Surfactants complexes with aromatic compound

Complex Formation of Surfactants with Aromatic Compounds and their Pharmaceutical Applications... 

In the previous section, only the complexes comprising aromatic compounds without hetero rings were analysed. A variety of aromatic compounds with a hetero ring also form complexes with cationic surfactants. In this section, five kinds of complex crystal structures are discussed. 

Complex Formation of Anionic Surfactants with Aromatic Compounds [54]... 

In the above sections, the surfactant molecules are cationic. However, there are many anionic and nonionic surfactants. The anionic surfactants, such as sodium dodecyl sulfate (SDS), were reported to form a micelle in an aqueous solution with aromatic compounds [75]. Although much spectroscopic work has been conducted, the micelle structure is still unclear [76]. We tried to obtain crystals of the representative complexes suitable for X-ray work. After many trials, the single crystals were obtained from an aqueous methanol solution for the complex formed between the anionic surfactant, sodium octyl sulfate (SOS), and the aromatic compound, 2-naphthol. 

Sfiica impregnated with saturated and unsaturated hydrocarbons (squalene, paraffin oil), silicone and plant oils, complexing agents (silver ions, boric add and borates, unsaturated and aromatic compounds), tigands (EDTA, digitonin), and transition metal salts silanized silica gel impregnated with anionic and cationic surfactants Cross-linked, polymeric dextran gels (Sephadex)... 

So different types of pesticides, i.e., carbamates [47, 48], chloro-phenoxyacetic acids [49], phenyl- and sulfonylureas [50-54], halogenated triazines [46], as well as non-ionic surfactants [55], polycyclic aromatic hydrocarbons (PAH) [56-58] and polar pharmaceutical compounds [59] were determined. This technique first used a steel wire which later was substituted by a Kapton ribbon. However, it was soon replaced by the particle-beam interface, because the complex mechanical device led to considerable difficulties with the endless, continuously moving belt... 

Electron microscopy showed that gigantic rod-like micelles were formed in viscoelastic solutions in the presence of several aromatic compounds as shown in Figure 4.1(a) [48-50]. It was very surprising that single crystals, mixed with the gigantic micelles, were found to co-exist in these viscoelastic solutions, as shown in Figure 4.1(b) [51]. From the aqueous solution composed of hexadecyltrimethylammonium bromide and several phenolic derivatives, similar crystalline materials were obtained. These were assumed to be complexes composed of the surfactant and the respective phenolic derivative based on elementary and thermal analyses [52]. The crystal structiu e was analysed by X-rays and a variety of complexes with similar structures were obtained [53]. 

In the previous sections, all described complexes were formed between the aromatic compounds and surfactant molecules which have alkyl groups with even-number carbon atoms, such as hexadecyl, tetradecyl, dodecyl and decyl groups. These even-carbon-chain surfactants are utilized widely in vitro and are commercially available. However, there are several odd-carbon-chain fatty acids in vivo, although most fatty acids have even-carbon chains. The former acids are digested in the rumen of ruminants. The odd-carbon-chain surfactants were synthesized from the corresponding odd-carbon-chain fatty acids [56-58]. Two kinds of surfactant molecules with alkyl groups of odd-number carbon atoms, pentadecyl- and tridecyltrimethylammonium bromides (PTAB and TTAB, respectively), were prepared and their complexes with biphenyl were formed. The crystals were obtained from aqueous solutions. 

Figure 4.20 shows the crystal structures of CTAB itself viewed along the b- and a-axes [59]. The structure also has the characteristics of the complexes described above except that it contains no aromatic compound. A flat sheet composed of CTAs and the bromide anions is formed. When CTAB makes a complex with an aromatic compound, the anti-parallel alkyl groups of the neighbouring surfactant molecules slide in opposite... 

Complex formation only by grinding a mixture in a mortar was examined for a variety of combinations of the surfactant and aromatic compounds. The CTAB, MTAB, LTAB and DTAB surfactants were selected along with hydrophilic aromatic compounds containing hydroxyl, carboxyl and imino groups, and hydrophobic aromatic compounds such as acridine, anthracene, biphenyl and phenanthrene. Table 4.2 shows the results of the complex formation, in which the letters A, B and C mean that the complex was formed completely, partly and hardly, respectively. (The asterisk indicates that the single crystals have been analysed by X-rays). It is clear that ... 

Table 4.3 Ratio of complex formation obatined by mixing and grinding the component crystals of aromatic compounds with heteroatoms and the cationic surfactants. The ratios were calculated using the peak heights of the low-angle diffractions of their X-ray powder patterns...

Such C-H... Tt interactions play an important role in the complex formation between the aromatic compounds with hydrogen donor groups and surfactant molecules. Figure 4.30 shows the molecular structures in the CTAB-o-iodophenol complex, V, where the strong hydrogen bond formed between the hydroxyl group and the... 

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