Bifunctional System Research Articles

A Bifunctional Metal Probe with Independent Signal Outputs and Regulable Detection Limits

AbstractA bifunctional metal detection system with independent signal outputs and regulable detection limits was developed by using a photochromic diarylethene with an imidazole unit as the ligand. The sensor can be used for the detection of Cu2+ by fluorescence recognition and for the detection of Na+ or K+ by colorimetric recognition. Moreover, the amount of component of the probe can be modulated and manipulated by photomodulation, which results in changes in the upper detectable limits; this enlarges the window of detectable limits for metal ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Enamine–Metal Lewis Acid Bifunctional Catalysis: Application to Direct Asymmetric Aldol Reaction of Ketones

AbstractUnprecedented bifunctional enamine–metal Lewis acid catalysts have been developed. In this bifunctional catalytic system, a tridentate ligand tethered with a chiral secondary amine was designed to solve the acid–base self‐quenching problem leading to catalyst inactivation. This new bifunctional enamine–metal Lewis acid catalyst was found to catalyze aldol reactions of ketones efficiently in high yields and good to excellent diastereoselectivities and enantioselectivities.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Construction of bifunctional phage display for biological analysis and immunoassay

A phage display-based bifunctional display system was developed for simple and sensitive immunoassay. The resulting bifunctional phage could simultaneously display a few single-chain variable fragment (ScFv) and many copies of the gold-binding peptide on its surface, thereby mediating antigen recognition and signal amplification. As a demonstration study, it was possible for bifunctional phage-based immunoassay to identify Bacillus anthracis spores from other Bacillus strains with detection sensitivity 10-fold higher than that of conventional phage enzyme-linked immunosorbent assay (ELISA). This protocol may be applied to build other bifunctional phage clones for broad applications (e.g., immunoassay kits, affinity biosensors, biorecognition assays).

Development of NiMH-based Fuel Cell/Battery (FCB) system: Characterization of Ni(OH)2/MnO2 positive electrode for FCB

Abstract The performance of the positive electrode composed of a mixture of nickel hydroxide (Ni(OH) 2 ) and a small amount of manganese dioxide (MnO 2 ) was investigated for the positive electrode of Fuel Cell/Battery (FCB) system. It was found that the positive electrode can function not only as an active material of secondary batteries when it is charged but also as a catalyst of fuel cells when oxygen is supplied, which was confirmed by the following characterization: electrochemical characterization was performed with cyclic voltammetry (CV) and galvanostatic discharge curve in oxygen and oxygen-free atmosphere. CV of Ni(OH) 2 /MnO 2 positive electrode exhibited the redox reaction of Ni(OH) 2 as well as oxygen reduction reaction. It was observed that the discharge curves of positive electrode had two working potentials in half cell test when the electrode was charged and oxygen was supplied: one from the reactions of nickel oxyhydroxide (NiOOH); the other from the fuel cell reactions of manganese dioxide (MnO 2 ). It was also observed that the discharge curves had two working voltages in full cell test when the cell was fully charged and oxygen was supplied: one at 1.2 V from the battery reactions of NiOOH; the other at 0.8 V from the fuel cell reactions of MnO 2 . In particular, the discharge capacity of overcharged cell was improved approximately 2 times compared with a battery of the same electrode quantity due to the additional function of this system as a fuel cell by using oxygen generated by water electrolysis. XRD analysis showed that there was no crystal structure change before and after (over)charge–discharge cycles. In summary, these experimental results showed that the novel bi-functional FCB system could provide an improved overall energy density per weight compared with conventional secondary batteries.

Highly Enantioselective Synthesis of α-Diazo-β-hydroxy Esters Using a Bifunctional Titanium Complex

A bifunctional titanium catalyst system has been developed for the asymmetric direct-type aldol reaction of ethyl diazo­acetate with aldehydes, which produced the desired products in good yields (up to 83%) with excellent enantioselectivities (up to 94% ee). A wide range of aromatic, heteroaromatic and aliphatic aldehydes were found to be suitable substrates in the presence of (S)-BINOL (5 mol%), cinchonine (5 mol%), Ti(Oi-Pr)4 (5 mol%) and H2O (15 mol%). On the basis of the experimental results and previous reports, a possible working model has been proposed to explain the origin of the activation and asymmetric induction.

Migration of Potassium in an Fe2O3/H‐ZSM‐5 Composite Catalyst

AbstractThe migration of potassium in an iron/H‐ZSM‐5 bifunctional system was investigated by pressing K/Fe2O3 and H‐ZSM‐5 in a pellet using 2 t of pressure. These pellets were heated at 350 °C in air for a number of days. Migration of potassium was visualized using energy‐dispersive X‐ray profiling. The distribution of potassium in the Fe2O3 phase and the H‐ZSM‐5 phase was approximately constant, with a step change over the phase boundary. The step change varied as a function of the heating time. The amount of potassium migrated from the Fe2O3 phase to the H‐ZSM‐5 phase was quantified using NH3‐TPD. It is shown that an equilibrium distribution between potassium in the Fe2O3 phase and the H‐ZSM‐5 phase is obtained after ca. 7 days of heating.

Development of Bifunctional Carbon Nanotube-Supported Co-Porphyrin Electrocatalytic System for Oxygen Reduction

Combination of multiwalled carbon nanotubes, cobalt porphyrin and tungsten oxide produces a multifunctional electrocatalytic system capable of the effective reduction of oxygen in acid medium. The resulting inks have been utilized during sequential deposition of components. Co-existence of Co-porphyrin, tungsten oxide together with dispersed carbon nanotubes leads to synergistic effect that is evident from positive shift of the oxygen reduction potentials, significant increase of voltammetric currents (relative to those observed at a system not containing carbon nanotube-supported tungsten oxide) and decrease of hydrogen peroxide produced during oxygen reduction. It is reasonable to expect that the reduction of oxygen is initiated at metalloporphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at partially reduced tungsten oxide. In addition to the methanol tolerance other important issue is the tolerance of the proposed system to ethanol that may appear due to crossover in the cathode compartments of ethanol fuel cells.

An Efficient Enantioselective Method for Asymmetric Friedel–Crafts Alkylation of Indoles with α,β‐Unsaturated Aldehydes

Abstractmagnified imageThe Lewis base‐Lewis base bifunctional catalytic system has been developed and successfully applied to the asymmetric Friedel–Crafts alkylation of indoles with α,β‐unsaturated aldehydes. The reactions are promoted by chiral diphenylprolinol trimethylsilyl ether in the presence of triethylamine. By this protocol, optically active 3‐substituted indoles can be obtained in an organocatalytic process that is free of Lewis or protic acid in high yields with up to 98% ee. Besides, this reaction could be carried out on a gram scale without any loss in the enantioselectivity.

Photo-hydrogen-evolving activity of chloro(terpyridine)platinum(ii): a single-component molecular photocatalyst

[PtCl(terpy)]Cl x 2 H(2)O (terpy = 2,2':6',2''-terpyridine) (1Cl x 2 H(2)O) is the first example serving as a bifunctional system promoting both photosensitization and hydrogenic activation as an H(2)-evolving catalyst in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light illumination. The rate of H(2) formation has turned out to be quadratic to the concentration of 1, suggesting that a bimolecular path determines the overall reaction rate for the photoinduced H(2) formation. It is suggested that the bimolecular mechanism operates at the photosensitization process through the formation of the so-called (3)MMLCT excited state and thus formed dinuclear photosensitizer itself provides a site for the hydrogenic activation (MMLCT = metal-metal-to-ligand charge transfer). The stability of the complex during the photolysis was successfully confirmed by ESI-TOF mass spectrometry. The photolysis was carried out in both the absence and the presence of mercury to rule out the formation of colloidal platinum. The rate of H(2) evolution considerably decreases when the photolysis was carried out by using acetate, propionate, or phosphate as a buffer reagent instead of MES (MES = 2-morpholinoethanesulfonic acid), which was used in typical experiments. The major chemical species in MES, acetate, propionate, and phosphate buffer solutions were respectively ascertained to be [PtCl(terpy)](+), [Pt(acetato)(terpy)](+), [Pt(propionato)(terpy)](+) and [Pt(H(2)PO(4))(terpy)](+) by ESI-TOF mass spectrometry. It is concluded that the original chloro species (i.e., [PtCl(terpy)](+)) plays a crucial role in the photochemical H(2) formation. The saturation kinetics for the H(2) formation with regard to the EDTA concentration was observed, revealing that the dimer of 1 (i.e., (1)(2)(2+)) and the dianionic form of EDTA form an ion-pair adduct to facilitate the electron injection from EDTA during the photochemical processes.

Hollow Manganese Oxide Nanoparticles as Multifunctional Agents for Magnetic Resonance Imaging and Drug Delivery

MRI jack-o'-lanterns? Hollow manganese oxide nanoparticles (HMON) show greatly improved relaxivities and drug-loading capacities compared to those with solid interiors (WMON). Their efficient cellular uptake demonstrates their potential as a bifunctional medical system that combines diagnostic imaging and targeted therapy.

Bifunctional Nanocomposites with Long-Term Stability as SERS Optical Accumulators for Ultrasensitive Analysis

In this work, we have devised and fabricated a magnetic + optical, bifunctional colloidal system that combines flexible handling and efficient SERS analytical capabilities. This system comprises silica-coated magnetic γ-Fe2O3 (maghemite) cores, coated with a dense monolayer of gold nanorods presenting long-term optical stability and a high density of hot spots per area unit. The magnetic functionality allows for the use of a small number of capsules that can be later concentrated under a magnetic field for SERS analysis thereby increasing the detection limits.

Asymmetric Henry reaction catalyzed by bifunctional copper‐based catalysts

A new bifunctional copper-based catalytic system has been developed from readily available salen ligand 7 together with Cu(OAc)(2).H(2)O in situ for asymmetric nitro-aldol reactions between nitromethane and aldehydes, affording corresponding adducts with moderate to good yields and enantioselectivities.

Edge‐to‐Face CH/π Aromatic Interaction and Molecular Self‐Recognition in epi‐Cinchona‐Based Bifunctional Thiourea Organocatalysis

The impact of cooperativity between intermolecular interactions is demonstrated by the molecular self-recognition properties of highly enantioselective epi-cinchona bifunctional thiourea organocatalysts. Low-temperature NMR experiments in inert solvents have revealed two sets of nonequivalent resonances in equal population for thiourea-modified members of the epi-quinine and epi-quinidine families. In solution, the predominance of an asymmetric (C1) dimeric self-assembly with noteworthy structural motifs became evident: simultaneous intra- and intermolecular thiourea hydrogen bonding and a CH/pi interaction were observed. Both the stereochemical and the diverse conformational features of the system favor the observed quinoline T-shaped aromatic pi-pi stacking interaction. The structure findings are supported by quantitative proton-proton distance data that were available from NOE buildup curves. The 3D structure of the dimeric assembly has been modeled in agreement with the H-H distance restraints. Owing to the geometrical preference associated with the dimerization process, the self-assembled bifunctional system is interpreted as a charge-transfer complex with the potential for catalyst self-activation.

Changes in leucocyte populations following murine bifunctional antibody infusion in colon cancer patients

This study was undertaken to determine whether infusion of a unique ZCE/CHA bifunctional antibody (BFA, 5-40 mg) could alter the composition and functions of peripheral blood leucocytes in 18 patients with colon cancer. The BFA is made by combining chemically the Fab' fragments of two murine monoclonal antibodies. One fragment (ZCE 025) binds to the carcino-embryonic antigen (CEA) and the other (CHA 225) to an epitope, present on an 111In-benzyl EDTA analog of bleomycin (BLEDTA IV) and on 111In-hydroxy-ethyl-thiourea benzyl EDTA (EOTUBE). The radiolabelled epitope (111In-BLEDTA IV or 111In-EOTUBE) was given 4 days after prelocalization with BFA. Peripheral blood samples were tested before BFA infusion, at the end of infusion (1 h later), and at 4 and 7 days post-infusion. A 50% or greater suppression in lymphocyte responsiveness to phytohaemagglutinin (PHA) and concanavalin A (Con A) was seen in 13 out of 18 and 12 out of 18 subjects, respectively, at some time after BFA infusion; this was especially evident in those patients with pre-infusion stimulation indices of greater than 50 (PHA) and/or greater than 10 (Con A). In contrast, natural killer (NK) cell cytotoxicity and oxygen radical production increased in five out of 15 and in seven out of 18 subjects, respectively. Little or no change was observed in CD3, CD4, CD8, CD16, and CD19 markers on lymphocyte subpopulations as determined by flow cytometry. These data suggest that significant changes in mitogen-induced lymphoproliferation. NK cell cytotoxicity, and oxygen radical production can occur in a substantial proportion of cancer patients after infusion of the ZCE/CHA bifunctional antibody system. The immunomodulation was unrelated to initial BFA dose, dose of BFA as a carrier, or to subsequent infusion of either form of the 111In epitope. The clinical significance of these phenomena, if any, remains to be determined.

A New Strategy for Designing Non‐C2‐Symmetric Monometallic Bifunctional Catalysts and Their Application in Enantioselective Cyanation of Aldehydes

A monometallic bifunctional catalyst, in which only one imidazolyl moiety is directly attached at the 3-position of a binaphthol moiety, has been developed. The ligand (R)-1, which lacks C2-symmetry and flexible linkers, in combination with Ti(OiPr)4, has been demonstrated to promote the enantioselective cyanation of aldehydes with trimethylsilylcyanide (TMSCN), giving excellent enantioselectivities of up to 98 % ee and high yields of up to 99 %. The use of this bifunctional catalytic system obviates the need for additives and is extremely simple as the reagents are added in one portion at the beginning of the reaction. The protocol has been found to tolerate a relatively wide range of aldehydes when 10 mol % of the (R)-1/Ti(OiPr)4 complex is deployed in CH2Cl2 at -40 degrees C, the conditions which proved most practical and effective. The asymmetric cyanations also proceeded with lower catalyst loadings (5 mol %, or even 2 mol %), still giving satisfactory enantiomeric excesses and yields. Interestingly, the use of freshly distilled TMSCN dried over CaH2 gave a low enantioselectivity and only a moderate yield of the adduct as compared with direct use of the commercial reagent. The results of 13C NMR spectroscopic studies implicate HCN as the actual reactive nucleophile.

Highly Enantioselective Allylation of Aromatic α‐Keto Phosphonates Catalyzed by Chiral N,N′‐Dioxide‐Indium(III) Complexes

AbstractThe ramipril derivative N,N′‐dioxide 3g‐indium(III) complex was found to be an efficient catalyst for the allylation of the aromatic α‐keto phosphonates. The corresponding α‐hydroxy phosphonates were obtained with high yields (up to 98 %) and high enantioselectivities (up to 91 % ee). A bifunctional catalyst system was described with an N‐oxide as Lewis base activating tetraallyltin and indium as Lewis acid activating aromatic α‐keto phosphonates. A possible catalytic cycle has been proposed to explain the mechanism of the reaction.

Disproportionation of Alkanes via Molecular Redistribution and Molecular Averaging

In this paper the disproportionation of alkanes via molecular redistribution (MR) and molecular averaging (MA) is discussed. MR/MA chemistry consists of three steps occurring in one single catalyst bed over a bifunctional catalyst system: dehydrogenation of alkanes to olefinic intermediates, metathesis (disproportionation) of these olefin species and hydrogenation of the metathesis products to alkanes. MR/MA represents a unique and rare example of bifunctional heterogeneous catalysis while there are many examples of acid components being one of the bifunctional elements with a metal, e.g., in reforming, hydrocracking and isomerization reactions. MR/MA chemistry provides simple processes which can be accomplished otherwise only via combinations of other existing chemistries. In this paper, we will use MR of pentanes as an example to demonstrate one industrial application of the MR chemistry.

Highly enantioselective cyanosilylation of ketones catalyzed by a bifunctional Ti(IV) complex

A bifunctional catalyst system composed of (S)-prolinamide (2a), titanium(IV) isopropoxide, and phenolic N-oxide (3f) exhibited high catalytic efficiency in the enantioselective cyanosilylation of ketones. In the presence of 2.5mol% catalyst, a variety of aromatic and aliphatic ketones were converted into the corresponding tertiary cyanohydrin O-TMS ethers in excellent yields (up to 96%) and high enantioselectivities (up to 96% ee). A proposed catalytic cycle was illustrated to explain the origin of the asymmetric induction.

Statistical analysis of the performance of a bi-functional catalyst under operating conditions of LPDME process

Abstract Liquid phase direct synthesis of dimethyl ether (LPDME™) under various operating conditions (temperature, H2/CO molar ratio of feed) was conducted in a mechanically agitated slurry reactor system. Each run was monitored for 60 h time on stream (TOS) in order to confirm the high activity and long-term stability of a bi-functional catalytic system (CuO–ZnO–Al2O3/H-MFI-90). Statistical experimental design was applied for determining the optimum operating conditions under which the catalytic system shows the highest performance. A significant improvement in the performance of the bi-functional catalyst was observed when the temperature and H2/CO molar ratio of feed were increased from 200 to 240 °C and 1 to 2, respectively at a constant pressure of 35 bar and GHSV equal to 1100 mLn/(g-cat h). CO conversion was increased from 9.1 mol% at T = 200 °C and H2/CO = 1 to 79.6 mol% at T = 240 °C and H2/CO = 2 and the yield and selectivity of DME also increased from 7.11% to 47.05% and 41.57% to 59.96%, (molar basis) respectively. No significant deactivation has been observed during 60 h TOS at different operating conditions. Furthermore, from the main effect plots and response table results, it was concluded that the most effective factor on activity and stability of bi-functional catalytic system is temperature.

Palladium catalysts immobilized in thin films of ionic liquid for the direct addition of aniline to styrene

Immobilization of organometallic complexes in thin supported films of ionic liquid has been used to generate a new class of hydroamination catalysts. High activities for the addition of aniline to styrene were obtained with a bi-functional system comprising [Pd(DPPF)](CF 3CO 2) 2 and CF 3SO 3H immobilized in silica supported imidazolium salts. In this environment, the metal complexes are concluded to be enclosed in solvent cages of ion pairs of the ionic liquid. With increasing temperature, the imidazolium cations gain mobility until the solvent cages break down at a specific temperature, which is noticeable as phase transition. At temperatures below the phase transition, the catalytic activity was strongly influenced by the choice of the ionic liquid. At temperatures above the phase transition, the activity for formation of the Markownikoff product was, in contrast, nearly identical with all ionic liquids tested. Under these conditions, also the formation of the anti-Markownikoff product was observed.