Martin-Luther-Universität Halle-Wittenberg

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Einleitung
TP4_Blume_.pdf (884,1 KB)  vom 15.04.2010

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Verantwortlich:
Prof. Dr. Alfred Blume

Telefon: 0345 5525850
Telefax: 0345 5527157

Raum 1.11.0
von-Danckelmann-Platz 4
06129 Halle

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Postanschrift:
Martin-Luther-Universität Halle-Wittenberg
Naturwissenschaftliche Fakultät II
Institut für Chemie
Physikalische Chemie
von-Danckelmann-Platz 4
06120 Halle (Saale)
GERMANY

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Interactions of polyphilic molecules with lipid monolayers and bilayers


Goal of the project is a basic and systematic investigation of the interaction of low molecular weight and polymeric polyphilic molecules in aqueous solution with phospholipid model membranes and with lipid monolayers. The interface of the lipid membrane or of the monolayer can serve as a template for organizing the polyphilic molecules in special ways after their interaction with the interface. This interaction is driven by hydrophobic effects and also by polar interactions in the headgroup region of the membranes. Polyphilic molecules with fluorophilic groups can lead to special micro-phase separation in membranes and monolayers. The orientation of the molecules can be influenced by the synthesis of the polyphilic molecules and the connection of the different hydrophobic, hydrophilic or fluorophilic groups.

Fig 1:
Scheme of possible interactions of polyphilic molecules with lipid monolayers and bilayers. 
Blue: hydrophilic groups
Grey: hydrophobic groups
Green: fluorophilic groups

Fig 1: Scheme of possible interactions of polyphilic molecules with lipid monolayers and bilayers. Blue: hydrophilic groups Grey: hydrophobic groups Green: fluorophilic groups

Fig 1:
Scheme of possible interactions of polyphilic molecules with lipid monolayers and bilayers.
Blue: hydrophilic groups
Grey: hydrophobic groups
Green: fluorophilic groups

The basic thermodynamic techniques to investigate these interactions are calorimetric techniques, such as differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC). With these techniques binding constants, binding enthalpies and entropies can be determined. On the other hand spectroscopic techniques, such as infrared spectroscopy or fluorescence spectroscopy give information on the interactions on the molecular level. For lipid monolayers at the air-water interface infrared reflection absorption spectroscopy (IRRAS) give information also on the orientation of specific segments of the molecules with respect to the monolayer surface. Similar information can be obtained with lipid bilayers on solid supports with attenuated total reflection infrared spectroscopy (ATR-IR). On the microscopic range Brewster angle microscopy (BAM) and epifluorescence spectroscopy on lipid monolayers will be used to obtain information on domain formation in these systems. Low molecular weight molecules of various chemical structures will be synthesized in TP 1 (Tschierske) and triphilic block copolymers will be supplied from the projects TP 2 (Binder) and TP 3 (Kreßler). The spectroscopic characterization with NMR will be performed in TP 5 (Saalwächter)

Low molecular weight polyphilic molecules

An example for a low molecular weight polyphilic molecule is shown in Fig. 2. This molecule can be dissolved in water shows lyotropic as well as thermotropic polymorphism.

Fig 2:
Facial amphiphilic molecule (A6/6) with large lateral hydrophilic group (Chen et al. (2005) J. Am. Chem. Soc 127, 16578-16591)

Fig 2: Facial amphiphilic molecule (A6/6) with large lateral hydrophilic group (Chen et al. (2005) J. Am. Chem. Soc 127, 16578-16591)

Fig 2:
Facial amphiphilic molecule (A6/6) with large lateral hydrophilic group (Chen et al. (2005) J. Am. Chem. Soc 127, 16578-16591)

In aequeous suspension a transition can be observed by differential scanning calorimetry indicating that different lyotropic phases are formed. Electron microscopy showed at low temperature the existence of thin extended flat sheets with high stability. At present, the exact structure of these sheets is unknown. When A6/6 is mixed with the phospholipid DMPC the DSC scans indicate that the molecule is incorporated into the lipid bilayer. Electron microscopy indicates the presence of bicelles with hexagonal form.

Fig 3
DSC scans of A6/6, DMPC, and a mixture of both indicating incorporation of A6/6 into DMPC bilayers.

Fig 3 DSC scans of A6/6, DMPC, and a mixture of both indicating incorporation of A6/6 into DMPC bilayers.

Fig 3
DSC scans of A6/6, DMPC, and a mixture of both indicating incorporation of A6/6 into DMPC bilayers.

Polymeric polyphilic molecules

An example for a block copolymer with hydrophilic end groups and hydrophobic middle block is shown in Fig. 4. The behaviour of aqeous solutions of this block copolymer and its interactions with lipid monolayers and bilayers have been extensively studied

Fig. 4
Chemical structure of ABA block copolymer with hydrophilic end blocks 
Amado et al. Langmuir 24 (2008) 10041 
Amado et al. Soft Matter 5 (2009) 669

Fig. 4 Chemical structure of ABA block copolymer with hydrophilic end blocks Amado et al. Langmuir 24 (2008) 10041 Amado et al. Soft Matter 5 (2009) 669

Fig. 4
Chemical structure of ABA block copolymer with hydrophilic end blocks
Amado et al. Langmuir 24 (2008) 10041
Amado et al. Soft Matter 5 (2009) 669

The interaction with lipid monolayers was studied using infrared reflection absorption spectroscopy (IRRAS). Fig 5 shows the experimental setup and the measuring principle using a Langmuir trough.

Fig. 5:
Left: Experimental IRRAS setup. The Langmuir sample and reference troughs are covered with a Plexiglas hood. The IR-spectrometer is located on the left side. The angle of incidence and the polarization of the IR-beam can be changed.
Right: Scheme of the IRRAS setup with Langmuir troughs

Fig. 5: Left: Experimental IRRAS setup. The Langmuir sample and reference troughs are covered with a Plexiglas hood. The IR-spectrometer is located on the left side. The angle of incidence and the polarization of the IR-beam can be changed. Right: Scheme of the IRRAS setup with Langmuir troughs

Fig. 5:
Left: Experimental IRRAS setup. The Langmuir sample and reference troughs are covered with a Plexiglas hood. The IR-spectrometer is located on the left side. The angle of incidence and the polarization of the IR-beam can be changed.
Right: Scheme of the IRRAS setup with Langmuir troughs

Using the IRRAS setup the incorporation of the ABA triblockcopolymer was investigated after injection of the copolymer underneath a monolayer of deuterated DPPC. Fig. 6 shows the intensities of various IR-bands as a function of time after injection into the subphase. The incorporation occurs in a two-step mechanism. The shift of the CD2-stretching bands of the lipids indicate an ordering of the lipid film as depicted in the left-hand side of Fig. 6 induced by the incorporation of the hydrophobic block of the copolymer (Amado et al., Langmuir 24 (2008) 10041; Amado et al., Soft Matter 5 (2009) 669)

Fig. 6
Intensity of infrared bands as a function of time (spectrum number) after injection of the block copolymer underneath a DPPC-d62 monolayer. The surface pressure increases due to the incorporation of the polymer and the chains of the lipid become ordered.

Fig. 6 Intensity of infrared bands as a function of time (spectrum number) after injection of the block copolymer underneath a DPPC-d62 monolayer. The surface pressure increases due to the incorporation of the polymer and the chains of the lipid become ordered.

Fig. 6
Intensity of infrared bands as a function of time (spectrum number) after injection of the block copolymer underneath a DPPC-d62 monolayer. The surface pressure increases due to the incorporation of the polymer and the chains of the lipid become ordered.

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