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Sarkar P, Chattopadhyay A. Membrane Dipole Potential: An Emerging Approach to Explore Membrane Organization and Function. J Phys Chem B 2022; 126:4415-4430. [PMID: 35696090 DOI: 10.1021/acs.jpcb.2c02476] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Biological membranes are complex organized molecular assemblies of lipids and proteins that provide cells and membrane-bound intracellular organelles their individual identities by morphological compartmentalization. Membrane dipole potential originates from the electrostatic potential difference within the membrane due to the nonrandom arrangement (orientation) of amphiphile and solvent (water) dipoles at the membrane interface. In this Feature Article, we will focus on the measurement of dipole potential using electrochromic fluorescent probes and highlight interesting applications. In addition, we will focus on ratiometric fluorescence microscopic imaging technique to measure dipole potential in cellular membranes, a technique that can be used to address novel problems in cell biology which are otherwise difficult to address using available approaches. We envision that membrane dipole potential could turn out to be a convenient tool in exploring the complex interplay between membrane lipids and proteins and could provide novel insights in membrane organization and function.
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Affiliation(s)
- Parijat Sarkar
- CSIR-Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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2
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Shen Y, Liu B, Cui J, Xiang J, Liu M, Han Y, Wang Y. Hydration Shell Changes in Surfactant Aggregate Transitions Revealed by Raman-MCR Spectroscopy. J Phys Chem Lett 2020; 11:7429-7437. [PMID: 32803982 DOI: 10.1021/acs.jpclett.0c02140] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Hydration states of many self-assemblies directly relate to their structures and functions. Here, we use Raman multivariate curve resolution (Raman-MCR) assisted by differential scanning calorimetry and nuclear magnetic resonance to explore the hydration properties of aggregates formed by three cationic ammonium surfactants, trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12(Br)2), didodecyldimethylammonium bromide (DDAB), and dodecyltrimethylammonium bromide (DTAB). For 12-3-12(Br)2, the transitions from spherical to rodlike and wormlike micelles lead to about 20% and 60% dehydration and gradually weaken water tetrahedral order and H-bond in hydration shells for both headgroup and hydrophobic chain. As to DDAB, unilamellar vesicles contain two kinds of hydration water species, but multicompartment vesicles exhibit decreased water order and weaker H-bond. DTAB only forms spherical micelles and its hydration structure is similar to that of the 12-3-12(Br)2 spherical micelles. This work provides a basis to explore the hydration states of complex biological self-assemblies.
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Affiliation(s)
- Yutan Shen
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Bin Liu
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Jie Cui
- Analysis and Test Center, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China
| | - Junfeng Xiang
- Analysis and Test Center, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China
| | - Meirong Liu
- Analysis and Test Center, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China
| | - Yuchun Han
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
| | - Yilin Wang
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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Mortara L, Chaimovich H, Cuccovia IM, Horinek D, Lima FS. Dehydration Determines Hydrotropic Ion Affinity for Zwitterionic Micelles. J Chem Inf Model 2019; 60:604-610. [PMID: 31790243 DOI: 10.1021/acs.jcim.9b00870] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Specific ion effects in zwitterionic micelles, especially for anions, are evident in reaction kinetics, zeta potential, and critical micelle concentration measurements. However, anion adsorption to zwitterionic micelles does not produce significant changes in shape, aggregation number, or interfacial hydration. Here we used molecular dynamics simulation of systems containing sulfobetaine zwitterionic micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DPS) and nine different salts to explore ion adsorption in terms of group dehydration. Our results, in line with those obtained for cationic micelles, showed that the adsorption degree of anions containing both hydrophobic and hydrophilic portions, i.e., hydrotropes, were correlated with the ion dehydration and were governed mainly by the hydrophobic portion dehydration upon adsorption.
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Affiliation(s)
- Laura Mortara
- Departamento de Química, Instituto de Química , Universidade de São Paulo , São Paulo 05513-970 , Brazil
| | - Hernan Chaimovich
- Departamento de Química, Instituto de Química , Universidade de São Paulo , São Paulo 05513-970 , Brazil
| | - Iolanda M Cuccovia
- Departamento de Química, Instituto de Química , Universidade de São Paulo , São Paulo 05513-970 , Brazil
| | - Dominik Horinek
- Institut für Physikalishe und Theoretische Chemie , Universität Regensburg , D-93040 Regensburg , Germany
| | - Filipe S Lima
- Departamento de Química Fundamental, Centro de Ciências Exatas e da Natureza , Universidade Federal de Pernambuco , Recife 50670-901 , Brazil
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Tarif E, Mukherjee K, Kumbhakar K, Barman A, Biswas R. Dynamics at the non-ionic micelle/water interface: Impact of linkage substitution. J Chem Phys 2019; 151:154902. [DOI: 10.1063/1.5121334] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Ejaj Tarif
- Chemical, Biological and Macromolecular Sciences (CBMS), S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
| | - Kallol Mukherjee
- Chemical, Biological and Macromolecular Sciences (CBMS), S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
| | - Kajal Kumbhakar
- Chemical, Biological and Macromolecular Sciences (CBMS), S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
| | - Anjan Barman
- Condensed Matter Physics and Material Sciences (CMPMS), S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
| | - Ranjit Biswas
- Chemical, Biological and Macromolecular Sciences (CBMS), S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106, India
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Surfactants with aromatic headgroups for optimizing properties of graphene/natural rubber latex composites (NRL): Surfactants with aromatic amine polar heads. J Colloid Interface Sci 2019; 545:184-194. [PMID: 30878784 DOI: 10.1016/j.jcis.2019.03.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Revised: 03/04/2019] [Accepted: 03/05/2019] [Indexed: 11/20/2022]
Abstract
HYPOTHESIS The compatibility of surfactants and graphene surfaces can be improved by increasing the number of aromatic groups in the surfactants. Including aniline in the structure may improve the compatibility between surfactant and graphene further still. Surfactants can be modified by incorporating aromatic groups in the hydrophobic chains or hydrophilic headgroups. Therefore, it is of interest to investigate the effects of employing anilinium based surfactants to disperse graphene nanoplatelets (GNPs) in natural rubber latex (NRL) for the fabrication of electrically conductive nanocomposites. EXPERIMENTS New graphene-philic surfactants carrying aromatic moieties in the hydrophilic headgroups and hydrophobic tails were synthesized by swapping the traditional sodium counterion with anilinium. 1H NMR spectroscopy was used to characterize the surfactants. These custom-made surfactants were used to assist the dispersion of GNPs in natural rubber latex matrices for the preparation of conductive nanocomposites. The properties of nanocomposites with the new anilinium surfactants were compared with commercial sodium surfactant sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and the previously synthesized aromatic tri-chain sodium surfactant TC3Ph3 (sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate). Structural properties of the nanocomposites were studied using Raman spectroscopy, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Electrical conductivity measurements and Zeta potential measurements were used to assess the relationships between total number of aromatic groups in the surfactant molecular structure and nanocomposite properties. The self-assembly structure of surfactants in aqueous systems and GNP dispersions was assessed using small-angle neutron scattering (SANS). FINDINGS Among these different surfactants, the anilinium version of TC3Ph3 namely TC3Ph3-AN (anilinium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3phenylpropoxy)carbonyl) pentane-2-sulfonate) was shown to be highly efficient for dispersing GNPs in the NRL matrices, increasing electrical conductivity eleven orders of magnitude higher than the neat rubber latex. Comparisons between the sodium and anilinium surfactants show significant differences in the final properties of the nanocomposites. In general, the strategy of increasing the number of surfactant-borne aromatic groups by incorporating anilinium ions in surfactant headgroups appears to be effective.
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Mortara L, Lima FDS, Cuccovia IM, Nazet A, Horinek D, Buchner R, Chaimovich H. Specific Ion Effects on Zwitterionic Micelles Are Independent of Interfacial Hydration Changes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:11049-11057. [PMID: 30126270 DOI: 10.1021/acs.langmuir.8b02115] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Zwitterionic micelles adsorb anions and several techniques were used to determine the specificity of this interaction. Although at a lower intensity, this adsorption can be compared to those observed in cationic micelles, which showed that interfacial dehydration is a fundamental property for the geometry and size of micelles. Because there is no information on the interfacial hydration of zwitterionic micelles, we used dielectric relaxation spectroscopy (DRS) together with molecular dynamics (MD) simulations to evaluate the importance of surface dehydration promoted by the binding of anions at the micellar interface (sodium bromide, sodium methanesulfonate, sodium trifluoroacetate, and sodium triflate) in N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (DPS) micelles. Our results, showing good agreement between DRS and MD simulations, strongly suggest that specific ion effects on zwitterionic micelles are unrelated to global changes in the interfacial hydration and depend on specific interactions of the headgroups with selected anions.
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Affiliation(s)
- Laura Mortara
- Departamento de Química, Instituto de Química , Universidade de São Paulo , São Paulo 05508-000 , Brazil
| | - Filipe da Silva Lima
- Departamento de Química Fundamental, Centro de Ciências Exatas e da Natureza , Universidade Federal de Pernambuco , Recife 50740-540 , Brazil
| | - Iolanda Midea Cuccovia
- Departamento de Bioquímica, Instituto de Química , Universidade de São Paulo , São Paulo 05508-000 , Brazil
| | - Andreas Nazet
- Institut für Physikalische und Theoretische Chemie , Universität Regensburg , D-93040 Regensburg , Germany
| | - Dominik Horinek
- Institut für Physikalische und Theoretische Chemie , Universität Regensburg , D-93040 Regensburg , Germany
| | - Richard Buchner
- Institut für Physikalische und Theoretische Chemie , Universität Regensburg , D-93040 Regensburg , Germany
| | - Hernan Chaimovich
- Departamento de Bioquímica, Instituto de Química , Universidade de São Paulo , São Paulo 05508-000 , Brazil
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Khan MN, Fagge II. Kinetics and Mechanism of Cationic Micelle/Flexible Nanoparticle Catalysis: A Review. PROGRESS IN REACTION KINETICS AND MECHANISM 2018. [DOI: 10.3184/146867818x15066862094905] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The aqueous surfactant (Surf) solution at [Surf] > cmc (critical micelle concentration) contains flexible micelles/nanoparticles. These particles form a pseudophase of different shapes and sizes where the medium polarity decreases as the distance increases from the exterior region of the interface of the Surf/H2O particle towards its furthest interior region. Flexible nanoparticles (FNs) catalyse a variety of chemical and biochemical reactions. FN catalysis involves both positive catalysis ( i.e. rate increase) and negative catalysis ( i.e. rate decrease). This article describes the mechanistic details of these catalyses at the molecular level, which reveals the molecular origin of these catalyses. Effects of inert counterionic salts (MX) on the rates of bimolecular reactions (with one of the reactants as reactive counterion) in the presence of ionic FNs/micelles may result in either positive or negative catalysis. The kinetics of cationic FN (Surf/MX/H2O)-catalysed bimolecular reactions (with nonionic and anionic reactants) provide kinetic parameters which can be used to determine an ion exchange constant or the ratio of the binding constants of counterions.
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Affiliation(s)
- Mohammad Niyaz Khan
- Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
| | - Ibrahim Isah Fagge
- Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
- Department of Chemistry, Faculty of Science, Kano University of Science and Technology, Wudil, Nigeria
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Dar AA, Romsted LS, Nazir N, Zhang Y, Gao X, Gu Q, Liu C. A novel combined chemical kinetic and trapping method for probing the relationships between chemical reactivity and interfacial H 2O, Br - and H + ion molarities in CTAB/C 12E 6 mixed micelles. Phys Chem Chem Phys 2018. [PMID: 28627562 DOI: 10.1039/c7cp03413j] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A delicate balance-of-forces governs the interactions responsible for surfactant self-assembly and chemical reactivity within them. Chemical reactions in micellar media generally occur in the interfacial region of micelles that is a complex mixture of: water, headgroups, counterions, co-ions, acids or bases, organic solvents, and the reactants themselves. We have carried out a detailed study of a complex chemical reaction in mixed CTAB/C12E6 micelles by using the chemical kinetic (CK) and chemical trapping (CT) methods. The results provide a detailed quantitative treatment of the reaction of the anion of the antioxidant t-butylhydroquinone, TBHQ-, with 4-hexadecylbenzenediazonium, 16-ArN2+, within the interfacial region of the mixed micelles in the C12E6 mole fraction range of 0 to 1 at three different total surfactant concentrations. CK experiments showed that this reaction is monophasic in C12E6 micelles, but biphasic in mixed micelles. The results were fully consistent with a complex mechanism in which TBHQ- reacts with 16-ArN2+ to give a transient diazoether intermediate that competitively breaks down into products and or reverts to starting materials. The kinetics are the same in mixed micelles of CTAB/C12E6 (grow) and CTAB/C12E8 (don't grow) showing that the rates only depend on micelle composition, not shape. CT results provided estimates of interfacial molarities of H2O are approximately constant at ca. 39 and Br- decreases from ca. 2.75 to 0.05 moles per liter of interfacial volume as C12E6 mole fraction increases from 0 to 1. Combined CK/CT results provided values for interfacial pH, ranging from ca. 4.25 in cationic micelles to 1.5 in nonionic micelles despite a constant bulk pH of 1.5 and the TBHQ interfacial pKa = 3.8 at all C12E6 molar fractions. In totality, these results yielded an extraordinary amount of quantitative information about the relationships between the chemical reactivity and interfacial compositions of the mixed micelles.
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Affiliation(s)
- Aijaz Ahmad Dar
- Physical Chemistry Division, Department of Chemistry, University of Kashmir, Hazratbal, Srinagar-190006, J&K, India.
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Lima FS, Andrade MFC, Mortara L, Gustavo Dias L, Cuccovia IM, Chaimovich H. Ion dehydration controls adsorption at the micellar interface: hydrotropic ions. Phys Chem Chem Phys 2018; 19:30658-30666. [PMID: 29119186 DOI: 10.1039/c7cp05283a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The properties of ionic micelles depend on the nature of the counterion, and these effects become more evident as the ion adsorption at the interface increases. Prediction of the relative extent of ion adsorption is required for rational design of ionic micellar aggregates. Unlike the well understood adsorption of monatomic ions, the adsorption of polyatomic ions is not easily predicted. We combined experimental and computational methods to evaluate the affinity of hydrotropic ions, i.e., ions with polar and apolar regions, to the surface of positively charged micelles. We analyzed cationic micelles of dodecyltrimethylammonium and six hydrotropic counterions: methanesulfonate, trifluoromethanesulfonate, benzenesulfonate, acetate, trifluoroacetate and benzoate. Our results demonstrated that the apolar region of hydrotropic ions had the largest influence on micellar properties. The dehydration of the apolar region of hydrotropic ions upon their adsorption at the micellar interface determined the ion adsorption extension, differently to what was expected based on Collins' law of matching affinities. These results may lead to more general models to describe the adsorption of ions, including polyatomic ions, at the micellar interface.
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Affiliation(s)
- Filipe S Lima
- Departamento de Química Fundamental, Centro de Ciências Exatas e da Natureza, Universidade Federal de Pernambuco, Recife, Brazil.
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Naqvi AZ, Kabir-Ud-Din. Clouding phenomenon in amphiphilic systems: A review of five decades. Colloids Surf B Biointerfaces 2018; 165:325-344. [PMID: 29547842 DOI: 10.1016/j.colsurfb.2018.01.060] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Revised: 01/26/2018] [Accepted: 01/29/2018] [Indexed: 11/26/2022]
Abstract
Phase separation in amphiphilic systems is an important phenomenon. The temperature at which an amphiphilic solution phase separates is known as Cloud Point (CP). This article reviews in detail the process of phase separation in various amphiphiles (surfactants, polymers and drugs) and effect of different classes of additives on the CP of these amphiphilic systems. Ions affect the CP of drugs in a different way: kosmotropes and hard bases decrease while chaotropes and soft bases increase the CP of nonionic and cationic surfactants. Anionic surfactants show CP in presence of quaternary salts only. Thus, depending upon the nature and concentration of additive, the CP of an amphiphilic system gets increased or decreased and, hence, properties of the system may be tuned as per the need and use. A system with CP at high concentration can be made to phase separate at lower concentration by simply introducing an appropriate additive in it. This makes the system cost effective. On the other hand, if not required, a low CP can be enhanced with the help of another type of a suitable additive.
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Affiliation(s)
- Andleeb Z Naqvi
- Department of Chemistry, Aligarh Muslim University, Aligarh 202 002, India.
| | - Kabir-Ud-Din
- Department of Chemistry, Faculty of Natural Sciences, Arba Minch University, Arba Minch, Ethiopia
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Sanchez-Fernandez A, Hammond OS, Jackson AJ, Arnold T, Doutch J, Edler KJ. Surfactant-Solvent Interaction Effects on the Micellization of Cationic Surfactants in a Carboxylic Acid-Based Deep Eutectic Solvent. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:14304-14314. [PMID: 29182879 DOI: 10.1021/acs.langmuir.7b03254] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Deep eutectic solvents have been demonstrated to support amphiphile self-assembly, providing potential alternatives as structure-directing agents in the synthesis of nanostructures, and drug delivery. Here we have expanded on this recent research to investigate the self-assembly of alkyltrimethylammonium bromide surfactants in choline chloride:malonic acid deep eutectic solvent and mixtures of the solvent with water. Surface tension and small-angle neutron scattering were used to determine the behavior of the amphiphiles. Surfactants were found to remain active in the solvent, and surface tension measurements revealed changes in the behavior of the surfactants with different levels of hydration. Small-angle neutron scattering shows that in this solvent the micelle shape depends on the surfactant chain length, varying from globular micelles (aspect ratio ∼2) for short chain surfactants to elongated micelles (aspect ratio ∼14) for long chain surfactants even at low surfactant concentration. We suggest that the formation of elongated micelles can be explained through the interaction of the solvent with the surfactant headgroup, since ion-ion interactions between surfactant headgroups and solvent may modify the morphology of the micelles. The presence of water in the deep eutectic solvents promotes an increase in the charge density at the micelle interface and therefore the formation of less elongated, globular micelles.
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Affiliation(s)
- Adrian Sanchez-Fernandez
- Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K
- European Spallation Source , Box 176, 22100 Lund, Sweden
| | - Oliver S Hammond
- Centre for Sustainable Chemical Technologies, University of Bath , Claverton Down, Bath BA2 7AY, U.K
| | - Andrew J Jackson
- European Spallation Source , Box 176, 22100 Lund, Sweden
- Department of Physical Chemistry, Lund University , SE-221 00 Lund, Sweden
| | - Thomas Arnold
- European Spallation Source , Box 176, 22100 Lund, Sweden
| | - James Doutch
- ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Didcot OX11 0QX, U.K
| | - Karen J Edler
- Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K
- Centre for Sustainable Chemical Technologies, University of Bath , Claverton Down, Bath BA2 7AY, U.K
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12
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Aggregation and reactivity in aqueous solutions of cationic surfactants and aromatic anions across concentration scales. Curr Opin Colloid Interface Sci 2017. [DOI: 10.1016/j.cocis.2017.10.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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13
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Chemical kinetic and chemical trapping methods: Unique approaches for determining respectively the antioxidant distributions and interfacial molarities of water, counter-anions, and other weakly basic nucleophiles in association colloids. Curr Opin Colloid Interface Sci 2017. [DOI: 10.1016/j.cocis.2017.09.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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14
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Cuccovia IM, da Silva Lima F, Chaimovich H. Counting ions and other nucleophiles at surfaces by chemical trapping. Biophys Rev 2017; 9:617-631. [PMID: 28852984 PMCID: PMC5662041 DOI: 10.1007/s12551-017-0299-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 07/27/2017] [Indexed: 12/30/2022] Open
Abstract
The interfaces of membranes and other aggregates are determined by the polarity, electrical charge, molecular volume, degrees of motional freedom and packing density of the head groups of the amphiphiles. These properties also determine the type of bound ion (ion selectivity) and its local density, i.e. concentration defined by choosing an appropriate volume element at the aggregate interface. Bulk and local ion concentrations can differ by orders of magnitude. The relationships between ion (or other compound) concentrations in the bulk solvent and in the interface are complex but, in some cases, well established. As the local ion concentration, rather than that in the bulk, controls a variety of properties of membranes, micelles, vesicles and other objects of theoretical and applied interests, measurement of local (interfacial, bound) ion concentrations is of relevance for understanding and characterizing such aggregates. Many experimental methods for estimating ion distributions between the bulk solution and the interface provide indirect estimates because they are based on concentration-dependent properties, rather than concentration measurements. Dediazoniation, i.e. the loss of N2, of a substituted diazophenyl derivative provides a tool for determining the number of nucleophiles (including neutral or negatively charged ions) surrounding the diazophenyl derivative prior to the dediazoniation event. This reaction, defined as chemical trapping, and the appropriate reference points obtained in bulk solution allow direct measurements of local concentrations of a variety of nucleophiles at the surface of membranes and other aggregates. Here we review our contributions of our research group to the use, and understanding, of this method and applications of chemical trapping to the description of local concentrations of ions and other nucleophiles in micelles, reverse micelles, vesicles and solvent mixtures. Among other results, we have shown that interfacial water determines micellar shape, zwitterionic vesicle-forming amphiphiles display ion selectivity and urea does not accumulate at micellar interfaces. We have also shown that reaction products can be predicted from the composition of the initial state, even in non-ideal solvent mixtures, supporting the usefulness of chemical trapping as a method to determine local concentrations. In addition, we have analysed the mechanism of dediazoniation, both on theoretical and experimental basis, and concluded that the formation of a free phenyl cation is not a necessary part of the reaction pathway.
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Affiliation(s)
- Iolanda Midea Cuccovia
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
| | - Filipe da Silva Lima
- Departamento de Química Fundamental, Centro de Ciências Exatas e da Natureza, Universidade Federal de Pernambuco, Recife, Brazil
| | - Hernan Chaimovich
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
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15
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Froehner S, Sánez J, Dombroski LF, Gracioto MP. Critical aggregates concentration of fatty esters present in biodiesel determined by turbidity and fluorescence. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2017; 24:20747-20758. [PMID: 28718020 DOI: 10.1007/s11356-017-9593-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 06/20/2017] [Indexed: 06/07/2023]
Abstract
Biodiesel for combustible engine is available as mixture of fossil diesel and fatty esters obtained by transesterification of vegetable oils. The use of biodiesel reduces the amount of SOx, mainly. However, it was already observed that biodiesel has a different behavior in environment in cases of accidental spill and groundwater contamination. It was noticed that the biodegradation of hydrocarbons (cyclic and aliphatic) in the presence of biodiesel are speeded, although the mechanism is still unclear. Considering the chemical structure of fatty esters, it was investigated the formation of aggregates in water solution by fatty esters present in commercial biodiesel. In Brazil, biodiesel is composed by 95% of fossil diesel and 5% of fatty esters mixture. In this work, fatty esters were treated as neutral surfactant, i.e., it was treated as a molecule with polar and non-polar part. Turbidity and fluorescence were used to determine the critical aggregates concentration (CAC). Water solutions containing fatty esters were examined exploiting changes in turbidity and fluorescence intensity of pyrene. Abrupt changes were attributed to aggregates formation, following the same behavior of traditional amphiphilic compounds. It was determined the CAC for ethyl palmitate, ethyl stearate, ethyl oleate, and ethyl linoleate. The values of CAC for fatty esters varied from 1.91 to 4.27 μmol/L, while CAC for the mixture of esters (biodiesel) was 2.01 for methyl esters and 1.19 for ethyl esters, both prepared using soybean oil. The aggregates formation was also determined by fluorescence measurements considering the changes in intensity of peaks I and III of pyrene. Pyrene senses the changes in environment polarity. The values found of CAC by fluorescence for individual ethyl esters varied from 1.85 to 3.21 μmol/L, while mixtures of ethyl esters was 2.23 and 2.07 μmol/L for mixture of methyl esters. The results clearly showed that fatty esters form aggregates and might be responsible for speed degradation of compounds by accommodation of them in inner part of aggregates.
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Affiliation(s)
- Sandro Froehner
- Department of Environmental Engineering, Federal University of Parana, Curitiba, PR, 81531-980, Brazil.
| | - Juan Sánez
- Department of Hydraulics and Sanitation, Federal University of Parana, Curitiba, PR, 81531-980, Brazil
| | - Luiz Fernando Dombroski
- Department of Hydraulics and Sanitation, Federal University of Parana, Curitiba, PR, 81531-980, Brazil
| | - Maria Paula Gracioto
- Graduate Program in Oceanography, Federal University of Santa Catarina, Florianópolis, SC, 88040-900, Brazil
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Yusof NSM, Said MNM, Khan MN. Quantitative correlation between counterion (X) binding affinity to cationic micelles and X – Induced micellar growth for substituted iodobenzoates (X). ARAB J CHEM 2017. [DOI: 10.1016/j.arabjc.2013.10.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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17
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Ramin MA, Sindhu KR, Appavoo A, Oumzil K, Grinstaff MW, Chassande O, Barthélémy P. Cation Tuning of Supramolecular Gel Properties: A New Paradigm for Sustained Drug Delivery. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1605227. [PMID: 28151562 DOI: 10.1002/adma.201605227] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 11/18/2016] [Indexed: 06/06/2023]
Abstract
Hydrogels formed by the self-assembly of low-molecular-weight gelators (LMWGs) are promising scaffolds for drug-delivery applications. A new biocompatible hydrogel, resulting from the self-assembly of nucleotide-lipid salts can be safely injected in vivo. The resulting hydrogel provides sustained-release of protein for more than a week.
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Affiliation(s)
- Michael A Ramin
- ARNA Laboratory, Inserm, U1212, CNRS 5320, Université de Bordeaux, F-33000, Bordeaux, France
| | | | - Ananda Appavoo
- ARNA Laboratory, Inserm, U1212, CNRS 5320, Université de Bordeaux, F-33000, Bordeaux, France
| | - Khalid Oumzil
- ARNA Laboratory, Inserm, U1212, CNRS 5320, Université de Bordeaux, F-33000, Bordeaux, France
| | - Mark W Grinstaff
- Departments of Biomedical Engineering and Chemistry, Boston University, Boston, MA, 02215, USA
| | | | - Philippe Barthélémy
- ARNA Laboratory, Inserm, U1212, CNRS 5320, Université de Bordeaux, F-33000, Bordeaux, France
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Gujt J, Bešter-Rogač M, Spohr E. Molecular dynamics study of stability and disintegration of long rod-like micelles: Dodecyltrimethylammonium chloride in solutions of hydroxybenzoates. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2016.09.067] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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19
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Burgos-Mármol JJ, Solans C, Patti A. Effective short-range Coulomb correction to model the aggregation behavior of ionic surfactants. J Chem Phys 2017; 144:234904. [PMID: 27334191 DOI: 10.1063/1.4954063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
We present a short-range correction to the Coulomb potential to investigate the aggregation of amphiphilic molecules in aqueous solutions. The proposed modification allows to quantitatively reproduce the distribution of counterions above the critical micelle concentration (CMC) or, equivalently, the degree of ionization, α, of the micellar clusters. In particular, our theoretical framework has been applied to unveil the behavior of the cationic surfactant C24H49N2O2 (+) CH3SO4 (-), which offers a wide range of applications in the thriving and growing personal care market. A reliable and unambiguous estimation of α is essential to correctly understand many crucial features of the micellar solutions, such as their viscoelastic behavior and transport properties, in order to provide sound formulations for the above mentioned personal care solutions. We have validated our theory by performing extensive lattice Monte Carlo simulations, which show an excellent agreement with experimental observations. More specifically, our coarse-grained model is able to reproduce and predict the complex morphology of the micelles observed at equilibrium. Additionally, our simulation results disclose the existence of a transition from a monodisperse to a bidisperse size distribution of aggregates, unveiling the intriguing existence of a second CMC.
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Affiliation(s)
- J Javier Burgos-Mármol
- School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, United Kingdom
| | - Conxita Solans
- Institut de Química Avançada de Catalunya (IQAC-CSIC) and CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), C/ Jordi Girona, 18-26, 08034 Barcelona, Spain
| | - Alessandro Patti
- School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Sackville Street, Manchester M13 9PL, United Kingdom
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Gujt J, Bešter-Rogač M, Spohr E. Structure and Stability of Long Rod-like Dodecyltrimethylammonium Chloride Micelles in Solutions of Hydroxybenzoates: A Molecular Dynamics Simulation Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:8275-8286. [PMID: 27442259 DOI: 10.1021/acs.langmuir.6b02076] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The relative position of the hydroxylic and carboxylic groups in the isomeric hydroxybenzoate (HB) anions is experimentally known to have a large impact on the thermodynamics of micellization of cationic surfactants, such as dodecyltrimethylammonium chloride (DTAC), and on the structure of the resulting micelles. To understand the effect of the different isomers on the molecular level, we employed atomistic molecular dynamics simulations to study systems containing infinitely long cylindrical DTAC micelles in aqueous solutions of the sodium salts of all three isomers of HB at a temperature and a pressure of 298.15 K and 1 atm. In all studied systems, the number of DTAC unimers is identical to the number of HB anions. At this concentration, the initially cylindrical micelles remain stable, irrespective of the nature of the isomer, whereas micelles rapidly disintegrated in the absence of HB anions. The HB isomers decrease the line density of unimers along the micellar axis and its concomitant thickness in the order o-HB > m-HB > p-HB. It is further observed that o-HB anions penetrate more deeply into the micellar core, induce a more ordered internal structure of the micelle, and are oriented more strongly than the other two isomers. In addition, the ortho isomer shows two different preferential orientations with respect to the radial direction of the cylindrical micelle; it can either be incorporated almost completely into the micelle or it can be attached through hydrogen bonding to one of those o-HB anions that are already incorporated into the micelle, and thus stick out of the micellar surface.
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Affiliation(s)
- Jure Gujt
- Chair of Theoretical Chemistry, Faculty of Chemistry, University of Duisburg-Essen , D-45141 Essen, Germany
- Chair of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana , SI-1000 Ljubljana, Slovenia
| | - Marija Bešter-Rogač
- Chair of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana , SI-1000 Ljubljana, Slovenia
| | - Eckhard Spohr
- Chair of Theoretical Chemistry, Faculty of Chemistry, University of Duisburg-Essen , D-45141 Essen, Germany
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21
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Leontidis E. Chaotropic salts interacting with soft matter: Beyond the lyotropic series. Curr Opin Colloid Interface Sci 2016. [DOI: 10.1016/j.cocis.2016.06.017] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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22
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Lutz-Bueno V, Pasquino R, Liebi M, Kohlbrecher J, Fischer P. Viscoelasticity Enhancement of Surfactant Solutions Depends on Molecular Conformation: Influence of Surfactant Headgroup Structure and Its Counterion. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:4239-4250. [PMID: 27081871 DOI: 10.1021/acs.langmuir.6b00776] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
During the anisotropic growth from globular to wormlike micelles, the basic interactions among distinct parts of the surfactant monomer, its counterion, and additives are fundamental to tune molecular self-assembly. We investigate the addition of sodium salicylate (NaSal) to hexadecyltrimethylammonium chloride and bromide (CTAC and CTAB), 1-hexadecylpyridinium chloride and bromide (CPyCl and CPyBr), and benzyldimethylhexadecylammonium chloride (BDMC), which have the same hydrophobic tail. Their potential to enhance viscoelasticity by anisotropic micellar growth upon salt addition was compared in terms of (i) the influence of the headgroup structure, and (ii) the influence of surfactant counterion type. Employing proton nuclear magnetic resonance ((1)H NMR), we focused on the molecular conformation of surfactant monomers in the core and polar shell regions of the micelles and their interactions with increasing concentration of NaSal. The viscoelastic response was investigated by rotational and oscillatory rheology. We show that micellar growth rates can be tuned by varying the flexibility and size of the surfactant headgroup as well as the dissociation degree of the surfactant counterion, which directly influences the strength of headgroup-counterion pairing. As a consequence, the morphological transitions depend directly on charge neutralization by electrostatic screening. For example, the amount of salt necessary to start the rodlike-to-wormlike micelle growth depends directly on the number of dissociated counterions in the polar shell.
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Affiliation(s)
- Viviane Lutz-Bueno
- Institute of Food, Nutrition and Health, ETH Zurich , 8092 Zurich, Switzerland
| | - Rossana Pasquino
- Department of Chemical Engineering, University of Naples Federico II , 80125 Naples, Italy
| | - Marianne Liebi
- Swiss Light Source, Paul Scherrer Institute , 5232 Villigen PSI, Switzerland
| | - Joachim Kohlbrecher
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , 5232 Villigen PSI, Switzerland
| | - Peter Fischer
- Institute of Food, Nutrition and Health, ETH Zurich , 8092 Zurich, Switzerland
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23
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Sorenson GP, Mahanthappa MK. Unexpected role of linker position on ammonium gemini surfactant lyotropic gyroid phase stability. SOFT MATTER 2016; 12:2408-2415. [PMID: 26806651 DOI: 10.1039/c5sm02671g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Arising from the water-driven self-assembly of amphiphiles over generally narrow temperature and composition phase windows, aqueous lyotropic liquid crystal (LLC) network phases are useful in applications as therapeutic delivery vehicles and templates for mesoporous material syntheses. While a clear set of amphiphile design rules that enables access to these intricate three-dimensional structures has yet to emerge, recent work indicates that bis(ammonium), bis(phosphonium), and dicarboxylate gemini ("twin tail") surfactants enable enhanced access to LLC network phases such as the double gyroid (G). In order to better understand the scope of this amphiphile design strategy, we investigated the synthesis and aqueous LLC self-assembly behaviors of a homologous series of quaternary gemini bis(ammonium) dichloride surfactants, in which we varied the position of the hydrophobic linker that connects the constituent single tail surfactants. These experiments demonstrate that the position of the linker directly impacts the maximum counterion-headgroup hydration capacity and the extent of counterion-headgroup association, all of which contribute to the aqueous lyotropic double gyroid network phase stability. Thus, judicious selection of the linker position in ionic gemini surfactants provides a new molecular design tool for manipulating LLC network phase stability.
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Affiliation(s)
- Gregory P Sorenson
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, WI 53703, USA
| | - Mahesh K Mahanthappa
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, WI 53703, USA and Department of Chemical Engineering & Materials Science, University of Minnesota, 421 Washington Ave., S.E., Minneapolis, MN 55455, USA.
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24
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Sarkar P, Chattopadhyay A. Micellar dipole potential is sensitive to sphere-to-rod transition. Chem Phys Lipids 2015; 195:34-8. [PMID: 26616562 DOI: 10.1016/j.chemphyslip.2015.11.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Revised: 11/16/2015] [Accepted: 11/17/2015] [Indexed: 12/31/2022]
Abstract
Structural transitions involving shape changes play an important role in cellular physiology. Charged micelles offer a convenient model system in which structural transitions can be suitably induced by increasing the ionic strength of the medium. In this paper, we have explored sphere-to-rod transition in charged micelles of SDS and CTAB by monitoring micellar dipole potential using the dual wavelength ratiometric approach utilizing the potential-sensitive membrane probe di-8-ANEPPS. Our results show that micellar dipole potential is sensitive to sphere-to-rod transition in charged micelles. Micellar dipole potential exhibited increase with increasing ionic strength (salt), irrespective of the nature of micellar charge, implying considerable dipolar reorganization underlying structural transitions. We interpret the increase in dipole potential due to sphere-to-rod transition because of an increase in the population of confined (nonrandom) dipoles induced by micellar organizational change. This is due to the fact that dipole potential arises due to the nonrandom arrangement of micellar dipoles and water molecules at the micelle interface. Our results constitute one of the first reports describing drastic dipolar reorganization due to micellar shape (and size) change. We envision that dipole potential measurements could provide novel insights into micellar processes that are associated with dipolar reorganization.
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Affiliation(s)
- Parijat Sarkar
- CSIR-Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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25
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Ito TH, Rodrigues RK, Loh W, Sabadini E. Calorimetric and Light Scattering Investigations of the Transition from Spherical to Wormlike Micelles of C₁₄TAB Triggered by Salicylate. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6020-6026. [PMID: 25978073 DOI: 10.1021/acs.langmuir.5b01027] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.
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Affiliation(s)
- Thiago Heiji Ito
- Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil
| | - Roberta Kamei Rodrigues
- Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil
| | - Watson Loh
- Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil
| | - Edvaldo Sabadini
- Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil
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Lima FS, Cuccovia IM, Buchner R, Antunes FE, Lindman B, Miguel MG, Horinek D, Chaimovich H. Sodium triflate decreases interaggregate repulsion and induces phase separation in cationic micelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:2609-2614. [PMID: 25689018 DOI: 10.1021/la5049216] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Dodecyltrimethylammonium triflate (DTATf) micelles possess lower degree of counterion dissociation (α), lower hydration, and higher packing of monomers than other micelles of similar structure. Addition of sodium triflate ([NaTf] > 0.05 M) to DTATf solutions promotes phase separation. This phenomenon is commonly observed in oppositely charged surfactant mixtures, but it is rare for ionic surfactants and relatively simple counterions. While the properties of DTATf have already been reported, the driving forces for the observed phase separation with added salt remain unclear. Thus, we propose an interpretation for the observed phase separation in cationic surfactant solutions. Addition of up to 0.03 M NaTf to micellar DTATf solutions led to a limited increase of the aggregation number, to interface dehydration, and to a progressive decrease in α. The viscosity of DTATf solutions of higher concentration ([DTATf] ≥ 0.06 M) reached a maximum with increasing [NaTf], though the aggregation number slightly increased, and no shape change occurred. We hypothesize that this maximum results from a decrease in interaggregate repulsion, as a consequence of increased ion binding. This reduction in micellar repulsion without simultaneous infinite micellar growth is, probably, the major driving force for phase separation at higher [NaTf].
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Affiliation(s)
- Filipe S Lima
- Instituto de Química, Universidade de São Paulo , São Paulo, Brazil
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27
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Lima FS, Chaimovich H, Cuccovia IM, Horinek D. Molecular dynamics shows that ion pairing and counterion anchoring control the properties of triflate micelles: a comparison with triflate at the air/water interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:1239-1249. [PMID: 24467445 DOI: 10.1021/la404260y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Micellar properties of dodecyltrimethylammonium triflate (DTA-triflate, DTATf) are very different from those of DTA-bromide (DTAB). DTATf aggregates show high aggregation numbers (Nagg), low degree of counterion dissociation (α), disk-like shape, high packing, ordering, and low hydration. These micellar properties and the low surface tension of NaTf aqueous solutions point to a high affinity of Tf(-) to the micellar and air/water interfaces. Although the micellar properties of DTATf are well defined, the source of the Tf(-) effect upon the DTA aggregates is unclear. Molecular dynamics (MD) simulations of Tf(-) (and Br(-)) at the air/water interface and as counterion of a DTA aggregate were performed to clarify the nature of Tf(-) preferences for these interfaces. The effect of NaTf or NaBr on surface tension calculated from MD simulations agreed with the reported experimental values. From the MD simulations a high affinity of Tf(-) toward the interface, which occurred in a specific orientation, was calculated. The micellar properties calculated from the MD simulations for DTATf and DTAB were consistent with experimental data: in MD simulations, the DTATf aggregate was more ordered, packed, and dehydrated than the DTAB aggregate. The Tf(-)/alkyltrimethylammonium interaction energies, calculated from the MD simulations, suggested ion pair formation at the micellar interface, stabilized by the preferential orientation of the adsorbed Tf(-) at the micellar interface.
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Affiliation(s)
- Filipe S Lima
- Instituto de Química, Universidade de São Paulo , São Paulo 05508-000, Brazil
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Gujt J, Podlipnik Č, Bešter-Rogač M, Spohr E. Ion mobility and clustering of sodium hydroxybenzoates in aqueous solutions: a molecular dynamics simulation study. Phys Chem Chem Phys 2014; 16:19314-26. [DOI: 10.1039/c4cp02425g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
At sufficiently high concentrations hydroxybenzoate anions in aqueous solutions form clusters of various sizes and shapes. Different degrees of cluster formation for each isomer lead to differences in their mobility.
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Affiliation(s)
- Jure Gujt
- Faculty of Chemistry and Chemical Technology
- University of Ljubljana
- SI-1000 Ljubljana, Slovenia
- Chair of Theoretical Chemistry
- Faculty of Chemistry
| | - Črtomir Podlipnik
- Faculty of Chemistry and Chemical Technology
- University of Ljubljana
- SI-1000 Ljubljana, Slovenia
| | - Marija Bešter-Rogač
- Faculty of Chemistry and Chemical Technology
- University of Ljubljana
- SI-1000 Ljubljana, Slovenia
| | - Eckhard Spohr
- Chair of Theoretical Chemistry
- Faculty of Chemistry
- University of Duisburg-Essen
- D-45141 Essen, Germany
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Lima FS, Chaimovich H, Cuccovia IM, Buchner R. Dielectric relaxation spectroscopy shows a sparingly hydrated interface and low counterion mobility in triflate micelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:10037-10046. [PMID: 23899188 DOI: 10.1021/la401728g] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The properties of ionic micelles are affected by the nature of the counterion. Specific ion effects can be dramatic, inducing even shape and phase changes in micellar solutions, transitions apparently related to micellar hydration and counterion binding at the micellar interface. Thus, determining the hydration and dynamics of ions in micellar systems capable of undergoing such transitions is a crucial step in understanding shape and phase changes. For cationic micelles, such transitions are common with large organic anions as counterions. Interestingly, however, phase separation also occurs for dodecyltrimethylammonium triflate (DTATf) micelles in the presence of sodium triflate (NaTf). Specific ion effects for micellar solutions of dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), methanesulfonate (DTAMs), and triflate (DTATf) were studied with dielectric relaxation spectroscopy (DRS), a technique capable of monitoring hydration and counterion dynamics of micellar aggregates. In comparison to DTAB, DTAC, and DTAMs, DTATf micelles were found to be considerably less hydrated and showed reduced counterion mobility at the micellar interface. The obtained DTATf and DTAMs data support the reported central role of the anion's -CF3 moiety with respect to the properties of DTATf micelles. The reduced hydration observed for DTATf micelles was rationalized in terms of the higher packing of this surfactant compared to that of other DTA-based systems. The decreased mobility of Tf(-) anions condensed at the DTATf interface strongly suggests the insertion of Tf(-) in the micellar interface, which is apparently driven by the strong hydrophobicity of -CF3.
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Affiliation(s)
- Filipe S Lima
- Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
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Lima FS, Cuccovia IM, Horinek D, Amaral LQ, Riske KA, Schreier S, Salinas RK, Bastos EL, Pires PAR, Bozelli JC, Favaro DC, Rodrigues ACB, Dias LG, El Seoud OA, Chaimovich H. Effect of counterions on the shape, hydration, and degree of order at the interface of cationic micelles: the triflate case. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:4193-4203. [PMID: 23473070 DOI: 10.1021/la304658e] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Specific ion effects in surfactant solutions affect the properties of micelles. Dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), and methanesulfonate (DTAMs) micelles are typically spherical, but some organic anions can induce shape or phase transitions in DTA(+) micelles. Above a defined concentration, sodium triflate (NaTf) induces a phase separation in dodecyltrimethylammonium triflate (DTATf) micelles, a phenomenon rarely observed in cationic micelles. This unexpected behavior of the DTATf/NaTf system suggests that DTATf aggregates have unusual properties. The structural properties of DTATf micelles were analyzed by time-resolved fluorescence quenching, small-angle X-ray scattering, nuclear magnetic resonance, and electron paramagnetic resonance and compared with those of DTAC, DTAB, and DTAMs micelles. Compared to the other micelle types, the DTATf micelles had a higher average number of monomers per aggregate, an uncommon disk-like shape, smaller interfacial hydration, and restricted monomer chain mobility. Molecular dynamic simulations supported these observations. Even small water-soluble salts can profoundly affect micellar properties; our data demonstrate that the -CF3 group in Tf(-) was directly responsible for the observed shape changes by decreasing interfacial hydration and increasing the degree of order of the surfactant chains in the DTATf micelles.
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Affiliation(s)
- Filipe S Lima
- Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
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31
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Kabir-ud-Din, Al-dahbali GA, Naqvi AZ, Akram M. Surface and micellar properties of some amphiphilic drugs in various salt solutions. COLLOID JOURNAL 2013. [DOI: 10.1134/s1061933x13020075] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Müller W, Déjugnat C, Zemb T, Dufrêche JF, Diat O. How Do Anions Affect Self-Assembly and Solubility of Cetylpyridinium Surfactants in Water. J Phys Chem B 2013; 117:1345-56. [DOI: 10.1021/jp3093622] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Wolfram Müller
- Institut de Chimie Séparative
de Marcoule (ICSM),
UMR 5257 (CEA/CNRS/UM2/ENSCM), Bagnols-sur-Cèze, France
| | - Christophe Déjugnat
- Institut de Chimie Séparative
de Marcoule (ICSM),
UMR 5257 (CEA/CNRS/UM2/ENSCM), Bagnols-sur-Cèze, France
| | - Thomas Zemb
- Institut de Chimie Séparative
de Marcoule (ICSM),
UMR 5257 (CEA/CNRS/UM2/ENSCM), Bagnols-sur-Cèze, France
| | - Jean-François Dufrêche
- Institut de Chimie Séparative
de Marcoule (ICSM),
UMR 5257 (CEA/CNRS/UM2/ENSCM), Bagnols-sur-Cèze, France
| | - Olivier Diat
- Institut de Chimie Séparative
de Marcoule (ICSM),
UMR 5257 (CEA/CNRS/UM2/ENSCM), Bagnols-sur-Cèze, France
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Chaudhuri A, Haldar S, Chattopadhyay A. Structural transition in micelles: novel insight into microenvironmental changes in polarity and dynamics. Chem Phys Lipids 2012; 165:497-504. [DOI: 10.1016/j.chemphyslip.2011.09.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 09/15/2011] [Accepted: 09/16/2011] [Indexed: 01/23/2023]
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Dharaiya N, Patriati A, Kuperkar K, Putra E, Bahadur P. Spectral and scattering microstructural investigation in cationic gemini surfactants (12-s-12) induced by p-toluidine. Colloids Surf A Physicochem Eng Asp 2012. [DOI: 10.1016/j.colsurfa.2011.11.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Paul BK, Guchhait N. Morphological transition of the host-structure influences solvent-relaxation: a wavelength-selective fluorescence exploration through environment-sensitive intramolecular charge transfer photophysics. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2011; 81:590-597. [PMID: 21764363 DOI: 10.1016/j.saa.2011.06.056] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Revised: 06/15/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
Here, we report the modulation of photo-induced intramolecular charge transfer (ICT) photophysics of N,N-dimethylaminonaphthyl-acrylo-nitrile (DMANAN) associated with sphere-to-rod structural transition of SDS micelles induced by increasing ionic strength of the medium. Emphasis is rendered on the exploration of solvent-relaxation associated with this transition on the basis of wavelength-selective fluorescence technique which includes monitoring of red-edge excitation shift (REES) and excitation/emission anisotropy profiles. Based on micropolarity determination and organization of solvent water around the probe microenvironment we argue that the present results advocate for rod-shaped micelles to be a better mimic for membrane bilayers than spherical micelles.
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Affiliation(s)
- Bijan Kumar Paul
- Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, West Bengal, India
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Lima FS, Maximiano FA, Cuccovia IM, Chaimovich H. Surface activity of the triflate ion at the air/water interface and properties of N,N,N-trimethyl-N-dodecylammonium triflate aqueous solutions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:4319-4323. [PMID: 21413729 DOI: 10.1021/la2004613] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The surface activity of salts added to water is orders of magnitude lower than that of surfactants. Sodium trifluoromethanesulfonate (NaTf) produced a change in surface tension with concentration, Δγ/Δc, of -13.2 mN·L/m·mol. This value is ca. 4-fold larger than those of simple salts and that of methanesulfonate. This unexpected surface effect suggested that positively charged micelles containing Tf could exhibit interesting properties. Dodecyltrimethylammonium triflate (DTATf) had a higher Kraft temperature (37 °C) and a lower cmc (5 × 10(-3) M) and degree of dissociation (0.11) than the chloride and bromide salts of DTA. Above the Kraft temperature, at a characteristic temperature t(1), the addition of NaTf above 0.05 M to a DTATf solution induced phase separation. By increasing the temperature of the two-phase system to above t(1), a homogeneous, transparent solution was obtained at a characteristic temperature t(2). These results, together with well-known triflate properties, led us to suggest that the Tf ion pairs with DTA and that the -CF(3) group may be dehydrated in the interfacial region, resulting in new and interesting self-aggregated structures.
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Affiliation(s)
- F S Lima
- Instituto de Química, Universidade de São Paulo, SP, Brazil
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37
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Khan MN, Ramakrishnan H. An Empirical Kinetic Approach for the Determination of the Ion Exchange Constants for Counterions of Cationic Micelles: The Rate of pH-Independent Hydrolysis of Phthalimide as the Kinetic Probe: Effects of (CH 3) 4N +on (X=Br −and Y=Cl −). J DISPER SCI TECHNOL 2011. [DOI: 10.1080/01932691003662373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Khan MN, Sinasamy S. A new semiempirical kinetic method for the determination of ion exchange constants for counterions of cationic micelles: Study of the rate of pH-independent hydrolysis of phthalimide as the kinetic probe. INT J CHEM KINET 2010. [DOI: 10.1002/kin.20522] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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39
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Khan MN. A new semi-empirical kinetic method for the determination of ion exchange constants for the counterions of cationic micelles. Adv Colloid Interface Sci 2010; 159:160-79. [PMID: 20673861 DOI: 10.1016/j.cis.2010.06.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 06/17/2010] [Accepted: 06/19/2010] [Indexed: 11/25/2022]
Abstract
A new method, based upon semi-empirical kinetic approach, for the determination of ion exchange constant for ion exchange processes occurring between counterions at the cationic micellar surface is described in this review article. Basically, the method involves a reaction kinetic probe which gives observed pseudo-first-order rate constants (k(obs)) for a nucleophilic substitution reaction between the nonionic and anionic reactants (R and S) in the presence of a constant concentration of both reactants as well as cationic micelles and varying concentrations of an inert inorganic or organic salt (MX). The observed data (k(obs), versus [MX]) fit satisfactorily (in terms of residual errors) to an empirical equation which could be derived from an equation explaining the mechanism of the reaction of the kinetic probe in terms of pseudophase micellar (PM) model coupled with another empirical equation. This (another) empirical equation explains the effect of [MX] on cationic micellar binding constant (K(S)) of the anionic reactant (say S) and gives an empirical constant, K(X/S). The magnitude of K(X/S) is the measure of the ability of X(-) to expel S(-) from a cationic micellar pseudophase to the bulk aqueous phase through ion exchange X(-)/S(-). The values of K(X/S) and K(Y/S) (where Y(-) is another inert counterion) give the ion exchange constant, K(X)(Y) (=K(X)/K(Y) where K(X) and K(Y) represent cationic micellar binding constants of X(-) and Y(-), respectively). The suitability of this method is demonstrated by the use of three different reaction kinetic probes and various MX.
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Manet S, Karpichev Y, Bassani D, Kiagus-Ahmad R, Oda R. Counteranion effect on micellization of cationic gemini surfactants 14-2-14: Hofmeister and other counterions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:10645-56. [PMID: 20394385 DOI: 10.1021/la1008768] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The effect of counterions was investigated and analyzed to probe the principal ionic effects influencing the micellization behavior of dimeric cationic surfactant ethanediylbis(dimethyltetradecylammonium), referred to as gemini 14-2-14. The 30 counterions were classified to four different families depending on their nature: (1) small and inorganic counterions which are typically taken from the Hofmeister series were studied to focus on the effect of ion type; (2) n-alkyl carboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions; (3) aromatic carboxylate counterions were included to focus on the effect of the position of substitutions; and (4) other counterions were included in order to shed light on other parameters. By investigating the critical micelle concentration (CMC), ionization degree of micelle (alpha), free energy of micellization (DeltaG(M)), and aggregation numbers N of the gemini surfactant with these different types of anions, we demonstrated the effect of different ion properties independently. This approach allowed us to describe the effect of counterions on the micellization behavior of the gemini surfactant in terms of complex interplay between hydrophobicity of anions and other ion properties such as counterion hydration, interfacial packing of ions, and ionic morphology. Indeed, our results clearly demonstrate that a counterion effect on micellization properties cannot be described as a result of one single parameter of ions, as is too often assumed, but rather the balancing effects cooperatively affect the propensity of counterions to form ion pairs with surfactant headgroups and the entropy gain upon micellization. These results provide new insight in understanding the effect of ions on the delicate balance of forces controlling aggregate morphology and solution properties of charged amphiphilic molecules.
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Affiliation(s)
- Sabine Manet
- Institut Européen de Chimie et Biologie, UMR 5248 CBMN, CNRS-Université de Bordeaux-ENITAB, 2 rue Robert Escarpit, F-33607 Pessac, France
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41
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Khan MN, Fui CT. Unusual Effects of Pure Nonionic and Mixed Nonionic–Cationic Micelles on the Rate of Alkaline Hydrolysis ofN-Hydroxyphthalimide. J DISPER SCI TECHNOL 2010. [DOI: 10.1080/01932690903223963] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Khan MN, Azri MHR. Effects of [NaBr] on the Rate of Intramolecular General Base-Assisted Hydrolysis of N-(2′-Hydroxyphenyl)phthalimide in the Presence of Cationic Micelles: Kinetic Evidence for the Probable Micellar Structural Transition. J Phys Chem B 2010; 114:8089-99. [DOI: 10.1021/jp102109q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. Niyaz Khan
- Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
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Abezgauz L, Kuperkar K, Hassan PA, Ramon O, Bahadur P, Danino D. Effect of Hofmeister anions on micellization and micellar growth of the surfactant cetylpyridinium chloride. J Colloid Interface Sci 2010; 342:83-92. [DOI: 10.1016/j.jcis.2009.08.045] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Revised: 08/16/2009] [Accepted: 08/31/2009] [Indexed: 11/16/2022]
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Zakharova L, Syakaev V, Voronin M, Semenov V, Valeeva F, Ibragimova A, Bilalov A, Giniyatullin R, Latypov S, Reznik V, Konovalov A. New self-assembling systems based on bola-type pyrimidinic surfactants. J Colloid Interface Sci 2010; 342:119-27. [DOI: 10.1016/j.jcis.2009.10.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Revised: 10/05/2009] [Accepted: 10/06/2009] [Indexed: 11/30/2022]
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Chaudhuri A, Haldar S, Chattopadhyay A. Organization and dynamics in micellar structural transition monitored by pyrene fluorescence. Biochem Biophys Res Commun 2009; 390:728-32. [DOI: 10.1016/j.bbrc.2009.10.037] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Accepted: 10/08/2009] [Indexed: 11/28/2022]
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Jäger C, Hirsch A, Schade B, Böttcher C, Clark T. Counterions Control the Self-Assembly of Structurally Persistent Micelles: Theoretical Prediction and Experimental Observation of Stabilization by Sodium Ions. Chemistry 2009; 15:8586-8592. [DOI: 10.1002/chem.200900885] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Sterpone F, Briganti G, Pierleoni C. Sphere versus cylinder: the effect of packing on the structure of nonionic C12E6 micelles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:8960-8967. [PMID: 19588924 DOI: 10.1021/la900591e] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Two independent series of calculations are performed simulating spherical and cylindrical C12E6 micelles in a temperature range around the experimental sphere-to-rod transition temperature for surfactant concentrations less than 20% by weight. A comparative analysis of these systems helps to shed light on the microscopic details of the micelle sphere-to-rod transition. In agreement with theoretical models, we find that spherical and cylindrical micelles have a different oil core packing; the core radius of a cylindrical micelle is reduced by a factor of 0.87 with respect to the core radius of a spherical micelle. Despite this contraction, the specific volume of the alkyl tails is larger in a cylindrical micelle than in a spherical micelle. In both geometries, this specific volume follows the same linear increase with temperature. Density measurement experiments are also performed in order to evaluate the specific volume of the hydrophobic tail of surfactants of the C12Ej family with j ranging from 5 to 8. We observe a good agreement between experimental data and simulation results. Our simulations also show that the spatial distribution of the head groups in the interface is more effective in screening the oil core in the cylindrical aggregate than in the spherical aggregate, reducing by a factor of 2 the oil surface per monomer exposed to water. This screening accounts for a free-energy difference of Deltafs=fssph-fscyl approximately +2.5kBT per monomer and mirrors the essential role that the hydrophobic interactions have on the shape transition. We also find that the different interface packing correlates with different conformations and flexibility of the hydrophilic fragments E6, that appear as an entropic reservoir for the transition. Finally, comparing the degree of hydration of a spherical micelle at T=283 K with that of a cylindrical micelle at T=318 K, we observe an amount of dehydration in agreement with reported experimental data across the sphere-to-rod transition. However, for aggregates of fixed shape, we find a much smaller amount of dehydration with temperature, suggesting that the shape transition is not a consequence of the measured temperature dehydration but rather the opposite.
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48
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Niyaz Khan M, Fui CT. Kinetic study on the effects of mixed nonionic–cationic micelles on the rate of alkaline hydrolysis of N-hydroxyphthalimide. J Mol Liq 2009. [DOI: 10.1016/j.molliq.2009.03.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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49
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Kinetic medium effects on organic reactions in aqueous colloidal solutions. ADVANCES IN PHYSICAL ORGANIC CHEMISTRY 2009. [DOI: 10.1016/s0065-3160(08)00001-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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50
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Abstract
This article reviews known approaches to generating viscoelastic and gel-like surfactant systems focusing on how the formation of these viscous phases are often sensitive to a variety of chemical and physio-chemical factors. An understanding of this sensitivity is essential for generating high viscosity surfactant phases in more challenging solvent environments. The initial focus is on the generation of worm-like and reverse worm-like micelles. In addition, other approaches for using surfactant self-assembly for viscosity enhancement have been examined, namely gelatin microemulsion based organogels and the addition of substituted phenols to AOT reverse micelles.
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