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Amphiphilic Molecules in Aqueous Solution

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Amphiphilic Molecules in Aqueous Solution Amphiphilic Molecules in Aqueous Solution Effects of Some Different Counterions The Monoolein/Octylglucoside/Water System Gerd Persson 2003 Department of Chemistry Department of Natural and Biophysical Chemistry Environmental Sci ences Umeå University Mid Sweden University Sweden Sweden Amphiphilic Molecules in Aqueous Solution Effects of Some Different Counterions The Monoolein/Octylglucoside/Water System Doctoral Thesis Gerd Persson Sundsvall and Umeå 2003 Avhandling som med vederbörligt tillstånd av rektorsämbetet vid Umeå universitet för avläggande av filosofie doktorsexamen vid teknisk -naturvetenskapliga fakulteten vid Umeå Universitet kommer att försvaras vid en offentlig disputation i SCA -salen (O102), Kornboden, Mitthögskolan, Sundsvall fredagen den 3 oktober 2003, kl. 13.00. Fakultetsopponent: Prof. Björn Lindman, Lunds Universitet, Lund, Sverige. Department of Chemistry Department of Natural and Biophysical Chemist ry Environmental Sciences Umeå University Mid Sweden University Sweden Sweden Amphiphilic Molecules in Aqueous Solution Effects of Some Different Counterions The Monoolein/Octylglucoside/Water System Abstract The aim of this thesis was to investigate amphiphilic molecules in aqueous solution. The work was divided into two parts. In the first part the effects of different counterions on phase behavior was investigated, while the second part concerns the 1 -monooleoyl -rac -glycerol 2 (MO)/n -octyl --D-glucoside (OG)/ H2O-system. The effects of mixing monovalent and divalent counterions were studied for two surfactant systems, sodium/calcium octyl sulfate, and piperidine/piperazine octanesulfonate. It was found that mixing monovalent and divalent co unterions resulted in a large decrease in cmc already at very low fractions of the divalent counterion. Moreover, the degree of counterion binding for piperidine in the piperidine/piperazine octanesulfonate system was much higher than predicted, probably due to the larger hydrophobic moiety of piperidine. The effects of hydrophobic counterions were studied for eight alkylpyridinium octanesulfonates (APOS). The results were discussed in terms of packing constraints. The 2 anomalous behavior of the H2O quadru polar splittings in the lamellar phases was explained by the presence of two or more binding sites at the lamellae surface. The MO/OG/water system was studied in general and the MO -rich cubic phases in particular. When mixing MO and OG it was found that O G-rich structures (micelles, hexagonal and cubic phase of space group Ia 3d) could solubilize quite large amounts of MO, while the MO - rich cubic structures where considerable less tolerant towards the addition of OG. The micelles in the OG -rich L 1 phase wer e found to remain rather small and discrete in the larger part of the L 1 phase area, but at low water concentration and high MO content a bicontinuous structure was indicated. Only small fractions of OG was necessary to convert the MO -rich cubic Pn 3m structure to an Ia 3d structure, and upon further addition of OG a lamellar (L ) phase formed. Since the larger part of the phase diagram contains a lamellar structure (present either as a single L phase or as a dispersion of lamellar particles together with other phases), the conclusion was that introducing OG in the MO structures , forces the MO bilayer to become more flat. Upon heating the cubic phases, structures with more negative curvature were formed. The transformation between the cubic structures required very little energy, and this resulted in the appearance of additional peaks in the diffractograms. Key words: liquid crystal, phase diagrams, counterions, alkylpyridinium octanesulfonates, 1- monooleoyl -rac-glycerol, n-octyl- -D-glucoside, cubic phases Language: English ISBN: 91-7305-501-8 Signature: Date: 11 August 2003 Amphiphilic Molecules in Aqueous Solution Effects of Some Different Counterions The Monoolein/Octylglucoside/Water System Gerd Persson Department of Chemistry Department of Natural and Biophysical Chemistry Environ mental Sciences Umeå University Mid Sweden University Sweden Sweden Front cover: The two main principles of Judo. The left column reads in Japanese: “Jita Kyoei”, meaning “ Mutual welfare and benefit”. The right column reads in Japanese: “Sei ryoku Zenyo”, meaning “Maximum efficiency”. Copyright © 2003 by Gerd Persson ISBN 91-7305-501-8 Printed by Kaltes Grafiska AB, Sundsvall, 2003 ii Till Gabriel och Görgen iii iv Abstract The aim of this thesis was to investigate amphiphilic molecules in aqueous solution. The work was divided into two parts. In the first part the effects of different counterions on phase behavior was investigated, while the second part concerns the 1 -monooleoyl -rac -glycerol 2 (MO)/n -octyl --D-glucoside (OG)/ H2O-system. The effects of mixing monovalent and divalent counterions were studied for two surfactant systems, sodium/calcium octyl sulfate, and piperidine/piperazine octanesulfonate. It was found that mixing monovalent and divalent co unterions resulted in a large decrease in cmc already at very low fractions of the divalent counterion. Moreover, the degree of counterion binding for piperidine in the piperidine/piperazine octanesulfonate system was much higher than predicted, probably due to the larger hydrophobic moiety of piperidine. The effects of hydrophobic counterions were studied for eight alkylpyridinium octanesulfonates (APOS). The results were discussed in terms of packing constraints. The 2 anomalous behavior of the H2O quadru polar splittings in the lamellar phases was explained by the presence of two or more binding sites at the lamellae surface. The MO/OG/water system was studied in general and the MO -rich cubic phases in particular. When mixing MO and OG it was found that O G-rich structures (micelles, hexagonal and cubic phase of space group Ia 3d) could solubilize quite large amounts of MO, while the MO - rich cubic structures where considerable less tolerant towards the addition of OG. The micelles in the OG -rich L 1 phase wer e found to remain rather small and discrete in the larger part of the L 1 phase area, but at low water concentration and high MO content a bicontinuous structure was indicated. Only small fractions of OG was necessary to convert the MO -rich cubic Pn 3m structure to an Ia 3d structure, and upon further addition of OG a lamellar (L ) phase formed. Since the larger part of the phase diagram contains a lamellar structure (present either as a single L phase or as a dispersion of lamellar particles together with other phases), the conclusion was that introducing OG in the MO structures , forces the MO bilayer to become more flat. Upon heating the cubic phases, structures with more negative curvature were formed. The transformation between the cubic structures required very little energy, and this resulted in the appearance of additional peaks in the diffractograms. v List of papers The thesis is based on the following papers, which are referred to in the text by their roman numerals: I. Competition between Monovalent and Divalent Counterions in Surfactant Systems. Carlsson, I.; Edlund, H.; Persson, G.; Lindström, B. J. Colloid Interface Sci ., 1996 , 180, 598. II. Phase Behavior of N-Alkylpyridinium Octanesulfonates. Effect of Alkylpyridinium Counterion Size. Gerd Persson, Håkan Edlund, Erik Hedenström and Göran Lindblom submitted to Langmuir III. The 1-Monooleoyl -rac-Glycerol /n -Octyl --D-Glucoside/Water – System. Phase Diagram and Phase Structures Determined by NMR and X-ray Diffraction. Persson, G.; Edlund, H.; Amenitsch, H.; Laggner, P.; Lindblom, G. Langmuir , 2003 , 19, 5813. IV. Thermal behaviour of cubic phases rich in 1-monooleoyl -ra c-glycerol in the ternary system 1-monooleoyl -rac-glycerol/ n-octyl --D-glucoside/water. Persson, G.; Edlund, H.; Lindblom, G. Eur. J. Biochem ., 2003 , 270, 56. vi Table of contents Abstract v List of papers vi Introduction 1 1. Surfactants 2 1.1. General structure and criteria for surfactants 2 1.2. Different types of surfactants 3 Ionic surfactants 3 Non-ionic surfactants 4 1.3. Nonsoluble amphiphilic molecules 5 2. Phase structures 6 2.1. Isotropic solution phases: L1, L2 and L 3 6 2.2. Vesicles 7 2.3. Liquid crystalline phases 7 2.4. Packing parameter and curvature 8 Cpp 10 Spontaneous curvature 10 3. Phase equilibria in surfactant systems 11 3.1. Krafft temperature 11 3.2. Micelle formation 11 3.3. Presentati on of surfactant systems -phase diagrams 11 Gibbs phase rule 12 Binary phase diagrams and the lever rule 12 Ternary phase diagrams 13 4. Methods for characterization of surfactant systems 14 4.1. Polarizing microscopy 14 4.2. Surface tension 16 4.3. Conductivity 17 4.4. DSC 18 vii 4.5. NMR 18 1H NMR 19 Pulsed Gradient NMR 19 Quadrupolar splitting 22 4.6. SAXD 24 5. Results 26 5.1. Effects of different counterions 26 Paper I 26 Paper II 27 2 5.2. The 1-monooleoyl -rac -glyc erol/ n-octyl- -D-glucoside/ H2O system 29 Paper III 30 Paper IV 31 6. Ideas for future work 32 Acknowledgements 34 References 35 Papers I - IV 39 viii Introduction In our daily life the utilization of amphiphilic molecules is very important. In man y areas including such diverse fields as cleaning products, food, paint, medicine, cosmetics and industrial as well as biological processes, this type of molecules play a crucial role. The self - organization of these molecules results in a diversity of stru ctures, among which micelles and bilayers can be mentioned. Now, the question is what exactly is an amphiphilic molecule? The word amphiphile is derived from the Greek words µ (amphi) = both and (philios) = friend. Thus, the word itself means something that likes, or rather is friendly to, both. In chemistry this is generally considered to mean two things that are immiscible, such as oil and water. So, an amphiphilic molecule likes both oil and water. Now, what does that mean and what can we use it for? Basically, this is the solution to a lot of problems involving oil and water. The use of amphiphilic molecules creates a means to dissolve water into oil and oil into water, which is something necessary for many applications.
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