Pyrene curvature

The effect of curvature on the aromatic character of polyaromatic hydrocarbons (PAHs) can be studied by comparing planar PAHs and their curved analogues. In order to address this issue a variety of [n](2,7)pyrenophanes (n = 7-10) in which the pyrene (22) moiety is strongly distorted from planarity have been synthesized and studied45. The degree of distortion from planarity and therefore the strain in these systems is controlled by the length and type of the tether that connects the two remote ends (positions 2 and 7) of 22. 

Other oxidants like thallium(III) oxide, vanadium(V) oxyfluoride, palladium ) acetate, and ruthenium(IV) tetrakis(trifluoracetate) have been developed as powerful tools for the intramolecular biaryl coupling reaction [7,93,113]. Nevertheless, DDQ is still one of the most versatile reagents in oxidative coupling reactions (see Scheme 14 and 29 [82,114]). The highly strained dioxa[8](2,7)pyrenophane (65), portraying an overall curvature of nearly 90° for the pyrene subunit, was finally obtained from the mefa-cyclophanediene (66) by dehydrogenation with DDQ in refluxing benzene in 67% yield [114]. 

Table 13. Correlation Coefficients for the Scatter Plots between Aromaticity Indices NICS and HOMA and the Ring Critical Points for a and 7t Framework (pc. Ape, and the Curvature of p. A) for Benzene, Naphthalene, Anthracene, Pyrene, Tetracene, Tiphenylene, Chrysene, Perylene, and Coronene ...

Studies carried out by Incardona et al. (2006), about induction of alterations in zebrafish embryos by PAHs constituted by four aromatic rings, pointed out that chrysene did not show any embryotoxic and teratogenic effect in these embryos. The exposition to benzo[b] anthracene resulted in mortality in all the concentrations between 8 and 10 pM and defects in the development as a failure of head straightening, lack of finfold development and poor cardiac looping with pericardial edema hemorrhage, for concentrations between 2 and 6 pM. The continuous expositions to doses superior to 5 pM of pyrene resulted in systemic toxicity that occurred in the initial phases of the larval development, including dorsal curvature of the body axis, reduction in the peripheral circulation, anemia and pericardial edema. 

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