1
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Coelho FM, Vinogradov J, Derksen JJ, Franco LFM. Electrokinetic properties of NaCl solution via molecular dynamics simulations with scaled-charge electrolytes. J Chem Phys 2024; 161:044508. [PMID: 39072421 DOI: 10.1063/5.0219098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2024] [Accepted: 06/30/2024] [Indexed: 07/30/2024] Open
Abstract
Scaling ionic charges has become an alternative to polarizable force fields for representing indirect charge transfer effects in molecular simulations. In our work, we apply molecular dynamics simulations to investigate the properties of NaCl aqueous solutions in homogeneous and confined media. We compare classical integer- and scaled-charge force fields for the ions. In the bulk, we validate the force fields by computing equilibrium and transport properties and comparing them with experimental data. Integer-charge ions overestimate dielectric saturation and ionic association. Both force fields present an excess in ion-ion correlation, which leads to a deviation in the ionic conductivity at higher ionic strengths. Negatively charged quartz is used to simulate the confinement effect. Electrostatic interactions dominate counter-ion adsorption. Full-charge ions have stronger and more defined adsorption planes. We obtain the electroosmotic mobility of the solution by combining the shear plane location from non-equilibrium simulations with the ionic distribution from equilibrium simulations. From the Helmholtz-Smoluchowski equation, the zeta potential and the streaming potential coupling coefficient are computed. From an atomic-scale perspective, our molecular dynamics simulations corroborate the hypothesis of maximum packing of the Stern layer, which results in a stable and non-zero zeta potential at high salinity. The scaled-charge model representation of both properties is in excellent qualitative and quantitative agreement with experimental data. With our work, we demonstrate how useful and precise simple scaled-charge models for electrolytes can be to represent complex systems, such as the electrical double layer.
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Affiliation(s)
- Felipe M Coelho
- Universidade Estadual de Campinas (UNICAMP), Faculdade de Engenharia Química, Campinas-SP 13083-852, Brazil
| | - Jan Vinogradov
- Department of Mechanical Engineering and Mechatronics, Ariel University, 40700 Ariel, Israel
| | - Jos J Derksen
- School of Engineering, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom
| | - Luís F M Franco
- Universidade Estadual de Campinas (UNICAMP), Faculdade de Engenharia Química, Campinas-SP 13083-852, Brazil
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2
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Judd KD, Parsons SW, Eremin DB, Fokin VV, Dawlaty JM. Visualizing partial solvation at the air-water interface. Chem Sci 2024; 15:8346-8354. [PMID: 38846382 PMCID: PMC11151832 DOI: 10.1039/d4sc01311e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2024] [Accepted: 04/08/2024] [Indexed: 06/09/2024] Open
Abstract
Despite significant research, the mechanistic nuances of unusual reactivity at the air-water interface, especially in microdroplets, remain elusive. The likely contributors include electric fields and partial solvation at the interface. To reveal these intricacies, we measure the frequency shift of a well-defined azide vibrational probe at the air-water interface, while independently controlling the surface charge density by introducing surfactants. First, we establish the response of the probe in the bulk and demonstrate that it is sensitive to both electrostatics and hydrogen bonding. From interfacial spectroscopy we infer that the azide is neither fully hydrated nor in a completely aprotic dielectric environment; instead, it experiences an intermediate environment. In the presence of hydrogen bond-accepting sulphate surfactants, competition arises for interfacial water with the azide. However, the dominant influence stems from the electrostatic effect of their negative heads, resulting in a significant blue-shift. Conversely, for the positive ammonium surfactants, our data indicate a balanced interplay between electrostatics and hydrogen bonding, leading to a minimal shift in the probe. Our results demonstrate partial solvation at the interface and highlights that both hydrogen bonding and electrostatics may assist or oppose each other in polarizing a reactant, intermediate, or product at the interface, which is important for understanding and tuning interfacial reactivity.
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Affiliation(s)
- Kenneth D Judd
- Department of Chemistry, The University of Southern California Los Angeles CA 90089 USA
| | - Sean W Parsons
- Department of Chemistry, The University of Southern California Los Angeles CA 90089 USA
| | - Dmitry B Eremin
- Department of Chemistry, The University of Southern California Los Angeles CA 90089 USA
| | - Valery V Fokin
- Department of Chemistry, The University of Southern California Los Angeles CA 90089 USA
| | - Jahan M Dawlaty
- Department of Chemistry, The University of Southern California Los Angeles CA 90089 USA
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3
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Rozak H, Nihonyanagi S, Myalitsin A, Roy S, Ahmed M, Tahara T, Rzeznicka II. Adsorption of SARS-CoV-2 Spike (N501Y) RBD to Human Angiotensin-Converting Enzyme 2 at a Lipid/Water Interface. J Phys Chem B 2023; 127:4406-4414. [PMID: 37171105 DOI: 10.1021/acs.jpcb.3c00832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The receptor binding domain (RBD) of spike proteins plays a crucial role in the process of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) attachment to the human angiotensin-converting enzyme 2 (ACE2). The N501Y mutation and later mutations introduced extra positive charges on the spike RBD and resulted in higher transmissibility, likely due to stronger binding with the highly negatively charged ACE2. Consequently, many studies have been devoted to understanding the molecular mechanism of spike protein binding with the ACE2 receptor. Most of the theoretical studies, however, have been done on isolated proteins. ACE2 is a transmembrane protein; thus, it is important to understand the interaction of spike proteins with ACE2 in a lipid matrix. In this study, the adsorption of ACE2 and spike (N501Y) RBD at a lipid/water interface was studied using the heterodyne-detected vibrational sum frequency generation (HD-VSFG) technique. The technique is a non-linear optical spectroscopy which measures vibrational spectra of molecules at an interface and provides information on their structure and orientation. It is found that ACE2 is effectively adsorbed at the positively charged 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) lipid monolayer via electrostatic interactions. The adsorption of ACE2 at the DPTAP monolayer causes a reorganization of interfacial water (D2O) from the D-down to the D-up orientation, indicating that the originally positively charged DPTAP interface becomes negatively charged due to ACE2 adsorption. The negatively charged interface (DPTAP/ACE2) allows further adsorption of positively charged spike RBD. HD-VSFG spectra in the amide I region show differences for spike (N501Y) RBD adsorbed at D2O, DPTAP, and DPTAP/ACE2 interfaces. A red shift observed for the spectra of spike RBD/DPTAP suggests that spike RBD oligomers are formed upon contact with DPTAP lipids.
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Affiliation(s)
- Harison Rozak
- College of Engineering, Shibaura Institute of Technology, Saitama City, Saitama 337-8570, Japan
| | - Satoshi Nihonyanagi
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Anton Myalitsin
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- ANVOS Analytics Co., 4-168 Motomachi, Naka-ku, Yokohama, Kanagawa 231-0861, Japan
| | - Subhadip Roy
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Mohammed Ahmed
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Tahei Tahara
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Izabela I Rzeznicka
- College of Engineering, Shibaura Institute of Technology, Saitama City, Saitama 337-8570, Japan
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4
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Nayak S, Kumal RR, Lee SE, Uysal A. Elucidating Trivalent Ion Adsorption at Floating Carboxylic Acid Monolayers: Charge Reversal or Water Reorganization? J Phys Chem Lett 2023; 14:3685-3690. [PMID: 37036360 DOI: 10.1021/acs.jpclett.3c00225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
We study the adsorption of trivalent neodymium on floating arachidic acid films at the air-water interface by two complementary surface specific probes, sum frequency generation spectroscopy and X-ray fluorescence near total reflection. In the absence of background ions, neodymium ions compensate for the surface charge of the arachidic acid film at a bulk concentration of 50 μM without any charge reversal. Increasing the bulk concentration to 1 mM does not change the neodymium surface coverage but affects the interfacial water structure significantly. In the presence of a high concentration of NaCl, there is overcharging at 1 mM Nd3+, i.e., 30% more Nd3+ than needed to compensate for the surface charge. These results show that the total coverage of neodymium ions is not enough to describe the complete picture at the interface, and interfacial water and ion coverage needs to be considered together to understand more complex ion adsorption and transport processes.
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Affiliation(s)
- Srikanth Nayak
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Raju R Kumal
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Seung Eun Lee
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Ahmet Uysal
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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5
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Sthoer A, Adams EM, Sengupta S, Corkery RW, Allen HC, Tyrode EC. La 3+ and Y 3+ interactions with the carboxylic acid moiety at the liquid/vapor interface: Identification of binding complexes, charge reversal, and detection limits. J Colloid Interface Sci 2022; 608:2169-2180. [PMID: 34798383 DOI: 10.1016/j.jcis.2021.10.052] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 09/30/2021] [Accepted: 10/11/2021] [Indexed: 10/20/2022]
Abstract
Specific interactions of yttrium and lanthanum ions with a fatty acid Langmuir monolayer were investigated using vibrational sum frequency spectroscopy. The trivalent ions were shown to interact with the charged form of the carboxylic acid group from nanomolar concentrations (<300 nM). Analysis of the spectral features from both the symmetric and the asymmetric carboxylate modes reveals the presence of at least three distinct coordination structures linked to specific binding configurations. Although the same species were identified for both La3+ and Y3+, they display a different concentration dependence, highlighting the ion-specificity of the interaction. From the analysis of the response of interfacial water molecules, the reversal of the surface charge, as well as the formation of yttrium hydroxide complexes, were detected upon increasing the amount of salt in solution. The binding interaction and kinetics of absorption are sensitive to the solution pH, showing a distinct ion speciation in the interfacial region when compared to the bulk. Changing the subphase pH or adding a monovalent background electrolyte that promotes deprotonation of the carboxylic acid headgroup could further improve the detection limit of La3+ and Y3+ to concentrations < 100 nM. These findings demonstrate that nM concentrations of trace metals contaminants, typically found on monovalent salts, can significantly influence the binding structure and kinetics in Langmuir monolayers.
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Affiliation(s)
- Adrien Sthoer
- Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
| | - Ellen M Adams
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43210, USA; Department of Physical Chemistry II, Ruhr-Universität Bochum, 44801 Bochum, Germany(1)
| | - Sanghamitra Sengupta
- Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden; Ultrafast Spectroscopy, AMOLF, 1098 XG Science Park, Amsterdam, The Netherlands(1)
| | - Robert W Corkery
- Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden; Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra, ACT0200, Australia
| | - Heather C Allen
- Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Eric C Tyrode
- Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
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6
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Judd KD, Gonzalez NM, Yang T, Cremer PS. Contact Ion Pair Formation Is Not Necessarily Stronger than Solvent Shared Ion Pairing. J Phys Chem Lett 2022; 13:923-930. [PMID: 35050629 DOI: 10.1021/acs.jpclett.1c03576] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Vibrational sum frequency spectroscopy (VSFS) and pressure-area Langmuir trough measurements were used to investigate the binding of alkali metal cations to eicosyl sulfate (ESO4) surfactants in monolayers at the air/water interface. The number density of sulfate groups could be tuned by mixing the anionic surfactant with eicosanol. The equilibrium dissociation constant for K+ to the fatty sulfate interface showed 10 times greater affinity than for Li+ and approximately 3 times greater than for Na+. All three cations formed solvent shared ion pairs when the mole fraction of ESO4 was 0.33 or lower. Above this threshold charge density, Li+ formed contact ion pairs with the sulfate headgroups, presumably via bridging structures. By contrast, K+ only bound to the sulfate moieties in solvent shared ion pairing configurations. The behavior for Na+ was intermediate. These results demonstrate that there is not necessarily a correlation between contact ion pair formation and stronger binding affinity.
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Affiliation(s)
- Kenneth D Judd
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Nicole M Gonzalez
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Tinglu Yang
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Paul S Cremer
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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7
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Singh PC, Ahmed M, Nihonyanagi S, Yamaguchi S, Tahara T. DNA-Induced Reorganization of Water at Model Membrane Interfaces Investigated by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy. J Phys Chem B 2022; 126:840-846. [DOI: 10.1021/acs.jpcb.1c08581] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Prashant Chandra Singh
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Mohammed Ahmed
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Satoshi Nihonyanagi
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Shoichi Yamaguchi
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
| | - Tahei Tahara
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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8
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Moll C, Versluis J, Bakker HJ. Direct Observation of the Orientation of Urea Molecules at Charged Interfaces. J Phys Chem Lett 2021; 12:10823-10828. [PMID: 34726406 PMCID: PMC8591664 DOI: 10.1021/acs.jpclett.1c03012] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Dissolving urea into water induces special solvation properties that play a crucial role in many biological processes. Here we probe the properties of urea molecules at charged aqueous interfaces using heterodyne-detected vibrational sum-frequency generation (HD-VSFG) spectroscopy. We find that at the neat water/air interface urea molecules do not yield a significant sum-frequency generation signal. However, upon the addition of ionic surfactants, we observe two vibrational bands at 1660 and 1590 cm-1 in the HD-VSFG spectrum, assigned to mixed bands of the C═O stretch and NH2 bend vibrations of urea. The orientation of the urea molecules depends on the sign of the charge localized at surface and closely follows the orientation of the neighboring water molecules. We demonstrate that urea is an excellent probe of the local electric field at aqueous interfaces.
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9
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Moll CJ, Versluis J, Bakker HJ. Direct Evidence for a Surface and Bulk Specific Response in the Sum-Frequency Generation Spectrum of the Water Bend Vibration. PHYSICAL REVIEW LETTERS 2021; 127:116001. [PMID: 34558941 DOI: 10.1103/physrevlett.127.116001] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 08/02/2021] [Accepted: 08/06/2021] [Indexed: 05/19/2023]
Abstract
We study the bending mode of pure water and charged aqueous surfaces using heterodyne-detected vibrational sum-frequency generation spectroscopy. We observe a low (1626 cm^{-1}) and a high (1656 cm^{-1}) frequency component that can be unambiguously assigned to an interfacial dipole and a bulk quadrupolar response, respectively. We thus demonstrate that probing the bending mode provides structural and quantitative information on both the surface and the bulk.
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Affiliation(s)
- C J Moll
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098XG Amsterdam, Netherlands
| | - J Versluis
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098XG Amsterdam, Netherlands
| | - H J Bakker
- AMOLF, Ultrafast Spectroscopy, Science Park 104, 1098XG Amsterdam, Netherlands
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10
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Uematsu Y. Electrification of water interface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33. [PMID: 34280896 DOI: 10.1088/1361-648x/ac15d5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 07/19/2021] [Indexed: 05/04/2023]
Abstract
The surface charge of a water interface determines many fundamental processes in physical chemistry and interface science, and it has been intensively studied for over a hundred years. We summarize experimental methods to characterize the surface charge densities developed so far: electrokinetics, double-layer force measurements, potentiometric titration, surface-sensitive nonlinear spectroscopy, and surface-sensitive mass spectrometry. Then, we elucidate physical ion adsorption and chemical electrification as examples of electrification mechanisms. In the end, novel effects on surface electrification are discussed in detail. We believe that this clear overview of state of the art in a charged water interface will surely help the fundamental progress of physics and chemistry at interfaces in the future.
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Affiliation(s)
- Yuki Uematsu
- Department of Physics, Kyushu University, Fukuoka 819-0395, Japan
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11
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Kusaka R, Watanabe M. Stoichiometry of Lanthanide-Phosphate Complexes at the Water Surface Studied Using Vibrational Sum Frequency Generation Spectroscopy and DFT Calculations. J Phys Chem B 2021; 125:6727-6731. [PMID: 34124914 DOI: 10.1021/acs.jpcb.1c04583] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the solvent extraction of metal ions, the transport mechanism of metal ions through the liquid-liquid organic/aqueous interface remains unclear. In this study, the adsorption process of trivalent lanthanide ions from the aqueous phase to the interface in the solvent extraction of lanthanides with di(2-ethylhexyl)phosphoric acid (HDEHP) extractant is investigated by using a model interface-water surface covered with HDEHP (air/HDEHP/aqueous interface). As a result, symmetric POO- stretch signals of HDEHP observed by vibrational sum frequency generation spectroscopy and density functional theory calculations show that the stoichiometric ratio of lanthanide-HDEHP complexes formed at the air/HDEHP/aqueous interface is 1:1. The formation of the interfacial 1:1 lanthanide-HDEHP complex could be an elementary chemical process occurring just before the transfer of lanthanide ions to the side of the organic phase.
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Affiliation(s)
- Ryoji Kusaka
- Nuclear Science and Engineering Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata, Tokai, Ibaraki 319-1195, Japan
| | - Masayuki Watanabe
- Nuclear Science and Engineering Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata, Tokai, Ibaraki 319-1195, Japan
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12
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Döpke MF, Hartkamp R. The importance of specifically adsorbed ions for electrokinetic phenomena: Bridging the gap between experiments and MD simulations. J Chem Phys 2021; 154:094701. [DOI: 10.1063/5.0038161] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- Max F. Döpke
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
| | - Remco Hartkamp
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
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13
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Abi A, Safavi A. Determination of the binding site size of hexaammineruthenium(iii) inside monolayers of DNA on gold. Analyst 2020; 146:547-557. [PMID: 33165468 DOI: 10.1039/d0an01685c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Hexaammineruthenium(iii), RuHex3+, is a DNA-binding metal complex that is widely used as a redox marker for the indirect determination of DNA coverage at the electrode surface. The conversion of electrochemically quantifiable surface excess of RuHex3+ into DNA surface coverage requires the knowledge of the binding site size of RuHex3+ (s). Traditionally, s on surface-immobilized DNA has been assumed to be equivalent to that on solution-phase DNA, which was experimentally determined in previous studies. Nevertheless, the different local microenvironments existing inside DNA monolayers in comparison to that in bulk solutions cast doubt on the validity of this assumption. In this report, we used electrochemical techniques to investigate s on surface-immobilized DNA. The values of s inside the DNA monolayers were found to be significantly smaller than that reported on solution-phase DNA. Besides, s was found to depend on the DNA packing density and became larger by increasing the DNA surface coverage or hybridizing the surface-tethered DNAs with complementary strands. Our data indicate that the RuHex3+ method, in which an s value of 3 nucleotides is used for the conversion of RuHex3+ to DNA surface coverage, does not always give reliable results.
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Affiliation(s)
- Alireza Abi
- Department of Chemistry, Faculty of Sciences, Shiraz University, Shiraz 7194684795, Iran.
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14
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Fries MR, Stopper D, Skoda MWA, Blum M, Kertzscher C, Hinderhofer A, Zhang F, Jacobs RMJ, Roth R, Schreiber F. Enhanced protein adsorption upon bulk phase separation. Sci Rep 2020; 10:10349. [PMID: 32587383 PMCID: PMC7316800 DOI: 10.1038/s41598-020-66562-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 05/11/2020] [Indexed: 11/08/2022] Open
Abstract
In all areas related to protein adsorption, from medicine to biotechnology to heterogeneous nucleation, the question about its dominant forces and control arises. In this study, we used ellipsometry and quartz-crystal microbalance with dissipation (QCM-D), as well as density-functional theory (DFT) to obtain insight into the mechanism behind a wetting transition of a protein solution. We established that using multivalent ions in a net negatively charged globular protein solution (BSA) can either cause simple adsorption on a negatively charged interface, or a (diverging) wetting layer when approaching liquid-liquid phase separation (LLPS) by changing protein concentration (cp) or temperature (T). We observed that the water to protein ratio in the wetting layer is substantially larger compared to simple adsorption. In the corresponding theoretical model, we treated the proteins as limited-valence (patchy) particles and identified a wetting transition for this complex system. This wetting is driven by a bulk instability introduced by metastable LLPS exposed to an ion-activated attractive substrate.
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Affiliation(s)
- Madeleine R Fries
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany
| | - Daniel Stopper
- Institute for Theoretical Physics, Auf der Morgenstelle 14, University of Tübingen, 72076, Tübingen, Germany
| | - Maximilian W A Skoda
- ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford-Appleton Laboratory, Didcot, OX11 0QX, United Kingdom
| | - Matthias Blum
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany
| | - Christoph Kertzscher
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany
| | - Alexander Hinderhofer
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany
| | - Fajun Zhang
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany
| | - Robert M J Jacobs
- Surface Analysis Facility, Chemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, United Kingdom
| | - Roland Roth
- Institute for Theoretical Physics, Auf der Morgenstelle 14, University of Tübingen, 72076, Tübingen, Germany.
| | - Frank Schreiber
- Institute for Applied Physics, Auf der Morgenstelle 10, University of Tübingen, 72076, Tübingen, Germany.
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15
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Richert ME, Gochev GG, Braunschweig B. Specific Ion Effects of Trivalent Cations on the Structure and Charging State of β-Lactoglobulin Adsorption Layers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11299-11307. [PMID: 31398284 DOI: 10.1021/acs.langmuir.9b01803] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The properties of proteins at interfaces are important to many processes as well as in soft matter materials such as aqueous foam. Particularly, the protein interfacial behavior is strongly linked to different factors like the solution pH or the presence of electrolytes. Here, the nature of the electrolyte ions can significantly modify the interfacial properties of proteins. Therefore, molecular level studies on interfacial structures and charging states are needed. In this work, we addressed the effects of Y3+ and Nd3+ cations on the adsorption of the whey protein β-lactoglobulin (BLG) at air-water interfaces as the function of electrolyte concentration. Both cations caused very similar but dramatic changes at the interface and in the bulk solution. Here, measurements of the electrophoretic mobility and with vibrational sum-frequency generation (SFG) spectroscopy were applied and consistently showed a reversal of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40 (interface) μM of Y3+ or Nd3+ for a BLG concentration of 15 μM. SFG spectra of carboxylate stretching vibrations from Asp or Glu residues of interfacial BLG showed significant changes in the resonance frequency, which we associate to specific and efficient binding of Y3+ or Nd3+ ions to the proteins carboxylate groups. Characteristic reentrant condensation for BLG moieties with bound trivalent ions was found in a broad concentration range around the point of zero net charge. The highest colloidal stability of BLG was found for ion concentrations <20 μM and >50 μM. Investigations on macroscopic foams from BLG solutions revealed the existence of structure-property relations between the interfacial charging state and the foam stability. In fact, a minimum in foam stability at 20 μM ion concentration was found when the interfacial net charge was negligible. At this concentration, we propose that the persistent BLG molecules and weakly charged BLG aggregates drive foam stability, while outside the bulk reentrant zone the electrostatic disjoining pressure inside foam lamellae dominates foam stability. Our results provide new information on the charge reversal at the liquid-gas interface of protein/ion dispersions. Therefore, we see our findings as an important step in the clarification of reentrant condensation effects at interfaces and their relevance to foam stability.
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Affiliation(s)
- Manuela E Richert
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
| | - Georgi G Gochev
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
| | - Björn Braunschweig
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
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Voukadinova A, Gillespie D. Energetics of counterion adsorption in the electrical double layer. J Chem Phys 2019; 150:154706. [PMID: 31005115 DOI: 10.1063/1.5087835] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The energetics of the electrical double layer (EDL) is studied in a systematic way to define how different components of the chemical potential help or hinder cation adsorption at a negatively charged wall. Specifically, the steric (i.e., excluded-volume interactions), mean electrostatic, and screening (i.e., electrostatic correlations beyond the mean field) components were computed using classical density functional theory of the primitive model of ions (i.e., ions as charged, hard spheres in a background dielectric). The reduced physics of the primitive model allows for an extensive analysis over a large parameter space: cation valences +1, +2, and +3, cation diameters 0.15, 0.30, 0.60, and 0.90 nm, bulk concentrations ranging from 1 µM to 1M, and surface charges ranging from 0 to -0.50 C/m2. Our results show that all components are necessary to understand the physics of the EDL. The screening component is always significant; for small monovalent cations such as K+, it is generally much larger than the steric component, and for multivalent ions, charge inversion cannot occur without it. At moderate surface charges, the screening component makes the electrostatic potential less negative than in classical Poisson-Boltzmann theory, sometimes even positive (charge inversion). At high surface charges, this is overcome by the repulsive potential of the steric component as the first ion layer becomes extremely crowded. Large negative electrostatic potentials counteract this to draw even more cations into the first layer. Although we used an approximate model of the EDL, the physics inherent in these trends appears to be quite general.
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Affiliation(s)
- Adelina Voukadinova
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois 60612-3833, USA
| | - Dirk Gillespie
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois 60612-3833, USA
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