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Instruments / Technical Area	Publication Details	Published
I07-Surface & interface diffraction	Structure of the electrochemical interface: Ag(hkl) in an alkaline electrolyte Angeline Kasina , Elizabeth Cocklin , Sarah Horswell , Yvonne Grunder , Christopher A. Lucas The Journal Of Physical Chemistry C 9 DOI: 10.1021/acs.jpcc.4c03154 Diamond Proposal Number(s): [9653, 12715, 22272] Open Access Show Abstract ▼ Abstract: The structure of the electrochemical double layer at the interface between Ag(hkl) electrodes and 0.1 M NaOH electrolyte has been probed using in situ surface X-ray diffraction (SXRD) measurements. The three low-index Ag(hkl) surfaces were prepared and characterized under ultra-high vacuum (UHV) conditions before being transferred into the electrochemical environment. Crystal truncation rod (CTR) measurements were made at negative potentials (just negative of the pzc), where there is no specific adsorption onto the electrode surfaces, and at more positive potentials, where hydroxide species is specifically adsorbed. The measurements quantify the relaxation at the metal electrode surfaces and, through the specular CTR, give information about layering on the electrolyte side of the interface. Strong layering effects are observed on the Ag(111) and Ag(110) surfaces, whereas on Ag(001) the layering is much weaker and we attribute this to the symmetry mismatch to the adsorbing water network. The effect of saturating the electrolyte with carbon monoxide (CO) was also examined, and structural changes were only observed on the Ag(110) surface. The changes observed suggest a stabilization of a coadsorbed CO–OH adlayer due to charge redistribution that delays the onset of CO oxidation.	Jul 2024
I07-Surface & interface diffraction	Effect of anionic lipids on mammalian plasma cell membrane properties Alexandra L. Martin , Philip N. Jemmett , Thomas Howitt , Mary H. Wood , Andrew W. Burley , Liam R. Cox , Timothy R. Dafforn , Rebecca J. L. Welbourn , Mario Campana , Maximilian W. A. Skoda , Joseph J. Thompson , Hadeel Hussain , Jonathan L. Rawle , Francesco Carla , Christopher L. Nicklin , Thomas Arnold , Sarah L. Horswell Langmuir DOI: 10.1021/acs.langmuir.2c03161 Diamond Proposal Number(s): [14670, 16423, 19542] Open Access Show Abstract ▼ 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.	Feb 2023
I07-Surface & interface diffraction	Influence of the lipid backbone on electrochemical phase behavior Philip N. Jemmett , David C. Milan , Richard J. Nichols , Thomas Howitt , Alexandra L. Martin , Thomas Arnold , Jonathan L. Rawle , Christopher L. Nicklin , Timothy R. Dafforn , Liam R. Cox , Sarah L. Horswell Langmuir 10 DOI: 10.1021/acs.langmuir.2c02370 Diamond Proposal Number(s): [15539, 18202] Open Access Show Abstract ▼ Abstract: Sphingolipids are an important class of lipids found in mammalian cell membranes with important structural and signaling roles. They differ from another major group of lipids, the glycerophospholipids, in the connection of their hydrocarbon chains to their headgroups. In this study, a combination of electrochemical and structural methods has been used to elucidate the effect of this difference on sphingolipid behavior in an applied electric field. N-Palmitoyl sphingomyelin forms bilayers of similar coverage and thickness to its close analogue di-palmitoyl phosphatidylcholine. Grazing incidence diffraction data show slightly closer packing and a smaller chain tilt angle from the surface normal. Electrochemical IR results at low charge density show that the difference in tilt angle is retained on deposition to form bilayers. The bilayers respond differently to increasing electric field strength: chain tilt angles increase for both molecules, but sphingomyelin chains remain tilted as field strength is further increased. This behavior is correlated with disruption of the hydrogen-bonding network of small groups of sphingomyelin molecules, which may have significance for the behavior of molecules in lipid rafts in the presence of strong fields induced by ion gradients or asymmetric distribution of charged lipids.	Nov 2022

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