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Determinants of nucleic acid adduct formation
National Cancer Institute Monograph
|December 1, 1981
Summary
Computational chemistry explains aromatic amine carcinogen reactivity. MINDO/3 and Hückel molecular orbital calculations clarify reaction pathways, challenging previous interpretations of triplet states and predicting DNA adducts.
Area of Science:
- Computational Chemistry
- Chemical Carcinogenesis
- Molecular Orbital Theory
Background:
- N-aryl or N-acetyl-N-arylnitrenium ions are implicated as reactive species in aromatic amine and amide carcinogenicity.
- A unified understanding of the diverse reactions of ultimate carcinogens derived from these species remains elusive.
- Previous experimental data suggested triplet states for certain nitrenium ions, requiring further investigation.
Purpose of the Study:
- To elucidate the reaction mechanisms of three ultimate carcinogens from the aromatic amine class using computational methods.
- To reconcile experimental observations with theoretical predictions regarding nitrenium ion reactivity.
- To provide a coherent explanation for the varied reactions of N-acetoxy-2-fluorenylacetamide (N-AcO-2-FAA) and its interactions with biological macromolecules.
Main Methods:
- Self-consistent field-molecular orbital (MINDO/3) calculations were employed for cations derived from acetoxy-substituted aromatic amines.
- Iterative extended Hückel theory calculations were performed to analyze reaction pathways and electronic properties.
- Electrostatic potential maps and frontier orbital theory were utilized to explain reaction selectivity.
Main Results:
- MINDO/3 calculations indicated that nitrenium ions derived from 3-acetoxyxanthine, N-acetoxy-2-fluorenylacetamide, and N-acetoxy-4-acetamidostilbene are unlikely to exist in a triplet state.
- Extended Hückel theory calculations explained observed reactions, previously interpreted as triplet-state involvement, using hard/soft acid/base theory.
- Computational models successfully predicted major DNA adducts for N-hydroxy-2-naphthylamine, though secondary product predictions require refinement.
Conclusions:
- The study provides a theoretical framework for understanding the reactivity of aromatic amine ultimate carcinogens.
- Computational methods, including Hückel molecular orbital theory, offer valuable insights into carcinogen-DNA interactions.
- Further refinement of theoretical models is necessary for accurate prediction of all reaction products in chemical carcinogenesis.