Protonation behavior and stability of micelles of N-lauroylaminoalkyl-dimethylamine oxides--effects of added salt concentration and spacer length.

The protonation behavior and the stability of micelles of N-lauroylaminopropyl-N',N'- dimethylamine oxide (C12AmCn; n=3) were studied by the hydrogen ion titration and the equilibrium surface tension measurement. The surface potential of C12AmC3 micelles estimated from the results of hydrogen ion titration was lower than that of dodecyldimethylamine oxide micelles at added NaCl concentration, C(S), of 0.1M. The critical micelle concentration (cmc) estimated from surface tension measurements revealed that a reversal of the stability of the cationic and the nonionic micelles of C12AmC3 takes place in the range of C(S) higher than about 0.2M, that is, the cationic micelles become more stable than the nonionic ones in the range C(S) >or= 0.2M. In addition, the surface tension measurements were carried out for C12AmCn with different spacer length, n, ranging from 2 to 6 methylene units at C(S) = 0.1M. The cmc values of nonionic species were kept at almost constant for n or= 4. The cmc values of cationic species also tended to decrease with n for n >or= 4. These results were compared with those obtained for alkyldimethylamine oxides, and the effect of amide group and spacer groups introduced into amine oxide surfactants was discussed.

Hydrogen ion titration of alkyldimethylamine oxides by 13C and 1H NMR and conventional methods.

In the hydrogen ion titration of micelles, the degree of ionization of the micelle at a given pH has to be evaluated to obtain a pKa value of micelles (Ka being the proton dissociation constant) at the pH. We compared the degree of ionization obtained from 13C and 1H NMR spectra with that obtained from the stoichiometric method. We used dodecyldimethylamine oxide (C12DMAO) and hexyldimethylamine oxide (C6DMAO) to examine the titration behavior of micelles and monomers, respectively. We determined pKa values of amine oxides both in H2O and D2O. As to the monomer (C6DMAO), the degree of ionization from NMR, alpha(NMR), coincided with that from the conventional stoichiometric method alpha. The difference of pK1 of amine oxide monomer between D2O and H2O was about 0.5: pK1(D) approximately pK1(H) + 0.5. The difference was about the same as that for carboxylic acids. As to the C12DMAO micelle, alphaNMR did not coincide with alpha over a considerable range of alpha. The NMR chemical shift might be influenced by micellar structure changes induced by the ionization, such as the sphere-to-rod transition. The intrinsic logarithmic dissociation constants of the micelle were 5.9+/-0.1 for H2O, and 6.5+/-0.1 for D2O.

Mixed micelles containing sodium oleate: the effect of the chain length and the polar head group.

We have investigated the mixing behavior of binary mixtures of the alkylglucosides (CnG) octyl beta-D-glucoside and decyl D-glucoside in combination with sodium oleate (NaOl), and the amine oxide surfactants (AO) N,N-dimethyldodecylamine oxide, N,N-bis (2-hydroxyethyl)dodecylamine oxide, and 3-lauramidopropyl-N,N-dimethylamine oxide in combination with NaOl. From the equilibrium surface tension measurements, the critical micelle concentration (cmc) data were obtained as functions of the composition. Values of the cmc were analyzed according to both the regular solution model developed by Rubingh for mixed micelles and Maeda's formulation for ionic/nonionic mixed micelles. Two interaction parameters, beta and B1, were estimated from the regular solution model and Maeda's formulation, respectively. For NaOl/CnG mixed systems, a decrease in the hydrocarbon chain length of CnG resulted in a stronger interaction with NaOl from both beta and B1 values. For NaOl/AO mixed systems, the bulkiness of a polar head group of AO surfactants influenced the interaction between NaOl and AO. The dynamic surface tension measurements show that all surface tension values of surfactant solutions examined decreased with the time. We found that the time dependence of surface tension values for NaOl mixed systems was greatly influenced by the presence of NaOl rather than the other component.

Superior mesenteric arterial embolism: treatment by trans-catheter thrombo-aspiration.

A 57-year-old woman with hypertension, mixed mitral valve disease, and atrial fibrillation was admitted to our hospital because of abdominal pain continuing for several hours. On the following day, colonoscopy was performed, and diffuse yellow-white pseudomembranous changes were seen in the right hemicolon, but there were no abnormal findings in the left hemicolon; 24 h after onset, a diagnosis of superior mesenteric arterial embolism was made on the computed tomography (CT) scan findings. Abdominal angiography was performed and showed complete occlusion of the superior mesenteric artery (SMA). Then conservative treatment, using per-catheteric thrombus aspiration, was done, followed by intraarterial injection of tissue type plasminogen activator. After the thrombo-aspiration, the filling deficit of the main artery had disappeared, and the branches on the right side were clearly delineated. After the treatment, the symptoms such as abdominal pain and diarrhea improved accordingly. She was discharged from the hospital 27 days later. Our case suggests that trans-catheter thrombo-aspiration is a possible alternative to open embolectomy for some cases of SMA embolism more than 10 h post-onset.