Microporous water with high gas solubilities.

Liquids with permanent microporosity can absorb larger quantities of gas molecules than conventional solvents1, providing new opportunities for liquid-phase gas storage, transport and reactivity. Current approaches to designing porous liquids rely on sterically bulky solvent molecules or surface ligands and, thus, are not amenable to many important solvents, including water2-4. Here we report a generalizable thermodynamic strategy to preserve permanent microporosity and impart high gas solubilities to liquid water. Specifically, we show how the external and internal surface chemistry of microporous zeolite and metal-organic framework (MOF) nanocrystals can be tailored to promote the formation of stable dispersions in water while maintaining dry networks of micropores that are accessible to gas molecules. As a result of their permanent microporosity, these aqueous fluids can concentrate gases, including oxygen (O2) and carbon dioxide (CO2), to much higher densities than are found in typical aqueous environments. When these fluids are oxygenated, record-high capacities of O2 can be delivered to hypoxic red blood cells, highlighting one potential application of this new class of microporous liquids for physiological gas transport.

Single-chain heteropolymers transport protons selectively and rapidly.

Precise protein sequencing and folding are believed to generate the structure and chemical diversity of natural channels1,2, both of which are essential to synthetically achieve proton transport performance comparable to that seen in natural systems. Geometrically defined channels have been fabricated using peptides, DNAs, carbon nanotubes, sequence-defined polymers and organic frameworks3-13. However, none of these channels rivals the performance observed in their natural counterparts. Here we show that without forming an atomically structured channel, four-monomer-based random heteropolymers (RHPs)14 can mimic membrane proteins and exhibit selective proton transport across lipid bilayers at a rate similar to those of natural proton channels. Statistical control over the monomer distribution in an RHP leads to segmental heterogeneity in hydrophobicity, which facilitates the insertion of single RHPs into the lipid bilayers. It also results in bilayer-spanning segments containing polar monomers that promote the formation of hydrogen-bonded chains15,16 for proton transport. Our study demonstrates the importance of the adaptability that is enabled by statistical similarity among RHP chains and of the modularity provided by the chemical diversity of monomers, to achieve uniform behaviour in heterogeneous systems. Our results also validate statistical randomness as an unexplored approach to realize protein-like behaviour at the single-polymer-chain level in a predictable manner.

Functional enzyme-polymer complexes.

SignificanceThe use of biological enzyme catalysts could have huge ramifications for chemical industries. However, these enzymes are often inactive in nonbiological conditions, such as high temperatures, present in industrial settings. Here, we show that the enzyme PETase (polyethylene terephthalate [PET]), with potential application in plastic recycling, is stabilized at elevated temperature through complexation with random copolymers. We demonstrate this through simulations and experiments on different types of substrates. Our simulations also provide strategies for designing more enzymatically active complexes by altering polymer composition and enzyme charge distribution.

Proteomimetic Polymers Trigger Potent Antigen-Specific T Cell Responses to Limit Tumor Growth.

Elicitation of effective antitumor immunity following cancer vaccination requires the selective activation of distinct effector cell populations and pathways. Here we report a therapeutic approach for generating potent T cell responses using a modular vaccination platform technology capable of inducing directed immune activation, termed the Protein-like Polymer (PLP). PLPs demonstrate increased proteolytic resistance, high uptake by antigen-presenting cells (APCs), and enhanced payload-specific T cell responses. Key design parameters, namely payload linkage chemistry, degree of polymerization, and side chain composition, were varied to optimize vaccine formulations. Linking antigens to the polymer backbone using an intracellularly cleaved disulfide bond copolymerized with a diluent amount of oligo(ethylene glycol) (OEG) resulted in the highest payload-specific potentiation of antigen immunogenicity, enhancing dendritic cell (DC) activation and antigen-specific T cell responses. Vaccination with PLPs carrying either gp100, E7, or adpgk peptides significantly increased the survival of mice inoculated with B16F10, TC-1, or MC38 tumors, respectively, without the need for adjuvants. B16F10-bearing mice immunized with gp100-carrying PLPs showed increased antitumor CD8+ T cell immunity, suppressed tumor growth, and treatment synergy when paired with two distinct stimulator of interferon gene (STING) agonists. In a human papillomavirus-associated TC-1 model, combination therapy with PLP and 2'3'-cGAMP resulted in 40% of mice completely eliminating implanted tumors while also displaying curative protection from rechallenge, consistent with conferment of lasting immunological memory. Finally, PLPs can be stored long-term in a lyophilized state and are highly tunable, underscoring the unique properties of the platform for use as generalizable cancer vaccines.

Allosteric regulation in SARS-CoV-2 spike protein.

Allosteric regulation is common in protein-protein interactions and is thus promising in drug design. Previous experimental and simulation work supported the presence of allosteric regulation in the SARS-CoV-2 spike protein. Here the route of allosteric regulation in SARS-CoV-2 spike protein is examined by all-atom explicit solvent molecular dynamics simulations, contrastive machine learning, and the Ohm approach. It was found that peptide binding to the polybasic cleavage sites, especially the one at the first subunit of the trimeric spike protein, activates the fluctuation of the spike protein's backbone, which eventually propagates to the receptor-binding domain on the third subunit that binds to ACE2. Remarkably, the allosteric regulation routes starting from the polybasic cleavage sites share a high fraction (39-67%) of the critical amino acids with the routes starting from the nitrogen-terminal domains, suggesting the presence of an allosteric regulation network in the spike protein. Our study paves the way for the rational design of allosteric antibody inhibitors.

Water follows polar and nonpolar protein surface domains.

The conformation of water around proteins is of paramount importance, as it determines protein interactions. Although the average water properties around the surface of proteins have been provided experimentally and computationally, protein surfaces are highly heterogeneous. Therefore, it is crucial to determine the correlations of water to the local distributions of polar and nonpolar protein surface domains to understand functions such as aggregation, mutations, and delivery. By using atomistic simulations, we investigate the orientation and dynamics of water molecules next to 4 types of protein surface domains: negatively charged, positively charged, and charge-neutral polar and nonpolar amino acids. The negatively charged amino acids orient around 98% of the neighboring water dipoles toward the protein surface, and such correlation persists up to around 16 Å from the protein surface. The positively charged amino acids orient around 94% of the nearest water dipoles against the protein surface, and the correlation persists up to around 12 Å. The charge-neutral polar and nonpolar amino acids are also orienting the water neighbors in a quantitatively weaker manner. A similar trend was observed in the residence time of the nearest water neighbors. These findings hold true for 3 technically important enzymes (PETase, cytochrome P450, and organophosphorus hydrolase). Our results demonstrate that the water-amino acid degree of correlation follows the same trend as the amino acid contribution in proteins solubility, namely, the negatively charged amino acids are the most beneficial for protein solubility, then the positively charged amino acids, and finally the charge-neutral amino acids.

Efficient encapsulation of proteins with random copolymers.

Membraneless organelles are aggregates of disordered proteins that form spontaneously to promote specific cellular functions in vivo. The possibility of synthesizing membraneless organelles out of cells will therefore enable fabrication of protein-based materials with functions inherent to biological matter. Since random copolymers contain various compositions and sequences of solvophobic and solvophilic groups, they are expected to function in nonbiological media similarly to a set of disordered proteins in membraneless organelles. Interestingly, the internal environment of these organelles has been noted to behave more like an organic solvent than like water. Therefore, an adsorbed layer of random copolymers that mimics the function of disordered proteins could, in principle, protect and enhance the proteins' enzymatic activity even in organic solvents, which are ideal when the products and/or the reactants have limited solubility in aqueous media. Here, we demonstrate via multiscale simulations that random copolymers efficiently incorporate proteins into different solvents with the potential to optimize their enzymatic activity. We investigate the key factors that govern the ability of random copolymers to encapsulate proteins, including the adsorption energy, copolymer average composition, and solvent selectivity. The adsorbed polymer chains have remarkably similar sequences, indicating that the proteins are able to select certain sequences that best reduce their exposure to the solvent. We also find that the protein surface coverage decreases when the fluctuation in the average distance between the protein adsorption sites increases. The results herein set the stage for computational design of random copolymers for stabilizing and delivering proteins across multiple media.

Insights into the Enhanced Catalytic Activity of Cytochrome c When Encapsulated in a Metal-Organic Framework.

The encapsulation of enzymes within porous materials has shown great promise, not only in protecting the enzymes from denaturation under nonbiological environments, but also, in some cases, in facilitating their enzymatic reaction rates at favorable reaction conditions. While a number of hypotheses have been developed to explain this phenomenon, the detailed structural changes of the enzymes upon encapsulation within the porous material, which are closely related to their activity, remain largely elusive. Herein, the structural change of cytochrome c (Cyt c) upon encapsulation within a hierarchical metal-organic framework, NU-1000, is investigated through a combination of experimental and computational methods, such as electron paramagnetic resonance, solid-state ultraviolet-visible spectroscopy, and all-atom explicit solvent molecular dynamics simulations. The enhanced catalytic performance of Cyt c after being encapsulated within NU-1000 is supported by the physical and in silico observations of a change around the heme ferric active center.

Protein Surface Printer for Exploring Protein Domains.

The surface of proteins is vital in determining protein functions. Herein, a program, Protein Surface Printer (PSP), is built that performs multiple functions in quantifying protein surface domains. Two proteins, PETase and cytochrome P450, are used to validate that the program supports atomistic simulations with different combinations of programs and force fields. A case study is conducted on the structural analysis of the spike proteins of SARS-CoV-2 and SARS-CoV and the human cell receptor ACE2. Although the surface domains of both spike proteins are highly similar, their receptor-binding domains (RBDs) and the O-linked glycan domains are structurally different. The O-linked glycan domain of SARS-CoV-2 is highly positively charged, which may promote binding to negatively charged human cells.

PDADMAC/PSS Oligoelectrolyte Multilayers: Internal Structure and Hydration Properties at Early Growth Stages from Atomistic Simulations.

We analyze the internal structure and hydration properties of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) oligoelectrolyte multilayers at early stages of their layer-by-layer growth process. Our study is based on large-scale molecular dynamics simulations with atomistic resolution that we presented recently [Sánchez et al., Soft Matter 2019, 15, 9437], in which we produced the first four deposition cycles of a multilayer obtained by alternate exposure of a flat silica substrate to aqueous electrolyte solutions of such polymers at 0.1M of NaCl. In contrast to any previous work, here we perform a local structural analysis that allows us to determine the dependence of the multilayer properties on the distance to the substrate. We prove that the large accumulation of water and ions next to the substrate observed in previous overall measurements actually decreases the degree of intrinsic charge compensation, but this remains as the main mechanism within the interface region. We show that the range of influence of the substrate reaches approximately 3 nm, whereas the structure of the outer region is rather independent from the position. This detailed characterization is essential for the development of accurate mesoscale models able to reach length and time scales of technological interest.

Atomistic simulation of PDADMAC/PSS oligoelectrolyte multilayers: overall comparison of tri- and tetra-layer systems.

By employing large-scale molecular dynamics simulations of atomistically resolved oligoelectrolytes in aqueous solutions, we study in detail the first four layer-by-layer deposition cycles of an oligoelectrolyte multilayer made of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS). The multilayers are grown on a silica substrate in 0.1 M NaCl electrolyte solutions and the swollen structures are then subsequently exposed to varying added salt concentration. We investigated the microscopic properties of the films, analyzing in detail the differences between three- and four-layer systems. Our simulations provide insights into the early stages of growth of a multilayer, which are particularly challenging for experimental observations. We found rather strong complexation of the oligoelectrolytes, with fuzzy layering of the film structure. The main charge compensation mechanism is for all cases intrinsic, whereas extrinsic compensation is relatively enhanced for the layer of the last deposition cycle. In addition, we quantified other fundamental observables of these systems, such as the film thickness, water uptake, and overcharge fractions for each deposition layer.

Liquid worm-like and proto-micelles: water solubilization in amphiphile-oil solutions.

Noncovalent interactions determine the structure-property relationship of materials. Self-assembly originating from weak noncovalent interactions represents a broad variety of solution-based transformations spanning micellization and crystallization, which, nevertheless, conforms to neither colloid nor solution sciences. Here, we investigate the weak self-assembly in water-amphiphile-oil solutions to understand the connection between the amphiphilic molecular structure and water solubilization in oil. X-ray and neutron scattering, converged with large-scale atomistic molecular dynamics simulations, support the fact that the amphiphiles assemble into liquid worm-like micelles and loose inverted proto-micelles. The inverted proto-micelles are energetically ready to accommodate a higher amount of water. These structures arise from a balance of intermolecular interactions controlled by the amphiphile tail-group structures. Thus, by linking the aggregate morphology to the molecular structure, this work provides insights on the molecular design for control of water solubility and dispersion in oil.

Water Dynamics from the Surface to the Interior of a Supramolecular Nanostructure.

Water within and surrounding the structure of a biological system adopts context-specific dynamics that mediate virtually all of the events involved in the inner workings of a cell. These events range from protein folding and molecular recognition to the formation of hierarchical structures. Water dynamics are mediated by the chemistry and geometry of interfaces where water and biomolecules meet. Here we investigate experimentally and computationally the translational dynamics of vicinal water molecules within the volume of a supramolecular peptide nanofiber measuring 6.7 nm in diameter. Using Overhauser dynamic nuclear polarization relaxometry, we show that drastic differences exist in water motion within a distance of about one nanometer from the surface, with rapid diffusion in the hydrophobic interior and immobilized water on the nanofiber surface. These results demonstrate that water associated with materials designed at the nanoscale is not simply a solvent, but rather an integral part of their structure and potential functions.

Complexation Enhancement Drives Water-to-Oil Ion Transport: A Simulation Study.

We address the structures and energetics of ion solvation in aqueous and organic solutions to understand liquid-liquid ion transport. Atomistic molecular dynamics (MD) simulations with polarizable force field are performed to study the coordination transformations driving lanthanide (LnIII ) and nitrate ion transport between aqueous and an alkylamide-oil solution. An enhancement of the coordination behavior in the organic phase is achieved in contrast with the aqueous solution. In particular, the coordination number of Ce3+ increases from 8.9 in the aqueous to 9.9 in the organic solutions (from 8 in the aqueous to 8.8 in the organic systems for Yb3+ ). Moreover, the local coordination environment changes dramatically. Potential of mean force calculations show that the LnIII -ligand coordination interaction strengths follow the order of LnIII -nitrate>LnIII -water>LnIII -DMDBTDMA. They increase 2-fold in the lipophilic environment in comparison to the aqueous phase, and we attribute this to the shedding of the outer solvation shell. Our findings highlight the importance of outer sphere interactions on the competitive solvation energetics that cause ions to migrate between immiscible phases; an essential ingredient for advancing important applications such as rare earth metal separations. Some open questions in simulating the coordination behavior of heavy metals are also addressed.

Ion Transport Mechanisms in Liquid-Liquid Interface.

Interfacial liquid-liquid ion transport is of crucial importance to biotechnology and industrial separation processes including nuclear elements and rare earths. A water-in-oil microemulsion is formulated here with density and dimensions amenable to atomistic molecular dynamics simulation, facilitating convergent theoretical and experimental approaches to elucidate interfacial ion transport mechanisms. Lutetium(III) cations are transported from the 5 nm diameter water pools into the surrounding oil using an extractant (a lipophilic ligand). Changes in ion coordination sphere and interactions between the interfacial components are studied using a combination of synchrotron X-ray scattering, spectroscopy, and atomistic molecular dynamics simulations. Contrary to existing hypotheses, our model system shows no evidence of interfacial extractant monolayers, but rather ions are exchanged through water channels that penetrate the surfactant monolayer and connect to the oil-based extractant. Our results highlight the dynamic nature of the oil-water interface and show that lipophilic ion shuttles need not form flat monolayer structures to facilitate ion transport across the liquid-liquid interface.

Subtle Effects of Aliphatic Alcohol Structure on Water Extraction and Solute Aggregation in Biphasic Water/n-Dodecane.

Organic phase aggregation behavior of 1-octanol and its structural isomer, 2-ethylhexanol, in a biphasic n-dodecane-water system is studied with a combination of physical measurement, small-angle X-ray scattering (SAXS), and atomistic molecular dynamic simulations. Physical properties of the organic phases are probed following their mixing and equilibration with immiscible water phases. Studies reveal that the interfacial tension decreases as a function of increasing alcohol concentration over the solubility range of the alcohol with no evidence for a critical aggregate concentration (cac). An uptake of water into the organic phases is quantified, as a function of alcohol content, by Karl Fischer titrations. The extraction of water into dodecane was further assessed as a function of alcohol concentration via the slope-analysis method sometimes employed in chemical separations. This method provides a qualitative understanding of solute (water/alcohol) aggregation in the organic phase. The physical results are supported by analyses of SAXS data that reveals an emergence of aggregates in n-dodecane at elevated alcohol concentrations. The observed aggregate structure is dependent on the alcohol tail group geometry, consistent with surfactant packing parameter. The formation of these aggregates is discussed at a molecular level, where alcohol-alcohol and alcohol-water H-bonding interactions likely dominate the occurrence and morphology of the aggregates.

The Lanthanide Contraction beyond Coordination Chemistry.

The lanthanide contraction is conceptualized traditionally through coordination chemistry. Here we break this mold in a structural study of lanthanide ions dissolved in an amphiphilic liquid. The lanthanide contraction perturbs the weak interactions between molecular aggregates that drive mesoscale assembly and emergent behavior. The weak interactions correlate with lanthanide ion transport properties, suggesting new strategies for rare-earth separation that exploit forces outside of the coordination sphere.

Crystalline polymorphism induced by charge regulation in ionic membranes.

The crystallization of molecules with polar and hydrophobic groups, such as ionic amphiphiles and proteins, is of paramount importance in biology and biotechnology. By coassembling dilysine (+2) and carboxylate (-1) amphiphiles of various tail lengths into bilayer membranes at different pH values, we show that the 2D crystallization process in amphiphile membranes can be controlled by modifying the competition of long-range and short-range interactions among the polar and the hydrophobic groups. The pH and the hydrophobic tail length modify the intermolecular packing and the symmetry of their crystalline phase. For hydrophobic tail lengths of 14 carbons (C14), we observe the coassembly into crystalline bilayers with hexagonal molecular ordering via in situ small- and wide-angle X-ray scattering. As the tail length increases, the hexagonal lattice spacing decreases due to an increase in van der Waals interactions, as demonstrated by atomistic molecular dynamics simulations. For C16 and C18 we observe a reentrant crystalline phase transition sequence, hexagonal-rectangular-C-rectangular-P-rectangular-C-hexagonal, as the solution pH is increased from 3 to 10.5. The stability of the rectangular phases, which maximize tail packing, increases with increasing tail length. As a result, for very long tails (C22), the possibility of observing packing symmetries other than rectangular-C phases diminishes. Our work demonstrates that it is possible to systematically exchange chemical and mechanical energy by changing the solution pH value within a range of physiological conditions at room temperature in bilayers of molecules with ionizable groups.

Tips and Tricks in the Modeling of Supramolecular Peptide Assemblies.

Supramolecular peptide assemblies (SPAs) hold promise as materials for nanotechnology and biomedicine. Although their investigation often entails adapting experimental techniques from their protein counterparts, SPAs are fundamentally distinct from proteins, posing unique challenges for their study. Computational methods have emerged as indispensable tools for gaining deeper insights into SPA structures at the molecular level, surpassing the limitations of experimental techniques, and as screening tools to reduce the experimental search space. However, computational studies have grappled with issues stemming from the absence of standardized procedures and relevant crystal structures. Fundamental disparities between SPAs and protein simulations, such as the absence of experimentally validated initial structures and the importance of the simulation size, number of molecules, and concentration, have compounded these challenges. Understanding the roles of various parameters and the capabilities of different models and simulation setups remains an ongoing endeavor. In this review, we aim to provide readers with guidance on the parameters to consider when conducting SPA simulations, elucidating their potential impact on outcomes and validity.

A Biomimetic Multi-Component Subunit Vaccine via Ratiometric Loading of Hierarchical Hydrogels.

The development of subunit vaccines that mimic the molecular complexity of attenuated vaccines has been limited by the difficulty of intracellular co-delivery of multiple chemically diverse payloads at controllable concentrations. We report on hierarchical hydrogel depots employing simple poly(propylene sulfone) homopolymers to enable ratiometric loading of a protein antigen and four physicochemically distinct adjuvants in a hierarchical manner. The optimized vaccine consisted of immunostimulants either adsorbed to or encapsulated within nanogels, which were capable of noncovalent anchoring to subcutaneous tissues. These 5-component nanogel vaccines demonstrated enhanced humoral and cell-mediated immune responses compared to formulations with standard single adjuvant and antigen pairing. The use of a single simple homopolymer capable of rapid and stable loading and intracellular delivery of diverse molecular cargoes holds promise for facile development and optimization of scalable subunit vaccines and complex therapeutic formulations for a wide range of biomedical applications.