Water-Soluble Molecularly Imprinted Nanoparticle Receptors with Hydrogen-Bond-Assisted Hydrophobic Binding

Determining the Role of Surfactant on the Cytosolic Delivery of DNA Cross-Linked Micelles

Nucleic Acid Nanocapsules (NANs) are nucleic acid nanostructures that radially display oligonucleotides on the surface of cross-linked surfactant micelles. Their chemical makeup affords the stimuli-responsive release of therapeutically active DNA-surfactant conjugates into the cells. While NANs have so far demonstrated the effective cytosolic delivery of their nucleic acid cargo, as seen indirectly by their gene regulation capabilities, there remain gaps in the molecular understanding of how this process happens. Herein, we examine the enzymatic degradation of NANs and confirm the identity of the DNA-surfactant conjugates formed by using mass spectrometry (MS). With surface enhanced (resonance) Raman spectroscopy (SE(R)RS), we also provide evidence that the energy-independent translocation of such DNA-surfactant conjugates is contingent upon their release from the NAN structure, which, when intact, otherwise buries the hydrophobic surfactant tail in its interior. Such information suggests a critical role of the surfactant in the lipid disruption capability of the DNA surfactant conjugates generated from degradation of the NANs. Using NANs made with different tail lengths (C12 and C10), we show that this mechanism likely holds true despite significant differences in the physical properties (i.e., critical micelle concentration (CMC), surfactants per micelle, Nagg) of the resultant particles (C12 and C10 NANs). While the total cellular uptake efficiencies of C12 and C10 NANs are similar, there were differences observed in their cellular distribution and localized trafficking, even after ensuring that the total concentration of DNA was the same for both particles. Ultimately, C10 NANs appeared less diffuse within cells and colocalized less with lysosomes over time, achieving more significant knockdown of the target gene investigated, suggesting more effective endosomal escape. These differences indicate that the surfactant assembly and disassembly properties, including the number of surfactants per particle and the CMC can have important implications for the cellular delivery efficacy of DNA micelles and surfactant conjugates.

Selective Hydrolysis of Nonactivated Aryl Esters at pH 7 through Cooperative Catalysis

Most reported artificial esterases only hydrolyze highly activated substrates. We here report synthetic catalysts that hydrolyze nonactivated aryl esters at pH 7, via cooperative action of a thiourea group that mimics the oxyanion hole of a serine protease and a nearby nucleophilic/basic pyridyl group. The molecularly imprinted active site distinguishes subtle structural changes in the substrate, including elongation of the acyl chain by two carbons or shift of a remote methyl group by one carbon.

Synthesis of a magnetic micelle molecularly imprinted polymers to selective adsorption of rutin from Sophora japonica

Rutin is a naturally active compound with biological and medical value. The traditional extraction and separation method not only destroys the structure and activity of rutin, but results in a low extraction rate. In this work, the magnetic micellar molecularly imprinted polymer of rutin with a selective recognition function, i.e., RMMMIP was synthesized from 4 to Vinylphenylboron acid and 4-Vinylpyridine as functional monomer, derivatives of cholic acid as amphiphilic molecules. The internal hydrophobic and external hydrophilic characteristics of micelle was used to weaken the solvation of rutin and strengthen the non-covalent interaction between functional monomer and rutin. Fe₃O₄, as the core, endowed the composite materials with good magnetic responsiveness and was easy to separate solid from liquid. Then its structure and adsorption were studied, adsorbing capacity and recognition specific factor of RMMMIP are 11.9 mg·g^-1 and 3.55 respectively. RMMMIP was used for the separation of rutin from crude extracts of Sophora japonica Linn and showed a better selective adsorption capacity than quercetin, naringin and cyanidin-3-O-glucose. It indicated that RMMMIP as a specific adsorbent had the potential to be a practical way to purify rutin from rutin crude extracts in the future.

Oxidative Cleavage of Glycosidic Bonds by Synthetic Mimics of Lytic Polysaccharide Monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) cleave polysaccharides through copper-bound oxyl radicals. We report a synthetic mimic of LPMO that uses micelle-stabilized hydrogen bonds to bind a glycan and two molecularly imprinted hydrophobic pockets to accommodate the alkyl tail of the glycoside and a copper cofactor, respectively. Cleavage of alkyl glycosides and oligosaccharides with hydrogen peroxide occurs at room temperature in aqueous solution, with selectivities for both the glycan and the alkyl aglycon.

Factors Affecting Preparation of Molecularly Imprinted Polymer and Methods on Finding Template-Monomer Interaction as the Key of Selective Properties of the Materials

Molecular imprinting is a technique for creating artificial recognition sites on polymer matrices that complement the template in terms of size, shape, and spatial arrangement of functional groups. The main advantage of Molecularly Imprinted Polymers (MIP) as the polymer for use with a molecular imprinting technique is that they have high selectivity and affinity for the target molecules used in the molding process. The components of a Molecularly Imprinted Polymer are template, functional monomer, cross-linker, solvent, and initiator. Many things determine the success of a Molecularly Imprinted Polymer, but the Molecularly Imprinted Polymer component and the interaction between template-monomers are the most critical factors. This review will discuss how to find the interaction between template and monomer in Molecularly Imprinted Polymer before polymerization and after polymerization and choose the suitable component for MIP development. Computer simulation, UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Proton-Nuclear Magnetic Resonance (¹H-NMR) are generally used to determine the type and strength of intermolecular interaction on pre-polymerization stage. In turn, Suspended State Saturation Transfer Difference High Resolution/Magic Angle Spinning (STD HR/MAS) NMR, Raman Spectroscopy, and Surface-Enhanced Raman Scattering (SERS) and Fluorescence Spectroscopy are used to detect chemical interaction after polymerization. Hydrogen bonding is the type of interaction that is becoming a focus to find on all methods as this interaction strongly contributes to the affinity of molecularly imprinted polymers (MIPs).

Substrate Protection in Controlled Enzymatic Transformation of Peptides and Proteins

Proteins are involved in practically every single biological process. The many enzymes involved in their synthesis, cleavage, and posttranslational modification (PTM) carry out highly specific tasks with no usage of protecting groups. Yet, the chemists' strategy of protection/deprotection potentially can be highly useful, for example, when a specific biochemical reaction catalyzed by a broad-specificity enzyme needs to be inhibited, during infection of cells by enveloped viruses, in the invasion and spread of cancer cells, and upon mechanistic investigation of signal-transduction pathways. Doing so requires highly specific binding of peptide substrates in aqueous solution with biologically competitive affinities. Recent development of peptide-imprinted cross-linked micelles allows such protection and affords previously impossible ways of manipulating peptides and proteins in enzymatic transformations.

Tunable Artificial Enzyme-Cofactor Complex for Selective Hydrolysis of Acetals

Enzymes frequently use unimpressive functional groups such as weak carboxylic acids for efficient, highly selective catalysis including hydrolysis of acetals and even amides. Much stronger acids generally have to be used for such purposes in synthetic systems. We report here a method to position an acidic group near the acetal oxygen of 2-(4-nitrophenyl)-1,3-dioxolane bound by an artificial enzyme. The hydrolytic activity of the resulting artificial enzyme-cofactor complex was tuned by the number and depth of the active site as well as the hydrophobicity and acidity of the cofactor. The selectivity of the complex was controlled by the size and shape of the active site and enabled less reactive acetals to be hydrolyzed over more reactive ones.

Synthetic Glycosidase Distinguishing Glycan and Glycosidic Linkage in Its Catalytic Hydrolysis

Selective hydrolysis of carbohydrates is vital to the processing of these molecules in biology but has rarely been achieved with synthetic catalysts. The challenge is especially difficult because the catalyst needs to distinguish the inversion of a single hydroxyl and the α or β glycosidic bonds that join monosaccharide building blocks. Here we report synthetic glycosidase prepared through molecular imprinting within a cross-linked micelle. The nanoparticle catalyst resembles natural enzymes in dimension, water-solubility, and a hydrophilic/hydrophobic surface-core topology. Its boronic acid-functionalized active site binds its targeted glycoside substrate and an acid cofactor simultaneously, with the acidic group in close proximity to the exocyclic glycosidic oxygen. The hydrophobically anchored acid cofactor is tunable in acidity and causes selective cleavage of the targeted glycoside in mildly acidic water. Selectivity for both the glycan and the α/β glycosidic bond can be rationally designed through the molecular imprinting process.

Synthetic glycosidases for the precise hydrolysis of oligosaccharides and polysaccharides

Glycosidases are an important class of enzymes for performing the selective hydrolysis of glycans. Although glycans can be hydrolyzed in principle by acidic water, hydrolysis with high selectivity using nonenzymatic catalysts is an unachieved goal. Molecular imprinting in cross-linked micelles afforded water-soluble polymeric nanoparticles with a sugar-binding boroxole in the imprinted site. Post-modification installed an acidic group near the oxygen of the targeted glycosidic bond, with the acidity and distance of the acid varied systematically. The resulting synthetic glycosidase hydrolyzed oligosaccharides and polysaccharides in a highly controlled fashion simply in hot water. These catalysts not only broke down amylose with similar selectivities to those of natural enzymes, but they also could be designed to possess selectivity not available with biocatalysts. Substrate selectivity was mainly determined by the sugar residues bound within the active site, including their spatial orientations. Separation of the product was accomplished through in situ dialysis, and the catalysts left behind could be used multiple times with no signs of degradation. This work illustrates a general method to construct synthetic glycosidases from readily available building blocks via self-assembly, covalent capture, and post-modification. In addition, controlled, precise, one-step hydrolysis is an attractive way to prepare complex glycans from naturally available carbohydrate sources.

Multifuntional Gold Nanoparticles for the SERS Detection of Pathogens Combined with a LAMP-in-Microdroplets Approach

We developed a droplet-based optofluidic system for the detection of foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with surface-enhanced Raman scattering (SERS), which offers an excellent method for DNA ultradetection. However, the direct SERS detection of DNA compromises the simplicity of data interpretation due to the variability of its SERS fingerprints. Therefore, we designed an indirect SERS detection method using multifunctional gold nanoparticles (AuNPs) based on the formation of pyrophosphate generated during the DNA amplification by LAMP. Towards this goal, we prepared multifunctional AuNPs involving three components with key roles: (1) thiolated poly(ethylene glycol) as stabilizing agent, (2) 1-naphthalenethiol as Raman reporter, and (3) glutathione as a bioinspired chelating agent of magnesium (II) ions. Thus, the variation in the SERS signal of 1-naphthalenethiol was controlled by the aggregation of AuNPs triggered by the complexation of pyrophosphate and glutathione with free magnesium ions. Using this strategy, we detected Listeria monocytogenes, not only in buffer, but also in a food matrix (i.e., ultra-high temperaturemilk) enabled by the massive production of hotspots as a result of the self-assemblies that enhanced the SERS signal. This allowed the development of a microdroplet-LAMP-SERS platform with isothermal amplification and real-time identification capabilities.

Multifuntional Gold Nanoparticles for the SERS Detection of Pathogens Combined with a LAMP-in-Microdroplets Approach

We developed a droplet-based optofluidic system for the detection of foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with surface-enhanced Raman scattering (SERS), which offers an excellent method for DNA ultradetection. However, the direct SERS detection of DNA compromises the simplicity of data interpretation due to the variability of its SERS fingerprints. Therefore, we designed an indirect SERS detection method using multifunctional gold nanoparticles (AuNPs) based on the formation of pyrophosphate generated during the DNA amplification by LAMP. Towards this goal, we prepared multifunctional AuNPs involving three components with key roles: (1) thiolated poly(ethylene glycol) as stabilizing agent, (2) 1-naphthalenethiol as Raman reporter, and (3) glutathione as a bioinspired chelating agent of magnesium (II) ions. Thus, the variation in the SERS signal of 1-naphthalenethiol was controlled by the aggregation of AuNPs triggered by the complexation of pyrophosphate and glutathione with free magnesium ions. Using this strategy, we detected Listeria monocytogenes, not only in buffer, but also in a food matrix (i.e., ultra-high temperaturemilk) enabled by the massive production of hotspots as a result of the self-assemblies that enhanced the SERS signal. This allowed the development of a microdroplet-LAMP-SERS platform with isothermal amplification and real-time identification capabilities.

Tracking nucleic acid nanocapsule assembly, cellular uptake and disassembly using a novel fluorescently labeled surfactant

Intracellular trafficking and delivery of nucleic acids is an area of growing interest, particularly as it relates to therapeutic applications. Spectroscopic methods have been used to observe and quantitatively measure the delivery of oligonucleotides both in vitro and in vivo. Herein we demonstrate the use of a new fluorophore labeled surfactant presenting a solvatochromatic chromophore for tracking the assembly and degradation of a hybrid biomaterial we refer to as a nucleic acid nanocapsule (NAN). We show that the surfactant enables critical micelle concentration determination, monitoring of NAN disassembly in vitro, and the ability to track the cellular movement and activity of surfactant–oligonucleotide conjugates in cells when coupled with quantitative PCR analysis.

By introducing a solvatochromatic chromophore to a DNA–surfactant conjugate, the dynamics of its assembly and disassembly can be monitored using fluorescence spectroscopy.

Zwitterionic Molecularly Imprinted Cross-Linked Micelles for Alkaloid Recognition in Water

Molecular imprinting within surface/core doubly cross-linked micelles afforded water-soluble nanoparticle receptors for their template molecules. Extremely strong imprinting effects were consistently observed, with the imprinting factor >100:1 in comparison to nonimprinted nanoparticles prepared without the templates. The ionic nature of the cross-linkable surfactant strongly impacted the imprinting and binding process. Imprinted receptors prepared with a zwitterionic cross-linkable surfactant (4) outperformed a similar cationic one (1) when the template was zwitterionic or cationic and preferred their templates over structural analogues regardless of their ionic characteristics. Electrostatic interactions, however, dominated the receptors made with the cationic surfactant. The same micellar imprinting applied to simple as well as complex alkaloids. Imprinted receptors from 4 were also shown to categorize their alkaloid guests according to their structural similarity.

Effects of nano-confinement and conformational mobility on molecular imprinting of cross-linked micelles

Molecular imprinting is a facile method to create guest-complementary binding sites in a cross-linked polymeric network. When performed within cross-linked micelles, the resulting molecularly imprinted nanoparticles (MINPs) exhibited an extraordinary ability to distinguish subtle structural changes in the guest, including the shift of a hydrophilic or hydrophobic group by 1 carbon and addition of a single methylene/methyl group. A high surface-cross-linking density prior to core-cross-linking was key to the high-fidelity imprinting, enhancing both the binding affinity of the imprinted micelle for the template and selectivity among structural analogues. Whereas the imprinted site closely complemented the hydrophilic surface anchoring group and rigid hydrophobic aromatic core, it was expanded significantly for a conformationally mobile small group (i.e., methoxy).

Sequence-Selective Recognition of Peptides in Aqueous Solution: A Supramolecular Approach through Micellar Imprinting

Sequence-selective recognition of peptides in water has been one of the most important and yet unsolved problems in bioorganic and supramolecular chemistry. The motivation comes from not only the importance of these molecules in biology but also the fundamental challenges involved in the research. Molecular imprinting in doubly cross-linked surfactant micelles offers a unique solution to this problem by creating a "supramolecular code" on the micelle surface that matches the structural features of the peptide chain. Hydrophobic "dimples" are constructed on imprinted micelles that match the hydrophobic side chains of the peptide precisely in size and shape. Polar binding functionalities are installed at correct positions to interact with specific acidic and basic groups on the peptide. Secondary hydrogen-bonding and electrostatic interactions are introduced through imprinting to enhance the binding affinity and specificity further. Binding affinities of tens of nanomolar are readily achieved in water for biological peptides with over a dozen residues. Excellent binding selectivity is observed even for subtly different peptides. The synthesis of these protein-sized nanoparticles involves a one-pot reaction complete within 2 days; purification requires nothing but precipitation and solvent washing. These features make the molecularly imprinted nanoparticles (MINPs) highly promising peptide-binding "artificial antibodies" for chemical and biological applications.

Selective Binding of Folic Acid and Derivatives by Imprinted Nanoparticle Receptors in Water

Folate receptors are overexpressed on cancer cells and frequently used for targeted delivery. Creation of synthetic receptors to bind folic acid and its analogues in water, however, is challenging because of its complex hydrogen-bonding patterns and competition for hydrogen bonds from the solvent. Micellar imprinting within cross-linkable surfactants circumvented these problems because the nonpolar micellar environment strengthened the hydrogen bonds between the amide group in the surfactant and the template molecule. Incorporation of polymerizable thiouronium functional monomers further enhanced the binding through hydrogen-bond-reinforced ion pairs with the glutamate moiety of the template. The resulting imprinted micelles were able to bind folate and their analogues with submicromolar affinity and distinguish small changes in the hydrogen-bonding patterns as well as the number/position of carboxylic acids. The binding constant obtained was 2-3 orders of magnitude higher than those reported for small-molecule synthetic receptors. Our binding study also revealed interesting details in the binding. For example, the relative contributions of different segments of the molecule to the binding followed the order of carboxylates > pyrimidine ring > pyrazine ring.

Water-Soluble Nanoparticle Receptors Supramolecularly Coded for Acidic Peptides

Sequence-specific recognition of peptides is of enormous importance to many chemical and biological applications, but has been difficult to achieve due to the minute differences in the side chains of amino acids. Acidic peptides are known to play important roles in cell growth and gene expression. In this work, we report molecularly imprinted micelles coded with molecular recognition information for the acidic and hydrophobic side chains of acidic peptides. The imprinted receptors could distinguish acidic amino acids from other polar and nonpolar amino acids, with dissociation constants of tens of nanomolar for biologically active peptides containing up to 18 amino acids.

Imprinting Technology in Electrochemical Biomimetic Sensors

Biosensors are a promising tool offering the possibility of low cost and fast analytical screening in point-of-care diagnostics and for on-site detection in the field. Most biosensors in routine use ensure their selectivity/specificity by including natural receptors as biorecognition element. These materials are however too expensive and hard to obtain for every biochemical molecule of interest in environmental and clinical practice. Molecularly imprinted polymers have emerged through time as an alternative to natural antibodies in biosensors. In theory, these materials are stable and robust, presenting much higher capacity to resist to harsher conditions of pH, temperature, pressure or organic solvents. In addition, these synthetic materials are much cheaper than their natural counterparts while offering equivalent affinity and sensitivity in the molecular recognition of the target analyte. Imprinting technology and biosensors have met quite recently, relying mostly on electrochemical detection and enabling a direct reading of different analytes, while promoting significant advances in various fields of use. Thus, this review encompasses such developments and describes a general overview for building promising biomimetic materials as biorecognition elements in electrochemical sensors. It includes different molecular imprinting strategies such as the choice of polymer material, imprinting methodology and assembly on the transduction platform. Their interface with the most recent nanostructured supports acting as standard conductive materials within electrochemical biomimetic sensors is pointed out.

A General Method for Selective Recognition of Monosaccharides and Oligosaccharides in Water

Molecular recognition of carbohydrates plays vital roles in biology but has been difficult to achieve with synthetic receptors. Through covalent imprinting of carbohydrates in boroxole-functionalized cross-linked micelles, we prepared nanoparticle receptors for a wide variety of mono- and oligosaccharides. The boroxole functional monomer bound the sugar templates through cis-1,2-diol, cis-3,4-diol, and trans-4,6-diol. The protein-sized nanoparticles showed excellent selectivity for d-aldohexoses in water with submillimolar binding affinities and completely distinguished the three biologically important hexoses (glucose, mannose, and galactose). Glycosides with nonpolar aglycon showed stronger binding due to enhanced hydrophobic interactions. Oligosaccharides were distinguished on the basis of their monosaccharide building blocks, glycosidic linkages, chain length, as well as additional functional groups that could interact with the nanoparticles.