Molecular structure of benzo(a)pyrene 4,5-oxide

Area of Science:

• Chemical Crystallography
• Molecular Toxicology
• Organic Chemistry

Background:

• Benzo(a)pyrene (BP) is a potent environmental carcinogen.
• Metabolites of BP, such as BP 4,5-oxide, are implicated in its carcinogenic activity.
• Understanding the molecular geometry of BP metabolites is crucial for elucidating their reactivity and toxicological mechanisms.

Purpose of the Study:

• To determine the precise three-dimensional structure of benzo(a)pyrene 4,5-oxide using X-ray crystallography.
• To investigate how epoxidation of the 4,5-double bond affects the planarity and electronic properties of the benzo(a)pyrene carbon skeleton.
• To compare the structural features of benzo(a)pyrene 4,5-oxide with other K-region epoxides of polycyclic aromatic hydrocarbons.

Main Methods:

• Single-crystal X-ray diffraction analysis was performed on benzo(a)pyrene 4,5-oxide.
• Experimental bond lengths and angles were meticulously measured and analyzed.
• Computational analysis was used to interpret electronic properties and potential reactivity.

Main Results:

• The carbon skeleton of benzo(a)pyrene 4,5-oxide remains largely planar, with minimal perturbation from the epoxide group.
• Epoxidation increased the double bond character of C-11--C-12, C-9--C-10, and C-7--C-8 bonds.
• A weak C-H...O interaction suggests potential acidity at the C-3 position.
• The epoxide ring is symmetrical, with longer C-O bond lengths compared to other epoxides, including that of 7,12-dimethylbenz(a)anthracene-5,6-oxide.

Conclusions:

• The structural study provides detailed geometric information on benzo(a)pyrene 4,5-oxide.
• The epoxide ring in benzo(a)pyrene 4,5-oxide exhibits distinct structural characteristics compared to K-region oxides of other potent carcinogens.
• These structural differences may contribute to variations in the reactivity and biological activity of these carcinogenic metabolites.