Hierarchical Nanomaterials Assembled from Peptoids and Other Sequence-Defined Synthetic Polymers

In nature, the self-assembly of sequence-specific biopolymers into hierarchical structures plays an essential role in the construction of functional biomaterials. To develop synthetic materials that can mimic and surpass the function of these natural counterparts, various sequence-defined bio- and biomimetic polymers have been developed and exploited as building blocks for hierarchical self-assembly. This review summarizes the recent advances in the molecular self-assembly of hierarchical nanomaterials based on peptoids (or poly-N-substituted glycines) and other sequence-defined synthetic polymers. Modern techniques to monitor the assembly mechanisms and characterize the physicochemical properties of these self-assembly systems are highlighted. In addition, discussions about their potential applications in biomedical sciences and renewable energy are also included. This review aims to highlight essential features of sequence-defined synthetic polymers (e.g., high stability and protein-like high-information content) and how these unique features enable the construction of robust biomimetic functional materials with high programmability and predictability, with an emphasis on peptoids and their self-assembled nanomaterials.

Array-Based Screening of Silver Nanoparticle Mineralization Peptides

The use of biomolecules in nanomaterial synthesis has received increasing attention, because they can function as a medium to produce inorganic materials in ambient conditions. Short peptides are putative ligands that interact with metallic surfaces, as they have the potential to control the synthesis of nanoscale materials. Silver nanoparticle (AgNP) mineralization using peptides has been investigated; however, further comprehensive analysis must be carried out, because the design of peptide mediated-AgNP properties is still highly challenging. Herein, we employed an array comprising 200 spot synthesis-based peptides, which were previously isolated as gold nanoparticle (AuNP)-binding and/or mineralization peptides, and the AgNP mineralization activity of each peptide was broadly evaluated. Among 10 peptides showing the highest AgNP-synthesis activity (TOP10), nine showed the presence of EE and E[X]E (E: glutamic acid, and X: any amino acid), whereas none of these motifs were found in the WORST25 (25 peptides showing the lowest AgNP synthesis activity) peptides. The size and morphology of the particles synthesized by TOP3 peptides were dependent on their sequences. These results suggested not only that array-based techniques are effective for the peptide screening of AgNP mineralization, but also that AgNP mineralization regulated by peptides has the potential for the synthesis of AgNPs, with controlled morphology in environmentally friendly conditions.

Influence of anions and solvent molecules on the packing and emission spectra of coordination polymers based on silver ions and an anthracene derivative

The structure-property relationships in Ag-coordination polymers with an anthracene-derived ligand are studied.

Biosynthesis of Metal Nanoparticles: Novel Efficient Heterogeneous Nanocatalysts

This review compiles the most recent advances described in literature on the preparation of noble metal nanoparticles induced by biological entities. The use of different free or substituted carbohydrates, peptides, proteins, microorganisms or plants have been successfully applied as a new green concept in the development of innovative strategies to prepare these nanoparticles as different nanostructures with different forms and sizes. As a second part of this review, the application of their synthetic ability as new heterogonous catalysts has been described in C-C bond-forming reactions (as Suzuki, Heck, cycloaddition or multicomponent), oxidations and dynamic kinetic resolutions.

Size-Controlled Formation of Noble-Metal Nanoparticles in Aqueous Solution with a Thiol-Free Tripeptide

A combinatorial screening revealed the peptide H-His-d-Leu-d-Asp-NH2 (1) as an additive for the generation of monodisperse, water-soluble palladium nanoparticles with average diameters of 3 nm and stabilities of over 9 months. The tripeptide proved to be also applicable for the size-controlled formation of other noble-metal nanoparticles (Pt and Au). Studies with close analogues of peptide 1 revealed a specific role of each of the three amino acids for the formation and stabilization of the nanoparticles. These data combined with microscopic and spectroscopic analyses provided insight into the structure of the self-assembled peptidic monolayer around the metal core. The results open interesting prospects for the development of functionalized metal nanoparticles.

Antimicrobial activity of cobalt imidazolate metal-organic frameworks

Two cobalt imidazolate metal-organic frameworks were evaluated as a bactericidal material against the growth of the Gram-negative bacteria Pseudomonas putida and Escherichia coli. Under the most unfavourable conditions, within the exponential growth phase and in the culture media for both microorganisms, the growth inhibition reached over 50% for concentrations of biocidal material in the 5-10mgL(-1) range. The release of metal gives excellent durability with the antibacterial effect persisting after 3months. Both cobalt-based materials can be prepared with simple, cheap and easily accessible commercial ligands, leading to a more affordable possible future application as antimicrobial materials.

Synthesis of functionalized fluorescent silver nanoparticles and their toxicological effect in aquatic environments (Goldfish) and HEPG2 cells

Silver nanoparticles, AgNPs, are widely used in our daily life, mostly due to their antibacterial, antiviral, and antifungal properties. However, their potential toxicity remains unclear. In order to unravel this issue, emissive AgNPs were first synthetized using an inexpensive photochemical method, and then their permeation was assessed in vivo in goldfish and in vitro in human hepatoma cells (HepG2). In addition, the oxidative stress caused by AgNPs was assessed in enzymes such as glutathione-S-transferase (GST), catalase (CAT), and in lipid peroxidation (LPO). This study demonstrates that the smallest sized AgNPs@3 promote the largest changes in gold fish livers, whereas AgNPs@1 were found to be toxic in HEPG2 cells depending on both the size and functionalized/stabilizer ligand.

Nanosilver-based antibacterial drugs and devices: mechanisms, methodological drawbacks, and guidelines

Despite the current advancement in drug discovery and pharmaceutical biotechnology, infection diseases induced by bacteria continue to be one of the greatest health problems worldwide, afflicting millions of people annually. Almost all microorganisms have, in fact, an intrinsic outstanding ability to flout many therapeutic interventions, thanks to their fast and easy-to-occur evolutionary genetic mechanisms. At the same time, big pharmaceutical companies are losing interest in new antibiotics development, shifting their capital investments in much more profitable research and development fields. New smart solutions are, thus, required to overcome such concerns, and should combine the feasibility of industrial production processes with cheapness and effectiveness. In this framework, nanotechnology-based solutions, and in particular silver nanoparticles (AgNPs), have recently emerged as promising candidates in the market as new antibacterial agents. AgNPs display, in fact, enhanced broad-range antibacterial/antiviral properties, and their synthesis procedures are quite cost effective. However, despite their increasing impact on the market, many relevant issues are still open. These include the molecular mechanisms governing the AgNPs-bacteria interactions, the physico-chemical parameters underlying their toxicity to prokaryotes, the lack of standardized methods and materials, and the uncertainty in the definition of general strategies to develop smart antibacterial drugs and devices based on nanosilver. In this review, we analyze the experimental data on the bactericidal effects of AgNPs, discussing the complex scenario and presenting the potential drawbacks and limitations in the techniques and methods employed. Moreover, after analyzing in depth the main mechanisms involved, we provide some general strategies/procedures to perform antibacterial tests of AgNPs, and propose some general guidelines for the design of antibacterial nanosystems and devices based on silver/nanosilver.

Green synthesis of nanocomposites consisting of silver and protease alpha chymotrypsin

The synergy of ultrasonication and the exposure to light radiation was found to be necessary in the formation of nanocomposites of silver and a protease alpha chymotrypsin. The reaction was carried out in aqueous medium and the process took just less than 35 min. Ultrasonication alone formed very negligible number of nanoparticles of <100 nm size whereas light alone produced enough number but the size of the particles was >100 nm. The effects of pH (in the range of 3-5, 9-10), ultrasonication time periods (0-30 min), ultrasonication intensity (33-83 W cm(-2)), energy of light radiation (short UV, long UV and Fluorescent light) and time period of exposure (5-60 min) to different light radiations were studied. The formation of nanocomposites under these effects was followed by surface plasmon resonance (SPR) spectra, dynamic light scattering (DLS), transmission electron microscopy (TEM). Ag-chymotrypsin nanocomposites of sizes ranging from 13 to 72 nm were formed using the synergy of ultrasonication and exposure to short UV radiation. Results show that ultrasonication promoted nuclei formation, growth and reduction of polydispersity by Ostwald ripening.

Strategies for specifically directing metal functionalization of protein nanotubes: constructing protein coated silver nanowires

Biological molecules that self-assemble in the nanoscale range are useful multifunctional materials. Rotavirus VP6 protein self-assembles into tubular structures in the absence of other rotavirus proteins. Here, we present strategies for selectively directing metal functionalization to the lumen of VP6 nanotubes. The specific in situ metal reduction in the inner surface of nanotube walls was achieved by the simple modification of a method previously reported to functionalize the nanotube outer surface. Silver nanorods and nanowires as long as 1.5 μm were formed inside the nanotubes by coalescence of nanoparticles. Such one-dimensional structures were longer than others previously obtained using bioscaffolds. The interactions between silver ions and the nanotube were simulated to understand the conditions that allowed nanowire formation. Molecular docking showed that a naturally occurring arrangement of aspartate residues enabled the stabilization of silver ions on the internal surface of the VP6 nanotubes. This is the first time that such a spatial arrangement has been proposed for the nucleation of silver nanoparticles, opening the possibility of using such an array to direct functionalization of other biomolecules. These results demonstrate the natural capabilities of VP6 nanotubes to function as a versatile biotemplate for nanomaterials.

What controls the magnetic interaction in bis-μ-alkoxo Mn(III) dimers? A combined experimental and theoretical exploration

The synthesis and magnetic characterisation of a series of bis-μ-alkoxide bridged Mn(III) dinuclear complexes of general formula [Mn(III)(2)(μ-OR)(2)(biphen)(2)(ROH)(x)(L)(y)] (where R = Me, Et; H(2) biphen = 2,2'-biphenol and L = terminally bonded N-donor ligand) is described, doubling the literature basis set for this type of complex. Building on these findings we have categorised all known μ-OR bridged Mn(III) dinuclear complexes into one of three classifications with respect to their molecular structures. We have then employed DFT and MO calculations to assess all potential magneto-structural correlations for this class of compound in order to identify the structural requirements for constructing ferromagnetic family members. Our analysis indicates that the most influential parameter which governs the exchange interaction in this class of compounds is the relative orientation of the JT axes of the Mn(III)  atoms. A perpendicular orientation of the JT axes leads to a large ferromagnetic contribution to the exchange. These results also suggest that a large ferromagnetic interaction and a large anisotropy are unlikely to co-exist in such structural types.

Highly size- and shape-controlled synthesis of silver nanoparticles via a templated Tollens reaction

A mild, facile one-step synthetic strategy for the preparation of size- and shape-controlled silver nanoparticles (AgNPs) is presented. The high degree of size- and shape-control of these AgNPs is achieved by the use of triazole sugar ligands scaffolded by a central resorcinol ether core. Both the triazoles and the resorcinol ether core mediate the nucleation, growth, and passivation phases of the preparation of AgNP in the presence of the Tollens reagent as the silver source. Kinetic and (1)H NMR titration data is presented describing the nature of the interactions between the Tollens reagent and these ligands.

Silver nanoparticles assemblies mediated by functionalized biomimetic oligomers

The interaction between biopolymers and metal nanoparticles (AgNPs) is a key element in the development of biomimetic nanomaterials with applications in catalysis, delivery, and recognition. Here we report a facile method for the functionalization of AgNPs by N-substituted glycine oligomers, "peptoids." Based on the established affinity between phenanthroline ligand and Ag(0), we synthesized a peptoid bearing 1,10-phenanthroline at the N-terminus (PHP). Treatment of AgNPs that were pre-stabilized by citrate ions, with PHP, leads to the formation of aggregates as suggested by UV-vis spectroscopy. Transmission electron microscopy (TEM) revealed that the replacement of citrate ions by PHP yields spherical assemblies of AgNPs. These peptoids/AgNPs hybrids, as well as the ability of functional biomimetic oligomers to mediate the assembly of metal nanoparticles, hold potential for applications in sensor materials, biology, and catalysis.

Of Chains and Rings: Synthetic Strategies and Theoretical Investigations for Tuning the Structure of Silver Coordination Compounds and Their Applications

Varying the polyethyleneglycol spacer between two (iso)-nicotinic groups of the ligand systems, a large structural variety of silver coordination compounds was obtained, starting with zero-dimensional ring systems, via one-dimensional chains, helices and double-helices to two-dimensional polycatenanes. Theoretical calculations help to understand their formation and allow predictions in some cases. These structures can be tuned by careful design of the ligand, the use of solvent and the counter ions, influencing also other important properties such as light stability and solubility. The latter is important in the context of biomedical applications, using silver compounds as antimicrobial agents.

Reproducible, high-throughput synthesis of colloidal nanocrystals for optimization in multidimensional parameter space

While colloidal nanocrystals hold tremendous potential for both enhancing fundamental understanding of materials scaling and enabling advanced technologies, progress in both realms can be inhibited by the limited reproducibility of traditional synthetic methods and by the difficulty of optimizing syntheses over a large number of synthetic parameters. Here, we describe an automated platform for the reproducible synthesis of colloidal nanocrystals and for the high-throughput optimization of physical properties relevant to emerging applications of nanomaterials. This robotic platform enables precise control over reaction conditions while performing workflows analogous to those of traditional flask syntheses. We demonstrate control over the size, size distribution, kinetics, and concentration of reactions by synthesizing CdSe nanocrystals with 0.2% coefficient of variation in the mean diameters across an array of batch reactors and over multiple runs. Leveraging this precise control along with high-throughput optical and diffraction characterization, we effectively map multidimensional parameter space to tune the size and polydispersity of CdSe nanocrystals, to maximize the photoluminescence efficiency of CdTe nanocrystals, and to control the crystal phase and maximize the upconverted luminescence of lanthanide-doped NaYF(4) nanocrystals. On the basis of these demonstrative examples, we conclude that this automated synthesis approach will be of great utility for the development of diverse colloidal nanomaterials for electronic assemblies, luminescent biological labels, electroluminescent devices, and other emerging applications.