Signaling by sulfur-containing molecules. Quantitative aspects

Area of Science:

• Biochemistry
• Chemical Thermodynamics
• Bioinorganic Chemistry

Background:

• Sulfur-containing molecules are of interest for potential roles in biological signaling.
• Understanding the thermodynamic stability of these compounds is crucial for elucidating their function.

Purpose of the Study:

• To compile and estimate thermodynamic data for sulfur-containing molecules.
• To construct a Frost diagram at pH 7 to visualize redox potentials.
• To assess the thermodynamic feasibility of various sulfur compound reactions relevant to biological systems.

Main Methods:

• Collection of standard Gibbs energies of formation and electrode potentials.
• Estimation of missing thermodynamic data with high confidence.
• Construction of a Frost diagram at pH 7.

Main Results:

• The electrode potential for the RSS/RSS^- couple at pH 7 is +0.68 V.
• S₂^- is thermodynamically unstable, disproportionating into HSS^- and S₂.
• Most polysulfur compounds, except RSSR, are unstable and tend to form S_8(s).
• Formation of RSS^- from RSSR and HS^- is nearly thermoneutral.
• Formation of HNO from HS^- and SNO^- or RSNO is unfavorable.
• In vivo formation of SSNO^- is kinetically unlikely.

Conclusions:

• Sulfur compounds exhibit varying thermodynamic stabilities, with many polysulfur species prone to disproportionation.
• Specific redox potentials and reaction energetics provide insights into the potential biological roles and transformations of sulfur molecules.
• While many sulfur compounds are unstable, reactions like RSS^- formation are energetically accessible, suggesting potential signaling pathways.