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Structural Studies of Oligo(ethylene glycol)-Containing Assemblies on Gold
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presents in this thesis has been focused on structural  characterization of a series of selected well-defined molecular architectures for the application as biomimetic membranes. The molecular architectures were prepared by self-assembly from dilute solution onto gold substrates, so called self-assembled monolayers (SAMs).

Biological membranes are essential components for all living systems; their molecular organizations and interactions with intra- and extracellular networks are key factors of cell functions. Many important biological processes are regulated at membrane interfaces via interactions between membrane proteins. Therefore, identification of the cell structures and understanding of the processes associated with membranes are crucial. However, the intrinsic complexity of the cell membrane systems makes direct investigation extra difficult. Based on this reason, artificial model membranes have become a useful strategy. Especially, solid supported tethered lipid membranes on SAMs allow for controlling the composition and geometry of biomimetic assemblies on molecular scale. However, the underlying mechanisms of lipid vesicle fusion on SAMs remain unclear. In this thesis, a series of thiolate SAMs containing alkyl chains and oligo(ethylene glycol) (OEG) portions of different length as well as amide linking groups were prepared and characterized in detail by employing a number of surface analyzing methods. In parallel, a set of ab initio modeling was undertaken for the best interpretation of the experimental infrared spectra. Investigation of small unilamellar vesicles interact with such SAMs is included as well.

The results show this type of assemblies forms highly ordered and oriented SAMs regardless of the length of the extended alkyl chains. The two layers of lateral hydrogen bonding networks through the two amide linking groups improve further the structural robustness of the assemblies. Furthermore, the use of deuterated terminal alkyl chains enables a direct relation between the surface density of the anchor molecules and the properties of the lipidbilayers. IRRAS data and ab initio modeling confirm that orientation of the helical OEG is affected by the second hydrogen bonding layer rather than the extended alkyl tails. Nanopatterns consisting of such SAMs with different extended alkyl chains can be employed as supports for the assembly of artificial cell membranes.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 62 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1446
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-77056ISBN: 978-91-7519-898-9 (print)OAI: oai:DiVA.org:liu-77056DiVA: diva2:524740
Public defence
2012-05-31, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2012-06-29Bibliographically approved
List of papers
1. Long-Chain Alkylthiol Assemblies Containing Buried In-Plane Stabilizing Architectures
Open this publication in new window or tab >>Long-Chain Alkylthiol Assemblies Containing Buried In-Plane Stabilizing Architectures
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2009 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 24, 13959-13971 p.Article in journal (Refereed) Published
Abstract [en]

A series of alkylthiol compounds were synthesized to study the formation and structure of complex self-assembled monolayers (SAMs) consisting of interchanging structural modules stabilized by intermolecular hydrogen bonds. The chemical structure of the synthesized compounds, HS(CH2)(15)CONH(CH2CH2O)(6)CH2CONH-X, where X refers to the extended chains of either -(CH2)(n)CH3 or -(CD2)(n)CD3, with n = 0, 1, 7, 8, 15, was confirmed by NMR and elemental analysis. The formation of highly ordered, methyl-terminated SAMs oil gold from diluted ethanolic solutions of these compounds was revealed using contact angle goniometry, mill ellipsometry, cyclic voltammetry, and infrared reflection absorption spectroscopy. The experimental work was complemented with extensive DFT modeling of infrared spectra and molecular orientation. New assignments were introduced for both nondeuterated and deuterated Compounds. The latter set of compounds also served as a convenient tool to resolve the packing, conformation, and orientation of the buried and extended modules within the SAM. Thus, it was shown that the lower alkyl portion together with the hexa(ethylene glycol) portion is stabilized by the two layers of lateral hydrogen bonding networks between the amide groups, and they provide it Structurally robust support for the extended alkyls, The presented system can be considered to be an extension of the well-known alkyl SAM platform, enabling precise engineering of nanoscopic architectures oil the length scale from a Few to similar to 60 angstrom for applications such as cell membrane mimetics, molecular nanolithography, and so forth.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-52826 (URN)10.1021/la901668u (DOI)
Available from: 2010-01-12 Created: 2010-01-12 Last updated: 2017-12-12Bibliographically approved
2. Mixed Self-Assembled Monolayers with Deuterated Terminal Anchors for Tethered Lipid Membrane Formation
Open this publication in new window or tab >>Mixed Self-Assembled Monolayers with Deuterated Terminal Anchors for Tethered Lipid Membrane Formation
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The aim of this study was to develop a stable and flexible self-assembled monolayer (SAM) for tethered lipid bilayer membrane (tBLM) formation that in the future might be employed for mimetics of more complex cell membrane architectures. Our model SAM surface conisted of a mixture of a filling molecule,  HS(CH2)15CONHCH2CH2OH, and an anchor molecule, HS(CH2)15CONH(CH2CH2O)6CH2CONH-X, where X is either –(CD2)7CD3 or – (CD2)15CD3. We have prepared and characterized their structure and chemical composition as well as the adsorption of lipids on the SAM by means of ellipsometry, contact angle goniometry, and infrared reflection-absorption spectrometry (IRRAS). The use of deuterated terminal alkyl chains enabled us to establish a correlation between the relative surface density of the anchors and the properties of the lipid bilayers formed via small unilamellar vesicle (SUV) fusion. Further on, we monitored SUV fusion kinetics on the mixed SAM  surface using quartz crystal microbalance with dissipative monitoring (QCM-D). The QCM-D analysis revealed that a critical vesicle concentration has to be reached on the SAM for vesicle rupture and bilayer formation.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77050 (URN)
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2012-05-03
3. On the quality and structural characteristics of oligo(ethylene glycol) assemblies on gold: An experimental and theoretical study
Open this publication in new window or tab >>On the quality and structural characteristics of oligo(ethylene glycol) assemblies on gold: An experimental and theoretical study
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2009 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, Vol. 172, no 1-3, 9-20 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents results of several years of experimental and theoretical work on a library of oligo(ethylene glycol)-containing self-assembled monolayers (OEG SAMs) on gold. The library consists of 15 different thiol compounds, which all contain alkyl and OEG portions of different length, as well as amide moieties forming a stabilizing lateral hydrogen bonding network. We have investigated the quality, conformation, orientation, defect structure and infrared (IR) signatures of these OEG SAMs prepared by spontaneous adsorption from dilute solutions. It is shown that solution concentration and incubation time are important factors to obtain high quality SAMs, in particular for those containing long OEG chains. Further on, the thiol compounds should contain a sufficiently long alkyl spacer to provide in plane van der Waals interactions strong enough to govern the formation of a densely packed alkylthiolate overlayer on the Au(1 1 1) surface. Such a highly ordered alkyl support, which is additionally stabilized by the lateral hydrogen bonds, enables us to vary the length of the terminal OEG portion from 1 to at least 12, without affecting the integrity and conformational characteristics of the supporting (alkyl) part of the SAM. Also, we discuss the importance of appropriate modeling tools to advance the understanding of IR signatures of the OEG SAMs. Finally, we demonstrate the generality of our "modular approach" by analyzing the structure of OEG SAMs formed by compounds extended with an additional terminal amide and an alkyl tail. Thus, the SAMs discussed herein provide an attractive platform for construction of advanced nanoarchitectures on surfaces, not only limited to biomaterials and fouling applications.

Keyword
Ab initio modeling; Hydrogen bonding; Infrared spectroscopy; Oligo(ethylene glycol); Self-assembled monolayers; X-ray photoelectron spectroscopy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-18753 (URN)10.1016/j.elspec.2009.03.016 (DOI)
Available from: 2009-06-03 Created: 2009-06-03 Last updated: 2015-05-29
4. Spectroscopic Characterization and Modeling of Methyl- and Hydrogen-Terminated Oligo (ethylene glycol) Self-Assembled Monolayers
Open this publication in new window or tab >>Spectroscopic Characterization and Modeling of Methyl- and Hydrogen-Terminated Oligo (ethylene glycol) Self-Assembled Monolayers
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2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 22, 12008-12016 p.Article in journal (Refereed) Published
Abstract [en]

Two series of oligo (ethylene glycol) (OEG) thiol compounds HS-(CH2CH2O)nR with R = CH3, H and n = 5, 6, 7, have been synthesized and used to form self-assembled monolayers (SAMs) on gold. The data from null ellipsometry, infrared reflection-absorption spectroscopy and ab initio calculations of this type of OH- and CH3-terminated OEG SAMs are used to examine the rarely addressed in-SAM orientation of oligo (ethylene glycols) and to provide detailed assignments of infrared bands in the fingerprint and CH-stretching regions. Based on these results, a new spectral band has been observed at 2947 cm-1 and identified by the firstprinciple calculations as localized vibrations that are specific for hydrogen-terminated OEG thiolate SAMs. This band can be used as an indicator of a high crystalline like ordering. It is further more stressed that theory agrees with the experimentally obtained CH-stretching spectra remarkably well if, and only if, the OEG helix axis within studied SAMs is tilted by about 20o with respect to the surface normal.

Keyword
Oligo(ethylene glycol) self-assembled monolayers, infrared reflection absorption spectroscopy, first-principle calculations
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77052 (URN)10.1021/jp212400z (DOI)000304888700021 ()
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
5. Tethered Lipid Membrane Formation on Assemblies with Controlled Presentation of Anchor Molecules: A QCM-D Study
Open this publication in new window or tab >>Tethered Lipid Membrane Formation on Assemblies with Controlled Presentation of Anchor Molecules: A QCM-D Study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We have recently described a binary self-assembled monolayer (SAM) platform for studies of tethered bilayer lipid membrane (tBLM) formation using surface analysis techniques (Lee et al). Namely, this type of mixed SAMs consisted of a matrix molecule, HS-(CH2)15-CONHCH2CH2OH, and an anchor molecule, HS-(CH2)15-CONH-(CH2CH2O)6-CH2CONH-X, where X is -(CD2)7CD3 or -(CD2)15CD3. In the present work, we have employed quartz crystal microbalance with dissipation monitoring (QCM-D) to study in more detail small unilamellar vesicle (SUV) fusion on such SAMs formed from solutions with a range of mole fractions of the anchor. Using the QCM frequency and dissipation signals we were able to relate tBLM formation to the density of surface anchors. The QCM-D analysis revealed a critical SUV concentration on the surface is necessary for vesicle rupture and bilayer formation. We found that the critical SUV concentration decreased with increasing density of anchoring groups. Dissipation signal indicated the most pronounced release of water enclosed by the SUVs (related to vesicle rupturing) for the SAMs formed in the range of mole fractions between 1 and 10%. Also, we observed only minute differences in the behavior of the SUVs on SAMs terminated with -(CD2)7CD3 or -(CD2)15CD3 anchors, respectively.

Keyword
suported lipid membrane, tethered bilayer lipid membrane, self-assembled monolayers, quartz crystal microbalance
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-77053 (URN)
Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2012-05-03Bibliographically approved
6. Saccharide-Functionalized Alkanethiols for Fouling-Resistant Self-Assembled Monolayers: Synthesis, Monolayer Properties, and Antifouling Behavior
Open this publication in new window or tab >>Saccharide-Functionalized Alkanethiols for Fouling-Resistant Self-Assembled Monolayers: Synthesis, Monolayer Properties, and Antifouling Behavior
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2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 24, 15034-15047 p.Article in journal (Refereed) Published
Abstract [en]

We describe the synthesis of a series of mono-, di-, and trisaccharide-functionalized alkanethiols as well as the formation of fouling-resistant self-assembled monolayers (SAMs) from these. The SAls,,Is were characterized using ellipsometry, wetting measurements, and infrared reflection absorption spectroscopy (WAS). We show that the structure of the carbohydrate moiety affects the packing density and that this also alters the alkane chain organization. Upon increasing the size of the sugar moieties (from mono- to di- and trisaccharides), the structural qualities of the monolayers deteriorated with increasing disorder, and for the trisaccharide, slow reorganization dynamics in response to changes in the environmental polarity were observed. The antifouling properties of these SAMs were investigated through protein adsorption experiments from buffer solutions as well as settlement (attachment) tests using two common marine fouling species, zoospores of the green macroalga Ulva linza and cypris larvae of the barnacle Balanus amphitrite. The SAMs showed overall good resistance to fouling by both the proteins and the tested marine organisms. To improve the packing density of the SAMs with bulky headgroups, we employed mixed SAMs where the saccharide-thiols are diluted with a filler molecule having a small 2-hydroxyethyl headgroup. This method also provides a means by which the steric availability of sugar moieties can be varied, which is of interest for specific interaction studies with surface-bound sugars. The results of the surface dilution study and the low nonspecific adsorption onto the SAMs both indicate the feasibility of this approach.

Place, publisher, year, edition, pages
American Chemical Society, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-75120 (URN)10.1021/la202774e (DOI)000298118500040 ()
Note

Funding Agencies|AMBIO|NMP-CT-2005-011827|European Commission||

Available from: 2012-02-21 Created: 2012-02-17 Last updated: 2017-05-31Bibliographically approved

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