Solubilization, hydrophobic organic compounds

Humic and fulvic adds are ill-defined and heterogeneous mixtures of naturally-occurring organic molecules that possess surface active properties The molecules that comprise this mixture are also known to form aggregates of colloidal dimensions Humic and fulvic adds are shown to be able to solubilize hydrophobic organic compounds (HOC) in a manner that is consistent with known, micelle-forming surfactants, but not at organic carbon concentrations that are environmentally relevant In addition, it is found that some HOCs are not solubilized to the same extent as other HOCs Some implications of the micellar nature of humic materials are briefly discussed ... 

Because aqueous micelles have a hydrophobic core they can, in effect, act as a second, nonaqueous phase in a system and greatly enhance the apparent water solubility of relatively insoluble hydrophobic organic compounds (HOC). Because this solubility enhancement is only observed at, or after, the onset of micelle formation, it is a criterion for identifying the formation of a micelle (3). The coincidence of the onset of a constant surface tension and the abrupt solubilization of a HCX is a definitive test for micelle formation. 

Ongoing research is investigating mechanisms of nonionic surfactant sorption onto soil, nonionic surfactant solubilization of hydrophobic organic compounds (HOCs) from soil, and microbial degradation of HOCs in soil-aqueous systems with nonionic surfactants. The equilibrium solubilization of HOC from soil can be described by a physicochemical model with parameters obtained from independent experiments. The microbial degradation of phenanthrene in soil-aqueous systems is inhibited by addition of alkyl ethoxylate, alkylphenyl ethoxylate, and Tween-type surfactants at doses that result in micellization and solubilization of phenanthrene from soil. 

Sites contaminated by chlorinated pesticides (e.g. dichlorodiphenyltrichloroethane (DDT), aldrin, dieldrin, and endrin) and herbicides (e.g. atrazine, molinate and bentazone) due to agricultural activities and accidental spills have received little attention (Chapters 11 and 12). These contaminants are nonpolar in characteristics and sorb strongly to the soil. Similar to other hydrophobic organic compounds, desorption using solubilizing agents such as surfactants and cosolvents as well as... 

The above has led to the identification of five areas of research needed that, eventually, advanced the usage of surfactants in soil and more so aquifer remediation (1) solubilization of hydrophobic organic compounds, (2) mobilization of hydrophobic organic compounds, (3) modification of colloidal stability, (4) immobilization of hydrophobic organic compounds, and (5) alteration of the matrix formation permeability. 

The most useful characteristic of the micelle arises from its inner (alkyl chain) part (Figure 3.17). The inner part consists of alkyl groups that are closely packed. It is known that these clusters behave as liquid paraffin (Cn H2n+2). The alkyl chains are thus not fully extended. Hence, one would expect that this inner hydrophobic part of the micelle should exhibit properties that are common to alkanes, such as ability to solubilize all kinds of water-insoluble organic compounds. The solute enters the alkyl core of the micelle and it swells. Equilibrium is reached when the ratio between moles soluteimoles detergent is reached corresponding to the thermodynamic value. 

Phospholipids, when dispersed in water, may exhibit self-assembly properties (either as micellar self-assembly aggregates or larger structures). This may lead to aggregates that are called liposomes or vesicles. Liposomes are structures that are empty cells and that are currently being used by some industries. They are microscopic vesicles or containers formed by the membrane alone, and are widely used in the pharmaceutical and cosmetic fields because it is possible to insert chemicals inside them. Liposomes may also be used solubilize (in its hydrophobic part) hydro-phobic chemicals (water-insoluble organic compounds) such as oily substances so that they can be dispersed in an aqueous medium by virtue of the hydrophilic properties of the liposomes (in the alkyl region). 

The solubility of an organic compound in a micelle depends on the surfactant structure and chemical properties, micelle geometry, ionic strength and composition, temperature, and solute structure and properties. Almgren M.A. et al. (1979) and Jafvert C.T. (1991) have shown that for hydrophobic compounds solubilized within micelles, a Poisson distribution is obeyed that is the solubilization of one molecule does not affect the solubilization of another. Solubilization of compounds generally is initiated at the cmc and is proportional to the surfactant concentration beyond this point. Kile D.E. and Chiou... 

It is also noteworthy that micelle-forming surfactants may solubilize organic compounds sometimes in a very low concentration of the surfactant (still above the CMC). This embedding depends on the charge of surfactant and the charge of reactant. Only hydrophobic reactants may permeate into the hydrophobic core. Important for good solubilization properties is the hydrophile-lipophile balance (HLB) of the surfactant because sufficient water-solubility is required [12] (cf. Sec-... 

The length of surfactant side chain determines dimensions of the hydrophobic domain and consequently unit cell of a liquid crystal. Pores of different diameter can be obtained by changing surfactant size. This initially allowed MCM-41 pore adjustment from about 20 A up to 50-60 A. Further expansion was possible based on another phenomenon, i.e. micelle swelling by solubilized organic compounds. MCM-41 with pores up to 120 A was obtained with mesitylene as an auxiliary organic (expander) in a hexadecyltrimethylammonium tcmplated preparation [4]. Triblock copolymers were found to afford hexagonal structure, SBA-15, with a pore diameter up to 300 A [33]. Pore dimensions can also be tailored by adjusting the synthesis temperature and post-synthesis treatment with amines 118]. 

In samples with hydrophobic compounds, enumeration of SRB and general anaerobic bacteria (GAnB) may be compromised because of the low solubilization of these compounds in the culture medium. The study of the influence of surfactants in the SRB and GAnB estimation in oil samples may become an alternative to improve the MPN method under these conditions. Surfactants are organic compounds that present both a hydrophobic part and a hydrophilic part in the same molecule. This hydrophilic part allows surlaclants to be soluble in water, whereas the hydrophobic part causes them to concentrate at interfaces [4]. 

One single property of micelles is more important than any other they solubilize organic compounds in water. A single sodium dodecyl sulfate (SDS) micelle, for example, dissolves up to 40 benzene molecules or a single porphyrin molecule or one hydrophobized AT pair (Fig. 2.5.4). Very often micelles made of long-chain sulfonates are chosen as solubilizers instead of the natural carboxy-lates, because carboxylates tend to precipitate with bivalent metal and ammonium counterions. Sulfonate micelles are much more hydrated and remain, for... 

In aqueous solution, this copolymer adopts a pseudo-micellar conformation, i.e. the macromolecules form hydrophobic microdomains capable of solubilizing organic compounds that are sparingly soluble in water. Table 14.1 presents typical systems explored in this work. 

This relationship resulted from the spontaneous tendency for the analyte, initially solubilized in an aqueous matrix, to partition into the surface monolayer of hydrophobic octadecyl- or octyl-bonded silica. Organic compounds as analytes will have a unique value for the thermodynamic distribution constant. One fundamental difference between LEE and SPE stands out Partition or adsorption of solute molecules onto a solid surface follows the principles of the Eangmuir adsorption isotherm, whereas EEE does not. We will briefly develop the principles below. This model assumes that an analyte A combines with a site of adsorption, S, in which there is a finite number of such sites according to... 

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