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The Structure of Model Membranes Studied by Vibrational Sum Frequency Spectroscopy
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0003-2734-2847
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-8935-8070
KTH, School of Biotechnology (BIO), Glycoscience.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2010 (English)In: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 137, 9-12 p.Article in journal (Refereed) Published
Abstract [en]

The structure and order of insoluble Langmuir monolayers consisting of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC or 18:0 PC) and the surrounding water molecules have been investigated by vibrational sum frequency spectroscopy (VSFS). At surface pressures of 1, 15, and 57 mN/m corresponding to molecular areas of 53, 50, and 43 Å2, respectively, the DSPC molecules formed a well ordered film. Both the VSF signal from the methyl stretching vibrations of the lipid and the surrounding water increased with enhanced surface pressure, as a result of the higher surface density and increased order of the system. Water molecules hydrating the polar parts of the headgroup and in close contact to the hydrocarbon groups of the lipid were observed in all three polarization combinations of the laser beams, and distinguished by their different vibrational frequencies.

Place, publisher, year, edition, pages
Berlin Heidelberg: Springer-Verlag , 2010. Vol. 137, 9-12 p.
Keyword [en]
Vibrational sum frequency spectroscopy, SFG, DSPC, Langmuir film, membrane
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-24458DOI: 10.1007/978-3-642-13461-6_3ISI: 000295079000003Scopus ID: 2-s2.0-79957827955OAI: oai:DiVA.org:kth-24458DiVA: diva2:350010
Note

QC 20100924

Available from: 2010-09-09 Created: 2010-09-09 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Biomimetic Membranes:: Molecular Structure and Stability Studies by Vibrational Sum Frequency Spectroscopy
Open this publication in new window or tab >>Biomimetic Membranes:: Molecular Structure and Stability Studies by Vibrational Sum Frequency Spectroscopy
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the research presented in this licentiate thesis the surface specific technique Vibrational Sum Frequency Spectroscopy, VSFS, combined with the Langmuir trough has been utilized to investigate Langmuir monolayers and Langmuir-Blodgett (LB) deposited mono- and bilayers of phospholipids. Their molecular structure, stability, and hydration were probed to gain additional understanding of important properties aiming at facilitating the use of such layers as model systems for biological membranes.

VSFS was applied to in situ studies of the degradation of Langmuir monolayers of 1,2-diacyl-phosphocholines with identical C-18 chains having various degrees of unsaturation. The time-dependent change of the monolayer area at constant surface pressure as well as the sum frequency intensity of the vinyl-CH stretch at the C=C double bonds were measured to monitor the degradation. It was shown that a rapid degradation of the monolayers of unsaturated phospholipids occurred when exposed to the laboratory air compared to the fully saturated lipid, and that the degradation could be inhibited by purging the ambient air with nitrogen. The degradation was attributed to oxidation mediated by reactive species in the air.

The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The spectroscopic data indicated a well ordered monolayer at all surface pressures with a more intense signal at higher pressures attributed to the subsequent increase of the number density and more ordered lipid molecules due to the tighter packing. Water molecules hydrating the headgroups or being in contact with the hydrophobic parts were observed and distinguished by their vibrational frequencies, and found to have different average orientations.

Additionally, monolayers of 18:0 PC, its fully deuterated analogue, and 1,2-distearoyl-phosphoserine (18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and VSFS was used to investigate the structure and order of the films as well as the hydrating water. The CH-region, water region, and lower wavenumber region containing phosphate, ester, carboxylic acid, and amine signals were probed to obtain a complete picture of the molecule. The data indicates that all deposited monolayers formed a well ordered and stable film and the average orientation of the aliphatic chains was determined using the antisymmetric methyl stretch.

Abstract [sv]

I forskningen som presenteras i denna licentiatavhandling har den ytspecifika vibrationssumfrekvensspektroskopin, VSFS, använts tillsammans med Langmuirtråget för att studera Langmuir-monolager och Langmuir-Blod-gett (LB) deponerade monolager och bilager av fosfolipider. För att utvidga förståelsen av egenskaper som är viktiga för att underlätta användandet av dem som modellsystem för biologiska membran undersöktes såväl deras molekylära struktur som stabilitet och hydratisering.

VSFS användes för att genomföra in situ-studier av nedbrytningen av Langmuir-monolager av 1,2-diacyl-fosfokoliner med identiska 18 kolatomer långa sidokedjor med varierande antal omättade kol-kol-bindningar. För att övervaka nedbrytningen mättes såväl den tidsberoende förändringen av monolagernas area vid konstant yttryck som sumfrekevensintensiteten från dubbelbindningarnas CH-vibration. När monolagerna bestående av omättade fosfolipider utsattes för laboratorieluften bröts de ner hastigt jämfört med det helt mättade monolagret. Denna nedbrytning som sannolikt orsakades av reaktiva ämnen i luften kunde inhiberas fullständigt genom att ersätta den omgivande luften med kvävgas.

Den molekylära strukturen och ordningen hos Langmuir-monolager av 1,2-distearoyl-fosfokolin (18:0 PC) och deras hydratiseringsvatten undersöktes vid olika yttryck med VSFS. Den spektroskopiska datan visar att monolagerna är välordnade vid alla yttryck samt att sumfrekvenssignalens styrka ökar med ökande yttryck på grund av såväl det större antalet molekyler per ytenhet som den högre ordningen då molekylerna packas tätare. Vattenmolekyler som hydratiserar huvudgrupperna eller är i kontakt med hydrofoba delar och har olika medelorientering observerades och kunde identifieras genom sina vibrationsfrekvenser.

Vidare deponerades monolager av 18:0 PC, dess fullt deuterade analog och 1,2-distearoyl-fofsfoserin (18:0 PS) på substrat av CaF2 och VSFS användes för att undersöka filmernas struktur och ordning såväl som hydratiseringsvattnet. CH- och vattenregionerna samt lågvågtalsområdet som innehåller fosfat-, ester-, karboxylsyra- och aminsignaler undersöktes för att få en fullständig bild av den molekylära strukturen. Data visar att alla deponerade monolager bildade en välordnad och stabil film och kolvätekedjornas medelorientering bestämdes med hjälp av signalen från den antisymmetriska metylvibrationen.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vii, 52 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:30
Keyword
Vibrational Sum Frequency Spectroscopy (VSFS), Langmuir monolayer, LB depositon, phospholipids, oxidation, biomimetic membranes
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-24465 (URN)978-91-7415-708-6 (ISBN)
Presentation
2010-10-08, YKI, konferensrum 3, Drottning Kristinas väg 45, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20100924Available from: 2010-09-24 Created: 2010-09-09 Last updated: 2010-09-24Bibliographically approved
2. A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
Open this publication in new window or tab >>A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Monolayers of molecules are capable of completely changing the nature of surfaces and their interactions with the surroundings despite their almost negligible thickness. In the research presented in this doctoral thesis the surface specific technique Vibrational Sum Frequency Spectroscopy (VSFS) was combined with the Langmuir trough to investigate various manifestations of monolayers, such as biomimetic membranes, mono methyl branched long chain fatty acids in contact with air, and hydrophobic silane monolayers in contact with water.

VSFS was applied to in situ studies of the oxidative degradation of Langmuir monolayers of 1,2-diacylphosphocholines with identical C-18 chains featuring various degrees of unsaturation. The monolayer area and vinyl CH signal intensity were probed at constant surface pressure to monitor the degradation. The rapid degradation of the unsaturated lipids in contact with the ambient air is attributed to oxidation of the C=C bonds mediated by reactive species in the air and can be inhibited by purging the compartment surrounding the monolayer with nitrogen.

The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The monolayers are conformationally well ordered at all surface pressures and the signal intensity increases due to larger molecular number density at increasing surface pressures. Also, water signals with different vibrational frequencies are observed in different polarization combinations.

Additionally, a selection of common phospholipids (18:0 PC, 18:0 PC-D83 and 18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and the CH- and OH-stretching regions as well as lower wavenumber regions were probed using VSFS. The orientation of the conformationally well ordered aliphatic chains was determined to be approximately perpendicular to the sample surface.

Monolayers of eicosanoic acid, its iso (19-MEA), and anteiso (18-MEA) analogues were investigated with VSFS, AFM imaging, and the Langmuir trough. The EA forms smooth, featureless monolayers when deposited on silica, while 19-MEA and 18-MEA form 10 -50 nm large domains with homogeneous size distribution. It was not possible to discriminate between the monolayers of racemic and chiral 18-MEA using any of the techniques employed

The influence of the experimental geometry on the SF spectral shape and en-hancement at and near total internal reflection conditions (TIR) were systematically investigated by comparing simulations with recorded data from a hydrophobized silica / water interface. The data agree qualitatively, but not quantitatively, with the simulations, and the reasons were critically discussed.

The water structure next to ordered and disordered hydrophobic silane monolayers on silica was investigated using VSFS. The results indicate that the structure of water next to a well ordered hydrophobic monolayer, with the exception of the first layer of water molecules, is not much different from that in the isotropic bulk. This is in contrast to the previous notion where such monolayers were assumed to induce a more ordered interfacial water structure.

Abstract [sv]

Trots sin begränsade tjocklek har monolager förmågan att totalt kunna förändra en ytas egenskaper och dess växelverkan med omgivningen. I forskningen som beskrivs i denna doktorsavhandling har den ytspecifika tekniken vibrationssumfrekvensspektroskopi (VSFS) kombinerats med Langmuir-tråget för att undersöka olika varianter av monolager, såsom biomimetiska membran, monometylgrenade långkedjiga fettsyror och hydrofoba silanmonolager i kontakt med vatten.

VSFS användes för att genomföra in situ undersökningar av den oxidativa nedbrytningen av Langmuir-monolager av 1,2-diacylfosfokoliner med identiska 18 kolatomer långa kedjor med varierande grader av omättnad. Monolagerarean och vinylCH-signalens intensitet mättes vid konstant yttryck för att övervaka nedbrytningen. Den snabba nedbrytningen av de omättade lipiderna i kontakt med den omgivande luften tillskrivs oxidation orsakad av reaktiva ämnen i luften och kan inhiberas fullständigt genom att genomblåsa utrymmet som omger monolagret med kvävgas.

Den molekylära strukturen och ordningen hos Langmuir-monolager av 1,2-distearoylfosfokolin (18:0 PC) och deras hydratiseringsvatten undersöktes vid olika yttryck med VSFS. Monolagerna har en välordnad konformation vid alla yttryck och signalintensiteten ökar vid ökande yttryck på grund av den större numerära molekyltätheten. Dessutom observeras vattensignaler med olika vibrationsfrekvenser i olika polarisationskombinationer.

Vidare LB-deponerades ett urval av vanligt förekommande fosfolipider (18:0 PC, 18:0 PC-D83 och 18:0 PS) på ett substrat av CaF2 varefter CH- och vattenregionen såväl som lågvågtalsområdet undersöktes med hjälp av VSFS. Orienteringen hos kolvätekedjorna, som hade en välordnad konformation, befanns vara ungefär vinkelrät mot provytan.

Monolager av eicosansyra, samt dess iso (19-MEA), och anteiso (18-MEA) analoger undersöktes med VSFS, AFM avbildning och Langmuirtråget. Eicosanssyran bildar jämna, strukturlösa monolager då den deponeras på kiseldioxid medan 19-MEA och 18-MEA formar 10 – 50 nm stora domäner med homogen storleksfördelning. Ingen av de använda teknikerna kunde särskilja racemisk och kiral 18-MEA.

Inverkan av försöksuppställningens geometri på SF-spektrumets form och förstärkning vid och i närheten av total internreflektion (TIR) undersöktes systematiskt genom att jämföra simuleringar med mätdata från en gränsyta mellan hydro-foberad kiseldioxid och vatten. Mätdata överensstämmer kvalitativt, men inte kvantitativt, med simuleringarna och orsakerna till detta diskuterades kritiskt.

Vattenstrukturen intill ordnade och oordnade hydrofoba silanmonolager undersöktes med VSFS. Resultaten visar att vattenstrukturen nära ett välordnat hydrofobt monolager, med undantag av det första lagret av vattenmolekyler, inte är särskilt olik den isotropa bulkfasens. Detta är i motsats till den tidigare uppfattningen att sådana monolager ansågs orsaka en mera välordnad vattenstruktur.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 80 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:35
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-101081 (URN)978-91-7501-436-4 (ISBN)
Public defence
2012-09-21, KTH, Hörsal F3, Lindstedtsvägen 26, KTH, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20120824

Available from: 2012-08-24 Created: 2012-08-23 Last updated: 2012-08-24Bibliographically approved

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