Presence Of Triton X-100 Micelles Research Articles

Reaction Kinetics of Phenolic Antioxidants toward Photoinduced Pyranine Free Radicals in Biological Models.

8-Hydroxy-1,3,6-pyrenetrisulfonic acid (pyranine, PyOH) free radicals were induced by laser excitation at visible wavelengths (470 nm). The photochemical process involves photoelectron ejection from PyO- to produce PyO• and PyO•- with maxima absorption at 450 and 510 nm, respectively. The kinetic rate constants for phenolic antioxidants with PyO•, determined by nanosecond time-resolved spectroscopy, were largely reliant on the ionic strength depending on the antioxidant phenol/phenolate dissociation constant. Further, the apparent rate constant measured in the presence of Triton X100 micelles was influenced by the antioxidant partition between the micelle and the dispersant aqueous media but limited by its exit rates from the micelle. Similarly, the rate reaction between ascorbic acid and PyO• was markedly affected by the presence of human serum albumin responding to the dynamic of the ascorbic acid binding to the protein.

Antioxidant Capacity of Pure Compounds and Complex Mixtures Evaluated by the ORAC-Pyrogallol Red Assay in the Presence of Triton X-100 Micelles

The protective effect of different antioxidants and complex mixtures on the consumption of pyrogallol red (PGR) induced by peroxyl radicals was studied in the absence and presence of Triton X-100 micelles. The presence of micelles decreased significantly the protection of PGR afforded by lipophilic antioxidants (β-carotene, octyl gallate), while no effect of micelles was observed for hydrophilic antioxidants such as Trolox, caffeic acid, gallic acid, and ascorbic acid. In the presence of complex mixtures a clear effect of Triton X-100 micelles was also observed in the protection afforded by wines, tea infusions, and seed extracts of Eugenia jambolana and Myrciaria cauliflora. On the other hand, no effect of micelles was observed for orange juice and pulp fruit extracts. The ORAC (Oxygen Radical Absorbance Capacity) index was evaluated in the absence (ORAC-PGR) and presence of Triton X-100 micelles (ORAC-PGRMIC). Triton X-100 micelles affect ORAC-PGR values of antioxidants in a lipophilicity-dependent way. From the obtained results, we conclude that ORAC-PGR and ORAC-PGRMIC assays could be considered as an alternative to estimate the antioxidant ability (ORAC-PGR) and to infer the association to Triton X-100 micelles (ORAC-PGR/ORAC-PGRMIC) of pure antioxidants and their complex mixtures.

Micelles as Containers for Self‐Assembled Nanodevices: A Fluorescent Sensor for Lipophilicity

Potentiometric titrations, fluorescence versus pH titrations, dynamic light scattering and fluorescence polarization anisotropy studies demonstrate that inside the nanodimensioned Triton X-100 micelles, 1-pyrenecarboxylic acid, PCOO(-), forms an apical complex with the Zn(2+) cation encircled by a lipophilic cyclen ligand and hugely increasing its fluorescence. The ability of the Zn(2+)-cyclen-PCOO(-) complex plus its micellar container to act as a fluorescent sensor to evaluate the lipophilicity of molecular species is demonstrated on the fatty acid series CH(3)(CH(2))(x)COOH (x=0-16). At pH 7.4 a decrease in fluorescence is observed on the addition of fatty acids that is directly related to their chain length, that is, to their tendency to enter the micellar containers, where they dislocate PCOO(-) from the Zn(2+) centre. The independent determination of fatty acid pK(a) values in the presence of Triton X-100 micelles confirms that our fluorescent micellar device is capable of sensing their lipophilicity.

Mechanism of the oxidation of d-glucose onto colloidal MnO2 surface in the absence and presence of TX-100 micelles

Aqueous colloidal manganese dioxide (MnO2) was prepared via titration by using potassium permanganate and sodium thiosulphate in aqueous neutral medium. The kinetics of oxidation of d-glucose onto the surface of colloidal MnO2 have been studied spectrophotometrically. The results show that the rate of initial stage (nonautocatalytic path) increases with increasing the [d-glucose], [H+], and temperature and also upon addition of nonionic surfactant Triton X-100 (TX-100), which indicates that the surfactant enhances the concentration of d-glucose at the surface of the colloidal MnO2. Hydrogen bonding interaction seemingly arises between –OH groups of d-glucose and oxygen of the ether linkages of polyoxyethylene chain of TX-100. A possible mechanism of the oxidative degradation of d-glucose is discussed in terms of d-glucose/TX-100 and colloidal MnO2 interaction.

Thermodynamics of anionic dye–cationic surfactant interactions in cationic–nonionic surfactant mixtures in comparison with binary systems

The thermodynamics of the interactions between the anionic dye Acid Red 88 (AR88) and the cationic surfactant dodecyltrimethylammonium bromide (DTA) in the aqueous solution of the nonionic surfactant Triton X-100 (TX100) at different temperatures has been investigated by using potentiometry. The standard free energy change, Δ G o 1, the standard enthalpy change, Δ H o 1, and the standard entropy change, Δ S o 1, for the first association step of DTA–AR88 complex formation in the presence of TX100 micelles were determined and compared to the thermodynamic functions of DTA–AR88 and DTA–TX100 interactions in binary systems. From Δ G o 1 results, it has been observed that irrespective of the studied temperature the binding free energy of DTA cation to AR88 anion as well as the complex stability is lower in TX100 solution than in binary mixture. The increase in the TX100 concentration causes the decrease in the tendency of DTA–AR88 complex formation. From this it can be seen that the mode and the strength of intermolecular interactions strongly depend on the presence of TX100 micelles. The values of Δ H o 1 and Δ S o 1 for DTA–AR88 complex formation in TX100 solution which are directly affected by the ratio of AR88 and TX100 concentrations are much higher compared to those obtained in binary mixtures without TX100. These results also lead to a conclusion that the binding of DTA cation to AR88 anion in the presence of TX100 micelles, which is an entropy-driven process, is much more different from the enthalpy-controlled formation process of DTA–AR88 complex in binary mixtures.

Selective amphipathic nature of chlorpromazine binding to plasma membrane bilayers

Chlorpromazine (CPZ), an antipsychotic agent shown to inhibit the action of various neurophysiological receptors, also exhibits preferential association with the plasma membrane, inducing stomatocytic morphological response in red blood cells (RBC). Given the cationic nature of CPZ, fluorimetry, pH titration, and red cell morphological studies were performed to assess the associative predilection of CPZ for anionic membrane components. CPZ fluorescence intensity increased 320–370% upon addition of phosphatidylcholine (PC) small unilamellar vesicles (SUVs) to aqueous CPZ, indicating an affinity of the drug for lipidic phases. After removal of unbound drug, CPZ fluorescence increased up to 92% with increasing phosphatidylserine (PS) in the lipid phase (up to 30 mol% of total lipid), suggesting a preferential association of the drug with anionic lipids. In studies of pH titration, the p K a of CPZ in the presence of Triton X-100 micelles or phospholipid SUVs increased with increasing anionicity of the lipidic phase [7.8 with Triton X-100, 8.0 with PC, 8.3 with phosphatidylglycerol (PG)], lending further support to preferential drug interaction with anionic lipidic components. At 0 °C, CPZ-induced red cell shape change was less extensive in cells made echinocytic by adenosine triphosphate (ATP) depletion, compared to cells made echinocytic by PS treatment following vanadate preincubation. This suggests that polyphosphoinositide lipids are CPZ membrane binding sites. Since polyphosphoinositide lipids are implicated as important intermediates in a number of receptor-mediated cell signaling pathways, evidence of association with these specific lipids provides a means by which psychoactive drugs may induce neurophysiological effects through direct interaction with general membrane components.

A study of anionic dye–cationic surfactant interactions in mixtures of cationic and nonionic surfactants

Interactions between anionic azo dye C.I. Acid Red 88 (AR88) and cationic surfactant dodecyltrimethylammonium bromide (DTA) in mixtures of DTA and nonionic surfactant Triton X-100 (TX100) at 25 °C have been quantitatively investigated by means of potentiometry based on the DTA surfactant cation-selective electrode. For this reason the treatment of mononuclear complex formation in aqueous solution has been used. Association constants K 1 for the formation of DTA–AR88 complex in the TX100 solutions of different concentrations in its micellar concentration range have been determined and compared to those obtained in the binary mixtures. It has been observed that the addition of TX100 into the mixture of DTA and AR88 causes a significant decrease of K 1, suggesting that the stability of DTA–AR88 complex is reduced in the presence of TX100 micelles. The results show that the decrease of the value of K 1 is directly affected by the DTA-TX100 and AR88-TX100 interactions in the solution. Since the solubilization of the DTA-AR88 complexes has been appeared in the TX100 solution our results support the conclusion that adding TX100 influences the hydrophobic–hydrophylic balance of the studied complexes. Comparison of the stability of DTA–AR88 complexes to that obtained between DTA and the anionic azo dye C.I. Acid Orange 7 (AO7) without added TX100 shows that under the same experimental conditions DTA strongly interact with AR88 than with AO7. Such behaviour can be explained as a consequence of more hydrophobic character of AR88 compared to AO7. The addition of TX100 into DTA-AO7 mixtures significantly affects the nature of the binding process.

Effect of phospholipids, Triton X-100 and biological membranes on redox systems involving tetrazolium salt reduction. Its implications for the assay of enzymatic activities

The influence of phospholipids and Triton X-100 on the time course of chemical and enzyme-mediated reductions of a commonly used tetrazolium salt, MTT, was studied. MTT reduction was followed by the absorbance changes at 570 nm. With ascorbate as reducing agent, a 3-fold increase in the initial rates of the absorbance changes and a 24 % increase in the final absorbance values were observed in the presence of Triton X-100 micelles or phospholipid vesicles. The enzyme-mediated reduction of MTT with NADH generated by the NAD-dependent lactate dehydrogenase was also enhanced in the presence of Triton X-100, phospholipids or erythrocyte membranes. No enhancement was observed following the enzymatic generation of NADH at 340 nm in the absence of MTT. The above findings were interpreted as arising from: a) solubilization or reduced MTT in the detergent micelles or phospholipid vesicles which favors the redox reaction occurring in the aqueous fase, and b) changes in the spectral properties of reduced MTT in aqueous and lipid-like media.

Application of enantiomeric 2- sn-phosphatidylcholines in interfacial enzyme kinetics of lipolysis

Two enantiomeric 2- sn-phosphatidylcholines containing hexanoyl and dodecanoyl acyl chains have been synthesized, enabling the study of the action of phospholipase A 2 (EC 3.1.1.4) at lipid-water interfaces characterized by identical physico-chemical properties. Monolayer kinetics and bulk kinetics in the presence of Triton X-100 micelles were studied but the interpretation of the results is impeded by the fact that interfacial saturation conditions cannot be reached. In contrast, the use of the substrate analog n-tetradecylphosphorylcholine allows the determination of the interfacial kinetic parameters k cat and K m ∗ . Dodecanoic acid is released from the most susceptible isomer about 13 times more rapidly than hexanoic acid from the stereoisomer in spite of the higher K m ∗ of the former. The results are discussed in terms of the particular active site architecture and the possible influence of the “quality of the interface” on the kinetic parameters.