Solubilization Site Research Articles

High performance controlled reactors from micellar assemblies of aromatic amino acid amphiphiles for nanoparticle synthesis

The micellar assemblies of lauryl esters of tyrosine (LET) and phenylalanine (LEP) show extraordinary emulsification properties. The structural similarity in respect of the aromatic ring between the dispersed phase, styrene, and the surfactants facilitates solubilization of styrene up to four times the weight of LEP and 11times that of LET. We propose that the solubilization site varies between core in the LEP and shell in the LET micelles. LET affords double emulsions, water in oil in water (w/o/w) over a narrow phase composition, for example at R=7.15, where R represents ratio of weight of styrene to LET. A schematic model depicting the solubilization site of styrene at different regions in LET and LEP micelles has been proposed. On polymerization, the emulsions with LET and LEP micelles generated high molecular weight polymer nanoparticles of size 12–49nm with low polydispersity index (Pd). This demonstrates that micellar assemblies act as templating controlled reactors for the polymerization reaction. We demonstrate that PS nanoparticle dispersion of size 49nm with polymer weight fraction as high as 42.80% could be produced from emulsions with the LET surfactant, in contrast to LEP that is 50% less efficient. Polymerization of these emulsions occurs predominantly through a micellar nucleation mechanism. It is significant to note that under the same conditions, the control experiments with sodium dodecylsulfate (SDS) micelles resulted in polymers with broad distribution, Pd>3.0 in molecular weight.

Micellar solubilization of octan-1-ol in aqueous solutions of SDBS and TTAB

Speed of sound and density measurements of aqueous solutions of anionic surfactant, sodium dodecylbenzene sulfonate (SDBS) and cationic surfactant, tetradecyltrimethyl- ammonium bromide (TTAB) in the presence of octan-1-ol, have been measured as a function of concentration of surfactants (0.05 and 0.10) mol·kg−1 at T=(298.15, 303.15 and 308.15) K. From these measurements, the apparent molar volume (Φv) and isentropic compressibility (ks) of octan-1-ol have been computed. The standard partial molar volume (Φov) has been calculated for rationalizing various interactions in the studied solutions. 1H and 13C NMR chemical shift measurements in micelle solutions containing monohydric alcohols have also been carried out in order to interpret the preferential solubilization site of alcohol on the studied micellar systems. Further, FTIR studies suggest that the peak values of OH and –CC– stretching are considerable in hydrophobic alcohols. The results obtained are analyzed in terms of the solute–solvent interaction.

테트라데실트리메틸암모늄 브로마이드의 수용액에서 4-알킬벤조산 이성질체들의 가용화에 대한 연구

The interaction of 4-alkylbenzoic acid isomers with the micellar system of TTAB (tetradecyltrimethylammonium bromide) was studied by the UV/Vis spectrophotometric method. The solubilization constants () of 4-alkylbenzoic acid isomers into the TTAB micellar system and the critical micelle concentration (CMC) of TTAB have been measured with the change of temperature. Various thermodynamic parameters have been calculated and analyzed from those measurements. The results show that the values of for the solubilization of all the isomers are negative and the values of and are all positive within the measured temperature range. The effects of additives (n-butanol and NaCl) on the solubilization of 4-alkylbenzoic acid isomers have been also measured. There was a great change on the values of and CMC simultaneously with these additives. From these changes we can postulate that the solubilization sites of 4-alkylbenzoic acids are the core or deep palisade region of the TTAB micelle.

Mass Spectrometry of Surfactant Aggregates

In contrast with the enormous amount of literature produced during many decades in the field of surfactant aggregation in liquid, liquid crystalline and solid phases, only a few investigations concerning surfactant self- assembling in the gas phase as charged aggregates have been carried out until now. This lack of interest is disappointing in view of the remarkable theoretical and practical importance of the inherent knowledge. The absence of surfactant-solvent interactions makes it easier to study the role of surfactant-surfactant forces in determining their peculiar self-assembling features as well as the ability of these assemblies to incorporate selected solubilizate molecules. Thus, the study of gas-phase surfactant and surfactant-solubilizate aggregates is a research subject which has exciting potential, including mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in interstellar space. On the other hand, the structural and dynamic properties of surfactant aggregates in the gas phase could be exploited in a number of interesting applications such as atmospheric cleaning agents, transport and protection of pulmonary drugs or biomolecules and as nanoreactors for specialized chemical reactions in confined space. Spectrometric techniques, together with molecular dynamics simulations, have been the principal investigative tools in this field and appearto be particularly suited to gaining fundamental information on the structure and stability of surfactant-based supramolecular aggregates, charge state effects, entrapment of solubilizate molecules, preferential solubilization sites and chemical reactions localized in a single organized aggregate. The main aim of this review is to present the actual state of the art in this novel and exciting research field underlining the knowledge acquired up to now as well as the aspects needing a more deep understanding. Moreover, intriguing departures of the behavior of surfactant solutions under electrospray ionization conditions from that of ionic, polar and apolar analytes will be discussed.

Effect of Hydrophobicity of PEO–PPO–PEO Block Copolymers on Micellization and Solubilization of a Model Drug Nimesulide

AbstractThe present work explored the molecular implications governing the solubilization of a model drug nimesulide (NIM) in micelles of ethylene oxide‐propylene oxide (EO–PO) triblock copolymers. The aggregation behavior and solubilization studies on four copolymers each with the same mol mass of central PPO block equal to 2,250 and varying % PEO was examined by means of UV–VIS. Moreover, high‐sensitivity differential scanning calorimetry, and Fourier transform infrared spectrometry measurements were used to evaluate the critical micellization temperature. The solubilization at different temperatures (30, 37, 45 °C), pH (2 to 10) and in the presence of added sodium chloride (0–2 M) was monitored and the partition coefficient (P) and the free energy of solubilization (ΔGso) were calculated. The site of solubilization of NIM in micelles was also probed. The NIM solubility decreased with increases in the PEO molecular weight; the drug resides in the micelle core.

Solubilization of griseofulvin by nononic surfactants.

Abstract Four nonionic surfactants, Me[CH2]15·[OCH2·CH2]xOH where x = 10, 22, 45 and 60, and polyoxyethylene glycols 200, 400 and 1000 increased the solubility of griseofulvin over its value in water. Cetomacrogol micelles solubilize two molecules of griseofulvin per micelle. The site of solubilization seems likely to be the polyoxyethylene part of the micelles. The partial molal heats and entropies of solution decrease as surfactant or polyoxyethylene glycol concentration is increased.

Relationships between poloxamer structure and the solubilization of some para-substituted acetanilides.

Saturation solubilities of several para-substituted acetanilides have been measured at 37 degrees C in aqueous solutions of structurally related polyoxyethylene-polyoxypropylene block copolymers-poloxamers L62, L63, L64, P65 and F68. These poloxamers differ only in the amount of ethylene oxide in the hydrophil. Solubilities increased with increasing poloxamer concentration. As the oxyethylene chain length of the poloxamer increased, then the solubilizing capacity per equivalent of oxyethylene decreased. The moles of acetanilide derivative solubilized per mole of poloxamer increased with poloxamer oxyethylene content in the case of the less hydrophobic acetanilides but was invariant in the more hydrophobic ones. The solubilizing capacities have been discussed in terms of the inter-relationships between the hydrophobic nature of the solubilizate and solubilizer and the site of solubilization on the poloxamer molecule.

Identification of the site of solubilization of various compounds by cetomacrogol.

Abstract Solubilization of some of the esters of p-hydroxybenzoic acid by cetomacrogol 1000 solutions has been investigated by ultraviolet spectrophotometry, nuclear magnetic resonance spectrometry and viscometry to provide evidence on the environment of each part of the solubilizate molecule as well as the detergent molecule. Hydration of the micelles calculated from the viscometry results, gave further evidence on the site of solubilization of the compounds. On the basis of these results and solubility results published previously it is suggested that the compounds are solubilized as follows: p-Hydroxybenzoic acid is wholly solubilized deep in the oxyethylene layer of the micelle. Ethyl p-hydroxybenzoate is solubilized mostly in the oxyethylene layer and is situated adjacent to the core: some solubilization occurs within the core. Butyl p-hydroxybenzoate is solubilized mainly at the oxyethylene-hydrocarbon junction, the phenyl ring in the oxyethylene layer and the butyl chain in the core: some solubilizate is wholly present in the core. Methyl p-methoxybenzoate: most of the compound is dissolved in the micellar core, but some is also present in the oxyethylene layer. Benzene is solubilized in a similar manner to methyl p-methoxybenzoate.

Preparation of protein nanoparticles using AOT reverse micelles

Biopolymeric nanoparticles made of protein via cross-linking reaction was prepared using sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle system as a nanoreactor. The prepared ribonuclease A nanoparticles were stably dispersed in aqueous solutions and the size of the nanoparticles was controlled in the range of 6–100 nm with water content in the system. Solvent species formulating the reverse micellar organic phase also can control the nanoparticle size. These effects on the nanoparticle size would be attributed to the dynamic behavior of reverse micelles. In contrast, cytochrome c nanoparticles were stably dispersed in ethanol while completely precipitated in both aqueous solutions and non-polar organic solvents. These findings indicate that a specific interaction of protein with AOT, which depends on the solubilization site of each protein in reverse micelles, is a significant factor to affect the surface properties of protein nanoparticles.

Location of anti-TB drugs and microstructural changes in organized surfactant media using optical properties

Microstructure elucidation is a critical step in the understanding of organized surfactant media such as microemulsions. In this work, a systematic approach for revelation of microstructure changes of Tween 80 microemulsion has been carried out using photophysical properties. Microemulsion structural changes have been monitored using pyrene and different solvatochromic probes for the presence of oil-rich, water-rich, and bicontinuous microstructures. The hydrophobic optical probe, Nile red (NR), has been used to report from the side of the oil–surfactant interface and to complement this, a hydrophilic optical probe tris(2,2′-bipyridine)ruthenium(II) dichloride (RC) from the side of the water–surfactant interface. The results show the partitioning of probes into different microenvironments within the system. NR occupies the interface toward the apolar side and RC toward the polar. The analysis also indicates conspicuous dependence of the emission/absorbance behavior of optical probes on the water:surfactant molar ratio ( ω). Quantitative estimates have been obtained for the polarities (ET(30)) of solubilization sites of the probes in different regions of microemulsions and are well correlated with a Stokes shift. Lastly, these probes of different solubilities have been used to locate the position of anti-tuberculosis drugs, i.e., rifampicin (hydrophobic), pyrazinamide, and isoniazid (hydrophilic) of variable solubilities loaded in Tween 80 systems.

Role of added counterions in the micellar growth of bisquaternary ammonium halide surfactant (14- s-14): 1H NMR and viscometric studies

The change in the morphology of a series of dicationic gemini surfactants C 14H 29(CH 3) 2N +−(CH 2) s −N +(CH 3) 2C 14H 29, 2Br − (14- s-14; s = 4–6) on their interaction with inorganic (KBr, KNO 3, KSCN) and organic salts (NaBenz, NaSal) have been thoroughly investigated by means of 1H NMR spectral analysis and the results are well supported by viscosity measurements. The presence of salt counterions results in structural transition (spherical to nonspherical) of gemini micelles in aqueous solution. With an increase in salt concentration all the three gemini surfactants showed changes in their aggregate morphology. This change is dependent on the nature and size of the added counterion. The effect of inorganic counterions on the micellar growth is observed to follow the Hofmeister series ( Br - < NO 3 - < SCN - ). The roles of organic counterions are discussed on the basis of probable solubilization sites of the substrate molecule in the gemini micelles, showing more growth in case of Sal − than Benz −. The results are confirmed in terms of the obtained values of chemical shift ( δ), line width at half height ( lw), and relative viscosity ( η r ). Also, the growth of micelles was most pronounced for the gemini surfactant with the shortest spacer ( s = 4). This was attributed to the unique molecular structure of gemini surfactant micelles having flexible polymethylene spacer chain linking the twin polar headgroups.

Probing solubilization sites in block copolymer micelles using fluorescence quenching

The solubilization sites provided by micelles formed by a diblock copolymer with one neutral hydrophobic block, polystyrene, and one charged hydrophilic block, poly(acrylic acid) or poly(methacrylic acid), have been studied by fluorescence quenching of pyrene by polar and nonpolar quenchers. Pyrene solubilized into these micelles is distributed between the inner corona and the micelle core. The fraction of pyrene residing in the inner corona is almost unity for star micelles, where the corona-forming blocks are larger than the core-forming blocks, and around 0.5 for crew-cut micelles where the opposite situation prevails. The kinetics of the quenching process depends on the pyrene location, i.e. is static in the micelle core, and largely dynamic in the inner corona at low quencher concentration. The rate constants for fluorescence quenching by nitromethane are shown to increase with increasing pH.

Pore-size expansion of hexagonal-structured nanocrystalline titania/CTAB Nanoskeleton using cosolvent organic molecules

Pore-size expansion of hexagonal-structured assembly of nanocrystalline titania (anatase) combined with cetyltrimethyammonium bromide (CH 3(CH 2) 15N +(CH 3) 3Br −, CTAB) (named as Hex-ncTiO 2/CTAB Nanoskeleton) was achieved with the aid of cosolvent organic molecules (COMs). The pore-size expanded Hex-ncTiO 2/CTAB Nanoskeleton was prepared through the sol–gel reaction of titanium oxysulfate sulfuric acid hydrate (TiOSO 4· xH 2SO 4· xH 2O, TiOSAH) in an aqueous solution initiated by CTAB swollen micelles pre-prepared with the addition of COMs into aqueous CTAB micellar solutions at 60 °C (the product was named as Hex-ncTiO 2/CTAB/COM Nanoskeleton). Long-chain alcohol (1-hexadecanol, C16OH), normal alkane ( n-decane, C10) and benzene derivatives (benzene, Bz; 1,3,5-trimethylbenzene, TMB; 1,3,5-triethylbenzene, TEB; 1,3,5-triisopropylbenzene, TiPB) were used as COMs to evaluate the effects of COM solubilization site in CTAB micelles and COM molecular size on the pore-size expansion of the Hex-ncTiO 2/CTAB/COM Nanoskeleton. We found that 1,3,5-trimethylbenzene (TMB) and 1,3,5-triethylbenzene (TEB) act as effective COMs for pore-size expansion of the Hex-ncTiO 2/CTAB/COM Nanoskeleton in aqueous media. Pore sizes (average diameters) of the Hex-ncTiO 2/CTAB/TMB Nanoskeleton and Hex-ncTiO 2/CTAB/TEB Nanoskeleton were enlarged up to 4.2 nm and 4.3 nm, respectively, while pore size (average diameter) of the Hex-ncTiO 2/CTAB Nanoskeleton prepared in the absence of any COMs was 2.9 nm. We also revealed that thermal stability of the Hex-ncTiO 2/CTAB/TMB Nanoskeleton became higher than that of Hex-ncTiO 2/CTAB Nanoskeleton. The hexagonally pore-structure of the Hex-ncTiO 2/CTAB/TMB Nanoskeleton was retained up to 400 °C, while the hexagonally pore-structure of the Hex-ncTiO 2/CTAB Nanoskeleton was kept up to 300 °C.

양이온성 계면활성제의 수용액에서 Dichlorophenol 이성질체들의 가용화에 대한 연구

양이온성 계면활성제인 TTAB(tetradecyltrimethylammonium bromide)의 수용액에서 dichlorophenol 이성질체들의 가용화현상을 UV/Vis 분광광도법을 이용하여 연구하였다. 온도의 변화에 따른 가용화상수값(<TEX>$K_s$</TEX>)의 변화를 측정함으로써 열역학적으로 분석하였으며, 그 결과 모든 이성질체들의 가용화에 대한 <TEX>${\Delta}Go^{\circ}_s$</TEX>와 <TEX>${\Delta}H^{\circ}_s$</TEX> 값은 측정한 범위 내에서 모두 음의 값을 나타내었다. 또한 dichlorophenol 이성질체들의 가용화현상에 미치는 n-부탄올과 NaCl의 효과에 대하여 조사하였다. 이러한 첨가제는 <TEX>$K_s$</TEX>와 CMC 값을 동시에 큰 폭으로 변하게 하였으며, 그런 결과로부터 각 dichlorophenol 이성질체들이 미셀 내에서 가용화되는 위치를 예측할 수 있었다. The interaction of dichlorophenol isomers with the micellar system of TTAB (tetradecyltrimethylammonium bromide) was studied by the UV/Vis spectrophotometric method. The solubilization constants (<TEX>$K_s$</TEX>) of dichlorophenol isomers into the micellar system have been measured with the change of temperature and the various thermodynamic parameters have been calculated and analyzed from these changes. The results show that the values of <TEX>${\Delta}G^{\circ}_s$</TEX> and <TEX>${\Delta}H^{\circ}_s$</TEX> are all negative within the measured temperature range. The effects of additives (n-butanol and NaCl) on the solubilization of dichlorophenol isomers have been also measured. There was a great change on the values of <TEX>$K_s$</TEX> and CMC simultaneously with these additives. From these changes we can postulate the solubilization sites of each isomers in the micellar system of TTAB.

Localization of HydrophobicN-Diazeniumdiolates in Aqueous Micellar Solution

The interaction of phenyl-substituted zwitterionic N-diazeniumdiolates PhCH(2)N[N(O)NO](-)(CH(2))(2)NH(3)(+) (1) and PhCH(2)N[N(O)NO](-)(CH(2))(2)NH(2)(+)CH(2)Ph (2) with aqueous micellar solutions of prototypal surfactants was investigated by means of UV/vis and (1)H NMR spectroscopy in order to establish the localization of hydrophobic N-diazeniumdiolates in micelles as a model for the binding of the NO donors in biological membranes. In the presence of sodium dodecyl sulfate (SDS), significant shifts of the apparent pK(a) values of 1 and 2 were observed, suggesting strong electrostatic interaction between the diazeniumdiolates and the negatively charged SDS micelles. No effect on both pK(a) and rate of NO release was found in the presence of Triton X-100. The solubilization site of micellar bound N-diazeniumdiolates was established by (1)H NMR spectroscopic studies, taking advantage of the spectroscopic effects induced by CH-pi interactions. The spectra indicate that in alkaline solutions of SDS 1 resides preferably at the micellar surface within the interfacial region, whereas the more hydrophobic NO donor 2 penetrates into the apolar region of the micelle. This suggests hydrophobic interaction as the main driving force for micellar binding of 2 in alkaline solution. Similar studies in presence of Triton X-100 indicate that 1 and 2 are adsorbed within the poly(oxyethylene) layer of the micellar surface rather than penetrating the palisade layer of the micelles. In alkaline solutions of hexadecyltrimethylammonium bromide (CTAB), 1 and 2 bind to the cationic micellar aggregates, whereby the solubilization site strongly depends on the hydrophobicity of the substrate. Up to a moderate pH of 8, the hydrophobic NO donor 2 penetrates the hydrocarbon region of the micelles. As a result, the rate of NO release from 2 is noticeably inhibited by the micellar aggregates due to the higher local concentration of hydroxide ions along the micelle-water interface. From solubilization studies, guidelines for the development and application of future NONOates can be derived. The rate of NO release from micellar bound diazeniumdiolates is determined by the surface charge of the micelles. This ability to tune stability is significant for the design and selection of potential NO delivery systems (drug formulations).

Interaction of a β‐sheet breaker peptide with lipid membranes

Aggregation of beta-amyloid peptides into senile plaques has been identified as one of the hallmarks of Alzheimer's disease. An attractive therapeutic strategy for Alzheimer's disease is the inhibition of the soluble beta-amyloid aggregation using synthetic beta-sheet breaker peptides that are capable of binding Abeta but are unable to become part of a beta-sheet structure. As the early stages of the Abeta aggregation process are supposed to occur close to the neuronal membrane, it is strategic to define the beta-sheet breaker peptide positioning with respect to lipid bilayers. In this work, we have focused on the interaction between the beta-sheet breaker peptide acetyl-LPFFD-amide, iAbeta5p, and lipid membranes, studied by ESR spectroscopy, using either peptides alternatively labeled at the C- and at the N-terminus or phospholipids spin-labeled in different positions of the acyl chain. Our results show that iAbeta5p interacts directly with membranes formed by the zwitterionic phospholipid dioleoyl phosphatidylcholine and this interaction is modulated by inclusion of cholesterol in the lipid bilayer formulation, in terms of both peptide partition coefficient and the solubilization site. In particular, cholesterol decreases the peptide partition coefficient between the membrane and the aqueous medium. Moreover, in the absence of cholesterol, iAbeta5p is located between the outer part of the hydrophobic core and the external hydrophilic layer of the membrane, while in the presence of cholesterol it penetrates more deeply into the lipid bilayer.

Partition of Indicaxanthin in Membrane Biomimetic Systems. A Kinetic and Modeling Approach

The solubilization site of indicaxanthin (Ind) in lipid bilayers was investigated by the kinetics of Ind oxidation by peroxyl radicals in water and in aqueous/L-alpha-dipalmitoyl-phosphatidylcholine (DPPC) vesicles, pH 7.4, and 37.0 and 48.0 degrees C, that is, in a gel-like and a crystal liquidlike bilayer state, respectively. The time-dependent Ind absorbance decay, matched with a successful simulation of the reaction kinetic mechanism by Gepasi software, supported a multistep pathway. Computer-assisted analysis allowed calculation of the rate constants associated with the reactions involved, the values of which decreased with increasing DPPC concentration. The binding constant calculated according to a pseudo two-phase distribution model did not vary with the physicochemical state of the vesicle, indicating location of Ind in a region whose state is not affected by temperature changes, at the interface between hydrophobic core and hydrophilic head groups. Other measurements carried out in the presence of dimyristoyl-phosphatidylcholine vesicles, indicated that the phytochemical was confined to the aqueous phase.

A Fluorescence Study of Novel Styrylindoles in Homogenous and Microhetrogeneous Media

In this paper are presented absorption and fluorescence emission properties of 3-styrylindoles viz. 3-(2-phenylethenyl-E)-NH-indole (1), 3-[2-(4-nitrophenyl)ethenyl-E)-NH-indole (2), 3-[2-(4-cyanophenyl)ethenyl-E]-N-ethylindole (3) and 3-[2-(4-cyanophenyl)ethenyl-E]-NH-indole (4) in organic solvents, 1,4-dioxane-water binary mixtures and micelles (SDS, CTAB and Triton-X-100). The fluorescence properties of 2-4 have been utilized to probe the microenvironment (binding constant, CMC, micropolarity and solubilization site) of the micelles.

Characterization of Nonionic Microemulsions by EPR. Part II. The Effect of Competitive Solubilization of Cholesterol and Phytosterols on the Nanostructure

One of the theories for the reduction of cholesterol (CH) in the blood stream by the consumption of phytosterols (PS) states that these two types of sterols compete for solubilization within the dietary mixed micelles (DMM). In this study, a fully dilutable nonionic microemulsion system was used as a model to explain a possible competitive solubilization mechanism of CH and PS molecules using an electron paramagnetic resonance (EPR) technique that reveals relevant intramicellar properties. The effect of the solubilized sterols on the structural changes occurring in the vicinity of the surfactant head groups or closer to the oil phase was examined by controlling the pH of the environment, which influences the probe locus between the surfactant molecules. The results indicate that the structure transformations in the surfactant layer closer to the vicinity of the head groups region are more pronounced than the structural changes occurring in the region between the surfactant tails closer to the oil phase, except for the oil-in-water (O/W) micelles region. The study also shows that when each of the sterols is solubilized alone, they occupy different solubilization sites within the microemulsion nanostructures, in comparison to their solubilization together. This behavior is most pronounced in 3:1 (wt ratio) CH/PS systems. The main conclusion is that cosolubilization of these sterols leads to competitive solubilization between the surfactant tails closer to the oil phase locus, where the CH molecules are pushed toward the interface by the PS molecules. This conclusion might better explain the competitive solubilization of the two sterols in the human digestive tract.

Photochromism of 7,4′-Dihydroxyflavylium in an AOT Reversed Micelle System

The investigation of a flavylium compound in AOT reverse micelles shows photochromic enhancement in a wide pH range, with features previously unobserved in other colloidal systems. In equilibrium, 7,4'-dihydroxyflavylium transforms into trans-chalcone species at pH above 2, but ion-pair formation of the flavylium species with the negatively charged AOT is observed until pH = 5. After irradiation, trans-chalcone species are transformed with high quantum yields into both flavylium and its quinoidal base (through cis-chalcone and hemiketal species) until pH equal to 9. While trans-chalcone is located at the hydrophobic side of the reverse micelle interface, flavylium species tend to solubilize in the water pool. Flash photolysis experiments probe essentially the trans-chalcone solubilization site, showing that photochromic conversion to flavylium species can be achieved without acid catalysis with a unimolecular rate constant of 0.22 s(-1), while the slow recovery to equilibrium after irradiation probes essentially the water pool with a experimental pH-dependent rate constant. The photochromic mechanism is discussed, promising new insights about the possibility of changing the reversed micelle interfacial properties using photoresponsive addictives like flavylium compounds.