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Gustafsson E, Hellsing MS, Rennie AR, Welbourn RJL, Campana M, Hughes A, Li P, Bowden TM. Understanding interactions of plasticisers with a phospholipid monolayer. Soft Matter 2024; 20:2892-2899. [PMID: 38465518 DOI: 10.1039/d3sm01611k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
The use of DEHP (diethylhexyl phthalate) is now banned for most applications in Europe; the exception is for blood bags, where its toxicity is overshadowed by its ability to extend the storage life of red blood cells. Another plasticiser, BTHC (butanoyl trihexyl citrate), is used in paediatric blood bags but does not stabilise blood cells as effectively. Interactions between plasticisers and lipids are investigated with a phospholipid, DMPC, to understand the increased stability of blood cells in the presence of DEHP as well as bioaccumulation and identify differences with BTHC. Mixed monolayers of DMPC and DEHP or BTHC were studied on Langmuir troughs where surface pressure/area isotherms can be measured. Neutron reflection measurements were made to determine the composition and structure of these mixed layers. A large amount of plasticiser can be incorporated into a DMPC monolayer but once an upper limit is reached, plasticiser is selectively removed from the interface at high surface pressures. The upper limit is found to occur between 40-60 mol% for DEHP and 20-40 mol% for BTHC. The areas per molecule are also different with DEHP being in the range of 50-100 Å2 and BTHC being 65-120 Å2. Results indicate that BTHC does not fit as well as DEHP in DMPC monolayers which could help explain the differences observed with regards to the stability of blood cells.
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Affiliation(s)
- Emil Gustafsson
- Department of Chemistry, Ångström Laboratory, Uppsala University, Box 538, 752 37 Uppsala, Sweden.
| | - Maja S Hellsing
- RISE Research Institutes of Sweden, Box 5604, 114 86 Stockholm, Sweden
| | - Adrian R Rennie
- Department of Chemistry, Ångström Laboratory, Uppsala University, Box 538, 752 37 Uppsala, Sweden.
- Centre for Neutron Scattering, Ångström Laboratory, Uppsala University, Box 538, 752 37 Uppsala, Sweden
| | - Rebecca J L Welbourn
- ISIS Pulsed Neutron and Muon Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, UK
| | - Mario Campana
- ISIS Pulsed Neutron and Muon Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, UK
| | - Arwel Hughes
- ISIS Pulsed Neutron and Muon Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, UK
| | - Peixun Li
- ISIS Pulsed Neutron and Muon Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX, UK
| | - Tim Melander Bowden
- Department of Chemistry, Ångström Laboratory, Uppsala University, Box 538, 752 37 Uppsala, Sweden.
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2
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Armstrong AJ, Apóstolo RFG, McCoy TM, Allen FJ, Doutch J, Cattoz BN, Dowding PJ, Welbourn RJL, Routh AF, Camp PJ. Experimental and simulation study of self-assembly and adsorption of glycerol monooleate in n-dodecane with varying water content onto iron oxide. Nanoscale 2024; 16:1952-1970. [PMID: 38175178 DOI: 10.1039/d3nr05080g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The self-assembly and surface adsorption of glycerol monooleate (GMO) in n-dodecane are studied using a combination of experimental and molecular dynamics simulation techniques. The self-assembly of GMO to form reverse micelles, with and without added water, is studied using small-angle neutron scattering and simulations. A large-scale simulation is also used to investigate the self-assembly kinetics. GMO adsorption onto iron oxide is studied using depletion isotherms, neutron reflectometry, and simulations. The adsorbed amounts of GMO, and any added water, are determined experimentally, and the structures of the adsorbed films are investigated using reflectometry. Detailed fitting and analysis of the reflectometry measurements are presented, taking into account various factors such as surface roughness, and the presence of impurities. The reflectometry measurements are complemented by molecular dynamics simulations, and good consistency between both approaches is demonstrated by direct comparison of measured and simulated reflectivity and scattering length density profiles. The results of this analysis are that in dry systems, GMO adsorbs as self-assembled reverse micelles with some molecules adsorbing directly to the surface through the polar head groups, while in wet systems, the GMO is adsorbed onto a thin layer of water. Only at high surface coverage is some water trapped inside a reverse-micelle structure; at lower surface coverages, the GMO molecules associate primarily with the water layer, rather than self-assemble.
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Affiliation(s)
- Alexander J Armstrong
- ISIS Neutron and Muon Source, Didcot, UK
- Institute for Energy & Environmental Flows and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Rui F G Apóstolo
- EPCC, Bayes Centre, 47 Potterrow, Edinburgh EH8 9BT, Scotland, UK
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland, UK.
| | - Thomas M McCoy
- Institute for Energy & Environmental Flows and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | | | | | | | | | | | - Alexander F Routh
- Institute for Energy & Environmental Flows and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Philip J Camp
- School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland, UK.
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3
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Robson T, Shah DSH, Welbourn RJL, Phillips SR, Clifton LA, Lakey JH. Fully Aqueous Self-Assembly of a Gold-Nanoparticle-Based Pathogen Sensor. Int J Mol Sci 2023; 24:ijms24087599. [PMID: 37108766 PMCID: PMC10145400 DOI: 10.3390/ijms24087599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Revised: 04/11/2023] [Accepted: 04/18/2023] [Indexed: 04/29/2023] Open
Abstract
Surface plasmon resonance (SPR) is a very sensitive measure of biomolecular interactions but is generally too expensive for routine analysis of clinical samples. Here we demonstrate the simplified formation of virus-detecting gold nanoparticle (AuNP) assemblies on glass using only aqueous buffers at room temperature. The AuNP assembled on silanized glass and displayed a distinctive absorbance peak due to the localized SPR (LSPR) response of the AuNPs. Next, assembly of a protein engineering scaffold was followed using LSPR and a sensitive neutron reflectometry approach, which measured the formation and structure of the biological layer on the spherical AuNP. Finally, the assembly and function of an artificial flu sensor layer consisting of an in vitro-selected single-chain antibody (scFv)-membrane protein fusion was followed using the LSPR response of AuNPs within glass capillaries. In vitro selection avoids the need for separate animal-derived antibodies and allows for the rapid production of low-cost sensor proteins. This work demonstrates a simple approach to forming oriented arrays of protein sensors on nanostructured surfaces that uses (i) an easily assembled AuNP silane layer, (ii) self-assembly of an oriented protein layer on AuNPs, and (iii) simple highly specific artificial receptor proteins.
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Affiliation(s)
- Timothy Robson
- Biosciences Institute, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
| | - Deepan S H Shah
- Orla Protein Technologies Ltd., Biosciences Centre, International Centre for Life, Times Square, Newcastle upon Tyne NE1 4EP, UK
| | - Rebecca J L Welbourn
- ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 OQX, UK
| | - Sion R Phillips
- Orla Protein Technologies Ltd., Biosciences Centre, International Centre for Life, Times Square, Newcastle upon Tyne NE1 4EP, UK
| | - Luke A Clifton
- ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 OQX, UK
| | - Jeremy H Lakey
- Biosciences Institute, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
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Martin A, Jemmett PN, Howitt T, Wood MH, Burley AW, Cox LR, Dafforn TR, Welbourn RJL, Campana M, Skoda MW, Thompson JJ, Hussain H, Rawle JL, Carlà F, Nicklin CL, Arnold T, Horswell SL. Effect of Anionic Lipids on Mammalian Plasma Cell Membrane Properties. Langmuir 2023; 39:2676-2691. [PMID: 36757323 PMCID: PMC9948536 DOI: 10.1021/acs.langmuir.2c03161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/20/2022] [Revised: 01/19/2023] [Indexed: 06/18/2023]
Abstract
The effect of lipid composition on models of the inner leaflet of mammalian cell membranes has been investigated. Grazing incidence X-ray diffraction and X-ray and neutron reflectivity have been used to characterize lipid packing and solvation, while electrochemical and infrared spectroscopic methods have been employed to probe phase behavior in an applied electric field. Introducing a small quantity of the anionic lipid dimyristoylphosphatidylserine (DMPS) into bilayers of zwitterionic dimyristoylphosphatidylethanolamine (DMPE) results in a significant change in the bilayer response to an applied field: the tilt of the hydrocarbon chains increases before returning to the original tilt angle on detachment of the bilayer. Equimolar mixtures, with slightly closer chain packing, exhibit a similar but weaker response. The latter also tend to incorporate more solvent during this electrochemical phase transition, at levels similar to those of pure DMPS. Reflectivity measurements reveal greater solvation of lipid layers for DMPS > 30 mol %, matching the greater propensity for DMPS-rich bilayers to incorporate water. Taken together, the data indicate that the range of 10-35 mol % DMPS provides optimum bilayer properties (in flexibility and function as a barrier), which may explain why the DMPS content of cell membranes tends to be found within this range.
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Affiliation(s)
- Alexandra
L. Martin
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Philip N. Jemmett
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Thomas Howitt
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Mary H. Wood
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Andrew W. Burley
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Liam R. Cox
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Timothy R. Dafforn
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
| | - Rebecca J. L. Welbourn
- ISIS
Pulsed Neutron and Muon Source, Science
and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, OxfordshireOX11 0QX, U.K.
| | - Mario Campana
- ISIS
Pulsed Neutron and Muon Source, Science
and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, OxfordshireOX11 0QX, U.K.
| | - Maximilian W.
A. Skoda
- ISIS
Pulsed Neutron and Muon Source, Science
and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, OxfordshireOX11 0QX, U.K.
| | - Joseph J. Thompson
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
| | - Hadeel Hussain
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
| | - Jonathan L. Rawle
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
| | - Francesco Carlà
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
| | - Christopher L. Nicklin
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
| | - Thomas Arnold
- ISIS
Pulsed Neutron and Muon Source, Science
and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, OxfordshireOX11 0QX, U.K.
- Diamond
Light Source, Harwell Science and Innovation
Campus, Chilton, Didcot, OxfordshireOX11 0DE, U.K.
- European
Spallation Source ERIC PO Box 176, SE-221 00Lund, Sweden
- Department
of Chemistry, University of Bath, Claverton Down, BathBA2 7AY, U.K.
| | - Sarah L. Horswell
- School of
Chemistry and School of Biosciences, University of Birmingham, Edgbaston, BirminghamB15 2TT, U.K.
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5
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Wood MH, Rubio-Lara J, Armstrong AJ, Welbourn RJL. Adsorption Behavior of the Coenzyme NADH at the Carbon/Electrolyte Interface Determined by Neutron Reflectometry. Langmuir 2023; 39:668-678. [PMID: 36579816 DOI: 10.1021/acs.langmuir.2c03026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The adsorption behavior of β-nicotinamide adenine dinucleotide (NADH) at the carbon/electrolyte interface has been studied using a combination of neutron reflectometry (NR) and solution depletion isotherms. Coupling the NR technique with an electrochemical cell allowed in situ observation of the reversible adsorption and desorption of the molecule at the electrode surface over a range of applied potentials. The overall surface coverage was low (30-50%), suggesting adsorption only at specific defect sites on the surface. Isotherms conducted over a range of temperatures were used to extract thermodynamic parameters, which implied strong physisorption via electrostatic interactions. In addition, changes in the outermost layer of the carbon electrode were observed as the applied potential was varied, which were confirmed with ex situ X-ray reflectivity measurements (XRR). X-ray photoelectron spectroscopy (XPS) measurements of the carbon surface demonstrated the majority of carbon atoms were in an sp2 state.
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Affiliation(s)
- Mary H Wood
- Ecole Polytechnique Fédérale de Lausanne, 1015Lausanne, Switzerland
| | - Juan Rubio-Lara
- York Biomedical Research Institute, University of York, YorkYO10 5DD, U.K
| | | | - Rebecca J L Welbourn
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, DidcotOX11 0QX, U.K
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6
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Gerelli Y, Eriksson Skog A, Jephthah S, Welbourn RJL, Klechikov A, Skepö M. Correction to "Spontaneous Formation of Cushioned Model Membranes Promoted by an Intrinsically Disordered Protein". Langmuir 2022; 38:15888. [PMID: 36493364 PMCID: PMC9894529 DOI: 10.1021/acs.langmuir.2c03141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Indexed: 06/17/2023]
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7
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Armanious A, Gerelli Y, Micciulla S, Pace HP, Welbourn RJL, Sjöberg M, Agnarsson B, Höök F. Probing the Separation Distance between Biological Nanoparticles and Cell Membrane Mimics Using Neutron Reflectometry with Sub-Nanometer Accuracy. J Am Chem Soc 2022; 144:20726-20738. [DOI: 10.1021/jacs.2c08456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Antonius Armanious
- Department of Physics, Chalmers University of Technology, 41296Gothenburg, Sweden
| | - Yuri Gerelli
- Institut Max von Laue-Paul Langevin (ILL), 38042Grenoble, France
- Department of Life and Environmental Sciences, Università Politecnica delle Marche, 60131Ancona, Italy
| | | | - Hudson P. Pace
- Department of Physics, Chalmers University of Technology, 41296Gothenburg, Sweden
| | - Rebecca J. L. Welbourn
- ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, OxonOX11 0QX, United Kingdom
| | - Mattias Sjöberg
- Department of Physics, Chalmers University of Technology, 41296Gothenburg, Sweden
| | - Björn Agnarsson
- Department of Physics, Chalmers University of Technology, 41296Gothenburg, Sweden
| | - Fredrik Höök
- Department of Physics, Chalmers University of Technology, 41296Gothenburg, Sweden
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8
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Slastanova A, Campbell RA, Islas L, Welbourn RJL, R P Webster J, Vaccaro M, Chen M, Robles E, Briscoe WH. Interfacial complexation of a neutral amphiphilic 'tardigrade' co-polymer with a cationic surfactant: Transition from synergy to competition. J Colloid Interface Sci 2022; 606:1064-1076. [PMID: 34487929 DOI: 10.1016/j.jcis.2021.08.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2021] [Revised: 07/22/2021] [Accepted: 08/02/2021] [Indexed: 11/24/2022]
Abstract
HYPOTHESIS Neutral amphiphilic PEG-g-PVAc co-polymer (a "tardigrade" polymer consisting of a hydrophilic polyethylene glycol, PEG, backbone with hydrophobic polyvinyl acetate, PVAc, grafts) can form complexes at the air-water interface with cationic dodecyltrimethylammonium bromide (DTAB) via self-assembly. Compared to anionic SDS, cationic DTAB headgroups are expected to interact strongly with the negatively charged OH- groups from the partial dissociation of the PVAc grafts. We anticipate a transition from synergistic to competitive behaviour, which is expected to be dependent on the surfactant structural characteristics and concentration. EXPERIMENTS DTAB/PEG-g-PVAc mixtures were investigated using a combination of dynamic and equilibrium surface tension measurements, neutron reflectivity (NR) at the air-water interface, and foaming tests. We varied the concentrations of both the DTAB (0.05 to 5 critical micelle concentration, cmc) and that of PEG-g-PVAc (0.2 and 2 critical aggregation concentration, cac). FINDINGS Our results show that the interfacial interactions between DTAB and PEG-g-PVAc were both synergistic and antagonistic, depending sensitively on the surfactant concentration. At DTAB concentrations below its cmc, a pronounced cooperative adsorption behaviour was likely driven by the hydrophobic interactions between the DTAB tail and the PVAc grafts and the attraction between the DTAB headgroups and the partially dissociated -O- groups in the partially hydrolysed PVAc grafts, forming a mixed layer. This synergistic adsorption behaviour transitioned to a competitive adsorption behaviour at DTAB concentrations above its cmc, leading to polymer-surfactant partition, forming a "hanging" polymer layer underlying a surfactant monolayer at the interface. We postulate that DTAB/PEG-g-PVAc complexation in the bulk contributed to partial depletion of the mixture from the interface. We therefore consider this polymer/surfactant system to be a moderately interacting system at the air-water interface. No discernible differences in the foaming behaviour were observed between the DTAB/PEG-g-PVAc systems and the pure surfactant. Our results suggest that surfactant headgroup characteristics (particularly charges) were crucial in determining the structure and composition of polymer-surfactant complexes at the air-water interface, as well as the foamability and foam stability, whilst the coexistence of the synergistic and competitive adsorption behaviour is attributed to the unique architecture of the tardigrade polymer with amphiphilicity and partial charge, facilitating different surfactant-polymer interactions at different DTAB concentrations.
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Affiliation(s)
- Anna Slastanova
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
| | - Richard A Campbell
- Division of Pharmacy and Optometry, Faculty of Biology, Medicine and Health, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK; Institut Laue-Langevin, 71 Avenue des Martyrs, CS20156, Grenoble 38042, France
| | - Luisa Islas
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
| | - Rebecca J L Welbourn
- ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - John R P Webster
- ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - Mauro Vaccaro
- Procter & Gamble, Temselaan 100, 1853 Strombeek-Bever, Brussels, Belgium
| | - Meng Chen
- Procter & Gamble Beijing Innovation Centre, 35 Yu'an Rd, Shunyi District, Beijing, China
| | - Eric Robles
- Household Care Analytical, Procter & Gamble Newcastle Innovation Centre, Whitley Road, Longbenton, Newcastle NE12 9TS, UK
| | - Wuge H Briscoe
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
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9
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Cavaye H, Welbourn RJL, Gluschke JG, Hughes P, Nguyen KV, Micolich AP, Meredith P, Mostert AB. Systematic in situ hydration neutron reflectometry study on Nafion thin films. Phys Chem Chem Phys 2022; 24:28554-28563. [DOI: 10.1039/d2cp03067e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Nafion thin films continuously form an increasing number of lamellae layers (high Q peak) near a substrate surface with increasing hydration content, as opposed to exhibiting a phase transition like change.
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Affiliation(s)
- Hamish Cavaye
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Science and Technology Facilities Council, Didcot, OX11 0QX, UK
| | - Rebecca J. L. Welbourn
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Science and Technology Facilities Council, Didcot, OX11 0QX, UK
| | - Jan G. Gluschke
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - Paul Hughes
- Centre for Nano Health, College of Engineering, Swansea University, Swansea SA2 8PP, UK
| | - Ky V. Nguyen
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - Adam P. Micolich
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - Paul Meredith
- Department of Physics, Swansea University, Singleton Park, SA2 8PP, Wales, UK
- School of Mathematics and Physics, University of Queensland, St Lucia Campus, Brisbane Queensland 4072, Australia
| | - A. Bernardus Mostert
- Department of Chemistry, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
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10
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Gibson CP, Litwinowicz MA, Tellam JP, Welbourn RJL, Skoda MWA, Claussen J, Thompson RL. Water-Resistant Surface Modification of Hydrophobic Polymers with Water-Soluble Surfactant Additives. Polymers (Basel) 2021; 13:polym13193407. [PMID: 34641221 PMCID: PMC8512660 DOI: 10.3390/polym13193407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 09/28/2021] [Accepted: 09/29/2021] [Indexed: 11/16/2022] Open
Abstract
Water-soluble nonionic surfactant, pentaethylene glycol monododecyl ether, C12E5, spontaneously blooms to the surface of spin-cast hydrophobic polyisoprenes, generating hydrophilic surfaces. This system provides a simple model for hydrophilic chemical modification of rubbery polymers that demonstrates surprisingly rich, complex, and unexpected behaviour. The vertical depth profiles were quantified using neutron reflectometry (NR) using a novel procedure to account for undulations in the film thickness. Surface properties were characterized using contact angle analysis and atomic force microscopy (AFM). Despite the low surface tension of the toluene solvent used in film preparation and the low surface energy of the polyisoprene (PI) matrix, NR depth profiles revealed clear evidence of surfactant segregation. This surface layer was typically thicker than a monolayer, but incomplete, yet was remarkably stable with respect to dissolution, even when exposed to hundreds of thousands of times the volume of water required to dissolve all the surfactant on the surface. Despite the apparent resistance to removal from the surface, water exposure does alter the subsequent wettability of the surface, with a hydrophilic-to-hydrophobic transition occurring after rinsing. Complementary AFM images of these C12E5/cis-PI films showed unexpected strand-like features on the surface of the film, which we attribute to a non-uniform lateral distribution of some of the surfactant. This surface structure becomes more evident after rinsing, and it appears that there are two distinct populations of surfactant on the PI film surface. We conclude that some of the bloomed surfactant exists as layers, which are relatively inert with respect to rinsing or surface modification, and some is laterally inhomogeneous. This latter population is primarily responsible for surface wetting behaviour but is not detected by specular NR.
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Affiliation(s)
- Colin P. Gibson
- Department of Chemistry, Durham University, Durham DH1 3LE, UK; (C.P.G.); (M.A.L.)
| | | | - James P. Tellam
- STFC ISIS Neutron and Muon Source, Rutherford Appleton Laboratories, Didcot OX11 0QX, UK; (J.P.T.); (R.J.L.W.); (M.W.A.S.)
| | - Rebecca J. L. Welbourn
- STFC ISIS Neutron and Muon Source, Rutherford Appleton Laboratories, Didcot OX11 0QX, UK; (J.P.T.); (R.J.L.W.); (M.W.A.S.)
| | - Maximilian W. A. Skoda
- STFC ISIS Neutron and Muon Source, Rutherford Appleton Laboratories, Didcot OX11 0QX, UK; (J.P.T.); (R.J.L.W.); (M.W.A.S.)
| | - Jan Claussen
- Procter & Gamble, German Innovation Center, Sulzbacher Str. 40, 65824 Schwalbach am Taunus, Germany;
| | - Richard L. Thompson
- Department of Chemistry, Durham University, Durham DH1 3LE, UK; (C.P.G.); (M.A.L.)
- Correspondence: ; Tel.: +44-191-334-2139
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11
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Boyd H, Gonzalez-Martinez JF, Welbourn RJL, Ma K, Li P, Gutfreund P, Klechikov A, Arnebrant T, Barker R, Sotres J. Effect of nonionic and amphoteric surfactants on salivary pellicles reconstituted in vitro. Sci Rep 2021; 11:12913. [PMID: 34155330 PMCID: PMC8217253 DOI: 10.1038/s41598-021-92505-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 06/11/2021] [Indexed: 11/15/2022] Open
Abstract
Surfactants are important components of oral care products. Sodium dodecyl sulfate (SDS) is the most common because of its foaming properties, taste and low cost. However, the use of ionic surfactants, especially SDS, is related to several oral mucosa conditions. Thus, there is a high interest in using non-ionic and amphoteric surfactants as they are less irritant. To better understand the performance of these surfactants in oral care products, we investigated their interaction with salivary pellicles i.e., the proteinaceous films that cover surfaces exposed to saliva. Specifically, we focused on pentaethylene glycol monododecyl ether (C12E5) and cocamidopropyl betaine (CAPB) as model nonionic and amphoteric surfactants respectively, and investigated their interaction with reconstituted salivary pellicles with various surface techniques: Quartz Crystal Microbalance with Dissipation, Ellipsometry, Force Spectroscopy and Neutron Reflectometry. Both C12E5 and CAPB were gentler on pellicles than SDS, removing a lower amount. However, their interaction with pellicles differed. Our work indicates that CAPB would mainly interact with the mucin components of pellicles, leading to collapse and dehydration. In contrast, exposure to C12E5 had a minimal effect on the pellicles, mainly resulting in the replacement/solubilisation of some of the components anchoring pellicles to their substrate.
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Affiliation(s)
- Hannah Boyd
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Juan F Gonzalez-Martinez
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Rebecca J L Welbourn
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Kun Ma
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Peixun Li
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Philipp Gutfreund
- Institut Laue Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
| | - Alexey Klechikov
- Institut Laue Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
- Department of Physics and Astronomy, Uppsala University, 75120, Uppsala, Sweden
| | - Thomas Arnebrant
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Robert Barker
- School of Physical Sciences, University of Kent, Canterbury, CT2 7NZ, UK
| | - Javier Sotres
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden.
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12
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Armstrong AJ, McCoy TM, Welbourn RJL, Barker R, Rawle JL, Cattoz B, Dowding PJ, Routh AF. Towards a neutron and X-ray reflectometry environment for the study of solid-liquid interfaces under shear. Sci Rep 2021; 11:9713. [PMID: 33958678 PMCID: PMC8102579 DOI: 10.1038/s41598-021-89189-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 04/12/2021] [Indexed: 11/14/2022] Open
Abstract
A novel neutron and X-ray reflectometry sample environment is presented for the study of surface-active molecules at solid–liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide–dodecane interface at a shear rate of \documentclass[12pt]{minimal}
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\begin{document}$$7.0\times {}10^{2}$$\end{document}7.0×102\documentclass[12pt]{minimal}
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\begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of \documentclass[12pt]{minimal}
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\begin{document}$$7.0\times {}10^{2}$$\end{document}7.0×102\documentclass[12pt]{minimal}
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\begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be \documentclass[12pt]{minimal}
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\begin{document}$$24.3^{+9.9}_{-10.2}$$\end{document}24.3-10.2+9.9 Å under direct shear at \documentclass[12pt]{minimal}
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\begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 and \documentclass[12pt]{minimal}
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\begin{document}$$25.8^{+4.4}_{-5.2}$$\end{document}25.8-5.2+4.4 Å when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at \documentclass[12pt]{minimal}
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Affiliation(s)
- Alexander J Armstrong
- BP Institute and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Thomas M McCoy
- BP Institute and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | | | - Robert Barker
- School of Physical Sciences, University of Kent, Ingram Building, Canterbury, UK
| | - Jonathan L Rawle
- Diamond Light Source Ltd, Diamond House, Harwell Campus, Didcot, OX11 0DE, UK
| | | | | | - Alexander F Routh
- BP Institute and Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK.
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13
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Allen FJ, Truscott CL, Welbourn RJL, Clarke SM. Influence of surfactants on a pre-adsorbed cationic layer: Removal and modification. J Colloid Interface Sci 2021; 588:427-435. [PMID: 33429339 DOI: 10.1016/j.jcis.2020.12.047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 12/15/2020] [Accepted: 12/16/2020] [Indexed: 11/29/2022]
Abstract
Removal of organic species from solid surfaces is a crucial process. The use of oppositely charged surfactants provides a potential method for enhanced removal. Neutron reflectometry has been used to investigate the complex behaviour of a pre-adsorbed and tenacious layer of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on a mica surface, during exposure to different organic species in solution. The anionic surfactant sodium dodecylsulfate (SDS) was shown to be able to remove the cationic layer, but only if anionic micelles were present in solution. To facilitate comparison with the behaviour of a non-ionic surfactant, the direct adsorption of pentaethylene glycol monododecyl ether (C12E5) to mica was also studied; low surface coverage adsorption was seen at the critical micelle concentration and above. C12E5 was then found not to remove the cationic layer, but did include into the layer to some degree. The presence of cationic surfactant on the mica was however shown to significantly modify the adsorption behaviour of the non-ionic surfactant.
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Affiliation(s)
- Finian J Allen
- Department of Chemistry and BP Institute, University of Cambridge, Cambridge, UK.
| | - Chris L Truscott
- Department of Chemistry and BP Institute, University of Cambridge, Cambridge, UK.
| | - Rebecca J L Welbourn
- ISIS Pulsed Neutron Facility, Harwell Science and Innovation Campus, STFC, Rutherford Appleton Laboratory, Didcot, Oxon, UK.
| | - Stuart M Clarke
- Department of Chemistry and BP Institute, University of Cambridge, Cambridge, UK.
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14
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Boyd H, Gonzalez-Martinez JF, Welbourn RJL, Gutfreund P, Klechikov A, Robertsson C, Wickström C, Arnebrant T, Barker R, Sotres J. A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films. J Colloid Interface Sci 2020; 584:660-668. [PMID: 33198975 DOI: 10.1016/j.jcis.2020.10.124] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 10/06/2020] [Accepted: 10/27/2020] [Indexed: 01/01/2023]
Abstract
HYPOTHESIS Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure. EXPERIMENTS Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry. FINDINGS Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.
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Affiliation(s)
- Hannah Boyd
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden.
| | - Juan F Gonzalez-Martinez
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Rebecca J L Welbourn
- ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - Philipp Gutfreund
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble 38000, France
| | - Alexey Klechikov
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble 38000, France; Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| | - Carolina Robertsson
- Department of Oral Biology and Pathology & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Claes Wickström
- Department of Oral Biology and Pathology & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Thomas Arnebrant
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Robert Barker
- School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK
| | - Javier Sotres
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden.
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15
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Pabois O, Ziolek RM, Lorenz CD, Prévost S, Mahmoudi N, Skoda MWA, Welbourn RJL, Valero M, Harvey RD, Grundy MML, Wilde PJ, Grillo I, Gerelli Y, Dreiss CA. Morphology of bile salts micelles and mixed micelles with lipolysis products, from scattering techniques and atomistic simulations. J Colloid Interface Sci 2020; 587:522-537. [PMID: 33189321 DOI: 10.1016/j.jcis.2020.10.101] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 10/23/2020] [Accepted: 10/25/2020] [Indexed: 12/17/2022]
Abstract
HYPOTHESES Bile salts (BS) are biosurfactants released into the small intestine, which play key and contrasting roles in lipid digestion: they adsorb at interfaces and promote the adsorption of digestive enzymes onto fat droplets, while they also remove lipolysis products from that interface, solubilising them into mixed micelles. Small architectural variations on their chemical structure, specifically their bile acid moiety, are hypothesised to underlie these conflicting functionalities, which should be reflected in different aggregation and solubilisation behaviour. EXPERIMENTS The micellisation of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ by one hydroxyl group on the bile acid moiety, was assessed by pyrene fluorescence spectroscopy, and the morphology of aggregates formed in the absence and presence of fatty acids (FA) and monoacylglycerols (MAG) - typical lipolysis products - was resolved by small-angle X-ray/neutron scattering (SAXS, SANS) and molecular dynamics simulations. The solubilisation by BS of triacylglycerol-incorporating liposomes - mimicking ingested lipids - was studied by neutron reflectometry and SANS. FINDINGS Our results demonstrate that BS micelles exhibit an ellipsoidal shape. NaTDC displays a lower critical micellar concentration and forms larger and more spherical aggregates than NaTC. Similar observations were made for BS micelles mixed with FA and MAG. Structural studies with liposomes show that the addition of BS induces their solubilisation into mixed micelles, with NaTDC displaying a higher solubilising capacity.
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Affiliation(s)
- Olivia Pabois
- Institut Laue-Langevin, Grenoble 38000, France; Institute of Pharmaceutical Science, King's College London, London SE1 9NH, United Kingdom.
| | - Robert M Ziolek
- Department of Physics, King's College London, London WC2R 2LS, United Kingdom.
| | - Christian D Lorenz
- Department of Physics, King's College London, London WC2R 2LS, United Kingdom.
| | | | - Najet Mahmoudi
- ISIS Neutron & Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
| | - Maximilian W A Skoda
- ISIS Neutron & Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
| | - Rebecca J L Welbourn
- ISIS Neutron & Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
| | - Margarita Valero
- Department of Physical Chemistry, University of Salamanca, Salamanca 37007, Spain.
| | - Richard D Harvey
- Department of Pharmaceutical Chemistry, University of Vienna, Vienna A-1090, Austria.
| | | | - Peter J Wilde
- Quadram Institute Bioscience, Norwich Research Park, Norwich NR4 7UQ, United Kingdom.
| | | | - Yuri Gerelli
- Institut Laue-Langevin, Grenoble 38000, France; Department of Life and Environmental Sciences, Polytechnic University of Marche, Ancona 60131, Italy.
| | - Cécile A Dreiss
- Institute of Pharmaceutical Science, King's College London, London SE1 9NH, United Kingdom.
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16
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Gerelli Y, Eriksson Skog A, Jephthah S, Welbourn RJL, Klechikov A, Skepö M. Spontaneous Formation of Cushioned Model Membranes Promoted by an Intrinsically Disordered Protein. Langmuir 2020; 36:3997-4004. [PMID: 32212610 PMCID: PMC7311080 DOI: 10.1021/acs.langmuir.0c00120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
In this article, it is shown that by exposing commonly used lipids for biomembrane mimicking studies, to a solution containing the histidine-rich intrinsically disordered protein histatin 5, a protein cushion spontaneously forms underneath the bilayer. The underlying mechanism is attributed to have an electrostatic origin, and it is hypothesized that the observed behavior is due to proton charge fluctuations promoting attractive electrostatic interactions between the positively charged proteins and the anionic surfaces, with concomitant counterion release. Hence, we anticipate that this novel "green" approach of forming cushioned bilayers can be an important tool to mimic the cell membrane without the disturbance of the solid substrate, thereby achieving a further understanding of protein-cell interactions.
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Affiliation(s)
- Yuri Gerelli
- Partnership
for Soft Condensed Matter, Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
- Department
of Life and Environmental Sciences, Polytechnic
University of Marche, 60131 Ancona, Italy
| | - Amanda Eriksson Skog
- Partnership
for Soft Condensed Matter, Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
- Division
of Theoretical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Stephanie Jephthah
- Partnership
for Soft Condensed Matter, Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
| | - Rebecca J. L. Welbourn
- ISIS
Pulsed Neutron Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, STFC, Didcot, Oxon OX11 0QX, United Kingdom
| | - Alexey Klechikov
- Department
of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-75120 Uppsala, Sweden
| | - Marie Skepö
- Division
of Theoretical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
- LINXS—Lund
Institute of Advanced Neutron and X-ray Science, Scheelevägen 19, SE-233 70 Lund, Sweden
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17
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Wood MH, Humphreys EK, Welbourn RJL. Structural Changes in Adsorbed Cytochrome c upon Applied Potential Characterized by Neutron Reflectometry. Langmuir 2019; 35:6055-6063. [PMID: 30966748 DOI: 10.1021/acs.langmuir.9b00691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The structural behavior of an electron-transfer protein, cytochrome c, at the 316L stainless steel electrode/aqueous interface was investigated over a range of applied potentials using neutron reflectometry supported by solution depletion isotherms, X-ray reflectometry, and quartz crystal microbalance measurements. A custom-made electrochemical cell allowed in situ observation of the adsorbed protein across a range of applied potentials; models fitted to the NR data showed a compact inner protein layer at the metal/electrolyte interface and a further thicker but highly diffuse layer that could be removed by rinsing. The overall amount adsorbed was found to be strongly dependent on the applied potential and buffer pH. Subtle but significant changes in the structure of the adsorbed protein layer were seen as the potential was swept between ±0.40 V, reflecting changing attractive/repulsive interactions between the protein's charged side groups and the surface. At greater applied potentials, irreversible changes in the stainless steel film structure were also observed and attributed to deuterium absorption into the metal.
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Affiliation(s)
- Mary H Wood
- School of Chemistry , University of Birmingham , Birmingham B15 2TT , U.K
| | - Elizabeth K Humphreys
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB3 1EW , U.K
| | - Rebecca J L Welbourn
- ISIS Neutron & Muon Source, Rutherford Appleton Laboratory , Didcot OX11 0QX , U.K
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18
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Allen FJ, Truscott CL, Gutfreund P, Welbourn RJL, Clarke SM. Potassium, Calcium, and Magnesium Bridging of AOT to Mica at Constant Ionic Strength. Langmuir 2019; 35:5753-5761. [PMID: 30950624 DOI: 10.1021/acs.langmuir.9b00533] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The bridging effect of a series of common cations between the anionic mica surface and the AOT anion has been studied in a condition of constant ionic strength and surfactant concentration. It was found that sodium ions did not show any bridging effect in this system; however, calcium, magnesium, and potassium all caused adsorption of the organic to the mica surface. The concentrations at which bridging occurred was probed, revealing that only a very low bridging cation concentration was required for binding. The bridged layer stability was also investigated, and the interaction was shown to be a weak one, with the bound layer in equilibrium with the species in the bulk and easily removed. Even maintaining ionic strength and bridging ion concentration was not sufficient to retain the layer when the free organic in solution was removed.
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Affiliation(s)
- Finian J Allen
- Department of Chemistry and BP Institute , University of Cambridge , Cambridge , Cambs CB2 1EW , U.K
| | - Chris L Truscott
- Department of Chemistry and BP Institute , University of Cambridge , Cambridge , Cambs CB2 1EW , U.K
| | - Philipp Gutfreund
- Institut Laue Langevin , 71 avenue des Martyrs , Grenoble 38000 , France
| | - Rebecca J L Welbourn
- ISIS Pulsed Neutron Facility, Rutherford Appleton Laboratory , Harwell Science and Innovation Campus, STFC , Didcot , Oxon OX11 0QX , U.K
| | - Stuart M Clarke
- Department of Chemistry and BP Institute , University of Cambridge , Cambridge , Cambs CB2 1EW , U.K
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19
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Li Z, Pan F, Li R, Pambou E, Hu X, Ruane S, Ciumac D, Li P, Welbourn RJL, Webster JRP, Bishop SM, Narwal R, van der Walle CF, Lu JR. Coadsorption of a Monoclonal Antibody and Nonionic Surfactant at the SiO 2/Water Interface. ACS Appl Mater Interfaces 2018; 10:44257-44266. [PMID: 30500160 DOI: 10.1021/acsami.8b16832] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
During the formulation of therapeutic monoclonal antibodies (mAbs), nonionic surfactants are commonly added to attenuate structural rearrangement caused by adsorption/desorption at interfaces during processing, shipping, and storage. We examined the adsorption of a mAb (COE-3) at the SiO2/water interface in the presence of pentaethylene glycol monododecyl ether (C12E5), polysorbate 80 (PS80-20EO), and a polysorbate 80 analogue with seven ethoxylates (PS80-7EO). Spectroscopic ellipsometry was used to follow COE-3 dynamic adsorption, and neutron reflection was used to determine interfacial structure and composition. Neither PS80-20EO nor C12E5 had a notable affinity for COE-3 or the interface under the conditions studied and thus did not prevent COE-3 adsorption. In contrast, PS80-7EO did coadsorb but did not influence the dynamic process or the equilibrated amount of absorbed COE-3. Near equilibration, COE-3 underwent structural rearrangement and PS80-7EO started to bind the COE-3 interfacial layer and subsequently formed a well-defined surfactant bilayer via self-assembly. The resultant interfacial layer comprised an inner mAb layer of about 70 Å thickness and an outer surfactant layer of a further 70 Å, with distinct transitional regions across the mAb-surfactant and surfactant-bulk water boundaries. Once formed, such interfacial layers were very robust and worked to prevent further mAb adsorption, desorption, and structural rearrangement. Such robust interfacial layers could be anticipated to exist for formulated mAbs stored in type II glass vials; further research is required to understand the behavior of these layers for siliconized glass syringes.
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Affiliation(s)
- Zongyi Li
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Fang Pan
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Ruiheng Li
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Elias Pambou
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Xuzhi Hu
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Sean Ruane
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Daniela Ciumac
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
| | - Peixun Li
- ISIS Neutron Facility , STFC , Chilton , Didcot OX11 0QZ , U.K
| | | | | | - Steven M Bishop
- MedImmune LLC , Gaithersburg , Maryland 20878 , United States
| | | | | | - Jian Ren Lu
- Biological Physics Laboratory, School of Physics and Astronomy , University of Manchester , Oxford Road, Schuster Building , Manchester M13 9PL , U.K
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20
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Dugger JW, Li W, Chen M, Long TE, Welbourn RJL, Skoda MWA, Browning JF, Kumar R, Lokitz BS. Nanoscale Resolution of Electric-field Induced Motion in Ionic Diblock Copolymer Thin Films. ACS Appl Mater Interfaces 2018; 10:32678-32687. [PMID: 30180545 DOI: 10.1021/acsami.8b11220] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Understanding the responses of ionic block copolymers to applied electric fields is crucial when targeting applications in areas such as energy storage, microelectronics, and transducers. This work shows that the identity of counterions in ionic diblock copolymers substantially affects their responses to electric fields, demonstrating the importance of ionic species for materials design. In situ neutron reflectometry measurements revealed that thin films containing imidazolium based cationic diblock copolymers, tetrafluoroborate counteranions led to film contraction under applied electric fields, while bromide counteranions drove expansion under similar field strengths. Coarse-grained molecular dynamics simulations were used to develop a fundamental understanding of these responses, uncovering a nonmonotonic trend in thickness change as a function of field strength. This behavior was attributed to elastic responses of microphase separated diblock copolymer chains resulting from variations in interfacial tension of polymer-polymer interfaces due to the redistribution of counteranions in the presence of electric fields.
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Affiliation(s)
- Jason W Dugger
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Wei Li
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Mingtao Chen
- Macromolecules Innovation Institute (MII), Department of Chemistry , Virginia Polytechnic Institute and State University , Blacksburg , Virginia 24061 , United States
| | - Timothy E Long
- Macromolecules Innovation Institute (MII), Department of Chemistry , Virginia Polytechnic Institute and State University , Blacksburg , Virginia 24061 , United States
| | - Rebecca J L Welbourn
- ISIS , Science and Technology Facilities Council, Rutherford Appleton Laboratory , Didcot , OX11 0QX , U.K
| | - Maximilian W A Skoda
- ISIS , Science and Technology Facilities Council, Rutherford Appleton Laboratory , Didcot , OX11 0QX , U.K
| | - James F Browning
- Neutron Scattering Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Rajeev Kumar
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Computational Sciences and Engineering Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Bradley S Lokitz
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
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21
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Wood MH, Wood TJ, Welbourn RJL, Poon J, Madden DC, Clarke SM. An X-ray and Neutron Reflectometry Study of Iron Corrosion in Seawater. Langmuir 2018; 34:5990-6002. [PMID: 29719961 DOI: 10.1021/acs.langmuir.8b00378] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The corrosive breakdown of thin iron films supported on silicon substrates under a number of conditions is presented-in particular to understand better how iron, and hence ferritic steel, behaves in a salty water environment. A combination of X-ray and neutron reflectometry was used to monitor the structures of both metal and oxide surface layers and also organic corrosion inhibitors adsorbed at the iron/aqueous interface. A range of behavior in seawater was observed, including complete dissolution and void formation under the metal surface. Importantly, two simple treatments-UV/ozone or soaking in ultrapure water-were found to significantly protect the iron surface for considerable lengths of time, although evidence of pitting corrosion began after around 10 days. The underlying causes of the efficacies of these treatments were further investigated using X-ray photoelectron spectroscopy. In addition, three potential corrosion inhibitors were investigated: (i) dodecyltrimethylammonium bromide (DTAB) demonstrated no ability to protect the surface; (ii) sodium dodecyl sulfate (SDS) appeared to accelerate corrosion; and (iii) bis(2-ethylhexyl)phosphate showed an impressive level of protection (the neutron reflectometry results indicated a thick diffuse layer of surfactant of 23% surface coverage). These findings have been interpreted in terms of preferential inhibitor adsorption at cathodic and anodic surface sites (depending on the nature of the inhibitor).
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Affiliation(s)
- Mary H Wood
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , U.K
| | - Thomas J Wood
- ISIS Neutron & Muon Source, Rutherford Appleton Laboratory , Didcot OX11 0QX , U.K
| | - Rebecca J L Welbourn
- ISIS Neutron & Muon Source, Rutherford Appleton Laboratory , Didcot OX11 0QX , U.K
| | - Jeffrey Poon
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , U.K
| | - David C Madden
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , U.K
| | - Stuart M Clarke
- Department of Chemistry , University of Cambridge , Lensfield Road , Cambridge CB2 1EW , U.K
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Xu H, Li P, Ma K, Welbourn RJL, Penfold J, Roberts DW, Thomas RK, Petkov JT. Adsorption of Methyl Ester Sulfonate at the Air-Water Interface: Can Limitations in the Application of the Gibbs Equation be Overcome by Computer Purification? Langmuir 2017; 33:9944-9953. [PMID: 28871785 DOI: 10.1021/acs.langmuir.7b02725] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We describe a new laboratory synthesis of the α-methyl ester sulfonates based on direct sulfonation of the methyl ester by SO3 introduced from the vapor phase. This was used to synthesize a chain deuterated sample of αC14MES, which was then used to measure the surface excess of αC14MES directly at the air/water interface over a wide range of concentration using neutron reflection. The adsorption isotherm could be fitted to an empirical equation close to a Langmuir isotherm and gave a limiting surface excess of (3.4 ± 0.1) × 10-6 mol m-2 in the absence of added electrolyte. The neutron-measured surface excesses were combined with the integrated Gibbs equation to fit the variation in surface tension with concentration (σ-ln C curve). The fit was exact provided that we used a prefactor consistent with the counterion at the surface being an impurity divalent ion, as has previously been found for sodium diethylhexylsulfosuccinate (aerosol OT or AOT) and various perfluorooctanoates. The critical micelle concentration (CMC) was determined from this fit to be 2.4 ± 0.3 mM in the absence of electrolyte. In the presence of 100 mM NaCl, this contamination was suppressed and the σ-ln C curve could be fitted using the integrated Gibbs equation with the expected prefactor of 1. The new data were used to reinterpret measurements by Danov et al. on an unpurified sample of αC14MES for which computer refinement was used to try to eliminate the effects of the impurities.
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Affiliation(s)
- Hui Xu
- KLK Oleo, SDN BHD, Menara KLK, Muliara Damansara, 47810 Petaling, Jaya Selanger, Malaysia
| | - Peixun Li
- Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
| | - Kun Ma
- Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
| | | | - Jeffrey Penfold
- Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
- Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | | | - Robert K Thomas
- Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Jordan T Petkov
- KLK Oleo, SDN BHD, Menara KLK, Muliara Damansara, 47810 Petaling, Jaya Selanger, Malaysia
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Allen FJ, Griffin LR, Alloway RM, Gutfreund P, Lee SY, Truscott CL, Welbourn RJL, Wood MH, Clarke SM. An Anionic Surfactant on an Anionic Substrate: Monovalent Cation Binding. Langmuir 2017; 33:7881-7888. [PMID: 28731354 DOI: 10.1021/acs.langmuir.7b01837] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Neutron reflectometry has been used to study the adsorption of the anionic surfactant bis(2-ethylhexyl) sulfosuccinate cesium salt on the anionic surface of mica. Evidence of significant adsorption is reported. The adsorption is reversible and changes little with pH. This unexpected adsorption behavior of an anionic molecule on an anionic surface is discussed in terms of recent models for surfactant adsorption such as cation bridging, where adsorption has been reported with the divalent ion calcium but not previously observed with monovalent ions.
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Affiliation(s)
- Finian J Allen
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | - Lucy R Griffin
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | - Richard M Alloway
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | | | - Seung Yeon Lee
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | - Chris L Truscott
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | - Rebecca J L Welbourn
- ISIS Pulsed Neutron Facility, Harwell Science and Innovation Campus, STFC, Rutherford Appleton Laboratory , Didcot, Oxon OX11 0QX, United Kingdom
| | - Mary H Wood
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
| | - Stuart M Clarke
- Department of Chemistry and BP Institute, University of Cambridge , Cambridge CB2 1EW, United Kingdom
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Welbourn RJL, Bartholomew F, Gutfreund P, Clarke SM. Neutron Reflectometry of an Anionic Surfactant at the Solid-Liquid Interface under Shear. Langmuir 2017; 33:5982-5990. [PMID: 28530832 DOI: 10.1021/acs.langmuir.7b00530] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Neutron reflectometry with in situ rheology is used to measure the shear response of an adsorbed anionic surfactant (sodium bis(2-ethylhexyl) sulfosuccinate, AOT) at the alumina-water interface. A low surfactant concentration is measured where a single bilayer adsorbs at the interface as well as a higher concentration where a multilamellar structure forms. The low concentration structure does not change with the imposed shear (oscillatory or steady). However, the lamellar phase shows a loss of structure under both steady and oscillatory shear. There are differences between the steady and oscillatory cases, which are discussed, with both showing a strong dependence on the strain amplitude.
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Affiliation(s)
- Rebecca J L Welbourn
- BP Institute and Department of Chemistry, University of Cambridge , Madingley Rise, Madingley Road, Cambridge, U.K
| | - Felicity Bartholomew
- BP Institute and Department of Chemistry, University of Cambridge , Madingley Rise, Madingley Road, Cambridge, U.K
| | | | - Stuart M Clarke
- BP Institute and Department of Chemistry, University of Cambridge , Madingley Rise, Madingley Road, Cambridge, U.K
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Wood MH, Casford MT, Steitz R, Zarbakhsh A, Welbourn RJL, Clarke SM. Comparative Adsorption of Saturated and Unsaturated Fatty Acids at the Iron Oxide/Oil Interface. Langmuir 2016; 32:534-540. [PMID: 26707597 DOI: 10.1021/acs.langmuir.5b04435] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.
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Affiliation(s)
- Mary H Wood
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - M T Casford
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - R Steitz
- Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, Berlin 14109, Germany
| | - A Zarbakhsh
- School of Biological and Chemical Science, Queen Mary, University of London , Joseph Priestly Building, Mile End Road, London WC1E 7HU, United Kingdom
| | - R J L Welbourn
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
| | - Stuart M Clarke
- Department of Chemistry and BP Institute, Cambridge University , Cambridge, CB2 1EW, United Kingdom
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Humphreys EK, Allan PK, Welbourn RJL, Youngs TGA, Soper AK, Grey CP, Clarke SM. A Neutron Diffraction Study of the Electrochemical Double Layer Capacitor Electrolyte Tetrapropylammonium Bromide in Acetonitrile. J Phys Chem B 2015; 119:15320-33. [DOI: 10.1021/acs.jpcb.5b08248] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Elizabeth K. Humphreys
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Phoebe K. Allan
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
- Gonville and Caius College, Trinity
Street, Cambridge CB2 1TA, United Kingdom
| | - Rebecca J. L. Welbourn
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
- BP Institute, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, United Kingdom
| | - Tristan G. A. Youngs
- ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX, United Kingdom
| | - Alan K. Soper
- ISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX, United Kingdom
| | - Clare P. Grey
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Stuart M. Clarke
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
- BP Institute, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, United Kingdom
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Abstract
Polarized neutron reflectometry has been used to investigate the detailed adsorption behavior and corrosion inhibition mechanism of two surfactants on a nickel surface under acidic conditions. Both the corrosion of the nickel surface and the structure of the adsorbed surfactant layer could be monitored in situ by the use of different solvent contrasts. Layer thicknesses and roughnesses were evaluated over a range of pH values, showing distinctly the superior corrosion inhibition of one negatively charged surfactant (sodium dodecyl sulfate) compared to a positively charged example (dodecyl trimethylammonium bromide) due to its stronger binding interaction with the surface. It was found that adequate corrosion inhibition occurs at significantly less than full surface coverage.
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Affiliation(s)
- Mary H Wood
- †Department of Chemistry and BP Institute, Cambridge University, Cambridge CB2 1EW, U.K
| | - Rebecca J L Welbourn
- †Department of Chemistry and BP Institute, Cambridge University, Cambridge CB2 1EW, U.K
| | - Ali Zarbakhsh
- ‡School of Biological and Chemical Science, Queen Mary, University of London, Joseph Priestly Building, Mile End Road, London, U.K
| | | | - Stuart M Clarke
- †Department of Chemistry and BP Institute, Cambridge University, Cambridge CB2 1EW, U.K
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Welbourn RJL, Lee SY, Gutfreund P, Hughes A, Zarbakhsh A, Clarke SM. Neutron reflection study of the adsorption of the phosphate surfactant NaDEHP onto alumina from water. Langmuir 2015; 31:3377-84. [PMID: 25761046 DOI: 10.1021/la504837s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The adsorption of a phosphorus analogue of the surfactant AOT, sodium bis(2-ethylhexyl) phosphate (NaDEHP), at the water/alumina interface is described. The material is found to adsorb as an essentially water-free bilayer from neutron reflection measurements. This is similar to the behavior of AOT under comparable conditions, although AOT forms a thicker, more hydrated layer. The NaDEHP shows rather little variation with added salt, but a small thickening of the layer on increasing the pH, in contrast to the behavior of AOT.
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Affiliation(s)
- Rebecca J L Welbourn
- †BP Institute and Department of Chemistry, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, UK
| | - Seung Yeon Lee
- †BP Institute and Department of Chemistry, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, UK
| | | | - Arwel Hughes
- §ISIS, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, UK
| | | | - Stuart M Clarke
- †BP Institute and Department of Chemistry, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, UK
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