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Hoffmann M, Drescher S, Schwieger C, Hinderberger D. Influence of a single ether bond on assembly, orientation, and miscibility of phosphocholine lipids at the air-water interface. Phys Chem Chem Phys 2021; 23:5325-5339. [PMID: 33634294 DOI: 10.1039/d0cp06520j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
How does a small change in the structure of a phospholipid affect its supramolecular assembly? In aqueous suspensions, the substitution of one ester linkage in DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) by an ether linkage alters its phase behaviour completely. To unravel the effect of replacing a phospholipid's ester linkage by an ether linkage in lipid monolayers, we characterized pure monolayers of the model lipid DPPC and its sn-2 ether analogue PHPC (1-palmitoyl-2-O-hexadecyl-sn-glycero-3-phosphocholine) as well as mixtures of both by measurements of surface pressure-molecular area (π-Amol) isotherms. In addition, we used infrared reflection absorption spectroscopy (IRRAS) to study lipid condensation, lipid chain orientation, headgroup hydration, and lipid miscibility in all samples. Mixed monolayers consisting of DPPC and PHPC were studied further using epifluorescence microscopy. Our results indicate a strong influence of the sn-2 ether linkage on headgroup hydration and ordering effects in the regions of the apolar chains and the headgroups. Both effects could originate from changes in glycerol conformation. Furthermore, we observed a second plateau in the π-Amol isotherms of DPPC/PHPC mixtures and analysis of the mixed π-Amol isotherms reveals a non-ideal mixing behaviour of both lipids which may be caused by conformational differences in their headgroups.
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Affiliation(s)
- Matthias Hoffmann
- Institute of Chemistry, Martin Luther University (MLU) Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany. and Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg, Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Simon Drescher
- Institute of Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany and Phospholipid Research Center, Im Neuenheimer Feld 515, 69120 Heidelberg, Germany
| | - Christian Schwieger
- Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg, Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Dariush Hinderberger
- Institute of Chemistry, Martin Luther University (MLU) Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany. and Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg, Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
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Hoffmann M, Drescher S, Ihling C, Hinderberger D, Schwieger C. An Azidolipid Monolayer - Transitions, Miscibility, and UV Reactivity Studied by Infrared Reflection Absorption Spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:12804-12815. [PMID: 33090001 DOI: 10.1021/acs.langmuir.0c01726] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this study, we characterized monolayers of an azide-modified lipid at the air-water interface, pure and in its mixtures with the model lipid DPPC, with the aim of proving its potential to be applied for photo-cross-linking with other molecules. We chose a phospholipid bearing a terminal azide group in one of its hydrophobic tails to study its monolayer characteristics with the Langmuir film balance technique. Furthermore, we performed infrared reflection absorption spectroscopy (IRRAS) to get detailed insights into the organization of those monolayers as well as high-resolution mass spectrometry (HRMS) to see the effects of UV-irradiation on the lipids' chemical structure and organization. Our results suggest that in expanded monolayers of pure azide-modified membrane lipids, the azido-terminated chain folds back toward the air-water interface. Above the LE/LC (liquid-expanded/liquid-condensed) phase transition, the chains stretched, and thus, the azide group detaches from the interface. From temperature-dependent monolayer compressions, we evaluated all relevant thermodynamic parameters of the monolayers, such as the phase transition pressure, the critical temperature, and the triple point, and compare them to those of model lipids. For future applications, we studied the miscibility of the azide-modified lipid with DPPC in monolayers and found at least a certain miscibility over all investigated mixing ratios ranging from 10 to 75% of the azidolipid. Finally, we irradiated the azidolipid monolayer with UV light at 305 nm and measured photodissociation of the azide, leading to chemical cross-linking with other lipids, which shows the potential to be used as a cross-linking agent within self-assembled lipid or lipid/protein layers.
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Affiliation(s)
- Matthias Hoffmann
- Institute of Chemistry - Complex Self-Organizing Systems, Martin Luther University (MLU) Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
- Institute of Biochemistry and Biotechnology - Interdisciplinary Research Center HALOmem, Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Simon Drescher
- Institute of Pharmacy - Biophysical Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany
- Phospholipid Research Center, Im Neuenheimer Feld 515, 69120 Heidelberg, Germany
| | - Christian Ihling
- Institute of Pharmacy - Pharmaceutical Chemistry and Bioanalytics, Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Dariush Hinderberger
- Institute of Chemistry - Complex Self-Organizing Systems, Martin Luther University (MLU) Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
- Institute of Biochemistry and Biotechnology - Interdisciplinary Research Center HALOmem, Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Christian Schwieger
- Institute of Chemistry - Complex Self-Organizing Systems, Martin Luther University (MLU) Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
- Institute of Biochemistry and Biotechnology - Interdisciplinary Research Center HALOmem, Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
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