FLUORESCENCE PROBE STUDIES ON THE SECOND CRITICAL MICELLE CONCENTRATION OF SEVERAL KINDS OF SURFACTANTS

The fluorescence intenstiy ratios (F₂/F₁) of excimer (F₂) to monomer (F₁) of probe (pyrene) were measured as a function of the concentration of the surfactant in several systems, which consist of sodium hexadecyl sulfonate (C₁₆As)-anionic surfactant, cetyltrimethylammonium bromide (CTAB)-cationic surfactant and pentaoxyethylene decyl ether (C₁₀E₅)-nonionic surfactant. The second CMC values were obtained according to F₂/F₁ ~ surfactant concentration curve break. In addition, we also studied the variation of second CMC vs NaCl concentration. It was found that the second CMC values of C₁₆A₅ and CTAB decreased with the increase of NaCl concentration. But the present of NaCl had no influence on the second CMC value of C₁₀E₅. Results showed that sphere-shaped micelles turn into rod-like micelle at the second CMC. The results were interpreted in terms of diffusion of pyrene molecules and the distribution of pyrene among micelles.     

Aggregation behaviors of amine-oxide gemini surfactants

The micellar aggregation of a series of gemini surfactants [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl?=?C₁₁H₂₃, C₁₃H₂₇, C₁₅H₃₁)] in aqueous media has been investigated. The results show that there is an excellent agreement among the critical micelle concentration (CMC) values obtained by surface tension and steady-state fluorescence methods. Because of the occurrence of self-coiling or the formation of pre-micellization, the CMC values, the I₁/I₃ values, and the micelle aggregation numbers (N_agg) at CMC (N_m) increase with the hydrophobic alkyl chain length increasing. Besides, vesicles are observed above the CMC for all these surfactants.     

Surface and Solution Properties of Cationic Gemini Surfactants with Primary Linear Alkanols

Using surface tension and fluorescence methods, the surface and solution properties of two cationic gemini surfactants {pentanediyl-1,5-bis(dimethylcetylammonium bromide) and hexanediyl-1,6-bis(dimethylcetylammonium bromide)} (referred to as 16-5-16 and 16-6-16) have been studied in the presence and absence of primary linear alkanols. Parameters studied include the critical micelle concentration (CMC), C ₂₀ (the surfactant concentration required to reduce the surface tension of the solvent by 20 mN·m^?1), Г _max (maximum surface excess), and A _min (minimum surface area per molecule). These parameters indicate mixed micelle formation and, therefore, surfactant-additive interaction parameters in mixed micelles and mixed monolayers, as well as activity coefficients, were calculated. A synergistic effect was observed in all instances and was found to be correlated with the chain length of the alkanols. The CMC values of 16-s-16 (s = 5, 6) decrease with increasing alkanol concentration and the extent of this effect follows the sequence: 1-octanol (C₈OH) > 1-heptanol (C₇OH) > hexan-1-ol (C₆OH) > 1-pentanol (C₅OH) > butanol (C₄OH). The micelle aggregation number (N _agg) of mixed micelles has been obtained using the steady state fluorescence quenching method. The micropolarity of gemini/alkanol systems has been evaluated from the ratio of intensity of peaks (I ₁/I ₃) of the pyrene fluorescence emission spectra. Results are interpreted on the basis of the structure of mixed micelles and monolayers.     

Surfactant ion electrode measurements of sodium alkylsulfate and alkyltrimethylammonium bromide micellar solutions

EMF measurements in water at 25°C have been made using surfactant ion and counterion electrodes on two homologous series of long chain surfactants, the sodium alkylsulfates (R=n-C₈H₁₇ to n-C₁₄H₂₉) and the alkyltrimethylammonium bromides (R=C₁₀H₂₁ to C₁₆H₃₃). The data show evidence of association below the critical micelle concentration (CMC) but not of micelle ordering due to coulombic repulsion above this concentration.     

BINDING OF IONIC SURFACTANTS ON OPPOSITELY CHARGED POLYELECTROLYTES OBSERVED BY FLUORESCENCE METHODS

Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C_(12)E_8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity I_E/I_M of a cationic probe l-pyrenemethylamine hydrochloride(PyMeA·HCl) and the non-radiative energy transfer (NRET) I_(Py)/I_(Np) of naphthalene to pyrene for labeled polyelectrolyteswere chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes. The 1:1aggregation of polyelectrolyte-CTAB with respect to the charge was found as long as the CTAB concentration was slightlyhigher than its critical aggregation concentration (CAC). The intermolecular NRET indicated that the CTAB-boundpolyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails. However, neither 1:1polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to itsweaker hydrophobicity of 12 carbon atoms in the tail, which is shorter than that of CTAB. As known from the fluorescenceresults, nonionic surfactant C_(12)E_8 did not bind on the anionic polyelectrolytes, but the presence of PAMPS promoted themicelle formation for C_(12)E_8 at the CAC slightly below its critical micelle concentration (CMC). The solid complex of dansyllabeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of thepolyelectrolyte or with alkane tail length of the surfactant. SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC, respectively.     

Effect of structural variation within cationic azo-surfactant upon photoresponsive function in aqueous solution

The cationic azo-surfactants possessing different spacers and tail alkyl chain lengths have been synthesized by azocoupling ofp-alkylaniline orop-ethoxyaniline with phenol, followed by alkylation and quaternalization with dibromoalkane and trimethylamine, respectively. These surfactants showed a good solubility in water. A reversibletrans-cis isomerization of the azosurfactants by photoirradiation was assessed by UV-Vis absorption spectra. Due to a difference in HLB between thetrans- andcis-surfactants, the observed critical micelle concentration (CMC) values and the electric conductivity of the surfactant solution at above the CMC were significantly affected by the photoinducedtrans-cis isomerization. The azo-surfactants bearing moderate alkyl chain lengths such as surfactants 6 (R₂=C₂H₄, R₃=C₄H₉) and 9 (R₂=C₄H₈, R₃=C₂H₅) were found to be effective to achieve large CMC changes (3.6 mmol/L for 6 and 5.9 mmol/L for 9) by UV-light irradiation. The replacement of the tail chain species also affected the photoresponsive function. The surfactant 12, possessingp-ethoxy group as the tail chain, was found to form a stable micelle aggregation as compared with the structurally related surfactant 10 having ethyl unit as its tail group, but it exhibited a large CMC change (5.3 mmol/L) by UV-light irradiation.     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

A ferric-cyanide-bridged one-dimensional dirhodium complex with (18-­crown-6)­potassium cations

The crystal structure of the title compound, catena-poly[bis[aqua(18-crown-6)­potassium] di­aqua(18-crown-6)­potassium [[tetra-μ-benzoato-2:3κ⁸O:O′-μ-cyano-1:2κ²C:N-tetra­cyano-1κC-irondirhodium(Rh—Rh)]-μ-cyano-1κC:3′κN] octahydrate], [K(18-crown-6)(H₂O)]₂[K(18-crown-6)(H₂O)₂]­[FeRh₂(C₇H₅O₂)₄(CN)₆]·8H₂O, where (18-crown-6) is 1,4,7,10,13,16-hexaoxa­cyclo­octa­decane (C₁₂H₂₄O₆), has been determined. Ferric cyanides connect the dirhodium units to form a one-dimensional chain compound. [K(18-crown-6-ether)(H₂O)₂] cations (with inversion symmetry) and [K(18-crown-6-ether)(H₂O)] cations (in general positions) are located between the chains.     

青霉素G钾盐对SDS水溶液物理化学性质的影响及其在SDS/n-C5H11OH/H2O体系中的释放

The effects of penicillin potassium salt （PenK） on the solubility, Krafft temperature TK, critical micelle concentration CMC of SDS micelle and the phase behavior of SDS/n-C5H11OH/H2O system were studied. The partial phase diagrams of SDS/PenK/H2O system at different temperatures were determined. The release amounts of PenK in SDS/n-C5H11OH/H2O system and the distribution coefficient of PenK between micelle and water were measured by UV-Vis spectroscopy. The results show that in the presence of PenK, the CMC of SDS was decreased while the TK of SDS was increased and the solubility of SDS in both water and SDS/n-C5H11OH/H2O oil in water （O/W） microemulsion was decreased, but increased in water in oil （W/O） microemulsion. SDS micelles and SDS/n- C5H11OH/H20 O/W microemulsion could accelerate the release rate of PenK. The addition of SDS and water could both increase the release rate of PenK, whereas the presence of n-C5H11OH reduced the release rate of PenK. The above results were related to the electrostatic repulsion between PenK and SDS.     

Ein Netzwerk aus Iodid-Ionen und Iod-Molekülen in der Kristallstruktur von [Pr(Benzo-15-Krone-5)2]I21

A Three Dimensional Network of Iodide Ions and Iodine Molecules in the Crystal Structure of [Pr(Benzo-15-Crown-5)₂]I₂₁ Black polyhedra of [Pr(benzo-15-crown-5)₂]I₂₁ were grown from an ethanol / dichlormethane solution of PrI₃, benzo-15-crown-5 and I₂. The crystal structure (orthorhombic, P2₁cn, a = 1201.1(1), b = 2168.3(1), c = 2571.1(1) pm, Z = 4) is built up from sandwich like cations [Pr(benzo-15-crown-5)₂]³⁺ and polyiodide anions I₂₁^3-. This unique polyiodide anion exhibits a complex connection pattern of iodide ions and iodine molecules with variable bond lengths forming a complicated network.     

Preparation and Application of Cholesteryl‐Macrocyclic Polyether Liquid Crystals and Surfactants

Macrocyclic polyethers containing a cholesteryl moiety, e.g., cholesteryl benzo‐15‐crown‐5 (C₂₇H₄₅OOC‐B15C5) and cholesteryl cryptand22 (C₂₇H₄₅OOC‐Cryptand22), were synthesized. The cholesteryl crown ether C₂₇H₄₅OOC‐B15C5 showed liquid crystal characteristics which were observed by polarizing microscopy. In contrast, the cholesteryl cryptand C₂₇H₄₅OOC‐Cryptand22 showed no liquid crystal characteristics. The doping effect of inorganic salts on the liquid crystal formation of cholesteryl benzo‐15‐crown‐5 was also investigated, revealing that the addition of salts resulted in narrower liquid crystal temperature ranges. Both cholesteryl cryptand C₂₇H₄₅OOC‐Cryptand22 and cholesteryl crown ether C₂₇H₄₅OOC‐B15C5 also exhibited the distinctive characteristics of surfactants in solutions. Fluorescence probe of pyrene and surface tension measurement were applied as sensitive tools to study the formation of the micelles and determine the critical micellar concentration (CMC) of the cholesteryl cryptand and crown ether surfactants. The salt effect on the CMC of the cholesteryl cryptand surfactant was also investigated and is discussed. Furthermore, the cholesteryl benzo‐15‐crown‐5 was successfully employed as a quite good phase transfer catalyst for the oxidation of alcohols, e.g., benzhydrol, with NaMnO₄ as an oxidant. Effects of temperature, solvent and concentration of the crown ether catalyst on the oxidation of benzhydrol were also investigated.     

Study of mixed micellar aqueous solutions of sodium dodecyl sulfate and amino acids

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I ₁/I ₃ ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.     

Metal-containing ditopic receptors for molecular recognition of diammonium cations

Two new ditopic receptors for α,ω-alkanediyldiammonium cations based on a tetraazamacrocyclic (cyclidene) nickel(II) complex bearing two crown-ether residues were synthesized. The studies of the host-guest interaction between the receptors and a series of α,ω-diammonium salts by NMR titration in acetonitrile-d₃ showed that 1:1 complexes are formed with K_assoc∼10³-10⁵ M⁻¹. Receptor 1 with benzo-15-crown-5 arms showed substantial selectivity in binding of trimethylene- and tetramethylenediammonium dications, and 1-2 orders of magnitude weaker binding of shorter (C₂) or longer (C₅ and C₆) diammonium cations. Receptor 2 with benzo-18-crown-6 arms showed higher affinity to all studied diammonium cations, but the recognition of the length of α,ω-diammonium cations was less pronounced.     

Zur Struktur zweier Isothiazolium‐Polyiodide (C19H16FeNS)I5 und (C15H12NS)2I8

On the Structure of Two Isothiazolium Polyiodides (C₁₉H₁₆FeNS)I₅ and (C₁₅H₁₂NS)₂I₈ By oxidation of 3‐phenylamino thiopropenones with iodine two isothiazolium polyiodides were obtained, whose structures have been determined by X‐ray structure analysis. 2‐Phenyl‐5‐ferrocenyl‐isothiazolium pentaiodide(C₁₉H₁₆FeNS)I₅ forms a layer structure with isothiazolium cations and polyiodide anions. The polyiodide layers contain pentaiodide ions I₅^–, triiodide ions I₃^– and iodine molecules I₂. Bis(2,5‐diphenyl‐isothiazolium) octaiodide (C₁₅H₁₂NS)₂I₈ also forms a layer structure with isothiazolium cations and polyiodide anions. The polyiodide layers are built up by octaiodide ions I₈^2–, pentaiodide ions I₅^– and triiodide ions I₃^–.     

A UV-Visible Study of Partitioning of Pyrene in an Anionic Surfactant Sodium Dodecyl Sulfate

The interaction of hydrophobic dye pyrene with sodium dodecyl sulphate (SDS), an anionic surfactant, was studied in the process of solubilization. Difference UV-Visible spectroscopy was used to carry out the study. The partition coefficient (K_x), and number of dye molecules incorporated per micelle (n) was calculated. High K_x value shows that pyrene is partitioned strongly from polar to nonpolar environment. Steady-state fluorescence spectroscopy is used to check the environment of the pyrene as it is a well-known fluorescent probe. Onset of slope in curves is used to determine the critical micelle concentration (CMC).     

Hexadecyltrimethylammonium bromide micellization in glycine,diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg^?1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔG _HP ^○ , free energy associated with the surface contributions, ΔG _S ^○ , standard free energy, ΔG _m ^○ , enthalpy, ΔH _m ^○ , and entropy, ΔS _m ^○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I ₁/I ₃ ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.     

Micellar parameters of diblock copolymers and their interactions with ionic surfactants

The interactions of non-ionic amphiphilic diblock copolymer poly（oxyethylene/oxybutylene）(E₃₉B₁₈) with anionic surfactant sodium dodecyl sulphate（SDS） and cationic surfactant hexadecyltrimethylammonium bromide（CTAB） were studied by using various techniques such as surface tension,conductivity,steady-state fluorescence and dynamic light scattering.Surface tension measurements were used to determine the critical micelle concentration（CMC） and thereby the free energy of micellization(△G_mic),free energy of adsorption(△G_ads),surface excess concentration（Γ） and minimum area per molecule（A）.Conductivity measurements were used to determine the critical micelle concentration（CMC）,critical aggregation concentration（CAC）,polymer saturation point（PSP）,degree of ionization（α） and counter ion binding（β）. Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles taken place due to the interactions of diblock copolymers with ionic surfactants.The ratio of the first and third vibronic peaks（I₁/I₃） indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant interactions.Aggregation number（N）,number of binding sites（n） and free energy of binding （△G_b） for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching method.     

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with ¹H and ¹³C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K_v for pyrene in the micelle and in aqueous solution was about 10⁵. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R_h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.     

Interaction of slightly cross-linked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate. Diffusion of surfactant ions in gel

The dynamics of the changing microenvironment of the fluorescent probe pyrene in slightly cross-linked networks of poly(diallyldimethylmmonium bromide) during diffusion of sodium dodecyl sulfate (SDS) in the gel phase has been investigated by fluorescence spectroscopy. Values of the spectral ratio I₃/I₁ for pyrene monomer included in SDS micelles in the swollen networks fall between the corresponding values for pyrene in water and for pyrene dissolved in SDS micelles in aqueous solution. In the narrow interval of the surfactant concentrations in the gel phase, the formation of pyrene excimers is observed. The values of the critical micelle concentration in the gel phase (ca. 5 × 10^?4 to 8 × 10^?4 mol/L) are tenfold lower than in aqueous solutions of the surfactant. The effective micellar diffusion coeffecient D in the gel phase increases with increasing swelling of the network. © 1993 John Wiley & Sons, Inc.