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Interactions Between Biopolymers and Surfactants with Focus on Fluorosurfactants and Proteins
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis was to obtain a better understanding of the association between surfactants and biopolymers in bulk solutions and at solid/aqueous liquid interface. In order to do this, the interactions between surfactants and biopolymers were investigated with a variety of experimental techniques.

The main focus has been on the interactions between fluorosurfactants and proteins, which are important during electrophoresis of proteins in silica capillaries. Electrophoretic separation of positively charged proteins is often complicated by non-specific adsorption of protein onto capillary wall, while it was found to improve when cationic fluorosurfactants were added into the background buffer. We investigated the interactions between a cationic fluorosurfactant, FC134, and a positively charged protein, lysozyme. By employing Nuclear Magnetic Resonance (NMR) and tensiometry we could conclude that the cationic fluorosurfactant did not associate with positively charged lysozyme in bulk solutions. At the solid/aqueous liquid interface, the adsorption of fluorosurfactants and lysozyme onto silica was studied by the surface force technique (MASIF), ellipsometry, reflectrometry, Quartz Crystal Microbalance (QCM-D) and Atomic Force Microscopy (AFM). Cationic fluorosurfactant FC134 was found to adsorb onto the silica surface in a form of bilayer aggregates, which led to a charge reversal of the originally negatively charged substrate. The adsorption of lysozyme onto silica was also extensive and it corresponded to the more than monolayer coverage. When adsorbing from mixed solutions, the presence of the cationic fluorosurfactant in the solution led to an elimination of the lysozyme in the resulting adsorbed layer. For the lysozyme concentration of 0.2 mg/ml, which is typical for the electrophoretic separation, it was found that adsorption of protein was suppressed by more than 90% when only 30 μM of FC134 was added into the buffer. The presence of the low amounts of residual proteins in the adsorbed layers caused an enhancement of the adsorption of fluorosurfactants, which was attributed to adsorption of the fluorosurfactants between proteins in a form of large vesicles.

The interactions between a positively charged biopolymer chitosan and an anionic surfactant sodium dodecylsulfate (SDS) were studied with respect to the effect of the ionic strength of the background electrolyte, both in the bulk solution and at the silica/liquid interface. It was shown that SDS and chitosan form complexes in the bulk solution, which reverse their charge at higher SDS concentrations. At SDS concentrations above the critical micellar concentration, large aggregates were formed, which were trapped in long-lived nonequilibrium states at both high and low ionic strengths. SDS did not adsorb at the silica/liquid interface by itself. However, by employing QCM-D and ellipsometry we detected an extensive adsorption of SDS on the silica substrate, which has been modified by adsorbed chitosan. The structure of the chitosan layer on the lowly charged silica was strongly affected by the ionic strength of the solution from which the chitosan adsorption took place. The interactions between SDS and the pre-adsorbed chitosan were found to be similar on lowly charged silica and on highly charged mica.

A novel method based on the Bruggeman effective medium approximation was proposed for the evaluation of ellipsometric data characterizing composite adsorbed layers.

Finally, the effect of the adsorbed layer surface roughness on the QCM-D response in liquid was studied with focus on trapped water. It was found that QCM-D effectively senses water, which is mechanically trapped inside topographical structures with the size in nano-meter scale.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 97 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:54
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4475ISBN: 978-91-7178-739-2 (print)OAI: oai:DiVA.org:kth-4475DiVA: diva2:12439
Public defence
2007-09-14, Salongen, KTH Biblioteket, Osquara backe 31, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100809Available from: 2009-08-30 Created: 2007-08-30 Last updated: 2010-08-09Bibliographically approved
List of papers
1. Lack of association between a cationic protein and a cationic fluorosurfactant
Open this publication in new window or tab >>Lack of association between a cationic protein and a cationic fluorosurfactant
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2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 2, 771-775 p.Article in journal (Refereed) Published
Abstract [en]

Surface tension, F-19 and H-1 NMR spectroscopy, and cryotransmission electron microscopy are used to characterize the state of association in aqueous solutions of a fluorosurfactant CF3(CF2)(n)SO2NH(CH2)(3-4)N(CH3)(3)(+) I- (n = 8, 6) with and without lysozyme added. In the absence of lysozyme, we find monomers, small aggregates, and large vesicles to coexist, with the individual fluorosurfactant molecules exchanging slowly (> 1 ms) among those states. When both lysozyme and fluorosurfactant are present in the solution, they have no measurable influence on the physical state of the other. In contrast, a hydrogenated cationic surfactant with the same headgroup, hexadecyltrimethylammonium bromide, is shown to associate to lysozyme.

Keyword
Fluorescence; Monomers; Nuclear magnetic resonance; Proteins; Solutions; Surface tension; Transmission electron microscopy; Cationic fluorosurfactants; Cationic proteins; Cryotransmission electron microscopy; Individual fluorosurfactant molecules; Surface active agents; cation; cetrimide; lysozyme; surfactant; article; chemical structure; chemistry; cryoelectron microscopy; hydrogen bond; methodology; nuclear magnetic resonance spectroscopy; physical chemistry; protein folding; surface property; surface tension; transmission electron microscopy; Cations; Cetrimonium Compounds; Chemistry, Physical; Cryoelectron Microscopy; Hydrogen Bonding; Magnetic Resonance Spectroscopy; Microscopy, Electron, Transmission; Molecular Structure; Muramidase; Protein Folding; Surface Properties; Surface Tension; Surface-Active Agents
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-7413 (URN)10.1021/la062469z (DOI)000243338500061 ()17209632 (PubMedID)2-s2.0-33846852625 (Scopus ID)
Note

QC 20150721

Available from: 2009-08-30 Created: 2009-08-30 Last updated: 2015-07-21Bibliographically approved
2. Fluorosurfactant self-assembly at solid/liquid interfaces
Open this publication in new window or tab >>Fluorosurfactant self-assembly at solid/liquid interfaces
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2002 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 21, 8085-8095 p.Article in journal (Refereed) Published
Abstract [en]

Fluorosurfactants have some unique properties that are advantageously used in a range of applications. Their solutions are commonly in contact with solid surfaces onto which the molecules adsorb. Despite this, the adsorption behavior of fluorosurfactants at solid/liquid interfaces is not sufficiently understood, and there is a need for more information. In this study we focus on cationic fluorosurfactant adsorption on negatively charged hydrophilic surfaces, especially with respect to the adsorbed layer structure, long-range interactions, and adhesion forces. To this end we combined results obtained from bimorph and interferometric surface force instruments and ellipsometry techniques. The initial adsorption to the oppositely charged surfaces occurs due to the electrostatic attraction between the charged headgroups and the surface. Further adsorption, driven by hydrophobic interactions, occurs readily as the surfactant concentration is increased. Surface force and ellipsometric experiments indicate that the surfactants self-assemble in the form of bilayer aggregates. The thickness of the bilayer aggregates was found to be consistent with the molecular structure. Further, ellipsometric measurements indicate that no complete bilayers were formed but rather that bilayer aggregates were present on the surface even at concentrations well above the cmc. Surface force data for low fluorosurfactant concentrations demonstrate that upon compression the bilayer aggregates assembled on the isolated surfaces are transformed, and as a result monolayer structures build up between the surfaces in contact. The force required to attain bilayer-bilayer contact increases with the surfactant bulk concentration due to an increase in the repulsive double-layer force. The force required to drive out surfactant molecules to achieve monolayer-monolayer contact also increases with surfactant concentration. Above the cmc some additional aggregates are present on top of the bilayer aggregates coating the surface. The adhesion found between the monolayer aggregates is an order of magnitude larger than between the bilayer aggregates. However, it is an order of magnitude lower than the corresponding value for Langmuir-Blodgett monolayer films of similar fluorosurfactants.

Keyword
Adhesion; Adsorption; Aggregates; Electrostatics; Ellipsometry; Hydrophilicity; Hydrophobicity; Langmuir Blodgett films; Molecular structure; Monolayers; Phase interfaces; Positive ions; Self assembly; Fluorosurfactants; Surface active agents
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-7414 (URN)10.1021/la025989c (DOI)000178589700049 ()
Note
QC 20100809Available from: 2009-08-30 Created: 2009-08-30 Last updated: 2012-02-10Bibliographically approved
3. Competitive adsorption of lysozyme and cationic fluorosurfactant onto silica
Open this publication in new window or tab >>Competitive adsorption of lysozyme and cationic fluorosurfactant onto silica
(English)Manuscript (Other academic)
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-7415 (URN)
Note
QC 20100809Available from: 2009-08-30 Created: 2009-08-30 Last updated: 2010-08-09Bibliographically approved
4. The effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water
Open this publication in new window or tab >>The effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water
2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, 12436-12444 p.Article in journal (Refereed) Published
Abstract [en]

The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses Were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C-12)(2)-DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C(16)TAB (CTAB), and dodecyltrimethylammonium bromide C(12)TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies

Keyword
Adsorption; Cationic surfactants; Energy dissipation; Quartz crystal microbalances; Reflectometers; Surface roughness; Dissipation monitoring; Optical reflectometry; Trapped water; Polymer films
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-7417 (URN)10.1021/la7014308 (DOI)000250976700077 ()2-s2.0-36649000928 (Scopus ID)
Note

QC 20100809

Available from: 2009-08-30 Created: 2009-08-30 Last updated: 2016-05-18Bibliographically approved
5. Interactions between Chitosan and SDS at a Low-Charged Silica Substrate Compared to Interactions in the Bulk: The Effect of Ionic Strength
Open this publication in new window or tab >>Interactions between Chitosan and SDS at a Low-Charged Silica Substrate Compared to Interactions in the Bulk: The Effect of Ionic Strength
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 8, 3814-3827 p.Article in journal (Refereed) Published
Abstract [en]

The effect of ionic strength on association between the cationic polysaccharide chitosan and the anionic surfactant sodium dodecyl sulfate, SDS, has been studied in bulk solution and at the solid/liquid interface. Bulk association was probed by turbidity, clectrophoretic mobility, and surface tension measurements. The critical aggregation concentration, cac, and the saturation binding of surfactants were estimated from surface tension data. The number of associated SDS molecules per chitosan segment exceeded one at both salt concentrations. As a result, a net charge reversal of the polymer-surfactant complexes was observed, between 1.0 and 1.5 mM SDS, independent of ionic strength. Phase separation occurs in the SDS concentration region where low charge density complexes form, whereas at high surfactant concentrations (up to several multiples of cmc SDS) soluble aggregates are formed. Ellipsometry and QCM-D were employed to follow adsorption of chitosan onto low-charged silica substrates, and the interactions between SDS and preadsorbed chitosan layers. A thin (0.5 nm) and rigid chitosan layer was formed when adsorbed from a 0.1 mM NaNO3 solution, whereas thicker (2 nm) chitosan layers with higher dissipation/unit mass were formed from solutions at and above 30 mM NaNO3. The fraction of solvent in the chitosan layers was high independent of the layer thickness and rigidity and ionic strength. In 30 mM NaNO3 Solution, addition of SDS induced a collapse at low concentrations, while at higher SDS concentrations the viscoelastic character of the layer was recovered. Maximum adsorbed mass (chitosan + SDS) was reached at 0.8 times the cmc of SDS, after which surfactant-induced polymer desorption occurred. In 0.1 mM NaNO3. the initial collapse was negligible and further addition of surfactant lead to the formation of a nonrigid, viscoelastic polymer layer until desorption began above a surfactant concentration of 0.4 times the cmc of SDS.

Keyword
sodium dodecyl-sulfate; quartz-crystal microbalance; solid-liquid interface; air-water-interface; x-ray-scattering; anionic surfactant; cationic polyelectrolyte; viscoelastic properties; electrolyte-solutions; air/water interface
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-11138 (URN)10.1021/la702653m (DOI)000254647400020 ()2-s2.0-42449149169 (Scopus ID)
Note
QC 20100729Available from: 2009-09-22 Created: 2009-09-22 Last updated: 2010-08-09Bibliographically approved

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