Solubilization, hydrophobic organic

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 ... 

Cyclodextrins can solubilize hydrophobic molecules in aqueous media through complex formation (5-8). A nonpolar species prefers the protective environment of the CDx cavity to the hulk aqueous solvent. In addition, cyclodextrins create a degree of structural rigidity and molecular organization for the included species. As a result of these characteristics, these macrocycles are used in studies of fluorescence and phosphorescence enhancement (9-11), stereoselective catalysis (.12,13), and reverse-phase chromatographic separations of structurally similar molecules (14,15). These same complexing abilities make cyclodextrins useful in solvent extraction. 

SIAX is a hydrophobic reagent that should penetrate membrane structures with good efficiency. The crosslinker must be solubilized in organic solvent (DMF or DMSO) prior to transferring a small amount to an aqueous reaction medium. 

One inherent property of peptides that interact with membranes is that self-association or even aggregation will interfere with solubilization by organic solvents or micelles. The preparation, purification and sample preparation of extremely hydrophobic (often transmembrane) peptides is nontrivial and has been addressed by only a few papers [74—79]. 

The catalytic principle of micelles as depicted in Fig. 6.2, is based on the ability to solubilize hydrophobic compounds in the miceUar interior so the micelles can act as reaction vessels on a nanometer scale, as so-called nanoreactors [14, 15]. The catalytic complex is also solubihzed in the hydrophobic part of the micellar core or even bound to it Thus, the substrate (S) and the catalyst (C) are enclosed in an appropriate environment In contrast to biphasic catalysis no transport of the organic starting material to the active catalyst species is necessary and therefore no transport limitation of the reaction wiU be observed. As a consequence, the conversion of very hydrophobic substrates in pure water is feasible and aU the advantages mentioned above, which are associated with the use of water as medium, are given. Often there is an even higher reaction rate observed in miceUar catalysis than in conventional monophasic catalytic systems because of the smaller reaction volume of the miceUar reactor and the higher reactant concentration, respectively. This enhanced reactivity of encapsulated substrates is generally described as micellar catalysis [16, 17]. Due to the similarity to enzyme catalysis, micelle and enzyme catalysis have sometimes been correlated in literature [18]. 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

Properties of surfactant and cosolvent additives affect the rate of apparent solubilization of organic contaminants in aqueous solutions and may serve as a tool in remediation of subsurface water polluted by NAPLs. Cosolvents (synthetic or natural) are organic solutes present in sufficient quantities in the subsurface water to render the aqueous phase more hydrophobic. Surfactants allow NAPLs to partition into the... 

Thayumanavan s group reported dendrimers containing polar and apolar groups at every repeat unit that inverts from a normal to inverted micellar-type conformation going from aqueous to organic media (Fig. 11.9 Basu et al. 2004 Aathimanikandan et al. 2005 Klaikherd et al. 2006). This solvent-sensitive conformational behavior affords a unique capability to solubilize hydrophobic molecules in water and hydrophilhc molecules in lipophilic media. 

Equilibrium constants for the binding between substrates and micelles — Reaction (G) — generally range from 103 to 106 for hydrophobic organic substrates. Furthermore, they are expected to increase as the hydrophobic character of the substrate increases. Figure 8.10b shows that this effect sometimes overshoots optimum solubilization. The figure shows, on a... 

Organized media including micellar solutions and cyclodextrins (CDs) have been the subject of continuous interest. These media are able to solubilize hydrophobic compounds in water and modify significantly their physicochemical properties. 

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. 

Micellar solutions have also been used as media for organic reactions. Reactions in micellar solutions have much in common with reactions in microemulsions but the capability to solubilize hydrophobic components is much smaller in micellar solutions than in microemulsions. Micellar solutions are therefore of limited value for preparative purposes. For both systems separation of the surfactant from the product may constitute a work-up problem. 

We have developed an oil-in-water and bicontinuous microemulsion inkjet ink composition comprising a solubilized hydrophobic dye which forms nanoparticles ("pigment-like") upon application on a substrate surface. The concept was demonstrated for direct patterning of water-insoluble organic molecules in the form of nanoparticles. The method is based on formation of thermodynamically stable oil-in-water microemulsions, in which volatile "oil" contains the dissolved organic molecules. As schematically illustrated in Fig. 3, the microemulsion droplets are converted into organic nanoparticles upon impact with the substrate surface due to evaporation of the volatile solvent. 

Additional substances (buffer additives) are often added to the buffer solution to alter selectivity and/or to improve efficiency, and the wall of the capillary may be treated to reduce adsorptive interactions with solute species. Organic solvents, surfactants, urea and chiral selectors are among the many additives that have been recommended (table 4-24). Many alter or even reverse the EOF by affecting the surface charge on the capillary wall, whilst some help to solubilize hydrophobic solutes, form ion-pairs, or minimize solute adsorption on the capillary wall. Chiral selectors enable racemic mixtures to be separated by differential interactions with the two enantiomers which affects their electrophoretic mobilities. Deactivation of the capillary wall to improve efficiency by minimizing internet ions. with solute species can be achieved by permanent chemical modification such as silylaytion or the... 

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. 

Organic Solvents May increase solubility at low levels Solubilize hydrophobic residues Protein denaturation... 

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