Electron density analyses of opioids: a comparative study.

Area of Science:

• Chemical Physics
• Crystallography
• Computational Chemistry

Background:

• Understanding electron density distribution is crucial for characterizing molecular properties.
• The Atoms in Molecules (AIM) theory provides a framework for analyzing chemical bonds and atomic properties.
• Experimental validation of theoretical models like AIM is essential for advancing chemical understanding.

Purpose of the Study:

• To experimentally determine and compare electron densities and derived properties for five morphine-related molecules.
• To investigate the transferability of submolecular properties, a key aspect of AIM theory, across chemically similar compounds.
• To analyze topological differences in electron density related to varying chemical environments and molecular states.

Main Methods:

• High-resolution X-ray diffraction experiments using Mo Kalpha and synchrotron radiation at low temperatures.
• Application of Bond Topological Analyses and Bader's zero flux surfaces for partitioning molecules.
• Calculation of atomic volumes and charges, followed by comparison with theoretical computations and prior experimental data.

Main Results:

• Experimental and theoretical properties for chemically equivalent bonds showed excellent agreement, supporting AIM theory's transferability principle.
• Topological differences were observed in regions with distinct chemical environments, highlighting sensitivity to molecular structure.
• Electron density differences were visualized between neutral and protonated naltrexone, particularly around the nitrogen atom.

Conclusions:

• Experimental verification of the transferability of chemically equivalent submolecular properties in morphine-related molecules.
• Confirmation of the validity of the Atoms in Molecules (AIM) theory in an experimental context for this molecular class.
• Demonstration of the ability to experimentally detect and visualize subtle topological differences influenced by chemical environment and charge state.