Electron-transfer processes in dendrimers and their implication in biology, catalysis, sensing and nanotechnology

Reduction of Li+ within a borate anion

Group 1 elements exhibit the lowest electronegativity values in the Periodic Table. The chemical reduction of Group 1 metal cations M+ to M(0) is extremely challenging. Common tetraaryl borates demonstrate limited redox properties and are prone to decomposition upon oxidation. In this study, by employing simple yet versatile bipyridines as ligands, we synthesized a series of redox-active borate anions characterized by NMR and X-ray single-crystal diffraction. Notably, the borate anion can realize the reduction of Li+, generating elemental lithium metal and boron radical, thereby demonstrating its potent reducing ability. Furthermore, it can serve as a powerful two-electron-reducing reagent and be readily applied in various reductive homo-coupling reactions and Birch reduction of acridine. Additionally, this borate anion demonstrates its catalytic ability in the selective two-electron reduction of CO2 into CO.

Ferrocene-Based Drugs, Delivery Nanomaterials and Fenton Mechanism: State of the Art, Recent Developments and Prospects

Ferrocene has been the most used organometallic moiety introduced in organic and bioinorganic drugs to cure cancers and various other diseases. Following several pioneering studies, two real breakthroughs occurred in 1996 and 1997. In 1996, Jaouen et al. reported ferrocifens, ferrocene analogs of tamoxifen, the chemotherapeutic for hormone-dependent breast cancer. Several ferrocifens are now in preclinical evaluation. Independently, in 1997, ferroquine, an analog of the antimalarial drug chloroquine upon the introduction of a ferrocenyl substituent in the carbon chain, was reported by the Biot-Brocard group and found to be active against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Ferroquine, in combination with artefenomel, completed phase IIb clinical evaluation in 2019. More than 1000 studies have been published on ferrocenyl-containing pharmacophores against infectious diseases, including parasitic, bacterial, fungal, and viral infections, but the relationship between structure and biological activity has been scarcely demonstrated, unlike for ferrocifens and ferroquines. In a majority of ferrocene-containing drugs, however, the production of reactive oxygen species (ROS), in particular the OH. radical, produced by Fenton catalysis, plays a key role and is scrutinized in this mini-review, together with the supramolecular approach utilizing drug delivery nanosystems, such as micelles, metal-organic frameworks (MOFs), polymers, and dendrimers.

Plants anatomically engineered by nanomaterials

Anatomical characteristics are essential in determining the stress that affects plants. In addition, they provided a piece of evidence for environmental pollution. The increasing use of nanomaterials (EnNos) in industries, medicine, agriculture, and all fields. Nanomaterials also have many uses as a new science; they have toxic effects that have not been studied well. Therefore, this research was interested in recording recent studies on (EnNos) and their impact on the anatomical characteristics of plants. Moreover, the possibility of using anatomical characteristics as evidence of nano contamination (nanotoxicity) in plants comprises a crucial living component of the ecosystem. Studies on the effect of EnNos (carbon) on plant anatomy indicated that excess EnNos content affects the anatomical structure of the plant from the vital structures of the root, stem and leaves. Toxicological effect on xylem and phylum vessels from toxicological studies to date, Toxicological effects on EnNos of various kinds can be toxic if they are not bound to a substrate or freely circulating in living systems. Different types of EnNos, behavior, and plant capacity generate different paths. Moreover, different, or even conflicting, conclusions have been drawn from most studies on the interactions of EnNos with plants. Therefore, this paper comprehensively reviews studies on different types of carbon EnNos and their interactions with different plant species at the anatomical responses. Keywords: Anatomical characteristics, nanomaterials, nanotoxicity, Fullerene and Carbon Nanotubes

From sandwich complexes to dendrimers: journey toward applications to sensing, molecular electronics, materials science, and biomedicine

This review links various areas of inorganic chemistry around the themes developed by our research group during the last four decades. It is firstly based on the electronic structure of iron sandwich complexes, showing how the metal electron count dictates their reactivities, with various applications (via C-H activation, C-C bond formation) as reducing and oxidizing agents, redox and electrocatalysts and precursors of dendrimers and catalyst templates through bursting reactions. Various electron-transfer processes and consequences are explored, including the influence of the redox state on the acidity of robust ligands and the possibility to iterate in situ C-H activation and C-C bond formation to build arene-cored dendrimers. Examples of how these dendrimers are functionalized are illustrated using the cross olefin metathesis reactions, with application to the synthesis of soft nanomaterials and biomaterials. Mixed and average valence complexes give rise to remarkable subsequent organometallic reactions, including the salt influence on these reactions. The stereo-electronic aspect of these mixed valencies is pointed out in star-shaped multi-ferrocenes with a frustration effect and other multi-organoiron systems, with the perspective of understanding electron-transfer processes among dendrimer redox sites involving electrostatic effects and application to redox sensing and polymer metallocene batteries. Dendritic redox sensing is summarized for biologically relevant anions such as ATP^2- with supramolecular exoreceptor interactions at the dendrimer periphery in parallel with the seminal work on metallocene-derived endoreceptors by Beer's group. This aspect includes the design of the first metallodendrimers that have applications in both redox sensing and micellar catalysis with nanoparticles. These properties provide the opportunity to summarize the biomedical (mostly anticancer) applications of ferrocenes, dendrimers and dendritic ferrocenes in biomedicine (in particular the contribution from our group, but not only). Finally, the use of dendrimers as templates for catalysis is illustrated with numerous reactions including C-C bond formation, click reactions and H₂ production reactions.

Heterogeneous Dendrimer-Based Catalysts

The present review compiles the advances in the dendritic catalysis within the last two decades, in particular concerning heterogeneous dendrimer-based catalysts and their and application in various processes, such as hydrogenation, oxidation, cross-coupling reactions, etc. There are considered three main approaches to the synthesis of immobilized heterogeneous dendrimer-based catalysts: (1) impregnation/adsorption on silica or carbon carriers; (2) dendrimer covalent grafting to various supports (silica, polystyrene, carbon nanotubes, porous aromatic frameworks, etc.), which may be performed in a divergent (as a gradual dendron growth on the support) or convergent way (as a grafting of whole dendrimer to the support); and (3) dendrimer cross-linking, using transition metal ions (resulting in coordination polymer networks) or bifunctional organic linkers, whose size, polarity, and rigidity define the properties of the resulted material. Additionally, magnetically separable dendritic catalysts, which can be synthesized using the three above-mentioned approaches, are also considered. Dendritic catalysts, synthesized in such ways, can be stored as powders and be easily separated from the reaction medium by filtration/centrifugation as traditional heterogeneous catalysts, maintaining efficiency as for homogeneous dendritic catalysts.

Cobalt sandwich-stabilized rhodium nanocatalysts for ammonia borane and tetrahydroxydiboron hydrolysis

A bulky organocobalt sandwich-supported Rh nanoparticle is an efficient, stable and recyclable nanocatalyst for hydrolysis of both ammonia borane and tetrahydroxydiboron to H2.

Magnetically Directed Co-nanoinitiators for Cross-Linking Adhesives and Enhancing Mechanical Properties

Magnetically directed localized polymerization is of immense interest for its extensive impacts and applications in numerous fields. The use of means untethered from an external magnetic field to localize initiation of polymerization to develop a curing system is a novel concept, with a sustainable, efficient, and eco-friendly approach and a wide range of potential in both science and engineering. However, the conventional means for the initiation of polymerization cannot define the desirable location of polymerization, which is often exacerbated by the poor temporal control in the curing system. Herein, the copper-immobilized dendrimer-based magnetic iron oxide silica (MNPs-G2@Cu²⁺) co-nanoinitiators are rationally designed as initiators for redox radical polymerization. The nanoinitiators are magnetically responsive and therefore enable localized polymerization using an external magnetic field. In this work, anaerobic polymerization of an adhesive composed of triethylene glycol dimethacrylate, tert-butyl peroxybenzoate, and MNPs-G2@Cu²⁺ as the magnetic co-nanoinitiators has been investigated. The use of a magnet locates and promotes redox free radical polymerization through the synergistic functions between peroxide and MNPs-G2@Cu²⁺ co-nanoinitiators. The mechanical properties of the resulting polymer are considerably reinforced because the MNPs-G2@Cu²⁺ co-nanoinitiators concurrently play another crucial role as nanofillers. This strategy provides a novel approach for magnetically tunable localized polymerization, which allows new opportunities to govern the formulation of advanced adhesives through polymerization under hazard-free conditions for various promising applications.

Aspirin-Based Organoiron Dendrimers as Promising Anti-Inflammatory, Anticancer, and Antimicrobial Drugs

Designing nanocarriers with actions directed at a specific organ or tissue is a very promising strategy since it can significantly reduce the toxicity of a bioactive drug. In this study, an organometallic dendrimer was used to synthesize a biocompatible drug delivery system by attaching aspirin to the periphery of the dendrimer. Our goal is to enhance the bioavailability and anticancer activity of aspirin and reduce its toxicity through successive generations of organoiron dendrimers. The biological activity of aspirin-based dendrimer complexes was evaluated. The result of antimicrobial activity of the synthesized dendrimers also demonstrated an increase in their antimicrobial activity with increased generation of the dendrimers for most types of microorganisms. This study reveals for the first time that organoiron dendrimers linked with aspirin exhibit an excellent Gram-negative activity comparable to the reference drug Gentamicin. All synthesized dendrimers were tested for their anticancer activity against breast cancer cell lines (MCF-7), hepatocellular cell lines (Hep-G2), and a non-cancer cell line, Human Embryonic Kidney (HEK293), using the MTT cell viability assay and compared against a standard anticancer drug, Doxorubicin. Compounds G3-D9-Asp and G4-D12-Asp exhibited noticeable activity against both cell lines, both of which were more effective than aspirin itself. In addition, the in vivo anti-inflammatory activity and histopathology of swollen paws showed that the designed aspirin-based dendrimers displayed significant anti-inflammatory activity; however, G2-D6-Asp showed the best anti-inflammatory activity, which was more potent than the reference drug aspirin during the same period. Moreover, the coupling of aspirin to the periphery of organoiron dendrimers showed a significant reduction in the toxicity of aspirin on the stomach.

Ferrocenyl-terminated polyphenylene-type "click" dendrimers as supports for efficient gold and palladium nanocatalysis

Although dendrimer supports have been known as key parts of nanocatalysts, the capability of rigid dendrimers for this function has not yet been reported. Here, the study is focused on ferrocenylmethylenetriazolyl-terminated dendrimers (FcMTPD) as supports of remarkably efficient nanogold and nanopalladium catalysts. A biphasic system is elaborated to evaluate the catalytic activity of FcMTPD-supported Au and Pd nanoparticles (NPs) for the reduction of 4-nitrophenol to 4-aminophenol by NaBH₄ at 20 °C, and FcMTPD-supported PdNPs are found to be the best nanocatalysts with a rate constant k_app = 7.8 × 10^-2 s^-1. Excellent catalytic results are also obtained in this reaction for FcMTPD-supported AuNPs with a rate constant k_app = 5.6 × 10^-2 s^-1. For both Pd NPs and AuNPs, the kinetic results are shown to strongly depend on the method of preparation of these NPs that influences the NP size and thus their catalytic efficiency. The FcMTPD-stabilized PdNPs are easily recovered and reused at least 13 times, and their catalytic performance displays only a slight decrease during the first seven runs.

ROMP Synthesis of Side-Chain Ferrocene-Containing Polyelectrolyte and Its Redox-Responsive Hydrogels Showing Dramatically Improved Swelling with β-Cyclodextrin

A new side-chain ferrocene (Fc)-containing polyelectrolyte has been synthesized by controlled ring-opening metathesis polymerization of a water-soluble Fc-containing norbornene-based quaternary ammonium salt, as well as the corresponding covalently cross-linked polyelectrolyte hydrogel. In order to provide Fc-containing supramolecular polyelectrolyte hydrogels whose swelling property is largely improved by host-guest interaction, a covalently cross-linked polyelectrolyte hydrogel is soaked into the β-CD aqueous solution to form β-CD@Fc supramolecular polyelectrolyte hydrogel, or alternatively the quaternary ammonium salt supramolecular monomer is first formed, then copolymerized with a crosslinking agent to fabricate the supramolecular hydrogel with better water absorption ability. All the Fc-containing hydrogels exhibited good redox-responsiveness with swelling-shrinking behaviors by chemically reversibly adjusting the disassembly/assembly of β-CD@Fc inclusion complexes. This is the first example of side-chain Fc-containing polycationic supramolecular hydrogels possessing swelling-shrinking properties based on the splitting/combining of β-CD and Fc units, and potential applications are expected as controlled drug delivery and actuators.

Dendrimers: A New Race of Pharmaceutical Nanocarriers

Dendrimers are nanosized, symmetrical molecules in which a small atom or group of atoms is surrounded by the symmetric branches known as dendrons. The structure of dendrimers possesses the greatest impact on their physical and chemical properties. They grow outwards from the core-shell which further reacts with monomers having one reactive or two dormant molecules. Dendrimers' unique characteristics such as hyperbranching, well-defined spherical structure, and high compatibility with the biological systems are responsible for their wide range of applications including medical and biomedical areas. Particularly, the dendrimers' three-dimensional structure can incorporate a wide variety of drugs to form biologically active drug conjugates. In this review, we focus on the synthesis, mechanism of drug encapsulations in dendrimers, and their wide applications in drug delivery.

Pharmacological Evaluation of Novel Organoiron Dendrimers as Antimicrobial and Anti-Inflammatory Agents

The synthesis of a novel and attractive class of nonsteroidal anti-inflammatory and antimicrobial organoiron dendrimers attached to the well-known drug ibuprofen is achieved. The structures of these dendrimers are established by spectroscopic and analytical techniques. The antimicrobial activity of these dendrimers is investigated and tested against five human pathogenic Gram-positive and Gram-negative bacteria, and minimum inhibitory concentrations are reported. Some of these synthesized dendrimers exhibit higher inhibitory activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and Staphylococcus warneri compare to the reference drugs. As well, the in vitro and in vivo anti-inflammatory activities of these dendrimers are evaluated. The results of in vivo anti-inflammatory activity and histopathology of inflamed paws show that all dendrimers display considerable anti-inflammatory activity; however, second-generation dendrimer (G2-D6) shows the best anti-inflammatory activity, which is more potent than the commercial drug ibuprofen at the same tested dose. Results of the toxicity study reveal that G2-D6 is the safest drug on biological tissues.

Design of Organoiron Dendrimers Containing Paracetamol for Enhanced Antibacterial Efficacy

Paracetamol (acetaminophen) is a common painkiller and antipyretic drug used globally. Attachment of paracetamol to a series of organoiron dendrimers was successfully synthesized. The aim of this study is to combine the benefits of the presence of these redox-active organoiron dendrimers, their antimicrobial activities against some human pathogenic Gram-positive, and the therapeutic characteristics of paracetamol. The antimicrobial activity of these dendrimers was investigated and tested with a minimum inhibitory concentration and this has been reported. Some of these newly synthesized dendrimers exhibited the highest inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and Staphylococcus warneri compared to reference drugs. The results of this study indicate that the antimicrobial efficacy of the dendrimers is dependent on the size of the redox-active organoiron dendrimer and its terminal functionalities. The best result has been recorded for the fourth-generation dendrimer 11, which attached to 48 paracetamol end groups and has 90 units composed of the η⁶-aryl-η⁵-cyclopentadienyliron (II) complex. This dendrimer presented inhibition of 50% of the growth (IC₅₀) of 0.52 μM for MRSA, 1.02 μM for VRE, and 0.73 μM for Staphylococcus warneri. The structures of the dendrimers were characterized by elemental analysis, Fourier transform infrared (FT-IR), nuclear magnetic resonance (¹H-NMR), and ¹³C-NMR spectroscopic techniques. In addition, all synthesized dendrimers displayed good thermal stability in the range of 300–350 °C following the degradation of the cationic iron moieties which occurred around 200 °C.

Multiple applications of polymers containing electron-reservoir metal-sandwich complexes

Ferrocene-containing polymers have been investigated for more than six decades, and more recently modern synthetic methods have allowed the fabrication of precise polymers that contain a variety of transition-metal complexes. Trends are now oriented towards applications, such as optics, energy conversion and storage, electrochemistry, magnetics, electric conductors and biomedicine. Metal-sandwich complexes such as those of ferrocene type and other related complexes that present redox-robust groups in polymers, i.e. that are isolable in both their oxidized and reduced forms, are of particular interest, because it is possible to address them using electronic or photonic redox stimuli for application. Our research groups have called such complexes Electron-Reservoirs and introduced them in the main chain or in the side chains of well-defined polymers. For instance, polymers with ferrocene in the main chain or in the side chain are oxidized to stable polycationic polyelectrolytes only if ferrocene is part of a biferrocene unit, because biferrocene oxidation leads to the biferrocenium cation that is stabilized by the mixed valency. Then a group of several redox-robust iron sandwich complexes were fabricated and incorporated in precise polymers including multi-block copolymers whose controlled synthesis and block incorporation was achieved for instance using ring-opening-metathesis polymerization. Applications of this family of Electron-Reservoir-containing polymers includes electrochemically induced derivatization of electrodes by decorating them with these polymers, molecular recognition and redox sensing, electrochromics with multiple colours, generation of gold and silver nanoparticles of various size by reduction of gold(iii) and silver(i) precursors and their use for nanocatalysis towards depollution and biomedicine.

Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters

In this report, we present a method to characterize the kinetics of electron transfer across the bilayer of a unilamellar liposome composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The method utilizes synthetic phospholipids containing noninvasive nitroxide spin labels having the >N-O• moiety at well-defined distances from the outer surface of the liposome to serve as reporters for their local environment and, at the same time, permit measurement of the kinetics of electron transfer. We used 5-doxyl and 16-doxyl stearic acids. The paramagnetic >N-O• moiety is photo-oxidized to the corresponding diamagnetic oxoammonium cation by a ruthenium electron acceptor formed in the solution. Electron transfer is monitored by three independent spectroscopic methods: by both steady-state and time-resolved electron paramagnetic resonance and by optical spectroscopy. These techniques allowed us to differentiate between the electron transfer rates of nitroxides located in the outer leaflet of the phospholipid bilayer and of those located in the inner leaflet. Measurement of electron transfer rates as a function of temperature revealed a low-activation barrier (ΔG‡ ∼ 40 kJ/mol) that supports a tunneling mechanism.

Antioxidant and Antibacterial Properties of Carbosilane Dendrimers Functionalized with Polyphenolic Moieties

A new family of polyphenolic carbosilane dendrimers functionalized with ferulic, caffeic, and gallic acids has been obtained through a straightforward amidation reaction. Their antioxidant activity has been studied by different techniques such as DPPH (2,2′-diphenyl-1-picrylhydrazyl) radical scavenging assay, FRAP assay (ferric reducing antioxidant power), and cyclic voltammetry. The antioxidant analysis showed that polyphenolic dendrimers exhibited higher activities than free polyphenols in all cases. The first-generation dendrimer decorated with gallic acid stood out as the best antioxidant compound, displaying a correlation between the number of hydroxyl groups in the polyphenol structure and the antioxidant activity of the compounds. Moreover, the antibacterial capacity of these new systems has been screened against Gram-positive (+) and Gram-negative (−) bacteria, and we observed that polyphenolic dendrimers functionalized with caffeic and gallic acids were capable of decreasing bacterial growth. In contrast, ferulic carbosilane dendrimers and free polyphenols showed no effect, establishing a correlation between antioxidant activity and antibacterial capacity. Finally, a viability assay in human skin fibroblasts cells (HFF-1) allowed for corroborating the nontoxicity of the polyphenolic dendrimers at their active antibacterial concentration.

The supramolecular redox functions of metallomacromolecules

Abstract

Metallomacromolecules are frequently encountered in redox proteins including metal-tanned hide collagen and play crucial roles involving supramolecular properties in biological electron-transfer processes. They are also currently found in non-natural families, such as: metallopolymers, metallodendrimers and metallodendronic polymers. This mini-review discusses the supramolecular redox functions of such nanomaterials developed in our research group. Electron-transfer processes are first examined in mono-, bis- and hexa-nuclear ferrocenes and other electron-reservoir organoiron systems showing the influence of supramolecular and reorganization aspects on their mechanism. Then applications of electron-transfer processes using these same organoiron redox systems in metallomacromolecules and their supramolecular functions are discussed including redox recognition/sensing, catalysis templates, electrocatalysis, redox catalysis, molecular machines, electrochromes, drug delivery device and nanobatteries.

Graphical Abstract

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

Rational Design of Reversible Redox Shuttle for Highly Efficient Light-Driven Microswimmer

The light-driven micro/nanomotor (LMNM) is machinery that harvests photon energy and generates self-propulsion in varieties of liquid media. Though visions are made that these tiny swimming machines can serve future medicine for accurate drug delivery and noninvasive microsurgery, their biomedical application is still impeded by the insufficient propulsion efficiency. Here we provide a holistic model of LMNM by considering (i) photovoltaic, (ii) electrochemical, and (iii) electrokinetic processes therein. Such a quantitative model revealed the pivotal role of reaction kinetics and diffusion properties of shuttle ions in the propulsion efficiency of LMNM. With the guidance of this model, a group of ferrocene-based reversible redox shuttles, which generate slow-diffusion ions, was identified, showcasing a high locomotion velocity of ∼500 μm/s (∼100 body length per second) at an ultralow concentration (70 μM). Owing to the in-depth understanding of the fundamental energy conversion processes in LMNM, we anticipate that the development of other high-performance supporting chemicals and LMNM systems will be greatly motivated, foreseeing the advent of LMNM systems with superior efficiency.

Molecular and Supramolecular Multiredox Systems

The design and synthesis of molecular and supramolecular multiredox systems have been summarized. These systems are of great importance as they can be employed in the next generation of materials for energy storage, energy transport, and solar fuel production. Nature provides guiding pathways and insights to judiciously incorporate and tune the various molecular and supramolecular design aspects that result in the formation of complex and efficient systems. In this review, we have classified molecular multiredox systems into organic and organic-inorganic hybrid systems. The organic multiredox systems are further classified into multielectron acceptors, multielectron donors and ambipolar molecules. Synthetic chemists have integrated different electron donating and electron withdrawing groups to realize these complex molecular systems. Further, we have reviewed supramolecular multiredox systems, redox-active host-guest recognition, including mechanically interlocked systems. Finally, the review provides a discussion on the diverse applications, e. g. in artificial photosynthesis, water splitting, dynamic random access memory, etc. that can be realized from these artificial molecular or supramolecular multiredox systems.

Synthesis and Reactivity of Poly(propyleneimine) Dendrimers Functionalized with Cyclopentadienone N-Heterocyclic-Carbene Ruthenium(0) Complexes

Ligand design in metal chemistry is a fundamental step when pursuing compounds with specific reactivity. In this paper, the functionalization of the OH group in the lateral chain of the N-heterocyclic-carbene (NHC) ligand bound to a bis-carbonyl cyclopentadienone NHC ruthenium(0) complex allowed the decoration of five generations of poly(propyleneimine) (PPIs) dendrimers with up to 64 organometallic moieties. The coupling was achieved by employing carbonyldiimidazole and the formation of carbamate linkages between dendritic peripheral NH2 and lateral OH groups on ruthenium complexes. The synthetic procedure, chemical purification, and spectroscopic characterization of the five generations of dendrimers (3g1–5) are here described. The ruthenium-modified dendrimers were activated as catalysts in the transfer hydrogenation of the model compound 4-fluoroacetophenone in the presence of cerium ammonium nitrate as their mononuclear congeners. The catalytic activity, being similar for the five generations, shows a decrease if compared to mononuclear complexes. This detrimental effect might be ascribed to the –CH2NH– functionalization, largely present in dendrimer skeleton and that can compete with the hydrogen transfer mechanism, but also partially to a dendritic effect caused by steric encumbrance.

Scalable Synthesis of Functionalized Ferrocenyl Azides and Amines Enabled by Flow Chemistry

A scalable access to functionalized ferrocenyl azides has been realized in flow. By halogen-lithium exchange of ferrocenyl halides and trapping with tosyl azide, a variety of functionalized ferrocenyl azides were obtained in high yields. To allow a scalable preparation of these potentially explosive compounds, a flow protocol was developed accelerating the reaction time to minutes and circumventing accumulation of potentially hazardous intermediates. The corresponding ferrocenyl amines were then prepared by a reliable reduction process.

Electrochemical Anion Sensing: Supramolecular Approaches

Anions play a vital role in a broad range of environmental, technological, and physiological processes, making their detection/quantification valuable. Electroanalytical sensors offer much to the selective, sensitive, cheap, portable, and real-time analysis of anion presence where suitable combinations of selective (noncovalent) recognition and transduction can be integrated. Spurred on by significant developments in anion supramolecular chemistry, electrochemical anion sensing has received considerable attention in the past two decades. In this review, we provide a detailed overview of all electroanalytical techniques that have been used for this purpose, including voltammetric, impedimetric, capacititive, and potentiometric methods. We will confine our discussion to sensors that are based on synthetic anion receptors with a specific focus on reversible, noncovalent interactions, in particular, hydrogen- and halogen-bonding. Apart from their sensory properties, we will also discuss how electrochemical techniques can be used to study anion recognition processes (e.g., binding constant determination) and will furthermore provide a detailed outlook over future efforts and promising new avenues in this field.

Synthesis, characterization, and anticancer activity of folate γ-ferrocenyl conjugates

Novel folate γ-ferrocene conjugates were synthesized through a regiospecific route, and showed selectivity and enhanced cytotoxicity against Frα-positive malignant cells.

Tunable Redox Potential, Optical Properties, and Enhanced Stability of Modified Ferrocene-Based Complexes

We report a series of ferrocene-based derivatives and their corresponding oxidized forms in which the introduction of simple electron donating groups like methyl or tert-butyl units on cyclopentadienyl-rings afford great tunability of Fe^+III/Fe^+II redox potentials from +0.403 V down to -0.096 V versus saturated calomel electrode. The spin forbidden d-d transitions of ferrocene derivatives shift slightly toward the blue region with an increasing number of electron-donating groups on the cyclopentadienyl-rings with very little change in absorptivity values, whereas the ligand-to-metal transitions of the corresponding ferricinium salts move significantly to the near-IR region. The electron-donating groups also contribute in the strengthening of electron density of Fe^+III d-orbitals, which therefore improves the chemical stability against the oxygen reaction. Further, density functional theory calculations show a reducing trend in outer shell reorganization energy with an increasing number of the electron donating units.

Nanoparticle-Plant Interactions: Two-Way Traffic

In this Review, an effort is made to discuss the most recent progress and future trend in the two-way traffic of the interactions between plants and nanoparticles (NPs). One way is the use of plants to synthesize NPs in an environmentally benign manner with a focus on the mechanism and optimization of the synthesis. Another way is the effects of synthetic NPs on plant fate with a focus on the transport mechanisms of NPs within plants as well as NP-mediated seed germination and plant development. When NPs are in soil, they can be adsorbed at the root surface, followed by their uptake and inter/intracellular movement in the plant tissues. NPs may also be taken up by foliage under aerial deposition, largely through stomata, trichomes, and cuticles, but the exact mode of NP entry into plants is not well documented. The NP-plant interactions may lead to inhibitory or stimulatory effects on seed germination and plant development, depending on NP compositions, concentrations, and plant species. In numerous cases, radiation-absorbing efficiency, CO2 assimilation capacity, and delay of chloroplast aging have been reported in the plant response to NP treatments, although the mechanisms involved in these processes remain to be studied.

Tuning the size, shape and structure of RNA nanoparticles for favorable cancer targeting and immunostimulation

The past decade has shown exponential growth in the field of RNA nanotechnology. The rapid advances of using RNA nanoparticles for biomedical applications, especially targeted cancer therapy, suggest its potential as a new generation of drug. After the first milestone of small molecule drugs and the second milestone of antibody drugs, it was predicted that RNA drugs, either RNA itself or chemicals/ligands that target RNA, will be the third milestone in drug development. Thus, a comprehensive assessment of the current therapeutic RNA nanoparticles is urgently needed to meet the drug evaluation criteria. Specifically, the pharmacological and immunological profiles of RNA nanoparticles need to be systematically studied to provide insights in rational design of RNA-based therapeutics. By virtue of its programmability and biocompatibility, RNA molecules can be designed to construct sophisticated nanoparticles with versatile functions/applications and highly tunable physicochemical properties. This intrinsic characteristic allows the systemic study of the effects of various properties of RNA nanoparticles on their in vivo behaviors such as cancer targeting and immune responses. This review will focus on the recent progress of RNA nanoparticles in cancer targeting, and summarize the effects of common physicochemical properties such as size and shape on the RNA nanoparticles' biodistribution and immunostimulation profiles. This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.