Polyaromatic system

Complexation with polyaromatic systems has also been observed. For instance, Mlnaphthalenelj, M = Cr (88,183), Mo (183), V (183), or Ti (183) may be synthesized in a solution reactor with the appropriate, metal vapors at liquid-nitrogen temperature. The Cr/naphthalene complex is less stable (dec. 160°C) than CrtCsH ) (m.p. 283-284° C). In fact, the naphthalene ligand is sufficiently labile to allow reaction under mild conditions, to afford CrL (L = CO or Bu NC), or Cr(naphth)Ls [L = PFj, P(OMe)3, or PMea]. The Mo, V, and Ti species are equally reactive. Analogous 1-methylnaphthalene complexes were also isolated (183). In addition, the complexes shown in Fig. 38 were synthesized by reaction, at the temperature of liquid nitrogen, of Cr atoms with 1,4-diphenylbutane (35, 201, 202). Analogous complexes were formed with 1,5-diphenylbutane (202). 

Although they are superb for achieving planarity and rigidity, polyaromatic systems may come accompanied with the risk of a side-effect—carcinogenicity. Such rigid. 

Because of the presence of the cyclic four-membered amide connected to the multicyclic ring systems, an effort to define their mechanism of action would be highly important. Despite a number of synthetic efforts, a relatively small amount of research had been focused on the use of compounds related to PAHs as anticancer agents. Bair et al. [152, 153] reported a close correlation between antitumor activity and the shape of the polyaromatic system. However, his group did not make a definitive correlation between the ability of these compounds to bind to deoxyribonucleic acid (DNA) and their cytotoxic activity. Bair s group developed... 

Face-capping arene compounds, in Ru-Os clusters bonding, 6, 827 polyaromatic systems, 6, 827 properties, 6, 825... 

Polyarenes, iron-containing compounds, 6, 326 Polyaromatic systems... 

A free-radical hydrogen transfer mechanism is proposed that may lead to rapid H-exchange in polyaromatic systems. 

A wide variety of fluorinated aromatic and polyaromatic systems are accessible via the BS synthesis, such as 11, 13, 16, and 18-21 presented earlier. Other examples are fluorinated mesitylenes,43 several polyfluorinated benzenes,44, 4-chloro-2-fluoronitro-benzene,4S bromofluorotoluenes,46 7-fluoroindanone, 8 fluorinated polycyclic aromatic hydrocarbons,17,47 4-tritylfluorobenzene,48 fluorinated diaryl thioethers, fluorophenols,50 fluoronorepinephrines, fluorinated estrogens,19,S2 and an unusual metacyclophane.53 A selection of these compounds is shown here. 

Many aromatic systems have been oxidized by Fremy s salt, including phenols, naphthols, anilines, quinolines, indoles, carbazoles, and polyaromatic systems. The review articles by Zimmer and Parker can be consulted for specific examples. Slight modifications of the mechanism presented in Scheme 20 explain the oxidation of most of these classes of compounds [63], Oxidations by Fremy s salt and related nitroxides have been used in the total synthesis of several biologically active compounds [64], Recent examples can be found in the syntheses of the antitumor antibiotic streptonigrone (34), the antitumor agent EO-9 (35), the anti-rheumatic agent epoxyquinomicin B (36), and the antineoplastic agent makaluvamine C (37) (Scheme 21) [65]. 

The long-term stability of natural polymers can be assessed from geological samples (Table 3). Besides aromatic ring structures of lignin and tannin, the polyaromatic systems of steranes... 

In polyaromatic systems, the single bonds between aromatic cycles allow for interannular rotations that may limit the orbital overlap of Tr-electrons along the conjugated backbone and hence contribute to Eg by a quantity On the other hand, the aromatic resonance energy of the cycle tends to... 

Direct resolution by HPLC is performed using sdica gel stationary phases coated with optically active tetranitrofluorenyhdene (TAPA) derivatives. This is a peculiar method for polyaromatic systems, in that it is based on... 

The Elbs reaction provides rapid access to polyaromatic systems, particularly due to the ease of preparing many substrates for the reaction. When the Elbs reaction proceeds smoothly, it may provide the best known means to synthesize a certain substrate. For example, 3-methylcholanthrene and derivatives have been shown to be potent carcinogenic agents. The reaction has been used to prepare several methylcholantlu ene analogues and other polyaromatic species, the products were isolated and tested in carcinogenic studies to probe characteristics of polyaromatics as potential carcinogenic... 

Updated art on polyaromatic systems showing localized double bond structures and not coincident aromatic rings. 

Fluorescence spectroscopy showed a large red shift after the reaction to obtain 33. This shift indicated the increase of conjugation in the structure due to the formation of a planar and fused polyaromatic system. 

As clearly described in paper I and in refs.3 and 14-17 SI has been defined empirically and rigorously (from MO calculations on the excited state of short oligomers [94]) for polyacetylene. These concepts have been extrapolated for the case of polyaromatic systems thus making possible to defineas a linear combination of the chemical internal coordinates R associated with the stretching of the C-C and C=C bonds. 

Fig.2 Sketch of the total evergy vs. the coordinate for a few polyaromatic systems.

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