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A new chiral MeO-PEG-supported ferrocenyl oxazoline was synthesized and successfully employed in the enantioselective phenyl transfer to aldehydes. The products were obtained in high yields and with excellent enantioselectivities (up to 97% ee). Furthermore, the recovery of the ferrocene was facile, and catalyst efficiency was maintained in subsequent reactions.
A series of ferrocenyl chalcones were synthesized and evaluated for in vitro antimalarial activity against a chloroquine-resistant strain of Plasmodium falciparum. The most active compounds were 1-(3-pyridyl)-3-ferrocenyl-2-propen-1-one (6) and 1-ferrocenyl-3-(4-nitrophenyl)-2-propen-1-one (28) with IC(50) of 4.5 and 5.1 microM, respectively. Differences in activity were not readily explained by the size and lipophilicity characteristics of these compounds.
Herein, we disclose results of our research into a class of benzimidazolium compounds active against the Leishmania infantum parasite strain L1. We have discovered that N-ferrocenylmethyl, N'-methyl-2-aryl (or styryl) benzimidazolium iodide salts show in vitro activity against this strain.
Based on the standard 2D Polarization inversion experiment, a new pulse sequence (PI-TAPF) is proposed. It represents a combination of Polarization Inversion and TAPF (time averaged precession frequency) sequences. The depolarization period consists of phase-alternating intervals of different duration in the I channel. The pulse sequence yields transient oscillations under the strongly mismatched HH conditions where the required power for the dilute spins is reduced by a factor of 5. Experimental results recorded for a sample of ferrocene powder are well reproduced by numerical simulations.
The prevention of ferrocene leakage from an electrode by physical retention of mediator in a matrix of cellulose acetate membrane is reported. Five types of the cellulose acetate membranes were prepared, containing 1.8%, 5.3%, 8.5%, 20.0% of ferrocene and a membrane containing 1.8% of ferrocene and 0.05 % of Nafion in the matrix. Ferrocene embedded membranes were successfully applied in the construction of a fructose biosensor by immobilization of PQQ-dependent fructose dehydrogenase (FDH). The biosensor comprising a cellulose acetate membrane with 1.8% of ferrocene and 0.05% of Nafion had good stability characteristics, retained almost 40% of the initial response after 8 h of continuous use with an initial sensitivity of 226 nA mM(-1) and response time of 75 s.
Oxidation of ferrocene in acetonitrile resulted in films on Pt electrodes under voltammetric conditions. Films were more readily formed with tetrabutylammonium tetrafluoroborate as the electrolyte than with perchlorate salts. No films were detected when ferrocene was oxidized in aqueous 0.05 M cetyltrimethylammonium bromide (CTAB). Analysis of the films by FT-IR and Auger spectroscopy confirmed iron-containing oxidation products on Pt, presumably from chemical reactions of ferricinium ions. Oxidation of 50-100 mM ferrocene in acetonitrile on Pt yielded insoluble precipitates. Analyses by MS, FT-IR, and UV-visible (water extract), suggested a mixture of oligomeric material and a small fraction of ferricinium ions. Film formation had much less influence on voltammograms on 12.5-micron-radius Pt microdisks than on 0.5-mm-radius Pt. This is consistent with the smaller sensitivity of microelectrodes to chemical reactions following charge transfer. The smaller apparent heterogeneous rate constants (k zero') found for ferrocene on macroelectrodes than on microelectrodes could possibly be influenced by film formation on larger Pt electrodes. Correlations between macro- and microelectrode kinetic data suggest that macroelectrode k zero' values may be valid in a relative sense when ohmic drop is negligible. Bias in k zero's on conventional-sized electrodes should be small in solutions giving minimal film formation, such as micellar CTAB.
The reaction of amylose with NaH and FcCH2NMe3+I- in dimethyl sulfoxide brought about a redox-labeled polymer with a low degree of modification, viz. 1 ferrocene residue per 60 glucose units. The preparation, (0.017ferrocene)amylose, displays one-electron irreversible behavior at a pyrographite electrode in terms of the Delahay formalism, the formal redox potential E degree' being equal to 0.38 V at pH 6 and 40 degrees C versus SCE. Specific to amylose enzymes endo-depolymerases, which carry out random hydrolysis, accept the labeled amylose providing a significant increase in the peak current on cyclic voltammograms. The absence of potential drifts suggests that the effect is due an increase in the diffusion coefficients of the amylose fragments in the course of enzymatic digestion of (0.017ferrocene)amylose. This proposal was confirmed by the simulation of experimental cyclic voltammograms. Several practical applications of the results of this study for electrochemical assaying the amylolytic activity and evaluation of the mechanisms of the enzymatic catalysis by amylases have been demonstrated.
A new homogeneous electroenzymatic immunoassay was developed to determine antibody concentration using glucose oxidase and ferrocene as enzymatic and electrochemical amplifier, respectively. Digoxin (Dig)-conjugated glucose oxidase (GOx) was modified with ferrocene (Fec) to form Fec-GOx-Dig conjugate. After immunocomplex formation between the Fec-GOx-Dig conjugate and the anti-digoxin antibody, the complex underwent less electrochemical reaction due to the steric hindrance of the antibody. The ferrocene multilabeled conjugate was provided for the determination of anti-digoxin antibody. Since the strategy taken here is based on a combined effect of GOx and ferrocene, i.e., enzymatic amplification by GOx and electrochemical amplification by multilabeled ferrocenes, the antibody concentration was determined in the range from 1/50 to 1/500 dilution.
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A versatile spectroelectrochemical apparatus is introduced to study the changes in IR spectra of organic and inorganic compounds upon oxidation or reduction. The design is based on an attenuated total reflection device, which permits the study of a wide spectral range of 16,700 (600 nm)-250 cm(-1), with a small opaque region of 2250-1900 cm(-1). In addition, an IR data collection protocol is introduced to deal with electrochemically nonreversible background signals. This method is tested with ferrocene in acetonitrile; concentrations as low as 1 mM produce results that agree with those in the literature.
A novel detection strategy for DNA sequencing applications that utilizes a frequency-based electrochemical method is reported. Sinusoidal voltammetry is used to selectively identify four unique redox molecules that are covalently attached to the 5'-end of a 20-base sequencing primer. The tags used in this work are ferrocene derivatives with different substituents attached to the ferrocene ring, where the electron-donating or -withdrawing character of the substituent alters the half-wave potential of the modified ferrocene. Therefore, each tag has a unique SV frequency spectrum that can be easily identified in the frequency domain. In this work, the discrimination of one tag versus all others is accomplished through a "phase-nulling" technique. The signal for each tag is selectively eliminated while the other three responses remain virtually unchanged. This analysis scheme allows for the selective identification of each tagged oligonucleotide eluting in sieving polymer capillary gel electrophoresis with a separation efficiency of 2 x 10(6) theoretical plates per meter. This separation efficiency is sufficient to perform "low-resolution" DNA sequencing; the conditions used in this work have not yet been optimized for high-resolution sequencing applications.
We report an electrochemical sensor for an electrochemically inactive organic compound using a self-assembled monolayer (SAM) formed on the gold surface from a solution of thiolated alpha-cyclodextrin (alpha-CD). The SAM makes up an array of ultramicroelectrodes, which capture electroactive molecules such as those of ferrocene. When this SAM-modified electrode is exposed to a solution containing an electrochemically inactive compound, e.g., glucose, the captured ferrocene molecules are replaced by the electroinactive molecules via an equilibrium established between the two compounds, lowering the current for ferrocene oxidation. The decrease in current is directly proportional to the amount of glucose added and the glucose can be analyzed up to approximately 0.80 mM, which is approximately 1/10 of a typical physiological concentration in blood serum. Formation constants of the surface-bound alpha-CD molecules with ferrocene and glucose are also reported.
This paper describes an on-chip-type electrochemical flow immunoassay system with a multichanneled matrix column. The multichanneled matrix column was functionally coated with cation-exchange resin and used for separation of proteins. Antihistamine immunoglobulin G (IgG) antibody conjugated with ferrocenemonocarboxylic acid (Fc) was also prepared and used as a novel analytical reagent. Antibody-antigen complexes were separated from free Fc-conjugated IgG antibody (Fc-IgG) on the basis of differences in isoelectric point (pI) using the multichanneled matrix column coated with cation-exchange resin. The assay yields a good relationship between current and histamine concentration in the range of 200-2000 ng/mL. This simple technique enables the assay of histamine released in whole blood within 2 min. Furthermore, a good correlation was found between the response of the electrochemical immunoassay described in this paper and the conventional RIA (radioimmunoassay). This on-chip-type electrochemical flow immunoassay requires only minute quantities of whole blood samples and generates highly reproducible results.
A new stepwise self-assembly procedure is described for the preparation of functional cyclodextrin-modified electrodes. The approach is based on the formation of alkanethiol/lipoylamide-beta-cyclodextrin monolayers with the thiol component responsible for blocking of the electrode surface and lipoylamide-beta-cyclodextrin molecules-for controlled opening of the access of the electroactive probe to the electrode. Functionalization of the electrode is achieved by means of a new cyclodextrin derivative-mono(6-deoxy-6-lipoylamide)-per-2,3,6-O-acetyl-beta-cyclodextrin-prepared in the peracetyl form and deacetylated directly on the electrode surface following the cyclodextrin self-assembly. The progress of deacetylation was monitored by the MALDI MS technique. Deacetylation caused opening of the active sites toward solution probes. The response toward ferrocene was found to be highly improved when ferrocene was added to the solution following self-assembly of cyclodextrin but prior to the thiol self-assembly step (imprinting method). The proposed synthesis and sequential monolayer formation scheme lead to well-organized and stable modified electrode surfaces with improved sensitivity toward solution species compared to other procedures of electrode modification with the cyclodextrin derivatives.
We have developed a sandwich-type enzyme-linked DNA sensor as a new electrochemical method to detect DNA hybridization. A partially ferrocenyl-tethered poly(amidoamine) dendrimer (Fc-D) was used as an electrocatalyst to enhance the electronic signals of DNA detection as well as a building block to immobilize capture probes. Fc-D was immobilized on a carboxylic acid-terminated self-assembled monolayer (SAM) by covalent coupling of unreacted amine in Fc-D to the acid. Thiolated capture probe was attached to the remaining amine groups of Fc-D on the SAM via a bifunctional linker. The target DNA was hybridized with the capture probe, and an extension in the DNA of the target was then hybridized with a biotinylated detection probe. Avidin-conjugated alkaline phosphatase was bound to the detection probe and allowed to generate the electroactive label, p-aminophenol, from p-aminophenyl phosphate enzymatically. p-Aminophenol diffuses into the Fc-D layer and is then electrocatalytically oxidized by the electronic mediation of the immobilized Fc-D, which leads to a great enhancement in signal. Consequently, the amount of hybridized target can be estimated using the intensity of electrocatalytic current. This DNA sensor exhibits a detection limit of 20 fmol. Our method was also successfully applied to the sequence-selective discrimination between perfectly matched and single-base mismatched target oligonucleotides.