Supramolecular Assemblies for Transporting Proteins Across an Immiscible Solvent Interface

Using Nanoscopic Solvent Defects for the Spatial and Temporal Manipulation of Single Assemblies of Molecules

Here we report the use of defects in ordered solvents to form, manipulate, and characterize individual molecular assemblies of either small-molecule amphiphiles or polymers. The approach exploits nanoscopic control of the structure of nematic solvents (achieved by the introduction of topological defects) to trigger the formation of molecular assemblies and the subsequent manipulation of defects using electric fields. We show that molecular assemblies formed in solvent defects slow defect motion in the presence of an electric field and that time-of-flight measurements correlate with assembly size, suggesting methods for the characterization of single assemblies of molecules. Solvent defects are also used to transport single assemblies of molecules between solvent locations that differ in composition, enabling the assembly and disassembly of molecular "nanocontainers". Overall, our results provide new methods for studying molecular self-assembly at the single-assembly level and new principles for integrated nanoscale chemical systems that use solvent defects to transport and position molecular cargo.

Facile Fabrication of 1-Methylimidazole/Cu Nanozyme with Enhanced Laccase Activity for Fast Degradation and Sensitive Detection of Phenol Compounds

Facile construction of functional nanomaterials with laccase-like activity is important in sustainable chemistry since laccase is featured as an efficient and promising catalyst especially for phenolic degradation but still has the challenges of high cost, low activity, poor stability and unsatisfied recyclability. In this paper, we report a simple method to synthesize nanozymes with enhanced laccase-like activity by the self-assembly of copper ions with various imidazole derivatives. In the case of 1-methylimidazole as the ligand, the as-synthesized nanozyme (denoted as Cu-MIM) has the highest yield and best activity among the nanozymes prepared. Compared to laccase, the K_m of Cu-MIM nanozyme to phenol is much lower, and the v_max is 6.8 times higher. In addition, Cu-MIM maintains excellent stability in a variety of harsh environments, such as high pH, high temperature, high salt concentration, organic solvents and long-term storage. Based on the Cu-MIM nanozyme, we established a method for quantitatively detecting phenol concentration through a smartphone, which is believed to have important applications in environmental protection, pollutant detection and other fields.

Cluster-Assembled Nanoporous Super-Hydrophilic Smart Surfaces for On-Target Capturing and Processing of Biological Samples for Multi-Dimensional MALDI-MS

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) on cluster-assembled super-hydrophilic nanoporous titania films deposited on hydrophobic conductive-polymer substrates feature a unique combination of surface properties that significantly improve the possibilities of capturing and processing biological samples before and during the MALDI-MS analysis without changing the selected sample target (multi-dimensional MALDI-MS). In contrast to pure hydrophobic surfaces, such films promote a remarkable biologically active film porosity at the nanoscale due to the soft assembling of ultrafine atomic clusters. This unique combination of nanoscale porosity and super-hydrophilicity provides room for effective sample capturing, while the hydrophilic-hydrophobic discontinuity at the border of the dot-patterned film acts as a wettability-driven containment for sample/reagent droplets. In the present work, we evaluate the performance of such advanced surface engineered reactive containments for their benefit in protein sample processing and characterization. We shortly discuss the advantages resulting from the introduction of the described chips in the MALDI-MS workflow in the healthcare/clinical context and in MALDI-MS bioimaging (MALDI-MSI).

Enzyme Catalysis in Non-Native Environment with Unnatural Selectivity Using Polymeric Nanoreactors

The utilization of enzymes for catalysis in organic solvents, while exhibiting selectivity to different substrates, is a big challenge. We report an amphiphilic random copolymer system that self-assembles with enzymes in an organic solvent to form nanoreactors. These encapsulated enzymes are not denatured and they do preserve the catalytic activity. The cross-linkable functional groups in the hydrophobic compartments of the polymers offer to control accessibility to the enzyme. This varied accessibility due to the polymer host, rather than the enzyme itself, endows the nanoreactor with an unnatural selectivity. The findings here highlight the significant potential of simple polymer-based enzyme nanoreactors to execute selective organic reactions under non-native conditions.

Tuning Net Charge in Aliphatic Polycarbonates Alters Solubility and Protein Complexation Behavior

A synthetic strategy yielded polyelectrolytes and polyampholytes with tunable net charge for complexation and protein binding. Organocatalytic ring-opening polymerizations yielded aliphatic polycarbonates that were functionalized with both carboxylate and ammonium side chains in a post-polymerization, radical-mediated thiol-ene reaction. Incorporating net charge into the polymer architecture altered the chain dimensions in phosphate buffered solution in a manner consistent with self-complexation and complexation behavior with model proteins. A net cationic polyampholyte with 5% of carboxylate side chains formed large clusters rather than small complexes with bovine serum albumin, while 50% carboxylate polyampholyte was insoluble. Overall, the aliphatic polycarbonates with varying net charge exhibited different macrophase solution behaviors when mixed with protein, where self-complexation appears to compete with protein binding and larger-scale complexation.

K. S, Panigrahi NR, Mishra RK, Saraogi I. Amphiphilic Small-Molecule Assemblies to Enhance the Solubility and Stability of Hydrophobic Drugs

Amphiphilic assemblies made from diverse synthetic building blocks are well known for their biomedical applications. Here, we report the synthesis of gemini-type amphiphilic molecules that form stable assemblies in water. The assembly property of molecule M2 in aqueous solutions was first inferred from peak broadening observed in the proton NMR spectrum. This was supported by dynamic light scattering and transmission electron microscopy analysis. The assembly formed from M2 (M2agg) was used to solubilize the hydrophobic drugs curcumin and doxorubicin at physiological pH. M2agg was able to effectively solubilize curcumin as well as protect it from degradation under UV irradiation. Upon solubilization in M2agg, curcumin showed excellent cell permeability and higher toxicity to cancer cells over normal cells, probably because of enhanced cellular uptake and increased stability. M2agg also showed pH-dependent release of doxorubicin, resulting in controlled toxicity on cancer cell lines, making it a promising candidate for the selective delivery of drugs to cancer cells.

Tunable Polymeric Scaffolds for Enzyme Immobilization

The number of methodologies for the immobilization of enzymes using polymeric supports is continuously growing due to the developments in the fields of biotechnology, polymer chemistry, and nanotechnology in the last years. Despite being excellent catalysts, enzymes are very sensitive molecules and can undergo denaturation beyond their natural environment. For overcoming this issue, polymer chemistry offers a wealth of opportunities for the successful combination of enzymes with versatile natural or synthetic polymers. The fabrication of functional, stable, and robust biocatalytic hybrid materials (nanoparticles, capsules, hydrogels, or films) has been proven advantageous for several applications such as biomedicine, organic synthesis, biosensing, and bioremediation. In this review, supported with recent examples of enzyme-protein hybrids, we provide an overview of the methods used to combine both macromolecules, as well as the future directions and the main challenges that are currently being tackled in this field.

Polymeric nanoassemblies for enrichment and detection of peptides and proteins in human breast milk

Human breast milk is an understudied biological fluid that may be useful for early detection of breast cancer. Methods for enriching and detecting biomarkers in human breast milk, however, are not as well-developed as compared with other biological fluids. In this work, we demonstrate a new enrichment method based on polymeric nanoassemblies that is capable of enhancing the mass spectrometry-based detection of peptides and proteins in human breast milk. In this method, positively charged nanoassemblies are used to selectively deplete abundant proteins in milk based on electrostatic interactions, which simplifies the mixture and enhances detection of positively charged peptides and proteins. Negatively charged nanoassemblies are used in a subsequent enrichment step to further enhance the detection and quantification of trace-level peptides and proteins. Together the depletion and enrichment steps allow model biomarkers to be detected at low nM levels, which are close to instrumental limits of detection. This new method not only demonstrates the ability to detect proteins in human breast milk but also provides an alternative approach for targeted protein detection in complex biological matrices. Graphical abstract.

Atom Transfer Radical Polymerization for Biorelated Hybrid Materials

Proteins, nucleic acids, lipid vesicles, and carbohydrates are the major classes of biomacromolecules that function to sustain life. Biology also uses post-translation modification to increase the diversity and functionality of these materials, which has inspired attaching various other types of polymers to biomacromolecules. These polymers can be naturally (carbohydrates and biomimetic polymers) or synthetically derived and have unique properties with tunable architectures. Polymers are either grafted-to or grown-from the biomacromolecule's surface, and characteristics including polymer molar mass, grafting density, and degree of branching can be controlled by changing reaction stoichiometries. The resultant conjugated products display a chimerism of properties such as polymer-induced enhancement in stability with maintained bioactivity, and while polymers are most often conjugated to proteins, they are starting to be attached to nucleic acids and lipid membranes (cells) as well. The fundamental studies with protein-polymer conjugates have improved our synthetic approaches, characterization techniques, and understanding of structure-function relationships that will lay the groundwork for creating new conjugated biomacromolecular products which could lead to breakthroughs in genetic and tissue engineering.

Ligand-Regulated Uptake of Dipolar-Aromatic Guests by Hydrophobically Assembled Suprasphere Hosts

The selective uptake of guests by capsules, cages, and containers, and porous solid-state materials such as zeolites and metal-organic frameworks (MOFs), is generally controlled by pore size and by the dimensions and chemical properties of interior host domains. For soluble and solid-state structures, however, few options are available for modifying their outer pores to impart chemoselectivity to the uptake of similarly sized guests. We now show that by using alkane-coated gold cores as structural building units (SBUs) for the hydrophobic self-assembly of water-soluble suprasphere hosts, ligand exchange can be used to tailor the chemical properties at the pores that provide access to their interiors. For polar polyethylene glycol functionalized ligands, occupancies after equal times increase linearly with the dipole moments of chloro-, nitro- dichloro-, and dinitro- (o-, m-, and p-) benzene guests. Selectivity is reversed, however, upon incorporation of hydrophobic ligands. The findings demonstrate how self-assembled gold-core SBUs, with replaceable ligands, inherently provide for rationally introducing finely tuned and quantitatively predictable chemoselectivity to host-guest chemistry in water.

Bio-inspired temporal regulation of ion-transport in nanochannels

Temporal regulation of mass transport across the membrane is a vital feature of biological systems. Such regulatory mechanisms rely on complex biochemical reaction networks, often operating far from equilibrium. Herein, we demonstrate biochemical reaction mediated temporal regulation of mass transport in nanochannels of mesoporous silica sphere. The rationally designed nanochannels with pH responsive electrostatic gating are fabricated through a hetero-functionalization approach utilizing propylamine and carboxylic acid moieties. At basic pH, cationic small molecules can diffuse into the nanochannels which release back to the solution at acidic pH. The transient ion transport is temporally controlled using a base as fuel along with esterase enzyme as the mediator. The slow enzymatic hydrolysis of a dormant deactivator (ethyl acetate) determines the lifetime of transient encapsulated state, which can be programmed easily by modulating the enzymatic activity of esterase. This system represents a unique approach to create autonomous artificial cellular models.

Tunable enzyme responses in amphiphilic nanoassemblies through alterations in the unimer-aggregate equilibrium

Developing design rules that offer tailorability in materials' response to enzymes is of great importance, as such materials are of interest in a variety of biomedical applications including sensing, diagnostics and drug delivery. Using an amphiphilic oligomeric platform, we show that the degree of polymerization and hydrophilic-lipophilic balance variations can be utilized to alter the unimer-aggregate equilibrium, which in turn offers robust tunability of the host-guest properties of the amphiphilic nanoassemblies. We found that oligomeric assemblies with higher degree of polymerization are less sensitive to enzymatic degradation and release the guest molecules at a slower rate. Similarly, increasing the hydrophilicity makes these assemblies more sensitive to enzymes. These trends can be understood by correlating these changes to predictable modifications in the dynamics of the unimer-aggregate equilibrium, which affects the substrate availability for enzymes. These findings provide insights into rationally tuning the response of enzyme-sensitive supramolecular assemblies.

Supramolecular Polymeric Assemblies for the Selective Depletion of Abundant Acidic Proteins in Serum

The analysis of low-level protein biomarkers in serum is precluded by the presence of other highly abundant serum proteins. Hence, the preliminary removal of serum albumin along with other abundant proteins in serum (i.e., immunoglobulins, transferrin, haptoglobin, α-2-macroglobulin, and apolipoproteins) is often a requirement prior to any biomarker analysis. In this work, we take advantage of the low isoelectric points (pI's) of these highly abundant proteins to selectively deplete them from serum by extraction using functionalized amphiphilic polymeric nanoassemblies. The selectivity of extraction is dependent on the pI of the protein and the extraction pH, which holds true even for extremely complex protein mixtures like serum. High extraction capacity is achieved by optimizing the extraction conditions and is found to be comparable to currently available methods for depletion. Depletion of these abundant acidic proteins allows for the enhanced detection of higher pI proteins and enables a 3 orders of magnitude increase in detection sensitivity for a putative cancer biomarker, demonstrating the utility of these polymeric assemblies for enhancing the analysis of the serum proteome.

Improved mass spectrometric detection of acidic peptides by variations in the functional group pKa values of reverse micelle extraction agents

Polymeric reverse micelles can be used to selectively extract peptides from complex mixtures via a two-phase extraction approach. In previous work, we have shown that the charge polarity of the hydrophilic functional group that is in the interior of the reverse micelle dictates the extraction selectivity. To investigate how the extraction is influenced by the inherent pKa of the functional group, we designed and tested a series of polymeric reverse micelles with variations in the hydrophilic functional group. From this series of polymers, we find that the extraction capability of the reverse micelles in an apolar phase is directly related to the aqueous phase pKa of the interior functional group, suggesting that the functional groups maintain their inherent chemistry even in the confined environment of the reverse micelle interior. Because these functional groups maintain their inherent pKa in the reverse micelle interior, they provide predictable extraction selectivity upon changes in aqueous phase pH. We exploit this finding to demonstrate that sulfonate-containing polymers can be used to remove basic peptides from complex mixtures, thereby allowing the improved detection of acidic peptides. Using these new materials, we also demonstrate a new means of isoelectric point (pI) bracketing that allows the mass spectrometric detection of peptides with a defined and narrow range of pI values.