Anionic surfactants sodium cholate

FIGURE 6.13 (A) Viability of RAW 264.7 macrophages treated with different SLN formulations compared with cells treated with pure medium (100% viability). Viability is related to the total surfactant concentration in the cell culture medium and was quantified by an MTT assay. All SLN contained 10% Dynasan 114 and 1% of different surfactants (the anionic surfactants sodium cholate [NaCh] or lecithin [S75] or the cationic surfactant cetylpyridinium chloride [CPC]). (B) Viability of RAW 264.7 macrophages treated with different surfactant solutions (the anionic surfactants sodium cholate [NaCh] or lecithin [S75] or the cationic cetylpyridinium chloride [CPC]) compared to cells treated with pure medium (100% viability). Viability is related to the total surfactant concentration in the cell culture medium and was quantified by an MTT assay. 

This reaction in DMSO is much faster than that in water, and reaction of an anionic nucleophile in water should be inhibited by an anionic surfactant, e.g., sodium cholate. The evidence is consistent with formation of a complex between substrate and steroid, and it was suggested that the carboxylate group of the cholate ion could act as a nucleophile or general base. 

The solubility of clofazimine was enhanced in aqueous micellar systems, containing both naturally occuring surfactants e.g bile salts, and synthetic surfactants, e.g the non ionic Cremophor EL and Triton XI00, and the anionic sodium dodecyl sulphate. The incorporation of fatty acids to form mixed micelles brought about a further enhancement in drug solubility in the case of naturally occuring surfactants (approximately 300 fold with sodium cholate linoleic acid relative to buffer). In contrast, with synthetic surfactants this enhancement decreased (Fahelelbom et al., 1991 O Driscoll et al., 1991). 

Bile salts are natural and chiral anionic surfactants which form helical micelles of reversed micelle conformation. The first report on enantiomer separation by MEKC using bile salts was the enantioseparation of dansylated DL-amino acids (Dns-o,L-AAs) and, since then, numerous papers have been available. Nonconjugated bile salts, such as sodium cholate (SC) and sodium deoxycholate (SDC), can be used at pH > 5, whereas taurine-conjugated forms, such as sodium taurocholate (STC) and sodium taurodeox-ycholate (STDC), can be used under more acidic conditions (i.e., pH > 3). Several enantiomers, such as diltiazem hydrochloride and related compounds, carboline derivatives, trimetoquinol and related compounds, binaphthyl derivatives, Dhs-dl-AAs, mephenytoin and its metabolites, and 3-hydroxy-l,4-benzodiazepins have been successfully separated by MEKC with bile salts. In general, STDC is considered as the the most effective chiral selector among the bile salts used in MEKC. 

Burman et al. (2014) studied the interaction of a variety of anionic surfactants including sodium dodecyl sulfate (SDS), sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium taurode-oxycholate (NaTDC) with a nonionic polymer of hydroxy propyl cellulose (HPC). They applied the microcalorimetric, conductometric, and fluorimetric methods to study the interactions. Using calorimetric and conductometric techniques, they could obtain some of the solution properties such as the critical aggregation concentration (CAC), critical micelle concentration (CMC), polymer saturation concentration (PSP), and the extent of binding of the surfactants with polymer. They concluded that the hydrophobicity and charge density of surfactant have a strong effect on micelliza-tion. The fluorescence results showed that increasing the surfactant concentration decreased the micro-polarity. 

SDS, an anionic tensioaclive and with single-chain structure, is the surfactant mostly employed in the development of a microonulsion at concentrations in the range between 50 and lOOmM. Selectivity can be modified by mixing SDS with another surfactant like a bile salt (sodium cholate) or polyoxyethylaieglycol ethers [43], Cationic surfactants have been used in MEEKC resulting in the reverse of polarity [19],... 

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