Scopine Isolated in the Gas Phase.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Organic Chemistry

Background:

• Tropane alkaloids are a class of naturally occurring compounds with significant pharmacological activity.
• Understanding the gas-phase structure and dynamics of alkaloids like scopine is crucial for elucidating their biological interactions.
• Previous studies using conventional heating methods faced challenges with molecular isomerization.

Purpose of the Study:

• To detect and analyze the rotational spectrum of scopine in the gas phase.
• To investigate the conformational stability and structural parameters of scopine.
• To explore a novel method for gas-phase introduction of non-volatile molecules.

Main Methods:

• Fourier transform microwave spectroscopy in a pulsed supersonic jet.
• A nonconventional gas-phase introduction technique involving laser vaporization of a solid mixture (scopine syrup and glycine powder).
• Quantum chemical calculations to predict the most stable conformer.

Main Results:

• The rotational spectrum of scopine was successfully detected, revealing a single, stable conformer.
• Accurate determination of rotational and centrifugal distortion constants.
• Identification of fine and hyperfine structures providing insights into methyl group rotation and ¹⁴N nuclear quadrupole interactions.

Conclusions:

• Laser vaporization is an effective method for preserving the integrity of complex molecules like scopine during gas-phase analysis.
• The study determined the N-methyl inversion angle (131.8-137.8°) and the internal rotation barrier of the methyl group (6.235(1) kJ/mol).
• The observed conformer is the most energetically stable, as supported by theoretical calculations.