Pyrene solubility dependence

On the low density side of these traces (below pr = 1), the rise in WIm (as one approaches a reduced density of unity) is a result of pyrene continually being solubilized by the fluid (Figure 5). This observation is consistent with Johnston s report of pyrene solubility in CO2 (17). Again, recall that excimer formation is a generally believed (10,11) to be a bimolecular process, i.e., the rate is concentration dependent. Thus, because the actual analytical concentration of solubilized pyrene in the solution is lower due to solubility, the amount (fraction) of excimer is "artificially" lower. Thus, in the low density region (pr = 0.5 -0.8) the observed trends are simply a result of solubility effects. However, solubility does not help to explain the results seen over the remainder (pr = 0.8 - 1.8) of the density range investigated. 

Skin is also important as an occupational exposure route. Lipid-soluble solvents often penetrate the skin, especially as a liquid. Not only solvents, but also many pesticides are, in fact, preferentially absorbed into the body through the skin. The ease of penetration depends on the molecular size of the compound, and the characteristics of the skin, in addition to the lipid solubility and polarity of the compounds. Absorption of chemicals is especially effective in such areas of the skin as the face and scrotum. Even though solid materials do not usually readily penetrate the skin, there are exceptions (e.g., benzo(Lt)pyrene and chlorophenols) to this rule. 

Fig. 3. I) Solubility of pentane and hexane in PMA aqueous solution. Dependence of the ratio K between excess hydrocarbon sokubility in PMA solution (with respect to water) anf PMA concentration (expressed in equivAt) on the degree of neutralization a [from reference (12)]. II) Dependence of K values (see above) for pyrene, P, and 3—4 benzpyrene, 3—4 BP, respectively in PMA aqueous solution, on the degree of neutralization a [from reference (13)]...

More work with other aromatic compounds will be necessary to verify this conclusion. However, the results for anthracene certainly suggest that the results obtained in the reaction are strongly dependent upon the aromatic substrate. The results obtained thus far also suggest that the reduction and subsequent alkylation of large polycyclic molecules, e.g., compounds such as pyrene, are not the most critical factors for the formation of soluble alkylation products. Studies of the molecular weight distributions and spectroscopic properties of the alkylation products obtained with different metals and different electron transfer agents are underway to resolve this issue. 

Occupational studies provide evidence that inhaled PAHs are absorbed by humans. Animal studies also show that pulmonary absorption of benzo[a]pyrene occurs and may be influenced by carrier particles and solubility of the vehicle however, the extent of absorption is not known. Absorption of benzo[a]pyrene following ingestion is low in humans, while oral absorption in animals varies among the PAH compounds depending on the lipophilicity. Oral absorption increases with more lipophilic compounds or in the presence of oils in the gastrointestinal tract. Percutaneous absorption of PAHs appears to be rapid for both humans and animals, but the extent of absorption is variable among... 

Section 2.2.1.1 highlighted how the vibrational fine structure of pyrene, when dispersed under relatively dilute conditions, in the absence of excimer formation, can be used to reveal the pH-dependent response of PMAA. An alternative approach has used the occurrence of intermolecular excimer formation between dispersed pyrenyl probes under relatively concentrated conditions to monitor the conformational switch of the polymer [6,71]. When dispersed in PMAA, at concentrations higher than its solubility limit in water, partitioning of the probe between the hydrophobic polymer coil and the aqueous phase results [6,71]. Dependent on the pH of the solution and consequently the conformational state of the polyelectrolyte, the balance between these two distinct populations can be affected. For example, Fig. 2.7 shows the fluorescence emission spectra for the probe l,3-bis(l-pyrenyl)propane (1,3PP) when dispersed in aqueous solutions of PMAA [71]. At low pH, an emission spectrum consistent with that of monomeric unassociated pyrene is observed centered around... 

Figure B-9. Temperature dependence of the aqueous solubility of pyrene...

This method was then applied to study pyrene-sulfonate adsorption and dimerization at the Fl20-1,2-DCE interface [141]. More recently, Nagatani et al. extended their PMF spectroscopy investigation to the study of the adsorption and transfer of free-base, water-soluble porphyrins, namely, cationic meso-tetrakis (N-methylpyridyl) porphyrin (H2TMPyP +) and anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (HTPPS" ) [142]. The PMF response indicated the presence of an adsorption process for all systems, depending on the... 

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