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Biomimetic Membranes:: Molecular Structure and Stability Studies by Vibrational Sum Frequency Spectroscopy
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0003-2734-2847
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 [en]
Vibrational Sum Frequency Spectroscopy (VSFS), Langmuir monolayer, LB depositon, phospholipids, oxidation, biomimetic membranes
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-24465ISBN: 978-91-7415-708-6 (print)OAI: oai:DiVA.org:kth-24465DiVA: diva2:353065
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
List of papers
1. Phospholipid Monolayers Probed by Vibrational Sum Frequency Spectroscopy: Instability of Unsaturated Phospholipids
Open this publication in new window or tab >>Phospholipid Monolayers Probed by Vibrational Sum Frequency Spectroscopy: Instability of Unsaturated Phospholipids
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2010 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, L50-L52 p.Article in journal, Letter (Refereed) Published
Abstract [en]

The surface specific technique vibrational sum frequency spectroscopy has been applied to in situ studies of the degradation of Langmuir monolayers of 1,2-diacyl-phosphocholines with various degrees of unsaturation in the aliphatic chains. To monitor the degradation of the phospholipids, the time-dependent change of the monolayer area at constant surface pressure and the sum frequency intensity of the vinyl CH stretch at the carbon-carbon double bonds were measured. The data show a rapid degradation of monolayers of phospholipids carrying unsaturated aliphatic chains compared to the stable lipids carrying fully saturated chains when exposed to the ambient laboratory air. In addition, the degradation of the phospholipids can be inhibited by purging the ambient air with nitrogen. This instability may be attributed to spontaneous degradation by oxidation mediated by various reactive species in the air. To further elucidate the process of lipid oxidation in biological membranes artificial Langmuir monolayers probed by a surface specific spectroscopic technique as in this study can serve as a model system for studying the degradation/oxidation of cell membrane constituents.

Place, publisher, year, edition, pages
Cell Press, 2010
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24456 (URN)10.1016/j.bpj.2010.02.009 (DOI)000277858400002 ()2-s2.0-77952778434 (Scopus ID)
Note

QC 20100924

Available from: 2010-09-09 Created: 2010-09-09 Last updated: 2017-12-12Bibliographically approved
2. Supported Phospholipid Monolayers: The Molecular Structure Investigated by Vibrational Sum Frequency Spectroscopy
Open this publication in new window or tab >>Supported Phospholipid Monolayers: The Molecular Structure Investigated by Vibrational Sum Frequency Spectroscopy
2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 21, 10617-10629 p.Article in journal (Refereed) Published
Abstract [en]

The molecular structure, packing properties, and hydrating water of Langmuir-Blodgett monolayers of the phospholipids 1,2-distearoyl-sn-glyercophosphatidylcholine (DSPC, 18:0 PC), its deuterated analogue (18:0 PC-d83), and 1,2-distearoyl-sn-glyerco-phosphatidylserine (DSPC, 18:0 PS) deposited on planar calcium fluoride (CaF2) substrates have been investigated using the surface-specific nonlinear optical technique vibrational sum frequency spectroscopy (VSFS). Compression isotherms were recorded before the deposition of the monolayers at a surface pressure of 35 mN/m, mimicking the conditions of biological cell membranes. The CH and CD stretch regions, the water region, and the lower wavenumber region, containing phosphate, ester, carboxylate, and amine signals, thus partly covering the fingerprint region, were probed to obtain a complete map of the molecules. The data indicate that all deposited monolayers formed a well-ordered and stable film, and probing the water region revealed significant differences in hydration for the different headgroups. In addition, the tilt angle of the aliphatic chains relative to the surface normal was estimated to be approximately 4 degrees to 10 degrees based on orientational analysis using the antisymmetric methyl stretching vibration. Orientational analysis of the ester C=O groups was also performed, and the result was consistent with the estimated tilt angle of the aliphatic chains.

Keyword
Vibrational sum frequency spectroscopy, SFG, DSPC, DSPS, Langmuir film, membrane
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24464 (URN)10.1021/jp111587e (DOI)000290914700040 ()2-s2.0-79957845982 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20100924. Uppdaterad från manuscript till published. Tidigare titel: Supported Phospholipid Monolayers: The Molecular Structure Investigated by Vibrational Sum Frequency Spectroscopy (VSFS)Available from: 2010-09-23 Created: 2010-09-09 Last updated: 2017-12-12Bibliographically approved
3. The Structure of Model Membranes Studied by Vibrational Sum Frequency Spectroscopy
Open this publication in new window or tab >>The Structure of Model Membranes Studied by Vibrational Sum Frequency Spectroscopy
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
Keyword
Vibrational sum frequency spectroscopy, SFG, DSPC, Langmuir film, membrane
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24458 (URN)10.1007/978-3-642-13461-6_3 (DOI)000295079000003 ()2-s2.0-79957827955 (Scopus ID)
Note

QC 20100924

Available from: 2010-09-09 Created: 2010-09-09 Last updated: 2017-12-12Bibliographically approved

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Liljeblad, Jonathan F.D.

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