Although the term nanozymes was coined by us in 2004 to highlight the enzyme-like properties of gold nanoparticles passivated with a monolayer of Zn(II)-complexes in the cleavage of phosphate ...diesters, systems resembling those metallo-nanoparticles, like micelles and vesicles, have been the subject of investigation since the mid-eighties of the last century. This paper reviews what has been done in the field and compares the different nanosystems highlighting the source of catalysis and frequent misconceptions found in the literature.
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-
Leu-Ile-His-Leu-
Leu-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
H-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
-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.
The highly basic and poorly nucleophilic phosphazene base P1‐t‐Bu promotes the Darzens condensation of α‐halo esters with aromatic aldehydes affording α,β‐epoxy esters in nearly quantitative yields ...under mild conditions and in short reaction times. The more basic P4‐t‐Bu phosphazene was found useful with low reactivity aldehydes. These reactions can be performed in aprotic organic solvents of low polarity, thus minimizing the hydrolysis of α,β‐epoxy esters which often accompanies the base‐promoted Darzens condensations.
The first Darzens reaction of α‐halo acetate esters with aromatic aldehydes promoted by phosphazene bases is reported. The reactions proceed smoothly, affording α,β‐epoxy esters in nearly quantitative yields, short time, and no side products. The phosphazene base P1‐t‐Bu can be used with aldehydes carrying electron‐withdrawing groups, while the base P4‐t‐Bu is preferable when the aldehydes carry electron donating substituents.
Gold nanoparticles (AuNPs) covered with mixtures of immiscible ligands present potentially anisotropic surfaces that can modulate their interactions at complex nano–bio interfaces. Mixed, ...self‐assembled, monolayer (SAM)‐protected AuNPs, prepared with incompatible hydrocarbon and fluorocarbon amphiphilic ligands, are used here to probe the molecular basis of surface phase separation and disclose the role of fluorinated ligands on the interaction with lipid model membranes and cells, by integrating in silico and experimental approaches. These results indicate that the presence of fluorinated amphiphilic ligands enhances the membrane binding ability and cellular uptake of gold nanoparticles with respect to those coated only with hydrogenated amphiphilic ligands. For mixed monolayers, computational results suggest that ligand phase separation occurs on the gold surface, and the resulting anisotropy affects the number of contacts and adhesion energies with a membrane bilayer. This reflects in a diverse membrane interaction for NPs with different surface morphologies, as determined by surface plasmon resonance, as well as differential effects on cells, as observed by flow cytometry and confocal microscopy. Overall, limited changes in monolayer features can significantly affect NP surface interfacial properties, which, in turn, affect the interaction of SAM‐AuNPs with cellular membranes and subsequent effects on cells.
The structure that matters. Patterning of gold nanoparticles due to self‐assembling monolayers of amphiphilic immiscible ligands determines their behavior at the nano–bio interface.
Monoclonal antibody-based immunotherapy is one of the pillars of cancer treatment. However, for an efficient and personalized approach to the therapy, a quantitative evaluation of the right dose for ...each patient is required. In this study, we developed a simple, label-free, and rapid approach to quantify Trastuzumab, a humanized IgG1 monoclonal antibody used against human epidermal growth factor receptor 2 (HER2), overexpressed in breast cancer patients, based on localized surface plasmon resonance (LSPR). The central idea of this work was to use gold nanoparticles (AuNPs) as plasmonic scaffolds, decorated with HER2 binders mixed with oligo-ethylene glycol (OEG) molecules, to tune the surface density of the attached macromolecules and to minimize nonspecific binding events. Specifically, we characterized and optimized a self-assembled monolayer of mixed alkylthiols terminated with nitrilotriacetic acid (NTA), and OEG3 as a spacing ligand to achieve both excellent dispersibility and high reliability in protein immobilization. The successful immobilization of histidine-tagged HER2 (His-tagged HER2) on NTA via cobalt (II) chelates was demonstrated, confirming the fully functional attachment of the proteins to the AuNP surface. The proposed design demonstrates the capability of producing a clear readout that enables the transduction of a Trastuzumab/HER2 binding event into optical signals based on the wavelength shifts in LSPR, which allowed for detecting clinically relevant concentrations of Trastuzumab down to 300 ng/mL in the buffer and 2 µg/mL in the diluted serum. This strategy was found to be fast and highly specific to Trastuzumab. These findings make the present platform an auspicious tool for developing affordable bio-nanosensors.
Gold nanoparticles carrying fluorinated ligands in their monolayer are, by themselves, contrast agents for
F magnetic resonance imaging displaying high sensitivity because of the high density of ...fluorine nuclei achievable by grafting suitable ligands on the gold core surface. Functionalization of these nanoparticles with Gd(III) chelates allows adding a further functional activity to these systems, developing materials also acting as contrast agents for proton magnetic resonance imaging. These dual mode contrast agents may allow capitalizing on the benefits of
H and
F magnetic resonance imaging in a single diagnostic session. In this work, we describe a proof of principle of this approach by studying these nanoparticles in a high field preclinical scanner. The Gd(III) centers within the nanoparticles monolayer shorten considerably the
F T1 of the ligands but, nevertheless, these systems display strong and sharp NMR signals which allow recording good quality
F MRI phantom images at nanoparticle concentration of 20 mg/mL after proper adjustment of the imaging sequence. The Gd(III) centers also influence the T1 relaxation time of the water protons and high quality
H MRI images could be obtained. Gold nanoparticles protected by hydrogenated ligands and decorated with Gd(III) chelates are reported for comparison as
H MRI contrast agents.
Gold nanoparticles coated by fluorinated ligands enable formation of new self-assembled materials, molecular recognition and new materials for biomedical applications.
•Fluorous gold nanoparticles ...are promising drug delivery and theranostic platforms.•Fluorophilic interactions are tools for nanoparticles self-assembly.•Fluorophilic interactions enable the formation of patterned mixed monolayers.
The development of fluorinated gold nanoparticles is presently arising and increasing attention across several fields of nanotechnology. The synthetic approaches evolved over time from the use of almost perfluorinated alkanethiols and perfluorinated arylthiols to amphiphilic fluorinated thiols capable of ensuring solubility in conventional organic solvents and water. The interest in these systems stems from the unique properties of both nanosized and fluorous compounds. In perspective, the development of our understanding of the fluorophilic interactions at the nanoscale will allow to devise novel strategies for self-assembly, molecular recognition and new materials for biomedical applications. In this paper we present, through selected examples, the potential of fluorous ligands in the synthesis of gold nanoparticles and the relevance of mastering the properties of these systems in the development of new materials.
Unprotected dipeptides are attractive building blocks for environmentally friendly hydrogel biomaterials by virtue of their low‐cost and ease of preparation. This work investigates the ...self‐assembling behaviour of the distinct stereoisomers of Ile‐Phe and Phe‐Ile in phosphate buffered saline (PBS) to form hydrogels, using transmission electron microscopy (TEM), attenuated total reflectance infrared spectroscopy (ATR‐IR), circular dichroism (CD), and oscillatory rheometry. Each peptide purity and identity was also confirmed by 1H‐ and 13C‐NMR spectroscopy and HPLC‐MS. Finally, single‐crystal XRD data allowed the key interactions responsible for the supramolecular packing into amphipathic layers or water‐channels to be revealed. The presence of the latter in the crystal structure is a distinctive feature of the only gelator of this work that self‐organizes into stable hydrogels, with fast kinetics and the highest elastic modulus amongst its structural isomers and stereoisomers.
The self‐assembling behaviour of the distinct stereoisomers of Ile‐Phe and Phe‐Ile was studied in phosphate buffered saline (PBS) and found to form hydrogels. Single‐crystal XRD data of the four non‐enantiomeric dipeptides revealed water‐channels as a distinctive feature only for the heterochiral hydrogelator D‐Phe‐L‐Ile.
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