DODAB surfactant

Riehl et al. also characterized the CL system lucigenin-hydrogen peroxide-A-methylacridone in the presence of different cationic surfactants such as HTAC, S-ClV-dodecyl-A lV-dimethylammonio) propane-1-sulfonate, and DODAB [41], Enhancement factors (ratio between CL intensity in the presence of organized medium and CL intensity in the absence of organized medium) of CL intensity were found of 3.4, 2.5, and 1.6, respectively. The alterations in CL intensity are explained in terms of the effect of the different surfactants on the rate of the reaction and on excitation efficiency. 

Other cationic surfactants such as TTAB, DTAB, DODAB, STAC, CEDAB, and DDDAB have been used in CL reactions with less frequency. Thus, tetradecyltrimethylammonium bromide [TTAB] has been used to increase the sensitivity of the method to determine Fe(II) and total Fe based on the catalytic action of Fe(II) in the oxidation of luminol with hydrogen peroxide in an alkaline medium [47], While other surfactants such as HTAB, hexadecylpiridinium bromide (HPB), Brij-35, and SDS do not enhance the CL intensity, TTAB shows a maximum enhancement at a concentration of 2.7 X 10 2 M (Fig. 11). At the same time it was found that the catalytic effect of Fe(II) is extremely efficient in the presence of citric acid. With regard to the mechanism of the reaction, it is thought that Fe(II) forms an anionic complex with citric acid, being later concentrated on the surface of the TTAB cationic micelle. The complex reacts with the hydrogen peroxide to form hydroxy radical or superoxide ion on the... 

Due to the relatively high viscosity of surfactant vesicle and microemulsion systems (refer to data on DODAB and CTAB/50J BuOH in Table X), their use in HPLC will be limited since lower flow rates would be required which would lengthen the required time for a separation. Additionally, most surfactant vesicular (112) as well as some micellar solutions are optically opaque which limits the wavelength range available for spectroscopic detection unless a postcolumn dilution step is employed (219). 

The problem with using surfactant-modified stationary phases in LC is that the surfactant will usually slowly elute (bleed) from the support thus resulting in different retention behavior of solutes with time. This is why most applications are in the area of GC or GLC. An exciting recent advance has been reported by Okahata, et al (181). Namely, a procedure has been developed for immobilizing a stable surfactant vesicle bilayer as the stationary phase in GC. A bilayer polyion complex composed of DODAB vesicles and sodium poly(styrene sulfonate) was deposited on Uniport HP and its properties as a GC stationary phase evaluated. Unlike previous lipid bilayers which exhibited poor physical stability, the DODAB polyion phase was stable. Additionally, the temperature-retention behavior of test solutes exhibited a phase transition inflection point. The work demonstrates that immobilized surfactant vesicle bilayer stationary phases can be employed in GC separations (181). Further work in this direction will likely lead to many such unique gas chromatographic supports and novel separations. 

Incorporation of monomers with similar characteristics to the hydrophobic tails of the surfactants involved (typically alkane chains of DODAB and DMPC) tends to suppress phase separation somewhat, and results in either multi-polymer bead aggregates (e.g., necklaces) or parachutes containing an elliptical rather than a spherical latex bead. Copolymerization of butyl methacrylate with ethylene glycol dimethacrylate in DODAB vesicles resulted in polymer necklaces where the polymer beads appear randomly dispersed in the vesicle bilayer [15] in contrast to the polymer shells observed by Hotz and Meier [10] for the same reaction in DODAC vesicles. Similarly, polymerization of octadecylacry-late, another straight-chain monomer, in DODAB vesicles produced parachutes with extremely elHpsoidal polymer beads in contrast to the rather spherical beads observed commonly for the polymerization of aromatic monomers such as styrene in DODAB [12]. Presumably these differences are caused by an increased compatibility between the surfactant bilayer and the monomer chosen. 

Polymerization of divinyl benzene in DODAB vesicles also resulted in phase separation where broccoH parachutes were observed [15]. The latex beads in these cases appear as clusters of fuzzy latex particles. Phase separation appears to be sHghtly suppressed by the cross-linking, but the incompatibiUty of the aromatic monomer with the surfactant bilayer apparently dominates the final morphology as phase separation is obvious. Interestingly, when the alkyl chain surfactant is replaced with an aromatic polymerizable one, phase separation is completely suppressed [16]. With the A1 and A2 surfactants illustrated in Fig. 4, German et al. were able to successfully copolymerize styrene and divinyl benzene. The authors concluded that using a polymerizable amphiphile is a prereq-... 

Recently the polymerization of styrene within lamellar and cubic phases of the surfactant DODAB (dioctadecyldimethylammonium bromide) was studied [50]. After polymerization, the polystyrene/water/DODAB system showed the same phase behavior as the binary water/DODAB system, a result suggesting a phase separation during polymerization into a polymer-rich (with M 400,000) and a lyotropic phase. 

Light scattering data reveal that micelles are often spherical at low surfactant concentration. At higher concentrations a transition to rodlike and disclike micelles is observed. Many surfactants depart from this scheme in a manner which is dictated by the molecular KOpeities of the aggregating units. For example, amphiphile molecules with two hydrocarbon chains R and R", such as dioctadecyldimethylammonium bromide DODAB or chloride DODAC as well as the biologically important phosphoglycerides... 

Figure 17. Fluorescence intensity ratio IJI (Jo = intensity in the absence of DODAB) of anthracene and pyrene (both at 0.02 mM) as a function of the molar fraction of DODAB in aqueous mixtures of DODAC and DODAB vesicles. Surfactant concentration 9.6mM.

FIG. 5 Idealized models for CdS-sensitized photoreduction of water in aqueous vesicle suspensions. The vesicles are from (a) DHP (b) DODAC or DODAB (c) polymerized n-Ci5H3iC02(CH2)2N+(CH3)[CH2QH4CH = CH2]Cr (d) DODAC and thiol-functionalized surfactant. (From Refs. 4 and 11-13.)... 

Cationic nanoparticles can also be obtained with cationic surfactants by incorporation during preparation or by incubation in a cationic surfactant. Didodecyldimethylammonium bromide (DMAB), dodecyltri-methylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), dimethyl(dioctyldodecyl)ammonium bromide (DODAB), benzyl-alkonium chloride and cetrimide are widely used as cationic surfactants for this purpose. PLGA nanoparticles which were coated with DMAB were developed for oral delivery of the anticancer drug paclitaxel. This formulation compared with intravenous administration of paclitaxel with cremo-phor showed an equivalent effect with a 50% lower dose of paclitaxel encapsulated in nanoparticles. ... 

The hydrocarbon chain melting in surfactant-based systems may give rise to the formation of liquid crystals or molecular or micellar solutions, depending on concentration. The addition of water to surfactant decreases and the enthalpy associated with the transition. This is probably due to a reduction in the cohesion of the polar headgroup network. The effect is especially strong in transitions from solid to solid plus liquid crystals. In pure dioctadecyldimethylammonium bromide (DODAB), the polar layer melts at 86.5°C with a A// of 130 J/g. The transition temperature decreases as water content increases and disappears at about 75% DODAB. At this point, the gel-liquid crystal transition happens at a temperature that is independent of water content [46]. 

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