Cationic Cetyltrimethylammonium Chloride Research Articles

Ionization and binding equilibria of papaverine in ionic micelles studied by 1H NMR and optical absorption spectroscopy

The binding of the vasodilator drug papaverine (PAV) to micelles of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS), cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecylsulfate (SDS) in aqueous solution was studied by 1H NMR and electronic absorption spectroscopy. In the presence of HPS or CTAC, the apparent p K a of PAV decreased by about 2 units, while it increased by about 2 units upon binding to SDS. However, the chemical shift patterns of both protonated (PAVH +) and deprotonated (PAV 0) forms of PAV are not sensitive to the type of surfactant. The association constants were estimated as 5 ± 2 M −1 for PAVH +-CTAC, 8 ± 3 M −1 for PAVH +-HPS, (7 ± 2) × 10 5 M −1 for PAVH +-SDS, and 1.5 × 10 3 to 3.0 × 10 3 M −1 for the complexes of PAV 0 with all three types of micelles. Using these data, an electrostatic potential difference on the micelle-water interface was calculated as 150 ± 10 mV for CTAC, 140 ± 10 mV for HPS and − 140 ± 10 mV for SDS. The results suggest that PAV aromatic rings are located in the hydrophobic part of the micelle. The electrostatic attraction or repulsion of the protonated quinoline nitrogen and surfactant headgroups changes the affinity of PAV to micelles and, thus, shifts the ionization equilibrium of PAV. The electrostatic potential of HPS micellar surface is determined by the cationic dimethylammonium headgroup fragment, whereas the anionic sulfate fragment attenuates the effective charge of HPS headgroup.

Mechanism of photosensitized oxidation of tyrosine by gallium or zinc phthalocyanine in homogeneous and aqueous micellar media

The mechanism of the photo-oxidation of tyrosine (Tyr) sensitized by sulphonated phthalocyanine at pH 10 in homogeneous aqueous solution or aqueous cetyltrimethylammonium chloride (CTAC) micellar medium was studied by kinetic analysis and laser flash photolysis. Cationic CTAC micelles promote the importance of a type I mechanism in the photo-oxidation of Tyr sensitized by sodium tetrasulphonated chlorogallium phthalocyanine (GaTSPC) whereas they have little effect on the photo-oxidation of Tyr sensitized by sodium disulphonated zinc phthalocyanine (ZnDSPC). In all cases studied, it was shown that the type I mechanism (electron transfer) takes place more easily using GaTSPC as sensitizer, whereas, using ZnDSPC as sensitizer, a type II mechanism (involving 1O 2) predominates. The results are discussed according to the mutual position of the sensitizer and the substrate in the aqueous micellar medium and the ability of the triplet state of the phthalocyanine to abstract an electron from Tyr.

Interaction of papaverine with micelles of surfactants with different charge studied by 1H-NMR

The interaction of the vasodilator drug papaverine (PAV) with micelles of surfactants with different charge of headgroups as well as the properties of PAV in D 2O solution were studied by 1H-NMR. At pD values above 6.4 deprotonated PAV molecules tend to precipitate, the signals of the heterocycle protons of solubilized PAV molecules being shifted to high field. At PAV concentration above 1 mM its protons experience upfield shifts which increase with pD value and are due to the stacking of aromatic rings. Incorporation into micelles caused shifts of all resonances. This effect is due to changes in the local chemical environment of PAV rather than to stacking, and, possibly, involves the deprotonation of the N atom of PAV heterocycle. Line broadening of PAV protons at the molar ratio surfactant/ PAV > 16 indicated their restricted mobility. Different complexes were formed due to interaction between the heterocycle of PAV and polar headgroups of cationic cetyltrimethylammonium chloride (CTAC) or anionic sodium dodecylsulfate (SDS). The binding of PAV to zwitterionic N- hexadecyl-N,N- dimethyl-3- ammonio-1- propanesulfonate (HPS) is similar to that of PAV to CTAC. Association constants were estimated from NMR data as 20, 60 and 350 M −1 at pD = 4.9±0.1 for HPS, CTAC and SDS, respectively. Thus, the mode of binding of PAV to HPS is defined by the cationic dimethylammonium headgroup fragment, whereas the negative sulfate fragment attenuates the effective charge of HPS headgroup.

Studies on surfactant toxicity to the freshwater alga Chlorella fusca: a common mode of action?

In order to study whether the impact of surfactants on algae depends on a common mode of action, the eukaryotic green alga Chlorella fusca was subjected to two surfactants with identical lipophilic chains (C 16), the nonionic diethyleneglycol monohexadecylether (C16E2) and the cationic cetyltrimethylammoniumchloride (CTAC). Concentration-effect relationships for growth (cell volume) and reproduction (cell number) of synchronized C. fusca were determined for a surfactant exposure of 24 h. The observed-effect concentrations for both surfactants range from 10 −7 to 5·10 −6 molar. Exposure to the C16E2 surfactant resulted in a concomittant inhibition of both cell growth and reproduction. The CTAC surfactant, in contrast, induced a strikingly different concentration-response relationship for both parameters. To find the reason for the observed inhibition, photosynthesis and respiration of C fusca were determined during acute (30 min) and after prolonged (24 h) exposure to the surfactants. Only the cationic CTAC surfactant induced a moderate acute inhibition of photosynthetic oxygen production of C. fusca, which is constant even after prolonged exposure. C16E2, in contrast, failed to inhibit photosynthesis during short-term exposure, while prolonged incubation resulted in a distinct inhibition. The alga's respiration was only slightly affected during acute exposure to CTAC, while prolonged exposure induced a considerable effect. The nonionic C16E2, on the other hand, immediately inhibits the respiration of C. fusca, resulting in an almost total inhibition of respiration after long-term exposure. The results suggest that surfactant toxicity to algae can be attributed to an interaction with membrane functions of photosynthesis and mainly respiration. In addition, however, the cationic CTAC surfactant is shown to interfere especially with cell reproduction. More than one mode of action of cationic surfactants on algae, therefore, has to be assumed.