Solubilization capacity

Most notably, the solubilization capacity of polysoaps is not correlated with their surface activity [78, 343], Thus any combination of these two properties can be realized in polysoaps, even unusual ones such as low surface activity with high solubilization capacity. The phenomenon is not understood, but might be related to different conformations taken at the gas-water interface and in solution (cf. Sect. 6.1), or to cosurfactant effects of the solubilizates. 

As mentioned above, there seems to be no lower limit for solubilization by high molecular weight polysoaps. Thus starting in the origin, the solubilization capacity increases linearly with the concentration for most polysoaps [46-48, 51-53, 78, 112, 113, 153, 196, 253] (Fig. 28). Exceptional cases show a break point with increasing capacity at intermediate concentrations [112, 113, 281] which were attributed to the transition from purely intramolecular aggregation to additionally superposed intermolecular aggregation [281], 

The effects of the polymer geometry and of the nature of the backbone are interdepending. Considering Fig. 29, only a hydrophobic backbone will provide a hydrophobic interior of polymeric micelles for polysoaps of the tail end geometry, whereas only a hydrophilic backbone will provide a favourable polarity profile for polysoaps of the head type . Accordingly, optimized  

When optimized polysoaps bearing the analogous surfactant structure were used, only gradual differences in solubilization capacity were found. More polar solubilizates which are assumed to reside close to the micellar surface are somewhat more efficiently solubilized by polysoaps of tail end geometry. In contrast, solubilisates of amphiphilic structure are somewhat more efficiently solubilized by polysoaps of mid tail geometry. Polysoaps of head geometry fall shorter in both cases [78, 343], Similar comparative studies for pure aromatic compounds and hydrocarbons are not available. The differences observed may be due to the respective positions of the polymer backbones, occupying space which is needed to accomodate the solubilizate. Notably, the results imply that the optimal polysoap structure does not exist, but the systems of choise will depend on the problem adressed. 

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In some systems containing surfactant mixtures, a synergistic effect on the water solubilization capacity has been observed [50]. 

Investigations of the solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems formed with AOT and nonionic surfactants in hydrocarbons emphasized the presence of a maximum solubilization capacity of water, occurring at a certain concentration of NaCl, which is significantly influenced by the solvent used [132],... 

In the process of realizing product quality factors by changing product formulation, the relevant performance indices have to be determined. The determination process in turn requires experience and technical expertise. For detergent products the performance indices need to be considered include (1) optimum hydrophilic-lipophilic balance, HLB0p (2) critical micelle concentration, CMC (3) soil solubilization capacity, S (4) Krafft point,... 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

Soil solubilization capacity, S Soil polarity In general, S is higher for polar soils than for non-polar ones... 

The target HLB can be obtained by using a mixture of anionic surfactant (HLB = 9.4) and nonionic surfactant HLB = 16.7) in the right proportions (1 3.75 based on the formula in Table 3). Such mixing of anionic and nonionic surfactants is expected to lower the individual CMC s and thus an increase of the soil solubilization capacity. The surfactants in the product should be in spherical micelle phase to give a transparent/translucent appearance and small viscosity (Table 6). 

It should be noted that this procedure needs to be carried out on a case-by-case basis—there is no indication that the relative solubilization capacity (ability of bile components or surfactants to enhance solubility/dissolution of a drug) is consistent from drug to drug. Therefore, use of a standard medium containing a synthetic surfactant to correspond to either FaSSIF or FeSSIF results is not possible. 

It appears from a survey of the literature that the essential properties of micelles in nonpolar solvents are understood, namely their stability and variations of size, the dissociation behavior, and their solubilizing capacities. Reverse micelles can dissolve relatively large amounts of water (1-10% w/v depending on emulsion formula) as well as polar solutes and, of course, water-soluble compounds. Consequently, they can be used as media for a number of reactions, including enzyme-catalyzed reactions. Very few attempts to investigate such reverse micelles at subzero temperatures are known, in spite of the fact that hydrocarbon solutions present very low freezing points. 

In most cases the enantiomeric excess (ee) in the presence of the polymerized micelles were higher compared with the monomeric counterpart. The catalytic efficiency is mainly controlled by the solubilization capacity of the amphiphiles. Results however are quite different as can be seen from the data summarized in Tab. 6.6. A major limitation of these polymerized micelles is their low molecular weight that makes it almost impossible to separate them from the products by nanofiltration methods. 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Shen D, Zhang R, Han BX, Dong Y, Wu WZ, Zhang JL, Li JC, Jiang T, Liu ZM (2004) Enhancement of the solubilization capacity of water in Triton X-lOO/cyclohexane/ water system by compressed gases. Chem Eur J 10 5123-5128... 

Nishikido (21) has done a systematic study o-f mixed sur-factant solubilization. In that study, solubilization in mixed systems was compared to that predicted by application o-f a linear mixing rule to the solubilizations in the pure surfactant component micelles. For example, in this "ideal case, a micelle composed of a 50/50 molar mixture of two surfactants would have a solubilization capacity which is an average of that of the two pure surfactants involved. A system showing negative deviation from ideality would have less solubilization than this ideal system a system having positive deviation from ideality would have more. 

Table 1 Comparison of CD Water Solubility and Theoretical Solubilizing Capacity...

Muller and Albers (1991) also reported that the combination of 1,2 propylene glycol ancJSCHP-induced a decrease in the solubilizing capacity ofthe system as compared with 2-HP-p-CD alone. 

Once it is conLrmed that a simple LBDDS provides measurable improvement in bioavailability, the next step is development and optimization of the formulation. Currently there are no deLnitive tests that will translate vitro measures tan vivo performance. At the same time, this does not mean that development of such formulations should be conducted using a trial-and-error approach. Pouton s classiLcation system points out that the factors to be considered in interpreitingvtde behavior of the formulations are effects of lipolysis, dispersibility, and solubilization capacity on dilution. It is important to understand that the balance of each of these effects will depend on the drug being formulated, and that there is unlikely to be a universal formulation that works for all compounds. 

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