1
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Drabik D, Hinc P, Stephan M, Cavalcanti RRM, Czogalla A, Dimova R. Effect of leaflet asymmetry on the stretching elasticity of lipid bilayers with phosphatidic acid. Biophys J 2024; 123:2406-2421. [PMID: 38822521 PMCID: PMC11365108 DOI: 10.1016/j.bpj.2024.05.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 05/03/2024] [Accepted: 05/29/2024] [Indexed: 06/03/2024] Open
Abstract
The asymmetry of membranes has a significant impact on their biophysical characteristics and behavior. This study investigates the composition and mechanical properties of symmetric and asymmetric membranes in giant unilamellar vesicles (GUVs) made of palmitoyloleoyl phosphatidylcholine (POPC) and palmitoyloleoyl phosphatidic acid (POPA). A combination of fluorescence quantification, zeta potential measurements, micropipette aspiration, and bilayer molecular dynamics simulations are used to characterize these membranes. The outer leaflet composition in vesicles is found consistent across the two preparation methods we employed, namely electroformation and inverted emulsion transfer. However, characterizing the inner leaflet poses challenges. Micropipette aspiration of GUVs show that oil residues do not substantially alter membrane elasticity, but simulations reveal increased membrane thickness and decreased interleaflet coupling in the presence of oil. Asymmetric membranes with a POPC:POPA mixture in the outer leaflet and POPC in the inner leaflet display similar stretching elasticity values to symmetric POPC:POPA membranes, suggesting potential POPA insertion into the inner leaflet during vesicle formation and suppressed asymmetry. The inverse compositional asymmetry, with POPC in the outer leaflet and POPC:POPA in the inner one yield less stretchable membranes with higher compressibility modulus compared with their symmetric counterparts. Challenges in achieving and predicting compositional correspondence highlight the limitations of phase-transfer-based methods. In addition, caution is advised when using fluorescently labeled lipids (even at low fractions of 0.5 mol %), as unexpected gel-like domains in symmetric POPC:POPA membranes were observed only with a specific type of labeled DOPE (dioleoylphosphatidylethanolamine) and the same fraction of unlabeled DOPE. The latter suggest that such domain formation may result from interactions between lipids and membrane fluorescent probes. Overall, this study underscores the complexity of factors influencing GUV membrane asymmetry, emphasizing the need for further research and improvement of characterization techniques.
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Affiliation(s)
- Dominik Drabik
- Department of Cytobiochemistry, Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland; Max Planck Institute of Colloids and Interfaces, Potsdam, Germany; Department of Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland.
| | - Piotr Hinc
- Department of Cytobiochemistry, Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland
| | - Mareike Stephan
- Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | | | - Aleksander Czogalla
- Department of Cytobiochemistry, Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland.
| | - Rumiana Dimova
- Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
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2
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De Mel JU, Klisch S, Gupta S, Schneider GJ. Ion-Mediated Structural Discontinuities in Phospholipid Vesicles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:14990-15000. [PMID: 38978402 PMCID: PMC11270981 DOI: 10.1021/acs.langmuir.4c01219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Revised: 06/28/2024] [Accepted: 07/01/2024] [Indexed: 07/10/2024]
Abstract
Despite intense research, methods for controlling soft matter's spontaneous self-assembly into well-defined layers remain a significant challenge. We observed ion-induced structural discontinuities of phospholipid vesicles that can be exploited for controlled self-assembly of soft materials, using DOPC and NaCl as a model system. The observations were made for the 0.25 wt % lipid concentration. We used dynamic light scattering, zeta-potential measurement, cryo-electron microscopy, small-angle X-ray, and small-angle neutron scattering to understand the reason for the discontinuities. For salt concentrations below 8 mM, we observed a decrease in the liposome diameter with increased NaCl concentration. Above 8 mM, we measured a discontinuity; the radius increases within a very narrow salt concentration range within less than 0.1 mM and then decreases for values greater than 8 mM. At 75 mM, the radius becomes constant until it grows again at around 500 mM. Microscopy and scattering experiments show a transition from unilamellar to bilamellar at 8 mM and to trilamellar at 75 mM. At 500 mM, we found a heterogeneous liposome system with many different bilayer numbers. All the experimental observations indicate that declining solvent quality and increasing osmotic pressure direct lipids to expel preferentially to the inner compartment. Upon reaching a critical concentration, excess lipids can form a new bilayer. This spontaneous self-assembly process causes simultaneous shrinkage of the aqueous core and expansion of the vesicle. This approach opens an intriguing path for controlling the self-assembly of bioinspired colloids.
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Affiliation(s)
- Judith U. De Mel
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Stefanie Klisch
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Sudipta Gupta
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Gerald J. Schneider
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
- Department
of Physics and Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
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3
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Orlikowska-Rzeznik H, Versluis J, Bakker HJ, Piatkowski L. Cholesterol Changes Interfacial Water Alignment in Model Cell Membranes. J Am Chem Soc 2024; 146:13151-13162. [PMID: 38687869 PMCID: PMC11099968 DOI: 10.1021/jacs.4c00474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 04/20/2024] [Accepted: 04/22/2024] [Indexed: 05/02/2024]
Abstract
The nanoscopic layer of water that directly hydrates biological membranes plays a critical role in maintaining the cell structure, regulating biochemical processes, and managing intermolecular interactions at the membrane interface. Therefore, comprehending the membrane structure, including its hydration, is essential for understanding the chemistry of life. While cholesterol is a fundamental lipid molecule in mammalian cells, influencing both the structure and dynamics of cell membranes, its impact on the structure of interfacial water has remained unknown. We used surface-specific vibrational sum-frequency generation spectroscopy to study the effect of cholesterol on the structure and hydration of monolayers of the lipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and egg sphingomyelin (SM). We found that for the unsaturated lipid DOPC, cholesterol intercalates in the membrane without significantly changing the orientation of the lipid tails and the orientation of the water molecules hydrating the headgroups of DOPC. In contrast, for the saturated lipids DPPC and SM, the addition of cholesterol leads to clearly enhanced packing and ordering of the hydrophobic tails. It is also observed that the orientation of the water hydrating the lipid headgroups is enhanced upon the addition of cholesterol. These results are important because the orientation of interfacial water molecules influences the cell membranes' dipole potential and the strength and specificity of interactions between cell membranes and peripheral proteins and other biomolecules. The lipid nature-dependent role of cholesterol in altering the arrangement of interfacial water molecules offers a fresh perspective on domain-selective cellular processes, such as protein binding.
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Affiliation(s)
- Hanna Orlikowska-Rzeznik
- Faculty
of Materials Engineering and Technical Physics, Poznan University of Technology, 60-965 Poznan, Poland
| | - Jan Versluis
- AMOLF,
Ultrafast Spectroscopy, 1098 XG Amsterdam, The Netherlands
| | - Huib J. Bakker
- AMOLF,
Ultrafast Spectroscopy, 1098 XG Amsterdam, The Netherlands
| | - Lukasz Piatkowski
- Faculty
of Materials Engineering and Technical Physics, Poznan University of Technology, 60-965 Poznan, Poland
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4
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Lee M, Lee E, Kim JH, Hwang H, Cho M, Sung J. Transport Dynamics of Water Molecules Confined between Lipid Membranes. J Phys Chem Lett 2024; 15:4437-4443. [PMID: 38626458 DOI: 10.1021/acs.jpclett.4c00323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2024]
Abstract
Water molecules confined between biological membranes exhibit a distinctive non-Gaussian displacement distribution, far different from that of bulk water. Here, we introduce a new transport equation for water molecules in the intermembrane space, quantitatively explaining molecular dynamics simulation results. We find that the unique transport dynamics of water molecules stems from the lateral diffusion coefficient fluctuation caused by their longitudinal motion in the direction perpendicular to the membranes. We also identify an interfacial region where water possesses distinct physical properties, which is unaffected by changes in the intermembrane separation.
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Affiliation(s)
- Minho Lee
- Creative Research Initiative Center for Chemical Dynamics in Living Cells, Chung-Ang University, Seoul 06974, Republic of Korea
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Euihyun Lee
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78757, United States
| | - Ji-Hyun Kim
- Creative Research Initiative Center for Chemical Dynamics in Living Cells, Chung-Ang University, Seoul 06974, Republic of Korea
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Hyonseok Hwang
- Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon, Gangwon-do 24341, Republic of Korea
| | - Minhaeng Cho
- Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Seoul 02841, Republic of Korea
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Jaeyoung Sung
- Creative Research Initiative Center for Chemical Dynamics in Living Cells, Chung-Ang University, Seoul 06974, Republic of Korea
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
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5
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Amărandi RM, Neamṭu A, Ştiufiuc RI, Marin L, Drăgoi B. Impact of Lipid Composition on Vesicle Protein Adsorption: A BSA Case Study. ACS OMEGA 2024; 9:17903-17918. [PMID: 38680315 PMCID: PMC11044229 DOI: 10.1021/acsomega.3c09131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 03/04/2024] [Accepted: 03/07/2024] [Indexed: 05/01/2024]
Abstract
Investigating the interaction between liposomes and proteins is of paramount importance in the development of liposomal formulations with real potential for bench-to-bedside transfer. Upon entering the body, proteins are immediately adsorbed on the liposomal surface, changing the nanovehicles' biological identity, which has a significant impact on their biodistribution and pharmacokinetics and ultimately on their therapeutic effect. Albumin is the most abundant plasma protein and thus usually adsorbs immediately on the liposomal surface. We herein report a comprehensive investigation on the adsorption of model protein bovine serum albumin (BSA) onto liposomal vesicles containing the zwitterionic lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), in combination with either cholesterol (CHOL) or the cationic lipid 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP). While many studies regarding protein adsorption on the surface of liposomes with different compositions have been performed, to the best of our knowledge, the differential responses of CHOL and DOTAP upon albumin adsorption on vesicles have not yet been investigated. UV-vis spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a strong influence of the phospholipid membrane composition on protein adsorption. Hence, it was found that DOTAP-containing vesicles adsorb proteins more robustly but also aggregate in the presence of BSA, as confirmed by DLS and TEM. Separation of liposome-protein complexes from unadsorbed proteins performed by means of centrifugation and size exclusion chromatography (SEC) was also investigated. Our results show that neither method can be regarded as a golden experimental setup to study the protein corona of liposomes. Yet, SEC proved to be more successful in the separation of unbound proteins, although the amount of lipid loss upon liposome elution was higher than expected. In addition, coarse-grained molecular dynamics simulations were employed to ascertain key membrane parameters, such as the membrane thickness and area per lipid. Overall, this study highlights the importance of surface charge and membrane fluidity in influencing the extent of protein adsorption. We hope that our investigation will be a valuable contribution to better understanding protein-vesicle interactions for improved nanocarrier design.
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Affiliation(s)
- Roxana-Maria Amărandi
- Nanotechnology
Laboratory, TRANSCEND Research Center, Regional
Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
- Department
of Bioinformatics, TRANSCEND Research Center, Regional Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
| | - Andrei Neamṭu
- Department
of Bioinformatics, TRANSCEND Research Center, Regional Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
- Department
of Physiology, “Grigore T. Popa”
University of Medicine and Pharmacy, 16 Universităṭii Street, 700115 Iaşi, Romania
| | - Rareş-Ionuṭ Ştiufiuc
- Nanotechnology
Laboratory, TRANSCEND Research Center, Regional
Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
- Department
of Nanobiophysics, MedFuture Research Center for Advanced Medicine, “Iuliu Hatieganu” University of Medicine
and Pharmacy, 4-6 Pasteur
Street, 400337 Cluj-Napoca, Romania
| | - Luminiṭa Marin
- Nanotechnology
Laboratory, TRANSCEND Research Center, Regional
Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
- “Petru
Poni” Institute of Macromolecular Chemistry of Romanian Academy, 41A Grigore Ghica Vodă Alley, 700487 Iaşi, Romania
| | - Brînduşa Drăgoi
- Nanotechnology
Laboratory, TRANSCEND Research Center, Regional
Institute of Oncology, 2-4 General Henri Mathias Berthelot Street, 700483 Iaşi, Romania
- Faculty of
Chemistry, Alexandru Ioan Cuza University of Iaşi, 11 Carol I Boulevard, 700506 Iaşi, Romania
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6
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Schlaich A, Daldrop JO, Kowalik B, Kanduč M, Schneck E, Netz RR. Water Structuring Induces Nonuniversal Hydration Repulsion between Polar Surfaces: Quantitative Comparison between Molecular Simulations, Theory, and Experiments. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:7896-7906. [PMID: 38578930 PMCID: PMC11025125 DOI: 10.1021/acs.langmuir.3c03656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 03/13/2024] [Accepted: 03/15/2024] [Indexed: 04/07/2024]
Abstract
Polar surfaces in water typically repel each other at close separations, even if they are charge-neutral. This so-called hydration repulsion balances the van der Waals attraction and gives rise to a stable nanometric water layer between the polar surfaces. The resulting hydration water layer is crucial for the properties of concentrated suspensions of lipid membranes and hydrophilic particles in biology and technology, but its origin is unclear. It has been suggested that surface-induced molecular water structuring is responsible for the hydration repulsion, but a quantitative proof of this water-structuring hypothesis is missing. To gain an understanding of the mechanism causing hydration repulsion, we perform molecular simulations of different planar polar surfaces in water. Our simulated hydration forces between phospholipid bilayers agree perfectly with experiments, validating the simulation model and methods. For the comparison with theory, it is important to split the simulated total surface interaction force into a direct contribution from surface-surface molecular interactions and an indirect water-mediated contribution. We find the indirect hydration force and the structural water-ordering profiles from the simulations to be in perfect agreement with the predictions from theoretical models that account for the surface-induced water ordering, which strongly supports the water-structuring hypothesis for the hydration force. However, the comparison between the simulations for polar surfaces with different headgroup architectures reveals significantly different decay lengths of the indirect water-mediated hydration-force, which for laterally homogeneous water structuring would imply different bulk-water properties. We conclude that laterally inhomogeneous water ordering, induced by laterally inhomogeneous surface structures, shapes the hydration repulsion between polar surfaces in a decisive manner. Thus, the indirect water-mediated part of the hydration repulsion is caused by surface-induced water structuring but is surface-specific and thus nonuniversal.
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Affiliation(s)
- Alexander Schlaich
- Stuttgart
Center for Simulation Science (SC SimTech), University of Stuttgart, 70569 Stuttgart, Germany
- Institute
for Computational Physics, University of
Stuttgart, 70569 Stuttgart, Germany
| | - Jan O. Daldrop
- Fachbereich
Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Bartosz Kowalik
- Fachbereich
Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Matej Kanduč
- Department
of Theoretical Physics, Jožef Stefan
Institute, SI-1000 Ljubljana, Slovenia
| | - Emanuel Schneck
- Institut
für Physik Kondensierter Materie, Technische Universität Darmstadt, Hochschulstrasse 8, Darmstadt 64289, Germany
| | - Roland R. Netz
- Fachbereich
Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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7
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Saak CM, Dreier LB, Machel K, Bonn M, Backus EHG. Biological lipid hydration: distinct mechanisms of interfacial water alignment and charge screening for model lipid membranes. Faraday Discuss 2024; 249:317-333. [PMID: 37795538 DOI: 10.1039/d3fd00117b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/06/2023]
Abstract
Studying lipid monolayers as model biological membranes, we demonstrate that water molecules interfacing with different model membranes can display preferential orientation for two distinct reasons: due to charges on the membrane, and due to large dipole fields resulting from zwitterionic headgroups. This preferential water orientation caused by the charge or the dipolar field can be effectively neutralized to net-zero water orientation by introducing monolayer counter-charges (i.e. lipids with oppositely charged headgroups). Following the Gouy-Chapman model, the effect of monolayer surface charge on water orientation is furthermore strongly dependent on the electrolyte concentration and thus on the counterions in solution. In contrast, the effect of ions in the subphase on the dipolar alignment of water is zero. As a result, the capability of monolayer counter-charges to null the effect of dipolar orientation is strongly electrolyte-dependent. Notably, the different effects are additive for mixed charged/zwitterionic lipid systems occurring in nature. Specifically, for an E. coli lipid membrane extract consisting of both zwitterionic and negatively charged lipids, the water orientation can be explained by the sum of the constituents. Our results can be quantitatively reproduced using Gouy-Chapman theory, revealing the relatively straightforward electrostatic effects on the hydration of complex membrane interfaces.
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Affiliation(s)
- Clara-Magdalena Saak
- Faculty of Chemistry, Institute of Physical Chemistry, University of Vienna, Währingerstrasse 42, 1090, Vienna, Austria.
| | - Lisa B Dreier
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
- Graduate School of Materials Science in Mainz, Staudingerweg 9, 55128, Mainz, Germany
| | - Kevin Machel
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
| | - Mischa Bonn
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
| | - Ellen H G Backus
- Faculty of Chemistry, Institute of Physical Chemistry, University of Vienna, Währingerstrasse 42, 1090, Vienna, Austria.
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
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8
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Becker M, Loche P, Rezaei M, Wolde-Kidan A, Uematsu Y, Netz RR, Bonthuis DJ. Multiscale Modeling of Aqueous Electric Double Layers. Chem Rev 2024; 124:1-26. [PMID: 38118062 PMCID: PMC10785765 DOI: 10.1021/acs.chemrev.3c00307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 11/17/2023] [Accepted: 11/30/2023] [Indexed: 12/22/2023]
Abstract
From the stability of colloidal suspensions to the charging of electrodes, electric double layers play a pivotal role in aqueous systems. The interactions between interfaces, water molecules, ions and other solutes making up the electrical double layer span length scales from Ångströms to micrometers and are notoriously complex. Therefore, explaining experimental observations in terms of the double layer's molecular structure has been a long-standing challenge in physical chemistry, yet recent advances in simulations techniques and computational power have led to tremendous progress. In particular, the past decades have seen the development of a multiscale theoretical framework based on the combination of quantum density functional theory, force-field based simulations and continuum theory. In this Review, we discuss these theoretical developments and make quantitative comparisons to experimental results from, among other techniques, sum-frequency generation, atomic-force microscopy, and electrokinetics. Starting from the vapor/water interface, we treat a range of qualitatively different types of surfaces, varying from soft to solid, from hydrophilic to hydrophobic, and from charged to uncharged.
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Affiliation(s)
| | - Philip Loche
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
- Laboratory
of Computational Science and Modeling, IMX, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Majid Rezaei
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
- Institute
of Theoretical Chemistry, Ulm University, 89081 Ulm, Germany
| | | | - Yuki Uematsu
- Department
of Physics and Information Technology, Kyushu
Institute of Technology, 820-8502 Iizuka, Japan
- PRESTO,
Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Roland R. Netz
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Douwe Jan Bonthuis
- Institute
of Theoretical and Computational Physics, Graz University of Technology, 8010 Graz, Austria
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9
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Hernández-Galván G, Mercado-Uribe H. Dehydration of biological membranes in a non-condensing environment. SOFT MATTER 2023; 19:9173-9178. [PMID: 37991897 DOI: 10.1039/d3sm01181j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2023]
Abstract
The study of the dehydration process in a cell membrane allows a better understanding of how water is bound to it. While in prior studies, cell dehydration was commonly analyzed under osmotic stress conditions, in the present work, we focus on the dehydration driven by evaporation in a restricted condensing environment. Using a thermogravimetry method, we studied the dehydration of Escherichia coli through isothermal evaporation in the presence of a gas flux. To figure out the loss of mass in this situation, we first evaluated the dynamics of water evaporation of a suspension of multilamellar liposomes. We found that the evaporation of liposomal suspensions composed of individual lipids is constant, although slightly restricted by the presence of liposomes, while the evaporation of liposomal suspensions composed of a mixture of different lipids follows an exponential decay. This is explained considering that the internal pressure at the air-water interface is proportional to the amount of bound water. The evaporation of water from a biomass sample follows this latter behaviour.
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Affiliation(s)
| | - H Mercado-Uribe
- CINVESTAV-Monterrey, PIIT, Apodaca, Nuevo León, 66600, Mexico.
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10
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Sam S, Sung S, Kim D. Sensitive Detection of Biomolecular Adsorption by a Low-Density Surfactant Layer Using Sum-Frequency Vibrational Spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:17412-17419. [PMID: 38050679 DOI: 10.1021/acs.langmuir.3c02546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/06/2023]
Abstract
Small molecules or proteins interact with a biomembrane in various ways for molecular recognition, structure stabilization, and transmembrane signaling. In this study, 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), having a choline group, was used to investigate this interaction by using sum-frequency vibrational spectroscopy. The sum-frequency spectrum characteristic of a neat monolayer changed to that of a bare air/water interface at a larger molecular area of the DPTAP molecules due to local laser heating. Upon introduction of the aromatic molecules in the subphase at around 120 Å2 per molecule, the sum-frequency signal suddenly reappeared due to molecular adhesion, and this was utilized to probe the adsorption of the aromatic ring molecules in the water subphase to the choline headgroup of the DPTAP by cation-π interaction. The onset concentrations of this sum-frequency signal change allowed a comparison of the relative interaction strengths between different aromatic molecules. A zwitterionic surfactant molecule (DPPC) was found to interact weakly compared to the cationic DPTAP molecule.
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Affiliation(s)
- Sokhuoy Sam
- Department of Physics, Sogang University, 35, Baekbeom-ro, Mapo-gu, Seoul, 04107, Korea
| | - Siheon Sung
- Department of Physics, Sogang University, 35, Baekbeom-ro, Mapo-gu, Seoul, 04107, Korea
| | - Doseok Kim
- Department of Physics, Sogang University, 35, Baekbeom-ro, Mapo-gu, Seoul, 04107, Korea
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11
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Hsiao Y, Chou TH, Patra A, Wen YC. Momentum-dependent sum-frequency vibrational spectroscopy of bonded interface layer at charged water interfaces. SCIENCE ADVANCES 2023; 9:eadg2823. [PMID: 37043576 PMCID: PMC10096568 DOI: 10.1126/sciadv.adg2823] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Accepted: 03/14/2023] [Indexed: 06/19/2023]
Abstract
Interface-specific hydrogen (H)-bonding network of water directly controls the energy transfer and chemical reaction pathway at many charged aqueous interfaces, yet to characterize these bonded water layer structures remains a challenge. We now develop a sum-frequency spectroscopic scheme with varying photon momenta as an all-optic solution for retrieving the vibrational spectra of the bonded water layer and the ion diffuse layer and, hence, microscopic structural and charging information about an interface. Application of the method to a model surfactant-water interface reveals a hidden weakly donor H-bonded water species, suggesting an asymmetric hydration-shell structure of fully solvated surfactant headgroups. In another application to a zwitterionic phosphatidylcholine lipid monolayer-water interface, we find a highly polarized bonded water layer structure associating to the phosphatidylcholine headgroup, while the diffuse layer contribution is experimentally proven to be negligible. Our all-optic method offers an in situ microscopic probe of electrochemical and biological interfaces and the route toward future imaging and ultrafast dynamics studies.
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12
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Garrett P, Shirley JC, Baiz CR. Forced Interactions: Ionic Polymers at Charged Surfactant Interfaces. J Phys Chem B 2023; 127:2829-2836. [PMID: 36926899 DOI: 10.1021/acs.jpcb.2c08636] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
Characterizing electrostatic interactions at heterogeneous interfaces is critical for developing a fundamental description of the dynamic processes at charged interfaces. Water-in-oil reverse micelles (RMs) offer a high degree of tunability across composition, polarity, and temperature, making them ideal systems for studying interactions at heterogeneous liquid-liquid interfaces. In the present study, we use a combination of ultrafast two-dimensional infrared spectroscopy and molecular dynamics (MD) simulations to determine the picosecond interfacial dynamics in RMs containing binary compositions of sorbitan monostearate and anionic or cationic cosurfactants, which are used to tune the ratio of charged to nonionic surfactants at the interface. The positively charged polyethylenimine (PEI) polymer is encapsulated within the RMs, and the carbonyl stretching mode of sorbitan monostearate reports on the interfacial hydrogen-bond populations and dynamics. The results show that hydrogen-bond populations are altered through the inclusion of both negatively and positively charged cosurfactants. Charged surfactants increase interfacial water penetration into the surfactant layer, and the surface localization of polymers decreases water penetration. Local hydrogen-bond dynamics undergo a slowdown with the inclusion of charged surfactants, and the encapsulation of polymers results in similar effects, irrespective of the charge.
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Affiliation(s)
- Paul Garrett
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Joseph C Shirley
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Carlos R Baiz
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
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13
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Interaction of new VV-hemorphin-5 analogues with cell membrane models. Colloids Surf B Biointerfaces 2022; 220:112896. [DOI: 10.1016/j.colsurfb.2022.112896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Revised: 09/23/2022] [Accepted: 10/01/2022] [Indexed: 11/05/2022]
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14
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Maltseva D, Gonella G, Ruysschaert JM, Bonn M. Phospholipid acyl tail affects lipid headgroup orientation and membrane hydration. J Chem Phys 2022; 156:234706. [PMID: 35732527 DOI: 10.1063/5.0092237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Biomembrane hydration is crucial for understanding processes at biological interfaces. While the effect of the lipid headgroup has been studied extensively, the effect (if any) of the acyl chain chemical structure on lipid-bound interfacial water has remained elusive. We study model membranes composed of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) lipids, the most abundant lipids in biomembranes. We explore the extent to which the lipid headgroup packing and associated water organization are affected by the lipid acyl tail unsaturation and chain length. To this end, we employ a combination of surface-sensitive techniques, including sum-frequency generation spectroscopy, surface pressure measurements, and Brewster angle microscopy imaging. Our results reveal that the acyl tail structure critically affects the headgroup phosphate orientational distribution and lipid-associated water molecules, for both PE and PC lipid monolayers at the air/water interface. These insights reveal the importance of acyl chain chemistry in determining not only membrane fluidity but also membrane hydration.
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Affiliation(s)
- Daria Maltseva
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Grazia Gonella
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Jean-Marie Ruysschaert
- Laboratory for the Structure and Function of Biological Membranes, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Brussels, Belgium
| | - Mischa Bonn
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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15
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Thangavelu P, Sundaram V, Gunasekaran K, Mujyambere B, Raju S, Kannan A, Arasu A, Krishna K, Ramamoorthi J, Ramasamy S, Velusamy T, Ramalingam S. Development of Optimized Novel Liposome Loaded with 6-gingerol and Assessment of its Therapeutic Activity Against NSCLC In vitro and In vivo Experimental Models. Chem Phys Lipids 2022; 245:105206. [PMID: 35483420 DOI: 10.1016/j.chemphyslip.2022.105206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 04/20/2022] [Accepted: 04/21/2022] [Indexed: 11/03/2022]
Abstract
6-Gingerol (Gn) is an active compound derived from ginger which possesses various biological activities. The therapeutic applications of Gn are limited due to its hydrophobic nature. To ease its administration, one of the nano-emulsion methods, liposome was selected to encapsulate Gn. Response Surface Methodology (RSM) was used to optimize liposome ratio. 97.2% entrapment efficiency was achieved at the ratio of 1:20:2 (Drug: Lipid: Cholesterol). The optimized liposome attained size below 200 d nm, spherical shape, negative surface charge and showed sustain release upon physical characterization methods such as FESEM, DLS, Zeta potential, Drug release. The signature FTIR peaks of both free Gn and free liposome (FL) were also observed in Lipo-Gn peak. Lipo-Gn showed significant cytotoxic effect on A549 cells (IC50 160.5 ± 0.74µM/ml) as well as inhibits the cell migration. DAPI staining showed higher apoptotic nuclear morphological change in the cells treated with Lipo-Gn, and also Lipo-Gn increased the apoptotic percentage in A549 as 39.89 and 70.32 for 12 and 24h respectively which were significantly more than free Gn. Moreover, the formulation of Lipo-Gn showed significant cell cycle arrest at the G2/M phase compared with free Gn (28.9 and 34.9% in Free Gn vs. 42.7 and 50.1% in Lipo -Gn for 12 and 24hours respectively). Lipo-Gn have been assessed in NSCLC induced BALB/c mice and showed significantly improved pharmacological properties compared to those of free Gn. Thus, Lipo-Gn may be considered for its widening applications against lung cancer.
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Affiliation(s)
| | - Viswanathan Sundaram
- Bharathiar Cancer Theranostics Research Center - RUSA-2.0, Bharathiar university
| | - Kaavya Gunasekaran
- Department of Biochemistry, Bharathiar University, Coimbatore, Tamil Nadu, India
| | | | - Sowndarya Raju
- Department of Biochemistry, Bharathiar University, Coimbatore, Tamil Nadu, India
| | - Arya Kannan
- Department of Biochemistry, Bharathiar University, Coimbatore, Tamil Nadu, India
| | - Ashok Arasu
- Department of Biotechnology, Bharathiar University, Coimbatore, Tamil Nadu, India
| | - Kathirvelu Krishna
- DRDO-BU Center for Life Sciences, Bharathiar University Campus, Coimbatore, Tamil Nadu. India.cs
| | - Jayaraj Ramamoorthi
- Theme lead, Flinders NT, Flinders University, Northern Territory 0909, Australia
| | - Sivasamy Ramasamy
- Department of Human Genetics and Molecular Biology, Bharathiar University, Coimbatore, Tamil nadu, India
| | | | - Suja Ramalingam
- Department of Biochemistry, Bharathiar University, Coimbatore, Tamil Nadu, India.
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16
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Lee E, You X, Baiz CR. Interfacial dynamics in inverted-headgroup lipid membranes. J Chem Phys 2022; 156:075102. [PMID: 35183070 PMCID: PMC8858029 DOI: 10.1063/5.0080153] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Inverted-headgroup (choline-phosphate) lipids are synthetic lipids that are not found in nature and are used as model systems to understand the role of headgroup dipole orientation. Recently, studies revealed that the net orientation of interfacial water strongly depends on the headgroup electrostatics, i.e., the charges and dipole generated by the phosphate and the choline groups. In order to characterize interfacial H-bond dynamics, we measured two-dimensional infrared spectra of the ester carbonyl band and performed molecular dynamics simulations in fully hydrated 1,2-dioleoyl-sn-glycero-3-phosphocholine and 2-((2,3-bis(oleoyloxy)propyl)-dimethyl-ammonio)ethyl ethyl phosphate (DOCPe) lipid bilayers. The experiments and simulations suggest that the reverse dipole generated by the inverted-headgroup in DOCPe does not affect the carbonyl H-bond populations or the interfacial water H-bond dynamics. However, while phosphate-associated waters in both lipids appear to show a similar H-bond structure, carbonyl-associated waters are characterized by a slightly disrupted H-bond structure in the DOCPe bilayer, especially within the second hydration shell. Our findings show that changes in net water orientation perturb the water H-bonds at the linker region between the headgroup and the lipid tail, although this perturbation is weak.
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17
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Lukas M, Backus EHG, Bonn M, Grechko M. Passively Stabilized Phase-Resolved Collinear SFG Spectroscopy Using a Displaced Sagnac Interferometer. J Phys Chem A 2022; 126:951-956. [PMID: 35113564 DOI: 10.1021/acs.jpca.1c10155] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Sum-frequency generation (SFG) vibrational spectroscopy is a powerful technique to study interfaces at the molecular level. Phase-resolved SFG (PR-SFG) spectroscopy provides direct information on interfacial molecules' orientation. However, its implementation is technologically demanding: it requires the generation of a local oscillator wave and control of its time delay with sub-fs accuracy. Commonly used noncollinear PR-SFG provides this control naturally but requires very accurate sample height control. Collinear PR-SFG spectroscopy is less demanding regarding sample positioning, but tuning the local oscillator time delay with this beam geometry is challenging. Here, we develop a collinear PR-SFG setup using a displaced Sagnac interferometer. This scheme allows full, independent control of the time delay and intensity of the local oscillator and provides long-time phase stabilization (better than 5° over 12 h) for the measured signal. This approach substantially reduces the complexity of an experimental setup and combines the advantages of collinear and noncollinear PR-SFG techniques.
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Affiliation(s)
- Max Lukas
- Molecular Spectroscopy Department, Max Planck Institute for Polymer Research, 55128 Mainz, Germany
| | - Ellen H G Backus
- Molecular Spectroscopy Department, Max Planck Institute for Polymer Research, 55128 Mainz, Germany.,Department of Physical Chemistry, University of Vienna, 1090 Vienna, Austria
| | - Mischa Bonn
- Molecular Spectroscopy Department, Max Planck Institute for Polymer Research, 55128 Mainz, Germany
| | - Maksim Grechko
- Molecular Spectroscopy Department, Max Planck Institute for Polymer Research, 55128 Mainz, Germany
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18
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Wolde-Kidan A, Netz RR. Interplay of Interfacial Viscosity, Specific-Ion, and Impurity Adsorption Determines Zeta Potentials of Phospholipid Membranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:8463-8473. [PMID: 34236206 DOI: 10.1021/acs.langmuir.1c00868] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Ion-specific induced changes of the ζ-potential of phospholipid vesicles are commonly used to quantify the affinity of different ions to the lipid interface. The negative ζ-potential of zwitterionic net-neutral phospholipid vesicles in neat water, which changes sign and increases in solutions of NaCl or KCl, is a phenomenon consistently observed in experiments but not fully understood theoretically. Using atomistic molecular dynamics simulations in the presence of applied electric fields which drive electroosmotic flows, in combination with an electrostatic continuum model based on the modified Poisson-Boltzmann and Helmholtz-Smoluchowski equations, we study the electrokinetic and electrostatic properties as well as the specific ion affinities to the phospholipid-water interface, in order to resolve these puzzling observations. Our modified continuum equations account for the dielectric profile at the lipid-water interface, ion-specific interactions between ions and the lipid-water interface, and the interfacial viscosity profile, which are all extracted from our atomistic simulations and rather accurately predict ion-density and electrostatic-potential distributions as well as ζ-potentials in comparison with our atomistic simulations. Our continuum model can explain experimental ζ-potentials only when we assume minute amounts of surface-active anionic impurities in the aqueous solution. In fact, the amount of impurities needed to explain the experimental data increases linearly with the salt concentration, suggesting that surface-active species, which might be already present in the lab water or lipid samples, could further be introduced through the added salt.
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Affiliation(s)
- Amanuel Wolde-Kidan
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Roland R Netz
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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19
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Abstract
The ubiquity of aqueous solutions in contact with charged surfaces and the realization that the molecular-level details of water-surface interactions often determine interfacial functions and properties relevant in many natural processes have led to intensive research. Even so, many open questions remain regarding the molecular picture of the interfacial organization and preferential alignment of water molecules, as well as the structure of water molecules and ion distributions at different charged interfaces. While water, solutes and charge are present in each of these systems, the substrate can range from living tissues to metals. This diversity in substrates has led to different communities considering each of these types of aqueous interface. In this Review, by considering water in contact with metals, oxides and biomembranes, we show the essential similarity of these disparate systems. While in each case the classical mean-field theories can explain many macroscopic and mesoscopic observations, it soon becomes apparent that such theories fail to explain phenomena for which molecular properties are relevant, such as interfacial chemical conversion. We highlight the current knowledge and limitations in our understanding and end with a view towards future opportunities in the field.
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20
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Venkatraman RK, Baiz CR. Ultrafast Dynamics at the Lipid-Water Interface: DMSO Modulates H-Bond Lifetimes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:6502-6511. [PMID: 32423219 DOI: 10.1021/acs.langmuir.0c00870] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Dimethyl sulfoxide (DMSO) is a common cosolvent and cryopreservation agent used to freeze cells and tissues. DMSO alters the H-bond structure of water, but its interactions with biomolecules and, specifically, with biological interfaces remain poorly understood. Here we investigate the effects of DMSO on the H-bond dynamics at the lipid-water interface using a combination of ultrafast two-dimensional infrared (2D IR) spectroscopy and molecular dynamics simulations. Ester carbonyl absorption spectra show that DMSO dehydrates the interface, and simulations show that the area per lipid is decreased. Ultrafast 2D IR spectra measure the time scales of frequency fluctuations at the ester carbonyl positions located precisely between the hydrophobic and hydrophilic regions of the membrane. 2D IR measurements show that low DMSO concentrations (<10 mol %) induce ∼40% faster H-bond dynamics compared with pure water, whereas increased concentrations (>10-20 mol %) once again slow down the dynamics. This slow-fast-slow trend is described in terms of two different solvation regimes. Below 10 mol %, DMSO weakens the interfacial H bond, leading to faster "bulk-like" dynamics, whereas above 10 mol %, water molecules become "relatively immobilized" as the H-bond networks becoming disrupted by the H-bond donor/acceptor imbalance at the interface. These studies are an important step toward characterizing the environments around lipid membranes, which are essential to numerous biological processes.
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Affiliation(s)
- Ravi Kumar Venkatraman
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Carlos R Baiz
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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21
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Deiseroth M, Bonn M, Backus EHG. Orientation independent vibrational dynamics of lipid-bound interfacial water. Phys Chem Chem Phys 2020; 22:10142-10148. [PMID: 32347258 DOI: 10.1039/d0cp01099e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Zwitterionic phospholipids are one of the main constituents of biological membranes. The electric field associated with the two opposite headgroup charges aligns water molecules in the headgroup region. Here, we study the role of water alignment on the sub-picosecond vibrational dynamics of lipid-bound water. To this end, we compare the dynamics of oppositely oriented water associated with, respectively, a phosphocholine (PC) headgroup and an inverse-phosphocholine with non-ethylated phosphate groups (CP). We find that the dynamics are independent of the water orientation, implying that the vibrational dynamics report on the local properties of the water molecules.
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Affiliation(s)
- Malte Deiseroth
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
| | - Mischa Bonn
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
| | - Ellen H G Backus
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany. and Department of Physical Chemisty, University of Vienna, Währinger Straße 42, 1090 Wien, Austria
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22
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Das S, Imoto S, Sun S, Nagata Y, Backus EHG, Bonn M. Nature of Excess Hydrated Proton at the Water-Air Interface. J Am Chem Soc 2020; 142:945-952. [PMID: 31867949 PMCID: PMC6966913 DOI: 10.1021/jacs.9b10807] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Indexed: 01/02/2023]
Abstract
Understanding the interfacial molecular structure of acidic aqueous solutions is important in the context of, e.g., atmospheric chemistry, biophysics, and electrochemistry. The hydration of the interfacial proton is necessarily different from that in the bulk, given the lower effective density of water at the interface, but has not yet been elucidated. Here, using surface-specific vibrational spectroscopy, we probe the response of interfacial protons at the water-air interface and reveal the interfacial proton continuum. Combined with spectral calculations based on ab initio molecular dynamics simulations, the proton at the water-air interface is shown to be well-hydrated, despite the limited availability of hydration water, with both Eigen and Zundel structures coexisting at the interface. Notwithstanding the interfacial hydrated proton exhibiting bulk-like structures, a substantial interfacial stabilization by -1.3 ± 0.2 kcal/mol is observed experimentally, in good agreement with our free energy calculations. The surface propensity of the proton can be attributed to the interaction between the hydrated proton and its counterion.
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Affiliation(s)
- Sudipta Das
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Sho Imoto
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Shumei Sun
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
- Department
of Physical Chemistry, University of Vienna, Währinger Strasse 42, 1090 Vienna, Austria
| | - Yuki Nagata
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Ellen H. G. Backus
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
- Department
of Physical Chemistry, University of Vienna, Währinger Strasse 42, 1090 Vienna, Austria
| | - Mischa Bonn
- Department
for Molecular Spectroscopy, Max Planck Institute
for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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