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Propofol adsorption at the air/water interface: a combined vibrational sum frequency spectroscopy, nuclear magnetic resonance and neutron reflectometry study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Propofol interaction with cell membrane has remarkable influence on neuronal function, yet data regarding its behaviour at an interface is still scarce. Here we present the results of propofol adsorption at the air/water interface studied by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS was utilized to elucidate the orientation change of propofol at the surface as a function of concentration, and the water of hydration was studied by probing the OH vibrational region of the spectrum in two different polarisation combinations. Data show that propofol adsorbs at the air/water interface in an ordered fashion showing strong interactions with the water of hydration, as well as weak interactions with water in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied (0 – 0.89 mM) there is almost no change in the orientation adopted at the interface. NR shows that propofol forms a dense monolayer with a thickness of 4.8 Å, and this result is consistent with a limiting area per molecule equivalent to a close-packed monolayer as demonstrated by surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded. Additionally, the ability of propofol to form associations/multimeric structures in water was studied using nuclear magnetic resonance (NMR). The 1H NMR chemical shifts recorded indicate that propofol does not form dimers or multimers in bulk water (D2O).

National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-220694OAI: oai:DiVA.org:kth-220694DiVA: diva2:1169903
Note

QC 20180103

Available from: 2017-12-30 Created: 2017-12-30 Last updated: 2018-01-03Bibliographically approved
In thesis
1. Adsorption, aggregation and phase separation in colloidal systems
Open this publication in new window or tab >>Adsorption, aggregation and phase separation in colloidal systems
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis presents work regarding amphiphilic molecules associated in aqueous solution or at the liquid/solid interface. Two main topics are included: the temperature-dependent behavior of micelles and the adsorption of dispersants on carbon nanotube (CNT) surfaces. Various NMR methods were used to analyze those systems, such as chemical shift detection, spectral intensity measurements, spin relaxation and, in particular, self-diffusion experiments. Besides this, small angle X-ray scattering (SAXS) was also applied for structural characterization.

 

A particular form of phase transition, core freezing, was detected as a function of temperature in micelles composed by a single sort of Brij-type surfactants. In mixed micelles, that phase transition still occurs accompanied by a reversible segregation of different surfactants into distinct aggregates. Adding a hydrophobic solubilizate shifts the core freezing point to a lower temperature. Upon lowering the temperature to the core freezing point, the solubilizate is released. The temperature course of the release curves with different initial solubilizate loadings is rationalized in terms of a temperature-dependent loading capacity.

 

The behavior of amphiphilic dispersant molecules in aqueous dispersions of carbon nanotubes (CNTs) has been investigated with a Pluronic-type block copolymer as frequent model dispersant. Detailed dispersion curves were recorded and the distribution of the dispersant among different available environments was analyzed. The amount of dispersed CNT was shown to be defined by a complex interplay of several factors during the dispersion process such as dispersant concentration, sonication time, centrifugation and CNT loading. In the dispersion process, high amphiphilic concentration is required because the pristine CNT surfaces made available by sonication must be rapidly covered by dispersants to avoid their re-attachment. In the prepared dispersions, the competitive adsorption of possible dispersants was investigated that provided information about the relative strength of the interaction of those with the nanotube surfaces. Anionic surfactants were found to have a strong tendency to replace Pluronics, which indicates a strong binding of those surfactants.

 

CNTs were dispersed in an epoxy resin to prepare nanotube-polymer composites. The molecular mobility of epoxy was investigated and the results demonstrated the presence of loosely associated CNT aggregates within which the molecular transport of epoxy is slow because of strong attractive intermolecular interactions between epoxy and the CNT surface. The rheological behavior is dominated by aggregate-aggregate jamming.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 62 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:88
Keyword
NMR, chemical shift, spin relaxation, self-diffusion, micelle, core freezing, segregation, solubilization, release, adsorption, binding, surfactant, carbon nanotube, block copolymer, dispersion, competitive adsorption, nanocomposite
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-220669 (URN)978-91-7729-647-8 (ISBN)
Public defence
2018-02-09, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20180103

Available from: 2018-01-03 Created: 2017-12-29 Last updated: 2018-01-03Bibliographically approved

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