Modeling solubilization

The phase diagram of some oil-solubilizer-water must be measured as a function of temperature in order to test the above approach. For this purpose decane (DEC) was chosen as a typical oil and 2-bu-toxyethanol (BE) as the solubilizer. We thought BE would be a good model solubilizer since the lower critical solution temperature for the BE-H2O system is 49 C this gives a good workable temperature range for our investigation. 

Szekeres, E., Acosta, E., Sabatini, D.A., and HarwelL J.H. 2006 Modeling solubilization of oil mixtures in anionic microemulsions 11. Mixtures of polar and nonpolar oils, J. Colloid Interf. Sci. 294 222-233. 

Surfactants have also been of interest for their ability to support reactions in normally inhospitable environments. Reactions such as hydrolysis, aminolysis, solvolysis, and, in inorganic chemistry, of aquation of complex ions, may be retarded, accelerated, or differently sensitive to catalysts relative to the behavior in ordinary solutions (see Refs. 205 and 206 for reviews). The acid-base chemistry in micellar solutions has been investigated by Drummond and co-workers [207]. A useful model has been the pseudophase model [206-209] in which reactants are either in solution or solubilized in micelles and partition between the two as though two distinct phases were involved. In inverse micelles in nonpolar media, water is concentrated in the micellar core and reactions in the micelle may be greatly accelerated [206, 210]. The confining environment of a solubilized reactant may lead to stereochemical consequences as in photodimerization reactions in micelles [211] or vesicles [212] or in the generation of radical pairs [213]. 

Micelles can solubilize gases. It has been demonstrated [49] that the Laplace model gives a good description of such solubilization for the case of ionic micelles ... 

It is of particular interest to be able to correlate solubility and partitioning with the molecular stmcture of the surfactant and solute. Likes dissolve like is a well-wom plirase that appears applicable, as we see in microemulsion fonnation where reverse micelles solubilize water and nonnal micelles solubilize hydrocarbons. Surfactant interactions, geometrical factors and solute loading produce limitations, however. There appear to be no universal models for solubilization that are readily available and that rest on molecular stmcture. Correlations of homologous solutes in various micellar solutions have been reviewed by Nagarajan [52]. Some examples of solubilization, such as for polycyclic aromatics in dodecyl sulphonate micelles, are driven by hydrophobic... 

Dissolution of 5 could be enhanced in H2O by solid dispersion systems with urea and mannitol (97MI27). A method for solubilizing 5 and 6 at near physiological pH was patented (98EUP856316). Solubility characteristics of 5 was investigated in an in vitro tear model (98MI24). 

In addition to solubilization, entrapment of polymers inside reversed micelles can be achieved by performing in situ suitable polymerization reactions. This methodology has some specific peculiarities, such as easy control of the polymerization degree and synthesis of a distinct variety of polymeric structures. The size and shape of polymers could be modulated by the appropriate selection of the reversed micellar system and of synthesis conditions [31,191]. This kind of control of polymerization could model and/or mimic some aspects of that occurring in biological systems. 

Fig. 10. Mechanisms of steady-slqte kinetics of sugar phosphorylation catalyzed by E-IIs in a non-compartmentalized system. (A) The R. sphaeroides 11 model. The model is based on the kinetic data discussed in the text. Only one kinetic route leads to phosphorylation of fructose. (B) The E. coli ll " model. The model in Fig. 8 was translated into a kinetic scheme that would describe mannitol phosphorylation catalyzed by Il solubilized in detergent. Two kinetic routes lead to phosphorylation of mannitol. Mannitol can bind either to state EPcy, or EPpe,. E represents the complex of SF (soluble factor) and 11 and II in A and B, respectively. EP represents the phosphorylated states of the E-IIs. Subscripts cyt and per denote the orientation of the sugar binding site to the cytoplasm and periplasm, respectively. PEP, phosphoenolpyruvate.

At the present time, "interest in reversed micelles is intense for several reasons. The rates of several types of reactions in apolar solvents are strongly enhanced by certain amphiphiles, and this "micellar catalysis" has been regarded as a model for enzyme activity (. Aside from such "biomimetic" features, rate enhancement by these surfactants may be important for applications in synthetic chemistry. Lastly, the aqueous "pools" solubilized within reversed micelles may be spectrally probed to provide structural information on the otherwise elusive state of water in small clusters. 

In experiments with lowland rice Oiyzci saliva L.) it was found that roots quickly exhausted available sources of P and sub.sequently exploited the acid-soluble pool with small amounts deriving from the alkaline soluble pool (18). More recalcitrant forms of P were not utilized. The zone of net P depletion was 4-6 mm wide and showed accumulation in some P pools giving rather complex concentration profiles in the rhizosphere. Several mechanisms for P solubilization could be invoked in a conceptual model to describe this behavior. However using a mathematical model with independently measured parameters (19), it was shown that it could be accounted for solely by root-induced acidification. The acidification resulted from H" produced during the oxidation of Fe by Oi released from roots into the anaerobic rhizosphere as well as from cation/anion imbalances in ion uptake (18). Rice was shown to depend on root-induced acidification for more than 80% of its P uptake. 

To evaluate the contribution of the SHG active oriented cation complexes to the ISE potential, the SHG responses were analyzed on the basis of a space-charge model [30,31]. This model, which was proposed to explain the permselectivity behavior of electrically neutral ionophore-based liquid membranes, assumes that a space charge region exists at the membrane boundary the primary function of lipophilic ionophores is to solubilize cations in the boundary region of the membrane, whereas hydrophilic counteranions are excluded from the membrane phase. Theoretical treatments of this model reported so far were essentially based on the assumption of a double-diffuse layer at the organic-aqueous solution interface and used a description of the diffuse double layer based on the classical Gouy-Chapman theory [31,34]. 

Thus, in contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of the intestinal carotenoid absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (TC OA supplementation), differentiated Caco-2 cells were able (1) to take up carotenoids at the apical side and to incorporate them into CM and (2) to secrete them at the basolateral side, associated with CM fractions. In this model, no attempt has yet been made to reproduce the in vivo physiochemical conditions occurring in the intestinal lumen, such as carotenoid release from the food matrix and solubilization into mixed lipid micelles. Carotenoids were delivered to Caco-2 cells in aqueous suspension with Tween 40 (During et al., 2002). Using this cell culture system in conjunction with an in vitro... 

The Influence of DNA Structure and Environment on the Intercalation of Hydrocarbon Metabolites and Metabolite Model Compounds. The physical binding of hydrocarbon metabolites to DNA is very sensitive to DNA structure and environment. This is demonstrated by the data in Figures 4 and 5, which show how heat denaturation of DNA inhibits hydrocarbon quenching. These results are consistent with early studies which indicate that the ability of native DNA to solubilize pyrene and BP is much greater than that of denatured DNA (40). 

One approach to the study of solubility is to evaluate the time dependence of the solubilization process, such as is conducted in the dissolution testing of dosage forms [70], In this work, the amount of drug substance that becomes dissolved per unit time under standard conditions is followed. Within the accepted model for pharmaceutical dissolution, the rate-limiting step is the transport of solute away from the interfacial layer at the dissolving solid into the bulk solution. To measure the intrinsic dissolution rate of a drug, the compound is normally compressed into a special die to a condition of zero porosity. The system is immersed into the solvent reservoir, and the concentration monitored as a function of time. Use of this procedure yields a dissolution rate parameter that is intrinsic to the compound under study and that is considered an important parameter in the preformulation process. A critical evaluation of the intrinsic dissolution methodology and interpretation is available [71]. 

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