Nola Etkin

Sandwich complex-containing macromolecules: property tunability through versatile synthesis.

Sandwich complexes feature unique properties as the physical and electronic properties of a hydrocarbon ligand or its derivative are integrated into the physical, electronic, magnetic, and optical properties of a metal. Incorporation of these complexes into macromolecules results in intriguing physical, electrical, and optical properties that were hitherto unknown in organic-based macromolecules. These properties are tunable through well-designed synthetic strategies. This review surveys many of the synthetic approaches that have resulted in tuning the properties of sandwich complex-containing macromolecules. While the past two decades have seen an ever-growing number of research publications in this field, gaps remain to be filled. Thus, we expect this review to stimulate research interest towards bridging these gaps, which include the insolubility of some of these macromolecules as well as expanding the scope of the sandwich complexes.

Antimicrobial organometallic dendrimers with tunable activity against multidrug-resistant bacteria

Multidrug-resistant pathogens are an increasing threat to public health. In an effort to curb the virulence of these pathogens, new antimicrobial agents are sought. Here we report a new class of antimicrobial organometallic dendrimers with tunable activity against multidrug-resistant Gram-positive bacteria that included methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Mechanistically, these redox-active, cationic organometallic dendrimers induced oxidative stress on bacteria and also disrupted the microbial cell membrane. The minimum inhibitory concentrations, which provide a quantitative measure of the antimicrobial activity of these dendrimers, were in the low micromolar range. AlamarBlue cell viability assay also confirms the antimicrobial activity of these dendrimers. Interestingly, these dendrimers were noncytotoxic to epidermal cell lines and to mammalian red blood cells, making them potential antimicrobial platforms for topical applications.

Antimicrobial resistance challenged with metal-based antimicrobial macromolecules.

Antimicrobial resistance threatens the achievements of science and medicine, as it deactivates conventional antimicrobial therapeutics. Scientists respond to the threat by developing new antimicrobial platforms to prevent and treat infections from these resistant strains. Metal-based antimicrobial macromolecules are emerging as an alternative to conventional platforms because they combine multiple mechanisms of action into one platform due to the distinctive properties of metals. For example, metals interact with intracellular proteins and enzymes, and catalyse various intracellular processes. The macromolecular architecture offers a means to enhance antimicrobial activity since several antimicrobial moieties can be conjugated to the scaffold. Further, these macromolecules can be fabricated into antimicrobial materials for contact-killing medical implants, fabrics, and devices. As volatilization or leaching out of the antimicrobial moieties from the macromolecular scaffold is reduced, these medical implants, fabrics, and devices can retain their antimicrobial activity over an extended period. Recent advances demonstrate the potential of metal-based antimicrobial macromolecules as effective platforms that prevent and treat infections from resistant strains. In this review these advances are thoroughly discussed within the context of examples of metal-based antimicrobial macromolecules, their mechanisms of action and biocompatibility.

Photoinduced Synthesis of Dual‐Emissive Tetraphenylethene‐Based Dendrimers with Tunable Aggregates and Solution States Emissions

Photoactive materials are actively researched, piloting breakthroughs that have enriched fundamental understanding of science, and have led to real applications. Tetraphenylethene, a photoactive molecule that is of interest from fundamental and applied perspectives, features photochemical properties that are not exploited in the design of photoactive, dual-emissive materials. Here, tetraphenylethene-based, dual-emissive dendrimers are constructed via a synthetic approach that involves a photochemical reaction that exploits the photochemistry of tetraphenylethene. These dendrimers are emissive in solution and in the aggregate state with tunable dual emissions at 368 and 469 nm. The photochemical reaction also tunes the size of the aggregates, increasing the size after UV irradiation. The reported synthetic strategy is a direct and facile approach to accessing dual-emissive macromolecules, especially tetraphenylethene-based systems for real applications.

Redox-active cationic organoiron complex: a promising lead structure for developing antimicrobial agents with activity against Gram-positive pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium

We report a new class of antimicrobial agent, a redox-active, cationic organometallic, η6-arene–η5-cyclopentadienyliron(II) complex, with activity against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Structure–property relationship investigations revealed that the antimicrobial activity against these pathogens, especially methicillin-resistant Staphylococcus aureus, is tunable. The ability of this new class of antimicrobial agent to induce cellular oxidative stress was confirmed using dichlorodihydrofluorescein assay. We attributed the induction of oxidative stress as a mechanism that contributes to the overall antimicrobial activity of these compounds. Generally, this antimicrobial agent was non-toxic to BJ fibroblast cell lines at ≤128 μg mL−1. The η6-arene–η5-cyclopentadienyliron(II) complex represents a potential lead structure for the development of topical antimicrobial therapeutics to combat resistant strains of Gram-positive bacteria.

CHAPTER 4:Functional Materials Based on Metal-Containing Polymers

Since the dawn of human civilization, there has been a demand for materials that include ceramics, metals, and polymers. Increasing demand as well as the need for enhanced performance has driven material scientists to research metal-containing polymers as complements of these materials. Consequently, metal-containing polymers that integrate the excellent thermal, electronic, optical, and magnetic properties of metals with the lightweight, low cost, and in some cases, the chemical stability of organic-based polymers have been designed, and used as catalysts, sensors, ceramic precursors, magnetic materials, and electrical conductors. This chapter provides an overview of some of these functional metal-containing polymers.

Dendritic polymers designed for photo-driven applications

Inspired by nature as well as by their imagination, material scientists design photoactive materials to facilitate work through the use of light. Dendritic polymers are an attractive scaffold for the design of these materials, given their unique 3D topology as well as other inherent properties such as solubility that allows easy processability. Through rational synthetic designs, chromophores and/or luminophores have been precisely built into dendritic polymeric frameworks to afford material precursors for photo-driven applications. These photoactive dendritic polymers are proposed for use in a wide range of applications that includes catalysis, photonics, electronics, and biomedicine. Here, we briefly examine these polymers to highlight their photophysical and photochemical properties that are useful in fundamental studies and practical applications.

Quaternized and Thiazole-Functionalized Free Radical-Generating Organometallic Dendrimers as Antimicrobial Platform against Multidrug-Resistant Microorganisms

New macromolecules such as dendrimers are increasingly needed to drive breakthroughs in diverse areas, for example, healthcare. Here, the authors report hybrid antimicrobial dendrimers synthesized by functionalizing organometallic dendrimers with quaternary ammonium groups or 2-mercaptobenzothiazole. The functionalization tunes the glass transition temperature and antimicrobial activities of the dendrimers. Electron paramagnetic resonance spectroscopy reveals that the dendrimers form free radicals, which have significant implications for catalysis and biology. In vitro antimicrobial assays indicate that the dendrimers are potent antimicrobial agents with activity against multidrug-resistant pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium as well as other microorganisms. The functionalization increases the activity, especially in the quaternary ammonium group-functionalized dendrimers. Importantly, the activities are selective because human epidermal keratinocytes cells and BJ fibroblast cells exposed to the dendrimers are viable after 24 h.

Tunable room-temperature soft ferromagnetism in magnetoceramics of organometallic dendrimers

The development of new methods of assembling matter to access advanced materials, such as magnetoceramics, remains a worthwhile research challenge. Several approaches to generate such materials include pyrolysis of linear and hyperbranched polymer precursors. In this study, homometallic iron-containing (Fe), and heterometallic iron- and cobalt-containing (Fe–Co) dendrimers were used to generate magnetoceramics with tunable room temperature and soft ferromagnetism. The yet-to-be-explored dendritic precursors offer opportunities to control the magnetic properties via dendritic effects and functionalization with multiple ferromagnetic metals. Indeed, we tuned the magnetic properties of the homometallic ceramics via dendritic effects. Specifically, the saturation magnetization (Ms) and coercivity (Hc) decrease as the generation of the dendrimer increases. Incorporating Co into the dendrimers to synthesize heterometallic dendrimers noticeably changed the magnetic properties of the ceramics. Ms and Hc increased in ceramics derived from the second-generation dendrimer but these properties decreased in ceramics derived from zeroth- and first-generation dendrimers. The ferromagnetism in the homometallic and heterometallic ceramics differs in its response to changes in temperature. For instance, we observed that the homometallic ceramics were less susceptible to the changes in temperature, exhibiting a magnetic phase transition at ∼210 K in contrast to the heterometallic ceramics with a transition at ∼110 K. Overall, the results present dendrimers as a new type of precursors for magnetoceramics and expand the parameter space toward understanding magnetism in ceramics, allowing for the development of ceramics with tunable magnetism.