Boosted molecular mobility during common chemical reactions

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Active Matter Physics

Background:

• Molecular mobility typically follows Brownian diffusion.
• Chemical reactions often involve energy release that can influence local dynamics.
• Understanding reaction-driven transport is key to controlling nanoscale processes.

Purpose of the Study:

• To investigate if chemical reactions can enhance molecular mobility beyond Brownian diffusion.
• To identify reaction types and conditions that exhibit this phenomenon.
• To explore the implications of reaction-driven transport for active matter.

Main Methods:

• Screening 15 organic chemical reactions.
• Utilizing pulsed-field gradient nuclear magnetic resonance (PFG-NMR) to measure diffusion coefficients.
• Employing microfluidics experiments to observe molecular migration in reaction gradients.

Main Results:

• Significant boosted diffusion observed in catalyzed bimolecular reactions, click chemistry, ring-opening metathesis polymerization, and Sonogashira coupling.
• Lesser boosted diffusion seen in the uncatalyzed Diels-Alder reaction.
• No significant deviation from normal diffusion observed for S_N1 and S_N2 substitution reactions within instrumental limits.
• Microfluidics confirmed uphill migration against diffusivity gradients.

Conclusions:

• Certain chemical reactions can overcome the limitations of Brownian diffusion by releasing energy.
• This reaction-enhanced transport mechanism, termed boosted diffusion, is prominent in catalyzed reactions.
• The phenomenon represents a form of active matter, where microscopic energy consumption drives mechanical motion.