Ferrocene Units Research Articles

A Redox‐Responsive Ferrocene‐Based Capsule Displaying Unusual Encapsulation‐Induced Charge‐Transfer Interactions

AbstractA ferrocene‐based capsule is spontaneously and quantitatively formed in water by the assembly of bent amphiphiles carrying two ferrocene units. The disassembly and assembly of the new organometallic capsule, with a well‐defined and highly condensed ferrocene core, are demonstrated by chemical redox stimuli in a fully reversible fashion under ambient conditions. In contrast to previously reported multiferrocene assemblies, only the present capsule efficiently encapsulates typical organic/inorganic dyes as well as electron‐accepting molecules in water. As a result, unusual host‐guest charge‐transfer (CT) interactions, displaying relatively wide absorption bands in the visible to near‐infrared region (λ=650–1350 nm), are observed upon the encapsulation of acceptors (i.e., chloranil and TCNQ). The resultant encapsulation‐induced CT interactions can be released by a redox stimulus through the disassembly of the capsule.

A Redox-Responsive Ferrocene-Based Capsule Displaying Unusual Encapsulation-Induced Charge-Transfer Interactions.

A ferrocene-based capsule is spontaneously and quantitatively formed in water by the assembly of bent amphiphiles carrying two ferrocene units. The disassembly and assembly of the new organometallic capsule, with a well-defined and highly condensed ferrocene core, are demonstrated by chemical redox stimuli in a fully reversible fashion under ambient conditions. In contrast to previously reported multiferrocene assemblies, only the present capsule efficiently encapsulates typical organic/inorganic dyes as well as electron-accepting molecules in water. As a result, unusual host-guest charge-transfer (CT) interactions, displaying relatively wide absorption bands in the visible to near-infrared region (λ=650-1350 nm), are observed upon the encapsulation of acceptors (i.e., chloranil and TCNQ). The resultant encapsulation-induced CT interactions can be released by a redox stimulus through the disassembly of the capsule.

Self-Amplified Cascade Degradation and Oxidative Stress Via Rational pH Regulation of Oxidation-Responsive Poly(ferrocene) Aggregates.

Precise activation of polymer nanoparticles at lesion sites is crucial to achieve favorable therapeutic efficacy. However, conventional endogenous stimuli-responsive polymer nanoparticles probably suffer from few triggers to stimulate the polymer degradation and subsequent functions. Here, we describe oxidation-responsive poly(ferrocene) amphiphiles containing phenylboronic acid ester and ferrocene as the repeating backbone units. Upon triggering by hydrogen peroxide inside the tumor cells, the phenylboronic acid ester bonds are broken and poly(ferrocene) units are degraded to afford free ferrocene and noticeable hydroxide ions. The released hydroxide ions can immediately improve the pH value within the poly(ferrocene) aggregates, and the degradation rate of the phenylboronic acid ester backbone is further promoted by the upregulated pH; thereupon, the accelerated degradation can release much more additional hydroxide ions to improve the pH, thus achieving a positive self-amplified cascade degradation of poly(ferrocene) aggregates accompanied by oxidative stress boosting and efficient cargo release. Specifically, the poly(ferrocene) aggregates can be degraded up to ∼90% within 12 h when triggered by H2O2, while ferrocene-free control nanoparticles are degraded by only 30% within 12 days. In addition, the maleimide moieties tethered in the hydrophilic corona can capture blood albumin to form an albumin-rich protein corona and significantly improve favorable tumor accumulation. The current oxidation-responsive poly(ferrocene) amphiphiles can efficiently inhibit tumors in vitro and in vivo. This work provides a proof-of-concept paradigm for self-amplified polymer degradation and concurrent oxidative stress, which is promising in actively regulated precision medicine.

Construction and multifunctional of hypercrosslinked porous organic polymers containing ferrocene unit for high-performance iodine adsorption and supercapacitor

BackgroundThe efficient capture of iodine and the reduction of CO2 emissions has become increasingly important in recent years due to their potential threats to human health and the environment. Hypercrosslinked Porous Organic Polymers (HPPs) are considered excellent adsorbent materials for these purposes due to their high surface areas, controllable structures, and thermal/chemical stabilities. MethodsThis work aimed to produce Fe-Bi HPP and An-Bi HPP materials for use in I2 uptake and supercapacitors applications. The preparation of these materials involved utilizing the Friedel-Crafts reaction of Fe-Di imidazole and An-Di imidazole with 4,4′-bis(chloromethyl)-1,1′-biphenyl (Bi-2Cl) in the presence of anhydrous FeCl3. Significant findingsThese materials exhibited a narrow range of pore sizes in the micropore range and had a high specific surface area of approximately 850 m2g−1. According to the results of the electrochemical analysis, the Fe-Bi HPP demonstrated an energy density of 21 Wh Kg−1 and capacitance of 147 F/g. The adsorption experiments demonstrated the effectiveness of both materials in capturing iodine. The Fe-Bi HPP has superior efficiency compared to the An-Bi HPP, which can be attributed to its larger surface area and the presence of the ferrocene unit. It exhibits an impressive I2 adsorption uptake of 112.84 mg g−1.

Spectroscopy, electrochemistry and liquid crystal properties of monosubstituted ferrocene based azobenzene derivatives with 1,2,3-triazole heterocycle

Monosubstituted ferrocene based azobenzene liquid crystals were synthesized, in which ferrocene was flexibly attached to the mesomorphic core by click reaction. The counterpart compounds without ferrocene unit were also prepared. Two series of compounds displayed liquid crystal behaviours during heating and cooling, and had wide mesophase range. In the process of cooling, the compounds underwent a transformation from nematic phase to smectic C phase. When ferrocene was introduced into the molecule, the melting point of most compounds decreased by 30–40 °C, and the mesophase range was still as wide as 71–97 °C. These compounds emitted fluorescence at 400–550 nm and had strong absorption near 280 nm and 350 nm. Under the irradiation of 365 nm ultraviolet light, these compounds transformed rapidly from E to Z isomers, while the reverse reaction occurred slowly in the dark, especially the molecules containing ferrocene. Cyclic voltammetry studies showed that ferrocene based azobenzene derivatives exhibited one electron transfer processes with low formal redox potentials, indicating that these compounds are easily oxidized.

Molecular design of ferrocene-based novel polymer using click chemistry via chemoselective polymerization and investigation of electrical properties as organic Schottky diode

Organic Schottky diodes are electronic devices that consist of a metal–semiconductor junction formed with an organic polymer as the semiconductor material. This work synthesized cinnamic acid side chain bearing polymer and its ferrocene-modified polymer. Thermal stability, dielectric and electrical properties of the initial polymer and the modified one were examined and the addition of a ferrocene unit to the initial polymer clearly improved the optical and electrical properties of the target polymer. Due to the influence of ferrocene, the dielectric constant increased from 8.69 to 18.92. Additionally, it was discovered that the ac conductivity value raised from 6.40x10−9 to 2.64x10−8. The Al/modified-polymer/p-Si structure exhibits an ideality factor of 2.22, a barrier height of 0.61 eV, and a reverse bias current of 1.28 10−5 A in the dark, according to the I-V measurements. These results demonstrated the fabricated diodes have a rectifier behavior. This diode exhibits unique electrical properties due to the characteristics of the organic polymer.

Bioisosteric ferrocenyl 1,3-thiazolidine-4-carboxylic acid derivatives: In vitro antiproliferative and antimicrobial evaluations

To improve the antiproliferative effect of ALC67 (diastereomeric mixture of ethyl 2-phenyl-3-propioloyl-1,3-thiazolidine-4-carboxylate), its structure was modified via (i) bioisosteric substitution of the phenyl ring by the ferrocene unit and (ii) replacing the propiolamide side-chain in ACL67 with other acyl groups having differing electrophilicities. In this way, a small library of methyl N-acyl-2-ferrocenyl-1,3-thiazolidine-4-carboxylates (13 compounds in total) was created and characterized by spectral and crystallographic means. The last N-acylation step was highly diastereoselective toward the cis-diastereomer. In solution, most of the obtained compounds existed as a mixture of two rotamers and displayed a preference for the syn-orientation around the CN bond. A twisted 5T4 envelope conformation was adopted by the derivative containing the N-phenoxyacetyl group in the crystalline state. Two derivatives with chloroacetyl and bromoacetyl groups in the N-3 side chain were cytotoxic to fibroblasts and hepatocellular cancer cells in the low micromolar range (IC50(MRC5) = 9.0 and 11.8 μM, respectively, and IC50(HepG2) = 10.6 and 18.4 μM, respectively) causing an effect similar to the lead compound (IC50(HepG2) = 10.0 μM) and cisplatin (IC50(MRC5) = 4.0 μM and IC50(HepG2) = 7.7 μM). Several derivatives also manifested modest antimicrobial effects against the studied microbial strains (MICs in the range from 0.44 to 4.0 μmol/mL). Our findings demonstrated that the introduction of a ferrocene core facilitated the preparation of optically pure analogs of ALC67 and that the cytotoxicity of compounds may be enhanced by adding proper electrophilic centers to the N-acyl side-chain.

Cancer Nanobombs Delivering Artoxplatin with a Polyigniter Bearing Hydrophobic Ferrocene Units Upregulate PD-L1 Expression and Stimulate Stronger Anticancer Immunity.

Poor immunogenicity seriously hampers the broader implementation of antitumor immunotherapy. Enhanced immunogenicity capable of achieving greater antitumor immunity is urgently required. Here, a novel polymer that contains hydrophobic ferrocene (Fc) units and thioketal bonds in the main chain, which further delivered a prodrug of oxaliplatin and artesunate, i.e., Artoxplatin, to cancer cells is described. This polymer with Fc units in the nanoparticle can work as a polyigniter to spark the peroxide bonds in Artoxplatin and generate abundant reactive oxygen species (ROS) to kill cancers as nanobombig for cancer therapy. Moreover, ROS can trigger the breakdown of thioketal bonds in the polymer, resulting in the biodegradation of the polymer. Importantly, nanobombig can facilitate the maturation of dendritic cells and promote the activation of antitumor immunity, through the enhanced immunogenic cell death effect by ROS generated in situ. Furthermore, metabolomics analysis reveals a decrease in glutamine in nanobombig -treated cancer cells, resulting in the upregulation of programmed death ligand 1 (PD-L1). Consequently, it is further demonstrated enhanced tumor inhibitory effects when using nanobombig combined with anti-PD-L1 therapy. Overall, the nanosystem offers a rational design of an efficient chemo-immunotherapy regimen to promote antitumor immunity by improving tumor immunogenicity, addressing the key challenges cancer immunotherapy faced.

Investigating the Electrochemically Driven Capture and Release of Long-Chain PFAS by Redox Metallopolymer Sorbents.

The remediation of perfluoroalkyl substances (PFAS) is an urgent challenge due to their prevalence and persistence in the environment. Electrosorption is a promising approach for wastewater treatment and water purification, especially through the use of redox polymers to control the binding and release of target contaminants without additional external chemical inputs. However, the design of efficient redox electrosorbents for PFAS faces the significant challenge of balancing a high adsorption capacity while maintaining significant electrochemical regeneration. To overcome this challenge, we investigate redox-active metallopolymers as a versatile synthetic platform to enhance both electrochemical reversibility and electrosorption uptake capacity for PFAS removal. We selected and synthesized a series of metallopolymers bearing ferrocene and cobaltocenium units spanning a range of redox potentials to evaluate their performance for the capture and release of perfluorooctanoic acid (PFOA). Our results demonstrate that PFOA uptake and regeneration efficiency increased with more negative formal potential of the redox polymers, indicating possible structural correlations with the electron density of the metallocenes. Poly(2-(methacryloyloxy)ethyl cobaltoceniumcarboxylate hexafluorophosphate) (PMAECoPF6) showed the highest affinity toward PFOA, with an uptake capacity of more than 90 mg PFOA/g adsorbent at 0.0 V vs Ag/AgCl and a regeneration efficiency of more than 85% at -0.4 V vs Ag/AgCl. Kinetics of PFOA release showed that electrochemical bias greatly enhanced the regeneration efficiency when compared to open-circuit desorption. In addition, electrosorption of PFAS from different wastewater matrices and a range of salt concentrations demonstrated the capability of PFAS remediation in complex water sources, even at ppb levels of contaminants. Our work showcases the synthetic tunability of redox metallopolymers for enhanced electrosorption capacity and regeneration of PFAS.

Crosslinked and Multi-Responsive Polymeric Vesicles as a Platform to Study Enzyme-Mediated Undocking Behavior: Toward Future Artificial Organelle Communication.

Various cellular functions are successfully mimicked, opening the door to the next generation of therapeutic approaches and systems biology. Herein, the first steps are taken toward the construction of artificial organelles for mimicking cell communication by docking and undocking of cargo in the membrane of swollen artificial organelles. Stimuli-responsive and crosslinked polymeric vesicles are used to allow docking processes at acidic pH at which ferrocene units in the swollen membrane state can undergo desired specific host-guest interaction using β-cyclodextrin as model cargo. The release of the cargo mediated by two different enzymes, glucose oxidase and α-amylase, is investigated, triggered by distinct enzymatic undocking mechanisms. Different release times for a useful transport are shown that can be adapted to different communication pathways. In addition, Försterresonanceenergytransfer(FRET) experiments further support the hypotheses of host-guest inclusion complexation formation and their time-dependent breakdown. This work paves a way to a platform based on polymeric vesicles for synthetic biology, cell functions mimicking, and the construction of multifunctional cargo delivery system.

Conjugated Microporous Polymers Based on Ferrocene Units as Highly Efficient Electrodes for Energy Storage

This work describes the facile designing of three conjugated microporous polymers incorporated based on the ferrocene (FC) unit with 1,4-bis(4,6-diamino-s-triazin-2-yl)benzene (PDAT), tris(4-aminophenyl)amine (TPA-NH2), and tetrakis(4-aminophenyl)ethane (TPE-NH2) to form PDAT-FC, TPA-FC, and TPE-FC CMPs from Schiff base reaction of 1,1'-diacetylferrocene monomer with these three aryl amines, respectively, for efficient supercapacitor electrodes. PDAT-FC and TPA-FC CMPs samples featured higher surface area values of approximately 502 and 701 m2 g-1, in addition to their possession of both micropores and mesopores. In particular, the TPA-FC CMP electrode achieved more extended discharge time compared with the other two FC CMPs, demonstrating good capacitive performance with a specific capacitance of 129 F g-1 and capacitance retention value of 96% next 5000 cycles. This feature of TPA-FC CMP is attributed to the presence of redox-active triphenylamine and ferrocene units in its backbone, in addition to a high surface area and good porosity that facilitates the redox process and provides rapid kinetics.

Thermo/β-cyclodextrin-responsive ferrocenyl hydrogels constructed by ROMP reaction

Hydrogels with stimuli-responsive behavior have been of great interest to researchers from many fields, such as biotechnology, drug delivery, and sensors, owing to their “smart” change in properties under external stimuli such as temperature, pH, pressure, redox, magnetic and electric fields. In this work, using the third generation Grubbs’ catalyst as the initiator, both temperature and β-cyclodextrin (β-CD) stimuli-responsive ferrocenyl hydrogels were prepared with different proportions of hydrophilic norbornene monomer NTEG, ferrocene-containing monomer NFc and crosslinker 1 by using one-pot ROMP (ring-opening metathesis polymerization) reaction. Based on the mechanical and rheological tests, it was found that NFc not only played a crucial role in maintaining the structure of ferrocenyl hydrogels, but also enhanced their physical strength. Comparatively, the increase of the NTEG content in the hydrogel system can improve the toughness of the resulting hydrogels. Furthermore, Results of the swelling ratio test demonstrated that these hydrogels possessed temperature-responsiveness, in which the NTEG block, which contained dendritic oligoethylene glycol structures in the side chain, played a decisive role. Simultaneously, it is worth noting that these ferrocenyl hydrogels also exhibited responsive behavior to β-CD solution due to the host-guest interaction of ferrocene unit with β-CD macromolecule. Therefore, we believe that this study provides a new idea for the design of covalently crosslinked ferrocenyl stimuli-responsive smart hydrogels.

Ferrocene-driven single-chain polymer compaction.

We introduce single-chain nanoparticles (SCNPs) exclusively folded by covalently bonded ferrocene units. Specifially, we demonstrate the ability of 2-ferrocenyl-1,10-phenanthroline to fuse single-chain collapse with the concomitant introduction of a donor functionality allowing the installation of a Pd-catalytic site, affording the first heterobimetallic ferrocene-functionalized SCNP.

Efficient ternary WORM memory devices from quinoline-based D-A systems by varying the redox behavior of ferrocene.

The design and synthesis of ferrocene-functionalized organic small molecules using quinoline cores are rendered to achieve a ternary write-once-read-many (WORM) memory device. Introducing an electron-withdrawing group into the ferrocene system changes the compounds' photophysical, electrochemical, and memory behavior. The compounds were synthesized with and without an acetylene bridge between the ferrocene unit and quinoline. The electrochemical studies proved the oxidation behavior with a slightly less intense reduction peak of the ferrocene unit, demonstrating that quinolines have more reducing properties than ferrocene with bandgaps ranging from 2.67-2.75 eV. The single crystal analysis of the compounds also revealed good interactive interactions, ensuring good molecular packing. This further leads to a ternary WORM memory with oxidation of the ferrocene units and charge transfer in the compounds. The devices exhibit on/off ratios of 104 and very low threshold voltages of -0.58/-1.02 V with stabilities of 103 s and 100 cycles of all the states through retention and endurance tests.

A convenient synthesis of ferrocene-(ethynylphenyl)thioacetates.

Ferrocene is popular within the field of molecular electronics due to its well-defined electronic properties. However, where the conductance of highly-conjugated oligophenylethylenes has been widely studied, work on analogous ferrocenyl systems has been relatively rare, possibly due to difficulties associated with the synthesis of molecules containing terminal thioacetates, which are often used to bind molecules to metallic electrodes. Herein, a widely applicable synthetic methodology is demonstrated which can be used to synthesize a variety of conjugated ferrocene-alkyne systems terminated with thioacetates, including symmetric, asymmetric and multi-ferrocene systems. Conjugation of the ferrocene units to their terminal atoms is then shown through the use of both UV/Vis spectroscopy and cyclic voltammetry. This work paves the way for future studies and applications of conjugated ferrocene systems in the field of nanoelectronics.

Discovery of Y-Shaped Supramolecular Polymers in a Self-Assembling Peptide Amphiphile System.

Supramolecular polymers (SPs) formed by self-assembly of peptide-based molecular units assume a variety of interesting one-dimensional (1D) morphologies. While the morphological complexity and phase behavior of self-assembling peptide conjugates bear some resemblance to those of low-molecular-weight and macromolecular surfactants, Y-junctions, or three-way connected constructs, a topological defect observed in traditional surfactants has not been identified, likely due to the intolerance of defective packing by the strong, associative interactions afforded by the peptide segments. Here we report our discovery of branched SPs with Y-junctions and occasionally enlarged spherical end-caps formed by micellization of a ferrocene-based peptide amphiphile in water. Our results suggest that the incorporation of two ferrocenes into the amphiphile design is key to ensure the formation of branched SPs. We hypothesize that the complex interplay of internal interactions limits the effective propagation of hydrogen bonding within the assemblies and, consequently, creates fragmented β-sheets that are more tolerant for supramolecular branching. Given the redox sensitivity of the ferrocene units, sequential addition of reductants and oxidants to the solution led the assemblies to reversibly transform between branched SPs and spherical aggregates.

Synthesis and coordination of a pair of isomeric ferrocene phosphinoamines

Ferrocene P,N-ligands have been extensively studied due to their favorable catalytic properties. This contribution focuses on a pair of new, isomeric ferrocene phosphinoamines, FcNHCH2CH2PPh2 (1) and FcN(Me)CH2PPh2 (2), which were prepared from aminoferrocene, converted to the respective phosphine selenides (1-Se and 2-Se) and further studied as ligands in Pd(II) complexes containing the 2-(dimethylamino-κN)phenyl-κC1 auxiliary (LNC) ligand. Thus, cleavage of the dimeric precursor [(LNC)Pd(μ-Cl)]2 with the phosphinoamines afforded the corresponding phosphine complexes [(LNC)PdCl(1-κP)] (5) and [(LNC)PdCl(2-κP)] (6) with trans-P,N configuration. The subsequent removal of the chloride ligand with AgClO4 from 5 produced the cationic bis-chelate complex [(LNC)PdCl(1-κ2P,N)]ClO4 (7), whereas an analogous reaction with 6 gave no defined product. The phosphinoamines and their complexes were characterized by elemental analysis and common spectroscopic methods, and the crystal structures of 1, 2, and 7 were determined by single-crystal X-ray diffraction analysis. A cyclic voltammetry study, supported by DFT calculations, revealed that the primary electrochemical oxidation of these compounds occurs at the ferrocene unit.

3 + 2] Cycloadditions in Asymmetric Synthesis of Spirooxindole Hybrids Linked to Triazole and Ferrocene Units: X-ray Crystal Structure and MEDT Study of the Reaction Mechanism

Derivatization of spirooxindole having triazole and ferrocene units was achieved by the [3 + 2] cycloaddition (32CA) reaction approach. Reacting the respective azomethine ylide (AY) intermediate generated in situ with the ethylene derivative produced novel asymmetric cycloadducts with four contiguous asymmetric carbons in an overall high chemical yield with excellent regioselectivity and diastereoselectivity. X-Ray single-crystal structure analyses revealed, with no doubt, the success of the synthesis of the target compounds. The 32CA reaction of AY 5b with ferrocene ethylene 1 has been studied within MEDT. This 32CA reaction proceeds via a two-stage one-step mechanism involving a high asynchronous transition state structure, resulting from the nucleophilic attack of AY 5b on the β-conjugated position of ferrocene ethylene 1. The supernucleophilic character of AY 5b and the strong electrophilic character of ferrocene ethylene 1 account for the high polar character of this 32CA reaction. Further, Hirshfeld analyses were used to describe the molecular packing of compounds 4b, 4e, 4h and 4i.

A Molecular Electron Density Theory Study of the [3+2] Cycloaddition Reaction of an Azomethine Ylide with an Electrophilic Ethylene Linked to Triazole and Ferrocene Units.

The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY) with an electrophilic ethylene linked to triazole and ferrocene units has been studied within the Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. The topology of the electron localization function (ELF) of this AY allows classifying it as a pseudo(mono)radical species characterized by the presence of two monosynaptic basins, integrating a total of 0.76 e, at the C1 carbon. While the ferrocene ethylene has a strong electrophilic character, the AY is a supernucleophile, suggesting that the corresponding 32CA reaction has a high polar character and a low activation energy. The most favorable ortho/endo reaction path presents an activation enthalpy of 8.7 kcal·mol−1, with the 32CA reaction being exergonic by −42.1 kcal·mol−1. This reaction presents a total endo stereoselectivity and a total ortho regioselectivity. Analysis of the global electron density transfer (GEDT) at the most favorable TS-on (0.23 e) accounts for the high polar character of this 32CA reaction, classified as forward electron density flux (FEDF). The formation of two intermolecular hydrogen bonds between the two interacting frameworks at the most favorable TS-on accounts for the unexpected ortho regioselectivity experimentally observed.

Construction of Ferrocene-based bimetallic CoFe-FcDA nanosheets for efficient oxygen evolution reaction

The development of low-cost, high-performance, and stable non-noble metal electrocatalysts for oxygen evolution reaction (OER) applications are crucial for future energy supply. Here, we designed ferrocene-based bimetallic CoFe-FcDA MOF nanosheets to realize high-efficient OER electrocatalysts. The resultant CoFe-FcDA nanosheets exhibited remarkable OER performance in an alkaline medium, OER required just a 251 mV overpotential to achieve a current density of 10 mA cm−2, which were superior to that of the counterpart CoFe-BDC catalyst. Electrochemical results showed that the ferrocene unit acted as an effective electron transfer intermediate, which was in charge of the brilliant OER performances. Density functional theory (DFT) calculations indicated that the overall electron transfer capability could be enhanced due to the ferrocene unit, resulting in a theoretical overpotential of 0.60 eV for CoFe-FcDA, which was lower than 0.68 eV for CoFe-BDC. These results provided a potential pathway to achieve high-performance OER electrocatalysts.