Mixed-micelle system

LJ Naylor, V Bakatselou, JB Dressman. Comparison of the mechanism of dissolution of hydrocortisone in simple and mixed micelle systems. Pharm Res 10 865-870, 1993. 

Recently, Rubingh ll) and Scamehorn et al. (9) have shown that the activity coefficients obtained by fitting the mixture CMC data can be correlated by assuming the mixed micelle to be a regular solution. This model proposed by Rubingh for binary mixtures has been extended to include multicomponent surfactant mixtures by Holland and Rubingh (10). Based on this concept Kamrath and Frances (11) have made extensive calculations for mixed micelle systems. 

The need -for a simple. universal method o-f measuring individual monomer activities in mixed micelle systems is the most pressing problem in this -field o-f research and deserves substantial attention. 

ULTRASONIC RELAXATION STUDY OF FAST EXCHANGE PROCESSES IN MIXED MICELLE SYSTEMS OF ALCOHOL-DECYLTRIMETHYLAMMONIUM BROMIDE-WATER... 

This study is a continuation of our previous investigations, in which the aggregation phenomena of surfactant molecules (amphiphiles) in aqueous media to form micelles above the critical micelle concentration (c.m.c.) has been described based on different physical methods (11-15). In the current literature, the number of studies where mixed micelles have been investigated is scarcer than for pure micelles (i.e., mono-component). Further, in this study we report various themodynamlc data on the mixed micelle system, e.g., ci H25soi4Na (NaDDS) and sodium deoxycholate (NaDOC), enthalpy of micelle formation (by calorimetry), and aggregation number and second virial coefficient (by membrane osmometry) (1 6). 

In all the measurements carried out in this study, for different ratios of NaDDS NaDOC, the dilution curves (Figure 1) of surfactant solution exhibited a clear break that corresponded with the c.m.c. as determined by other methods. This observation agrees with literature reports (1-11,18). The present data, however, show for the first time that mixed micelle systems also behave the same way as pure micellar systems, as measured by calorimetry. Further, because the aggregation number, N, of NaDDS Is much larger than that of NaDOC (16), Table I, the variation of enthalpy around the c.m.c. region is not related to the size of micelles. 

In addition to membrane-bound PLAiS, mammals have cytosolic PLAjS. Cytosolic PLAi activities have been studied in various tissues including heart, brain and testis. PA-PLAi has been purified from brain [45] and testes [39, 46]. Like other lipolytic enzymes, PLAi is affected by the assay conditions. Using a mixed micelle system Glomset and his colleagues [46] found that a 110 kDa enzyme from testes preferentially hydrolyzed phosphatidic acid. They cloned the PA-PLAi from bovine [16]. This PLAi lacks sequence similarity to type I PLAi, lysophospholipase, LCAT, and triacylglycerol lipases. 

In a Triton X-lOO-mixed micelle system, the activity of PA-PLAi against PA was 4-to lO-fold greater than the activities of PA-PI A, against PI, PS, PE, and PC [39]. The enzyme hydrolyzed diunsaturated molecular species of PA (dioleoyl PA and diarachidonoyl PA) in preference to l-pabnitoyl-2-oleoyl PA and l-stearoyl-2-ara-chidonoyl PA, in the same system. The substrate specificity of this enzyme varied according to the assay condition [39], as was also found by Nakajima et al. and Uchiyama et al. [18, 49]. In the absence of Triton X-100, PE was the best substrate for PA-PLAi [49]. Interestingly, hepatic hpase showed a substrate preference for PA and PS in the presence of Triton X-100 [50]. Further studies are needed to identify the real substrates within cells and in vivo. 

Naylor LJ, Bakatselou V, and Dressman JB. Comparison of the Mechanism of Dissolution of Hydrocortisone in Simple and Mixed Micelle Systems. Pharmaceutical Res 1993 10 865-870. 

TABLE 15.3. Retention factor (as log k) as a fnnction of McGown volnme for alkyl benzene and alkyl phenyl ketone homologons series in mixed micelle systems LDS/LPFOS... 

In one study, polyHis/PEG micelles were prepared at pH 8.0 via dialysis. DOX-encapsulated polyHis/PEG micelles, however, showed relative instability at pH 7.4. To overcome this limitation, a mixed micelle system composed of polyHis/PEG (75 wt%) and PLLA/PEG-folate (25 wt%) was prepared. The incorporation of a nonionizable block copolymer (PLLA/PEG) in the micellar structure of polyHis/PEG endowed it with improved stability at pH 7.4 due to... 

In summary, the relative activities of various antioxidants vary widely according to the site of action in different systems, the charge and solubility of components in micelle compared to emulsions, liposome systems and solutions (Table 10.16). The interfacial behavior of antioxidants varies between bulk oil and different colloidal lipid systems. For example, polar antioxidants such as Trolox are more active in mixed micelle systems consisting of emulsifiers and free fatty acids than in corn oil-in-water emulsions, where they partition mainly in the water phase (see next Section). Although linoleic acid is commonly used... 

Lo C-L, Lin S-J, Tsai FI-C, Chan W-H, Tsai C-H, Cheng C-HD, Hsiue G-H (2009) Mixed micelle systems formed from critical micelle concentration and temperature-sensitive diblock copolymers for doxorubicin delivery. Biomaterials 30(23-24) 3961-3970. doi 10.1016/j. biomaterials.2009.04.002... 

Hobson, R. A. Grieser, K Healy, T. W. Surface potential measurements in mixed micelle systems. J. Phys. Chem. 1994, 98, 274-278. 

Lake [117] used kinetic dialysis to examine the existence of cdc. The cdc of the sodium decanoate-sodium perfluorooctanoate mixed-micelle system was found to occur at a specific surfactant concentration and mole fraction. Ben Ghoulam et al. [118] determined the demixing diagram of the Neos Ftergent (a branched alkylbenzenesulfonate by surface tensiometry) and measured second critical micelle concentrations. However, a critical demicellization concentration was not observed. 

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