Dimethyl dodecylamine oxide

Figure 4. X-ray long spacings of a 69.6% dimethyl-dodecylamine oxide in deuterium oxide solution as a function of temperature (9)...

To provide a specific example, Imae and Ikeda (ref. 479) state that amine oxide is very hydrophilic and can constitute a good polar head group for nonionic surfactants at neutral pH. Dimethyl-dodecylamine oxide was first prepared by Hoh et al. (ref. 494), and its surface-active properties in aqueous solutions were investigated by measurements of surface tension (ref. 495), light scattering (ref. 496-498), and hydrodynamic properties (ref. 499). It was found that dimethyldodecylamine oxide can form only spherical micelles in water and aqueous NaCl solutions, when the micelle concentration is dilute (ref. 496,498). Similarly, the homolog dimethyltetradecylamine oxide forms only spherical micelles in water (ref. 496). 

The exponent b depends also on the polyelectrolyte linear charge density p and on the polyelectrolyte stiffness [130], which make it a nonuniversal characteristic for the used polyelectrolytes. Typically, polyelectrolytes with smaller p reveal a stronger dependence of <7 on The polyelectrolyte-sphere binding affinity was shown to decrease with the polymer persistence length and to increase with the polyelectrolyte linear charge density. Note that for complexation of polyelectrolytes of different p with the spherical dimethyl dodecylamine oxide (DMDAO) micelles, a modified dependence on the critical micelle charge density has been suggested, namely cT(. [128]. 

Aqueous or alcohol solutions of amine oxides are normally obtained by oxidizing tertiary amines with either hydrogen peroxide or a peracid.4 For example, N,N-dimethyldodecyl-amine oxide has been prepared by treating N,N-dimethyl-dodecylamine with aqueous hydrogen peroxide.5 The procedure illustrated in this preparation permits the oxidation of tertiary amines with /-butyl hydroperoxide in organic solvents under relatively anhydrous conditions.6 In this procedure the reaction time is short and the method is as convenient as the use of aqueous hydrogen peroxide or a peracid as the oxidant. Furthermore, isolation of the anhydrous amine oxide is often relatively simple. 

The solubilizing capacity of micelles and microemulsions prepared using the surfactant N,N-dimethyl-dodecylamine-N-oxide (C12AO), and containing either one of two semipolar ethyl ester oils (i.e., EH or EO) for the poorly water soluble, lipophilic steroidal drug, testosterone enanthate, has been determined recently (Barlow, D.J. Lawrence, M.J. Zuberi, T. Zuberi, S. Heenan, R.K. Personal communication, 2005). 

Figure 7.18 shows the adsorption isotherms of aerosol OT (AOT) on alumina and silica from cyclohexane. It can be seen that the anionic surfactant has a greater affinity for the basic oxide than for the acidic oxide. The situation is reversed in the case of the adsorption of the cationic surfactant dimethyl dodecylamine (DDA). DDA adsorbs more on acidic silica than on alumina (Figure 7.19). Calculations based on a plateau adsorption value of about 3x10 mol/m on alumina...

The coalescence of hydrocarbon chains allows the ordered hydration layers to be expelled into the bulk phase, resulting in a considerable net gain in entropy. Indeed, micelle formation is primarily an entropy-driven process the enthalpy of hydrocarbon association is comparatively weak and can even be endothermic (opposing association). As an example, dimethyl-n-dodecylamine oxide (illustrated in Fig. 2) undergoes or free energy change of micellization of AG = —6.2 kcal/mol (a fairly typical value), of which the enthalpic contribution AH = 4-1.1 kcal/mol and the entropic contribution — T A S = -7.9 kcal/mol. 

Well ordered three-dimensional crystals of the RC from Rps. viridis were obtained from RCs solubilized with the detergent N,N-dimethyl-dodecylamine-N-oxide (LDAO) the small amphiphile heptane-l,2,3-triol was an essential additive, and ammonium sulphate was the precipitant in a vapor diffusion experiment /9. The crystals have the symmetry of space group P432i2. The unit cell dimensions are a = b = 223.5 A, c = 113.6 A, with 1 RC molecule per asymmetric unit8,i0 about 70% of the unit cell s volume is occupied by solvent. The crystals diffract X-rays to at least 2.3 A resolution. 

---