1
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Spencer RKW, Smirnova YG, Soleimani A, Müller M. Transient pores in hemifusion diaphragms. Biophys J 2024:S0006-3495(24)00392-8. [PMID: 38867448 DOI: 10.1016/j.bpj.2024.06.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Revised: 05/07/2024] [Accepted: 06/07/2024] [Indexed: 06/14/2024] Open
Abstract
Exchange of material across two membranes, as in the case of synaptic neurotransmitter release from a vesicle, involves the formation and poration of a hemifusion diaphragm (HD). The nontrivial geometry of the HD leads to environment-dependent control, regarding the stability and dynamics of the pores required for this kind of exocytosis. This work combines particle simulations, field-based calculations, and phenomenological modeling to explore the factors influencing the stability, dynamics, and possible control mechanisms of pores in HDs. We find that pores preferentially form at the HD rim, and that their stability is sensitive to a number of factors, including the three line tensions, membrane tension, HD size, and the ability of lipids to "flip-flop" across leaflets. Along with a detailed analysis of these factors, we discuss ways that vesicles or cells may use them to open and close pores and thereby quickly and efficiently transport material.
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Affiliation(s)
- Russell K W Spencer
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
| | - Yuliya G Smirnova
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany; Technische Universität Dortmund, Dortmund, Germany
| | - Alireza Soleimani
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
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2
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Spencer RKW, Santos-Pérez I, Rodríguez-Renovales I, Martinez Galvez JM, Shnyrova AV, Müller M. Membrane fission via transmembrane contact. Nat Commun 2024; 15:2793. [PMID: 38555357 PMCID: PMC10981662 DOI: 10.1038/s41467-024-47122-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 03/20/2024] [Indexed: 04/02/2024] Open
Abstract
Division of intracellular organelles often correlates with additional membrane wrapping, e.g., by the endoplasmic reticulum or the outer mitochondrial membrane. Such wrapping plays a vital role in proteome and lipidome organization. However, how an extra membrane impacts the mechanics of the division has not been investigated. Here we combine fluorescence and cryo-electron microscopy experiments with self-consistent field theory to explore the stress-induced instabilities imposed by membrane wrapping in a simple double-membrane tubular system. We find that, at physiologically relevant conditions, the outer membrane facilitates an alternative pathway for the inner-tube fission through the formation of a transient contact (hemi-fusion) between both membranes. A detailed molecular theory of the fission pathways in the double membrane system reveals the topological complexity of the process, resulting both in leaky and leakless intermediates, with energies and topologies predicting physiological events.
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Affiliation(s)
- Russell K W Spencer
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
| | - Isaac Santos-Pérez
- Electron Microscopy and Crystallography Platform, Center for Cooperative Research in Biosciences (CIC bioGUNE), Derio, Spain
| | - Izaro Rodríguez-Renovales
- BREM Basque Resource for Electron Microscopy, Leioa, Spain
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain
| | - Juan Manuel Martinez Galvez
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Anna V Shnyrova
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain.
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain.
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
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3
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Tang Y, Cai T, Lin J, Zhang L. Precise Control over Positioning and Orientation of Nanorods in Block Copolymer Nanocomposites via Regulation of Coassembly Pathways. Macromolecules 2023. [DOI: 10.1021/acs.macromol.2c01996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Affiliation(s)
- Yutong Tang
- Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
| | - Tianyun Cai
- Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
| | - Jiaping Lin
- Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
| | - Liangshun Zhang
- Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
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4
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Blagojevic N, Müller M. Multiscale Modeling of Grain-Boundary Motion in Cylinder-Forming Block Copolymers. ACS POLYMERS AU 2022. [DOI: 10.1021/acspolymersau.2c00048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Niklas Blagojevic
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
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5
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Bai L, Kim K, Ha MY, Ahn Y, Jang J. Molecular Insights on the Wetting Behavior of a Surface Corrugated with Nanoscale Domed Pillars. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:9336-9345. [PMID: 34314174 DOI: 10.1021/acs.langmuir.0c03517] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Using all-atom molecular dynamics simulation, we investigated the wettability of a surface texturized with nanoscale pillars of domed, rectangular, or cylindrical shapes. The dewetted and wetted states of the gaps between the pillars were related to the Cassie-Baxter (CB) and Wenzel (WZ) states of a macroscopic water droplet resting on top of the pillars. We uncovered the structures and free energies of the intermediate states existing between the CB and WZ states. The contact line of the liquid-vapor-solid interface could not be depinned for the domed pillars due to their smooth curvatures unlike for the rectangular or cylindrical pillars. The liquid symmetrically penetrated down into the gap between the domed pillars by a liquid-vapor interface shape like a paraboloid, while the penetration for the rectangular or cylindrical pillars was often asymmetrical, giving a half-tubular liquid-vapor interface.
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Affiliation(s)
- Liyi Bai
- Department of Nanoenergy Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Kiduk Kim
- Department of Nanoenergy Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Man Yeong Ha
- School of Mechanical Engineering, Pusan National University, Busan 46241, Republic of Korea
| | - Yoonho Ahn
- School of Liberal Arts, Korea University of Technology and Education, Cheonan 31253, Republic of Korea
| | - Joonkyung Jang
- Department of Nanoenergy Engineering, Pusan National University, Busan 46241, Republic of Korea
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6
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Wei C, Pohorille A. Fast bilayer-micelle fusion mediated by hydrophobic dipeptides. Biophys J 2021; 120:2330-2342. [PMID: 33887225 DOI: 10.1016/j.bpj.2021.04.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 03/15/2021] [Accepted: 04/02/2021] [Indexed: 11/30/2022] Open
Abstract
To understand the transition from inanimate matter to life, we studied a process that directly couples simple metabolism to evolution via natural selection, demonstrated experimentally by Adamala and Szostak. In this process, dipeptides synthesized inside precursors of cells promote absorption of fatty acid micelles to vesicles, inducing their preferential growth and division at the expense of other vesicles. The process is explained on the basis of coarse-grained molecular dynamics simulations, each extending for tens of microseconds, carried out to model fusion between a micelle and a membrane, both made of fatty acids in the absence and presence of hydrophobic dipeptides. In all systems with dipeptides, but not in their absence, fusion events were observed. They involve the formation of a stalk made by hydrophobic chains from the micelle and the membrane, similar to that postulated for vesicle-vesicle fusion. The emergence of a stalk is facilitated by transient clusters of dipeptides, side chains of which form hydrophobic patches at the membrane surface. Committor probability calculations indicate that the size of a patch is a suitable reaction coordinate and allows for identifying the transition state for fusion. Free-energy barrier to fusion is greatly reduced in the presence of dipeptides to only 4-5 kcal/mol, depending on the hydrophobicity of side chains. The mechanism of mediated fusion, which is expected to apply to other small peptides and hydrophobic molecules, provides a robust means by which a nascent metabolism can confer evolutionary advantage to precursors of cells.
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Affiliation(s)
- Chenyu Wei
- NASA Ames Research Center, Moffett Field, California; Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California
| | - Andrew Pohorille
- NASA Ames Research Center, Moffett Field, California; Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California.
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7
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Smirnova YG, Müller M. How does curvature affect the free-energy barrier of stalk formation? Small vesicles vs apposing, planar membranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2021; 50:253-264. [PMID: 33547940 PMCID: PMC8071802 DOI: 10.1007/s00249-020-01494-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 12/08/2020] [Accepted: 12/31/2020] [Indexed: 11/26/2022]
Abstract
Using molecular simulations of POPC lipids in conjunction with the calculation of the Minimum Free-Energy Path (MFEP), we study the effect of strong membrane curvature on the formation of the first fusion intermediate—the stalk between a vesicle and its periodic image. We find that the thermodynamic stability of this hourglass-shaped, hydrophobic connection between two vesicles is largely increased by the strong curvature of small vesicles, whereas the intrinsic barrier to form a stalk, i.e., associated with dimple formation and lipid tails protrusions, is similar to the case of two, apposing, planar membranes. A significant reduction of the barrier of stalk formation, however, stems from the lower dehydration free energy that is required to bring highly curved vesicle into a distance, at which stalk formation may occur, compared to the case of apposing, planar membranes.
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Affiliation(s)
- Y G Smirnova
- Institute for Theoretical Physics, Georg-August University, 37077, Göttingen, Germany.
| | - M Müller
- Institute for Theoretical Physics, Georg-August University, 37077, Göttingen, Germany
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8
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Risselada HJ, Grubmüller H. How proteins open fusion pores: insights from molecular simulations. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2020; 50:279-293. [PMID: 33340336 PMCID: PMC8071795 DOI: 10.1007/s00249-020-01484-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 11/16/2020] [Accepted: 11/24/2020] [Indexed: 02/06/2023]
Abstract
Fusion proteins can play a versatile and involved role during all stages of the fusion reaction. Their roles go far beyond forcing the opposing membranes into close proximity to drive stalk formation and fusion. Molecular simulations have played a central role in providing a molecular understanding of how fusion proteins actively overcome the free energy barriers of the fusion reaction up to the expansion of the fusion pore. Unexpectedly, molecular simulations have revealed a preference of the biological fusion reaction to proceed through asymmetric pathways resulting in the formation of, e.g., a stalk-hole complex, rim-pore, or vertex pore. Force-field based molecular simulations are now able to directly resolve the minimum free-energy path in protein-mediated fusion as well as quantifying the free energies of formed reaction intermediates. Ongoing developments in Graphics Processing Units (GPUs), free energy calculations, and coarse-grained force-fields will soon gain additional insights into the diverse roles of fusion proteins.
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Affiliation(s)
- H Jelger Risselada
- Department of Theoretical Physics, Georg-August University of Göttingen, Göttingen, Germany. .,Leiden University, Leiden Institute of Chemistry (LIC), Leiden, The Netherlands.
| | - Helmut Grubmüller
- Max Planck Institute for Biophysical Chemistry, Theoretical and Computational Biophysics Department, Göttingen, Germany
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9
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Caparotta M, Tomes CN, Mayorga LS, Masone D. The Synaptotagmin-1 C2B Domain Is a Key Regulator in the Stabilization of the Fusion Pore. J Chem Theory Comput 2020; 16:7840-7851. [DOI: 10.1021/acs.jctc.0c00734] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Marcelo Caparotta
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
| | - Claudia N. Tomes
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
- Instituto de Histología y Embriología de Mendoza (IHEM) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
| | - Luis S. Mayorga
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
- Instituto de Histología y Embriología de Mendoza (IHEM) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
| | - Diego Masone
- Instituto de Histología y Embriología de Mendoza (IHEM) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
- Facultad de Ingeniería, Universidad Nacional de Cuyo (UNCuyo), Mendoza 5500, Argentina
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10
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Bezik CT, de Pablo JJ. Formation, Stability, and Annihilation of the Stitched Morphology in Block Copolymer Thin Films. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01777] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Cody T. Bezik
- Institute for Molecular Engineering, University of Chicago, Chicago, lllinois 60637, United States
| | - Juan J. de Pablo
- Institute for Molecular Engineering, University of Chicago, Chicago, lllinois 60637, United States
- Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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11
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Endter LJ, Smirnova Y, Risselada HJ. Density Field Thermodynamic Integration (DFTI): A "Soft" Approach to Calculate the Free Energy of Surfactant Self-Assemblies. J Phys Chem B 2020; 124:6775-6785. [PMID: 32631061 DOI: 10.1021/acs.jpcb.0c03982] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thermodynamic integration is one of the most established methods to quantify excess free energies between different metastable states. Excess intermolecular interactions in surfactant assemblies are on the scale of the energy of thermal fluctuations. Therefore, these materials can be deformed and topologically altered via relatively small mechanical stresses. It is thus intuitive to design reaction paths and associated order parameters that exploit the "soft" nature of these materials to mechanically rather than alchemically morph surfactant assemblies from state to state. Here, we propose a novel method coined "density field thermodynamic integration" (DFTI) that adopts the universality and transferability of alchemical methods while simultaneously exploiting the soft excess interactions between surfactant molecules. DFTI was designed for a rapid quantification of the free energy differences between different metastable structures in soft fluid materials. The DFTI method uses an external field coupled to the local density to mechanically morph the system between metastable states of interest. Here, we explored the capability of the DFTI method to swiftly and accurately calculate free energy differences between states. To this aim, we studied two different coarse-grained lipidic surfactant systems: (i) a fusion stalk and (ii) a worm-like micelle. Our results illustrate that DFTI can provide an efficient, versatile, and rather reliable method to calculate the free energy differences between surfactant assemblies.
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Affiliation(s)
- Laura Josefine Endter
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
| | - Yuliya Smirnova
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
| | - Herre Jelger Risselada
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany.,Leiden Institute of Chemistry (LIC), University of Leiden, 2311 Leiden,The Netherlands.,Chemical Deptartment, Leibniz Institute of Surface Modifications, 04318 Leipzig, Germany
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12
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Müller M. Process-directed self-assembly of copolymers: Results of and challenges for simulation studies. Prog Polym Sci 2020. [DOI: 10.1016/j.progpolymsci.2019.101198] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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13
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Han Y, Xu Z, Shi AC, Zhang L. Pathways connecting two opposed bilayers with a fusion pore: a molecularly-informed phase field approach. SOFT MATTER 2020; 16:366-374. [PMID: 31799560 DOI: 10.1039/c9sm01983a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A phase field model with two phase fields, representing the concentration and the head-tail separation of amphiphilic molecules, respectively, has been constructed using an extension of the Ohta-Kawasaki model (Macromolecules, 1986, 19, 2621-2632). It is shown that this molecularly-informed phase field model is capable of producing various self-assembled amphiphilic aggregates, such as bilayers, vesicles and micelles. Furthermore, pathways connecting two opposed bilayers with a fusion pore are obtained by using a combination of the phase field model and the string method. Multiple fusion pathways, including a classical pathway and a leaky pathway, have been obtained depending on the initial separation of the two bilayers. The study shed light on the understanding of the membrane fusion pathways and, more importantly, laid a foundation for further investigation of more complex membrane morphologies and transitions.
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Affiliation(s)
- Yucen Han
- Beijing International Center for Mathematical Research, Peking University, Beijing 100871, China.
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14
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Gardner JM, Abrams CF. Energetics of Flap Opening in HIV-1 Protease: String Method Calculations. J Phys Chem B 2019; 123:9584-9591. [PMID: 31640343 PMCID: PMC7375464 DOI: 10.1021/acs.jpcb.9b08348] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
HIV-1 protease (PR) is the viral protein responsible for virion maturation, and its mechanisms of action remain incompletely understood. PR is dimeric and contains two flexible, symmetry-related flaps, which act as a gate to inhibit access to the binding pocket and hold the polypeptide substrate in the binding pocket once bound. Wide flap opening, a conformational change assumed to be necessary for substrate binding, is a rare event in the closed and bound form. In this study, we use molecular dynamics (MD) simulations and advanced MD techniques including temperature acceleration and string method in collective variables to study the conformational changes associated with substrate unbinding of both wild-type and F99Y mutant PR. The F99Y mutation is shown via MD to decouple the closing of previously unrecognized distal pockets from substrate unbinding. To determine whether or not the F99Y mutation affects the energetic cost of wide flap opening, we use string method in collective variables to determine the minimum free-energy mechanism for wide flap opening in concert with distal pocket closing. The results indicate that the major energetic cost in flap opening is disengagement of the two flap-tip Ile50 residues from each other and is not affected by the F99Y mutation.
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Affiliation(s)
- Jasmine M Gardner
- Dept. of Chemical and Biological Engineering , Drexel University , 3141 Chestnut Street , Philadelphia , Pennsylvania 19104 , United States
- Department of Chemistry - BMC , Uppsala University , Box 576, 751 23 Uppsala , Sweden
| | - Cameron F Abrams
- Dept. of Chemical and Biological Engineering , Drexel University , 3141 Chestnut Street , Philadelphia , Pennsylvania 19104 , United States
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15
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Sun DW, Müller M. Numerical algorithms for solving self-consistent field theory reversely for block copolymer systems. J Chem Phys 2018; 149:214104. [PMID: 30525732 DOI: 10.1063/1.5063302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Besides dictating the equilibrium phase diagram, the rugged free-energy landscape of AB block copolymers gives rise to a multitude of non-equilibrium phenomena. Self-consistent field theory (SCFT) can be employed to calculate the mean-field free energy, F [ ϕ A t a r g e t ] , of a non-equilibrium unstable state that is characterized by a given spatial density distribution, ϕ A t a r g e t , in the incompressible system. Such a free-energy functional is the basis of describing the structure formation by dynamic SCFT techniques or the identification of minimum free-energy paths via the string method. The crucial step consists in computing the external potential fields that generate the given density distribution in the corresponding system of non-interacting copolymers, i.e., the potential-to-density relation employed in equilibrium SCFT calculations has to be inverted (reverse SCFT calculation). We describe, generalize, and evaluate the computational efficiency of two different numerical algorithms for this reverse SCFT calculation-the Debye-function algorithm based on the structure factor and the field-theoretic umbrella-potential (FUP) algorithm. In contrast to the Debye-function algorithm, the FUP algorithm only yields the exact mean-field values of the given target densities in the limit of a strong umbrella potential, and we devise a two-step variant of the FUP algorithm that significantly mitigates this issue. For Gaussian copolymers, the Debye-function algorithm is more efficient for highly unstable states that are far away from the equilibrium, whereas the improved FUP algorithm outperforms the Debye-function algorithm closer to metastable states and is easily transferred to more complex molecular architectures.
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Affiliation(s)
- De-Wen Sun
- Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Marcus Müller
- Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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16
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Hur SM, Thapar V, Ramírez-Hernández A, Nealey PF, de Pablo JJ. Defect Annihilation Pathways in Directed Assembly of Lamellar Block Copolymer Thin Films. ACS NANO 2018; 12:9974-9981. [PMID: 30226748 DOI: 10.1021/acsnano.8b04202] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Defects in highly ordered self-assembled block copolymers represent an important roadblock toward the adoption of these materials in a wide range of applications. This work examines the pathways for annihilation of defects in symmetric diblock copolymers in the context of directed assembly using patterned substrates. Past theoretical and computational studies of such systems have predicted minimum free energy pathways that are characteristic of an activated process. However, they have been limited to adjacent dislocations with opposite Burgers vectors. By relying on a combination of advanced sampling techniques and particle-based simulations, this work considers the long-range interaction between dislocation pairs, both on homogeneous and nanopatterned substrates. As illustrated here, these interactions are central to understanding the defect structures that are most commonly found in applications and in experimental studies of directed self-assembly. More specifically, it is shown that, for dislocation dipoles separated by several lamellae, multiple consecutive free energy barriers lead to effective kinetic barriers that are an order of magnitude larger than those originally reported in the literature for tightly bound dislocation pairs. It is also shown that annihilation pathways depend strongly on both the separation between dislocations and their relative position with respect to the substrate guiding stripes used to direct the assembly.
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Affiliation(s)
- Su-Mi Hur
- School of Polymer Science and Engineering , Chonnam National University , Gwangju 500-757 , Korea
| | - Vikram Thapar
- School of Polymer Science and Engineering , Chonnam National University , Gwangju 500-757 , Korea
- Institute for Molecular Engineering , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Abelardo Ramírez-Hernández
- Materials Science Division , Argonne National Laboratory , 9700 South Cass Avenue , Argonne , Illinois 60439 , United States
- Department of Biomedical Engineering, Chemical Engineering Program , The University of Texas at San Antonio , San Antonio , Texas 78249 , United States
| | - Paul F Nealey
- Institute for Molecular Engineering , The University of Chicago , Chicago , Illinois 60637 , United States
- Materials Science Division , Argonne National Laboratory , 9700 South Cass Avenue , Argonne , Illinois 60439 , United States
| | - Juan J de Pablo
- Institute for Molecular Engineering , The University of Chicago , Chicago , Illinois 60637 , United States
- Materials Science Division , Argonne National Laboratory , 9700 South Cass Avenue , Argonne , Illinois 60439 , United States
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17
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Sun T, Liu F, Tang P, Qiu F, Yang Y. Construction of Rod-Forming Single Network Mesophases in Rod–Coil Diblock Copolymers via Inversely Designed Phase Transition Pathways. Macromolecules 2018. [DOI: 10.1021/acs.macromol.8b00773] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tongjie Sun
- State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Faqiang Liu
- State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Ping Tang
- State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Feng Qiu
- State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Yuliang Yang
- State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
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18
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Ren Y, Müller M. Kinetics of pattern formation in symmetric diblock copolymer melts. J Chem Phys 2018; 148:204908. [DOI: 10.1063/1.5027741] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Affiliation(s)
- Yongzhi Ren
- Institut für Theoretische Physik, Universität Göttingen, 37077 Göttingen, Germany
| | - Marcus Müller
- Institut für Theoretische Physik, Universität Göttingen, 37077 Göttingen, Germany
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19
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Bezik CT, Garner GP, de Pablo JJ. Mechanisms of Directed Self-Assembly in Cylindrical Hole Confinements. Macromolecules 2018. [DOI: 10.1021/acs.macromol.7b02639] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Cody T. Bezik
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Grant P. Garner
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Juan J. de Pablo
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
- Argonne National
Laboratory, 9700 S Cass Ave., Argonne, Illinois 60439, United States
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20
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Amabili M, Meloni S, Giacomello A, Casciola CM. Activated Wetting of Nanostructured Surfaces: Reaction Coordinates, Finite Size Effects, and Simulation Pitfalls. J Phys Chem B 2017; 122:200-212. [PMID: 29200302 DOI: 10.1021/acs.jpcb.7b07429] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A liquid in contact with a textured surface can be found in two states, Wenzel and Cassie. In the Wenzel state the liquid completely wets the corrugations while in the Cassie state the liquid is suspended over the corrugations with air or vapor trapped below. The superhydrophobic properties of the Cassie state are exploited for self-cleaning, drag reduction, drug delivery, etc., while in the Wenzel state most of these properties are lost; it is therefore of great fundamental and technological interest to investigate the kinetics and mechanism of the Cassie-Wenzel transition. Computationally, the Cassie-Wenzel transition is often investigated using enhanced sampling ("rare events") techniques based on the use of collective variables (CVs). The choice of the CVs is a crucial task because it affects the free-energy profile, the estimation of the free-energy barriers, and the evaluation of the mechanism of the process. Here we investigate possible simulation artifacts introduced by common CVs adopted for the study of the Cassie-Wenzel transition: the average particle density in the corrugation of a textured surface and the coarse-grained density field at various levels of coarse graining. We also investigate possible additional artifacts associated with finite size effects. We focus on a pillared surface, a system often used in technological applications. We show that the use of a highly coarse-grained density (a single CV) of the fluid in the interpillar region brings to severe artifacts: errors of hundreds of kBT in the difference of free energy between the Cassie and Wenzel states, of tens of kBT in the estimate of the free-energy barriers, and erroneous wetting mechanisms. A proper description of the wetting mechanism and its energetics apparently requires a fine discretization of the density field. Concerning the finite-size effects, we have found that the typical systems employed in simulations of the Cassie-Wenzel transition, containing a single pillar within periodic boundary conditions, prevent the complete break of translational symmetry of the liquid-vapor meniscus during the process. Capturing this break of symmetry is crucial for describing the transition state along the wetting process and the early stage of the opposite process, the Wenzel-Cassie transition.
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Affiliation(s)
- M Amabili
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - S Meloni
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - A Giacomello
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - C M Casciola
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
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21
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Barragán Vidal IA, Müller M. Generalization of the swelling method to measure the intrinsic curvature of lipids. J Chem Phys 2017; 147:224902. [PMID: 29246037 DOI: 10.1063/1.5001858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Via computer simulation of a coarse-grained model of two-component lipid bilayers, we compare two methods of measuring the intrinsic curvatures of the constituting monolayers. The first one is a generalization of the swelling method that, in addition to the assumption that the spontaneous curvature linearly depends on the composition of the lipid mixture, incorporates contributions from its elastic energy. The second method measures the effective curvature-composition coupling between the apposing leaflets of bilayer structures (planar bilayers or cylindrical tethers) to extract the spontaneous curvature. Our findings demonstrate that both methods yield consistent results. However, we highlight that the two-leaflet structure inherent to the latter method has the advantage of allowing measurements for mixed lipid systems up to their critical point of demixing as well as in the regime of high concentration (of either species).
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Affiliation(s)
- I A Barragán Vidal
- Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - M Müller
- Institut für Theoretische Physik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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22
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Liu X, Tian F, Yue T, Zhang X, Zhong C. Pulling force and surface tension drive membrane fusion. J Chem Phys 2017; 147:194703. [PMID: 29166098 DOI: 10.1063/1.4997393] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Despite catalyzed by fusion proteins of quite different molecular architectures, intracellular, viral, and cell-to-cell fusions are found to have the essential common features and the nearly same nature of transition states. The similarity inspires us to find a more general catalysis mechanism for membrane fusion that minimally depends on the specific structures of fusion proteins. In this work, we built a minimal model for membrane fusion, and by using dissipative particle dynamics simulations, we propose a mechanism that the pulling force generated by fusion proteins initiates the fusion process and the membrane tension regulates the subsequent fusion stages. The model shows different features compared to previous computer simulation studies: the pulling force catalyzes membrane fusion through lipid head overcrowding in the contacting region, leading to an increase in the head-head repulsion and/or the unfavorable head-tail contacts from opposing membranes, both of which destabilize the contacting leaflets and thus promote membrane fusion or vesicle rupture. Our simulations produce a variety of shapes and intermediates, closely resembling cases seen experimentally. Our work strongly supports the view that the tight pulling mechanism is a conserved feature of fusion protein-mediated fusion and that the membrane tension plays an essential role in fusion.
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Affiliation(s)
- Xuejuan Liu
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Falin Tian
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Tongtao Yue
- State Key Laboratory of Heavy Oil Processing, Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, People's Republic of China
| | - Xianren Zhang
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Chongli Zhong
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
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23
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Parent LR, Bakalis E, Ramírez-Hernández A, Kammeyer JK, Park C, de Pablo J, Zerbetto F, Patterson JP, Gianneschi NC. Directly Observing Micelle Fusion and Growth in Solution by Liquid-Cell Transmission Electron Microscopy. J Am Chem Soc 2017; 139:17140-17151. [DOI: 10.1021/jacs.7b09060] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Lucas R. Parent
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Evangelos Bakalis
- Dipartimento
di Chimica “G. Ciamician”, Università di Bologna, Bologna 40126, Italy
| | - Abelardo Ramírez-Hernández
- Materials
Science Division and Institute for Molecular Engineering, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Institute
for Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jacquelin K. Kammeyer
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
| | - Chiwoo Park
- Department
of Industrial and Manufacturing Engineering, Florida State University, Tallahassee, Florida 32306, United States
| | - Juan de Pablo
- Materials
Science Division and Institute for Molecular Engineering, Argonne National Laboratory, Lemont, Illinois 60439, United States
- Institute
for Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
| | - Francesco Zerbetto
- Dipartimento
di Chimica “G. Ciamician”, Università di Bologna, Bologna 40126, Italy
| | - Joseph P. Patterson
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
- Laboratory
of Materials and Interface Chemistry and Center of Multiscale Electron
Microscopy, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands
| | - Nathan C. Gianneschi
- Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
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24
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Gleria I, Mocskos E, Tagliazucchi M. Minimum free-energy paths for the self-organization of polymer brushes. SOFT MATTER 2017; 13:2362-2370. [PMID: 28275766 DOI: 10.1039/c6sm02725c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A methodology to calculate minimum free-energy paths based on the combination of a molecular theory and the improved string method is introduced and applied to study the self-organization of polymer brushes under poor solvent conditions. Polymer brushes in a poor solvent cannot undergo macroscopic phase separation due to the physical constraint imposed by the grafting points; therefore, they microphase separate forming aggregates. Under some conditions, the theory predicts that the homogeneous brush and the aggregates can exist as two different minima of the free energy. The theoretical methodology introduced in this work allows us to predict the minimum free-energy path connecting these two minima as well as the morphology of the system along the path. It is shown that the transition between the homogeneous brush and the aggregates may involve a free-energy barrier or be barrierless depending on the relative stability of the two morphologies and the chain length and grafting density of the polymer. In the case where a free-energy barrier exists, one of the morphologies is a metastable structure and, therefore, the properties of the brush as the quality of the solvent is cycled are expected to display hysteresis. The theory is also applied to study the adhesion/deadhesion transition between two opposing surfaces modified by identical polymer brushes and it is shown that this process may also require surpassing a free-energy barrier.
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Affiliation(s)
- Ignacio Gleria
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Computación, Buenos Aires, Argentina
| | - Esteban Mocskos
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Computación, Buenos Aires, Argentina and CONICET, Centro de Simulación Computacional para Aplicaciones Tecnológicas (CSC), Buenos Aires, Argentina
| | - Mario Tagliazucchi
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Inorgánica, Analítica y Química-Física, Buenos Aires, Argentina. and CONICET-Universidad de Buenos Aires, Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE), Buenos Aires, Argentina
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25
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Sun DW, Müller M. Process-Accessible States of Block Copolymers. PHYSICAL REVIEW LETTERS 2017; 118:067801. [PMID: 28234527 DOI: 10.1103/physrevlett.118.067801] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Indexed: 06/06/2023]
Abstract
Process-directed self-assembly of block copolymers refers to thermodynamic processes that reproducibly direct the kinetics of structure formation from a starting, unstable state into a selected, metastable mesostructure. We investigate the kinetics of self-assembly of linear ACB triblock copolymers after a rapid transformation of the middle C block from B to A. This prototypical process (e.g., photochemical transformation) converts the initial, equilibrium mesophase of the ABB copolymer into a well-defined but unstable, starting state of the AAB copolymer. The spontaneous structure formation that ensues from this unstable state becomes trapped in a metastable mesostructure, and we systematically explore which metastable mesostructures can be fabricated by varying the block copolymer composition of the initial and final states. In addition to the equilibrium mesophases of linear AB diblock copolymers, this diagram of process-accessible states includes 7 metastable periodic mesostructures, inter alia, Schoen's F-RD periodic minimal surface. Generally, we observe that the final, metastable mesostructure of the AAB copolymer possesses the same symmetry as the initial, equilibrium mesophase of the ABB copolymer.
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Affiliation(s)
- De-Wen Sun
- Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D 37077 Göttingen, Germany
| | - Marcus Müller
- Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D 37077 Göttingen, Germany
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26
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Bubnis G, Risselada HJ, Grubmüller H. Exploiting Lipid Permutation Symmetry to Compute Membrane Remodeling Free Energies. PHYSICAL REVIEW LETTERS 2016; 117:188102. [PMID: 27834997 DOI: 10.1103/physrevlett.117.188102] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Indexed: 05/26/2023]
Abstract
A complete physical description of membrane remodeling processes, such as fusion or fission, requires knowledge of the underlying free energy landscapes, particularly in barrier regions involving collective shape changes, topological transitions, and high curvature, where Canham-Helfrich (CH) continuum descriptions may fail. To calculate these free energies using atomistic simulations, one must address not only the sampling problem due to high free energy barriers, but also an orthogonal sampling problem of combinatorial complexity stemming from the permutation symmetry of identical lipids. Here, we solve the combinatorial problem with a permutation reduction scheme to map a structural ensemble into a compact, nondegenerate subregion of configuration space, thereby permitting straightforward free energy calculations via umbrella sampling. We applied this approach, using a coarse-grained lipid model, to test the CH description of bending and found sharp increases in the bending modulus for curvature radii below 10 nm. These deviations suggest that an anharmonic bending term may be required for CH models to give quantitative energetics of highly curved states.
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Affiliation(s)
- Greg Bubnis
- Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen 37077, Germany
| | - Herre Jelger Risselada
- Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen 37077, Germany
- Chemistry Department, Leibniz Institute of Surface Modification, Leipzig 04318, Germany
- Deptartment of Theoretical Physics, Georg-August University Göttingen, Göttingen 37077, Germany
| | - Helmut Grubmüller
- Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen 37077, Germany
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27
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Smirnova YG, Müller M. Calculation of membrane bending rigidity using field-theoretic umbrella sampling. J Chem Phys 2016; 143:243155. [PMID: 26723640 DOI: 10.1063/1.4938383] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The free-energy change of membrane shape transformations can be small, e.g., as in the case of membrane bending. Therefore, the calculation of the free-energy difference between different membrane morphologies is a challenge. Here, we discuss a computational method - field-theoretic umbrella sampling - to compute the local chemical potential of a non-equilibrium configuration and illustrate how one can apply it to study free-energy changes of membrane transformations using simulations. Specifically, the chemical potential profile of the bent membrane and the bending rigidity of membrane are calculated for a soft, coarse-grained amphiphile model and the MARTINI model of a dioleoylphosphatidylcholine (DOPC) membrane.
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Affiliation(s)
- Y G Smirnova
- Institute for Theoretical Physics, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - M Müller
- Institute for Theoretical Physics, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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28
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Kawamoto S, Klein ML, Shinoda W. Coarse-grained molecular dynamics study of membrane fusion: Curvature effects on free energy barriers along the stalk mechanism. J Chem Phys 2016; 143:243112. [PMID: 26723597 DOI: 10.1063/1.4933087] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle-vesicle, vesicle-planar, and planar-planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusion of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion.
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Affiliation(s)
- Shuhei Kawamoto
- Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
| | - Michael L Klein
- Institute for Computational Molecular Science, Temple University, SERC Building 1925 North 12th Street, Philadelphia, Pennsylvania 19122, USA
| | - Wataru Shinoda
- Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
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29
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Li W, Müller M. Thermodynamics and Kinetics of Defect Motion and Annihilation in the Self-Assembly of Lamellar Diblock Copolymers. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01088] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Weihua Li
- Institute
for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
- State
Key Laboratory of Molecular Engineering of Polymers, Department of
Macromolecular Science, Fudan University, Shanghai 200433, China
| | - Marcus Müller
- Institute
for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
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30
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Kan D, He X. Tuning phase structures of a symmetrical diblock copolymer with a patterned electric field. SOFT MATTER 2016; 12:4449-4456. [PMID: 27102422 DOI: 10.1039/c5sm03154k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electric fields can induce the orientation of the phase interfaces of block copolymers and provide a potential method to tune polymer phase structures for nanomaterial manufacture. In this work, we applied self-consistent field theory to study the self-assembly of a diblock copolymer confined between two parallel neutral substrates on which a set of electrodes was imposed to form a patterned electric field. The results showed that an alternatively distributed electric field can induce the formation of a parallel lamellar phase structure, which exists stably only in the system with selective substrates. The phase structure was proved to be sensitive to the characteristics of the electric field distribution, such as the strength of the electric field, the size and position of the electrodes, and the corresponding phase diagram was calculated in detail. The transition pathway of the phase structure from the perpendicular layered phase to the parallel layered phase was further analysed using the minimum energy path method. It is shown that the path and the active energy barrier of the phase transition depend on the electric field strength. Compound electric field patterns that can be designed to control the formation of novel and complex microphase structures were also examined.
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Affiliation(s)
- Di Kan
- Department of Chemistry, School of Science, Tianjin University, 300072 Tianjin, China.
| | - Xuehao He
- Department of Chemistry, School of Science, Tianjin University, 300072 Tianjin, China.
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31
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Ryham RJ, Klotz TS, Yao L, Cohen FS. Calculating Transition Energy Barriers and Characterizing Activation States for Steps of Fusion. Biophys J 2016; 110:1110-24. [PMID: 26958888 PMCID: PMC4788739 DOI: 10.1016/j.bpj.2016.01.013] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Revised: 01/05/2016] [Accepted: 01/13/2016] [Indexed: 12/29/2022] Open
Abstract
We use continuum mechanics to calculate an entire least energy pathway of membrane fusion, from stalk formation, to pore creation, and through fusion pore enlargement. The model assumes that each structure in the pathway is axially symmetric. The static continuum stalk structure agrees quantitatively with experimental stalk architecture. Calculations show that in a stalk, the distal monolayer is stretched and the stored stretching energy is significantly less than the tilt energy of an unstretched distal monolayer. The string method is used to determine the energy of the transition barriers that separate intermediate states and the dynamics of two bilayers as they pass through them. Hemifusion requires a small amount of energy independently of lipid composition, while direct transition from a stalk to a fusion pore without a hemifusion intermediate is highly improbable. Hemifusion diaphragm expansion is spontaneous for distal monolayers containing at least two lipid components, given sufficiently negative diaphragm spontaneous curvature. Conversely, diaphragms formed from single-component distal monolayers do not expand without the continual injection of energy. We identify a diaphragm radius, below which central pore expansion is spontaneous. For larger diaphragms, prior studies have shown that pore expansion is not axisymmetric, and here our calculations supply an upper bound for the energy of the barrier against pore formation. The major energy-requiring deformations in the steps of fusion are: widening of a hydrophobic fissure in bilayers for stalk formation, splay within the expanding hemifusion diaphragm, and fissure widening initiating pore formation in a hemifusion diaphragm.
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Affiliation(s)
- Rolf J Ryham
- Department of Mathematics, Fordham University, Bronx, New York.
| | - Thomas S Klotz
- Department of Computational and Applied Mathematics, Rice University, Houston, Texas
| | - Lihan Yao
- Department of Mathematics, Fordham University, Bronx, New York
| | - Fredric S Cohen
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois
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32
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Tahir MA, Van Lehn RC, Choi SH, Alexander-Katz A. Solvent-exposed lipid tail protrusions depend on lipid membrane composition and curvature. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1207-15. [PMID: 26828121 DOI: 10.1016/j.bbamem.2016.01.026] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Revised: 01/20/2016] [Accepted: 01/27/2016] [Indexed: 10/22/2022]
Abstract
The stochastic protrusion of hydrophobic lipid tails into solution, a subclass of hydrophobic membrane defects, has recently been shown to be a critical step in a number of biological processes like membrane fusion. Understanding the factors that govern the appearance of lipid tail protrusions is critical for identifying membrane features that affect the rate of fusion or other processes that depend on contact with solvent-exposed lipid tails. In this work, we utilize atomistic molecular dynamics simulations to characterize the likelihood of tail protrusions in phosphotidylcholine lipid bilayers of varying composition, curvature, and hydration. We distinguish two protrusion modes corresponding to atoms near the end of the lipid tail or near the glycerol group. Through potential of mean force calculations, we demonstrate that the thermodynamic cost for inducing a protrusion depends on tail saturation but is insensitive to other bilayer structural properties or hydration above a threshold value. Similarly, highly curved vesicles or micelles increase both the overall frequency of lipid tail protrusions as well as the preference for splay protrusions, both of which play an important role in driving membrane fusion. In multi-component bilayers, however, the incidence of protrusion events does not clearly depend on the mismatch between tail length or tail saturation of the constituent lipids. Together, these results provide significant physical insight into how system components might affect the appearance of protrusions in biological membranes, and help explain the roles of composition or curvature-modifying proteins in membrane fusion.
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Affiliation(s)
- Mukarram A Tahir
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Reid C Van Lehn
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - S H Choi
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Alfredo Alexander-Katz
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
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33
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Hur SM, Thapar V, Ramírez-Hernández A, Khaira G, Segal-Peretz T, Rincon-Delgadillo PA, Li W, Müller M, Nealey PF, de Pablo JJ. Molecular pathways for defect annihilation in directed self-assembly. Proc Natl Acad Sci U S A 2015; 112:14144-9. [PMID: 26515095 PMCID: PMC4655562 DOI: 10.1073/pnas.1508225112] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Over the last few years, the directed self-assembly of block copolymers by surface patterns has transitioned from academic curiosity to viable contender for commercial fabrication of next-generation nanocircuits by lithography. Recently, it has become apparent that kinetics, and not only thermodynamics, plays a key role for the ability of a polymeric material to self-assemble into a perfect, defect-free ordered state. Perfection, in this context, implies not more than one defect, with characteristic dimensions on the order of 5 nm, over a sample area as large as 100 cm(2). In this work, we identify the key pathways and the corresponding free energy barriers for eliminating defects, and we demonstrate that an extraordinarily large thermodynamic driving force is not necessarily sufficient for their removal. By adopting a concerted computational and experimental approach, we explain the molecular origins of these barriers and how they depend on material characteristics, and we propose strategies designed to overcome them. The validity of our conclusions for industrially relevant patterning processes is established by relying on instruments and assembly lines that are only available at state-of-the-art fabrication facilities, and, through this confluence of fundamental and applied research, we are able to discern the evolution of morphology at the smallest relevant length scales-a handful of nanometers-and present a view of defect annihilation in directed self-assembly at an unprecedented level of detail.
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Affiliation(s)
- Su-Mi Hur
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439; Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637; School of Polymer Science and Engineering, Chonnam National University, Gwangju 500757, Korea
| | - Vikram Thapar
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853
| | - Abelardo Ramírez-Hernández
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439; Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637
| | - Gurdaman Khaira
- Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637
| | - Tamar Segal-Peretz
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439
| | | | - Weihua Li
- Institut für Theoretische Physik, Georg-August-Universität, 37077 Göttingen, Germany; Department of Macromolecular Science, Fudan University, 200433 Shanghai, China
| | - Marcus Müller
- Institut für Theoretische Physik, Georg-August-Universität, 37077 Göttingen, Germany
| | - Paul F Nealey
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439; Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637
| | - Juan J de Pablo
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439; Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637;
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34
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Fujisaki H, Moritsugu K, Matsunaga Y, Morishita T, Maragliano L. Extended Phase-Space Methods for Enhanced Sampling in Molecular Simulations: A Review. Front Bioeng Biotechnol 2015; 3:125. [PMID: 26389113 PMCID: PMC4558547 DOI: 10.3389/fbioe.2015.00125] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 08/10/2015] [Indexed: 01/12/2023] Open
Abstract
Molecular Dynamics simulations are a powerful approach to study biomolecular conformational changes or protein-ligand, protein-protein, and protein-DNA/RNA interactions. Straightforward applications, however, are often hampered by incomplete sampling, since in a typical simulated trajectory the system will spend most of its time trapped by high energy barriers in restricted regions of the configuration space. Over the years, several techniques have been designed to overcome this problem and enhance space sampling. Here, we review a class of methods that rely on the idea of extending the set of dynamical variables of the system by adding extra ones associated to functions describing the process under study. In particular, we illustrate the Temperature Accelerated Molecular Dynamics (TAMD), Logarithmic Mean Force Dynamics (LogMFD), and Multiscale Enhanced Sampling (MSES) algorithms. We also discuss combinations with techniques for searching reaction paths. We show the advantages presented by this approach and how it allows to quickly sample important regions of the free-energy landscape via automatic exploration.
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Affiliation(s)
| | - Kei Moritsugu
- Graduate School of Medical Life Science, Yokohama City University, Yokohama, Japan
| | | | - Tetsuya Morishita
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Luca Maragliano
- Center for Synaptic Neuroscience, Istituto Italiano di Tecnologia, Genova, Italy
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Fuhrmans M, Marelli G, Smirnova YG, Müller M. Mechanics of membrane fusion/pore formation. Chem Phys Lipids 2015; 185:109-28. [DOI: 10.1016/j.chemphyslip.2014.07.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 07/07/2014] [Accepted: 07/24/2014] [Indexed: 11/27/2022]
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Kawamoto S, Shinoda W. Free energy analysis along the stalk mechanism of membrane fusion. SOFT MATTER 2014; 10:3048-3054. [PMID: 24695575 DOI: 10.1039/c3sm52344f] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The free energy profile of the stalk model of membrane fusion has been calculated using coarse-grained molecular dynamics simulations. The proposed method guides the lipid configuration using a guiding wall potential to make the transition from two apposed membranes to a stalk and a fusion pore. The free energy profile is obtained with a thermodynamic integration scheme using the mean force working on the guiding wall as a response of the system. We applied the method to two apposed flat bilayers composed of dioleoyl phosphatidylethanolamine/dioleoyl phosphatidylcholine expanding over the simulation box under the periodic boundary conditions. The two transition states are identified as pre-stalk and pre-pore states. The free energy barrier for the latter is confirmed to be in good agreement with that estimated by the pulling method. The present method provides a practical way to calculate the free energy profile along the stalk mechanism.
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Affiliation(s)
- Shuhei Kawamoto
- Health Research Institute, National Institute of Advanced Industrial Science & Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan.
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Affiliation(s)
- Xiaofei Xu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125;
| | | | - Isamu Kusaka
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Koffolt Laboratories, The Ohio State University, Columbus, Ohio 43210
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125;
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Enhanced Sampling in Molecular Dynamics Using Metadynamics, Replica-Exchange, and Temperature-Acceleration. ENTROPY 2013. [DOI: 10.3390/e16010163] [Citation(s) in RCA: 282] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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39
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Müller M, Sun DW. Directing the self-assembly of block copolymers into a metastable complex network phase via a deep and rapid quench. PHYSICAL REVIEW LETTERS 2013; 111:267801. [PMID: 24483814 DOI: 10.1103/physrevlett.111.267801] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Indexed: 06/03/2023]
Abstract
The free-energy landscape of self-assembling block copolymer systems is characterized by a multitude of metastable minima. Using particle-based simulations of a soft, coarse-grained model, we explore opportunities to reproducibly direct the spontaneous ordering of these self-assembling systems into a metastable complex network morphology--specifically, Schoen's I-WP periodic minimal surface--starting from a highly unstable state that is generated by a rapid expansion. This process-directed self-assembly provides an alternative to fine-tuning molecular architecture or blending for fabricating complex network structures. Comparing our particle-based simulation results to recently developed free-energy techniques, we critically assess their ability to predict spontaneous formation and highlight the importance of nonequilibrium molecular conformations in the starting state and the local conservation of density.
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Affiliation(s)
- Marcus Müller
- Institut für Theoretische Physik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - De-Wen Sun
- Institut für Theoretische Physik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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Abstract
For multicomponent vesicles, the line tension of domain boundaries and the component-dependent elastic properties (e.g., spontaneous curvatures) are the two most important factors that mediate the budding behaviors of these vesicles. This paper especially focuses on their effects on the budding types and the budding number of a two-component vesicle. We found that the budding number is mainly determined by the component-dependent elastic properties while the budding types mediated by line tensions. A phase diagram is also obtained showing three different types of phase regions: (i) partially budding, (ii) partially bud-off, and (iii) totally bud-off regions. These inspiring results are, however, derived from a very simple spherical-cap model, and have been tested by computer simulations showing good agreement. We emphasize that, besides testing the spherical-cap model, the computer simulation techniques developed in the current work can be easily extended to other systems involving multicomponent vesicles.
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Affiliation(s)
- Jianfeng Li
- The State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China.
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