Lanthanide binding peptide surfactants at air-aqueous interfaces for interfacial separation of rare earth elements.

Rare earth elements (REEs) are critical materials to modern technologies. They are obtained by selective separation from mining feedstocks consisting of mixtures of their trivalent cation. We are developing an all-aqueous, bioinspired, interfacial separation using peptides as amphiphilic molecular extractants.

Selective regulation of macrophage lipid metabolism via nanomaterials' surface chemistry.

Understanding the interface between nanomaterials and lipoproteins is crucial for gaining insights into their impact on lipoprotein structure and lipid metabolism. Here, we use graphene oxide (GOs) nanosheets as a controlled carbon nanomaterial model to study how surface properties influence lipoprotein corona formation and show that GOs have strong binding affinity with low-density lipoprotein (LDL). We use advanced techniques including X-ray reflectivity, circular dichroism, and molecular simulations to explore the interfacial interactions between GOs and LDL.

X-ray Induced Cycling of Rare-Earth Elements between Bulk and Interfacial Liquid.

Reversible cycling of rare-earth elements between an aqueous electrolyte solution and its free surface is achieved by X-ray exposure. This exposure alters the competitive equilibrium between lanthanide ions bound to a chelating ligand, diethylenetriamine pentaacetic acid (DTPA), in the bulk solution and to insoluble monolayers of extractant di-hexadecyl phosphoric acid (DHDP) at its surface. Evidence for the exposure-induced temporal variations in the lanthanide surface density is provided by X-ray fluorescence near total reflection measurements.

Metastable precipitation and ion-extractant transport in liquid-liquid separations of trivalent elements.

The extractant-assisted transport of metal ions from aqueous to organic environments by liquid-liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion-extractant precipitates away from the liquid-liquid interface, separated from it by a depletion region without precipitates.

MFG-E8: a model of multiple binding modes associated with ps-binding proteins.

Membrane-binding proteins often associate with lipid membranes through a singular binding interface which is generally modeled as a two-state system: bound or unbound. However, even a single interface can engage with more than one mode of binding since a variety of interactions can contribute to the binding event. Unfortunately, the ability to clearly delineate the different binding modes of a singular binding interface has been elusive with existing models.

Relevance of Surface Adsorption and Aqueous Complexation for the Separation of Co(II), Ni(II), and Fe(III).

During the solvent extraction of metal ions from an aqueous to an organic phase, organic-soluble extractants selectively target aqueous-soluble ions for transport into the organic phase. In the case of extractants that are also soluble in the aqueous phase, our recent studies of lanthanide ion-extractant complexes at the surface of aqueous solutions suggested that ion-extractant complexation in the aqueous phase can hinder the solvent extraction process. Here, we investigate a similar phenomenon relevant to the separation of Co(II), Ni(II), and Fe(III).

Structural Flexibility of Proteins Dramatically Alters Membrane Stability─A Novel Aspect of Lipid-Protein Interaction.

Protein isoforms are structural variants with changes in the overall flexibility predominantly at the tertiary level. For membrane associated proteins, such structural flexibility or rigidity affects membrane stability by playing modulatory roles in lipid-protein interaction. Herein, we investigate the protein chain flexibility mediated changes in the mechanistic behavior of phospholipid model membranes in the presence of two well-known isoforms, erythroid (ER) and nonerythroid (NER) spectrin.

Differential Surface Adsorption Phenomena for Conventional and Novel Surfactants Correlates with Changes in Interfacial mAb Stabilization.

Protein adsorption on surfaces can result in loss of drug product stability and efficacy during the production, storage, and administration of protein-based therapeutics. Surface-active agents (excipients) are typically added in protein formulations to prevent undesired interactions of proteins on surfaces and protein particle formation/aggregation in solution. The objective of this work is to understand the molecular-level competitive adsorption mechanism between the monoclonal antibody (mAb) and a commercially used excipient, polysorbate 80 (PS80), and a novel excipient, -myristoyl phenylalanine--polyetheramine diamide (FM1000).

Knowledge-Based Design of 5-Fluororacil Prodrug Liposomal Formulation: Molecular Packing and Interaction Revealed by Interfacial Isotherms and X-ray Scattering Techniques.

Prodrugs and nanoformulations are two effective strategies for sustained drug release and targeting drug delivery. In this study, we combined the two strategies to judiciously design the liposome formulation incorporating an amphiphilic prodrug of 5-fouroracil (5-FU), named 5-FCPal, for sustained drug release and enhanced bioavailability. 5-FCPal is an analogue of capecitabine (N-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda) by substituting the pentyl group at the N position with the palmityl.

Interaction between dilute water vapor and dodecane thiol ligated Au nanoparticles: Hydrated structure and pair potential of mean force.

The interaction between two ligated nanoparticles depends on whether they are isolated or immersed in a liquid solvent. However, very little is known about the influence of solvent vapor on the interaction between two ligated nanoparticles. Recent experiments yield the surprising result that the cyclic exposure of solvent free suspended monolayers of dodecane thiol ligated gold nanoparticles (AuNPs) to water vapor and dry nitrogen generates reversible cyclic decreases and increases in Young's modulus of the monolayer, implying corresponding cyclic changes in the AuNP-AuNP interaction.

How Tim proteins differentially exploit membrane features to attain robust target sensitivity.

Immune surveillance cells such as T cells and phagocytes utilize integral plasma membrane receptors to recognize surface signatures on triggered and activated cells such as those in apoptosis. One such family of plasma membrane sensors, the transmembrane immunoglobulin and mucin domain (Tim) proteins, specifically recognize phosphatidylserine (PS) but elicit distinct immunological responses. The molecular basis for the recognition of lipid signals on target cell surfaces is not well understood.

No ordinary proteins: Adsorption and molecular orientation of monoclonal antibodies.

The interaction of monoclonal antibodies (mAbs) with air/water interfaces plays a crucial role in their overall stability in solution. We aim to understand this behavior using pendant bubble measurements to track the dynamic tension reduction and x-ray reflectivity to obtain the electron density profiles (EDPs) at the surface. Native immunoglobulin G mAb is a rigid molecule with a flat, "Y" shape, and simulated EDPs are obtained by rotating a homology construct at the surface.

Influence of Substitutional Groups on the Ordering and Crystallization of Amphiphilic Silsesquioxanes at the Air-Water Interface.

We report on the surface ordering and crystallization sequences in differently organic-substituted amphiphilic polyhedral silsesquioxane (POSS) variants induced by regulated compression at the air-water interface. Such molecular systems floating at the interface serve as a model system to study dynamic crystallization mediated by weak interactions. In situ grazing incidence X-ray scattering (GIXS) measurements, performed at a synchrotron X-ray source using a liquid surface diffractometer and corroborated with Brewster angle microscopy, revealed transformations for the different POSS variants (viz.

Free Thiols Regulate the Interactions and Self-Assembly of Thiol-Passivated Metal Nanoparticles.

Thiol ligands bound to the metallic core of nanoparticles determine their interactions with the environment and self-assembly. Recent studies suggest that equilibrium between bound and free thiols alters the ligand coverage of the core. Here, X-ray scattering and MD simulations investigate water-supported monolayers of gold-core nanoparticles as a function of the core-ligand coverage that is varied in experiments by adjusting the concentration of total thiols (sum of free and bound thiols).

Evolution and Reversible Polarity of Multilayering at the Ionic Liquid/Water Interface.

Highly correlated positioning of ions underlies Coulomb interactions between ions and electrified interfaces within dense ionic fluids such as biological cells and ionic liquids. Recent work has shown that highly correlated ionic systems behave differently than dilute electrolyte solutions, and interest is focused upon characterizing the electrical and structural properties of the dense electrical double layers (EDLs) formed at internal interfaces. It has been a challenge for experiments to characterize the progressive development of the EDL on the nanoscale as the interfacial electric potential is varied over a range of positive and negative values.

Spontaneous collapse of palmitic acid films on an alkaline buffer containing calcium ions.

Understanding the interaction of ions with fatty acids is important to identify their roles in various bioprocesses and to build novel biomimetic systems. In this study, the molecular organization of palmitic acid (PA) films on alkaline buffer solutions (pH 7.4) with and without divalent Ca was measured at a constant surface area using Langmuir troughs coupled with microscopy and X-ray interfacial techniques.

Armoring the Interface with Surfactants to Prevent the Adsorption of Monoclonal Antibodies.

The pharmaceutical industry uses surface-active agents (excipients) in protein drug formulations to prevent the aggregation, denaturation, and unwanted immunological response of therapeutic drugs in solution as well as at the air/water interface. However, the mechanism of adsorption, desorption, and aggregation of proteins at the interface in the presence of excipients remains poorly understood. The objective of this work is to explore the molecular-scale competitive adsorption process between surfactant-based excipients and two monoclonal antibody (mAb) proteins, mAb-1 and mAb-2.

Structure and dynamics of lipid membranes interacting with antivirulence end-phosphorylated polyethylene glycol block copolymers.

The structure and dynamics of lipid membranes in the presence of extracellular macromolecules are critical for cell membrane functions and many pharmaceutical applications. The pathogen virulence-suppressing end-phosphorylated polyethylene glycol (PEG) triblock copolymer (Pi-ABAPEG) markedly changes the interactions with lipid vesicle membranes and prevents PEG-induced vesicle phase separation in contrast to the unphosphorylated copolymer (ABAPEG). Pi-ABAPEG weakly absorbs on the surface of lipid vesicle membranes and slightly changes the structure of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) unilamellar vesicles at 37 °C, as evidenced by small angle neutron scattering.

The influence of fractional surface coverage on the core-core separation in ordered monolayers of thiol-ligated Au nanoparticles.

We report the results of grazing incidence X-ray diffraction (GIXD) measurements from water supported Langmuir monolayers of gold nanoparticles ligated with dodecanethiol (12 carbons), tetradecanethiol (14 carbons), hexadecanethiol (16 carbons), and octadecanethiol (18 carbons). These monolayers are formed from solutions with varying concentrations of the respective thiols. We show that equilibrium between adsorbed thiol molecules and the thiols in the bulk solution implies fractional coverage of the Au nanoparticle core.

Polyunsaturated Phospholipid Modified Membrane Degradation Catalyzed by a Secreted Phospholipase A2.

To optimize the compositions of the lipid-based nanomedicine and to advance understanding of the roles of polyunsaturated phospholipids in biological membranes, this study examined the effects of polyunsaturated phospholipids on the degradation of giant unilamellar vesicles catalyzed by a secreted phospholipase A2 (sPLA) using fluorescence microscopy. Molecular interfacial packing, interaction, and degradation of the films containing various mixing ratios of saturated and polyunsaturated phospholipids were quantified using a Langmuir trough integrated with synchrotron X-ray surface scattering techniques. It was found that a high molar fraction (0.

Stability of Ligands on Nanoparticles Regulating the Integrity of Biological Membranes at the Nano-Lipid Interface.

When nanoparticles interact with cellular or organelle membranes, the coating ligands are known to affect the integrity of the membranes, which regulate cell death and inflammation. However, the molecular mechanisms of this modulation remain unresolved. Here, we use synchrotron X-ray liquid surface scattering and molecular dynamics simulations to study interface structures between phospholipids and gold nanorods (AuNRs) coated by surfactant and polyelectrolyte.

Impact of Surface Amphiphilicity on the Interfacial Behavior of Janus Particle Layers under Compression.

Langmuir monolayers of silica/gold Janus particles with two different degrees of amphiphilicity have been examined to study the significance of particle surface amphiphilicity on the structure and mechanical properties of the interfacial layers. The response of the layers to the applied compression provides insight into the nature and strength of the interparticle interactions. Different collapse modes observed for the interfacial layers are linked to the amphiphilicity of Janus particles and their configuration at the interface.