This study systematically investigated the interactions of the tumor biomarker alpha-fetoprotein (AFP) and bovine serum albumin (BSA) with planar lipid membranes using neutron reflectometry, quartz crystal microbalance with dissipation monitoring, and atomistic molecular dynamics simulations. By examining a range of lipid compositions-including charged, neutral, and nanodomain-containing bilayers-we dissected the molecular mechanisms governing protein-membrane interactions. AFP consistently exhibited stronger interactions than BSA. While both proteins showed negligible binding to zwitterionic POPC bilayers, BSA only interacted significantly with negatively charged POPS membranes. In contrast, AFP strongly engaged with both SM/CHOL nanodomains and POPS-containing bilayers, leading to protein incorporation and lipid extraction, respectively. On positively charged DOTAP membranes, AFP formed a stable adsorbed layer. These findings reveal how lipid composition modulates protein adsorption, insertion, and membrane integrity, offering new mechanistic insights into the differential binding affinities of AFP and BSA. The results underscore the importance of protein-lipid interactions in clinical assays for blood tumor biomarkers, as these interactions may influence the formation of protein-lipid complexes and impact detection accuracy. This work may guide the optimization of biosensing strategies, particularly for glycosylated biomarkers, to enhance the sensitivity and reliability of clinical diagnostics.

Polymer brushes are a key technology for designing surfaces, with applications in biomedicine alone including biosensing, cell culture, regenerative medicine, and antibacterial coatings. The structuring of polymer brushes has the potential to precisely tailor interfaces for specific application requirements. However, complex fabrication processes can limit the applications of polymer brushes. Herein, a subtractive patterning process is reported, which decouples initial fabrication from the structuring process. Using radical ring-opening polymerization of cyclic monomers with photocleavable cyclobutane rings, photodegradable targets are directly embedded into the polymer brush main chains. After the initial fabrication, these brushes can be readily degraded with light, triggering photocleavage of the cyclobutane units. This enables continuous brush degradation of over 50% of brush height for topographical patterning without affecting brush properties such as hydrophilicity and adhesion force. The inherent photodegradability of the polymer brush eliminates the need for additional chemicals or catalysts and can be carried out using nothing but water and light at ambient temperature.

Supported lipid bilayers (SLBs) are crucial model membrane platforms to study the structure and dynamics of cellular membranes. Vesicle fusion (VF) is one of the most widely used approaches to forming SLBs, though it suffers from compositional limitations and substrate compatibility constraints. The solvent-assisted lipid bilayer (SALB) technique enables the possibility of forming SLBs using a wider range of membrane compositions and substrate platforms through organic-solvent-mediated bilayer assembly, yet questions remain regarding structural equivalence and potential organic solvent incorporation effects. Using neutron reflectometry (NR), we systematically compare the structure and composition of phosphatidylcholine-based SLBs formed by either VF or SALB methodologies. SALB conditions were optimized for NR solid/liquid cells, and structural characterization revealed comparable bilayer architectures between the two formation methods, although some changes in the lipid acyl chain thickness were observed. SALBs showed up to 99.2 ± 0.9% surface coverage using ultrapure water for solvent exchange, but the reproducibility of the method was poor. Enhanced-contrast NR using either deuterated lipids or solvents allowed for the quantitative detection of residual organic solvent incorporation of the SALBs, which was up to 3.3 ± 0.9 vol.% in the tail regions. Making use of 1 mM CaCl2 during solvent exchange substantially improved SALB reproducibility, reducing coverage variability from 21-30 to 2  vol.%. Validation studies using the antimicrobial peptide melittin demonstrated that membrane-peptide interactions proceeded according to established mechanisms, with peptide incorporation of 18 vol.% for the low-coverage (69.7 ± 0.8%) SALB. The quantified solvent incorporation levels and small changes in acyl chain layer thickness in the SALBs must be considered when interpreting protein-membrane interaction studies, which suggests that validation of the SALB methodology for membrane research applications requires assessment on a case by case basis.

Ionic liquids with [P66614] cations and new chelated bis(catecholato)borate anion architectures are introduced, showing emergent structural properties compared to conventional analogues, making them intriguing for electrochemistry, lubrication, and formulation. Small/wide-angle X-ray scattering of the neat bulk ILs suggests densified cation assemblies in the presence of catecholates. Upon dispersion in propylene carbonate as a proxy for lubricant oils and electrolyte formulations, small-angle neutron scattering shows major anion-dependent self-assembly modulation effects, particularly for bis(4-ethylcatecholato)borate [B4ECB] where there is significant aggregate lengthening. Neutron reflectivity measurements corroborate the solution aggregation behavior at the electrochemical double layer (EDL); the catechols form thicker and more electroresponsive interfacial layers, especially [B4ECB]. Ab initio DFT calculations unify these observations by proving electron resonance across the bis(catecholato)borates, which modulates the anion polarizability profile. The soft, delocalized character of the catecholate anions allows the charge to move more responsively, which dynamically enhances coulombic and solvophobically-driven self assembly. In other words, catecholate anions can function as an adaptive ‘ionic jigsaw piece’, allowing densification of the EDL, and revealing a pathway towards electrolyte structural design with tuneable surface coverage.

The inductive effect is a central concept in chemistry and is often exemplified by the pK a values of acetic acid derivatives. The reduction in pK a is canonically attributed to the reduction in the electron density of the carboxylate group through the inductive effect. However, wave functional theory calculations presented herein reveal that the charge density of the carboxylate group is not explained by the inductive effect. For a series of trihaloacetates (trichloro-, chlorodifluoro- and trifluoro-) we find that the trichloro group has the greatest reduction on the charge density of the carboxylate oxygen atoms; change in charge density is inversely related to substituent electronegativity. These puzzling results are experimentally supported by investigating three independent systems: literature gas phase acidities, specific ion effects in a model thermoresponsive polymer system, and nuclear magnetic resonance (NMR) spectroscopy of haloalkanes. Changes in the solubility of poly(N-isopropylacrylamide), PNIPAM, due to the presence of different (substituted) acetates allow ionic charge densities to be examined. These studies confirmed the unexpected charge density and substituent-electronegativity relationship. Further analysis of the literature showed anomalous charge densities for haloalkanes with 13C NMR spectroscopy and gas phase acidity of polyatomic acids. In summary, these independent results show that the induction effect does not explain pK a trends across the haloacetic acids.

Anionic biomembranes are vital features of all living cells and were perhaps key components of the earliest cell-like structures - protocells. In the absence of evolved protein machinery, any protocell membranes would have had their properties heavily influenced by the ambient environment, posing a systems chemistry challenge to understanding how such membranes functioned. Here we use a range of techniques to examine the effect of glycine and lysine, representative neutral and cationic amino acids, on the properties of model anionic membranes composed of equimolar POPC and POPG. Using QCM-D and neutron reflectometry, we find that unlike glycine, lysine strongly binds to the membrane, resulting in significant lipid loss and changes in the scattering length density and volume fraction of the lipids in the bilayer. Interestingly, we also find that even though lysine causes substantial changes in the physicochemical and structural properties of the anionic membrane, permeability studies show that lysine cannot permeate while glycine can, highlighting a disconnect between the structural changes observed for low curvature systems and the permeability trends observed in high curvature systems. This research provides mechanistic insights into single amino acid-anionic biomembrane interactions, and how they could have impacted evolving protocell membrane functions and stability.

Diffuse soft matter interfaces take many forms, from end-tethered polymer brushes or adsorbed surfactants to self-assembled layers of lipids. These interfaces play crucial roles across a multitude of fields, including materials science, biophysics, and nanotechnology. Understanding the nanostructure and properties of these interfaces is fundamental for optimising their performance and designing novel functional materials. In recent years, reflectometry techniques, in particular neutron reflectometry, have emerged as powerful tools for elucidating the intricate nanostructure of soft matter interfaces with remarkable precision and depth. This review provides an overview of selected recent developments in reflectometry and their applications for illuminating the nanostructure of diffuse interfaces. We explore various principles and methods of neutron and X-ray reflectometry, as well as ellipsometry, and discuss advances in their experimental setups and data analysis approaches. Improvements to experimental neutron reflectometry methods have enabled greater time resolution in kinetic measurements and elucidation of diffuse structure under shear or confinement, while innovation in analysis protocols has significantly reduced data processing times, facilitated co-refinement of reflectometry data from multiple instruments and provided greater-than-ever confidence in proposed structural models. Furthermore, we highlight some significant research findings enabled by these techniques, revealing the organisation, dynamics, and interfacial phenomena at the nanoscale. We also discuss future directions and potential advancements in reflectometry techniques. By shedding light on the nanostructure of diffuse interfaces, reflectometry techniques enable the rational design and tailoring of interfaces with enhanced properties and functionalities.

Hypothesis: Understanding the complex interactions between polymers and surfactants is required to optimise commercially relevant systems such as paint, toothpaste and detergent. Neutral polymers complex with surfactants, forming 'pearl necklace' structures that are often conceptualised as pseudo-polyelectrolytes. Here we pose two questions to test the limits of this analogy: Firstly, in the presence of salt, do these polymer-surfactant systems behave like polyelectrolytes? Secondly, do polymer-surfactant complexes resist geometric confinement like polyelectrolytes?CMC. However, at high NaCl concentrations (e.g., 500 mM) no brush collapse was observed at all (non-zero) concentrations of SDS studied, contrary to what is seen for many polyelectrolytes. Study of the polymer-surfactant system under confinement revealed that the physical volume of surfactant dominates the structure of the strongly confined system, which further differentiates it from the polyelectrolyte case.

Three nonhalogenated ionic liquids (ILs) dissolved in 2-ethylhexyl laurate (2-EHL), a biodegradable oil, are investigated in terms of their bulk and electro-interfacial nanoscale structures using small-angle neutron scattering (SANS) and neutron reflectivity (NR). The ILs share the same trihexyl(tetradecyl)phosphonium ([P-6,P-6,P-6,P-14](+)) cation paired with different anions, bis(mandelato)borate ([BMB](-)), bis(oxalato)borate ([BOB](-)), and bis(salicylato)borate ([BScB](-)). SANS shows a high aspect ratio tubular self-assembly structure characterized by an IL core of alternating cations and anions with a 2-EHL-rich shell or corona in the bulk, the geometry of which depends upon the anion structure and concentration. NR also reveals a solvent-rich interfacial corona layer. Their electro-responsive behavior, pertaining to the structuring and composition of the interfacial layers, is also influenced by the anion identity. [P-6,P-6,P-6,P-14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P-6,P-6,P-6,P-14][BMB] and [P-6,P-6,P-6,P-14][BScB] demonstrate minimal electroresponses across all studied potentials, related to their different dissociative and diffusive behavior. A mixed system is dominated by the least soluble IL but exhibits an increase in disorder. This work reveals the subtlety of anion architecture in tuning bulk and electro-interfacial properties, offering valuable molecular insights for deploying nonhalogenated ILs as additives in biodegradable lubricants and supercapacitors.

The surface of human hair is normally hydrophobic as it is covered by a lipid layer, mainly composed of 18-methyleicosanoic acid (18-MEA). When the hair is damaged, this layer can be partially or fully removed and more hydrophilic, mainly negatively charged surfaces are formed with a wide variety of physical and chemical characteristics. The cosmetic industry is currently embracing the opportunity of increasing the sustainability of their hair-care products whilst improving product performance. To do this, it is vital to have a deeper understanding of the hair surface and how it interacts with hair-care ingredients. This work contributes to this by harnessing the potential of neutron reflectometry (NR) with scattering contrast variation to describe hierarchical adsorption. Three types of hair-mimetic surfaces have been produced: two "healthy hair" models to probe the role of lipid structure, and one "damaged hair" model, to consider the effect of the surface charge. Adsorption of hair-care ingredients has then been studied. The results for these relatively short lipid models indicate that a methyl branch has little effect on adsorption. The "damaged hair" studies, however, reveal the unexpected apparent adsorption of an anionic surfactant to a negative surface. This preferential adsorption of the otherwise solubilised neutral components demonstrates a facile route to selectively deliver a protective film on a damaged hair fibre, without the need for a cationic species. On a more general note, this study also demonstrates the feasibility of using NR to characterize such complex systems. Hair surfaces are modeled with thiol surfaces for NR. Anionic surfactant adsorbs hydrophobically on "healthy hair", but as a protective, rinse-proof bilayer on damaged hair. A chitosan/SDS complex is retained on damaged hair.

Pertinent to cryopreservation as well as energy storage and batteries, nonaqueous electrolytes and their mixtures with water were investigated. In particular, specific ion-induced effects on the modulation of a poly(N-isopropylacrylamide) (PNIPAM) brush were investigated in various dimethyl sulfoxide (DMSO)-water solvent mixtures. Spectroscopic ellipsometry and neutron reflectometry were employed to probe changes in brush swelling and structure, respectively. In water-rich solvents (i.e., pure water and 6 mol % DMSO), PNIPAM undergoes a swollen to collapsed thermotransition with increasing temperature, whereby a forward Hofmeister series was noted; K+ and Li+ electrolytes composed of SCN- and I- salted-in (stabilized) PNIPAM chains, and electrolytes of Cl- and Br- salted-out (destabilized) the polymer. The cation was seen to play a lesser role than that of the anion, merely modulating the magnitude of the anion effect. In 70 mol % DMSO, a collapsed to swollen thermotransition was noted for PNIPAM. Here, concentration-dependent specific ion effects were observed; a forward series was observed in 0.2 mol % electrolytes, whereas increasing the electrolyte concentration to 0.9 mol % led to a series reversal. While no thermotransition was observed in pure DMSO, a solvent-induced specific ion series reversal was noted; SCN- destabilized the brush and Cl- stabilized the brush. Both series reversals are attributed to the delicate balance of interactions between the solvent, solute (ion), and substrate (brush). Namely, the stability of the solvent clusters was hypothesized to drive polymer solvation.

An oxygen-tolerant SI-PhotoRAFT technique has been developed for the efficient synthesis of surface-tethered polymer brushes under low-energy near-infrared (NIR) light. This technique takes advantage of the unique properties of NIR light, in particular enhanced penetration, to effectively prepare polymeric coatings, even through barriers that are opaque to visible light. The NIR-mediated SI-PhotoRAFT polymerization technique was utilized to precisely modulate brush height in direct correlation with the irradiation time. Additionally, this technique facilitated sequential chain extension, enabling the fabrication of block copolymer brushes. Moreover, the incorporation of a photoresponsive monomer, 7-[4-(trifluoromethyl)coumarin]acrylamide [2-(2-oxo-4-(trifluoromethyl)-2H-chromen-7-yl)acrylamide, TCAm], within the poly(N,N-dimethylacrylamide) brushes enables orthogonal control over polymerization and cross-linking processes through the use of two different wavelengths (NIR and UV light). When exposed to a UV source (? = 365 nm, 18.2 mW/cm2), the TCAm undergoes dimerization triggering cross-linking of the grafted brush "arms". Furthermore, by utilizing the enhanced penetration of NIR light, a polymeric coating was prepared on the inner walls of a tube that was opaque to visible light. Finally, this process is successfully applied to the synthesis of antifouling surfaces on poly(dimethylsiloxane)-coated silicon wafers, leading to inhibition of biofouling.

Hypothesis: Specific ion effects govern myriad biological phenomena, including protein-ligand interac-tions and enzyme activity. Despite recent advances, detailed understanding of the role of ion hydropho-bicity in specific ion effects, and the intersection with hydrotropic effects, remains elusive. Short chain fatty acid sodium salts are simple amphiphiles which play an integral role in our gastrointestinal health. We hypothesise that increasing a fatty acid's hydrophobicity will manifest stronger salting-out beha-viour. Experiments: Here we study the effect of these amphiphiles on an exemplar thermoresponsive polymer brush system, conserving the carboxylate anion identity while varying anion hydrophobicity via the carbon chain length. Ellipsometry and quartz crystal microbalance with dissipation monitoring were used to characterise the thermoresponse and viscoelasticity of the brush, respectively, whilst neutron reflectometry was used to reveal the internal structure of the brush. Diffusion-ordered nuclear magnetic resonance spectroscopy and computational investigations provide insight into polymer-ion interactions.Findings: Surface sensitive techniques unveiled a non-monotonic trend in salting-out ability with increasing anion hydrophobicity, revealing the bundle-like morphology of the ion-collapsed system. An intersection between ion-specific and hydrotropic effects was observed both experimentally and compu-tationally; trending from good anti-hydrotrope towards hydrotropic behaviour with increasing anion hydrophobicity, accompanying a change in hydrophobic hydration.(c) 2022 Elsevier Inc. All rights reserved.

Hypothesis: Anionic surfactants have been reported to interact with poly(N-isopropyl acrylamide) (PNIPAM), suppressing its thermoresponse. Scattering and NMR studies of the anionic sodium dodecyl-sulfate (SDS) system propose that the PNIPAM-surfactant interaction is purely hydrophobic. However, prior phenomenological investigations of a range of surfactant identities (anionic, cationic, nonionic) show that only anionic surfactants affect the thermoresponse and conformation of PNIPAM, implying that the hydrophilic head-group also contributes. Crucially, the phenomenological experiments do not mea-sure the affinity of the tested surfactants to the polymer, only their effect on its behaviour.Experiments: We study the adsorption of six surfactants within a planar PNIPAM brush system, elucidat-ing the polymer conformation, thermoresponse, and surfactant adsorption kinetics using ellipsometry, neutron reflectometry (NR), optical reflectometry and the quartz crystal microbalance technique. NR is used to measure the distribution of surfactants within the brush.Findings: We find that only anionic surfactants modify the structure and thermoresponse of PNIPAM, with the greater affinity of anionic surfactants for PNIPAM (relative to cationic and nonionic surfactants) being the primary reason for this behaviour. These results show that the surfactant head-group has amore critical role in mediating PNIPAM-surfactant interaction than previously reported. Taking inspira-tion from prior molecular dynamics work on the PEO-surfactant system, we propose an interaction mech-anism for PNIPAM and SDS that reconciles evidence for hydrophobic interaction with the observed head- group-dependent affinity.CO 2022 Elsevier Inc. All rights reserved.

Slippery covalently-attached liquid surfaces (SCALS) with low contact angle hysteresis (CAH, <5°) and nanoscale thickness display impressive anti-adhesive properties, similar to lubricant-infused surfaces. Their efficacy is generally attributed to the liquid-like mobility of the constituent tethered chains. However, the precise physico-chemical properties that facilitate this mobility are unknown, hindering rational design. This work quantifies the chain length, grafting density, and microviscosity of a range of polydimethylsiloxane (PDMS) SCALS, elucidating the nanostructure responsible for their properties. Three prominent methods are used to produce SCALS, with characterization carried out via single-molecule force measurements, neutron reflectometry, and fluorescence correlation spectroscopy. CO 2 snow-jet cleaning was also shown to reduce the CAH of SCALS via a modification of their grafting density. SCALS behavior can be predicted by reduced grafting density, Σ, with the lowest water CAH achieved at Σ≈2. This study provides the first direct examination of SCALS grafting density, chain length, and microviscosity and supports the hypothesis that SCALS properties stem from a balance of layer uniformity and mobility.

Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between predicted and observed screening lengths at high salt concentrations, a phenomenon referred to as underscreening. Herein we investigate underscreening using a cationic polyelectrolyte brush as an exemplar. Poly(2-(methacryloyloxy)ethyl)trimethylammonium (PMETAC) brushes were synthesised and their internal structural changes and swelling response was monitored with neutron reflectometry and spectroscopic ellipsometry. Both techniques revealed a monotonic brush collapse as the concentration of symmetric monovalent electrolyte increased. However, a non-monotonic change in brush thickness was observed in all multivalent electrolytes at higher concentrations, known as re-entrant swelling; indicative of underscreening. For all electrolytes, numerical self-consistent field theory predictions align with experimental studies in the low-to-moderate salt concentration regions. Analysis suggests that the classical theory of electrolytes is insufficient to describe the screening lengths observed at high salt concentrations and that the re-entrant polyelectrolyte brush swelling seen herein is consistent with the so-called regular underscreening phenomenon.

The capture of moisture from the atmosphere through condensation has the potential to provide a sustainable source of water. Here, we investigate the condensation of humid air at low subcooling condition (11 °C), similar to conditions for natural dew capture, and explore how water contact angle and contact angle hysteresis affect the rates of water capture. We compare water collection on three families of surfaces: (i) hydrophilic (polyethylene oxide, MPEO) and hydrophobic (polydimethylsiloxane, PDMS) molecularly thin coatings grafted on smooth silicon wafers, which produce slippery covalently attached liquid surfaces (SCALSs), with low contact angle hysteresis (CAH = 6°); (ii) the same coatings grafted on rougher glass, with high CAH (20°-25°); (iii) hydrophilic polymer surfaces [poly(N-vinylpyrrolidone), PNVP] with high CAH (30°). Upon exposure to water, the MPEO SCALS swell, which likely further increases their droplet shedding ability. MPEO and PDMS coatings collect similar volume of water (around 5 l m-2 day-1), both when they are SCALS and non-slippery. Both MPEO and PDMS layers collect about 20% more water than PNVP surfaces. We present a basic model showing that, under low heat flux conditions, on all MPEO and PDMS layers, the droplets are so small (600-2000 µm) that there is no/low heat conduction resistance across the droplets, irrespective of the exact value of contact angle and CAH. As the time to first droplet departure is much faster on MPEO SCALS (28 min) than on PDMS SCALS (90 min), slippery hydrophilic surfaces are preferable in dew collection applications where the collection time frame is limited.

Structural characterisation of thermoresponsive polymer brushes in binary DMSO–water mixtures reveals both LCST and UCST behaviour.

The performance of the Spatz neutron reflectometer is demonstrated. It has a variable wavelength resolution to suit experimental needs for reflectometry at air–solid and solid–liquid interfaces.

Time-of-flight neutron reflectometry (ToF-NR) performed under different relative humidity conditions demonstrates that polymer brushes constituted by hydrophilic, cyclic macromolecules exhibit a more compact conformation with lower roughness as compared to linear brush analogues, due to the absence of dangling chain ends extending at the polymer-vapor interface. In addition, cyclic brushes feature a larger swelling ratio and an increased solvent uptake with respect to their linear counterparts as a consequence of the increased interchain steric repulsions. It is proposed that differences in swelling ratios between linear and cyclic brushes come from differences in osmotic pressure experienced by each brush topology. These differences stem from entropic constraints. The findings suggest that to correlate the equilibrium swelling ratios at different relative humidity for different topologies a new form of the Flory-like expression for equilibrium thicknesses of grafted brushes is needed.