Imprinted Polymeric Nanoparticles as Artificial Enzymes for Ester Hydrolysis at Room Temperature and pH 7

Artificial amidase with modifiable active sites and designable substrate selectivity for aryl amide hydrolysis

Hydrolases are used by cells to process key biomolecules including peptides and esters. Previous synthetic mimics of proteases generally only hydrolyze highly active ester derivatives. We report a synthetic catalyst with an acid/base dyad in its active site that hydrolyzes aryl amides under near physiological conditions. The aspartic protease mimic achieves substrate selectivity by its imprinted active site, which is tunable through different template molecules used during molecular imprinting. It can be designed to maintain or override the intrinsic activities of aryl amides in a predictable manner.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Molecularly Imprinted Nanozymes for Selective Hydrolysis of Aromatic Carbonates Under Mild Conditions

Aliphatic polycarbonate (PC) can be readily hydrolyzed by lipase, but bisphenol A-derived PC (i.e., BPA-PC) lacks enzyme catalysts for their efficient hydrolysis due to the high hydrophobicity and rigidity of its polymer backbone. This study aims to develop an artificial nanozyme for the selective hydrolysis of small-molecule aromatic carbonates as model substrates for BPA-PC. The catalyst is prepared through molecular imprinting of cross-linkable micelles in a one-pot reaction using a thiourea template and a zinc-containing functional monomer. The resulting water-soluble nanoparticle resembles a hydrolytic metalloenzyme to bind the appropriately shaped aromatic carbonate substrate in the active site, with the nearby zinc acting as a cofactor to activate a water molecule for the nucleophilic attack on the carbonate. Catalytic hydrolysis is observed at room temperature and pH 7, with a rate acceleration of 1 × 106 for diphenyl carbonate.

Direct Synthesis of Artificial Esterase through Molecular Imprinting Using a Substrate-Mimicking Acylthiourea Template

Most reported artificial esterases hydrolyze only activated esters. We here report a one-pot synthesis of artificial esterases via molecular imprinting. An acylthiourea template hydrogen bonds with 4-vinylbenzoic acid and coordinates to a polymerizable zinc complex inside a cross-linkable surfactant micelle. Double cross-linking of the micelle yields a polymeric nanoparticle catalyst that mimics a metalloenzyme to activate a water molecule for nucleophilic attack on the bound ester. The catalyst hydrolyzes both activated and unactivated esters under mild conditions with selectivity.

Microwave-Assisted Hydrolysis of Ethyl Azolylacetates and Cinnamates with K2CO3: Synthesis of Potassium Carboxylates

In this study, the hydrolysis of ethyl azolylacetates and ethyl cinnamates using K2CO3/ethanol under microwave irradiation was developed. For this purpose, ethyl azolylacetates were first synthesized by nucleophilic substitution between the corresponding azole and ethyl bromoacetate under sonication at 50 °C for 3 h, yielding derivatives with 10-92% chemical yields, while ethyl cinnamates were obtained by a microwave-assisted Horner-Wadsworth-Emmons (HWE) reaction of triethyl phosphonoacetate with a variety of aryl aldehydes at 140 °C for 20 min, yielding derivatives with moderate to high yields (67-98%). Initially, the optimization of the hydrolysis reaction was performed using ethyl pyrazolylacetate as a model starting material while varying the temperature, time, and base equivalents; the best results were achieved by carrying out the reaction at 180 °C for 20 min with 3.0 eq of K2CO3. This simple and greener method facilitated the synthesis of potassium carboxylates in moderate to high yields, 80-98% for azolyl derivatives and 73-98% for cinnamate derivatives. The structures of all potassium carboxylates were confirmed by FTIR, 1H, 13C NMR, and HRMS.

Nanoparticles that Distinguish Chemical and Supramolecular Contexts of Lysine for Single-Site Functionalization of Protein

Lysine is one of the most abundant residues on the surface of proteins and its site-selective functionalization is extremely challenging. The existing methods of functionalization rely on differential reactivities of lysine on a protein, making it impossible to label less reactive lysines selectively. We here report polymeric nanoparticles that mimic enzymes involved in the posttranslational modifications of proteins that distinguish the chemical and supramolecular contexts of a lysine and deliver the labeling reagent precisely to its ε amino group. The nanoparticles are prepared through molecular imprinting of cross-linkable surfactant micelles, plus an in situ, on-micelle derivatization of the peptide template prior to the imprinting. The procedures encode the polymeric nanoparticles with all the supramolecular information needed for sequence identification and precise labeling, allowing single-site functionalization of a predetermined lysine on the target protein in a mixture.

A Theoretical-Computational Study of Phosphodiester Bond Cleavage Kinetics as a Function of the Temperature

The hydrolysis of the phosphodiester bond is an important chemical reaction involved in several biological processes. Here, we study the cleavage of this bond by means of a theoretical-computational method in a model system, the dineopentyl phosphate. By such an approach, we reconstructed the kinetics and related thermodynamics of this chemical reaction along an isochore. In particular, we evaluated the kinetic constants of all the reaction steps within a wide range of temperatures, mostly corresponding to conditions where no experimental measures are available due to the extremely slow kinetics. Our results, in good agreement with the experimental data, show the robustness of our theoretical-computational methodology which can be easily extended to more complex systems.

Tuning Active Site Electron Density for Enhanced Molecular Recognition and Catalysis

Enzymes have an extraordinary ability to utilize aromatic interactions for molecular recognition and catalysis. We here report molecularly imprinted nanoparticle receptors. The aromatic "wall" material in the imprinted binding site is used to enhance the molecular recognition of aromatic guests that have similar charges, shapes, and sizes but differ in π-electron density. Additionally, aromatic interactions are employed to activate an electron-rich aryl leaving group on a glycoside, mimicking the nucleoside hydrolase of the parasite Trypanosoma vivax.

Rational Design and Synthesis of an Artificial Enzyme for SN2 Reactions through Micellar Imprinting

The rational design of catalysts with enzyme-like properties is an elusive goal of chemists despite tremendous interest. Molecular imprinting inside surfactant micelles, followed by postmodification, creates a tailored active site in a water-soluble polymeric "artificial enzyme" for the benzylation of 4-nitrophenol. The reaction happens under neutral conditions with excellent substrate selectivity. Similar to many enzymes, electrostatics play vital roles in catalysis and can be tuned through different bases introduced into the active site.

Hydrolytic nanozymes: Preparation, properties, and applications

Hydrolytic nanozymes, as promising alternatives to hydrolytic enzymes, can efficiently catalyze the hydrolysis reactions and overcome the operating window limitations of natural enzymes. Moreover, they exhibit several merits such as relatively low cost, easier recovery and reuse, improved operating stability, and adjustable catalytic properties. Consequently, they have found relevance in practical applications such as organic synthesis, chemical weapon degradation, and biosensing. In this review, we highlight recent works addressing the broad topic of the development of hydrolytic nanozymes. We review the preparation, properties, and applications of six types of hydrolytic nanozymes, including AuNP-based nanozymes, polymeric nanozymes, surfactant assemblies, peptide assemblies, metal and metal oxide nanoparticles, and MOFs. Last, we discuss the remaining challenges and future directions. This review will stimulate the development and application of hydrolytic nanozymes.

Improving the Selectivity of the C-C Coupled Product Electrosynthesis by Using Molecularly Imprinted Polymer─An Enhanced Route from Phenol to Biphenol

We developed a procedure for selective 2,4-dimethylphenol, DMPh, direct electro-oxidation to 3,3',5,5'-tetramethyl-2,2'-biphenol, TMBh, a C-C coupled product. For that, we used an electrode coated with a product-selective molecularly imprinted polymer (MIP). The procedure is reasonably selective toward TMBh without requiring harmful additives or elevated temperatures. The TMBh product itself was used as a template for imprinting. We followed the template interaction with various functional monomers (FMs) using density functional theory (DFT) simulations to select optimal FM. On this basis, we used a prepolymerization complex of TMBh with carboxyl-containing FM at a 1:2 TMBh-to-FM molar ratio for MIP fabrication. The template-FM interaction was also followed by using different spectroscopic techniques. Then, we prepared the MIP on the electrode surface in the form of a thin film by the potentiodynamic electropolymerization of the chosen complex and extracted the template. Afterward, we characterized the fabricated films by using electrochemistry, FTIR spectroscopy, and AFM, elucidating their composition and morphology. Ultimately, the DMPh electro-oxidation was performed on the MIP film-coated electrode to obtain the desired TMBh product. The electrosynthesis selectivity was much higher at the electrode coated with MIP film in comparison with the reference nonimprinted polymer (NIP) film-coated or bare electrodes, reaching 39% under optimized conditions. MIP film thickness and electrosynthesis parameters significantly affected the electrosynthesis yield and selectivity. At thicker films, the yield was higher at the expense of selectivity, while the electrosynthesis potential increase enhanced the TMBh product yield. Computer simulations of the imprinted cavity interaction with the substrate molecule demonstrated that the MIP cavity promoted direct coupling of the substrate to form the desired TMBh product.

Carbonic anhydrase mimics with rationally designed active sites for fine-tuned catalytic activity and selectivity in ester hydrolysis

Numerous hydrolytic enzymes utilize zinc as a cofactor for catalysis. We here report water-soluble polymeric nanoparticles with zinc ions in active sites and a nearby base as a mimic of carbonic anhydrase (CA). Their pKa of 6.3-6.4 for zinc-bound water is lower than the 6.8-7.3 value for natural enzymes, which allows the catalyst to hydrolyze nonactivated alkyl esters under neutral conditions-a long sought-after goal for artificial esterases. The size and shape of the active site can be rationally tuned through a template used in molecular imprinting. Subtle structural changes in the template, including shifting an ethyl group by one C-N bond and removal of a methylene group, correlate directly with catalytic activity. A catalyst can be made to be highly specific or have broad substrate specificity through modular synthesis of templates.

Supramolecular Regulation of Catalytic Activity in Molecularly Responsive Catalysts

Some enzymes switch between an open form and a closed form. We report a molecularly tuned catalyst that accommodates a substrate and a signal molecule simultaneously. Binding of the signal molecule helps direct the reactive group of the substrate to the catalytic group and enhances the catalytic activity. Subtle structural changes in either the substrate or the signal molecule are readily detected. The switching mechanism also allows the catalytic reaction to be turned on and off reversibly by specific molecular signals.

Artificial Esterase for Cooperative Catalysis of Ester Hydrolysis at pH 7

Ester is one of the most prevalent functional groups in natural and man-made products. Natural esterases hydrolyze nonactivated alkyl esters readily but artificial esterases generally use highly activated p-nitrophenyl esters as substrates. We report synthetic esterases constructed through molecular imprinting in cross-linked micelles. The water-soluble nanoparticle catalysts contain a thiouronium cation to mimic the oxyanion hole and a nearby base to assist the hydrolysis. Whereas this catalytic motif readily affords large rate acceleration for the hydrolysis of p-nitrophenyl hexanoate, nonactivated cyclopentyl hexanoate demands catalytic groups that can generate a strong nucleophile (hydroxide) in the active site. The hydroxide is stabilized by the protonated base when the external solution is at pH 7, enabling the hydrolysis of activated and nonactivated esters under neutral conditions.

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.

Minimalistic Artificial Catalysts with Esterase-Like Activity from Multivalent Nanofibers Formed by the Self-Assembly of Dipeptides

Imitating and incorporating the multiple key structural features observed in natural enzymes into a minimalistic molecule to develop an artificial catalyst with outstanding catalytic efficiency is an attractive topic for chemists. Herein, we designed and synthesized one class of minimalistic dipeptide molecules containing a terminal -SH group and a terminal His-Phe dipeptide head linked by a hydrophobic alkyl chain with different lengths, marked as HS-C n+1-His-Phe (n = 4, 7, 11, 15, and 17; n + 1 represents the carbon atom number of the alkyl chain). The His (-imidazole), Phe (-CO2 -) moieties, the terminal -SH group, and a long hydrophobic alkyl chain were found to have important contributions to achieve high binding ability leading to outstanding absolute catalytic efficiency (k cat/K M) toward the hydrolysis reactions of carboxylic ester substrates.

Tailoring Protein-Polymer Conjugates as Efficient Artificial Enzymes for Aqueous Asymmetric Aldol Reactions

Artificial enzymes are becoming a powerful toolbox for selective organic syntheses. Herein, we first propose an advanced artificial enzyme by polymeric modularity as an efficient aldolase mimic for aqueous asymmetric aldol reactions. Based on an in-depth understanding of the aldolase reaction mechanism and our previous work, we demonstrate the modular design of protein-polymer conjugates by co-incorporating l-proline and styrene onto a noncatalytic protein scaffold with a high degree of controllability. The tailored conjugates exhibited remarkable catalytic performance toward the aqueous asymmetric aldol reaction of p-nitrobenzaldehyde and cyclohexanone, achieving 94% conversion and excellent selectivity (95/5 diastereoselectivity, 98% enantiomeric excess). In addition, this artificial enzyme showed high tolerance against extreme conditions (e.g., wide pH range, high temperature) and could be reused for more than four times without significant loss of reactivity. Experiments have shown that the artificial enzyme displayed broad specificity for various aldehydes.

Synergistic Hydrolysis of Cellulose by a Blend of Cellulase-Mimicking Polymeric Nanoparticle Catalysts

Enzyme-like catalysts by design have been a long sought-after goal of chemists but difficult to realize due to the challenges in the construction of multifunctionalized active sites with accurately positioned catalytic groups for complex substrates. Hydrolysis of cellulose is a key step in biomass utilization and requires multiple enzymes to work in concert to overcome the difficulty associated with hydrolyzing the recalcitrant substrate. We here report methods to construct synthetic versions of these enzymes through covalent molecular imprinting and strategic postmodification of the imprinted sites. The synthetic catalysts cleave a cellulose chain endolytically at multiple positions or exolytically from the nonreducing end by one or three glucose units at a time, all using the dicarboxylic acid motif found in natural cellulases. By mimicking the endocellulase, exocellulase, and β-glucosidase, the synthetic catalysts hydrolyze cellulose in a synergistic manner, with an activity at 90 °C in pH 6.5 buffer more than doubled that of Aspergillus niger cellulase at pH 5 and 37 °C and 44% of that of a commercial cellulase blend (from Novozyme). As robust cross-linked polymeric nanoparticles, the synthetic catalysts showed little changes in activity after preheating at 90 °C for 3 days and could be reused, maintaining 76% of activity after 10 reaction cycles.