1
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Ruixuan H, Majee A, Dobnikar J, Podgornik R. Electrostatic interactions between charge regulated spherical macroions. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2023; 46:115. [PMID: 38019363 DOI: 10.1140/epje/s10189-023-00373-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 10/20/2023] [Indexed: 11/30/2023]
Abstract
We study the interaction between two charge regulating spherical macroions with dielectric interior and dissociable surface groups immersed in a monovalent electrolyte solution. The charge dissociation is modelled via the Frumkin-Fowler-Guggenheim isotherm, which allows for multiple adsorption equilibrium states. The interactions are derived from the solutions of the mean-field Poisson-Boltzmann type theory with charge regulation boundary conditions. For a range of conditions we find symmetry breaking transitions from symmetric to asymmetric charge distribution exhibiting annealed charge patchiness, which results in like-charge attraction even in a univalent electrolyte-thus fundamentally modifying the nature of electrostatic interactions in charge-stabilized colloidal suspensions.
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Affiliation(s)
- Hu Ruixuan
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Arghya Majee
- Max Planck Institute for the Physics of Complex Systems, 01187, Dresden, Germany
| | - Jure Dobnikar
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
- CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- Wenzhou Institute of the University of Chinese Academy of Sciences, Wenzhou, Zhejiang, China
- Songshan Lake Materials Laboratory, Guangdong, 523808, Dongguan, China
| | - Rudolf Podgornik
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
- CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
- Wenzhou Institute of the University of Chinese Academy of Sciences, Wenzhou, 325011, Zhejiang, China.
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000, Ljubljana, Slovenia.
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2
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Tamrin SH, Phelps J, Nezhad AS, Sen A. Critical considerations in determining the surface charge of small extracellular vesicles. J Extracell Vesicles 2023; 12:e12353. [PMID: 37632212 PMCID: PMC10457570 DOI: 10.1002/jev2.12353] [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: 08/23/2022] [Revised: 07/10/2023] [Accepted: 07/14/2023] [Indexed: 08/27/2023] Open
Abstract
Small extracellular vesicles (EVs) have emerged as a focal point of EV research due to their significant role in a wide range of physiological and pathological processes within living systems. However, uncertainties about the nature of these vesicles have added considerable complexity to the already difficult task of developing EV-based diagnostics and therapeutics. Whereas small EVs have been shown to be negatively charged, their surface charge has not yet been properly quantified. This gap in knowledge has made it challenging to fully understand the nature of these particles and the way they interact with one another, and with other biological structures like cells. Most published studies have evaluated EV charge by focusing on zeta potential calculated using classical theoretical approaches. However, these approaches tend to underestimate zeta potential at the nanoscale. Moreover, zeta potential alone cannot provide a complete picture of the electrical properties of small EVs since it ignores the effect of ions that bind tightly to the surface of these particles. The absence of validated methods to accurately estimate the actual surface charge (electrical valence) and determine the zeta potential of EVs is a significant knowledge gap, as it limits the development of effective label-free methods for EV isolation and detection. In this study, for the first time, we show how the electrical charge of small EVs can be more accurately determined by accounting for the impact of tightly bound ions. This was accomplished by measuring the electrophoretic mobility of EVs, and then analytically correlating the measured values to their charge in the form of zeta potential and electrical valence. In contrast to the currently used theoretical expressions, the employed analytical method in this study enabled a more accurate estimation of EV surface charge, which will facilitate the development of EV-based diagnostic and therapeutic applications.
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Affiliation(s)
- Sara Hassanpour Tamrin
- Pharmaceutical Production Research Facility, Department of Chemical and Petroleum Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
- Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
- BioMEMS and Bioinspired Microfluidic Laboratory, Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
| | - Jolene Phelps
- Pharmaceutical Production Research Facility, Department of Chemical and Petroleum Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
- Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
| | - Amir Sanati Nezhad
- Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
- BioMEMS and Bioinspired Microfluidic Laboratory, Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
| | - Arindom Sen
- Pharmaceutical Production Research Facility, Department of Chemical and Petroleum Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
- Department of Biomedical Engineering, Schulich School of EngineeringUniversity of CalgaryCalgaryAlbertaCanada
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3
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Kimura Y, Inagawa A, Uehara N. Rapid acquisition of absorption spectra to monitor proton migration in nanoliter space using the RGB-spectrum-conversion method with a 10 ms interval. ANAL SCI 2023:10.1007/s44211-023-00348-y. [PMID: 37097514 DOI: 10.1007/s44211-023-00348-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Accepted: 04/13/2023] [Indexed: 04/26/2023]
Abstract
Acquisition protocol of absorption spectra at nanoliter spaces from the RGB values preserved in video data at 10 ms intervals was established using the principal-component-analysis-based RGB-conversion method. Proton behavior was monitored using a camera to acquire the video footage to monitor colorimetric change in the nanoliter space. The RGB values observed in the video were converted into a score vector using a conversion matrix. A linear combination of the predetermined loading vectors with the score values was calculated to reproduce the absorption spectra. The reproduced absorption spectra correlated well with those acquired using a conventional spectrophotometer during a short period. This method was applied to monitor the proton diffusion from a single cationic ion-exchange resin into hydrogels at low concentrations. The rapid acquisition and quick response of this method may enable the monitoring of the initial diffusion of protons, which is challenging with conventional spectrophotometry and electrochemical approaches.
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Affiliation(s)
- Yusuke Kimura
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya,, Tochigi, 321-8585, Japan
| | - Arinori Inagawa
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya,, Tochigi, 321-8585, Japan.
| | - Nobuo Uehara
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya,, Tochigi, 321-8585, Japan
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4
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Fossat MJ, Posey AE, Pappu RV. Uncovering the Contributions of Charge Regulation to the Stability of Single Alpha Helices. Chemphyschem 2023; 24:e202200746. [PMID: 36599672 PMCID: PMC10734359 DOI: 10.1002/cphc.202200746] [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: 10/10/2022] [Revised: 12/07/2022] [Indexed: 01/06/2023]
Abstract
The single alpha helix (SAH) is a recurring motif in biology. The consensus sequence has a di-block architecture that includes repeats of four consecutive glutamate residues followed by four consecutive lysine residues. Measurements show that the overall helicity of sequences with consensus E4 K4 repeats is insensitive to a wide range of pH values. Here, we use the recently introduced q-canonical ensemble, which allows us to decouple measurements of charge state and conformation, to explain the observed insensitivity of SAH helicity to pH. We couple the outputs from separate measurements of charge and conformation with atomistic simulations to derive residue-specific quantifications of preferences for being in an alpha helix and for the ionizable residues to be charged vs. uncharged. We find a clear preference for accommodating uncharged Glu residues within internal positions of SAH-forming sequences. The stabilities of alpha helical conformations increase with the number of E4 K4 repeats and so do the numbers of accessible charge states that are compatible with forming conformations of high helical content. There is conformational buffering whereby charge state heterogeneity buffers against large-scale conformational changes thus making the overall helicity insensitive to large changes in pH. Further, the results clearly argue against a single, rod-like alpha helical conformation being the only or even dominant conformation in the ensembles of so-called SAH sequences.
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Affiliation(s)
| | | | - Rohit V. Pappu
- Department of Biomedical Engineering and the Center for Biomolecular Condensates, James McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO 63130
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5
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Yasuda A, Inagawa A, Uehara N. Charge-Selective Aggregation Behavior of Thermoresponsive Polyelectrolytes Having Low Charge Density in Aqueous Solutions of Organic Counterions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:1730-1739. [PMID: 36696628 DOI: 10.1021/acs.langmuir.2c02286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The aggregation behavior of thermoresponsive polyelectrolytes with low charge density in aqueous solutions of organic counterions was investigated. We synthesized two thermoresponsive polyelectrolytes: anionic poly(N-isopropylacrylamide-co-(3-sulfopropyl)acrylamide potassium) (P-NIP-SPAK) and cationic poly(N-isopropylacrylamide-co-(3-acrylamidepropyl)trimethylammonium chloride) (P-NIP-AAPTAC). The polyelectrolytes remained soluble in their aqueous solutions even above the lower critical soluble temperature of P-NIP owing to the strong hydration property of the ionic groups. The aggregation occurred when organic counterions were added to the solution. In these solution systems, the concentration of counterions exceeds those of ionic groups introduced into the polyelectrolytes. The aggregation behavior is attributed to the salting-out effect of counterions accommodated near the polyelectrolyte surface by electrostatic interaction. This aggregation behavior was utilized for the charge-selective recognition of amino acids. P-NIP-SPAK aggregated only when basic amino acids were added under acidic conditions, whereas P-NIP-AAPTAC aggregated only when acidic amino acids were added under basic conditions. The results herein demonstrate that P-NIP-SPAK and P-NIP-AAPTAC have the potential to be used as charge-selective polymer sensors for amino acids without having to strictly control the experimental conditions.
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Affiliation(s)
- Asahi Yasuda
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya, Tochigi321-8585, Japan
| | - Arinori Inagawa
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya, Tochigi321-8585, Japan
| | - Nobuo Uehara
- Faculty of Engineering, Utsunomiya University, 7-1-2, Yoto, Utsunomiya, Tochigi321-8585, Japan
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6
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Mahanta S, Vallejo-Ramirez P, Karedla N, Puczkarski P, Krishnan M. Wide-field optical imaging of electrical charge and chemical reactions at the solid-liquid interface. Proc Natl Acad Sci U S A 2022; 119:e2209955119. [PMID: 36459653 PMCID: PMC9894211 DOI: 10.1073/pnas.2209955119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 10/26/2022] [Indexed: 12/04/2022] Open
Abstract
From molecules and particles to macroscopic surfaces immersed in fluids, chemical reactions often endow interfaces with electrical charge which in turn governs surface interactions and interfacial phenomena. The ability to measure the electrical properties of a material immersed in any solvent, as well as to monitor the spatial heterogeneity and temporal variation thereof, has been a long-standing challenge. Here, we describe an optical microscopy-based approach to probe the surface charge distribution of a range of materials, including inorganic oxide, polymer, and polyelectrolyte films, in contact with a fluid. The method relies on optical visualization of the electrical repulsion between diffusing charged probe molecules and the unknown surface to be characterized. Rapid image-based measurements enable us to further determine isoelectric points of the material as well as properties of its ionizable chemical groups. We further demonstrate the ability to optically monitor chemically triggered surface charge changes with millisecond time resolution. Finally, we present a scanning-surface probe technique capable of diffraction-limited imaging of spatial heterogeneities in chemical composition and charge over large areas. This technique will enable facile characterization of the solid-liquid interface with wide-ranging relevance across application areas from biology to engineering.
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Affiliation(s)
- Sushanta Mahanta
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, OxfordOX1 3QZ, United Kingdom
| | - Pedro Vallejo-Ramirez
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, OxfordOX1 3QZ, United Kingdom
| | - Narain Karedla
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, OxfordOX1 3QZ, United Kingdom
| | - Paweł Puczkarski
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, OxfordOX1 3QZ, United Kingdom
| | - Madhavi Krishnan
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, OxfordOX1 3QZ, United Kingdom
- The Kavli Institute for Nanoscience Discovery, OxfordOX1 3QU, United Kingdom
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7
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Bespalova M, Öz R, Westerlund F, Krishnan M. Single-Molecule Trapping and Measurement in a Nanostructured Lipid Bilayer System. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:13923-13934. [PMID: 36326814 PMCID: PMC9671048 DOI: 10.1021/acs.langmuir.2c02203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Revised: 10/15/2022] [Indexed: 06/16/2023]
Abstract
The repulsive electrostatic force between a biomolecule and a like-charged surface can be geometrically tailored to create spatial traps for charged molecules in solution. Using a parallel-plate system composed of silicon dioxide surfaces, we recently demonstrated single-molecule trapping and high precision molecular charge measurements in a nanostructured free energy landscape. Here we show that surfaces coated with charged lipid bilayers provide a system with tunable surface properties for molecular electrometry experiments. Working with molecular species whose effective charge and geometry are well-defined, we demonstrate the ability to quantitatively probe the electrical charge density of a supported lipid bilayer. Our findings indicate that the fraction of charged lipids in nanoslit lipid bilayers can be significantly different from that in the precursor lipid mixtures used to generate them. We also explore the temporal stability of bilayer properties in nanofluidic systems. Beyond their relevance in molecular measurement, such experimental systems offer the opportunity to examine lipid bilayer formation and wetting dynamics on nanostructured surfaces.
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Affiliation(s)
- Maria Bespalova
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, OxfordOX1 3QZ, United Kingdom
| | - Robin Öz
- Department
of Biology and Biological Engineering, Chalmers
University of Technology, 412 96Gothenburg, Sweden
| | - Fredrik Westerlund
- Department
of Biology and Biological Engineering, Chalmers
University of Technology, 412 96Gothenburg, Sweden
| | - Madhavi Krishnan
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, OxfordOX1 3QZ, United Kingdom
- The
Kavli Institute for Nanoscience Discovery, Sherrington Road, OxfordOX1 3QU, United Kingdom
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8
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Bakhshandeh A, Frydel D, Levin Y. Theory of Charge Regulation of Colloidal Particles in Electrolyte Solutions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:13963-13971. [PMID: 36318200 DOI: 10.1021/acs.langmuir.2c02313] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
We present a theory that enables us to (i) calculate the effective surface charge of colloidal particles and (ii) efficiently obtain titration curves for different salt concentrations. The theory accounts for the shift of pH of solution due to the presence of 1:1 electrolyte. It also accounts self-consistently for the electrostatic potential produced by the deprotonated surface groups. To examine the accuracy of the theory, we have performed extensive reactive Monte Carlo simulations, which show excellent agreement between theory and simulations without any adjustable parameters.
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Affiliation(s)
- Amin Bakhshandeh
- Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre, RSBrazil
| | - Derek Frydel
- Department of Chemistry, Universidad Técnica Federico Santa María, Campus San Joaquin, 7820275, Santiago, Chile
| | - Yan Levin
- Instituto de Física, Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre, RSBrazil
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9
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Kloes G, Bennett TJD, Chapet-Batlle A, Behjatian A, Turberfield AJ, Krishnan M. Far-Field Electrostatic Signatures of Macromolecular 3D Conformation. NANO LETTERS 2022; 22:7834-7840. [PMID: 36125326 PMCID: PMC9562458 DOI: 10.1021/acs.nanolett.2c02485] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
In solution as in vacuum, the electrostatic field distribution in the vicinity of a charged object carries information on its three-dimensional geometry. We report on an experimental study exploring the effect of molecular shape on long-range electrostatic interactions in solution. Working with DNA nanostructures carrying approximately equal amounts of total charge but each in a different three-dimensional conformation, we demonstrate that the geometry of the distribution of charge in a molecule has substantial impact on its electrical interactions. For instance, a tetrahedral structure, which is the most compact distribution of charge we tested, can create a far-field effect that is effectively identical to that of a rod-shaped molecule carrying half the amount of total structural charge. Our experiments demonstrate that escape-time electrometry (ETe) furnishes a rapid and facile method to screen and identify 3D conformations of charged biomolecules or molecular complexes in solution.
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Affiliation(s)
- Gunnar Kloes
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Timothy J. D. Bennett
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Alma Chapet-Batlle
- Clarendon
Laboratory, Department of Physics, University
of Oxford, Parks Road, Oxford OX1
3PU, United Kingdom
| | - Ali Behjatian
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Andrew J. Turberfield
- Clarendon
Laboratory, Department of Physics, University
of Oxford, Parks Road, Oxford OX1
3PU, United Kingdom
- The Kavli
Institute for Nanoscience Discovery, Sherrington Road, Oxford OX1 3QU, United Kingdom
| | - Madhavi Krishnan
- Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
- The Kavli
Institute for Nanoscience Discovery, Sherrington Road, Oxford OX1 3QU, United Kingdom
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10
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Bespalova M, Behjatian A, Karedla N, Walker-Gibbons R, Krishnan M. Opto-Electrostatic Determination of Nucleic Acid Double-Helix Dimensions and the Structure of the Molecule–Solvent Interface. Macromolecules 2022; 55:6200-6210. [PMID: 35910310 PMCID: PMC9330769 DOI: 10.1021/acs.macromol.2c00657] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
A DNA molecule is
highly electrically charged in solution. The
electrical potential at the molecular surface is known to vary strongly
with the local geometry of the double helix and plays a pivotal role
in DNA–protein interactions. Further out from the molecular
surface, the electrical field propagating into the surrounding electrolyte
bears fingerprints of the three-dimensional arrangement of the charged
atoms in the molecule. However, precise extraction of the structural
information encoded in the electrostatic “far field”
has remained experimentally challenging. Here, we report an optical
microscopy-based approach that detects the field distribution surrounding
a charged molecule in solution, revealing geometric features such
as the radius and the average rise per basepair of the double helix
with up to sub-Angstrom precision, comparable with traditional molecular
structure determination techniques like X-ray crystallography and
nuclear magnetic resonance. Moreover, measurement of the helical radius
furnishes an unprecedented view of both hydration and the arrangement
of cations at the molecule–solvent interface. We demonstrate
that a probe in the electrostatic far field delivers structural and
chemical information on macromolecules, opening up a new dimension
in the study of charged molecules and interfaces in solution.
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Affiliation(s)
- Maria Bespalova
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, U.K
| | - Ali Behjatian
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, U.K
| | - Narain Karedla
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, U.K
| | - Rowan Walker-Gibbons
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, U.K
| | - Madhavi Krishnan
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, U.K
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11
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Behjatian A, Krishnan M. Electrostatic free energies carry structural information on nucleic acid molecules in solution. J Chem Phys 2022; 156:134201. [DOI: 10.1063/5.0080008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Over the last several decades, a range of experimental techniques from x-ray crystallography and atomic force microscopy to nuclear magnetic resonance and small angle x-ray scattering have probed nucleic acid structure and conformation with high resolution both in the condensed state and in solution. We present a computational study that examines the prospect of using electrostatic free energy measurements to detect 3D conformational properties of nucleic acid molecules in solution. As an example, we consider the conformational difference between A- and B-form double helices whose structures differ in the values of two key parameters—the helical radius and rise per basepair. Mapping the double helix onto a smooth charged cylinder reveals that electrostatic free energies for molecular helices can, indeed, be described by two parameters: the axial charge spacing and the radius of a corresponding equivalent cylinder. We show that electrostatic free energies are also sensitive to the local structure of the molecular interface with the surrounding electrolyte. A free energy measurement accuracy of 1%, achievable using the escape time electrometry (ET e) technique, could be expected to offer a measurement precision on the radius of the double helix of approximately 1 Å. Electrostatic free energy measurements may, therefore, not only provide information on the structure and conformation of biomolecules but could also shed light on the interfacial hydration layer and the size and arrangement of counterions at the molecular interface in solution.
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Affiliation(s)
- Ali Behjatian
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Madhavi Krishnan
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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12
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Enderlein J, Sakhapov D, Gregor I, Croci M, Karedla N. Modeling charge separation in charged nanochannels for single-molecule electrometry. J Chem Phys 2022; 156:105104. [DOI: 10.1063/5.0074732] [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
We model the transport of electrically charged solute molecules by a laminar flow within a nanoslit microfluidic channel with electrostatic surface potential. We derive the governing convection–diffusion equation, solve it numerically, and compare it with a Taylor–Aris-like approximation, which gives excellent results for small Péclet numbers. We discuss our results in light of designing an assay that can measure simultaneously the hydrodynamic size and electric charge of single molecules by tracking their motion in such nanoslit channels with electrostatic surface potential.
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Affiliation(s)
- Jörg Enderlein
- III. Institute of Physics–Biophysics, Georg August University, 37077 Göttingen, Germany
- Cluster of Excellence “Multiscale Bioimaging: From Molecular Machines to Networks of Excitable Cells” (MBExC), Georg August University, 37077 Göttingen, Germany
| | - Damir Sakhapov
- III. Institute of Physics–Biophysics, Georg August University, 37077 Göttingen, Germany
| | - Ingo Gregor
- III. Institute of Physics–Biophysics, Georg August University, 37077 Göttingen, Germany
| | - Matteo Croci
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Narain Karedla
- The Rosalind Franklin Institute, Harwell Campus, Didcot OX11 0FA, United Kingdom
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13
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Bakhshandeh A, Frydel D, Levin Y. Reactive Monte Carlo simulations for charge regulation of colloidal particles. J Chem Phys 2022; 156:014108. [PMID: 34998334 DOI: 10.1063/5.0077956] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We use a reactive Monte Carlo simulation method and the primitive model of electrolyte to study acid-base equilibrium that controls charge regulation in colloidal systems. The simulations are performed in a semi-grand canonical ensemble in which colloidal suspension is in contact with a reservoir of salt and strong acid. The interior of colloidal particles is modeled as a low dielectric medium, different from the surrounding water. The effective colloidal charge is calculated for different numbers of surface acidic groups, pH, salt concentrations, and types of electrolyte. In the case of potassium chloride, the titration curves are compared with the experimental measurements obtained using potentiometric titration. A good agreement is found between simulations and experiments. In the case of lithium chloride, the specific ionic adsorption is taken into account through the partial dehydration of lithium ion.
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Affiliation(s)
- Amin Bakhshandeh
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil
| | - Derek Frydel
- Department of Chemistry, Universidad Técnica Federico Santa María, Campus San Joaquin, 7820275 Santiago, Chile
| | - Yan Levin
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil
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14
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Hosseini II, Liu Z, Capaldi X, AbdelFatah T, Montermini L, Rak J, Reisner W, Mahshid S. Nanofluidics for Simultaneous Size and Charge Profiling of Extracellular Vesicles. NANO LETTERS 2021; 21:4895-4902. [PMID: 34061534 DOI: 10.1021/acs.nanolett.0c02558] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Extracellular vesicles (EVs) are cell-derived membrane structures that circulate in body fluids and show considerable potential for noninvasive diagnosis. EVs possess surface chemistries and encapsulated molecular cargo that reflect the physiological state of cells from which they originate, including the presence of disease. In order to fully harness the diagnostic potential of EVs, there is a critical need for technologies that can profile large EV populations without sacrificing single EV level detail by averaging over multiple EVs. Here we use a nanofluidic device with tunable confinement to trap EVs in a free-energy landscape that modulates vesicle dynamics in a manner dependent on EV size and charge. As proof-of-principle, we perform size and charge profiling of a population of EVs extracted from human glioblastoma astrocytoma (U373) and normal human astrocytoma (NHA) cell lines.
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Affiliation(s)
- Imman I Hosseini
- Department of Bioengineering, McGill University, 3775 Rue University, Montreal, Quebec H3A 2B4, Canada
| | - Zezhou Liu
- Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada
| | - Xavier Capaldi
- Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada
| | - Tamer AbdelFatah
- Department of Bioengineering, McGill University, 3775 Rue University, Montreal, Quebec H3A 2B4, Canada
| | - Laura Montermini
- Research Institute of the McGill University Health Centre, 1001 Decarie Boul., Montreal, Quebec H4A 3J1, Canada
| | - Janusz Rak
- Department of Pediatrics, McGill University, Research Institute of the McGill University Health Centre, 1001 Decarie Boul., Montreal, Quebec H4A 3J1, Canada
| | - Walter Reisner
- Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada
| | - Sara Mahshid
- Department of Bioengineering, McGill University, 3775 Rue University, Montreal, Quebec H3A 2B4, Canada
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15
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Javidpour L, BoŽič A, Naji A, Podgornik R. Electrostatic interactions between the SARS-CoV-2 virus and a charged electret fibre. SOFT MATTER 2021; 17:4296-4303. [PMID: 33908595 DOI: 10.1039/d1sm00232e] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
While almost any kind of face mask offers some protection against particles and pathogens of different sizes, the most efficient ones make use of a layered structure where one or more layers are electrically charged. These electret layers are essential for the efficient filtration of difficult-to-capture small particles, yet the exact nature of electrostatic capture with respect to the charge on both the particles and the electret fibres as well as the effect of the immediate environment remain unclear. Here, we explore in detail the electrostatic interactions between the surface of a single charged electret fibre and a model of the SARS-CoV-2 virus. Using Poisson-Boltzmann electrostatics coupled to a detailed spike protein charge regulation model, we show how pH and salt concentration drastically change both the scale and the sign of the interaction. Furthermore, the configuration of the few spike proteins closest to the electret fibre turns out to be as important for the strength of the interaction as their total number on the virus envelope, a direct consequence of spike protein charge regulation. The results of our work elucidate the details of virus electrostatics and contribute to the general understanding of efficient virus filtration mechanisms.
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Affiliation(s)
- Leili Javidpour
- School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5531, Iran
| | - AnŽe BoŽič
- Department of Theoretical Physics, JoŽef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - Ali Naji
- School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5531, Iran and School of Nano Science, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5531, Iran
| | - Rudolf Podgornik
- School of Physical Sciences and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. and Wenzhou Institute of the University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325000, China
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16
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Bakhshandeh A, dos Santos AP, Levin Y. Interaction between Charge-Regulated Metal Nanoparticles in an Electrolyte Solution. J Phys Chem B 2020; 124:11762-11770. [DOI: 10.1021/acs.jpcb.0c09446] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Amin Bakhshandeh
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil
| | - Alexandre P. dos Santos
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil
| | - Yan Levin
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil
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17
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Behjatian A, Bespalova M, Karedla N, Krishnan M. Electroviscous effect for a confined nanosphere in solution. Phys Rev E 2020; 102:042607. [PMID: 33212723 DOI: 10.1103/physreve.102.042607] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 09/20/2020] [Indexed: 11/07/2022]
Abstract
A charged colloidal particle suspended in an electrolyte experiences electroviscous stresses arising from motion-driven electrohydrodynamic phenomena. Under certain conditions, the additional contribution from electroviscous drag forces to the total drag experienced by the moving particle can lead to measurable deviations of particle diffusion coefficients from values predicted by the well known Stokes-Einstein relation that describes diffusive behavior of small particles in an unbounded charge-free fluid. In this study, we investigate the role of electroviscous stresses on nanoparticle diffusion in confined geometries using both simulations and experiment. We compare our experimental measurements with the results of a numerically solved continuum model based on the Poisson-Nernst-Planck-Stokes system of equations and find good agreement between experiment and theory. Depending on the radius of the counterion species in solution and the degree of confinement, we find that the viscous drag on polystyrene nanoparticles can be augmented by approximately 10-25% compared to the values predicted by pure hydrodynamic models in the absence of free charge in the fluid. This enhancement corresponds approximately to a 5-10% increase compared to the electroviscous contribution for a charged particle in an unbounded fluid. Contrary to recent reports in the experimental literature, we find neither experimental nor theoretical evidence of an anomalously large enhancement of electroviscous forces on a confined charged nanoparticle in solution.
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Affiliation(s)
- Ali Behjatian
- Physical & Theoretical Chemistry Laboratory, Department of Chemistry, South Parks Road, University of Oxford, Oxford OX1 3QZ, United Kingdom
| | - Maria Bespalova
- Physical & Theoretical Chemistry Laboratory, Department of Chemistry, South Parks Road, University of Oxford, Oxford OX1 3QZ, United Kingdom
| | - Narain Karedla
- Physical & Theoretical Chemistry Laboratory, Department of Chemistry, South Parks Road, University of Oxford, Oxford OX1 3QZ, United Kingdom
| | - Madhavi Krishnan
- Physical & Theoretical Chemistry Laboratory, Department of Chemistry, South Parks Road, University of Oxford, Oxford OX1 3QZ, United Kingdom
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18
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Bakhshandeh A, Frydel D, Levin Y. Charge regulation of colloidal particles in aqueous solutions. Phys Chem Chem Phys 2020; 22:24712-24728. [PMID: 33104140 DOI: 10.1039/d0cp03633a] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
We study the charge regulation of colloidal particles inside aqueous electrolyte solutions. To stabilize a colloidal suspension against precipitation, colloidal particles are synthesized with either acidic or basic groups on their surface. On contact with water, these surface groups undergo proton transfer reactions, resulting in colloidal surface charge. The charge is determined by the condition of local chemical equilibrium between hydronium ions inside the solution and at the colloidal surface. We use a model of Baxter sticky spheres to explicitly calculate the equilibrium dissociation constants and to construct a theory which is able to quantitatively predict the effective charge of colloidal particles with either acidic or basic surface groups. The predictions of the theory for the model are found to be in excellent agreement with the results of Monte Carlo simulations. This theory is further extended to treat colloidal particles with a mixture of both acidic and basic surface groups.
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Affiliation(s)
- Amin Bakhshandeh
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil.
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19
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Kubincová A, Hünenberger PH, Krishnan M. Interfacial solvation can explain attraction between like-charged objects in aqueous solution. J Chem Phys 2020; 152:104713. [PMID: 32171222 DOI: 10.1063/1.5141346] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Over the past few decades, the experimental literature has consistently reported observations of attraction between like-charged colloidal particles and macromolecules in aqueous solution. Examples include nucleic acids and colloidal particles in the bulk solution and under confinement, and biological liquid-liquid phase separation. This observation is at odds with the intuitive expectation of an interparticle repulsion that decays monotonically with distance. Although attraction between like-charged particles can be rationalized theoretically in the strong-coupling regime, e.g., in the presence of multivalent counterions, recurring accounts of long-range attraction in aqueous solution containing monovalent ions at low ionic strength have posed an open conundrum. Here, we show that the behavior of molecular water at an interface-traditionally disregarded in the continuum electrostatics picture-provides a mechanism to explain the attraction between like-charged objects in a broad spectrum of experiments. This basic principle will have important ramifications in the ongoing quest to better understand intermolecular interactions in solution.
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Affiliation(s)
- Alžbeta Kubincová
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Philippe H Hünenberger
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Madhavi Krishnan
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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20
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Mimura M, Tsumura K, Matsuda A, Akatsuka N, Shiraki K. Effect of additives on liquid droplet of protein-polyelectrolyte complex for high-concentration formulations. J Chem Phys 2019; 150:064903. [PMID: 30769990 DOI: 10.1063/1.5063378] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Liquid droplets of protein-polyelectrolyte complexes (PPCs) have been developed as a new candidate for stabilization and concentration of protein drugs. However, it remains unclear whether additives affect the precipitation and redissolution yields of PPCs. In the present study, we investigated the PPC formation of human immunoglobulin G (IgG) and poly-L-glutamic acid (polyE) in the presence of various additives that have diverse effects, such as protein stabilization. Alcohols, including ethanol, successfully increased the PPC precipitation yield to over 90%, and the PPCs formed were completely redissolved at physiological ionic strength. However, poly(ethylene glycol), sugars, and amino acids did not improve the precipitation and redissolution yields of PPCs over those observed when no additives were included. Circular dichroism spectrometry showed that the secondary structure of polyE as well as electrostatic interactions play important roles in increasing the PPC precipitation yield when ethanol is used as an additive. The maximum concentration of IgG reached 100 mg/ml with the use of ethanol, which was 15% higher efficiency of the protein yield after precipitation and redissolution than that in the absence of additives. Thus, the addition of a small amount of ethanol is effective for the concentration and stabilization of precipitated PPCs containing IgG formulations.
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Affiliation(s)
- Masahiro Mimura
- Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
| | - Keisuke Tsumura
- Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
| | - Ayumi Matsuda
- Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
| | - Naoki Akatsuka
- Research and Development Center, Terumo Corporation, Nakai-machi, Ashigarakami-gun, Kanagawa 259-0151, Japan
| | - Kentaro Shiraki
- Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
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21
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Lošdorfer Božič A, Podgornik R. Anomalous multipole expansion: Charge regulation of patchy inhomogeneously charged spherical particles. J Chem Phys 2018; 149:163307. [DOI: 10.1063/1.5037044] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Anže Lošdorfer Božič
- Department of Theoretical Physics, Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - Rudolf Podgornik
- Department of Theoretical Physics, Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- School of Physical Sciences and Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
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22
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Ruggeri F, Krishnan M. Entropic Trapping of a Singly Charged Molecule in Solution. NANO LETTERS 2018; 18:3773-3779. [PMID: 29688720 DOI: 10.1021/acs.nanolett.8b01011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We demonstrate the ability to confine a single molecule in solution by spatial modulation of its local configurational entropy. Previously we established electrostatic trapping of a charged macromolecule by geometric tailoring of a repulsive electrical interaction potential in a parallel plate system. However, since the lifetime of the trapped state depends exponentially on the electrical charge of the molecule, the electrostatic interaction alone is often insufficient in magnitude to stably confine molecules carrying a net charge of magnitude ≤5 e. Here we show that the configurational entropy of a thermally fluctuating molecule in a geometrically modulated system can be exploited to spatially confine weakly charged molecules in solution. Measurement of the configurational entropy contribution reveals good agreement with theoretical expectations. This additional translational contribution to the total free energy facilitates direct optical imaging and measurement of the effective charge of molecules on the size scale of ∼1 nm and a charge as low as 1 e, physical properties comparable with those of a monovalent ion in solution.
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Affiliation(s)
- Francesca Ruggeri
- Department of Chemistry , University of Zürich , Winterthurerstrasse 190 , CH 8057 Zürich , Switzerland
| | - Madhavi Krishnan
- Department of Chemistry , University of Zürich , Winterthurerstrasse 190 , CH 8057 Zürich , Switzerland
- Department of Physics , University of Zürich , Winterthurerstrasse 190 , CH 8057 Zürich , Switzerland
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23
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Ruggeri F, Krishnan M. Spectrally resolved single-molecule electrometry. J Chem Phys 2018; 148:123307. [DOI: 10.1063/1.5008936] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Affiliation(s)
- F. Ruggeri
- Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
| | - M. Krishnan
- Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
- Department of Physics, University of Zürich, Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
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24
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Lošdorfer BoŽič A. From discrete to continuous description of spherical surface charge distributions. SOFT MATTER 2018; 14:1149-1161. [PMID: 29345714 DOI: 10.1039/c7sm02207g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The importance of electrostatic interactions in soft matter and biological systems can often be traced to non-uniform charge effects, which are commonly described using a multipole expansion of the corresponding charge distribution. The standard approach when extracting the charge distribution of a given system is to treat the constituent charges as points. This can, however, lead to an overestimation of multipole moments of high order, such as dipole, quadrupole, and higher moments. Focusing on distributions of charges located on a spherical surface - characteristic of numerous biological macromolecules, such as globular proteins and viral capsids, as well as of inverse patchy colloids - we develop a novel way of representing spherical surface charge distributions based on the von Mises-Fisher distribution. This approach takes into account the finite spatial extension of individual charges, and leads to a simple yet powerful way of describing surface charge distributions and their multipole expansions. In this manner, we analyze charge distributions and the derived multipole moments of a number of different spherical configurations of identical charges with various degrees of symmetry. We show how the number of charges, their size, and the geometry of their configuration influence the behavior and relative importance of multipole magnitudes of different order. Importantly, we clearly demonstrate how neglecting the effect of charge size leads to an overestimation of high-order multipoles. The results of our work can be applied to construct analytical models of electrostatic interactions and multipole expansion of charged particles in diverse soft matter and biological systems.
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25
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Ruggeri F, Krishnan M. Lattice diffusion of a single molecule in solution. Phys Rev E 2017; 96:062406. [PMID: 29347432 DOI: 10.1103/physreve.96.062406] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Indexed: 05/28/2023]
Abstract
The ability to trap a single molecule in an electrostatic potential well in solution has opened up new possibilities for the use of molecular electrical charge to study macromolecular conformation and dynamics at the level of the single entity. Here we study the diffusion of a single macromolecule in a two-dimensional lattice of electrostatic traps in solution. We report the ability to measure both the size and effective electrical charge of a macromolecule by observing single-molecule transport trajectories, typically a few seconds in length, using fluorescence microscopy. While, as shown previously, the time spent by the molecule in a trap is a strong function of its effective charge, we demonstrate here that the average travel time between traps in the landscape yields its hydrodynamic radius. Tailoring the pitch of the lattice thus yields two different experimentally measurable time scales that together uniquely determine both the size and charge of the molecule. Since no information is required on the location of the molecule between consecutive departure and arrival events at lattice sites, the technique is ideally suited to measurements on weakly emitting entities such as single molecules.
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Affiliation(s)
- Francesca Ruggeri
- Department of Chemistry, University of Zürich,Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
| | - Madhavi Krishnan
- Department of Chemistry, University of Zürich,Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
- Department of Physics, University of Zürich,Winterthurerstrasse 190, CH 8057 Zürich, Switzerland
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26
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Lošdorfer Božič A, Podgornik R. pH Dependence of Charge Multipole Moments in Proteins. Biophys J 2017; 113:1454-1465. [PMID: 28978439 DOI: 10.1016/j.bpj.2017.08.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 08/10/2017] [Accepted: 08/11/2017] [Indexed: 11/26/2022] Open
Abstract
Electrostatic interactions play a fundamental role in the structure and function of proteins. Due to ionizable amino acid residues present on the solvent-exposed surfaces of proteins, the protein charge is not constant but varies with the changes in the environment-most notably, the pH of the surrounding solution. We study the effects of pH on the charge of four globular proteins by expanding their surface charge distributions in terms of multipoles. The detailed representation of the charges on the proteins is in this way replaced by the magnitudes and orientations of the multipole moments of varying order. Focusing on the three lowest-order multipoles-the total charge, dipole, and quadrupole moment-we show that the value of pH influences not only their magnitudes, but more notably and importantly also the spatial orientation of their principal axes. Our findings imply important consequences for the study of protein-protein interactions and the assembly of both proteinaceous shells and patchy colloids with dissociable charge groups.
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Affiliation(s)
| | - Rudolf Podgornik
- Department of Theoretical Physics, Jožef Stefan Institute, Ljubljana, Slovenia; Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia
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27
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Krishnan M. Erratum: “A simple model for electrical charge in globular macromolecules and linear polyelectrolytes in solution” [J. Chem. Phys. 146, 205101 (2017)]. J Chem Phys 2017; 147:079901. [DOI: 10.1063/1.4999597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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