formaldehyde (1.0 eq.) and Ca(OH)2 (0.2 eq.) under N2 at 400 rpm, 90 min.
• Atmospheric compatibility: Glycolaldehyde dimer (850 mg, 0.5 eq.) with Ca(OH)2 (210 mg, 0.2 eq.) was milled (planetary mill, 400 rpm, 90 min) in jars evacuated and refilled with methane, nitrogen, air, or carbon dioxide to atmospheric pressure (gassing lids).
• Analysis: Products derivatized to silylated O-ethyl oximes (O-ethyl hydroxylamine then N-/O-bis(trifluoroacetamide)) with phenyl-β-D-glucopyranoside internal standard. GC-MS (SE-52 column) used for identification vs. reference standards; quantification via FID with effective carbon number correction. Highly volatile analytes (formaldehyde, methanol, formic acid) were measured by GC-TCD from DCM extracts. Reported values are means with standard deviations from duplicate reactions and duplicate derivatizations (four data points total unless noted).

• Broad mineral catalysis: All tested minerals except anhydrite (sulfate) and colemanite (borate) catalyzed mechanochemical aldol coupling of glycolaldehyde to even-carbon sugars (tetroses 4, hexoses 6). Schreibersite (meteoritic phosphide) was active without added water.
• Catalyst-dependent selectivity: Product distributions (aldoses vs ketoses; diastereomer ratios) strongly depended on mineral composition and class. • Tetroses generally dominated over hexoses; aldoses exceeded ketoses overall. • For portlandite, a tetrose (4) constituted >40% of products; for quartz and diaspore tetrose 4 was only in traces. • Calcite and fuchsite showed similar conversions, but calcite yielded ~0.3% hexoses while fuchsite produced only traces. • Aldotetrose/erythrulose ratio ranged from ~5 (basalt) to ~53 (chabazite). • Erythrose/threose ratio spanned 0.71 (brucite; favoring threose) to 1.23 (montmorillonite 1; favoring erythrose).
• Temperature tolerance: Reactions proceeded under liquid nitrogen cooling, albeit with reduced conversion, indicating tolerance to low temperatures.
• Incorporation of adsorbed formaldehyde: Zeolites and sheet silicates adsorbed formaldehyde and, when milled with glycolaldehyde, yielded trioses (glyceraldehyde 3a, dihydroxyacetone 3b), pentoses (including ribose), hexoses, and even heptoses. Adding Ca(OH)2 increased conversion but also increased side products (methanol, glycolic acid, lactic acid, glycerol, branched sugars like apiose). Formic acid (a Cannizzaro product) was not detected.
• Umpolung catalysis: Without glycolaldehyde, adsorbed formaldehyde did not convert under mineral-only mechanochemical conditions. With umpolung catalysts, ethyl-substituted thiazolium salts and 2-hydroxy-1-phenylethan-1-one afforded only traces of trioses/tetroses; 3-methylbenzothiazolium iodide was inactive.
• Atmospheric effects: Under methane, nitrogen, or air, conversion and product distributions were similar. Under CO2, conversion dropped markedly (from ~85% to ~40%), but monosaccharides still formed and no new side products were observed.

The study shows that mechanochemical formose chemistry is widely catalyzed by diverse mineral classes, providing a selective, solid-state route to monosaccharides with substantially reduced side reactions compared to aqueous conditions. Catalyst identity tunes both the extent of conversion and the distribution among aldoses/ketoses and sugar diastereomers, indicating that cation composition and mineral structure modulate enolization/aldol equilibria and isomerization. The reactions are robust across oxidizing and reducing atmospheres; oxygen does not inhibit as it does in water. Lower conversions under CO2 are consistent with in situ carbonate formation diminishing alkalinity under milling conditions. Adsorbed formaldehyde on zeolites and sheet silicates can be incorporated into higher sugars when combined with glycolaldehyde, producing biochemically relevant products (e.g., glyceraldehyde, ribose) with only small amounts of side products like lactic acid or apiose. Although mineral-only mechanochemical umpolung from formaldehyde was not observed, prebiotic sources of glycolaldehyde and the activity of thiazolium-type catalysts (precursors to vitamin B1) provide plausible initiators. These findings support both early Earth and extra-terrestrial scenarios (e.g., meteoritic mineral matrices) for sugar synthesis via water-free, mechanically driven pathways.

Mechanochemical formose reactions provide a robust, water-free route to monosaccharides under geochemically plausible conditions, catalyzed by many mineral classes and tolerant to a range of atmospheres and temperatures. Catalyst choice allows selective biasing of product distributions, and mineral-adsorbed formaldehyde can be incorporated into higher sugars when combined with glycolaldehyde. These results rationalize sugar detections in meteorites and offer a prebiotically relevant pathway independent of aqueous alteration. Potential future work includes: elucidating mechanistic details of mineral-specific selectivity; enabling efficient umpolung of formaldehyde under purely mineral mechanochemical conditions; expanding mineral/composition libraries; in situ monitoring of mechanochemical transformations; and exploring cyclical environmental mechanical processes that could drive such reactions in natural settings.

• Umpolung from formaldehyde alone was not achieved mechanochemically with mineral catalysis; glycolaldehyde or specialized umpolung catalysts were required, and even then only traces of sugars formed with thiazolium salts.
• Carbon dioxide atmospheres significantly reduced conversion (from ~85% to ~40%) likely due to carbonate formation and lowered alkalinity.
• While side reactions were reduced vs aqueous systems, some side products (e.g., methanol, glycolic and lactic acids, glycerol, branched sugars) appeared, especially upon adding Ca(OH)2 in formaldehyde incorporation experiments.
• The mechanochemical reactions proceeded with lower conversion at cryogenic temperatures and are generally slower than in aqueous reactions, although more selective.
• Detection limits and volatility constrained direct observation of some small products (e.g., formic acid was not detected and may have reacted further).