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Miyajima A, Nakao H, Ikeda K, Nakano M. The Nanometer-Scale Proximity of Bilayers Facilitates Intermembrane Lipid Transfer. J Phys Chem Lett 2023; 14:4172-4178. [PMID: 37114850 DOI: 10.1021/acs.jpclett.3c00154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Biological membranes approach one another in various biological phenomena, such as lipid transport at membrane contact sites and membrane fusion. The proximity of two bilayers may cause environmental changes in the interbilayer space and alter the dynamics of lipid molecules. Here, we investigate the structure and dynamics of vesicles aggregated due to the depletion attraction caused by polyethylene glycol (PEG) through static and dynamic small-angle neutron scattering. Manipulation of the interbilayer distance using PEG-conjugated lipids reveals that lipid molecules rapidly transfer between vesicles when the opposing bilayers are within ∼2 nm of each other. This distance corresponds to a region in which water molecules are more structured than in bulk water. Kinetic analysis suggests that the decrease in water entropy is responsible for the progression of lipid transfer. These results provide a basis for understanding the dynamic function of biomembranes in confined regions.
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Affiliation(s)
- Ayari Miyajima
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
| | - Hiroyuki Nakao
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
| | - Keisuke Ikeda
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
| | - Minoru Nakano
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
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Affiliation(s)
- Vladimir A. Baulin
- Departament Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel.lí Domingo s/n, 43007 Tarragona, Spain
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Bos I, Timmerman M, Sprakel J. FRET-Based Determination of the Exchange Dynamics of Complex Coacervate Core Micelles. Macromolecules 2021; 54:398-411. [PMID: 33456072 PMCID: PMC7808214 DOI: 10.1021/acs.macromol.0c02387] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 12/08/2020] [Indexed: 02/07/2023]
Abstract
Complex coacervate core micelles (C3Ms) are nanoscopic structures formed by charge interactions between oppositely charged macroions and used to encapsulate a wide variety of charged (bio)molecules. In most cases, C3Ms are in a dynamic equilibrium with their surroundings. Understanding the dynamics of molecular exchange reactions is essential as this determines the rate at which their cargo is exposed to the environment. Here, we study the molecular exchange in C3Ms by making use of Förster resonance energy transfer (FRET) and derive an analytical model to relate the experimentally observed increase in FRET efficiency to the underlying macromolecular exchange rates. We show that equilibrated C3Ms have a broad distribution of exchange rates. The overall exchange rate can be strongly increased by increasing the salt concentration. In contrast, changing the unlabeled homopolymer length does not affect the exchange of the labeled homopolymers and an increase in the micelle concentration only affects the FRET increase rate at low micelle concentrations. Together, these results suggest that the exchange of these equilibrated C3Ms occurs mainly by expulsion and insertion, where the rate-limiting step is the breaking of ionic bonds to expel the chains from the core. These are important insights to further improve the encapsulation efficiency of C3Ms.
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Affiliation(s)
- Inge Bos
- Physical Chemistry and Soft
Matter, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, The Netherlands
| | - Marga Timmerman
- Physical Chemistry and Soft
Matter, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, The Netherlands
| | - Joris Sprakel
- Physical Chemistry and Soft
Matter, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, The Netherlands
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König N, Willner L, Carlström G, Zinn T, Knudsen KD, Rise F, Topgaard D, Lund R. Spherical Micelles with Nonspherical Cores: Effect of Chain Packing on the Micellar Shape. Macromolecules 2020; 53:10686-10698. [PMID: 33335341 PMCID: PMC7735752 DOI: 10.1021/acs.macromol.0c01936] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 10/23/2020] [Indexed: 11/30/2022]
Abstract
Self-assembly of amphiphilic polymers into micelles is an archetypical example of a "self-confined" system due to the formation of micellar cores with dimensions of a few nanometers. In this work, we investigate the chain packing and resulting shape of C n -PEOx micelles with semicrystalline cores using small/wide-angle X-ray scattering (SAXS/WAXS), contrast-variation small-angle neutron scattering (SANS), and nuclear magnetic resonance spectroscopy (NMR). Interestingly, the n-alkyl chains adopt a rotator-like conformation and pack into prolate ellipses (axial ratio ϵ ≈ 0.5) in the "crystalline" region and abruptly arrange into a more spheroidal shape (ϵ ≈ 0.7) above the melting point. We attribute the distorted spherical shape above the melting point to thermal fluctuations and intrinsic rigidity of the n-alkyl blocks. We also find evidence for a thin dehydrated PEO layer (≤1 nm) close to the micellar core. The results provide substantial insight into the interplay between crystallinity and molecular packing in confinement and the resulting overall micellar shape.
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Affiliation(s)
- Nico König
- Department
of Chemistry, University of Oslo, P.O. Box 1033, Blindern, 0315 Oslo, Norway
- Jülich
Centre for Neutron Science (JCNS-1) and Institute of Biological Information
Processing (IBI-8), Forschungszentrum Jülich
GmbH, 52425 Jülich, Germany
| | - Lutz Willner
- Jülich
Centre for Neutron Science (JCNS-1) and Institute of Biological Information
Processing (IBI-8), Forschungszentrum Jülich
GmbH, 52425 Jülich, Germany
| | - Göran Carlström
- Centre
for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, 22100 Lund, Sweden
| | - Thomas Zinn
- ESRF
- The European Synchrotron, 38043 Grenoble, France
| | - Kenneth D. Knudsen
- Department
for Neutron Materials Characterization, Institute for Energy Technology, P.O. Box 40, 2027 Kjeller, Norway
| | - Frode Rise
- Department
of Chemistry, University of Oslo, P.O. Box 1033, Blindern, 0315 Oslo, Norway
| | - Daniel Topgaard
- Division
of Physical Chemistry, Department of Chemistry, Lund University, Lund, Sweden
| | - Reidar Lund
- Department
of Chemistry, University of Oslo, P.O. Box 1033, Blindern, 0315 Oslo, Norway
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