Scattering approaches to unravel protein solution behaviors in ionic liquids and deep eutectic solvents: From basic principles to recent developments.

Proteins in ionic liquids (ILs) and deep eutectic solvents (DESs) have gained significant attention due to their potential applications in various fields, including biocatalysis, bioseparation, biomolecular delivery, and structural biology. Scattering approaches including dynamic light scattering (DLS) and small-angle X-ray and neutron scattering (SAXS and SANS) have been used to understand the solution behavior of proteins at the nanoscale and microscale. This review provides a thorough exploration of the application of these scattering techniques to elucidate protein properties in ILs and DESs. Specifically, the review begins with the theoretical foundations of the relevant scattering approaches and describes the essential solvent properties of ILs and DESs linked to scattering such as refractive index, scattering length density, ion-pairs, liquid nanostructure, solvent aggregation, and specific ion effects. Next, a detailed introduction is provided on protein properties such as type, concentration, size, flexibility and structure as observed through scattering methodologies. This is followed by a review of the literature on the use of scattering for proteins in ILs and DESs. It is highlighted that enhanced data analysis and modeling tools are necessary for assessing protein flexibility and structure, and for understanding protein hydration, aggregation and specific ion effects. It is also noted that complementary approaches are recommended for comprehensively understanding the behavior of proteins in solution due to the complex interplay of factors, including ion-binding, dynamic hydration, intermolecular interactions, and specific ion effects. Finally, the challenges and potential research directions for this field are proposed, including experimental design, data analysis approaches, and supporting methods to obtain fundamental understandings of complex protein behavior and protein systems in solution. We envisage that this review will support further studies of protein interface science, and in particular studies on solvent and ion effects on proteins.

A deep eutectic solvent is an effective cryoprotective agent for platelets.

The most widely used method of platelet cryopreservation requires the addition of dimethyl sulfoxide (DMSO; Me2SO) as a cryoprotective agent (CPA) and pre-freeze removal of Me2SO before freezing to mitigate toxicity. However, alternative CPAs such as deep eutectic solvents (DES), which are less toxic could simplify this process. The aim of this study was to determine the effectiveness of a Proline-Glycerol (Prol-Gly 1:3) DES as a platelet CPA. Platelets were cryopreserved at -80 °C using 10 % Prol-Gly 1:3 (DES; n = 6), or in the absence of a cryoprotectant (no CPA; n = 6). Platelets were also cryopreserved according to the gold-standard blood-banking method using 5.5 % Me2SO (n = 6), with centrifugation and pre-freeze removal of the excess Me2SO. Platelet quality was assessed by flow cytometry and thromboelastography (TEG). Post-thaw recovery was similar between the three groups. The abundance of labile platelet glycoproteins GPIbα and GPVI were highest in the DES group, however, markers of activation (CD62P and annexin-V) were also higher in this group. In terms of function, the strength of the clot (maximum amplitude; TEG) and extent of clot retraction was better with DES platelets compared to no CPA, but lower than Me2SO platelets. DES provides a cryoprotective advantage to platelets when compared to no CPA. Importantly, when compared to Me2SO platelets, most quality parameters were similar in DES platelets. The major advantage with using a DES is biocompatibility, therefore it does not need to be removed prior to transfusion. This greatly simplifies the freezing and thawing process, avoiding the toxic effects of Me2SO.

Molecular interactions with bilayer membrane stacks using neutron and X-ray diffraction.

Lamellar unit cell reconstruction from neutron and X-ray diffraction data provides information about the disposition and position of molecules and molecular segments with respect to the bilayer. When supplemented with the judicious use of molecular deuteration, the technique probes the molecular interactions and conformations within the bilayer membrane and the water layer which constitute the crystallographic unit cell. The perspective is model independent, and potentially, with a higher degree of resolution than is available with other techniques. In the case of neutron diffraction the measurement consists of carefully normalised diffracted intensity under conditions of contrast variation of the water layer. The subsequent Fourier reconstruction of the unit cell is made using the phase information from variation of peak intensities with contrast. Although the phase problem is not as easily solved for the corresponding X-ray measurements, an intuitive approach can often suffice. Here we discuss the two complimentary techniques as probes of scattering length density profiles of a bilayer, and how such a perspective provides information about the location and orientation of molecules within or between lipid bilayers. Within the basic paradigm of lamellar phases this method has provided, for example, detailed insights into the location and interaction of cryoprotectants and stress proteins, of the mechanisms of actions of viral proteins, antimicrobial compounds and drugs, and the underlying structure of the stratum corneum. In this paper we review these techniques and provide examples of the systems that have been examined. We finish with a future outlook on the use of these techniques to improve our understanding of the interactions of membranes with biomolecules.

Deep Eutectic Solvent Eutectogels for Delivery of Broad-Spectrum Antimicrobials.

Gel-based wound dressings have gained popularity within the healthcare industry for the prevention and treatment of bacterial and fungal infections. Gels based on deep eutectic solvents (DESs), known as eutectogels, provide a promising alternative to hydrogels as they are non-volatile and highly tunable and can solubilize therapeutic agents, including those insoluble in hydrogels. A choline chloride:glycerol-cellulose eutectogel was loaded with numerous antimicrobial agents including silver nanoparticles, black phosphorus nanoflakes, and commercially available pharmaceuticals (octenidine dihydrochloride, tetracycline hydrochloride, and fluconazole). The eutectogels caused >97% growth reduction in Gram-positive methicillin-resistant Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa bacteria and the fungal species Candida albicans.

Biophysical Characterization and Cryopreservation of Mammalian Cells Using Ionic Liquids.

Ionic liquids (ILs) are a diverse class of solvents which can be selected for task-specific properties, making them attractive alternatives to traditional solvents. To tailor ILs for specific biological applications, it is necessary to understand the structure-property relationships of ILs and their interactions with cells. Here, a selection of carboxylate anion-based ILs were investigated as cryoprotectants, which are compounds added to cells before freezing to mitigate lethal freezing damage. The cytotoxicity, cell permeability, thermal behavior, and cryoprotective efficacy of the ILs were assessed with two model mammalian cell lines. We found that the biophysical interactions, including permeability of the ILs, were influenced by considering the IL pair together, rather than as single species acting independently. All of the ILs tested had high cytotoxicity, but ethylammonium acetate demonstrated good cryoprotective efficacy for both cell types tested. These results demonstrate that despite toxicity, ILs may be suitable for certain biological applications. It also demonstrates that more research is required to understand the contribution of ion pairs to structure-property relationships and that knowing the behavior of a single ionic species will not necessarily predict its behavior as part of an IL.

Phytantriol phase behaviour in choline chloride urea and water mixtures.

Deep eutectic solvents (DES) are tailorable non-aqueous solvents with promising properties for a range of applications, from industrial dissolution of plant products to biomedicine. They are mixtures of hydrogen bond donors and acceptors with low melting points that can be tailored to specific applications, and many support the self-assembly of amphiphilic molecules into lyotropic liquid crystal phases. Self-assembled lipid structures have potential for numerous applications, including drug delivery. These ordered structures can act as carriers, slow-release vehicles, or microreactors. Lipid self-assembly in non-aqueous solvents, such as deep eutectic solvents, is important for applications at extreme temperatures, or involving water-insoluble or water sensitive components. However, lipid self-assembly in these solvents remains largely unexplored. In this paper, we have examined the self-assembly of phytantriol, a non-ionic lipid, at 10 and 30 wt% in the deep eutectic solvent choline chloride:urea, with and without water. Self-assembly was assessed using small angle X-ray scattering and cross polarised optical microscopy at temperatures from 25-66 °C. We found that pure choline chloride:urea supports a Pn3m cubic phase similar to that formed in water. However, mixtures of the DES with water resulted in phytantriol forming an inverse hexagonal phase and influenced the phase transition temperatures. These results demonstrate that choline chloride:urea can support diverse phase behaviour, and also provides a mechanism for tailoring the phase for particular applications simply by controlling the amount of water in the solvent. In the future this could lead to methods of triggered release of drugs and biomolecules by the simple addition of water which could be critical for drug delivery applications.

Phase separation in a ternary DPPC/DOPC/POPC system with reducing hydration.

The maintenance of plasma membrane structure is vital for the viability of cells. Disruption of this structure can lead to cell death. One important example is the macroscopic phase separation observed during dehydration associated with desiccation and freezing, often leading to loss of permeability and cell death. It has previously been shown that the hybrid lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) can act as a line-active component in ternary lipid systems, inhibiting macroscopic phase separation and stabilising membrane microdomains in lipid vesicles [1]. The domain size is found to decrease with increasing POPC concentration until complete mixing is observed. However, no such studies have been carried out at reduced hydration. To examine if this phase separation is unique to vesicles in excess water, we have conducted studies on several binary and ternary model membrane systems at both reduced hydration ("powder" type samples and oriented membrane stacks) and in excess water (supported lipid bilayers) at 0.2 mol fraction POPC, in the range where microdomain stabilisation is reported. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) are used to map phase transition temperatures, with X-ray and neutron scattering providing details of the changes in lipid packing and phase information within these boundaries. Atomic force microscopy (AFM) is used to image bilayers on a substrate in excess water. In all cases, macroscopic phase separation was observed rather than microdomain formation at this molar ratio. Thus POPC does not stabilise microdomains under these conditions, regardless of the type of model membrane, hydration or temperature. Thus we conclude that the driving force for separation under these conditions overcomes any linactant effects of the hybrid lipid.

Dual-action silver functionalized nanostructured titanium against drug resistant bacterial and fungal species.

HYPOTHESIS: Titanium and its alloys are commonly used implant materials. Once inserted into the body, the interface of the biomaterials is the most likely site for the development of implant-associated infections. Imparting the titanium substrate with high-aspect-ratio nanostructures, which can be uniformly achieved using hydrothermal etching, enables a mechanical contact-killing (mechanoresponsive) mechanism of bacterial and fungal cells. Interaction between cells and the surface shows cellular inactivation via a physical mechanism meaning that careful engineering of the interface is needed to optimse the technology. This mechanism of action is only effective towards surface adsorbed microbes, thus any cells not directly in contact with the substrate will survive and limit the antimicrobial efficacy of the titanium nanostructures. Therefore, we propose that a dual-action mechanoresponsive and chemical-surface approach must be utilised to improve antimicrobial activity. The addition of antimicrobial silver nanoparticles will provide a secondary, chemical mechanism to escalate the microbial response in tandem with the physical puncture of the cells. EXPERIMENTS: Hydrothermal etching is used as a facile method to impart variant nanostrucutres on the titanium substrate to increase the antimicrobial response. Increasing concentrations (0.25 M, 0.50 M, 1.0 M, 2.0 M) of sodium hydroxide etching solution were used to provide differing degrees of nanostructured morphology on the surface after 3 h of heating at 150 °C. This produced titanium nanospikes, nanoblades, and nanowires, respectively, as a function of etchant concentration. These substrates then provided an interface for the deposition of silver nanoparticles via a reduction pathway. Methicillin-resistant Staphylococcous aureus (MRSA) and Candida auris (C. auris) were used as model bacteria and fungi, respectively, to test the effectiveness of the nanostructured titanium with and without silver nanoparticles, and the bio-interactions at the interface. FINDINGS: The presence of nanostructure increased the bactericidal response of titanium against MRSA from âˆ¼ 10 % on commercially pure titanium to a maximum of âˆ¼ 60 % and increased the fungicidal response from âˆ¼ 10 % to âˆ¼ 70 % in C. auris. Introducing silver nanoparticles increased the microbiocidal response to âˆ¼ 99 % towards both bacteria and fungi. Importantly, this study highlights that nanostructure alone is not sufficient to develop a highly antimicrobial titanium substrate. A dual-action, physical and chemical antimicrobial approach is better suited to produce highly effective antibacterial and antifungal surface technologies.

Behavior of Citrate-Capped Ultrasmall Gold Nanoparticles on a Supported Lipid Bilayer Interface at Atomic Resolution.

Nanomaterials have the potential to transform biological and biomedical research, with applications ranging from drug delivery and diagnostics to targeted interference of specific biological processes. Most existing research is aimed at developing nanomaterials for specific tasks such as enhanced biocellular internalization. However, fundamental aspects of the interactions between nanomaterials and biological systems, in particular, membranes, remain poorly understood. In this study, we provide detailed insights into the molecular mechanisms governing the interaction and evolution of one of the most common synthetic nanomaterials in contact with model phospholipid membranes. Using a combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we elucidate the precise mechanisms by which citrate-capped 5 nm gold nanoparticles (AuNPs) interact with supported lipid bilayers (SLBs) of pure fluid (DOPC) and pure gel-phase (DPPC) phospholipids. On fluid-phase DOPC membranes, the AuNPs adsorb and are progressively internalized as the citrate capping of the NPs is displaced by the surrounding lipids. AuNPs also interact with gel-phase DPPC membranes where they partially embed into the outer leaflet, locally disturbing the lipid organization. In both systems, the AuNPs cause holistic perturbations throughout the bilayers. AFM shows that the lateral diffusion of the particles is several orders of magnitude smaller than that of the lipid molecules, which creates some temporary scarring of the membrane surface. Our results reveal how functionalized AuNPs interact with differing biological membranes with mechanisms that could also have implications for cooperative membrane effects with other molecules.

Deep eutectic solvents as cryoprotective agents for mammalian cells.

Cryopreservation has facilitated numerous breakthroughs including assisted reproductive technology, stem cell therapies, and species preservation. Successful cryopreservation requires the addition of cryoprotective agents to protect against freezing damage and dehydration. For decades, cryopreservation has largely relied on the same two primary agents: dimethylsulfoxide and glycerol. However, both of these are toxic which limits their use for cells destined for clinical applications. Furthermore, these two agents are ineffective for hundreds of cell types, and organ and tissue preservation has not been achieved. The research presented here shows that deep eutectic solvents can be used as cryoprotectants. Six deep eutectic solvents were explored for their cryoprotective capacity towards mammalian cells. The solvents were tested for their thermal properties, including glass transitions, toxicity, and permeability into mammalian cells. A deep eutectic solvent made from proline and glycerol was an effective cryoprotective agent for all four cell types tested, even with extended incubation prior to freezing. This deep eutectic solvent was more effective and less toxic than its individual components, highlighting the importance of multi-component systems. Cells were characterised post-thawing using atomic force microscopy and confocal microscopy. Molecular dynamics simulations support the biophysical parameters obtained by experimentation. This is one of the first times that this class of solvents has been systematically tested for cryopreservation of mammalian cells and as such this research opens the way for the development of potentially thousands of new cryoprotective agents that can be tailored to specific cell types. The demonstrated capacity of cells to be incubated with the deep eutectic solvent at 37 °C for hours prior to freezing without significant loss of viability is a major step toward the storage of organs and tissues.

Illuminating the biochemical interaction of antimicrobial few-layer black phosphorus with microbial cells using synchrotron macro-ATR-FTIR.

In the fight against drug-resistant pathogenic bacterial and fungal cells, low-dimensional materials are emerging as a promising alternative treatment method. Specifically, few-layer black phosphorus (BP) has demonstrated its effectiveness against a wide range of pathogenic bacterial and fungal cells with studies suggesting low cytotoxicity towards healthy mammalian cells. However, the antimicrobial mechanism of action of BP is not well understood. Before new applications for this material can be realised, further in-depth investigations are required. In this work, the biochemical interaction between BP and a series of microbial cells is investigated using a variety of microscopy and spectroscopy techniques to provide a greater understanding of the antimicrobial mechanism. Synchrotron macro-attenuated total reflection-Fourier transform infrared (ATR-FTIR) micro-spectroscopy is used to elucidate the chemical changes occurring outside and within the cell of interest after exposure to BP nanoflakes. The ATR-FTIR data, coupled with high-resolution microscopy, reveals major physical and bio-chemical changes to the phospholipids and amide I and II proteins, as well as minor chemical changes to the structural polysaccharides and nucleic acids when compared to untreated cells. These changes can be attributed to the physical interaction of the BP nanoflakes with the cell membranes, combined with the oxidative stress induced by the degradation of the BP nanoflakes. This study provides insight into the biochemical interaction of BP nanoflakes with microbial cells, allowing for a better understanding of the antimicrobial mechanism of action that will be important for the next generation of applications such as implant coatings, wound dressings, or medical surfaces.

Bulk and interfacial nanostructure and properties in deep eutectic solvents: Current perspectives and future directions.

Deep eutectic solvents (DESs) are a tailorable class of solvents that are rapidly gaining scientific and industrial interest. This is because they are distinct from conventional molecular solvents, inherently tuneable via careful selection of constituents, and possess many attractive properties for applications, including catalysis, chemical extraction, reaction media, novel lubricants, materials chemistry, and electrochemistry. DESs are a class of solvents composed solely of hydrogen bond donors and acceptors with a melting point lower than the individual components and are often fluidic at room temperature. A unique feature of DESs is that they possess distinct bulk liquid and interfacial nanostructure, which results from intra- and inter-molecular interactions, including coulomb forces, hydrogen bonding, van der Waals interactions, electrostatics, dispersion forces, and apolar-polar segregation. This nanostructure manifests as preferential spatial arrangements of the different species, and exists over several length scales, from molecular- to nano- and meso-scales. The physicochemical properties of DESs are dictated by structure-property relationships; however, there is a significant gap in our understanding of the underlying factors which govern their solvent properties. This is a major limitation of DES-based technologies, as nanostructure can significantly influence physical properties and thus potential applications. This perspective provides an overview of the current state of knowledge of DES nanostructure, both in the bulk liquid and at solid interfaces. We provide definitions which clearly distinguish DESs as a unique solvent class, rather than a subset of ILs. An appraisal of recent work provides hints towards trends in structure-property relationships, while also highlighting inconsistencies within the literature suggesting new research directions for the field. It is hoped that this review will provide insight into DES nanostructure, their potential applications, and development of a robust framework for systematic investigation moving forward.

Rheological modification of partially oxidised cellulose nanofibril gels with inorganic clays.

This study aimed to quantify the influence of clays and partially oxidised cellulose nanofibrils (OCNF) on gelation as well as characterise their physical and chemical interactions. Mixtures of Laponite and montmorillonite clays with OCNF form shear-thinning gels that are more viscous across the entire shear range than OCNF on its own. Viscosity and other rheological properties can be fine-tuned using different types of clay at different concentrations (0.5-2 wt%). Laponite particles are an order of magnitude smaller than those of montmorillonite (radii of 150 Å compared to 2000 Å) and are therefore able to facilitate networking of the cellulose fibrils, resulting in stronger effects on rheological properties including greater viscosity. This work presents a mechanism for modifying rheological properties using renewable and environmentally-friendly nanocellulose and clays which could be used in a variety of industrial products including home and personal care formulations.

Cryopreservation of mammalian cells using protic ionic liquid solutions.

Cryopreservation has facilitated considerable advances in both medical technology and scientific research. However, further developments have been limited by the relatively low number of effective cryoprotective agents. Even after fifty years of research, most protocols rely on the same two toxic agents, i.e. dimethylsulfoxide or glycerol. Ionic liquids are a class of promising solvents which are known glass formers and may offer a less-toxic alternative. The research presented here investigates ten protic ionic liquids as potential cryoprotective agents. The liquids are screened for key properties including cellular toxicity, permeability and thermal behaviour. The most promising, ethylammonium acetate, was then tested as a cryoprotective agent on a model cell line and was found to be as effective as the common cryoprotectant, dimethylsulfoxide. This work reports the first use of a protic ionic liquid as an effective cryoprotective agent for a mammalian cell line. This will inform the development of a suite of potential new ionic liquid-based cryoprotectants that could potentially allow the cryopreservation of new cell types.

Analysis of Pathogenic Bacterial and Yeast Biofilms Using the Combination of Synchrotron ATR-FTIR Microspectroscopy and Chemometric Approaches.

Biofilms are assemblages of microbial cells, extracellular polymeric substances (EPS), and other components extracted from the environment in which they develop. Within biofilms, the spatial distribution of these components can vary. Here we present a fundamental characterization study to show differences between biofilms formed by Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative Pseudomonas aeruginosa, and the yeast-type Candida albicans using synchrotron macro attenuated total reflectance-Fourier transform infrared (ATR-FTIR) microspectroscopy. We were able to characterise the pathogenic biofilms' heterogeneous distribution, which is challenging to do using traditional techniques. Multivariate analyses revealed that the polysaccharides area (1200-950 cm-1) accounted for the most significant variance between biofilm samples, and other spectral regions corresponding to amides, lipids, and polysaccharides all contributed to sample variation. In general, this study will advance our understanding of microbial biofilms and serve as a model for future research on how to use synchrotron source ATR-FTIR microspectroscopy to analyse their variations and spatial arrangements.

Bottom-up cubosome synthesis without organic solvents.

HYPOTHESIS: Bottom-up synthesis of cubosomes is more energetically favourable than top-down approaches. However, bottom-up methods often rely on organic solvents such as ethanol as diluents, and lead to concurrent formation of liposomes. We propose using non-toxic diluents such as honey, glycerol and lactic acid for bottom-up cubosome synthesis. EXPERIMENTS: Cubosomes were prepared using solutions of phytantriol in a range of diluents including choline chloride-glycerol, honey, lactic acid, glycerol, and ethanol. These solutions were added dropwise to water containing the stabiliser, poloxamer 407, following an established method of cubosome synthesis. The resulting structures were characterised using small-angle X-ray scattering, DLS and cryo-TEM. FINDINGS: Cubosomes were successfully formed using a range of non-toxic diluents. This demonstrates that harmful organic solvents like ethanol are not required, and that the diluents need not be hydrotropes. Furthermore, unlike ethanol, these other diluents allowed formation of cubosomes without concurrent formation of liposomes. Given the huge potential for cubosomes in drug delivery, this new method offers a potentially useful low-cost, low-toxicity synthesis option.

Monovalent Salt and pH-Induced Gelation of Oxidised Cellulose Nanofibrils and Starch Networks: Combining Rheology and Small-Angle X-ray Scattering.

Water quality parameters such as salt content and various pH environments can alter the stability of gels as well as their rheological properties. Here, we investigated the effect of various concentrations of NaCl and different pH environments on the rheological properties of TEMPO-oxidised cellulose nanofibril (OCNF) and starch-based hydrogels. Addition of NaCl caused an increased stiffness of the OCNF:starch (1:1 wt%) blend gels, where salt played an important role in reducing the repulsive OCNF fibrillar interactions. The rheological properties of these hydrogels were unchanged at pH 5.0 to 9.0. However, at lower pH (4.0), the stiffness and viscosity of the OCNF and OCNF:starch gels appeared to increase due to proton-induced fibrillar interactions. In contrast, at higher pH (11.5), syneresis was observed due to the formation of denser and aggregated gel networks. Interactions as well as aggregation behaviour of these hydrogels were explored via ζ-potential measurements. Furthermore, the nanostructure of the OCNF gels was probed using small-angle X-ray scattering (SAXS), where the SAXS patterns showed an increase of slope in the low-q region with increasing salt concentration arising from aggregation due to the screening of the surface charge of the fibrils.

Selective ion transport across a lipid bilayer in a protic ionic liquid.

Ionic liquids (ILs) have exhibited enormous potential as electrolytes, designer solvents and reaction media, as well as being surprisingly effective platforms for amphiphile self-assembly and for preserving structure of complex biomolecules. This has led to their exploration as media for long-term biopreservation and in biosensors, for which their viability depends on their ability to sustain both structure and function within complex, multicomponent nanoscale compartments and assemblies. Here we show that a tethered lipid bilayer can be assembled directly in a purely IL environment that retains its structure upon exchange between IL and aqueous buffer, and that the membrane transporter valinomycin can be incorporated so as to retain its functionality and cation selectivity. This paves the way for the development of long-lived, non-aqueous microreactors and sensor assemblies, and demonstrates the potential for complex proteins to retain functionality in non-aqueous, ionic liquid solvents.

Nanostructure of a deep eutectic solvent at solid interfaces.

HYPOTHESIS: Deep eutectic solvents (DESs) are an attractive class of tunable solvents. However, their uptake for relevant applications has been limited due to a lack of detailed information on their structure-property relationships, both in the bulk and at interfaces. The lateral nanostructure of the DES-solid interfaces is likely to be more complex than previously reported and requires detailed, high-resolution investigation. EXPERIMENTS: We employ a combination of high-resolution amplitude-modulated atomic force microscopy and molecular dynamics simulations to elucidate the lateral nanostructure of a DES at the solid-liquid interface. Specifically, the lateral and near-surface nanostructure of the DES choline chloride:glycerol is probed at the mica and highly-ordered pyrolytic graphite interfaces. FINDINGS: The lateral nanostructure of the DES-solid interface is heterogeneous and well-ordered in both systems. At the mica interface, the DES is strongly ordered via polar interactions. The adsorbed layer has a distinct rhomboidal symmetry with a repeat spacing of ~0.9 nm comprising all DES species. At the highly ordered pyrolytic graphite interface, the adsorbed layer appears distinctly different, forming an apolor-driven row-like structure with a repeat spacing of ~0.6 nm, which largely excludes the chloride ion. The interfacial nanostructure results from a delicate balance of substrate templating, liquid-liquid interactions, species surface affinity, and packing constraints of cations, anions, and molecular components within the DES. For both systems, distinct near-surface nanostructural layering is observed, which becomes more pronounced close to the substrate. The surface nanostructures elucidated here significantly expand our understanding of DES interfacial behavior and will enhance the optimization of DES systems for surface-based applications.

Non-volatile conductive gels made from deep eutectic solvents and oxidised cellulose nanofibrils.

Ionogels offer huge potential for a number of applications including wearable electronics and soft sensors. However, their synthesis has been limited and often relies on non-renewable or non-biocompatible components. Here we present a novel two-component ionogel made using just deep eutectic solvents (DESs) and cellulose. DESs offer a non-volatile alternative to hydrogels with highly tuneable properties including conductivity and solvation of compounds with widely varying hydrophobicity. DESs can be easily made from cheap, biodegradable and biocompatible components. This research presents the characterisation of a series of soft conductive gels made from deep eutectic solvents (DESs), specifically choline chloride-urea and choline chloride-glycerol, with the sole addition of TEMPO-oxidised cellulose nanofibrils (OCNF). A more liquid-like rather than gel-like conductive material could be made by using the DES betaine-glycerol. OCNF are prepared from sustainable sources, and are non-toxic, and mild on the skin, forming gels without the need for surfactants or other gelling agents. These DES-OCNF gels are shear thinning with conductivities up to 1.7 mS cm-1 at ∼26 °C. Given the thousands of possible DESs, this system offers unmatched tunability and customisation for properties such as viscosity, conductivity, and yield behaviour.