Octanol, surfactants

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

The influence of the presence of alcohols on the CMC is also well known. In 1943 Miles and Shedlovsky [117] studied the effect of dodecanol on the surface tension of solutions of sodium dodecyl sulfate detecting a significant decrease of the surface tension and a displacement of the CMC toward lower surfactant concentrations. Schwuger studied the influence of different alcohols, such as hexanol, octanol, and decanol, on the surface tension of sodium hexa-decyl sulfate [118]. The effect of dodecyl alcohol on the surface tension, CMC, and adsorption behavior of sodium dodecyl sulfate was studied in detail by Batina et al. [119]. 

By small-angle neutron scattering experiments on water/AOT/hydrocarbon microemulsions containing various additives, the change of the radius of the miceUar core with the addition of small quantities of additives has been investigated. The results are consistent with a model in which amphiphilic molecules such as benzyl alcohol and octanol are preferentially adsorbed into the water/surfactant interfacial region, decreasing the micellar radius, whereas toluene remains predominantly in the bulk hydrocarbon phase. The effect of n-alcohols on the stability of microemulsions has also been reported [119],... 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Potential differences between the nitrobenzene and aqueous phases at the interfaces in the presence [Fig. 2(B)] and absence of surfactant (C) were measured simultaneously. KCl salt bridges were inserted into the octanol phase to monitor potential. Oscillation measurement data across the nitrobenzene membrane are given in Fig. 2(A) for comparison. The oscillation mode in Fig. 2(C) is virtually the same as that in (A) with respect to oscillatory period and amplitude but quite different with that in (B). Although the potential across the nitrobenzene membrane (A) was not recorded simultaneously with that between nitrobenzene-water phases (B) and (C) but successively, it was noted that the algebraic sum of (B) and (C) should be essentially the same as (A). This is an indication that potential oscillation across the nitrobenzene membrane is likely generated at the interface between the nitrobenzene phase and aqueous phase initially containing no surfactant. 

FIG. 6 Electrical potential oscillation across the octanol membrane with sodium dodecyl sulfate as surfactant (A) and between octanol and aqueous phases (B and C). All data were obtained using the inverted U-shaped cell (al) water, (a2) 8mM sodium dodecyl sulfate and 5M ethanol, (b) octanol containing 8mM tetrabutylammonium chloride, (c) Ag/AgCl electrode, (d) KCl salt bridge, and (e) saturated KCl. (Ref. 26.)... 

To clarify the relation between potential oscillation and features of interface o/wl, potential oscillation at the interface was measured in the presence of inorganic and organic electrolytes in phase wl, and potential oscillations in the octanol membrane system were compared with interfacial potential between octanol and aqueous solutions of a two-phase octanol-water system with and without surfactant [27]. Figure 8 shows potential oscilla-... 

To monitor the movement of surfactant ions in the octanol membrane visually, electrical potential oscillation across the octanol membrane was measured with eriochrome black T (EBT) as colored surfactant in phase w2 [20]. Migration of EBT from interface o/w2 toward bulk phase o could be seen during the induction period of oscillation. After EBT reached interface o/wl, the first pulse of oscillation started. Thus, surfactant ions at interface o/wl are indispensable for oscillation. Considerable convection in phase o and... 

It follows from the above that the mechanism for electrical potential oscillation across the octanol membrane in the presence of SDS would most likely be as follows dodecyl sulfate ions diffuse into the octanol phase (State I). Ethanol in phase w2 must be available for the transfer energy of DS ions from phase w2 to phase o to decrease and thus, facilitates the transfer of DS ions across this interface. DS ions reach interface o/wl (State II) and are adsorbed on it. When surfactant concentration at the interface reaches a critical value, a surfactant layer is formed at the interface (State III), whereupon, potential at interface o/wl suddenly shifts to more negative values, corresponding to the lower potential of oscillation. With change in interfacial tension of the interface, the transfer and adsorption of surfactant ions is facilitated, with consequent fluctuation in interface o/ wl and convection of phases o and wl (State IV). Surfactant concentration at this interface consequently decreased. Potential at interface o/wl thus takes on more positive values, corresponding to the upper potential of oscillation. Potential oscillation is induced by the repetitive formation and destruction of the DS ion layer adsorbed on interface o/wl (States III and IV). This mechanism should also be applicable to oscillation with CTAB. Potential oscillation across the octanol membrane with CTAB is induced by the repetitive formation and destruction of the cetyltrimethylammonium ion layer adsorbed on interface o/wl. Potential oscillation is induced at interface o/wl and thus drugs were previously added to phase wl so as to cause changes in oscillation mode in the present study. 

Figure 7.17 shows the asymmetry ratios of a series of compounds (acids, bases, and neutrals) determined at iso-pH 7.4, under the influence of sink conditions created not by pH, but by anionic surfactant added to the acceptor wells (discuss later in the chapter). The membrane barrier was constructed from 20% soy lecithin in dodecane. All molecules show an upward dependence on lipophilicity, as estimated by octanol-water apparent partition coefficients, log KdaA). The bases are extensively cationic at pH 7.4, as well as being lipophilic, and so display the highest responses to the sink condition. They are driven to interact with the surfactant by both hydrophobic and electrostatic forces. The anionic acids are largely indifferent... 

Figure 7.17 Surfactant-induced sink asymmetry ratio versus octanol-water apparent...

Table 7.23 shows the results for 47 specific PAMPA models tested at pION, according the the scheme in Fig. 7.58. The two columns on the right are the r2 values in the comparisons. The neutral-lipid models (1.0, 1A.0, 2.0, 3.0, and 4.0) at pH 7.4 do not explain the permeability trend indicated in the human jejunal permeabilities [56]. Octanol was least effective, with r2 0.01. This should not be too surprising, since we did note that the appearance of naproxen, ketoprofen, and piroxicam at the top of the HJP ordering was unexpected. Our expectations were based on the octanol-water lipophilicity scale, which clearly does not correlate with the HJP trend. Adding a sink condition to the 2% DOPC model (model 1.1) improves correlation (r1 increases from 0.33 to 0.53). The addition of cholesterol to the 2% DOPC/dodecane system made the model unstable to the surfactant-created sink condition. 

SCHEME 21. A nonionic surfactant prepared by glycosylation of octanol with glucose in the presence of H2S04-Si02. 

The correlation (or lack of correlation) of other physiochemical characteristics has not yet been established. For instance, are all surfactants irritants Can one classify severity by the size of the molecule Can octanol water partition coefficients predict irritation potential does a propensity to partition out of the ocular fluid mean that a compound presents more of an irritation hazard than one which is more water soluble Theoretically, these data should reflect the ability of a compound to penetrate the eye and cause an irreversible lesion. However, until definitive data are available, physical and chemical parameters will probably have limited utility in an overall assessment of irritation. 

The partial racemization of isolated 2-octanol suggests that the hydrolysis may proceed via ionization of optically active substrates as in the Sjjl hydrolysis in homogeneous solution. The hydrolysis via ionization may be suppressed in media with low dielectric constant like micelles (Okamoto and Kinoshita, 1972), resulting in net retention. The ineffectiveness of the stereochemical influence of the CTAB micelle may be interpreted as a consequence of the mutual repulsion of the positively charged head groups of [46] and CTAB, so there is need for molecules of solvent to be incorporated between surfactant head groups (Sukenik et al., 1975). An appreciable increase in retention was also observed in a reversed micellar system (Kinoshita and Okamoto, 1977). 

The host liquid crystalline matrix was composed of water, sodium octanoate and octanol. This combination was chosen in order to create an environment as closely matching the specific requirements of the problem as possible. In the first instance, the surfactant was Identical to the one used for the solubilization determinations (12) and the alcohol was present in order to resemble actual laundering conditions with "oily dirt" molecules present (12). 

In recent studies, Friberg and co-workers (J, 2) showed that the 21 carbon dicarboxylic acid 5(6)-carboxyl-4-hexyl-2-cyclohexene-1-yl octanoic acid (C21-DA, see Figure 1) exhibited hydrotropic or solubilizing properties in the multicomponent system(s) sodium octanoate (decanoate)/n-octanol/C2i-DA aqueous disodium salt solutions. Hydrotropic action was observed in dilute solutions even at concentrations below the critical micelle concentration (CMC) of the alkanoate. Such action was also observed in concentrates containing pure nonionic and anionic surfactants and C21-DA salt. The function of the hydrotrope was to retard formation of a more ordered structure or mesophase (liquid crystalline phase). 

TTAB) as surfactant and diethylether, n-heptane, cyclohexane, chloroform, or octanol as oil phase. Table 5 summarizes the values of N for the test mixtures in microemulsions containing different organic solvents with cationic surfactants. 

The used oils in microemulsion systems are, with rare exception, non-polar and hydrophobic. The hydrophobicity of the oil has a strong influence on the resulting enzyme activity. This was first explained as being due to the interactions of the oil with the surfactants [85]. By now the studies of Laane and co-workers have shown that the solubility of the oil in the water pool has more influence on the enzyme activity independent of the choice of surfactant [4,46]. They established the so called log P -concept to describe the correlation between the hydrophobicity of the oil and the resulting enzyme activity. P is the distribution coefficient of the oil in the mixture of water and 1-octanol. In general, very hydrophilic oils (log P < 2) are not suitable for the enzyme catalysis in microemulsion because the activity and stability of the biocatalysts in these mixtures is... 

The liquids to be studied in this experiment are water, hexane, n-octanol and aqueous solutions of CTAB. It is recommended that they be measured in the order written, where the most critical with respect to contamination is first. The water used should be the best available, such as double distilled, and should be stored in a sealed flask before use. Pure samples of the other liquids should also be used as well as top-quality water to make up the CTAB solutions. The CTAB solutions should be measured at concentrations of 0.01, 0.1, 0.3, 0.6, 1 and 10 mM at a temperature above 21°C. CTAB has a Krafft temperature around 20°C - below this temperature the surfactant will precipitate from aqueous solution at the higher concentrations (see later). 

Micellar and pre-micellar solutions of methanol in triolein were studied with three different surfactant systems using 2-octanol as a co-surfactant. Surfactants evaluated by viscosity, conductivity, density, refractive index and particle size data along with polarizing microscopic examinations were bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate. Data show phase equilibria regions of liquid crystalline phases as well as micellar solutions. All systems were effective for solubilizing methanol in triolein. The order of effectiveness for water tolerance is Tetradecyldimethylammonium linoleate>... 

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