Abstract EANA2025-6

On the early Earth, surface pools such as volcanic hot spring likely had access to multiple sources of organic precursors (e.g. via extraterrestrial delivery, atmospheric synthesis, or local geochemical synthesis). These pools were subjects to dynamic environmental conditions, particularly frequent wet-dry cycling driven by evaporation, precipitation, fluctuating water levels, and geyser activity (1). Such cycles have been proposed to facilitate the formation, stabilization, and evolution of polymers—potentially playing a crucial role in prebiotic chemistry (2-3).

Within this context, the formose reaction stands out as a prominent prebiotic pathway thought to have generated sugars relevant to early molecular systems (4-5). This complex network — involving the formation of sugars, polyols, and hydroxy acids from formaldehyde in a series of reactions — is inherently autocatalytic and sensitive to environmental parameters. Under specific conditions, selective product formation has been observed (6). However, due to its complex nature, the formose reaction remains a challenge to understand.

To investigate the feasibility of the formose reaction at the surface of early Earth, experiments were conducted under non-ideal conditions for this reaction (7), including moderate temperature and slightly acidic to neutral pH (bicarbonate buffer), in the absence of the typical Ca²⁺ catalyst. This mildly reactive environment was paired with repeated wet-dry cycles (up to 4), using gas flushing to mimic natural drying. Furthermore, we explored the influence of different drying gases (N2 and CO2), simulating varying atmospheric compositions. Reaction products have been analyzed using gas chromatography–mass spectrometry (GC-MS) and high resolution mass spectrometry (Orbitrap) equipped with an electrospray ionization source (ESI-MS). Initial tests were performed on glyceraldehyde, a C₃ sugar and known initiator of the formose reaction, and already revealed reactivity and selective effects emerging through repeated wet-dry cycles. Furthermore, preliminary results indicate a significant difference in product distribution depending on the type of drying gas used. Indeed, flushing with N2 appears to promote basification of the bicarbonate-buffered solution during drying, thereby driving the formation of larger sugars. In contrast, CO2 flushing helps maintain a neutral pH and prevent the onset of alkalinity-driven reactions during the drying process. These findings suggest that, under early Earth surface conditions, drying alone could initiate sugar formation depending on the composition of the early atmosphere.

 

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