Sulfur Analogs of the Core Formose Cycle: A Free Energy Map

Area of Science:

• Astrochemistry
• Biochemistry
• Organic Chemistry

Background:

• The formose reaction is a complex process for producing sugars from formaldehyde (CH₂O).
• Understanding its control mechanisms is crucial for prebiotic chemistry and synthetic biology.
• Uncontrolled formose reactions can lead to complex mixtures and low yields.

Purpose of the Study:

• To investigate the potential of hydrogen sulfide (H₂S) to regulate the formose reaction.
• To map the free energy landscape of sulfur-containing analogs in the formose reaction core cycle.
• To identify specific reaction pathways influenced by sulfur incorporation.

Main Methods:

• Computational chemistry methods were employed to analyze reaction thermodynamics and kinetics.
• Free energy maps were generated for sulfur analogs of key intermediates.
• The influence of H₂S on reaction pathways and side reactions was modeled.

Main Results:

• Mercaptoaldehyde, a sulfur analog, acts as a key C2 species, favoring kinetically certain aldol additions and enolizations.
• Thione formation is thermodynamically less favorable than aldehyde/ketone formation but linked via enolization.
• Sulfur incorporation can thermodynamically favor retroaldol transformations and select specific pathways.
• Cannizzaro side reactions are disfavored kinetically and thermodynamically with abundant H₂S.

Conclusions:

• Hydrogen sulfide (H₂S) can indeed modulate the formose reaction, steering it towards specific pathways.
• Sulfur analogs influence the reaction's kinetic and thermodynamic profiles.
• H₂S abundance suppresses unfavorable side reactions, offering a potential control mechanism for sugar synthesis.