Search

[Display omitted] • Solubilization of polycyclic aromatic compounds was studied using supralong-chain surfactants. • The solubilization ability of surfactant was maximized in the system of C22-2Am. • The solubilization site of compounds in the micelles shifted from the palisade layer to the vicinity of the hydrophilic groups. • Extension of the alkyl chain length of the surfactant was advantageous for solubilization. The dissolution of poorly water-soluble compounds in micelles via hydrophobic interactions is termed solubilization. The solubilization of polycyclic aromatic compounds, namely, naphthalene, anthracene, and pyrene, was studied using supralong-chain surfactants with two consecutive cationic hydrophilic groups [C n H 2n+1 N+(CH 3) 2 -(CH 2) 2 -N+(CH 3) 3 2Br-: C n -2Am (n = 18, 20, and 22)] and typical cationic surfactants [C n H 2n+1 N+(CH 3) 3 Br-: C n -Am (n = 12, 14, and 16)]. Long alkyl chains in hydrophobic surfactants are advantageous for forming a large micellar core. The maximum quantity of solubilized polycyclic aromatic compounds increased as the alkyl chain length of the surfactant increased. Therefore, the molar solubilization ratio (MSR), which represents the solubilization ability of the surfactant, was maximized when the alkyl chain length was C22-2Am. Similarly, the Gibbs free energy (Δ G 0) associated with the solubilization of polycyclic aromatic compounds was also lowest for C22-2Am. Surfactants with long alkyl chains functioned as excellent solubilizers. The solubilization sites of the polycyclic aromatic compounds were determined using two-dimensional NMR and small-angle X-ray scattering (SAXS) measurements. As the molecular size of the polycyclic aromatic compounds increased, the solubilization positions in the micelles shifted from the palisade layer to the vicinity of the hydrophilic groups. Extension of the alkyl chain length of the surfactant resulted in an increase in the palisade region of the micelles, which was advantageous for solubilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of charge on foam separation was studied using several anionic dyes. • The first-order rate constant (k) of these dyes were determined using DTAC. • The removal rate increased with increasing number of anionic groups. • The multiple anionic groups provided strong binding at the adsorption monolayer. • The number of ionic groups in the substance significantly affected the removal rate. Substances with an opposite charge to that of the ionic surfactant are preferentially removed during foam separation. The effect of charge on foam separation was studied using cationic surfactant dodecyltrimethylammonium chloride (DTAC) and several anionic dyes with different numbers of anionic groups: Acid Blue 119 (mono-anion), Ethyl Orange (mono-anion), Xylene Fast Yellow 2G (di-anion), and Acid Yellow 23 (tri-anion). The negatively charged surfactant counterion chloride (Cl-) and the anionic dye (Acid Blue 119) were competitively removed during foam separation. The first-order rate constant (k) for the removal of the two types of anions was estimated to be 8 × 10-4 min−1 for Cl- and 2 × 10-3 min−1 for Acid Blue 119. The results indicated that the target material Acid Blue 119 was removed 2.5 times faster than the surfactant counterion Cl-. The k values of these dyes were determined using the DTAC at 298 K. The results showed that the removal rate increased with increasing number of anionic groups among the investigated anionic dyes: Acid Blue 119 < Ethyl Orange < Xylene Fast Yellow 2G < Acid Yellow 23. The increase in the number of anionic groups in the dye provided binding at multiple points to the adsorption monolayer of the surfactant and became stronger in the foam. In foam separation using an ionic surfactant, it was found that the number of ionic groups in the substance significantly affected the removal rate. [ABSTRACT FROM AUTHOR]

Abstract: Double or triple quaternary ammonium head groups were designed to improve the solubility of supralong alkyl chain surfactants. In the surfactant head group, quaternary ammonium groups are connected by an ethylene spacer. Micellar shapes of divalent surfactants [C n H 2n +1N+(CH3)2–(CH2)2–N+(CH3)3 2Br−: C n -2Am (n =18, 20, and 22)] and trivalent surfactants [C n H 2n +1N+(CH3)2–(CH2)2–N+(CH3)2–(CH2)2–N+(CH3)3 3Br−: C n -3Am (n =18, 20, and 22)] were studied in aqueous solutions by means of dynamic light scattering (DLS) and transmission electron microscopy (TEM). Changes in the surfactant concentration have a small influence on the apparent hydrodynamic radii (rh ) of the molecular aggregates in both surfactant series. Average values of rh of aggregates are 60–90nm for C n -2Am (n =18, 20, and 22) and 2–40nm for C n -3Am (n =18, 20, and 22). TEM micrographs showed that aggregates of C n -2Am (n =18, 20, and 22) typically formed rod-like micelles. In contrast, trivalent surfactants of C n -3Am (n =18, 20, and 22) formed spherical (C18-3Am) or ellipsoidal micelles (C20-3Am and C22-3Am). Moreover, the degree of micellar counterion binding for these surfactants was determined by using a bromide ion-selective electrode, which indicated relatively high values (0.8–0.9) for C n -2Am (n =18, 20, and 22) and more common values (0.5–0.8) for C n -3Am (n =18, 20, and 22). The size of the aggregates is closely related to the degree of counterion binding. [Copyright &y& Elsevier]

Abstract: To investigate the effect of divalency on the micelle properties, we synthesized divalent cationic surfactants composed of fluorocarbons and double quaternary ammonium groups N,N-dimethyl-N-[2-(N′-trimethylammonium)ethyl]-1-(3-perfluoroalkyl-2-hydroxypropyl) ammonium bromide [; where n (=8 or 10) represents the number of carbon atoms in the fluorocarbon chain]. The double quaternary ammonium groups are continuously combined by the ethylene spacer in the surfactant head group, which clearly distinguishes the molecular design of the surfactant from those of the other typical divalent surfactants, bolaform and gemini types. The presence of the divalent head group results in an advantageous increase in their solubility [i.e., rise in the critical micelle concentration (cmc)]; however, the extra electrostatic repulsion between divalent cations decreases the surface activity in comparison with monovalent homologous fluorinated surfactants. The cmc, surface tension at cmc, and area occupied by a surfactant molecule in aqueous solution at 298.2K are 4.32mM, 30.6mNm−1, and 0.648nm2 molecule−1, respectively, for , and 1.51mM, 30.4mNm−1, and 0.817nm2 molecule−1, respectively, for . The micellar size and shape were investigated by dynamic light scattering and freeze-fracture transmission electron microscopy (TEM). The TEM micrographs show that (n =8 and 10) mainly forms ellipsoidal micelles approximately 10–100nm in size for n =8 and approximately 10–20nm in size for n =10. The degree of counterion binding to micelle was determined by selective electrode potential measurements, and the results of 0.7–0.8 agree with the average values for conventional monovalent ionic surfactants. [Copyright &y& Elsevier]

Abstract: The maximum solubilities of homologous series of n-alkylbenzene and n-perfluoroalkylbenzene in aqueous solutions of surfactants n-tetradecyltrimethylammonium chloride (TTAC) and N-(1,1-dihydroperfluorodecyl)--trimethylammonium chloride (C10F-TAC) were measured as a function of the surfactant concentration at 298.2 K. There are four solubilization systems in viewpoints of hydrocarbons and fluorocarbons. In general, in all systems, the maximum solubility decreased with an increase in the alkyl carbon length of the solubilizates. The homogeneous combinations of solubilizates and solubilizers have higher affinity than heterogeneous combinations. The affinity between a hydrocarbon and a fluorocarbon can be clarified by determining the Gibbs free energy () on solubilization by thermodynamic analysis. The largest negative value of was obtained for the homogeneous system of n-perfluoroalkylbenzene and C10F-TAC, whereas the smallest value was obtained for the heterogeneous system of n-perfluoroalkylbenzene and TTAC. The contributions of methylene and perfluoromethylene to Gibbs energy, namely, and , were found to be −2.6 and −2.9 kJ mol−1, respectively, for the TTAC solution, whereas the respective values for the C10F-TAC solution were −2.0 and −3.3 kJ mol−1. [Copyright &y& Elsevier]

New cationic fluorinated surfactants and new types of fluorinated surfactants having fluorocarbon–hydrocarbon hybrids, dimeric and polymeric structure have been synthesized recently. Their synthesis requires many steps and consequently requires much time and high expense. Since the fluorinated surfactants have unusual molecular aggregation properties, 19F-NMR, novel fluorescence probes and cryo-transmission electron microscope techniques have been applied to study their aggregation behaviour in aqueous systems. Their unique characteristics are summarized as follows: (1) the dissolution process from solid state to dissolved aggregate state requires a very long time for the long chain fluorinated surfactants under thermodynamic equilibrium. The equilibration time can be reduced at higher temperatures; (2) interfacial properties and critical micelle concentration (CMC) are influenced by the nature of the hydrophobic terminal groups (CF3− or H&z.sbnd;CF2−); (3) the fluorocarbon functionality can make it possible even for single-chain amphiphiles to form vesicles or lamellar structures; (4) the hybrid surfactant made of both hydrocarbon and fluorocarbon chains showed a life time of 2.0×10−3 s for the exchange rate between the monomeric and the micellar states at the CMC and moreover, these detergents can cosolubilize fluorocarbon–hydrocarbon mixed solubilizates. [Copyright &y& Elsevier]

Anionic surfactants that form floating bubbles can adsorb metal ions and change foams at the gas–liquid interface. The final rate of ion removal by foam separation determines the selectivity or priority of adsorption of ions. Foam separation was conducted to remove multi-component chlorides of period 4 transition metals (Mn, Fe, Co, Ni, Cu, and Zn) by using sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS) as surfactants. The first-order ion-removal rate constant (k) did not completely change with an increase the atomic number of transition metals. The difference in removal rate constant (k) between the elements was not significant in multi-component chlorides of transition metals. On the other hand, the foam separation was performed in a one-component of period 4 transition metal (Mn, Fe, Co, Ni, Cu, and Zn) using SDeS (8 mmol L−1) for comparing k from alkaline earth metals having different ionic radii, respectively. The transition metal was continuously removed over time, whereas the counter ion (sodium) of the surfactant was not efficiently removed. The results also showed that the k in the one-component 4 transition metal system also slightly increased with increasing ionic radius in 5 h of foam separation. A linear relationship was observed between the first-order ion-removal rate constant (k) by foam separation and the ionic radius of the divalent metal ion. These results indicated that the selectivity of cation adsorption on the soluble monolayer is closely related to the ionic radius of the metal ion. Unlabelled Image • Foam separation was applied to remove multi components of period 4 transition metal chlorides using anionic surfactants. • The removal rate constant (k) tended to slightly decrease with the increase of atomic number. • The difference in removal rate between the elements was not significant. • The removal rate of transition metal was on a straight line of ion size of the alkaline earth metal. • Priority of the cation adsorption on the soluble monolayer is closely related to the ionic radius. [ABSTRACT FROM AUTHOR]

The solubilization ability of surfactants is closely related to their molecular design. The number of alkyl chains in a surfactant molecule accordingly affects the forming of micellar structures. In the present study, the solubilization ability of cationic surfactants was studied by changing number of alkyl chains by using one of these three types of surfactants: star-shaped trimeric quaternary ammonium bromides (tris(N -alkyl- N , N -dimethyl-2-ammoniumethyl)amine bromides (3C n trisQ, n = 10, 12, and 14 is the number of carbon atoms in the alkyl chains)), dimeric surfactants (1,2-bis(alkyldimethylammonio)ethane dibromide (n -2- n , n = 10, 12, and 14)), and dodecyltrimethylammonium bromide (DTAB). The solubilization abilities of the above surfactants were studied using naphthalene and stearic acid at 298.2 K. Judging from the value of the molar solubilization ratios (MSR) for naphthalene and stearic acid, the solubilization ability generally improved as the number of alkyl chains of the surfactant molecules increased, as follows: DTAB <12-2-12 < 3C 12 trisQ. The Gibbs free energy change (Δ G 0) values for the solubilization of naphthalene and stearic acid into 3C 12 TrisQ solutions were relatively large negative numbers, −28.3 and −59.4 kJ mol−1, respectively. Moreover, small angle X-ray scattering analysis indicated that electron density at the ellipsoidal micellar surface of 3C 12 trisQ was decreased by solubilizing naphthalene and stearic acid, however, the micellar shape was not drastically changed from ellipsoidal micelle. These results indicated that the trimeric surfactant presented better potential as solubilizer compared to typical monomeric surfactants. Unlabelled Image • Number of alkyl chains in a surfactant molecule affects the solubilization ability. • The solubilization ability of trimeric, dimeric, and monomeric surfactants was studied using solubilizates. • The molar solubilization ratios were increased as the number of alkyl chains of the surfactant. • The trimeric surfactant presented better potential as solubilizer compared to typical monomeric surfactants. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D ROESY spectroscopy reveals progesterone solubilization in 14-6-14,2Br− micelles. • Detected proximity between progesterone and 14-6-14,2Br− indicates near-surface positioning. • Machine learning complements NMR, reinforcing solubilization insights. • Electron density map deciphers progesterone's molecular intricacies. • 3D visualization showcases interactions within micellar structures. We investigate the capabilities of micellar systems, specifically their role as solubilizing agents for hydrophobic substances. Our focus is on interaction of a Gemini surfactant of 14-6-14,2Br− with progesterone, a hydrophobic bioactive compound. Through the application of 1H NMR and 2D ROESY spectroscopic techniques, we provide a detailed analysis of the proton environments within the surfactant and their spatial organization within the micellar structure. Our results indicate that the integration of progesterone into the system does not significantly disrupt the micellar structure, highlighting the stability of the 14-6-14,2Br− micelles. Additionally, we present compelling evidence suggesting that progesterone is situated near the micellar surface, a critical insight into the positioning of solubilized molecules within micellar structures. The structural fingerprint and electron density map of progesterone further support this conclusion, indicating a potential interaction between the acetyl group of progesterone and the positively charged -N(CH 3) 2 headgroups of the surfactant near the micelle surface. This study enhances our understanding of micellar systems and their potential use in the solubilization of hydrophobic compounds, paving the way for advancements in drug delivery systems and related fields. [ABSTRACT FROM AUTHOR]

Abstract: Novel supra-long chain surfactants with double or triple quaternary ammonium salts (C n -2Am, C n -3Am, in which n represents a hydrocarbon chain length of 18, 20, and 22) were synthesized, and electrical conductivity and surface tension were used to characterize their properties depending on both the hydrocarbon chain length and number of hydrophilic groups. The Krafft temperatures decreased remarkably with an increase in the quaternary ammonium headgroups, resulting in a high solubility in water. The critical micelle concentration (cmc) increased with an increase in the number of quaternary ammonium moieties in the hydrophilic group, and the difference in the cmc was smaller for C n -2Am and C n -3Am than for C n -2Am and C n -Am of alkyltrimethylammonium bromide. The surface tension at the cmc was approximately 45 and 48mNm−1 for C n -2Am and C n -3Am with n =18–22, respectively. This indicated that the supra-long chain surfactants could not efficiently adsorb at the air/water interface and orient by themselves, as is known for conventional surfactants. [Copyright &y& Elsevier]

Abstract: Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N′-di(3-perfluoroalkyl-2-hydroxypropyl)-N,N′-diacetic acid ethylenediamine (2 edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2 edda (n =4, 6, and 8) showed a minimum for n =6. Furthermore, the lowest surface tension of 2 edda at the cmc was 16.4mNm−1. Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2 edda mainly formed aggregates with stringlike (n =4), cagelike (n =6), and distorted bilayer structures (n =8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains. [Copyright &y& Elsevier]

We report the role of a spacer chain in gemini surfactants for solubilization of poor soluble compounds to the aqueous medium. Solubilization of n -alkylbenzenes into micellar solutions of alkanediyl-1, s -bis(dimethyltetradecylammonium bromide) (14- s -14,2Br − , s = 2, 6, and 12) has been studied in the temperature range from 288.2 to 308.2 K. The equilibrium concentrations of all the solubilizates are determined spectrophotometrically. The solubility of the solubilizates remains constant below the critical micelle concentration (cmc) and increases linearly with an increase in the surfactant concentration above the cmc. The hydrodynamic diameter of the micellar aggregates with or without the solubilizates is measured by means of dynamic light scattering (DLS). The enthalpy, entropy, and Gibbs energy changes for the solubilization of n -alkylbenzenes have been calculated to evaluate a driving force of a transfer of the solubilizates into the micelle. These results indicate that the driving force and solubilization site in the aggregates are changed depending on the spacer chain length of surfactants. Furthermore, the inner core of the solubilized aggregates has been investigated by Fourier transform infrared (FTIR) spectra and two-dimensional nuclear Overhauser effect spectroscopy (2-D NOESY). [ABSTRACT FROM AUTHOR]

Abstract: Shape transitions were examined with regard to the solubilization of the poorly water-soluble drug indomethacin (IMC) in the nonionic surfactants heptaethylene oxide tetradecyl (C14E7) and hexadecyl (C16E7) ethers by means of a dynamic light scattering technique. The cloud points of the pure C14E7 and C16E7 micelles ranged from 58 to 62 °C and from 52.1 to 55.6 °C, respectively, at surfactant concentrations of 1 to 10 mM. The cloud points of IMC-solubilized micelles increased by approximately 1 to 5°. The sizes of the pure C14E7 micelles were 4 to 14 nm at 20 to 40 °C at a concentration of 2 to 20 mM. The apparent hydrodynamic radius () of pure C16E7 micelles varied with temperature and concentration. C16E7 surfactant formed small spherical micelles at 20 and 25 °C at concentrations below 5 mM; the size of the micelles was approximately 5 nm. On the other hand, from 30 to 40 °C and at a higher concentration, C16E7 formed elongated cylindrical micelles, and these elongated micelles entangled or overlapped each other. The of the IMC-solubilized C14E7 micelles at 20 to 40 °C and of C16E7 micelles at 20 °C increased compared to that of pure micelles. On the other hand, the cylindrical micelles of C16E7 decreased in size and turned into spherical ones because of the hydrophobicity between the micelles caused by solubilization of IMC. This phenomenon was confirmed by transmission electron microscope (TEM) images. [Copyright &y& Elsevier]

Abstract: Apparent hydrodynamic radii (R happ) of nonionic surfactant micelles in aqueous solutions of hepta- and hexa-ethyleneoxide monoalkylether (C14E7, C16E7, and C16E6) were measured at 20–40°C. Fluorescence spectra of pyrene in aqueous solutions of the nonionic surfactants were measured as a function of surfactant concentration and temperature. The cloud point of C16E6 was about 35°C at concentration range of 10−3 to 10−2 M. However, even at a higher temperature than the cloud point, the fluorescence intensity ratio of pyrene monomer, I m1/I m3, in C16E6 solution behaves similarly to other surfactants (C16E7 and C14E7), indicating that the pyrene molecules reside in a similar location of surfactants. The slope for the temperature dependence of the I m1/I m3 ratio also changed with the surfactant concentration, and the micelle size differed among the surfactants (C16E6, C16E7, and C14E7). The activation enthalpy of pyrene diffusion was evaluated using Stevens–Ban plot, and the value of 20–30kJmol−1 was obtained for surfactant concentrations of 5×10−4 to 10−2 M. The results were compared with those reported for ionic and nonionic surfactant micelles. [Copyright &y& Elsevier]