Proton nuclear magnetic resonance and laser photolysis studies of pyrene derivatives in aqueous and micellar solutions

Binary mixtures with novel monomeric and dimeric surfactants: influence of the head group nature and number of hydrophobic chains on non-ideality

The micellization and micellar growth in the mixtures of N,N-dimethyl, N-phenyl,N-dodecylammonium bromide, PH12, N,N-dimethyl,N-ciclohexylmethyl,N-dodecylammonium bromide, CH12, and their two dimeric counterparts m-dimethylphenyl-α-ω-bis(dodecyldimethylammonium) bromide, 12PH12, and m-dimethylciclohexyl-α-ω-bis(dodecyldimethylammonium) bromide, 12CH12, with dodecyltrimethylammoniumbromide, DTAB, and with N-decanoyl N-methylglucamide, MEGA10, were investigated at 303 K. Circular dichroism, CD, experiments showed the formation of mixed micelles. Two-dimensional, 2D, rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments indicated that the arrangement of the rings in the pure and mixed micelles is similar, with the rings bent into the micelle interior avoiding contact with water. Application of different theoretical approaches shows that PH12 and CH12 mixtures with DTAB and with MEGA10 behave almost ideally. The binary systems of 12PH12 and 12CH12 with DTAB and with MEGA10 show a non-ideal behavior. An increment in the solution mole fraction of MEGA10 and DTAB diminishes the tendency of the micellar aggregates to grow.

Effects of organic solvent addition on the aggregation and micellar growth of cationic dimeric surfactant 12-3-12,2Br-

The micellization and micellar growth of cationic dimeric surfactant propanediyl-alpha-omega-bis(dodecyldimethylammonium) bromide, 12-3-12,2Br-, have been studied in several water-organic solvent mixtures. The organic solvents were ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, acetonitrile, dioxane, formamide, and N,N-dimethylformamide. Results showed that the aggregation process was less favored in the binary mixtures than in pure water, which was explained by considering the influence of the solvophobic effect on micellization. The addition of organic solvents was accompanied by a diminution in the average aggregation number, Nagg, of the dimeric micelles. This diminution was due to the decrease in the interfacial Gibbs energy contribution, Delta G0interfacial, to the Gibbs energy of micellization caused by the decrease in the hydrocarbon/bulk-phase interfacial tension. As a result of the micelle size diminution, the concentration at which the sphere-to-rod transition occurred, C*, was higher in the mixtures than in pure water. Micelle size reduction is accompanied by a decrease in the ionic interactions and in the extra packing contribution to the deformation of the surfactants tails, making the formation of cylindrical micelles less favorable.

Acid–base equilibrium of puerarin in CTAB micelles

Electronic absorption spectra, fluorescence emission spectra, 1HNMR and ab initio quantum calculation are used to study the acid-base equilibrium of puerarin in cetytrimethylammonium bromide (CTAB) micelles with different microstructures and microenvironments. Experiments suggest the microenvironment provided by CTAB micelle cause the acid-base equilibrium of puerarin to move to the deprotonation reaction. The changes in the chemical shifts of the individual groups of protons in CTAB indicate that the location of puerarin changes from the inner to the outer of the CTAB micelles with an increase in puerarin concentration, which enhances the interaction between puerarin and CTAB. The binding of puerarin with CTAB micelle is a spontaneous (deltaG<0) and endothermic process (deltaH<0), and the hydrophobic and electrostatic force is the main driving force for its solubilization.

External Electric Field Effects on Fluorescence of Pyrene Butyric Acid in a Polymer Film: Concentration Dependence and Temperature Dependence

Fluorescence spectra and electrofluorescence spectra (plots of the electric field-induced change in fluorescence intensity as a function of wavelength) have been measured at different temperatures for pyrene butyric acid (PBA) in a PMMA film at different concentrations. At a low concentration of 0.5 mol % where fluorescence emitted from the locally excited state of PBA (LE fluorescence) is dominant, LE fluorescence spectra show only the Stark shift in the presence of an electric field (F), which results from the difference in molecular polarizability between the ground and emitting states. At a high concentration of 10 mol % where the so-called sandwich-type excimer fluorescence (EX(1)) is dominant, both EX(1) and LE fluorescence are quenched by F. Another fluorescence assigned to a partially overlapped excimer (EX(2)) also exists at room temperature, and this emission is enhanced by F. As the temperature decreases, three fluorescence emissions whose electric field effects are different from each other become clear besides EX(1) and LE fluorescence, indicating that at least five fluorescence components exist at high concentrations at low temperatures. At a medium concentration of 5 mol % where EX(1) is comparable in intensity to the LE fluorescence, the intensity of EX(1) is not affected by F at any temperature, but LE fluorescence and EX(2) are markedly influenced by F at room temperature, and four fluorescence emissions are confirmed at low temperatures.

New fluorescence method for the determination of the critical micelle concentration by photosensitive monoazacryptand derivatives

A novel fluorescence method for the determination of the critical micelle concentration (cmc) is reported. The cmc values of nonionic and anionic surfactants were evaluated utilizing a photosensitive monoazacryptand-Ba2+ complex, whose fluorescence intensity is sensitively changed by environmental conditions based on the photoinduced electron transfer (PET) mechanism as a fluorescent probe (PET method). Based on a comparison of the cmc values obtained by the PET method versus those obtained by conventional fluorescence-based methods as well as the values reported in the literature, one can conclude that the PET method is useful for the cmc determination. In particular, the PET method was more effective for the cmc determination of nonionic surfactants with very low cmc values (< 10(-5) M) than any other fluorescence-based method. In the cases of anionic surfactants, the PET method revealed the formation of the premicellar aggregates comprised of surfactant molecules and fluorescent probes below the cmc. Moreover, the hydrophobicity around the monoazacryptand-Ba2+ complex incorporated into various nonionic surfactant micelles was evaluated by this PET method.

Kinetic study in water-ethylene glycol cationic, zwitterionic, nonionic, and anionic micellar solutions

The spontaneous hydrolysis of phenyl chloroformate was studied in water-ethylene glycol, EG, cationic, zwitterionic, nonionic, and anionic micellar solutions, the surfactants being tetradecyltrimethylammonium bromide, tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, tricosaoxyethylene glycol ether, and sodium dodecyl sulfate. The dependence of the observed rate constant on surfactant concentration as well as on the percentage by weight of EG, varying from 0 to 50 wt %, was investigated. Information about changes in the critical micelle concentrations, in the micellar ionization degrees (for ionic surfactants), in the aggregation numbers, and in the polarity of the interfacial region of the micelles upon changing the weight percent of EG was obtained through conductivity, surface tension, spectroscopic, and fluorescence measurements. A simple pseudophase model was adequate to rationalize the kinetic data. Micellar medium effects were explained by considering charge-charge interactions and polarity, ionic strength, and water content in the micellar interfacial region. The acceleration of the reaction produced by an increase in the amount of EG present in the mixture was explained on the basis of the substantial decrease in the equilibrium binding constant of phenyl chloroformate molecules to the micelles, resulting in the contribution of the reaction taking place in the bulk water-EG phase being more important. The weight percent of EG did not substantially influence the rate constant in the micellar pseudophase.

Interaction of morin with CTMAB: aggregation and location in micellar

The aggregation and location of morin in CTMAB micellar solution was studied by light scattering spectra, electronic absorption spectra and pulsed FT NMR techniques. The difference in the light scattering property of morin with and without CTMAB proved that a large particle of the morin-CTMAB associate formed. Morin has a self-assembly tendency, but the assembly number is not high. With the increase of morin concentration, morin changed from a monomer to dimer. The hyperchromic and bathochromic effect of morin, with the increase in pH value or

A model for specific interactions of manganese-phthalocyanine in protic media

Extinction coefficients (e) changes of manganese phthalocyanine (Mn-Pc) were studied in different organic solvents and related to solvent polarity scales; (Kosower's values (Z), Dimroth's values (E T), donor numbers (DN) and linear solvation energy relationships (LSER) or linear free energy relationships (LFER));, theoretical molecular orbital calculations and ligand/solvent coordination processes in order to predict molecular interaction with the medium and identification of predominant intermolecular forces.

Increasing drug solubility by means of bile salt-phosphatidylcholine-based mixed micelles

Study of the solubilization of commercial grades of soya phosphatidylcholine (SPC) with different purities by bile salts (BS) indicated that only highly pure grades of SPC are suitable for the preparation of clear solutions of BS/SPC-mixed micelles (BS/SPC-MM). The solubilizing capacity of different BS towards SPC increased in the following order; Sodium cholate (SC) < sodium deoxycholate (SDC) < sodium glycocholate (SGC). Moreover, egg phosphatidylcholine (EPC) was solubilized to a higher extent than SPC. Furthermore, the solubility study of different drugs in the prepared MM showed substantial enhancement of solubility, the extent of which is essentially affected by the chemical nature of the drug and the composition of MM. Benzodiazepine drugs such as clonazepam, tetrazepam, diazepam, and lorazepam displayed higher affinity for MM compared with BS alone, whereas steroidal drugs, such as estradiol, prednisolone and progesterone, compared with benzodiazepines, displayed relatively higher affinity for BS alone. The solubilizing capacity of MM for the different drugs was increased to different degrees by the addition of benzyl alcohol which was comparable to the solubility of the drug in pure benzyl alcohol. The interaction between benzyl alcohol and the drug in MM could be proved by NMR.

Characterization of liposomes and other lipid assemblies by multiprobe fluorescence polarization

This minireview describes the use of fluorescence polarization to characterize the dynamics and organization of biological membranes, lipoproteins, liposomes and other lipid-based assemblies. The advantages, disadvantages and limitations of this method are discussed. There is special emphasis on the multiprobe approach, which can monitor various parts of the lipid membrane or assembly. The fluorescence polarization, anisotropy and the total fluorescence intensity are defined and their graphic presentation described. A user guide for the actual measurements is given. It describes how to apply fluorescence polarization, especially how to select the proper extrinsic probe and to optimize the measurement regarding theoretical and practical issues, the determination of a fluorescent probe location in the assembly, how to introduce the probe to the lipid assembly, what is the ideal ratio of the probe to the lipid, dealing with the spectrofluorimeter problems and how to overcome disturbances introduced by light scattering. It is shown here, that even though there are disadvantages in using fluorescence polarization, this approach provides a highly sensitive and simple means for assessing the subtle and more pronounced changes in the structure of lipid assemblies.

Characterization of the core and surface of human plasma lipoproteins. A study based on the use of five fluorophores

The physical properties of the core and the surface of five classes of human plasma lipoproteins were investigated using five fluorescent probes. The location of the fluorescence probes in the lipoprotein assembly was determined using collisional quenching and resonance energy transfer. The fluorophores monitor different regions of the lipoproteins, as shown by fluorescence quenching. Diphenylhexatriene (DPH) and methyl trans-parinaric acid (MTPA), which are apolar molecules, are localized mainly in the lipoprotein core. Their distribution into the surface is dependent upon the volume ratio of the hydrophobic part of the envelope and the core. The polar fluorophores, trimethylaminodiphenylhexatriene (TMADPH), hydroxycoumarin (HC) and trans-parinaric acid (TPA) are anchored in the glycerol skeleton region of the surface monolayer with the fluorophore group of HC in the headgroup region of the phospholipids. We determined the temperature-dependent steady-state fluorescence anisotropy (r) of these fluorophores in the four major classes of lipoproteins: VLDL, LDL, HDL2, HDL3 and in abnormal HDL from abetalipoproteinemia patients (HDLab). The hydrophobic probes, DPH and MTPA, reported the r values in the lipoproteins in the following order: LDL greater than HDL2 greater than HDL3 much greater than VLDL. This order correlates with the triglyceride-to-cholesterol ester (TG/CE) ratio in the core of lipoproteins. The polar probes HC, TPA and TMADPH reported the r value in a different order: HDL2, HDL3 greater than or equal to LDL much greater than VLDL. This is compatible with the decreasing order of the protein to lipid ratio in the envelope of these lipoproteins. HDLab was investigated by three fluorescent probes: DPH, TMADPH and HC. The anisotropy of DPH in HDLab was larger than that of either HDL2 or HDL3 in normal donors, probably due to the smaller TG/CE ratio in HDLab. The lower r values reported by HC and TMADPH for HDLab are not fully understood and may be related to other factors such as acyl chains composition. The characterization of lipoproteins by fluorescence depolarization using probes of known location in the lipoprotein assembly is very sensitive and may be used to report deviation from the norm.