A photochemical route to ferrocenyl‐substituted ferrapyrrolinone complexes

In the presence of iron pentacarbonyl, photochemical reaction between phenylisocyanate and ferrocenylacetylene results in ferrapyrrolinone complex [Fe₂(CO)₆(μ₂‐η³‐FcC═C(H)C(O)NPh)] ( 1 ) and maleimide 3‐ferrocenyl‐1‐phenyl‐1H ‐pyrrole‐2,5‐dione ( 2 ). Under similar experimental conditions, ferrocenyl−/phenyl‐substituted butadiyne primarily shows the activation of only one C☰C bond and results in ferrapyrrolinone complexes [Fe₂(CO)₆(μ₂‐η³‐FcC═C(C☰CR)C(O)NPh)] ( 3 , R = Fc; 3a , R = Ph), maleimides 3‐ferrocenyl‐1‐phenyl‐4‐(ferrocenylethynyl)‐1H –pyrrole‐2,5‐dione ( 5 ) and 3‐ferrocenyl‐1‐phenyl‐4‐(phenylethynyl)‐1H –pyrrole‐2,5‐dione ( 5a ) and [Fe₂(CO)₆(μ₂‐η³‐FcC═C(R)C(O)NPh)] ( 4 ; R  = 3‐ferrocenyl‐1‐phenyl‐1H ‐pyrrole‐2,5‐dione). Compound 4 consists of ferrapyrrolinone and a maleimide unit, formed by the activation of both C☰C bonds of diferrocenylbutadiyne. Activation of both C☰C bonds in a substituted butadiyne is a rare observation. Formation of the ferrapyrrolinone compounds is an advance over the earlier reported methods which generally use internal alkynes and involve prior synthesis of other clusters.     

Simple diazonium chemistry to develop specific gene sensing platforms

A simple strategy for covalent immobilizing DNA sequences, based on the formation of stable diazonized conducting platforms, is described. The electrochemical reduction of 4-nitrobenzenediazonium salt onto screen-printed carbon electrodes (SPCE) in aqueous media gives rise to terminal grafted amino groups. The presence of primary aromatic amines allows the formation of diazonium cations capable to react with the amines present at the DNA capture probe. As a comparison a second strategy based on the binding of aminated DNA capture probes to the developed diazonized conducting platforms through a crosslinking agent was also employed. The resulting DNA sensing platforms were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and spectroscopic ellipsometry. The hybridization event with the complementary sequence was detected using hexaamineruthenium (III) chloride as electrochemical indicator. Finally, they were applied to the analysis of a 145-bp sequence from the human gene MRP3, reaching a detection limit of 210 pg μL⁻¹.     

Synthesis of boron-dipyrromethene-ferrocene conjugates

Synthesis, spectral, electrochemical and photophysical properties of four BODIPY-ferrocene conjugates in which one or two ferrocenyl groups were covalently connected either directly to boron-dipyrromethene framework or to meso-phenyl group of boron-dipyrromethene unit are described. The BODIPY-ferrocene conjugates were prepared by adopting different synthetic routes. The absorption studies indicated the presence of charge transfer band in BODIPY-ferrocene conjugates in which the ferrocenyl group(s) were directly connected to boron-dipyrromethene framework. The electrochemical studies on conjugates indicated that ferrocenyl group was difficult to oxidize whereas boron-dipyrromethene unit was easier to reduce. The conjugates were non-fluorescent due to electron transfer from ferrocene to boron-dipyrromethene unit. However, when ferrocene was oxidized to ferrocenium ion with an oxidizing agent, the conjugates exhibited fluorescence with decent quantum yields (0.17-0.31) and lifetimes (3.8-5.2 ns).     

Tunable electronic coupling in iron-chromium mixed-valence ions of methylated Cp-indene ligands

A series of heterobimetallic η⁶-[(ferrocenyl)indene]-Cr(CO)₃ complexes differing for the position of the ferrocenyl group, 1-(ferrocenyl)indene and 2-(ferrocenyl)indene, and the degree of indene methylation (tetramethyl- and hexamethyl-) have been prepared and studied with the aim to stabilise the mono- and dications generated by chemical and electrochemical oxidation, and at same time to tune the metal-metal electronic coupling in the mixed-valence cations. The magnitude of electronic delocalisation and spin density in the cations have been monitored by means of optical techniques (UV-Vis, near-IR, mid-IR) and EPR spectroscopy. The results have been rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods, establishing that a metal-to-metal electronic coupling occurs the magnitude of which depends on the degree of indene methylation.     

Electropolymerized biotinylated poly (pyrrole–viologen) film as platform for the development of reagentless impedimetric immunosensors

We describe herein the synthesis and electrochemical polymerization of a viologen monomer functionalized by a biotin group and the use of its redox properties for the impedimetric sensing of protein binding. The electrochemical oxidation of the pyrrole group at 0.85 V in CH₃CN led to a biotinylated polypyrrole film allowing the successive anchoring of an avidin layer and a biotinylated cholera toxin layer. EIS performed at ?0.45 V/SCE without redox probe in solution showed the specific immobilization of the anti-cholera toxin antibody.     

Synthesis and properties study of novel ferrocenyl isoxazole derivatives

A synthetic procedure based on the 1,3‐dipolar cycloaddition reactions of nitrile oxides and ethynylferrocene derived from ferrocene has been developed to synthesize new ferrocenyl‐isoxazole derivatives. The stable solids were thoroughly characterized by ¹H NMR, FT‐IR, and mass spectroscopy. The structure of (η⁵‐C₅H₅) Fe (η⁵‐C₅H₄) C₃HNOC₆H₄CH₃ was determined by single‐crystal X‐ray diffraction. The electrochemical behaviors of the synthesized ferrocenyl‐isoxazole derivatives were also studied. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and electro-spectroelectrochemistry of ferrocenyl naphthaquinones

A practical approach to ferrocenyl naphthaquinone derivatives involving thermal rearrangement of variously substituted 4-aryl-4-hydroxycyclobutenones was described. The reaction of 3-ferrocenyl-4-isopropoxy-3-cyclobutene-1,2-dione with different aryl lithiums gave the corresponding 4-aryl-4-hydroxycyclobutenones, which were heated in p-xylene at reflux open to the air to yield ferrocenyl naphthaquinones. The redox chemistry of the ferrocenyl naphthaquinones was studied by electrochemical and in situ spectroelectrochemical techniques in CH₂Cl₂ solution and in CH₃CN solution with water, weak and strong acidic additives. Ferrocenyl naphthaquinones displayed reversible two reduction processes involving semiquinone radical anion (Fc-snq⁻), dianion (Fc-nq²⁻) species and a one-electron oxidation process based on the ferrocenium/ferrocene (Fc⁺-nq/Fc-nq) couple in CH₂Cl₂. The redox reaction mechanism of the ferrocenyl naphthaquinones in the presence of the additives proceeded via hydrogen bonding or proton-coupled electron transfer. Effects of the substituents on the reduction potentials and intramolecular charge-transfer bands of ferrocenyl naphthaquinones were also discussed.     

Some ferrocenyl Schiff bases with nonlinear optical properties

Eleven new ferrocenyl Schiff bases containing a benzene ring and C?N in a conjugating chain have been synthesized by facile methods and characterized by ¹H NMR, elemental analysis and fast atom bombardment mass spectrometry. Cyclic voltammetry was used to determine their electrochemical properties and electron‐withdrawing effects. It is shown that these pull–push ferrocenyl compounds have nonlinear optical responses according to their electronic absorption spectra and powder second harmonic generation measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis,characterization and crystal structure of 6-ferrocenyl-2,4-dihydroxy-2,4-di(pyridine-2-yl) cyclohexanecarbonyl ferrocene

A novel ferrocene derivative which has four stereo centers has been prepared by an efficient synthetic method based on a solvent-free reaction. The compound was characterized by IR, ¹H-NMR, ¹³C-NMR, ESI-MS, single crystal X-ray diffraction and TG analysis. The crystal structure shows that the cyclohexyl group is in a chair conformation and the two ferrocenyl moieties are nonequivalent. There are two intramolecular hydrogen bonds and two intermolecular hydrogen bonds in the compound, which involve two hydroxyls and generate a dimer, respectively. The electrochemical properties of the compound are discussed.     

Electrocatalytic assay of mercury(II) ions using a bifunctional oligonucleotide signal probe

Engineered nucleic acid probes containing recognition and signaling functions find growing interest in biosensor design. In this paper, we developed a novel electrochemical biosensor for sensitive and selective detecting of Hg²⁺ based on a bifunctional oligonucleotide signal probe combining a mercury-specific sequence and a G-quadruplex (G4) sequence. For constructing the electrochemical Hg²⁺ biosensor, a thiolated, mercury-specific oligonucleotide capture probe was first immobilized on gold electrode surface. In the presence of Hg²⁺, a bifunctional oligonucleotide signal probe was hybridized with the immobilized capture probe through thymine–mercury(II)–thymine interaction-mediated surface hybridization. The further interaction between G4 sequence of the signal probe and hemin generated a G4–hemin complex, which catalyzed the electrochemical reduction of hydrogen peroxide, producing amplified readout signals for Hg²⁺ interaction events. This electrochemical Hg²⁺ biosensor was highly sensitive and selective to Hg²⁺ in the concentration of 1.0 nM to 1 μM with a detection limit of 0.5 nM. The new design of bifunctional oligonucleotide signal probes also provides a potential alternative for developing simple and effective electrochemical biosensors capable of detecting other metal ions specific to natural or artificial bases.     

Molecular beacon mediated circular strand displacement strategy for constructing a ratiometric electrochemical deoxyribonucleic acid sensor

A novel ratiometric electrochemical sensor for sensitive and selective determination of deoxyribonucleic acid (DNA) had been developed based on signal-on and signal-off strategy. The target DNA hybridized with the loop portion of ferrocene (Fc) labeled hairpin probe immobilized on the gold electrode (GE), the Fc away from the surface of GE and the methylene blue (MB) was attached to an electrode surface by hybridization between hairpin probe and MB labeled primer. Such conformational changes resulted in the oxidation peak current of Fc decreased and that of MB increased, and the changes of dual signals are linear with the concentration of DNA. Furthermore, with the help of strand-displacement polymerization, polymerase catalyzed the extension of the primer and the sequential displacement of the target DNA, which led to the release of target and another polymerization cycle. Thus the circular strand displacement produced the multiplication of the MB confined near the GE surface and Fc got away from the GE surface. Therefore, the recognition of target DNA resulted in both the “signal-off” of Fc and the “signal-on” of MB for dual-signal electrochemical ratiometric readout. The dual signal strategy offered a dramatic enhancement of the stripping response. The dynamic range of the target DNA detection was from 10⁻¹³ to 10⁻⁸ mol L⁻¹ with a detection limit down to 28 fM level. Compared with the single signaling electrochemical sensor, the dual-signaling electrochemical sensing strategy developed in this paper was more selective. It would have important applications in the sensitive and selective electrochemical determination of other small molecules and proteins.     

New redox anion receptors based on calix[4]pyrrole bearing ferrocene amide

Two redox anion receptors based on calix[4]pyrrole and ferrocene have been synthesized. The electrochemical investigation revealed that these compounds can be response to the anions with different shifts of Fc/Fc⁺ couple. With the ¹H NMR titration study, the selectivity to F⁻ and AcO⁻ ions in CD₃CN solution was confirmed. The conformations of the mono-aromatic meso-substituted calix[4]pyrroles, which were the synthetical intermediate of the ferrocene based receptors, and their anion complexes in the solid state have also been studied by single X-ray crystallography, and the rationality of the crystal conformations was proved by theoretical study.     

Electrogeneration and characterization of a poly(pyrrole–nickel (II) chlorin) electrode

We describe herein, the electrochemical properties of an hydroporphyrin of Ni(II) substituted by two pyrrole groups in organic media (THF and CH₂Cl₂). In the anodic region it has been shown that the electrochemical behaviour of this complex investigated by cyclic voltammetry and coulometry coupled with UV–visible spectroscopy is strongly dependent on the nature of the solvent.Furthermore, the electrochemical oxidation of the pyrrrole groups has led to the first example of an electrogenerated polypyrrole–metallochlorin film. The resulting modified electrodes exhibit the same electrochemical properties as the monomer free in solution. Preliminary experiments have also demonstrated the possibility to study electrochemically this polymeric film in CH₃CN contrary to the Ni(II) chlorin, which is insoluble in this medium.     

Glucose oxidase as a blocking agent-based signal amplification strategy for the fabrication of label-free amperometric immunosensors

An effective electrochemical signal amplification strategy based on enzyme membrane modification and redox probe immobilization was proposed to construct an amperometric immunosensor.L-cysteine@ferrocene functionalized chitosan,which possessed not only efficient redox-activity but also excellent film-forming ability,was coated on the bare glass carbon electrode. Moreover,the thiol groups(SH)in the ferrocenyl compound were used for gold nanoparticles immobilization via the strong bonding interaction,which co...     

The potentiometric performances of cyclotetrahydroxysiloxane containing ferrocenyl moiety as an anion-selective membrane electrode

A test electrode based on cyclotetrasiloxane containing ferrocenyl, hydroxide and amine moiety exhibits very good potentiometric performance toward anions. Especially, acetate ion shows non-Hofmeister behavior on selectivity. The addition of the tetraalkylammonium salt provides lipophilic cationic sites within the membrane and enhances the response to more lipophilic anions. As expected, potentiometric performances of slopes and detection limits for the most of lipophilic anions, such as ClO₄⁻ and SCN⁻, are the most enhanced. However, the response to acetate ion was significantly decreased. In our knowledge, this is the first report that cyclic siloxane containing functional groups such as ferrocenyl moiety and hydroxyl group shows possible usage as a neutral carrier for an anion sensor.     

Synthesis and Electrochemical Characterization of a New Electropolymerizable Hydrophilic Viologen Designed for Enzyme Wiring

A new viologen derivative functionalized by an electropolymerizable pyrrole group via a long hydrophilic spacer has been synthesized. This redox monomer has been electrochemically characterized both for its presence in organic and in aqueous media. Its electrooxidation in both solvents leads to the formation of a polymeric film exhibiting the regular electrochemical behaviour of the viologen groups. The electropolymerization process was applied to the immobilization of isocitrate dehydrogenase as an enzyme model. An electrical connection between the redox polymer and the immobilized enzyme molecules has been observed in the presence of oxoglutarate and CO₂.     

Investigation of SPR and electrochemical detection of antigen with polypyrrole functionalized by biotinylated single-chain antibody: A review

An electrochemical label-free immunosensor based on a biotinylated single-chain variable fragment (Sc-Fv) antibody immobilized on copolypyrrole film is described. An efficient immunosensor device formed by immobilization of a biotinylated single-chain antibody on an electropolymerized copolymer film of polypyrrole using biotin/streptavidin system has been demonstrated for the first time. The response of the biosensor toward antigen detection was monitored by surface plasmon resonance (SPR) and electrochemical analysis of the polypyrrole response by differential pulse voltammetry (DPV). The composition of the copolymer formed from a mixture of pyrrole (py) as spacer and a pyrrole bearing a N-hydroxyphthalimidyl ester group on its 3-position (pyNHP), acting as agent linker for biomolecule immobilization, was optimized for an efficient immunosensor device. The ratio of py:pyNHP for copolymer formation was studied with respect to the antibody immobilization and antigen detection. SPR was employed to monitor in real time the electropolymerization process as well as the step-by-step construction of the biosensor. FT-IR demonstrates the chemical copolymer composition and the efficiency of the covalent attachment of biomolecules. The film morphology was analyzed by electron scanning microscopy (SEM).Results show that a well organized layer is obtained after Sc-Fv antibody immobilization thanks to the copolymer composition defined with optimized pyrrole and functionalized pyrrole leading to high and intense redox signal of the polypyrrole layer obtained by the DPV method. Detection of specific antigen was demonstrated by both SPR and DPV, and a low concentration of 1 pg mL⁻¹ was detected by measuring the variation of the redox signal of polypyrrole.     

Amidinium salts: Towards enabling electrochemistry in non-polar media from alkanes to ionic liquids

There is little known about electrochemical behavior in non-polar media due to lack of compatible, hydrophobic salts. In this work, this difficult challenge has been overcome by following a strategy based on designing and synthesizing a novel family of organic salts with highly-delocalized cations and anions. The salts are based on the amidinium cation with highly-delocalized positive charge and long alkyl groups that enable good miscibility in heptane, an archetypical, non-polar media, while being hydrophobic, room-temperature ionic liquids. The electrolyte solutions show ionic conductivities that span the range 10^− 11–10^− 4 S cm^− 1 and electrochemical activity which enable their application as antistatic agents and also as new type of hydrophobic electrolytes in various electrochemical devices.     

Electrochemical modification of polypyrrole films for imparting hemocompatible properties to hemosorbent

A method of production of hemosorbent based on thermally expanded graphite is developed. The method involves the electropolymerization of pyrrole on rolled thermally expanded graphite and subsequent cyclic electrochemical doping of polypyrrole film with Cl^? anions. The method enables one to produce a hemosorbent with an open-circuit potential, which is necessary for its biocompatibility.     

Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion

In the past decades, numerous electrochemical sensors based on exogenous electroactive substance have been reported. Due to non-specific interaction between the redox mediator and the target, the instability caused by false signal may not be avoided. To address this issue, in this paper, a new electrochemical sensor based on spiropyran skeleton, namely SPOSi, was designed for specific electrochemical response to fluoride ions (F⁻). The breakage of Si–O induced by F⁻ based on the specific nucleophilic substitution reaction between F⁻ and silica would directly produce a hydroquinone structure for electrochemical signal generation. To improve the sensitivity, SPOSi probe was assembled on the single-walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE) through the π–π conjugating interaction. This electrode was successfully applied to monitor F⁻ with a detection limit of 8.3 × 10⁻⁸ M. Compared with the conventional F⁻ ion selected electrode (ISE) which utilized noncovalent interaction, this method displays higher stability and a comparable sensitivity in the urine samples.