Polycyclic aromatic carbons, comparative

The alteration of hemoprotein(s) P-450 subpopulations in the rat may be observed spectrally, because after treatment of rats with polycyclic aromatic hydrocarbons, the Soret maximum of the carbonmonoxyferrocytochrome complex undergoes a hypsochromic shift from 450 to 448nm (50). This blue shift was not seen with rainbow trout hepatic microsomes (29,30). However, this does not preclude the induction of novel hemoproteins P-450 since (a) the induced hemoprotein(s) maty not differ spectrally from the constitutive enzymes and (b) the induced-hemoprotein may account for only a small proportion of total hemoprotein P-450, and hence its contribution to the position of the Soret maximum of carbon monoxide-treated reduced microsomes may be negligible. The latter suggestion is supported by the work of Bend et al. with the little skate. These workers have shown that hepatic microsomes from 1, 2,3,4-dibenzanthracene treated skates did not exhibit a hypsochromic shift when compared to control microsomes, however, partially purified hemoprotein exhibited an absorbance maxima at 448 nm (51). 

The relative effects of supercitical carbon dioxide density, temperature, extraction cell dimensions (I.D. Length), and cell dead volume on the supercritical fluid extraction (SFE) recoveries of polycyclic aromatic hydrocarbons and methoxychlor from octadecyl sorbents are quantitatively compared. Recoveries correlate directly with the fluid density at constant temperature whereas, the logarithms of the recoveries correlate with the inverse of the extraction temperature at constant density. Decreasing the extraction vessels internal diameter to length ratio and the incorporation of dead volume in the extraction vessel also resulted in increases in SFE recoveries for the system studied. Gas and supercritical fluid chromatographic data proved to be useful predictors of achievable SFE recoveries, but correlations are dependent on SFE experimental variables, including the cell dimensions and dead volume. 

Flame retardants may not only catalyze dehydration of the cellulose to more char and fewer volatiles but also enhance the condensation of the char to form cross-linked and thermally stable polycyclic aromatic structures (60). Cellulose was treated with various additives and then charred at 400 °C. The chars were then oxidized with permanganate see Chapter 13) and the results are in Table IV. The char yield was slightly higher for the sodium chloride-treated sample (17.5%) and substantially more for the sample containing diammonium phosphate (28.9%), as compared to the yield from the untreated sample (15.3%). Furthermore, the increased char formation was accompanied by increased aromaticity, as measured by the amount of the aromatic carbon obtained from the char and the amount obtained from the original cellulose molecules (60). 

Treating a bituminous coal with potassium hydroxide in glycols at 250°C yields a largely soluble product that results from the reduction of polycyclic aromatics and the cleavage of aryl ether linkages. The reduction in aromaticity was demonstrated in two ways. First, the fraction of aromatic carbons ( J of the soluble product, which was determined by NMR, was compared with the of the whole coal determined by fluorination. Secondly, the aromatic acids produced in a selective oxidation of both the product and coal were compared, and evidence for ether cleavage was obtained from the oxidation results. The effects of rank and different protic solvents on the reaction were examined. 

Compared to planar polycyclic aromatic hydrocarbons (PAHs), the curved structure of buckybowls endows them with additional interesting physical properties. For example, a bowl-shaped molecule has a dipole moment and a self complimentary shape that could lead to the formation of polar crystals. Moreover, buckyballs and carbon nanotubes are well known for their (potential) applications as electro-optical organic materials. Studies of buckybowls can provide fundamental information on buckyballs and carbon nanotubes. 

Undoubtedly, future research on SFC will expand its range of applications. While carbon dioxide remains the most widely used SFC eluent, investigations into the physico-chemical properties of other potential eluents should render more predictable separation results and increase the utility of SFC (e.g., 107). Applications to the isolation of natural products may prove uniquely suitable in difficult separations where pressure programming may complement relative adsorption to provide increased resolution. In this connection it is interesting to note a recent report on the use of liquid carbon dioxide as a solvent for TLC under sub-critical conditions for the separation of polycyclic aromatics (290). Resolution of the solute was good, but with a different order of elution compared to the use of hexane as mobile phase. 

---