Intermolecular chiral assemblies in R(-) and S(+) 2-butanol detected by microcalorimetry measurements

Area of Science:

• Supramolecular chemistry
• Physical chemistry
• Chirality studies

Background:

• Chiral molecules exhibit enantioselectivity, influencing their interactions in solutions.
• Understanding chiral solvation is crucial for molecular recognition and separation processes.

Purpose of the Study:

• To investigate the supramolecular chiral assemblies of 2-butanol enantiomers in neat form and in isobutanol.
• To quantify the differences in molecular organization and binding energies between R(-) and S(+) 2-butanol.
• To explore the formation of asymmetric solvent envelopes around chiral solutes in organic solvents.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to study the mixing of R(-) and S(+) 2-butanol.
• ITC dilution profiles were analyzed to determine solvent shell composition and binding energetics.
• Comparative analysis of neat enantiomers and their solutions in isobutanol.

Main Results:

• Dilution of R(-) 2-butanol in isobutanol released approximately double the heat compared to S(+) 2-butanol.
• ITC data suggested approximately 100 isobutanol molecules forming chiral solvent envelopes around each 2-butanol enantiomer.
• Mixing neat enantiomers resulted in endothermic ITC profiles, indicating lower supramolecular order and binding energies in racemic mixtures compared to pure enantiomers.

Conclusions:

• Chiral solutes in organic solvents form asymmetric solvent envelopes that differ between enantiomers.
• This study extends the understanding of chiral solvation phenomena beyond aqueous solutions.
• Differences in molecular organization and binding energies were observed between R(-) and S(+) 2-butanol and their racemic mixture.