Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems

Area of Science:

• Physical Chemistry
• Spectroscopy
• Molecular Chirality

Background:

• Chirality is a fundamental molecular property crucial in chemistry and biology.
• Probing molecular chirality in isotropic solutions presents unique challenges.
• Existing techniques like circular dichroism (CD) offer valuable but sometimes limited insights.

Purpose of the Study:

• To introduce and validate optically active sum frequency generation (OA-SFG) for probing molecular chirality.
• To investigate the chiral perturbations on achiral chromophores in amino acids using OA-SFG.
• To compare the capabilities of OA-SFG with traditional CD spectroscopy.

Main Methods:

• Utilized amino acids as model systems to study molecular chirality.
• Employed optically active sum frequency generation (OA-SFG) spectroscopy.
• Analyzed the extrachromophoric chiral perturbation on the carboxyl chromophore.

Main Results:

• Demonstrated OA-SFG's ability to probe chirality in molecules with chiral centers and achiral chromophores in solution.
• Observed that OA-SFG signals, like CD, arise from chiral perturbations near electronic resonance.
• Found variations in OA-SFG and CD strengths across different amino acids, linked to perturbation details.

Conclusions:

• OA-SFG is a novel and effective technique for investigating molecular chirality in solution.
• The study provides a deeper understanding of how chiral environments influence molecular spectroscopy.
• OA-SFG offers complementary information to CD spectroscopy for chiral analysis.