Self-assembly of a catalytic multivalent peptide-nanoparticle complex

In situ enzymatic control of colloidal phoresis and catalysis through hydrolysis of ATP

The ability to sense chemical gradients and respond with directional motility and chemical activity is a defining feature of complex living systems. There is a strong interest among scientists to design synthetic systems that emulate these properties. Here, we realize and control such behaviors in a synthetic system by tailoring multivalent interactions of adenosine nucleotides with catalytic microbeads. We first show that multivalent interactions of the bead with gradients of adenosine mono-, di- and trinucleotides (AM/D/TP) control both the phoretic motion and a proton-transfer catalytic reaction, and find that both effects are diminished greatly with increasing valence of phosphates. We exploit this behavior by using enzymatic hydrolysis of ATP to AMP, which downregulates multivalent interactivity in situ. This produces a sudden increase in transport of the catalytic microbeads (a phoretic jump), which is accompanied by increased catalytic activity. Finally, we show how this enzymatic activity can be systematically tuned, leading to simultaneous in situ spatial and temporal control of the location of the microbeads, as well as the products of the reaction that they catalyze. These findings open up new avenues for utilizing multivalent interaction-mediated programming of complex chemo-mechanical behaviors into active systems.

Effect of Modification Strategies on the Biological Activity of Peptides/Proteins

Covalent attachment of biologically active peptides/proteins with functional moieties is an effective strategy to control their biodistribution, pharmacokinetics, enzymatic digestion, and toxicity. This review focuses on the characteristics of different modification strategies and their effects on the biological activity of peptides/proteins and illustrates their relevant applications and potential.

Polyfluoroalkyl Chain-Based Assemblies for Biomimetic Catalysis

Amphiphobic fluoroalkyl chains are exploited for creating robust and diverse self-assembled biomimetic catalysts. Long terminal perfluoroalkyl chains (Cn F2n+1 with n=6, 8, and 10) linked with a short perhydroalkyl chains (Cm H2m with m=2 and 3) were used to synthesize several 1,4,7-triazacyclononane (TACN) derivatives, Cn F2n+1 -Cm H2m -TACN. In the presence of an equimolar amount of Zn2+ ions that coordinate the TACN moiety and drive the self-assembly into micelle-like aggregates, the critical aggregation concentration of polyfluorinated Cn F2n+1 -Cm H2m -TACN⋅Zn2+ was lowered by ∼1 order of magnitude compared to the traditional perhyroalkyl counterpart with identical carbon number of alkyl chain. When 2'-hydroxypropyl-4-nitrophenyl phosphate was used as the model phosphate substrate, polyfluorinated Cn F2n+1 -Cm H2m -TACN⋅Zn2+ assemblies showed higher affinity and catalytic activity, compared to its perhyroalkyl chain-based counterpart. Coarse-grained molecular dynamic simulations have been introduced to explore the supramolecular assembly of polyfluoroalkyl chains in the presence of Zn2+ ions and to better understand their enhanced catalytic activity.

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.

Supramolecular peptide nanotubes as artificial enzymes for catalysing ester hydrolysis

Peptide-based artificial enzymes are attracting significant interest because of their remarkable resemblance in both composition and structure to native enzymes. Herein, we report the construction of histidine-containing cyclic peptide-based supramolecular polymeric nanotubes to function as artificial enzymes for ester hydrolysis. The optimized catalyst shows a ca. 70-fold increase in reaction rate compared to the un-catalysed reaction when using 4-nitrophenyl acetate as a model substrate. Furthermore, the amphiphilic nature of the supramolecular catalysts enables an enhanced catalytic activity towards hydrophobic substrates. By incorporating an internal hydrophobic region within the self-assembled polymeric nanotube, we achieve a 55.4-fold acceleration in hydrolysis rate towards a more hydrophobic substrate, 4-nitrophenyl butyrate. This study introduces supramolecular peptide nanotubes as an innovative class of supramolecular scaffolds for fabricating artificial enzymes with better structural and chemical stability, catalysing not only ester hydrolysis, but also a broader spectrum of catalytic reactions.

Benchmarking Cationic Monolayer Protected Nanoparticles and Micelles for Phosphate-Mediated and Nucleotide-Selective Proton Transfer Catalysis

Both micelles and self-assembled monolayer (SAM)-protected nanoparticles are capable of efficiently hosting water-immiscible substrates to carry out organic reactions in aqueous media. Herein, we have analyzed the different catalytic effect of SAM-protected cationic nanoparticles and cationic surfactants of varying chain length towards base-catalyzed proton transfer mediated ring-opening reaction of 5-nitrobenzisoxazole (NBI) (also known as Kemp Elimination (KE) reaction). We use inorganic phosphate ion or different nucleotide (phosphate-ligated different nucleoside) as base to promote the reaction on micellar or nanoparticle interface. We find almost 2-3 orders of magnitude higher concentration of surfactants of comparable hydrophobicity required to reach the similar activity which attained by low cationic head group concentration bound on nanoparticle. Additionally, at low concentration of nanoparticle-bound surfactant or with high surfactant in micellar form, nucleotide-selectivity has been observed in activating KE reaction unlike free surfactant at low concentration. Finally, we showed enzyme-mediated nucleotide hydrolysis to generate phosphate ion which in situ upregulate the KE activity much more in GNP-based system compared to CTAB. Notably, we show a reasonable superiority of SAM-protected nanoparticles in activating chemical reaction in micromolar concentration of headgroup which certainly boost up application of SAM-based nanoparticles not only for selective recognition but also as eco-friendly catalyst.

Coordination-Induced Multivalent Self-Assembling Catalysts for Spectral Sensing Zn2+ with High Selectivity and Sensitivity

The introduction of signal amplification to molecular spectral sensing systems is an intriguing topic in supramolecular analytical chemistry. In this study, click chemistry was used to generate a triazole moiety to bridge with a long hydrophobic alkyl chain (C_n) and another short alkyl chain (C_m) bearing a 1,4,7-triazacyclonane (TACN) group for efficiently generating a self-assembling multivalent catalyst, C_n-triazole-C_m-TACN·Zn²⁺ (n and m represent the carbon numbers of both alkyl chains, respectively; n = 16, 18, and 20; m = 2 and 6), to catalyze the hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNPP) when Zn²⁺ was added. The triazole moiety introduced adjacent to the TACN group plays an important role in improving the selectivity of Zn²⁺ because the triazole moiety can participate in the coordination interaction between the Zn²⁺ and neighboring TACN group. The supplementary triazole complexing increases the space requirement for coordinated metal ions. This catalytic sensing system also shows high sensitivity, with a favorable limit of detection down to 350 nM, even if only UV-vis absorption spectra rather than more sensitive fluorescence techniques were used for signaling, and can be used to determine the concentration of Zn²⁺ in tap water, which demonstrates the practical application feasibility.

On-nanoparticle monolayers as a solute-specific, solvent-like phase

In addition to modifying surface properties, self-assembled monolayers, SAMs, on nanoparticles can selectively incorporate small molecules from the surrounding solution. This selectivity has been used in the design of substrate-specific catalytic systems but its degree has not been quantified. This work uses catalytic centers embedded in on-nanoparticle hydrophobic SAMs to monitor and quantify the partitioning of molecules between the bulk solvent and these monolayers. A combination of experiments and theory allows us to relate the logarithm of the incorporation-into-SAM constant to the "bulk" log P values, characterizing the incoming substrates. These results are in line with classic, semi-empirical linear free energy relationships between partitioning solvent systems; in this way, they substantiate the view of nanoscopic on-particle SAMs acting akin to a bulk solvent phase.

Controlled Self-Assembly of the Catalytic Core of Hydrolases Using DNA Scaffolds

Precisely organizing functional molecules of the catalytic cores in natural enzymes to promote catalytic performance is a challenging goal in respect to artificial enzyme construction. In this work, we report a DNA-scaffolded mimicry of the catalytic cores of hydrolases, which showed a controllable and hierarchical acceleration of the hydrolysis of fluorescein diacetate (FDA). The results revealed that the efficiency of hydrolysis was greatly increased by the DNA-scaffold-induced proximity of catalytic amino acid residues (histidine and arginine) with up to 4-fold improvement relative to the free amino acids. In addition, DNA-scaffolded one-dimensional and two-dimensional assemblies of multiple catalytic cores could further accelerate the hydrolysis. This work demonstrated that the DNA-guided assembly could be used as a promising platform to build enzyme mimics in a programmable and hierarchical way.

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.

A study on the catalytic activity of polypeptides toward the hydrolysis of glucoside compounds gastrodin, polydatin and esculin

The self-assembly of a series of catalytically active polypeptides toward hydrolysis of glucoside compounds, namely, gastrodin, polydatin and esculin was investigated. These active peptides are composed of two functional fragments: one is the hydrophobic sequence LHLHLRL, which forms assembling segments in the presence of Zn ions (Zn²⁺); another functional sequence of active peptides are catalytic sites such as Glu (E), Asp (D) and His (H), where carboxylic acids (-COOH) or imidazole groups act like scissors to cleave glucoside bonds of the compounds (according to the acid-base coupling mechanism). The effects of the amino acid sequence of the peptide, Zn²⁺ concentration, pH and the size or steric hindrance of glucoside compounds on the hydrolytic activity were studied. It was found that the crystalline structure of assembled peptides was crucial to provide the peptide with catalytic hydrolytic activity. Noncovalent interaction index was used to analyse the noncovalent interaction of PEs with glucoside compounds, including hydrogen bonds, van der Waals, and steric effect in the complexes. The binding energy of complexes, the direction and site of nucleophilic attack during deglycosylation processes were also investigated by molecular docking and the electron density Laplace function. This revealed that the differences in the hydrolytic activity of peptides toward glucoside compounds with different sizes originated from different hydrogen bond interactions between the peptides and substrates. These active peptides may find application in the preparation of drugs by de-glycosylation of natural compounds.

Small Peptides in the Detection of Mycotoxins and Their Potential Applications in Mycotoxin Removal

Mycotoxins pose significant risks to humans and livestock. In addition, contaminated food- and feedstuffs can only be discarded, leading to increased economic losses and potential ecological pollution. Mycotoxin removal and real-time toxin level monitoring are effective approaches to solve this problem. As a hot research hotspot, small peptides derived from phage display peptide libraries, combinatorial peptide libraries, and rational design approaches can act as coating antigens, competitive antigens, and anti-immune complexes in immunoassays for the detection of mycotoxins. Furthermore, as a potential approach to mycotoxin degradation, small peptides can mimic the natural enzyme catalytic site to construct artificial enzymes containing oxidoreductases, hydrolase, and lyase activities. In summary, with the advantages of mature synthesis protocols, diverse structures, and excellent biocompatibility, also sharing their chemical structure with natural proteins, small peptides are widely used for mycotoxin detection and artificial enzyme construction, which have promising applications in mycotoxin degradation. This paper mainly reviews the advances of small peptides in the detection of mycotoxins, the construction of peptide-based artificial enzymes, and their potential applications in mycotoxin control.

Structure-switchable aptamer-arranged reconfigurable DNA nanonetworks for targeted cancer therapy

The structural DNA nanotechnology holds great potential application in bioimaging, drug delivery and cancer therapy. Herein, an intelligent aptamer-incorporated DNA nanonetwork (Apt-Nnes) is demonstrated for cancer cell imaging and targeted drug delivery, which essentially is a micron-scale pattern with the thickness of double-stranded monolayer. Cancer cell-surface receptors can make it perform magical transformation into small size of nanosheet intermediates and specifically enter target cells. The binding affinity of Apt-Nnes is increased by 3-fold due to multivalent binding effect of aptamers and it can maintain the structural integrity in fetal bovine serum (FBS) for 8 h. More interestingly, target cancer cells can cause the structural disassembly, and each resulting unit transports 4963 doxorubicin (Dox) into target cells, causing the specific cellular cytotoxicity. The cell surface receptor-mediated disassembly of large size of DNA nanostructures into small size of fractions provides a valuable insight into developing intelligent DNA nanostructure suitable for biomedical applications.

Organosulphur and organoselenium compounds as emerging building blocks for catalytic systems for O-arylation of phenols, a C-O coupling reaction

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C-O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

Selective Fluorescence Imaging of Cancer Cells Based on ROS-Triggered Intracellular Cross-Linking of Artificial Enzyme

Inside living cells, regulation of catalytic activity of artificial enzymes remains challenging due to issues such as biocompatibility, efficiency, and stability of the catalyst, by which the practical applications of artificial enzymes have been severely hindered. Here, an artificial enzyme, PTT-SGH, with responsiveness to reactive oxygen species (ROS), was obtained by introducing a catalytic histidine residue to pentaerythritol tetra(3-mercaptopropionate) (PTT). The artificial enzyme formed large aggregates in cells via the intracellular ROS-mediated oxidation of thiol groups. The process was significantly facilitated in tumor cells because of the higher ROS concentration in the tumor microenvironment. The catalytic activity of this artificial enzyme was intensively enhanced through deprotonation of cross-linked PTT-SGH, which showed typical esterase activities. Selective fluorescence imaging of tumor cells was achieved using the artificial enzyme to trigger the cleavage of the ester bond of the caged fluorophore inside living cells.

Perpetuating enzymatically-induced spatiotemporal pH and catalytic heterogeneity of a hydrogel by nanoparticles

The attainment of spatiotemporally inhomogeneous chemical and physical properties within a system is gaining attention across disciplines due to the resemblance to environmental and biological heterogeneity. Notably, the origin of natural pH gradients and how they have been incorporated in cellular systems is one of the most important questions in understanding the prebiotic origin of life. Herein, we have demonstrated a spatiotemporal pH gradient formation pattern on a hydrogel surface by employing two different enzymatic reactions, namely, the reactions of glucose oxidase (pH decreasing) and urease (pH increasing). We found here a generic pattern of spatiotemporal change in pH and proton transfer catalytic activity that was completely altered in a cationic gold nanoparticle containing hydrogel. In the absence of nanoparticles, the gradually generated macroscopic pH gradient slowly diminished with time, whereas the presence of nanoparticles helped to perpetuate the generated gradient effect. This behavior is due to the differential responsiveness of the interface of the cationic nanoparticle in temporally changing surroundings with increasing or decreasing pH or ionic contents. Moreover, the catalytic proton transfer ability of the nanoparticle showed a concerted kinetic response following the spatiotemporal pH dynamics in the gel matrix. Notably, this nanoparticle-driven spatiotemporally resolved gel matrix will find applicability in the area of the membrane-free generation and control of spatially segregated chemistry at the macroscopic scale.

This work reports perpetuating effect in enzymatically generated spatiotemporal pH gradient across a hydrogel in presence of cationic gold nanoparticle; showing a new route in spatially resolved chemistry in a membrane-free environment.

Simple synthetic route to an enzyme-inspired transesterification catalyst

Self-assembling transesterification catalyst inspired by the catalytic triad.

Structurally Engineered Light-Responsive Nanozymes for Enhanced Substrate Specificity

Mimicking enzyme specificity via construction of on-demand geometric structures on nanozymes is of great interest in recent years. Although building substrate-specific polymers on nanozymes has achieved great success, polymer-blocked active sites would inevitably lead to decreased activity of nanozymes. Here, we have developed three photoactive metal-organic framework (MOF)-based nanozymes (called 2D-TCPP, 3D-TCPP, and AD-TCPP), which have different geometric structures as well as unshielded active sites. Together with their structural variations and excellent photoresponsive oxidase-like activities, these photoactive nanozymes exhibit structure-dependent specificity for three kinds of substrates (typical oxidase substrates, organic pollutants, and antioxidants). Moreover, AD-TCPP and 3D-TCPP show potential applications for environmental protection and bioanalysis, respectively. This work offers a promising approach to the development of nanozymes with enzyme-like specificity.

Fullerene-Based Mimics of Biocatalysts Show Remarkable Activity and Modularity

The design of catalysts with greater control over catalytic activity and stability is a major challenge with substantial impact on fundamental chemistry and industrial applications. Due to their unparalleled diversity, selectivity, and efficiency, enzymes are promising models for next-generation catalysts, and considerable efforts have been devoted to incorporating the principles of their mechanisms of action into artificial systems. We report a heretofore undocumented catalyst design that introduces fullerenes to the field of biocatalysis, which we refer to as fullerene nanocatalysts, and that emulates enzymatic active sites through multifunctional self-assembled nanostructures. As a proof-of-concept, we mimicked the reactivity of hydrolases using fullerene nanocatalysts functionalized with the basic components of the parent enzyme with remarkable activity. Owing to the versatile amino acid-based functionalization repertoire of fullerene nanocatalysts, these next-generation carbon/biomolecule hybrids have potential to mimic the activity of other families of enzymes and, therefore, offer new perspectives for the design of biocompatible, high-efficiency artificial nanocatalysts.

Water-Mediated Folding Behaviors and Chiroptical Inversion of Ferrocene-Conjugated Dipeptides

The hydration effect on the folding behavior of oligopeptides is of vital importance both in the structure basis of biomolecules and in the rational design of peptide-based materials, which however has rarely been addressed. Here we present the hydration impact on the spontaneous folding of dipeptides conjugated by the ferrocene spacer. In organic phase, the ferrocene-glycine-phenylalanine dipeptide formed a parallel β-sheet structure and Herrick's conformation, which underwent conformational transformation encountering aqueous media, by significantly switching dipeptide arm angles around the ferrocene axis up to 72°. The conformational transformation behavior aroused inversion of the chiroptical activity. Solid X-ray structures, proton nuclear magnetic resonance, chiroptical spectroscopy, and the density functional theory calculation were employed to unveil the hydration effect in the secondary structure transition, in which the rearrangement of hydrogen bonds played the vital role. This work deepens the understanding of water functioning in the structure modulation of biomolecules and also provides an alternative protocol in designing novel chiroptical switches and adaptive peptide-based biomaterials.

Organoselenium ligands for heterogeneous and nanocatalytic systems: development and applications

Organoselenium ligands have attracted great attention among researchers during the past two decades. Various homogeneous, heterogeneous and nanocatalytic systems have been designed using such ligands. Although reports on selenium ligated homogeneous catalysts are quite high in number, significant work has also been done on the development of heterogeneous and nanocatalytic systems using organoselenium ligands. A review article, focusing on the utility of organoselenium compounds in the development of catalytic systems, was published in 2012 (A. Kumar, G. K. Rao, F. Saleem and A. K. Singh, Dalton Trans., 2012, 41, 11949). Moreover, it mainly covered the homogeneous catalysts. There are no review articles in the literature on heterogeneous and nanocatalytic systems designed using organoselenium compounds and their applications. Hence, this perspective aims to cover the developments pertaining to the synthetic aspects of such catalytic systems (using organoselenium compounds) and their applications in catalysis of a variety of chemical transformations. Salient features and advantages of organoselenium compounds have also been highlighted to justify the rationale behind their use in catalyst development. Their performance in various chemical transformations [viz. Suzuki-Miyaura coupling, Heck coupling, Sonogashira coupling, O-arylation of phenol, transfer hydrogenation of aldehydes and ketones, aldehyde-alkyne-amine (A3) coupling, hydration of nitriles, conversion of aldehydes to amides, cross-dehydrogenative coupling (CDC), photodegradation of substrates (formic acid, methylene blue), reduction of nitrophenols, electrolysis (hydrogen evolution reaction and oxygen reduction reactions), organocatalysis and dye sensitized solar cells] and relevant aspects of catalytic processes (such as recyclability, substrate scope and green aspects) have been critically analyzed. Future perspectives have also been discussed.

Molecular Dynamics Simulations of a Catalytic Multivalent Peptide-Nanoparticle Complex

Molecular modeling of a supramolecular catalytic system is conducted resulting from the assembling between a small peptide and the surface of cationic self-assembled monolayers on gold nanoparticles, through a multiscale iterative approach including atomistic force field development, flexible docking with Brownian Dynamics and µs-long Molecular Dynamics simulations. Self-assembly is a prerequisite for the catalysis, since the catalytic peptides do not display any activity in the absence of the gold nanocluster. Atomistic simulations reveal details of the association dynamics as regulated by defined conformational changes of the peptide due to peptide length and sequence. Our results show the importance of a rational design of the peptide to enhance the catalytic activity of peptide-nanoparticle conjugates and present a viable computational approach toward the design of enzyme mimics having a complex structure-function relationship, for technological and nanomedical applications.

Peptide-Protein Interactions: From Drug Design to Supramolecular Biomaterials

The self-recognition and self-assembly of biomolecules are spontaneous processes that occur in Nature and allow the formation of ordered structures, at the nanoscale or even at the macroscale, under thermodynamic and kinetic equilibrium as a consequence of specific and local interactions. In particular, peptides and peptidomimetics play an elected role, as they may allow a rational approach to elucidate biological mechanisms to develop new drugs, biomaterials, catalysts, or semiconductors. The forces that rule self-recognition and self-assembly processes are weak interactions, such as hydrogen bonding, electrostatic attractions, and van der Waals forces, and they underlie the formation of the secondary structure (e.g., α-helix, β-sheet, polyproline II helix), which plays a key role in all biological processes. Here, we present recent and significant examples whereby design was successfully applied to attain the desired structural motifs toward function. These studies are important to understand the main interactions ruling the biological processes and the onset of many pathologies. The types of secondary structure adopted by peptides during self-assembly have a fundamental importance not only on the type of nano- or macro-structure formed but also on the properties of biomaterials, such as the types of interaction, encapsulation, non-covalent interaction, or covalent interaction, which are ultimately useful for applications in drug delivery.

Organosulfur, organoselenium, and organotellurium ligands in the development of palladium, nickel, and copper-based catalytic systems for Heck coupling

Organosulfur, organoselenium, and organotellurium ligands in designing Pd, Ni, and Cu-based homogeneous, heterogeneous, and nanocatalytic systems for Heck coupling.

Rational Design of Functional Peptide-Gold Hybrid Nanomaterials for Molecular Interactions

Gold nanoparticles (AuNPs) have been extensively used for decades in biosensing-related development due to outstanding optical properties. Peptides, as newly realized functional biomolecules, are promising candidates of replacing antibodies, receptors, and substrates for specific molecular interactions. Both peptides and AuNPs are robust and easily synthesized at relatively low cost. Hence, peptide-AuNP-based bio-nano-technological approaches have drawn increasing interest, especially in the field of molecular targeting, cell imaging, drug delivery, and therapy. Many excellent works in these areas have been reported: demonstrating novel ideas, exploring new targets, and facilitating advanced diagnostic and therapeutic technologies. Importantly, some of them also have been employed to address real practical problems, especially in remote and less privileged areas. This contribution focuses on the application of peptide-gold hybrid nanomaterials for various molecular interactions, especially in biosensing/diagnostics and cell targeting/imaging, as well as for the development of highly active antimicrobial/antifouling coating strategies. Rationally designed peptide-gold nanomaterials with functional properties are discussed along with future challenges and opportunities.

Biocatalysis of D,L-Peptide Nanofibrillar Hydrogel

Self-assembling peptides are attracting wide interest as biodegradable building blocks to achieve functional nanomaterials that do not persist in the environment. Amongst the many applications, biocatalysis is gaining momentum, although a clear structure-to-activity relationship is still lacking. This work applied emerging design rules to the heterochiral octapeptide sequence His-Leu-DLeu-Ile-His-Leu-DLeu-Ile for self-assembly into nanofibrils that, at higher concentration, give rise to a supramolecular hydrogel for the mimicry of esterase-like activity. The peptide was synthesized by solid-phase and purified by HPLC, while its identity was confirmed by 1H-NMR and electrospray ionization (ESI)-MS. The hydrogel formed by this peptide was studied with oscillatory rheometry, and the supramolecular behavior of the peptide was investigated with transmission electron microscopy (TEM) analysis, circular dichroism (CD) spectroscopy, thioflavin T amyloid fluorescence assay, and attenuated total reflectance (ATR) Fourier-transform infrared (FT-IR) spectroscopy. The biocatalytic activity was studied by monitoring the hydrolysis of p-nitrophenyl acetate (pNPA) at neutral pH, and the reaction kinetics followed an apparent Michaelis-Menten model, for which a Lineweaver-Burk plot was produced to determine its enzymatic parameters for a comparison with the literature. Finally, LC-MS analysis was conducted on a series of experiments to evaluate the extent of, if any, undesired peptide acetylation at the N-terminus. In conclusion, we provide new insights that allow gaining a clearer picture of self-assembling peptide design rules for biocatalysis.

Non-Equilibrium Polymerization of Cross-β Amyloid Peptides for Temporal Control of Electronic Properties

Hydrophobic collapse plays crucial roles in protein functions, from accessing the complex three-dimensional structures of native enzymes to the dynamic polymerization of non-equilibrium microtubules. However, hydrophobic collapse can also lead to the thermodynamically downhill aggregation of aberrant proteins, which has interestingly led to the development of a unique class of soft nanomaterials. There remain critical gaps in the understanding of the mechanisms of how hydrophobic collapse can regulate such aggregation. Demonstrated herein is a methodology for non-equilibrium amyloid polymerization through mutations of the core sequence of Aβ peptides by a thermodynamically activated moiety. An out of equilibrium state is realized because of the negative feedback from the transiently formed cross-β amyloid networks. Such non-equilibrium amyloid nanostructures were utilized to access temporal control over its electronic properties.

A minimalistic hydrolase based on co-assembled cyclic dipeptides

The self-assembly of small peptides into larger aggregates is an important process for the fundamental understanding of abiogenesis. In this article we demonstrate that blends of cyclic dipeptides (2,5-diketopiperazines - DKPs) bearing either histidine or cysteine in combination with a lipophilic amino acid form highly stable aggregates in aqueous solution with esterase-like activity. We demonstrate that the catalytic activity is based on an intermolecular cooperative behavior between histidine and cysteine. A high control of the molecular arrangement of the peptide assemblies was gained by C-H-π interactions between Phe and Leu or Val sidechains, resulting in a significant increase in catalytic activity. These interactions were strongly supported by Hartree-Fock calculations and finally confirmed via1H-NMR HRMAS NOE spectroscopy.

Advanced nanotechnology for hypoxia-associated antitumor therapy

Hypoxia is a hallmark of the tumor microenvironment, which promotes the proliferation, metastasis and invasion of tumors and stimulates the resistance of cancer treatments, leading to the serious consequence of tumor recurrence. Many nanotechnology-based studies have been conducted to improve the efficacy of cancer treatments using a hypoxia strategy. This is usually achieved by (i) activating bioreductive prodrugs in the tumor hypoxic/exacerbated hypoxic microenvironment, or (ii) delivering therapeutic agents to hypoxic tumor tissue using targeting molecules. Normally, a good therapeutic effect can be expected upon modulating the hypoxic microenvironment for tumor treatments. To achieve this, various nanotechnology strategies based on overcoming hypoxia have been exploited to alleviate tumor hypoxia and enhance the therapeutic efficacy of tumor therapy, including (i) reducing oxygen consumption by inhibiting cell respiration, (ii) normalizing tumor vessels to promote blood flow in the tumor, (iii) carrying exogenous oxygen into the tumor, and (iv) generating oxygen in situ. The strategy of in situ oxygen production is refined, and the scope of this strategy is further expanded. Finally, the inspiration of using advanced nanotechnology in hypoxia-associated antitumor therapy guides the study of tumor hypoxia for clinical use.

Aldolase Cascade Facilitated by Self-Assembled Nanotubes from Short Peptide Amphiphiles

Early evolution benefited from a complex network of reactions involving multiple C-C bond forming and breaking events that were critical for primitive metabolism. Nature gradually chose highly evolved and complex enzymes such as lyases to efficiently facilitate C-C bond formation and cleavage with remarkable substrate selectivity. Reported here is a lipidated short peptide which accesses a homogenous nanotubular morphology to efficiently catalyze C-C bond cleavage and formation. This system shows morphology-dependent catalytic rates, suggesting the formation of a binding pocket and registered enhancements in the presence of the hydrogen-bond donor tyrosine, which is exploited by extant aldolases. These assemblies showed excellent substrate selectivity and templated the formation of a specific adduct from a pool of possible adducts. The ability to catalyze metabolically relevant cascade transformations suggests the importance of such systems in early evolution.

Peptide interdigitation-induced twisted nanoribbons as chiral scaffolds for supramolecular nanozymes

Establishing reliable strategies for rationally manipulating the organization of peptide building blocks and thereby precisely creating chiral nanostructures is challenging, while meaningful toward development of advanced functional materials. Here we report on a peptide-interdigitating mechanism for the reliable self-assembly of lipid-inspired amphiphiles (LIPIAs) into robust twisted nanoribbons by grafting domains to one alkyl tail of lipids as an extended element. Peptide interdigitation promoted the self-assembly of LIPIAs into twisted or flat nanoribbons driven by antiparallel or parallel β-sheet hydrogen bonds, respectively, strongly associated with the connecting direction of the incorporated domains. We found that the LIPIAs containing N-terminus-connected domains with either bulky or small side chain groups formed twisted nanoribbons in a broad pH range, thus implying a sequence- and pH-independent strategy for creation of robust chiral nanostructures. Integrating the resulting twisted nanoribbons with gold nanoparticles led to supramolecular nanozymes exhibiting the excellent catalytic activity and enantioselectivity of asymmetric oxidation of 3,4-dihyroxy-phenylalanine molecules. Our finding demonstrates that the peptide-interdigitating mechanism is a reliable strategy for precise creation of chiral nanostructures serving as chiral matrices for supramolecular nanozymes with improved catalytic performance, thus potentially paving the way towards advanced biomimetic systems resembling natural systems.

Power Generation by Selective Self-Assembly of Biocatalysts

Through a careful chemical and bioelectronic design we have created a system that uses self-assembly of enzyme-nanoparticle hybrids to yield bioelectrocatalytic functionality and to enable the harnessing of electrical power from biomass. Here we show that mixed populations of hybrids acting as catalyst carriers for clean energy production can be efficiently stored, self-assembled on functionalized stationary surfaces, and magnetically re-collected to make the binding sites on the surfaces available again. The methodology is based on selective interactions occurring between chemically modified surfaces and ligand-functionalized hybrids. The design of a system with minimal cross-talk between the particles, outstanding selective binding of the hybrids at the electrode surfaces, and direct anodic and cathodic electron transfer pathways leads to mediator-less bioelectrocatalytic transformations which are implemented in the construction of a fast self-assembling, membrane-less fructose/O₂ biofuel cell.

A remote optically controlled hydrolase model based on supramolecular assembly and disassembly of its enzyme-like active site

A photoresponsive hydrolase model was constructed through the spatial organization of histidine/arginine-containing peptide supra-amphiphiles that are held together by cucurbit[8]uril (CB[8]) methylviologen (MV) azobenzene (Azo) ternary complexation and subsequently self-assemble into highly uniform giant vesicles. The reversible morphological transition of the vesicular structures to non-assembled peptide fragments was triggered by azobenzene photoisomerization. This enables the assembly/disassembly of its enzyme-like active site to cause a dramatic change in hydrolytic activity. The dynamic process can be directly monitored to determine the supramolecular structure-related enzymatic parameters, which may help to understand how the regulation of enzyme activity is coupled to the aggregation behaviors of natural enzymes.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.