15 results on '"Robert M. Ziolek"'
Search Results
2. Modular Software for Generating and Modeling Diverse Polymer Databases.
- Author
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Alejandro Santana-Bonilla, Raquel Lopez-Rios de Castro, Peike Sun, Robert M. Ziolek, and Christian D. Lorenz
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- 2023
- Full Text
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3. Constraints on Knot Insertion, Not Internal Jamming, Control Polycatenane Translocation Dynamics through Crystalline Pores
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Zifeng Wang, Robert M. Ziolek, and Mesfin Tsige
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Inorganic Chemistry ,Polymers and Plastics ,Organic Chemistry ,Materials Chemistry - Published
- 2023
4. Interplay of lipid and surfactant: Impact on nanoparticle structure
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David J. Barlow, Orathai Loruthai, Ann E. Terry, Christian D. Lorenz, M. Jayne Lawrence, Robert M. Ziolek, and Demi L. Pink
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Work (thermodynamics) ,Materials science ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Small-angle neutron scattering ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,Molecular dynamics ,Colloid and Surface Chemistry ,Pulmonary surfactant ,law ,Chemical physics ,Drug delivery ,Molecule ,lipids (amino acids, peptides, and proteins) ,Crystallization ,0210 nano-technology - Abstract
Liquid lipid nanoparticles (LLN) are oil-in-water nanoemulsions of great interest in the delivery of hydrophobic drug molecules. They consist of a surfactant shell and a liquid lipid core. The small size of LLNs makes them difficult to study, yet a detailed understanding of their internal structure is vital in developing stable drug delivery vehicles (DDVs). Here, we implement machine learning techniques alongside small angle neutron scattering experiments and molecular dynamics simulations to provide critical insight into the conformations and distributions of the lipid and surfactant throughout the LLN. We simulate the assembly of a single LLN composed of the lipid, triolein (GTO), and the surfactant, Brij O10. Our work shows that the addition of surfactant is pivotal in the formation of a disordered lipid core; the even coverage of Brij O10 across the LLN shields the GTO from water and so the lipids adopt conformations that reduce crystallisation. We demonstrate the superior ability of unsupervised artificial neural networks in characterising the internal structure of DDVs, when compared to more conventional geometric methods. We have identified, clustered, classified and averaged the dominant conformations of lipid and surfactant molecules within the LLN, providing a multi-scale picture of the internal structure of LLNs.
- Published
- 2021
5. Conformational Heterogeneity and Interchain Percolation Revealed in an Amorphous Conjugated Polymer
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Robert M. Ziolek, Alejandro Santana-Bonilla, Raquel López-Ríos de Castro, Reimer Kühn, Mark Green, and Christian D. Lorenz
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General Engineering ,General Physics and Astronomy ,General Materials Science - Abstract
Conjugated polymers are employed in a variety of application areas due to their bright fluorescence and strong biocompatibility. However, understanding the structure of amorphous conjugated polymers on the nanoscale is extremely challenging compared to their related crystalline phases. Using a bespoke classical force field, we study amorphous poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) with molecular dynamics simulations to investigate the role that its nanoscale structure plays in controlling its emergent (and all-important) optical properties. Notably, we show that a giant percolating cluster exists within amorphous F8BT, which has ramifications in understanding the nature of interchain species that drive the quantum yield reduction and bathochromic shift observed in conjugated polymer-based devices and nanostructures. We also show that distinct conformations can be unravelled from within the disordered structure of amorphous F8BT using a two-stage machine learning protocol, highlighting a link between molecular conformation and ring stacking propensity. This work provides predictive understanding by which to enhance the optical properties of next-generation conjugated polymer-based devices and materials by rational, simulation-led design principles.
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- 2022
6. NSAID solubilisation promotes morphological transitions in Triton X-114 surfactant micelles
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Hrachya Ishkhanyan, Robert M. Ziolek, David J. Barlow, M. Jayne Lawrence, Armen H. Poghosyan, and Christian D. Lorenz
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NSAIDs ,Indomethacin ,Materials Chemistry ,Ibuprofen ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Solubilisation ,Spectroscopy ,Atomic and Molecular Physics, and Optics ,Micelles ,Triton X-114 ,Electronic, Optical and Magnetic Materials - Abstract
The structural properties of micelles formed by the non-ionic surfactant, Triton X-114 (TX-114), were investigated using all-atom molecular dynamics (MD) simulations. Additionally, we investigated the effect of the solubilisation of the sodium salts of two nonsteroidal anti-inflammatory drugs, ibuprofen and indomethacin, upon the structural properties of TX-114 micelles. The micelle in absence of the drugs has an aspherical shape. We find that as the micelle continues to solubilise drug molecules, its shape becomes even more elongated. The solubilised drug molecules are observed to take orientations within the core of the micelle that allows their carboxyl groups to remain hydrated by the surrounding interfacial solvent. Also we find that the increased aggregation of indomethacin via π-π stacking of its chlorobenzene group leads to destabilisation of the micelle. In the ibuprofen-loaded micelle, where the solubilised drug molecules do not aggregate to the same degree, we find that the drug-loaded micelle remains stable. These results provide a mechanistic description of how the solubilisation of NSAIDs drives morphological changes in TX-114 micelles. Additionally, we show how the physico-chemical properties of both surfactants and drug molecules can play a significant role in the stabilisation of drug delivery vehicles.
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- 2022
7. Unsupervised Learning Unravels the Structure of Four-Arm and Linear Block Copolymer Micelles
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Demi L. Pink, Cécile A. Dreiss, Paul Smith, Robert M. Ziolek, and Christian D. Lorenz
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Materials science ,Polymeric micelles ,Flexibility (anatomy) ,Polymers and Plastics ,Organic Chemistry ,Structure (category theory) ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Micelle ,0104 chemical sciences ,Inorganic Chemistry ,medicine.anatomical_structure ,Materials Chemistry ,Copolymer ,medicine ,Unsupervised learning ,0210 nano-technology - Abstract
Understanding the nanoscale structure of polymeric micelles is challenging: their relatively small size tests the limits of most experimental techniques, while the great conformational flexibility of the individual polymer chains makes deriving insight from computer simulations difficult. Pluronics and Tetronics are amphiphilic block copolymers based on poly(ethylene oxide) and poly(propylene oxide) blocks that self-assemble into micelles, which have been widely studied experimentally given their extensive use as excipients in drug formulations and as biomaterials. In contrast to these wide-ranging applications, the characterization of their nanoscale structure and dynamics is still incomplete. In particular, how the architecture of the blocks in linear Pluronics and four-arm Tetronics influences the arrangement of the chains within a core–shell morphology is not well understood. We apply unsupervised machine learning techniques to provide an unprecedented level of detail regarding the distribution of polymer conformations within the micelles and identify the underlying structure in the seemingly disordered micellar corona. The methodology applied in this work improves our understanding of the structure of these industrially relevant nanoparticles and establishes a general methodology for investigating the conformational distribution of polymers in self-assembled structures.
- Published
- 2021
8. Understanding the pH-Directed Self-Assembly of a Four-Arm Block Copolymer
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Cécile A. Dreiss, Christian D. Lorenz, Gustavo González-Gaitano, Lionel Porcar, Wenjing Hu, Jasmin Omar, and Robert M. Ziolek
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Directed self assembly ,Polymers and Plastics ,Chemistry ,Organic Chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Combinatorial chemistry ,0104 chemical sciences ,Inorganic Chemistry ,Amphiphile ,Drug delivery ,Materials Chemistry ,Copolymer ,0210 nano-technology - Abstract
We investigated the pH-directed self-assembly of Tetronic 304 (T304), an amphiphilic four-arm block copolymer of interest for application in drug delivery systems. While T304 and its analogues have...
- Published
- 2020
9. On the interaction of hyaluronic acid with synovial fluid lipid membranes
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Elena Gazzarrini, Christian D. Lorenz, Robert M. Ziolek, Dylan M. Owen, and Paul Smith
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Molecular Structure ,Hydrogen bond ,Lipid Bilayers ,Phospholipid ,General Physics and Astronomy ,02 engineering and technology ,Molecular Dynamics Simulation ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Molecular dynamics ,Dextran ,Membrane ,chemistry ,Synovial Fluid ,Hyaluronic acid ,Biophysics ,Molecule ,lipids (amino acids, peptides, and proteins) ,Hyaluronic Acid ,Physical and Theoretical Chemistry ,0210 nano-technology ,Lipid bilayer - Abstract
All-atom molecular dynamics simulations have been used to investigate the adsorption of low molecular weight hyaluronic acid to lipid membranes. We have determined the interactions that govern the adsorption of three different molecular weight hyaluronic acid molecules (0.4, 3.8 & 15.2 kDa) to lipid bilayers that are representative of the surface-active phospholipid bilayers found in synovial joints. We have found that both direct hydrogen bonds and water-mediated interactions with the lipid headgroups play a key role in the binding of hyaluronic acid to the lipid bilayer. The water-mediated interactions become increasingly important in stabilising the adsorbed hyaluronic acid molecules as the molecular weight of hyaluronic acid increases. We also observe a redistribution of ions around bound hyaluronic acid molecules and the associated lipid headgroups, and that the degree of redistribution increases with the molecular weight of hyaluronic acid. By comparing this behaviour to that observed in simulations of the charge-neutral polysaccharide dextran (MW ∼ 15 kDa), we show that this charge redistribution leads to an increased alignment of the lipid headgroups with the membrane normal, and therefore to more direct and water-mediated interactions between hyaluronic acid and the lipid membrane. These findings provide a detailed understanding of the general structure of hyaluronic acid–lipid complexes that have recently been presented experimentally, as well as a potential mechanism for their enhanced tribological properties.
- Published
- 2019
10. Morphology of bile salts micelles and mixed micelles with lipolysis products, from scattering techniques and atomistic simulations
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Yuri Gerelli, Najet Mahmoudi, Rebecca J. L. Welbourn, Maximilian W. A. Skoda, Robert M. Ziolek, Sylvain Prévost, Christian D. Lorenz, Isabelle Grillo, Peter J. Wilde, Margarita Valero, Olivia Pabois, Cécile A. Dreiss, Richard D. Harvey, Myriam M.-L. Grundy, Institut Laue-Langevin (ILL), ILL, King‘s College London, ISIS Neutron and Muon Source (ISIS), STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC)-Science and Technology Facilities Council (STFC), Universidad de Salamanca, University of Vienna [Vienna], Physiologie, Environnement et Génétique pour l'Animal et les Systèmes d'Elevage [Rennes] (PEGASE), AGROCAMPUS OUEST, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Quadram Institute, Polytechnic University of Marche [Ancona, Italy], European Project: 654000, Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-INSTITUT AGRO Agrocampus Ouest, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Biotechnology and Biological Sciences Research Council (BBSRC), and Polytechnic University of Marche [Ancona, Italy] / Università Politecnica delle Marche [Ancona, Italia]
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Lipolysis products ,medicine.drug_class ,Lipolysis ,02 engineering and technology ,Bile salts ,010402 general chemistry ,01 natural sciences ,Micelle ,Bile Acids and Salts ,Biomaterials ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,X-Ray Diffraction ,Lipid digestion ,Scattering, Small Angle ,medicine ,Moiety ,[CHIM]Chemical Sciences ,Micelles ,Liposome ,Bile acid ,Small-angle X-ray scattering ,Bulk aggregation properties ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Chemical engineering ,Critical micelle concentration ,Liposomes ,Pyrene ,Small-angle scattering ,0210 nano-technology ,[SDV.AEN]Life Sciences [q-bio]/Food and Nutrition - Abstract
Hypotheses\ud \ud 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.\ud \ud \ud \ud Experiments\ud \ud 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.\ud \ud \ud \ud Findings\ud \ud 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.
- Published
- 2021
11. Structure and Dynamics of Nanoconfined Water Between Surfactant Monolayers
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Robert M. Ziolek, Christian D. Lorenz, Franca Fraternali, Ali Dhinojwala, and Mesfin Tsige
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Materials science ,Dynamics (mechanics) ,Direct response ,02 engineering and technology ,Surfaces and Interfaces ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Pulmonary surfactant ,Chemical physics ,Monolayer ,Electrochemistry ,General Materials Science ,0210 nano-technology ,Spectroscopy - Abstract
The properties of nanoconfined water arise in direct response to the properties of the interfaces that confine it. A great deal of research has focused on understanding how and why the physical properties of confined water differ greatly from the bulk. In this work, we have used all-atom molecular dynamics (MD) simulations to provide a detailed description of the structural and dynamical properties of nanoconfined water between two monolayers consisting of an archetypal ionic surfactant, cetrimonium bromide (CTAB, [CH3(CH2)15N(CH3)3]+Br-). Small differences in the area per surfactant of the monolayers impart a clear effect on the intrinsic density, mobility, and ordering of the interfacial water layer confined by the monolayers. We find that as the area per surfactant within a monolayer decreases, the mobility of the interfacial water molecules decreases in response. As the monolayer packing density decreases, we find that each individual CTAB molecule has a greater effect on the ordering of water molecules in its first hydration shell. In a denser monolayer, we observe that the effect of individual CTAB molecules on the ordering of water molecules is hindered by increased competition between headgroups. Therefore, when two monolayers with different areas per surfactant are used to confine a nanoscale water layer, we observe the emergence of noncentrosymmetry.
- Published
- 2019
12. Time-Resolved Fluorescence Anisotropy of a Molecular Rotor Resolves Microscopic Viscosity Parameters in Complex Environments
- Author
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Robert M. Ziolek, Bethan Cornell, I. Emilie Steinmark, Christian D. Lorenz, James A. Levitt, Carla Molteni, Klaus Suhling, Pei-Hua Chung, Paul Smith, Gokhan Yahioglu, and Carolyn Tregidgo
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Materials science ,Population ,Fluorescence Polarization ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Biomaterials ,Viscosity ,Molecular dynamics ,General Materials Science ,Anisotropy ,education ,Lipid bilayer ,Rotational correlation time ,Fluorescent Dyes ,education.field_of_study ,Optical Imaging ,technology, industry, and agriculture ,General Chemistry ,equipment and supplies ,021001 nanoscience & nanotechnology ,Lipids ,0104 chemical sciences ,Chemical physics ,Time-resolved spectroscopy ,0210 nano-technology ,Fluorescence anisotropy ,Biotechnology - Abstract
Understanding viscosity in complex environments remains a largely unanswered question despite its importance in determining reaction rates in vivo. Here, time-resolved fluorescence anisotropy imaging (TR-FAIM) is combined with fluorescent molecular rotors (FMRs) to simultaneously determine two non-equivalent viscosity-related parameters in complex heterogeneous environments. The parameters, FMR rotational correlation time and lifetime, are extracted from fluorescence anisotropy decays, which in heterogeneous environments show dip-and-rise behavior due to multiple dye populations. Decays of this kind are found both in artificially constructed adiposomes and in live cell lipid droplet organelles. Molecular dynamics simulations are used to assign each population to nano-environments within the lipid systems. The less viscous population corresponds to the state showing an average 25° tilt to the lipid membrane normal, and the more viscous population to the state showing an average 55° tilt. This combined experimental and simulation approach enables a comprehensive description of the FMR probe behavior within viscous nano-environments in complex, biological systems.
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- 2019
13. On the structure of solid lipid nanoparticles
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Orathai Loruthai, M. Jayne Lawrence, Demi L. Pink, Robert M. Ziolek, Christian D. Lorenz, Prawarisa Wasutrasawat, and Ann E. Terry
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02 engineering and technology ,Crystal structure ,Molecular Dynamics Simulation ,010402 general chemistry ,01 natural sciences ,Biomaterials ,chemistry.chemical_compound ,Molecular dynamics ,Solid lipid nanoparticle ,Molecule ,General Materials Science ,Triglycerides ,Chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,Small-angle neutron scattering ,Lipids ,0104 chemical sciences ,body regions ,Chemical engineering ,Yield (chemistry) ,Tripalmitin ,Drug delivery ,Nanoparticles ,0210 nano-technology ,Biotechnology - Abstract
Solid lipid nanoparticles (SLNs) have a crystalline lipid core which is stabilised by interfacial surfactants. SLNs are considered favorable candidates for drug delivery vehicles since their ability to store and release organic molecules can be tailored through the identity of the lipids and surfactants used. When stored, polymorphic transitions in the core of drug-loaded SLNs lead to the premature release of drug molecules. Significant experimental studies have been conducted with the aim of investigating the physico-chemical properties of SLNs, however, no molecular scale investigations have been reported on the behaviors that drive SLN formation and their polymorphic transitions. We have therefore used a combination of small angle neutron scattering (SANS) and all-atom molecular dynamics simulations (MS) to yield a detailed atomistic description of the internal structure of an SLN comprising of triglyceride, tripalmitin, and the nonionic surfactant, Brij O10 (C18:1E10). We uncover the molecular scale mechanisms by which the surfactants stabilise the crystalline structure of the SLN lipid core. By comparing these results to simulated liquid and solid aggregates of tripalmitin lipids, we demonstrate how the morphology of the lipids vary between these systems providing further insight into the mechanisms that control drug encapsulation and release from SLNs.
- Published
- 2019
14. Erratum: 'On the solvation of the phosphocholine headgroup in an aqueous propylene glycol solution' [J. Chem. Phys. 148, 135102 (2018)]
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Christian D. Lorenz, Sylvia E. McLain, M. Jayne Lawrence, Mohamed Ali al-Badri, Richard J. Gillams, Natasha H. Rhys, Robert M. Ziolek, and Louise Collins
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chemistry.chemical_compound ,Aqueous solution ,chemistry ,Solvation ,General Physics and Astronomy ,Physical chemistry ,Physical and Theoretical Chemistry ,Polyvinyl alcohol ,Phosphocholine - Published
- 2019
15. On the solvation of the phosphocholine headgroup in an aqueous propylene glycol solution
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Richard J. Gillams, Mohamed Ali al-Badri, Sylvia E. McLain, Christian D. Lorenz, Robert M. Ziolek, Natasha H. Rhys, Louise Collins, and M. Jayne Lawrence
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Phosphorylcholine ,Lipid Bilayers ,General Physics and Astronomy ,Molecular Dynamics Simulation ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Molecular dynamics ,0103 physical sciences ,Physical and Theoretical Chemistry ,Phosphocholine ,Aqueous solution ,010304 chemical physics ,Molecular Structure ,Hydrogen bond ,Bilayer ,Solvation ,Water ,Hydrogen Bonding ,Propylene Glycol ,0104 chemical sciences ,Crystallography ,Membrane ,chemistry ,Phosphatidylcholines ,Solvents ,Solvent effects - Abstract
The atomic-scale structure of the phosphocholine (PC) headgroup in 30 mol. % propylene glycol (PG) in an aqueous solution has been investigated using a combination of neutron diffraction with isotopic substitution experiments and computer simulation techniques - molecular dynamics and empirical potential structure refinement. Here, the hydration of the PC headgroup remains largely intact compared with the hydration of this group in a bilayer and in a bulk water solution, with the PG molecules showing limited interactions with the headgroup. When direct PG interactions with PC do occur, they are most likely to coordinate to the N(CH3)3+ motifs. Further, PG does not affect the bulk water structure and the addition of PC does not perturb the PG-solvent interactions. This suggests that the reason why PG is able to penetrate into membranes easily is that it does not form strong-hydrogen bonding or electrostatic interactions with the headgroup allowing it to easily move across the membrane barrier.
- Published
- 2018
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