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Electrochemical investigations on lipid cubic phases
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Britta Sethson)ORCID iD: 0000-0003-1578-8825
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrochemical Impedance Spectroscopy (EIS) was used to develop a novel methodology for studying ionic interaction with lipids arranged in a lipid cubic phase (LCP). Studying different types of ions, both cations and anions, validated the method. A free-standing LCP membrane was formed between two cell compartments and impedance experiments were carried out in a 2-electrode setup to estimate dielectric properties of the membrane, exposed to the following electrolyte solutions at different concentrations: KCl, CsBr, CaCl2, MgCl2, CsCl, NaCl, NaOAc and NaTryptophan. Two different LCP were used in this setup, i.e: Monoloein/water and the ternary system of monoolein/dioleoylphosphatidylcholine/water (MO/DOPC/H2O). SAXRD measurements were performed to determine the space group of the cubic phase and confirm the stability of the LCP during measurements.

Membrane resistances and capacitances were found from equivalent circuit fitting to the impedance data. The membrane resistance was shown to be related to ionic interaction with the lipid head group in the water channels of the LCP. Membrane capacitance were correlating to condensing and swelling effect of LCP due to the exposure of ions. The results correlated well with the SAXRD results and earlier published data.

The results also indicate that these membranes become less permeable to ions as they increase in size as well as in charge or polarity. 

Cyclic voltammetry was used to study the applications of a LCP for modification of the bioanode in a biofuel cell. The monoolein cubic phase was used to host Glucose oxidase (GOx) and a freely diffusing ferrocene carboxylate was used as mediator. The supported cubic phase had an intrinsic resistance in the same order of magnitude as the freestanding MO-LCP membrane as measured with EIS.

Abstract [sv]

Elektrokemisk impedans spektroskopi har använts för att utveckla en ny metod för att studera joners växelverkan med lipider som bildat en kubisk fas. Olika typer av joner, både positiva och negativa, användes för att validera metoden. Ett fristående membran uppbyggt av en kubisk fas separerade två avdelningar i en elektrokemisk cell. Cellen fylldes med elektrolyt-lösningar och impedansmätningar kunde utföras mellan två platina elektroder placerade i vardera avdelning. Membranet exponerades för följande elektrolytlösningar av olika koncentration: KCl, CsBr, CaCl2, MgCl2, CsCl, NaCl, NaOAc and NaTryptofan. Två olika kubiska faser användes i denna uppställning, dvs: Monoloein/vatten och det ternära systemet monoolein/dioleoylfosfatidylkolin/vatten(MO/DOPC/H2O). Med hjälp av SAXRD kunde den kubiska fasens kristallstruktur bestämmas och dess stabilitet under mätningarna bekräftas. De dielektriska egenskaperna hos membranet bestämdes genom att anpassa impedansspektrat till en ekvivalent krets bestående av resistanser, kapacitanser och konstant-faselement. Membranresistansen visade sig vara relaterad till jonernas växelverkan med lipidhuvudgruppen i vattenkanalerna i kubiska fasen. Ju starkare växelverkan desto högre var resistansen. Membrankapacitansen kunde korreleras med kondenserande och uppsvällande effekter på kubiska fasen förorsakade av exponeringen till joner. Resultaten bekräftades av SAXRD mätningar och även tidigare publicerade data. Resultaten indikerar också tydligt att permeabiliteten hos membranet minskar med ökad jonstorlek, jonladdningoch polaritet hos jonen. Cyklisk voltammetri användes för att studera en tillämpning av kubiska fasen i en tänkt applikation som bioanod i en biobränslecell. Elektroden modifierades med en kubisk fas innehållande GOx och tillsammans med en fritt diffunderande ferrocen karboxylat som mediator, där oxidation av glukos studeras. Det visade sig att den kubiska fasen hade en resistans av samma storleksordning som det fristående membranet uppmätt med impedansspektroskopi.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2017. , 46 p.
Keyword [en]
Monoolein, Electrochemical Impedance Spectroscopy, lipid cubic phase, ionic interaction, biofuel cell
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-130174ISBN: 978-91-7601-660-2 (print)OAI: oai:DiVA.org:umu-130174DiVA: diva2:1064969
Public defence
2017-02-08, Stora hörsalen KBE303, KBC-huset, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-01-25 Created: 2017-01-13 Last updated: 2017-02-09Bibliographically approved
List of papers
1. Investigation of metal ion interaction with a lipid cubic phase using electrochemical impedance spectroscopy
Open this publication in new window or tab >>Investigation of metal ion interaction with a lipid cubic phase using electrochemical impedance spectroscopy
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2016 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 482, 212-220 p.Article in journal (Refereed) Published
Abstract [en]

AbstractHypothesis Electrochemical impedance spectroscopy, EIS, can be used as a complementary technique to investigate ion interaction with the headgroup region in the aqueous channels of a lipid cubic phase, LCP. Experiments A freestanding membrane made of monoolein LCP was formed by filling a small aperture that separates two cell compartments. The cell compartments were filled with electrolyte solutions at two different ionic strengths: i.e.: 10 and 100 mM, of KCl, CsBr and CaCl2. Electrochemical impedance spectroscopy was recorded between two platinum electrodes that were present at each side of the membrane. Findings The membrane resistance and capacitance were estimated from equivalent circuit fitting of the impedance data. It was confirmed that calcium ions interacts strongly with the headgroup region in the aqueous channels giving significantly higher membrane resistances compared to monovalent alkali metal ions. The membrane capacitance with Ca2+(aq) in solution was concentration dependent, which for the first time indicates formation of two different cubic phases at these conditions.

Keyword
Lipid cubic phase, Electrochemical impedance spectroscopy, Monoolein, Lipid–ion interactions, Calcium, Cesium, Potassium, Ionic permeability, Membrane resistance, Membrane capacitance
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-124993 (URN)10.1016/j.jcis.2016.07.053 (DOI)000383305700025 ()27505274 (PubMedID)
Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2017-01-24Bibliographically approved
2. Cationic Interaction with Phosphatidylcholine in a lipid cubic phase studied with electrochemical impedance spectroscopy and Small Angle X-ray Scattering
Open this publication in new window or tab >>Cationic Interaction with Phosphatidylcholine in a lipid cubic phase studied with electrochemical impedance spectroscopy and Small Angle X-ray Scattering
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-130581 (URN)
Available from: 2017-01-24 Created: 2017-01-24 Last updated: 2017-01-24
3. Aspects on mediated glucose oxidation at a supported cubic phase
Open this publication in new window or tab >>Aspects on mediated glucose oxidation at a supported cubic phase
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-130584 (URN)
Available from: 2017-01-24 Created: 2017-01-24 Last updated: 2017-01-24
4. Interactions of anions with lipid cubic phase membranes, an electrochemical impedance study
Open this publication in new window or tab >>Interactions of anions with lipid cubic phase membranes, an electrochemical impedance study
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-130585 (URN)
Available from: 2017-01-24 Created: 2017-01-24 Last updated: 2017-01-24

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