Triton X-100 Micellar Solution Research Articles

Supramolecular chirality in self-assembly of zinc protobacteriochlorophyll-d analogs possessing enantiomeric esterifying groups

Zinc 3-hydroxymethyl-pyroprotopheophorbides-a esterified with a chiral secondary alcohol at the 17-propionate residue were prepared as bacteriochlorophyll-d analogs. The synthetic zinc 31-hydroxy-131-oxo-porphyrins self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted and broadened Soret and Qy absorption bands in comparison with their monomeric bands. The intense, exciton-coupled circular dichroism spectra of their self-aggregates were dependent on the chirality of the esterifying groups. The observation indicated that the self-aggregates based on the J-type stacking of the porphyrin cores were sensitive to the peripheral 17-propionate residues. The supramolecular structures of the present J-aggregates as models of bacteriochlorophyll aggregates in natural chlorosomes were remotely regulated by the esterifying groups.Graphical abstract

LOW TEMPERATURE ANALYTICAL CLOUD POINT EXTRACTION. 1: PROTOLYTIC PROPERTIES OF ACIDIC EXTRACTION INITIATORS IN ORGANIZED MEDIA

Cloud point extraction is a powerful tool for the analytical preconcentration of trace amounts of analytes. The standard cloud point extraction procedure requires prolonged heating of the solution, which is not always appropriate in the case of thermally unstable analytes or analytical forms and significantly limits the capabilities of the method. One of the ways to modify cloud point extraction is to find approaches to intensifying the process of analytical concentration. The main disadvantage of cloud point extraction is the need for thermal, ultrasonic, infrared or any other initiation of the formation of the surfactant-rich phase. The difficulty lies in the fact that such influence on the system is not always appropriate and possible, and can also negatively affect the formation of the target analytical form. The purpose of this work is to search for new initiators of cloud point extraction and justify the possibility of their analytical use. In the current paper, the ionization constants (pKa) of some cloud point extraction initiators such as aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids) in water and Triton X-100 micellar solutions at various concentrations of surfactant in the studied systems have been determined by the potentiometric titration method. It was found that the values of pKa of aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids) in water and Triton X‑100 micellar solutions naturally increase with increasing concentration of surfactant in the system. It is shown that the nature and the physico-chemical properties of the environment influence the nature and degree of change in the acid-base properties of the studied aromatic carboxylic acids (benzoic, 4-chlorobenzoic, 3-nitrobenzoic, 2,4-dihydroxybenzoic, o-, m-, p-toluic and salicylic acids). Criteria for the selection of cloud point extraction initiators are proposed, which allow analytical concentration to be carried out at room temperature.

Self-aggregation behavior of dimeric chlorophyll-a derivatives linked with ethynylene and m-phenylene moieties.

Chlorophyll(Chl)-a derivatives inserting an ethynylene-m-phenylene group between a zinc chlorin ring and a hydroxymethyl group, in which various substituents were introduced on the benzene spacer, were prepared as model compounds for the light-harvesting antennae (chlorosomes) of photosynthetic green bacteria. These compounds were synthesized from a C3-ethynylated Chl-a derivative via sequential Sonogashira cross-coupling reaction, and the effects of the substituents on the phenylene linker on their self-aggregation behaviors were investigated by electronic absorption, circular dichroism, and infrared absorption spectroscopic measurements. These studies exhibited that some compounds gave the disordered self-assemblies including several species; however, the zinc complex of the dimeric Chl-a derivative primarily allowed a single J-aggregate species in an aqueous Triton X-100 micellar solution. Additional control experiments revealed that its self-assembly was constructed through the hydrogen and coordination bonding involving the hydroxymethyl group on benzene ring, keto-carbonyl group at C13-position, and central zinc atom, and this is consistent with a conventional chlorosomal manner.

Quantifying the spontaneous emulsification of a heavy hydrocarbon with the presence of a strong surfactant

The rate of spontaneous emulsification phenomenon of heavy hydrocarbon in a non-ionic surfactant solution was studied experimentally. The size of a diminishing oil droplet was monitored photographically with the presence of an electrolyte. The obtained data were analysed using Axisymmetric Drop Shape Analysis (ADSA) software to measure the flux of emulsion droplets formed spontaneously. In contrast to all previous reports, a stable layer confined between the oil and aqueous solution was observed with a relatively constant thickness, ∼ 100 µm. The result shows that the rate of emulsification is reduced with the presence of electrolytes and is inversely correlated to its concentration. Considerable variation of the influence of electrolyte type on the kinetic of the spontaneous emulsification process for a given condition has been observed. Consequently, a new diffusion-control mechanism has been proposed, creating an extendable model to describe the process theoretically. The experimental data of emulsifying hexadecane in Triton X-100 micellar solution with the presence of potassium chloride and sodium chloride was well fitted to the proposed model. The results have important implications for surfactant-based cleaning processes.

Solubilization of aqueous-insoluble phenothiazine drug in TX-100 micellar solution and interactions of cationic/anionic surfactants with phenothiazine–TX-100 system

This article discusses the interaction of surfactants such as tetradecyltrimethylammonium bromide (TTAB), hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC), cetylpyridinium bromide (CPB) and sodium dodecylsulphate (SDS) in presence of poorly soluble drug phenothiazine (PTZ) in triton X-100 (TX-100) micellar aqueous media through the investigation of different physicochemical parameters. The interaction of surfactants in PTZ–TX-100 media has been studied using conductometric technique at pH 7.4 (SP buffer) and at three temperatures. The conductometric results reveal the sequence of critical micelle concentration (CMC) values of surfactants as SDS > TTAB > CPC > CPB > CTAB. UV–vis spectroscopy studies were used to learn the interactions of surfactants with the drug PTZ in TX-100 aqueous media (at 303.15 K and pH 7.4) which suggest the interactions are highly feasible (change of Gibbs energy; ΔGb < 0) and greatly improve beyond the CMC values of corresponding surfactants. The estimated parameters using the Benesi–Hildebrand equation indicate higher binding constant (Kb) for cetylpyridinium surfactants and least for SDS and the drug–surfactant complex formations are found to be in 1:2 stoichiometric ratios. Fluorescence technique has also been employed to study the aggregation number (Nagg), Stern-Volmer constant (KSV) and micro-polarity of TTAB/CTAB/SDS in PTZ–TX-100 systems at 303.15 K. The evaluated thermodynamic parameters such as change in Gibbs energy (ΔGm0), enthalpy (ΔHm0) and entropy (ΔSm0) of micellization show the process of micellization of all studied surfactants in PTZ–TX-100 aqueous media are spontaneous and exothermic.

Matching Effects in the Interaction of Ionic Surfactants with Fluorescent Reagents in Micellar Solutions of Triton X-100

The influence of cationic and anionic surfactant solutions on the character of the fluorescence spectra of reagents of different charge and hydrophobicity in aqueous solutions of nonionic surfactant Triton X-100 has been studied. An increase in the fluorescence intensity and a shift in the position of the fluorescence maximum with increasing hydrophobicity of reagents and ionic surfactants have been shown. The analytical signal of the surfactant is further amplified in the proximity of the charge values of the reagent and the counterion of the surfactant. The non-monotonic nature of the hydrophobicity effect of cationic surfactants on their analytical signal in the system has been shown. The observed effects are explained by the realization of charge and hydrophobic matching in the interaction of surfactants with the fluorescent reagents. The obtained effects are significant in the design of fluorescent systems for the determination and study of surfactant micelles. Conditions for detecting the content of cetylpyridinium chloride by reaction with eosin Y and sodium tetradecyl sulfate by reaction with rhodamine 6G in the presence of Triton X-100 were proposed. The methods have been tested in detecting the content of the ionic surfactants in pharmaceuticals.

Facile 132-methylation of chlorophyll-a derivative and (132R/S)-stereoselective self-aggregation of zinc bacteriochlorophyll-d analogs

Zinc methyl 3-hydroxymethyl-(132R/S)-methyl-pyropheophorbides-a were prepared as model compounds of bacteriochlorophyll-d by the chemical modification of naturally occurring chlorophyll-a. Both the HPLC-separated 132-epimers as well as the 132-unsubstituted counterpart self-aggregated in an aqueous Triton X-100 micellar solution to form large oligomers with red-shifted electronic absorption and intense circular dichroism bands, similarly as in natural chlorosomes, the main light-harvesting antennas of photosynthetic green bacteria. The substitution with a methyl group at the 132-position did not disturb the formation of chlorosomal self-aggregates in a J-type fashion, which were slightly dependent on the stereochemistry.

Synthesis of zinc 13-oxime-functionalized chlorophyll-a derivatives and their (131E/Z)-dependent self-aggregation

Zinc methyl 3-hydroxymethyl-pyropheophorbides-a possessing hydroxyimino, acetoxyimino, and benzoyloxyimino groups at the 131-position were prepared by chemical modification of naturally occurring chlorophyll-a. The (131E)- and (131Z)-stereoisomers of the obtained unsymmetric oximes were readily separated by column chromatography, and their stereochemistry was determined by 1H NMR spectroscopy. The synthetic O-(un)substituted oximes were monomeric in tetrahydrofuran and their electronic absorption spectra were dependent on the stereochemistry as well as the O-substituents in the oxime moiety. These chlorophyll-a derivatives self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted absorption bands. The J-aggregation ability of the (131E)-isomers was higher than that of the corresponding the (131Z)-isomers. Such stereoselective self-aggregation was comparable to that of bacteriochlorophylls-c, d, e, and f in the main light-harvesting antennas of green photosynthetic bacteria.

Effect of additional hydroxy group on self-aggregation of synthetic zinc bacteriochlorophyll-c analogs

Zinc methyl 3-hydroxymethyl-pyropheophorbides-a possessing a hydroxymethyl or 2-hydroxyethyl group at the 20-position were prepared by chemical modification of naturally occurring chlorophyll-a. The synthetic bacterio-chlorophyll-c analog bearing the 201-hydroxy group self-aggregated in an aqueous Triton X-100 micellar solution to give large oligomers with red-shifted and broadened electronic absorption bands, which was similar to the chlorophyllous J-aggregates in the main light-harvesting antennas of green photosynthetic bacteria. By contrast, the other 202-hydroxylated analog did not aggregate under the same conditions to remain its monomeric species. The red shift in the longest wavelength (Qy) band by the self-aggregation of the former analog was greater than that of the corresponding 201-methyl substitute with a similar size (CH3 ≈ OH). These results could be ascribable to the less sterically demanding and more electron-withdrawing 20-hydroxymethyl group, compared with more interacting 2-hydroxyethyl and more electron-donating ethyl groups at the 20-position.

Antioxidant Activity of Foods: Development of Singlet Oxygen Absorption Capacity (SOAC) Assay Method.

Recently a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants (AOs) and food extracts was proposed. Singlet oxygen (1O2) quenching rates (kQ) and the relative SOAC values were measured for many carotenoids and phenolic AOs in ethanol/chloroform/D2O (50 : 50 : 1, v/v/v) solution at 35ºC using UV-vis spectrophotometry. It has been clarified that the SOAC method is useful to evaluate the 1O2-quenching activity of lipophilic and hydrophilic AOs having 5 orders of magnitude different rate constants (kQ). Measurements of the kQ and SOAC values were also performed for 39 kinds of food extracts. The results indicate that the SOAC method is useful to evaluate the 1O2-quenching activity of food extracts having two orders of magnitude different kQ values. Further, the kQ values for the reaction of 1O2 with 8 carotenoids and 8 vitamin E homologues were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.4). Results obtained demonstrate that the kQ values of AOs in homogeneous and heterogeneous solutions vary notably depending on (i) polarity (dielectric constant (ε)) of the reaction field between AOs and 1O2, (ii) local concentration of AOs, and (iii) mobility of AOs in solution. Measurements of kQ and SOAC values in a micellar solution may be useful for evaluating the 1O2-quenching activity of AOs in biological systems. Furthermore, measurements of the SOAC values were performed for 32 kinds of food extracts using a microplate reader. The SOAC assay method was validated by inter-laboratory validation study due to 14 laboratories.

Measurements of Singlet Oxygen-Quenching Activity of Vitamin E Homologs and Palm Oil and Soybean Extracts in a Micellar Solution.

Recently, a new assay method that can quantify the singlet oxygen-absorption capacity (SOAC) of antioxidants (AO) and food extracts in homogeneous organic solvents has been proposed. In the present study, second-order rate constants (kQ ) for the reaction of singlet oxygen (1 O2 ) with vitamin E homologs (α-, β-, γ-, and δ-tocopherols [Toc] and α-, β-, γ-, and δ-tocotrienols [Toc-3]) were measured in an aqueous Triton X-100 (5.0 wt%) micellar solution (pH 7.4). Toc-3 showed kQ values larger than those of Toc in a micellar solution, although Toc and Toc-3 showed the same kQ values in a homogeneous solution. Similar measurements were performed for 5 palm oil extracts 1-5 and one soybean extract 6, which contained different concentrations of Toc, Toc-3, and carotenoids. It has been clarified that the 1 O2 -quenching rates (kQ ) (that is, the relative SOAC value) obtained for extracts 3-6 may be explained as the sum of the product <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfenced><mml:mrow><mml:mi>Σ</mml:mi><mml:msubsup><mml:mi>k</mml:mi><mml:mi>Q</mml:mi><mml:mrow><mml:mi>AO</mml:mi><mml:mo>-</mml:mo><mml:mi>i</mml:mi></mml:mrow></mml:msubsup><mml:mfenced><mml:mrow><mml:mi>AO</mml:mi><mml:mo>-</mml:mo><mml:mi>i</mml:mi></mml:mrow></mml:mfenced><mml:mo>/</mml:mo><mml:mn>100</mml:mn></mml:mrow></mml:mfenced></mml:math> of the rate constant ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>k</mml:mi><mml:mi>Q</mml:mi><mml:mrow><mml:mi>AO</mml:mi><mml:mo>-</mml:mo><mml:mi>i</mml:mi></mml:mrow></mml:msubsup></mml:math> ) and the concentration ([AO-i]/100) of AO-i contained. The UV-vis absorption spectra of Toc and Toc-3 were measured in a micellar solution and chloroform. The results obtained demonstrated that the kQ values of AO in homogeneous and heterogeneous solutions vary notably depending on (1) polarity (dielectric constant [ε]) of the reaction field between 1 O2 and AO, (2) the local concentration of AO, and (3) the mobility of AO in solution. The results suggest that the SOAC method is applicable to the measurement of 1 O2 -quenching activity of general food extracts in a heterogeneous micellar solution.

Photodegradation of 4,4′-dibrominated diphenyl ether in Triton X-100 micellar solution

This study has investigated the photochemical reactions of 4,4′-dibrominated diphenyl ether (BDE-15) in Triton X-100 (TX-100) solution by UV light. All photolysis experiments were performed in TX-100 solutions which were all above critical micelle concentration (CMC). BDE-15 photodegradation follows the pseudo-first-order kinetics under various conditions. The results showed that the degradation rates of BDE-15 increased with the increasing concentration of TX-100, and decreased when TX-100 was used in excess, because TX-100 can act as hydrogen donor, photosensitizer and light barrier. When the pH value was in the range of 1–11, the degradation rates increased with the increasing pH value due to the proton effect and free radical reaction. When pH reached 13, the corresponding degradation rate dropped significantly, which was attributed to the decreasing surface potential of micellar retarding the degradation process. BDE-15 was debrominated into 4-dibrominated diphenyl ether (BDE-3) and diphenyl ether (DE), subsequently. In addition, dibenzofuran (DF), ortho-hydroxydiphenyl and para-hydroxydiphenyl were identified as another group of photoproducts, indicating PBDEs can also undergo the photochemical rearrangement via CO bond cleavage and recombination of the radical fragments.

Molecular interactions involving aqueous Triton X-100 micelles and anionic surfactants: Investigations on surface activity and morphological transitions

The micellar solutions of nonionic surfactant Triton X-100 (TX-100) were investigated in the presence of several anionic surfactants, namely sodium 1-butanesulfonate, sodium 1-decanesulfonate, sodium octanoate, sodium perfluorooctanoate, sodium decanoate and sodium alkyl sulphates. The resultant structures formed have been analysed using cloud point (CP), wettability and scattering techniques (DLS and SANS). CP and DLS show marked morphological changes for existing TX-100 micellar solutions in presence of an anionic surfactant depending on its respective hydrophilicity or hydrophobicity. Hydrophobic anionic surfactants induced strong demicellization effect and shifted clouding temperature to higher values. SANS study shows typical transition in ellipsoidal shaped micelles of TX-100 based on the specific interactions. The analysis of SANS data revealed that ellipsoidal shaped TX-100 micelles transform to smaller ellipsoidal mixed micelles with lower axial ratio and smaller aggregation number. Wettability of TX-100 aqueous solution on PTFE surface changes significantly on addition of small amount of anionic surfactant. The water penetration through porous channels of packed PTFE powder in a metal cylinder depicts reduction in wettability due to formation of stable micelles in presence of fluorinated surfactants. The specific changes in CP and morphology of TX-100 micelles are explained in terms of critical molecular interactions as influenced by the hydrophobic chain length and polar head group of surfactants.

Properties of aqueous micellar solutions in the presence of ionic liquid

The physicochemical properties of aqueous surfactant solutions above their critical micelle concentrations (cmc) are governed by the micellar assemblies present within the solution. Due to their distinct structural features and properties, ionic liquids (ILs) can effectively and favorably modify the properties of aqueous micellar solutions. Effect of addition of a prototypical ‘hydrophobic’ IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), which exhibits only ∼2wt% miscibility in water at ambient conditions, on the properties of aqueous micellar solutions of four different surfactants, namely, nonionic triton X-100 (TX-100), anionic sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS), and zwitterionic dodecylsulfobetaine (SB-12), is assessed. Surface tension, density, refractive index, and dynamic viscosity along with fluorescence probe-reported microfluidity of the four aqueous micellar solutions are investigated in the absence and presence of up to 5wt% [bmim][PF6]. Density and refractive index of aqueous micellar solutions increase linearly with wt% [bmim][PF6]. Increasing [bmim][PF6] results in decrease in surface tension of anionic/zwitterionic micellar solutions; on the contrary, the surface tension of nonionic TX-100 micellar solution increases. This is due to the negative adsorption exhibited by [bmim][PF6] within aqueous micellar TX-100 solution. There is an initial increase, in general, in the dynamic viscosity of the four micellar solutions as [bmim][PF6] is added; however, this increase is way more dramatic for SDBS. This is attributed to a drastic increase in the size of the micelles as a result of the presence of both [bmim][PF6]-SDBS electrostatic as well as cation-π interactions. Response from the microfluidity probe does not necessarily scale with the dynamic viscosity of the micellar solutions as [bmim][PF6] is added. The water penetration into the palisade layer of the [bmim][PF6]-added anionic micelles, where the microfluidity probe solubilizes, is the reason for this outcome. The aqueous micellar media is perturbed significantly in the presence of IL and the extent of the changes in the properties is contingent on the identity of the surfactant.

Application of differential spectra from two different environments in simultaneous quantification of new fuchsine, crystal violet and malachite green in the presence of unmodeled interferents using first order multivariate calibration method

This paper proposes the possibility of applying first order calibration methods for unknown sample(s) with unmodeled component(s) using the differential spectra obtained from subtracting of the absorbance spectra of sample that are recorded in two different environments. The main interest is that the method can be performed to quantify systems if the spectra of their unmodeled component(s) are the same in two different phases using first order calibration methods. The procedure demonstrates simultaneous determination of new fuchsine, crystal violet and malachite green in the presence of sunset yellow, tartarazine and amaranth as unmodeled interferences, whose spectra differ in aqueous and nonionic micellar solution of Triton X-100. The obtained satisfactory results indicate the successful applicability of the proposed method in complex samples.

Aggregation Behavior of Triton X-100 with a Mixture of Two Room-Temperature Ionic Liquids: Can We Identify the Mutual Penetration of Ionic Liquids in Ionic Liquid Containing Micellar Aggregates?

In this manuscript, we have characterized two different micellar aggregates containing all nonvolatile components. We have shown (i) the effect of ethylammonium nitrate (EAN) addition on the properties of micellar solution of Triton X-100 in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)) and (ii) the effect of bmimPF(6) addition on the properties of micellar solution of Triton X-100 in EAN. To investigate the effect, we have used (1)H NMR, pulsed-field gradient spin-echo NMR (PFGSE NMR), and methyl orange (MO) and coumarin 153 (C-153) as absorption and emission probes, respectively. The penetration of added EAN inside the Triton X-100/bmimPF(6) micellar aggregates is indicated by (i) red shift in both the absorption spectra of MO and emission spectra of C-153 and (ii) downfield shift of proton signals of ethylene oxide units in Triton X-100. On the other hand, (1)H NMR and PFGSE NMR indicates the penetration of added bmimPF(6) inside the Triton X-100/EAN micellar aggregates. However, the constancy of both the absorption spectra of MO and emission spectra of C-153 indicates that the microenvironment around the probe molecules remains unaffected. We have also investigated the effect of micelle formation and the effect of penetration of ionic liquids (ILs) in micellar aggregates, on the solvation dynamics of C-153. The solvent relaxation around C-153 gets retarded on going from neat ILs to the micellar solution of Triton X-100 in ILs. In addition to this, we have also observed that with the addition of EAN in Triton X-100/bmimPF(6) micellar aggregates the solvation dynamics becomes faster, whereas with the addition of bmimPF(6) in Triton X-100/EAN micellar aggregates we did not observe any notable change in solvation dynamics. This observation further supports the conclusions drawn from UV-visible and NMR studies.

Exploiting Micelle-Driven Coordination To Evaluate the Lipophilicity of Molecules

We present a systematic study based on the calculation of complexation constants between a Zn-complex solubilized in Triton X-100 micellar solutions and a series of linear mono- and dicarboxylic acids, under physiological pH conditions, that allowed the evaluation of the lipophilicity of these molecules. This empirical lipophilicity parameter describes conveniently the partition of organic molecules between hydrophobic microdomains and water. The results can be used to predict the lipophilicity of molecules with similar structure and allows the distinction of intrinsic contributions of the carboxylates and of the methylene groups to the lipophilicity of the molecule.

Quantification of Specific Anion Binding to Non-Ionic Triton X-100 Micelles

Anion binding to nonionic micelles was quantified by self-diffusion. Four anions were probed by multinuclear PGSTE NMR measurements in a Triton X-100 micellar aqueous solution. The salt concentration used was sufficiently low to avoid any micellar growth affecting surface curvature. The micellar aggregates that provide a model surface are uncharged with hydrophilic headgroups so that electrostatic ion surface interactions play little or no role in prescribing specific anion binding. Anionic affinity to the micellar surface followed a Hofmeister series, (CH(3))(2)AsO(2)(-) ≫ CH(3)COO(-) > H(2)PO(4)(-) > F(-). The observed ion specificity is rationalized by calling into play the nonelectrostatic interactions occurring between the anions and the micellar surface.

Spectral and electrochemical studies of bis(diimine)copper(II) complexes in anionic, cationic and nonionic micelles

The spectral and redox behavior of bis(diimine)copper(II) complexes, where diimine is bipyridine, 1,10-phenanthroline, 4-methyl-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 5-nitro-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline and dipyrido-[3,2-d:2′,3′-f]-quinoxaline, are significantly different in aqueous and in aqueous SDS, CTAB and Triton X-100 micellar solutions. The 1H NMR spectral study in aqueous (D2O) and aqueous micelles reveals that the Cu(II) complexes interact more strongly with SDS than with CTAB and Triton X-100 micelles and at sites on SDS micelles different from those on the latter. Ligand Field spectral studies reveal that the complexes exist as the dicationic aquated species [Cu(diimine)2(H2O)2]2+, which interacts strongly with the anionic SDS micelles through columbic forces. However, they exist as [Cu(diimine)2(H2O)Cl]+ and/or [Cu(diimine)2H2] located in the hydrophobic microenvironments in Triton X-100 and CTAB micelles. The attainment of reversibility of the redox systems in the micellar microenvironments is remarkable and this illustrates that the Cu(II) and Cu(I) species undergo stereochemical changes suitable for reversible electron-transfer. The remarkable differences in spectral and electrochemical properties of Cu(II) complexes in aqueous and aqueous micellar solutions illustrate that the complexes are nestled largely within the micellar environments and imply that the accessibilities of the complexes to electron-transfer are different and are dependent on the nature of micelles as well as the nature and hydrophobicity of the diimine ligands.

Kinetic Study of the Quenching Reaction of Singlet Oxygen by Pyrroloquinolinequinol (PQQH2, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

A kinetic study of the quenching reaction of singlet oxygen ((1)O(2)) with pyrroloquinolinequinol (PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa(2) (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), α-tocopherol (α-Toc), ubiquinol-10 (UQ(10)H(2)), and β-carotene (β-Car)) has been performed. The second-order rate constants k(Q) (k(Q) = k(q) + k(r), physical quenching and chemical reaction) for the reaction of (1)O(2) with PQQH(2), PQQNa(2), and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV-visible spectrophotometry. The k(Q) values decreased in the order of β-Car > PQQH(2) > α-Toc > UA > UQ(10)H(2) > Vit C ∼ EGC > EC ≫ PQQNa(2). PQQH(2) is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH(2) was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH(2) was found to be 2.2 and 3.1 times as large as the corresponding activity of lipid-soluble antioxidants (α-Toc and UQ(10)H(2)). On the other hand, the activity of PQQH(2) is 6.4 times as small as that of β-Car. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction of (1)O(2) by PQQH(2). The result suggests that PQQH(2) may contribute to the protection of oxidative damage in biological systems, by quenching (1)O(2).