Electronic indices from semi-empirical calculations to identify carcinogenic activity of polycyclic aromatic hydrocarbons (original) (raw)
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Journal of Molecular Structure-theochem, 2001
Recently a new methodology to identify the carcinogenic activity of polycyclic aromatic hydrocarbons (PAHs) was proposed. This methodology named electronic indices methodology (EIM) is based on the use of local density of states (LDOS) calculations. In this work we perform a comparative study of this methodology with principal component analysis (PCA) and arti®cial neural networks (ANN). All the physicochemical descriptors were calculated from the molecular eigenstates/spectra obtained through the well-known semi-empirical method parametric method 3 (PM3). PCA and ANN results show that EIM descriptors are relevant to identify the carcinogenic activity of methylated and non-methylated PAHs. Also, we show that the combined use of these distinct methodologies can be an ef®cient and powerful tool in the structure±activity studies of PAHs or other organic compounds. We have studied 81 methylated and non-methylated PAHs, and our study shows that with the use of these methods it is possible to predict correctly the PAHs' carcinogenic activity with high accuracy (,80%). q
Correlated Electronic States of a Few Polycyclic Aromatic Hydrocarbons: A Computational Study
Journal of Physical Chemistry A, 2019
In recent years Polycyclic Aromatic Hydrocarbons (PAHs) have been studied for their electronic properties as they are viewed as nanodots of graphene. They have also been of interest as functional molecules for applications such as light emitting diodes and solar cells. Since last few years varying structural and chemical properties corresponding to the size and geometry of these molecules have been studied both theoretically and experimentally. In this paper, we carry out a systematic study of the electronic states of several PAHs using the Pariser-Parr-Pople model which incorporates long-range electron correlations. In all the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than one-half of the singlet-singlet gap in all cases and hence none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states which include bond orders and spin densities (in triplets) of these systems.
Chemico-Biological Interactions, 1979
In the contexjt of the bay region hypothesis for polycyclic aromatic: hydrocarbon (PAY) carcinogenesis, molecular properties were calculated for seventeen polycyclic aromatic hydrocarbons related to (1) intrinsic substrate reactivities towards activating and detoxifying metabolism and (2) the &abilities of the putative carbocation ultimate carcinogens. All-valence electron methods were used, avoiding the inherent difficulties found in the n-electron methods. The calculated substrate reactivities were found to predict major metabolites successfully, suppo.rting the validity of their use in attempted correlations with observed carcinogenic potencies. Positive correlations were found between observed carcinogenic potencies and (1) the reactivities of the parent polycyclic aromatic hydrocarbons towards the initial distal bay region epoxidation and (2) the stabilities of the diol epoxide carbocations. The reactivities: of the distal bay region dihydrodiols toward; an adjacent epoxidation, leading to bay region diol epoxides, were high for both carcinogenic and non-carcinogenic compounds!, implying that the second epoxidation does not determine relative carcinogenic activity. Support for a possible alternative hypothesis, that polycyclic aromatic hydrocarbons are activated by one electron oxidation, was also found.
Chemosphere, 2003
Multivariate characterization of 60 polycyclic aromatic hydrocarbons (PAHs) was performed using data from literature and semi-empirical molecular orbital calculations. This dataset was analyzed by principal component analysis and projections to latent structures by means of partial least square. The PAHs were found to distribute in the chemical domain in several groups mainly governed by the number of aromatic rings and the number of five-membered rings. The multivariate model and training set was used to predict GC retention times on a non-polar column (DB-5). Using a 2 4 experimental design on the principal components of the chemical characterization model, a test set of PAHs was selected dependent on the distribution in the chemical domain of the PAHs. Such a test set is expected to improve selection of PAHs for future testing and modeling of both biological and chemical responses. Although the model of GC retention times was good, the precision was however not good enough for practical use.
Chemical Physics, 2011
Homologous classes of Polycyclic Aromatic Hydrocarbons (PAHs) in their crystalline state are among the most promising materials for organic opto-electronics. Following previous works on oligoacenes we present a systematic comparative study of the electronic, optical, and transport properties of oligoacenes, phenacenes, circumacenes, and oligorylenes. Using density functional theory (DFT) and timedependent DFT we computed: (i) electron affinities and first ionization energies; (ii) quasiparticle correction to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap; (iii) molecular reorganization energies; (iv) electronic absorption spectra of neutral and ±1 charged systems. The excitonic effects are estimated by comparing the optical gap and the quasiparticle corrected HOMO-LUMO energy gap. For each molecular property computed, general trends as a function of molecular size and charge state are discussed. Overall, we find that circumacenes have the best transport properties, displaying a steeper decrease of the molecular reorganization energy at increasing sizes, while oligorylenes are much more efficient in absorbing low-energy photons in comparison to the other classes.
Spectroscopic properties of polycyclic aromatic compounds
Analytica Chimica Acta, 1993
BIBLIOGRAPHY iv 16. Molecular structures of PAH6 benzenoids AK-AV 17. Molecular structures of PAH6 benzenoids AW-BF 18. Molecular structures of PAH6 benzenoids derivatives A-L 19. Molecular structures of PAH6 benzenoids derivatives M-X 20. Molecular structures of PAH6 benzenoids derivatives Y-AC 21. Molecular structure of cyclopenta-PAH derivatives .... 22. Molecular structures of acenaphthylene derivatives .... 23. Molecular structures of acephenanthrylene derivatives .... 24. Molecular structures of fluoranthenoids and fluorenoids A-J. 25. Molecular structures of fluoranthenoids and fluorenoids K-Q. 26. Molecular structures of fluoranthenoid derivatives A-H 27. Molecular structures of fluoranthenoid derivatives I-P 28. Molecular structures of PAOHs and PASHs xii 65 66 76 77 78 79 pose significant health concerns due to the fact that many are known or suspected carcinogens and/or mutagens (2-10). Polycyclic aromatic compounds "are formed from the incomplete combustion of fossil fuels, tobacco products, food, and virtually any organic matter" (2). They can be found in coal, coal tars, and coal liquid factions as well as many of the refined coal products (11-13). For example, PAHs are found in automobile exhaust fumes, coal-powered factories and heating facilities' stack emissions, cigarette smoke, diesel fuels, motor oils, lubricating compounds, and even in our streams, lakes, and rivers (2, 11-13). They are priority pollutants due to the significant human exposure (2). These compounds are associated with the causes of such buzz-words as "acid-rain", "fly-ash", and tumors/cancer. For the most part, the toxicity of PACs is well characterized or easily predicted by structure activity analysis. "From the standpoint of structure activity analysis, PAHs represent an intriguing class of compounds for experimental investigation because seemingly small changes in the chemical structure can markedly affect carcinogenic activity" (2). According to Ashwood-Smith, Mitchell, and Kennedy, internal substitution on PAHs can completely alter the carcinogenic activity (4). For example, benzo[a]pyrene is one of the most studied PAH carcinogens, but by internally substituting methyl groups on the 10jb and 10c position the carcinogenic activity was completely eliminated (substitution by hydrogen atoms in this case yield an unstable compound) (4, 14). One can also add hydrogen atoms to the perimeter C=C double bonds. Such partially hydrogenated PAHs are obtained by a catalytic hydrocracking process used in the conversion of crude oil to gasoline (13). The reduction products are not very different in molecular size, although they may differ in shape, from the parent hydrocarbon and from each other. Several reduction products have been prepared in the past and have been shown either to be inactive or much less active than the parent hydrocarbons (7). For example, 7,8,9,10-tetrahydrobenzo[a]pyrene (7) is inactive; whereas, benzo[a]pyrene is a notorious carcinogen. One new technique being used to determine the reactivity of carcinogens with target DNA molecules is molecular dosimetry (15). Cancer researchers are using molecular dosimetry to measure the potency of carcinogens and determining if there are threshold levels of exposure. "This technique measures the chemical reactivity of a potential carcinogen, mutagen, or other genotoxin with a host 'target molecule' generally DNA....Molecular dosimetry may simplify animal studies-it may even shorten them by helping direct their focus on the most likely agents-but ultimately, it's not likely to replace them" (15). Large databases of known experimental mutagenic and carcinogenic properties have been developed for many PACs;
The aromaticity and local-aromaticity of a large set of polycyclic aromatic hydrocarbons (PAHs) is studied using multicenter delocalization indices from generalized population analysis and the popular nucleus independent chemical shift (NICS) index. A method for the fast computation of the NICS values is introduced, using the so-called pseudo-π-method. A detailed examination is made of the multidimensional nature of aromaticity. The lack of a good correlation between the NICS and the multicenter delocalization indices is reported and the grounds discussed. It is shown through a thorough statistical analysis that the NICS values arise not only from local aromaticity of the benzenoid rings, but also from other circuits. It is shown that the NICS indices do not reveal the individual aromatic nature of a specific ring, contrary to the delocalization indices.
Chemical Physics Letters, 2008
Electronic polarizability (a) is a property involved in environmental mechanisms through intermolecular interactions. Recent semiempirical PM6 method has been employed to determine a values of a series of 40 polycyclic aromatic hydrocarbons (PAHs) and of some fullerenes. PM6 results are superior to those obtained with AM1 and PM3 levels, reproducing experimental a values of some fullerenes and PAHs within 6%, and high-level correlated CCSD/Sadlej-pVTZ a values of some oligoacenes within 2-7 a.u.
Chemical Physics, 1993
In order to preselect possible candidates for the origin of diffuse interstellar bands observed, semiempirical quantum mechanical method INDO/S was applied to the optical spectra of neutral, cationic, and anionic states of naphthalene and its hydrogen abstraction and addition derivatives. Comparison with experiment shows that the spectra of naphthalene and its ions were reliably predicted. The configuration interaction calculations with single-electron excitations provided reasonable excited state wavefunctions compared to ab initio calculations that included higher excitations. The degree of similarity of the predicted spectra of the hydrogen abstraction and derivatives to those of naphthalene and ions depends largely on the similarity of the a electron contigurations. For the hydrogen addition derivatives, very little resemblance of the predicted spectra to naphthalene was found because of the disruption of the aromatic conjugation system. The relevance ofthese calculations to astrophysical issues is discussed within the context of these polycyclic aromatic hydrocarbon models. Comparing the calculated electronic energies to the diffuse interstellar bands (DIBs), a list of possible candidates of naphthalene derivatives is established which provides selected candidates for a definitive test through laboratory studies.