Solubilization of aromatic hydrocarbons

The relation between the extent of solubilization and the structures of solubi-lizate and surfactant-polymer complex is not completely clear. Aromatic hydrocarbons appear to be more highly solubilized than aliphatic hydrocarbons by complexes of anionic surfactants and hydrophilic polymers with no proton-donating groups, such as polyvinylpyrrolidone, but the nature of the forces involved is not clear. Some cationic surfactant-polymer complexes are broken by the solubilization of aromatic hydrocarbons. It has been suggested that structural compatibility between solubilizate and polymer may be a factor and that the function of the surfactant is to increase the hydrophilic character of the polymer and to promote contact between polymer and solubilizate (Saito, 1967). 

In previous studies, the solubilization of hydrophobic organic contaminants using surfactants has been shown to increase the rate of contaminant desorption from soil to water (Deitsch and Smith 1995 Yeom et al. 1995 Tiehm et al. 1997). A 3,000 mg/L solution of Triton X-100 (CMC = 140 mg/L) increased the rate of desorption of laboratory-contaminated TCE from a peat soil (Deitsch and Smith 1995). However, the solubilization effect was secondary compared to the surfactant s effect on the desorption rate coefficient. Yeom et al (1995) developed a model that satisfactorily predicted the extent of polycyclic aromatic hydrocarbon solubilization from a coal tar-contaminated soil. Only at high surfactant dosages did the model fail to accurately predict the ability of different surfactants to solubilize polycyclic aromatic hydrocarbons. It was hypothesized that mass-transfer limitations encountered by the polycyclic aromatic hydrocarbons in the soil caused the observed differences between the data and the model simulations. In another study (Tiehm et al. 1997), two nonionic surfactants, Arkopal N-300 and Saogenat T-300, increased the rate of polycyclic aromatic hydrocarbon desorption from a field-contaminated soil. The primary mechanism for the enhanced desorption of polycyclic aromatic hydrocarbons was attributed to surfactant solubilization of the polycyclic aromatic hydrocarbons. 

While various techniques, such as stopped flow, have been used to follow substrate kinetics, many kinetic measurements have involved the photophysical properties of solubilized probes. Because of the luminescent properties of their excited states, the aromatic hydrocarbons provide opportunities for monitoring movement of such probes across the micelle boundary. For example, long-lived phosphorescence of aromatic hydrocarbons has been monitored in micellar solutions containing ionic quenchers that themselves are repelled by the surfactant head groups. Since quenching must take place in the aqueous phase, phosphorescence lifetimes may be interpreted to provide rate constants for exit of the probe from the micelle. Some typical values obtained by this technique are given in Table III. Fluorescence data have also been used to obtain such information. 

The triplet state has received rather less attention than the singlet in micellar photochemistry. Phosphorescent decay of solubilized polynuclear aromatic hydrocarbons from their Tj state may be observed in heavy-metal ion lauryl sulphate micelles. This involves a conventional intersystem crossing from Si- Ti promoted by spin-orbit coupling with the heavy atom. 1-Bromonaphthalene readily forms a triplet excited-state in micelles, which may be quenched by added sodium nitrite in water, the lifetime then being reduced from 2.8 x 10 s to 5 x 10 s. There is efficient triplet energy transfer from N-methylphenothiazine (Ti) to trans-stilbene (So), which is irreversible but reversible energy-transfer to naphthalene (So) occurs. ... 

Bohon has used ultraviolet to determine the solubility of aromatic hydrocarbons in water and Howick has similarly determined the solubility of some amine tetra-phenylboron compounds. Riegelman et al. used ultraviolet spectra to show different modes of solubilization concerned with micelles. 

Barone, G., Crescenzi, V., Liquori, A.M., Quadrifoglio, F. (1967) Solubilization of polycyclic aromatic hydrocarbons in poly(meth-acrylic acid) aqueous solutions. J. Phys. Chem. 71, 2341-2345. 

Edwards, D.A., Euthy, R.G., and Eiu, Z. Solubilization of polycyclic aromatic hydrocarbons in micellar nonionic surfactant solutions. Environ. Scl. Technol, 25(1) 127-133, 1991. 

A combined effect of natural organic matter and surfactants on the apparent solubility of polycyclic aromatic hydrocarbons (PAHs) is reported in the paper of Cho et al. (2002). Kinetic studies were conducted to compare solubilization of hydro-phobic contaminants such as naphthalene, phenanthrene, and pyrene into distilled water and aqueous solutions containing natural organic matter (NOM) and sodium dodecyl sulfate (SDS) surfactant. The results obtained after 72hr equilibration are reproduced in Fig. 8.19. The apparent solubility of the three contaminants was higher in SDS and NOM solutions than the solubility of these compounds in distilled water. When a combined SDS-NOM aqueous solution was used, the apparent solubility of naphthalene, phenanthrene, and pyrene was lower than in the NOM-aqueous solution. 

The physical properties of many macrocyclic polyethers and their salt complexes have been already described. - Dibenzo-18-crown-6 polyether is useful for the preparation of sharpmelting salt complexes. Dicyclohexyl-18-crown-6 polyether has the convenient property of solubilizing sodium and potassium salts in aprotic solvents, as exemplified by the formation of a toluene solution of the potassium hydroxide complex (Note 13). Crystals of potassium permanganate, potassium Lbutoxide, and potassium palladium(II) tetrachloride (PdClj + KCl) can be made to dissolve in liquid aromatic hydrocarbons merely by adding dicyclohexyl-18-crown-6 polyether. The solubilizing power of the saturated macrocyclic polyethers permits ionic reactions to occur in aprotic media. It is expected that this [)ropcrty will find practical use in catalysis, enhancement of... 

Liu, Z Laha, S. Luthy, R. G. (1991). Surfactant solubilization of polycyclic aromatic hydrocarbon compounds insoil-water suspensions. WaterScienceandTechnology, 23,475-85. 

Aliphatic hydrocarbon solutes are primarily solubilized within the hydrocarbon core region of the surfactant micelles. Solubilization isotherms (activity coefLcient versus mole fraction, X) for these hydrophobic solutes exhibit curves that decrease from relatively large values at inLnite dilution to lower values as X increases toward unity (Figure 12.6). The aromatic hydrocarbons are intermediate in behavior between highly polar solutes, which are anchored in the micelle surface region, and aliphatic hydrocarbons, which preferentially solubilize in the hydrocarbon core region (Kondo et al., 1993). 

Yeom, I T., Ghosh, M.M., and Cox, C.D. (1996). Kinetic aspects of surfactant solubilization of soil-bound polycyclic aromatic hydrocarbons. Environ. Sci. Technol., 30, 1589-1595. 

It may be expected that other, highly structured solvents with a tri-dimensional network of strong hydrogen bonds, would also permit micelle formation by surfactants, but little evidence of such occurrences has been reported. On the other hand, surfactants in non-polar solvents, aliphatic or aromatic hydrocarbons and halocarbons tend to form so-called inverted micelles, but these aggregate in a stepwise manner rather than all at once to a definite average size. In these inverted micelles, formed, e.g., by long-chain alkylammonium salts or dinonyl-naphthalene sulfonates, the hydrophilic heads are oriented towards the interior, the alkyl chains, tails, towards the exterior of the micelles (Shinoda 1978). Water and hydrophilic solutes may be solubilized in these inverted micelles in nonpolar solvents, such as hydrocarbons. 

School the interaction corresponds only to the formation of a colloidal suspension of hydrocarbon particles, stabilized to some extent by DNA. This situation diminishes the significance of such an interaction for carcinogenesis. On the other hand, it does not touch upon the reality of the solubilization of hydrocarbons by free purines and upon the significance of the factors considered as being involved in this phenomenon. Generally speaking, the possibility exists that the nature of the interaction of the aromatic hydrocarbons with the nucleic acids is quite different from the nature of their interaction with the free constituents of these acids. Such a situation has been recently brought into evidence for actinomycin (Reich, E., Science 143, 684 (1964) Pullman, B. Biochim. Biophys. Acta 88, 140 (1964).)... 

Zheng, Z. Obbard, J. P. (2002). Polycyclic aromatic hydrocarbon removal from soil by surfactant solubilization and Phanerochaete chrysosporium oxidation. Journal of Environmental Quality, 31, 1842-7. 

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