Experimental and theoretical studies of nitrated polycyclic aromatic hydrocarbons

 
 
 
 

Experimental and theoretical studies of nitrated polycyclic aromatic hydrocarbons

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Title: Experimental and theoretical studies of nitrated polycyclic aromatic hydrocarbons
Author: Onchoke, Kefa Karimu
Description: Experimental and theoretical methods were used to study the structure, and spectroscopic properties of carcinogenic nitrated polycyclic aromatic hydrocarbons Structure-function and structure-spectroscopy correlations were examined. Initial investigations focused on the relationships between the orientation of the nitro group relative to the plane of the aromatic ring, vis-à-vis known mutagenic effects. Synthesis of specific isomers of nitro-PAHs and elucidation of their crystal structure is required to establish the validity of the structure-function relationships. Such studies are scarce. Fortunately, electronic structure calculations can be readily done. We used density functional theory calculations to predict structures of 1-, 2-nitronaphthalenes, 1-, 2-, 9-nitroanthracenes, 1-, 2-, 3-, 4-, 9-nitrophenanthrenes, 1-, 2-, 4-nitropyrenes, 6-nitrochrysene, 1-, 3- and 6-nitrobenzo[a]pyrenes. In accord with other studies, we showed that the mutagenic ability of one nitro-PAH isomer over another in the same ring may be predicted from its dihedral angle. However, 1-, 2- and 4-nitropyrene with calculated C-C-N-O angles of ~23°, 0° and 26°, respectively, presented contradictory results. We suggest that the nitrated pyrenes undergo different enzymatic reduction routes when interlocking to enzymes. For further insights into structure-function and structure-spectroscopy correlations, 1-, 3-, and 6-nitrobenzo[a]pyrene were synthesized. Detailed infrared and Raman spectroscopic data of BaP, and its three mononitrated isomers are provided for the first time. By utilizing B3LYP/6-311+G**, the molecular geometries and the vibrational spectra was calculated. Good agreement between calculated and experimental geometry for BaP was noted, and predictions of the vibrational data for all compounds were within ~5 cm-1 of the experimental data. νsNO2/νasNO2 assignments are proposed. The geometrical distortions of the BaP structure upon nitro group substitution and correlations between structural parameters and vibrational data, and structure-function relationships related to the mutagenicity are discussed. The profound influence and electronic effects of the nitro group was shown to correlate to quantum yield (Φf) trends. Nitro-PAHs whose nitro group was non-planar to the aromatic plane exhibited higher quantum yields, and showed absorption bands similar to the parent PAH. UV-Vis absorption bands of the singlet excitation states were assigned via TDDFT, and the πPAH ring→π*PAH ring excitations mainly predominated in nitro-PAHs with a non-planar nitro group.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=osu1143220534
http://hdl.handle.net/2374.OX/107114
Date: 2006

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