5-Methylchrysene structure

In 1979, based on our work on methylchrysenes and on literature data on other methylated PAH, we suggested that the structural requirements favoring tumorigenicity of methylated PAH were a bay region... 

We have described elsewhere the nature of the MI FTIR spectra of PAHs and their derivatives (1, 12, 13, 1J>, 18, 21-24) the following points are especially significant. First, FTIR spectra devoid of rotational structure and having individual bandwidths on the order of 2-7 cm are obtained both for PAHs and for polar derivatives thereof (such as nitrogen heterocycles) These spectra are sufficiently characteristic to enable identification of individual isomers to be made in mixtures [e.g., the six methylchrysenes (12) and the various mono- and dimethyl naphthalenes and biphenyls (24)]. Second, detection limits for individual PAHs can be as low as 50 ng, if special "micro samp ling 1 deposition apparatus is used (23) Third, Beer s law plots typically are linear over 1.5-2 decades in PAH concentration by the complementary use of two different deposition cells, linearity over 3 decades in PAH concentration for Beer s law plots can be approached (23). Finally, for both MI FTIR and MI fluorescence spectrometry, analytical precision of ca. 3-7 % relative standard deviation can be achieved. 

When the determination of a crystal structure is difficult or refinement gives a strangely shaped molecule, it is possible that the molecule is disordered in a site in the crystal. This happens when the available space in the crystal is such as to accommodate two different orientations of the molecule. For example, in the crystal structure of 5-methylchrysene, -one of the two molecules in the asymmetric unit is disordered. It was difficult to solve the crystal structure until the nature of the disorder was realized. In a given site, this disordered molecule may be in one of two possible orientations. In some places in the disordered electron density map, atoms in the two orientations of the disordered molecule are near each other and their positions can be approximated (erroneously) by the use of highly anisotropic temperature parameters. The result is that the anisotropic temperature parameters on refinement do not make any sense until the nature of the disorder is understood. 

There may be more than one molecule in the asymmetric unit. This appears to happen more frequently when the molecules have awkward shapes that do not accommodate well to simple packing principles. An example is provided by the crystal structure of 5-methylchrysene in... 

Zacharias, D. E., Prout, K., Myers, C. B, and Glusker, J. P. (1990) Structure and molecular orbital studies of potentially mutagenic methylchrysenes and their TT-TT electron donor-acceptor complexes, Acta Cryst. B47, 97-107 (1991). 

Several correlations were also found for positions of substitution on the aromatic molecules. 0 methyl-substituted isomers, such as 2- and 3-meth-ylphenanthrene, were more abundant than a-substituted isomers, such as 1- and 4-methylphenanthrene. This trend was observed for the methylna-phthalenes, methylphenanthrenes, and methylchrysenes (II). However, the relative abundances of positions of substitution were not consistent for the methyldibenzothiophenes and methylcarbazoles when compared with the methylphenanthrenes different factors are involved in their production. The methyl-substituted PACs are probably highly related to the alkyl linkages in the original coal structure. For the hydroxy- and amino-substituted PACs, hydrogenation in the SRC II process is an important factor. 

Abbreviations PAH, polycyclic aromatic hydrocarbon DE, diol epoxide PAHDE, polycyclic aromatic hydrocarbon diol epoxide PAHTC, polycyclic aromatic hydrocarbon triol carbocation TC, triol carbocation BaP, benzo[a]pyrene BeP, benzo[e]pyrene BA, benz[a]anthracene DBA, dibenz[a,h]anthracene BcPh, benzo[c)phenanthrene Ch, chrysene MCh, methylchrysene MBA, 7-methyl benz[a]anthracene DMBA, 7,12-dimethyl benz[a]anthracene EBA, 7-ethyl benz[a]anthracene DB(a,l)P, dibenzo[a,l]pyrene MSCR, mechanism-based structure-carcinogenicity relationship PMO, Perturbational molecular orbital method dA, deoxyadenosine dC, deoxycytosine dG, deoxyguanosine MOS, monoxygenase enzyme system EH, epoxide hydrolase enzyme system N2(G), exocyclic nitrogen of guanine C, electrophilic centre of PAHTC K, intercalation constant CD, circular dichroism LD, linear dichroism. 

In studies on the metabolic activation of 5-MeC (Fig. 9), in vitro metabolism was coupled with mutagenicity and carcinogenicity assays. This work illustrates some techniques which may be used to elucidate structure and determine active metabolites. The metabolic activation of 5-MeC was of interest because of its high carcinogenicity and mutagenicity compared with the other methylchrysene isomers (183). In addition, 5-MeC has two dissimilar bay regions available for formation of bay region dihydrodiol epoxides. 

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