Bicatalytic System Research Articles

Kinetic analysis and evaluation of galactose oxidase activation by hematin in the green oxidation of glycerol

Galactose oxidase (GAO) is the best-characterized member of a family of enzymes known as radical-copper oxidases, which use O2 as the final electron acceptor. GAO required an external oxidant to be fully activated and also an external scavenger of H2O2, the inhibiting product of the catalytic cycle. On the other hand, hematin (HEM) is a mimetic structure of heme peroxidases that also displays catalase-like activity. In this work, GAO was used in tandem with HEM towards glycerol (GLY) oxidation. Spectrometric and dissolved oxygen data are presented as evidence that the bi-catalytic system was active and stable. The optimized activity was 0.409 µmol h−1 UGAO−1, 5.2 times higher than with catalase. Optimum conditions were found at GAO 9.0 U/mL, GLY 1700 mM, HEM 108 µg/mL and a pH of 9.0. Kinetic modeling was used to propose a catalytic mechanism. The enzymatic constants KM and kb were obtained for GLY and galactose, the natural substrate of GAO. Moreover, the activation constant by HEM and the inhibition constant by H2O2 were estimated for GAO. Extrapolation of the model suggested a positive involvement of superoxide radicals in the activity of GAO, instead of triggering hematin inactivation.

Electrophotocatalytic C−H Azolation of Arenes

AbstractAn electrophotocatalytic method has been developed for the dehydrogenative cross coupling of arenes with azoles employing a bicatalytic system consisting of acridinium dye and (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO). The reactions are conducted in a simple undivided cell with visible‐light irradiation and requires no external chemical oxidant.

Unveiling complete lactate oxidation through a hybrid catalytic cascade

Although challenging, the generation of energy through the harvesting of electrons from biological fluids via fuel cells is a promising technology for wearable electronics. However, a current challenge is that neither a single molecular catalyst or an enzyme can completely oxidize fuels in biological fluids. With this issue in mind, herein, we report a hybrid bi-catalytic system allowing complete lactate oxidation by combining an organic catalyst, 4-amino-TEMPO (Amino-TEMPO), with a recombinant enzyme, oxalate decarboxylase (OxDc). This hybrid system was chosen due to the high oxidative catalytic activity of the molecular catalyst and the promiscuity of the recombinant enzyme to alternative substrates. The hybrid architecture enhanced the performance of the bioanode, enabling higher efficiency and improved stability of the energy-harvesting fuel cell. The hybrid system showed high catalytic activity, achieving a high and stable current density of 23.0 ± 1.5 mA cm−2 for lactate oxidation after 48 h of bulk electrolysis. Intermediate and product analysis by nuclear magnetic resonance (NMR) and gas chromatography (GC) coupled to a thermal conductivity detector (TCD) confirmed that the hybrid architecture acts in the multiples catabolic steps of lactate oxidation, enabling the complete oxidation of lactate to CO2 by collecting 12 electrons from the fuel molecule.

Developing Bicatalytic Cascade Reactions: Ruthenium-catalyzed Hydrogen Generation From Methanol.

A novel state-of-the-art bicatalytic system for hydrogen generation from aqueous methanol at low temperature and base concentration is described. Applying two molecularly defined ruthenium complexes A and B3 for methanol dehydrogenation at the same time under the same conditions, a synergistic effect is observed. This behavior is explained by the increase of the dehydrogenation of formic acid, which is formed as an intermediate, by the second catalyst B3.

Effect of Chemical Composition Variant and Oxygen Plasma Treatments on the Wettability of PLGA Thin Films, Synthesized by Direct Copolycondensation.

The synthesis of high molecular weight poly (lactic-co-glycolic) acid (PLGA) copolymers via direct condensation copolymerization is itself a challenging task. Moreover, some of the characteristic properties of polylactide (PLA)-based biomaterials, such as brittleness, hydrophobicity, and longer degradation time, are not suitable for certain biomedical applications. However, such properties can be altered by the copolymerization of PLA with other biodegradable monomers, such as glycolic acid. A series of high molecular weight PLGAs were synthesized through the direct condensation copolymerization of lactic and glycolic acids, starting from 0 to 50 mol% of glycolic acid, and the wettability of its films was monitored as a function of the feed molar ratio. Copolymerization was performed in the presence of a bi-catalytic system using stannous chloride dihydrate and methanesulfonic acid (MSA). The viscosity average molecular weight of the resulting PLGA was in the range of 80k to 135k g/mol. The PLGA films were prepared using the solvent casting technique, and were treated with oxygen plasma for 2 min. The water contact angle of the PLGA films was determined before and after the oxygen plasma treatments, and it was observed that the wettability increased with an increase in the glycolic acid contents, however, the manifolds increased after 2 min of oxygen plasma treatments.

Hollow nanoshell-sphere Fe@Fe/Pd reactors: a magnetically recoverable catalyst for the Csp–S cross-coupling reactions in water

The hollow Pd–PVP–Fe nanosphere and Fe–PVP nanoparticle catalysts were synthesized by thermal method. Mixing of two metallic nanocatalysts was applied in the Csp–S cross-coupling reactions between diphenyl disulfide and phenylacetylene under mild conditions in water. Results show that bi-catalytic system has higher catalytic efficiencies than their monocatalytic systems due to synergy between two catalysts. Order of adding two metallic catalysts were adjusted into the coupling reaction medium. Therefore, various bi-catalytic systems were obtained and characterized by XRD, SEM, EBSD, EDX, UV–Vis spectra, and particle size analyzer. Under special order of adding, the obtained hollow nanoshell-sphere Fe@Fe/Pd reactor showed higher catalytic activity in the coupling reaction compared to other bi-catalytic systems. The Csp–S coupling products obtained of various diaryl disulfides and phenylacetylene at presence Fe@Fe/Pd (only 7.3 × 10−5 mmol Pd) catalyst with moderate to high yields in water solvent and mild reaction conditions. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The recovered catalyst was characterized by XRD, SEM, EBSD, EDX, and UV–Vis spectra. The Fe@Fe/Pd was reused at least six repeating cycles without any loss of its high catalytic activity. Tuning morphology and chemical composition of bi-catalytic system are key mainstays of high activity of Fe@Fe/Pd in repeating cycles of cross-coupling reactions.

Cu/Pd‐Catalyzed C‐2–H Arylation of ­Quinazolin‐4(3H)‐ones with (Hetero)aryl Halides

AbstractThe regiospecific C‐2–H arylation of N‐3‐substituted quinazolin‐4(3H)‐ones with a wide range of aryl or (hetero)aryl halides under microwave irradiation was studied. A ligand‐dependent palladium/copper bicatalytic system was developed and allowed direct cross‐coupling with a variety of (hetero)aryl halides. This useful and scalable procedure promotes the construction of C(sp2)–C(sp2) bonds from arenes or (hetero)arenes and aryl or (hetero)aryl bromides and chlorides in a time‐efficient strategy. The extension of the reaction to various N‐3‐substituted quinazolin‐4(3H)‐ones with iodobenzene as well as the scope and limitations of the method were also investigated.

ChemInform Abstract: Sequential Friedel—Crafts‐Type α‐Amidoalkylation/Intramolecular Hydroarylation: Distinct Advantage of Combined Tf2NH/Cationic LAu(I) as a Consecutive or Binary Bicatalytic System.

AbstractThe process gives polycyclic heterocycles generally as separable mixtures of 6‐exo‐dig and 7‐endo‐dig cyclization products.

Sequential Friedel-Crafts-Type α-Amidoalkylation/Intramolecular Hydroarylation: Distinct Advantage of Combined Tf2NH/Cationic LAu(I) as a Consecutive or Binary Bicatalytic System.

The combined use of Tf2NH and L(Au)(+)X(-) as a dual or binary catalytic system clearly improves the efficiency and enlarges the scope of the tandem intermolecular Friedel-Crafts α-amidoalkylation/intramolecular hydroarylation sequence, compared to an "all gold" multicatalysis approach.

ChemInform Abstract: An Iron/Amine‐Catalyzed Cascade Process for the Enantioselective Functionalization of Allylic Alcohols.

AbstractA novel bicatalytic system consisting of an in situ generated Fe‐complex, obtained by CO‐decoordination with Me3NO, and L‐diphenylsilylprolinol allows the transformation of allylic alcohols into β‐chiral alcohols with high enantioselectivities (up to 90% e.e.).

Base-free hydrogen generation from methanol using a bi-catalytic system

A bi-catalytic system, in which Ru-MACHO-BH and Ru(H)2(dppe)2 interact in a synergistic manner, was developed for the base-free dehydrogenation of methanol. A total TON > 4200 was obtained with only trace amounts of CO contamination (<8 ppm) in the produced gas.

Formation of Secondary or Tertiary Aliphatic Amines in Aqueous Media

Secondary and tertiary amines can be easily obtained from primary and secondary amines, respectively, in completely aqueous media, in the presence of a bicatalytic system formed of cheap commercial aluminum (Al) powder and 5% rhodium (Rh) or ruthenium (Ru) deposed on charcoal.

Highly effective degradation of polychlorinated biphenyls in soil mediated by a Ca/Rh bicatalytic system

Treatment of PCBs in soil using metallic calcium and alcohol ultimately reduced 1300 × 10 −3 mg kg −1 PCB concentration to 1.8 × 10 −3 mg kg −1. Moreover, using the metallic calcium catalyst method to promote the effective use of hydrogen gas in the presence of a specific reducing catalyst such as Rh/C, the decomposition efficiency of PCBs was notably increased despite mild reaction conditions. The total PCB concentration of treated soils decreased from 1300 × 10 −3 mg kg −1 to 0.62 × 10 −3 mg kg −1 (decomp. avg. = 99.95%). Treatment of soils with metallic calcium and a Rh/C catalyst in alcohol under mild conditions such as 0.15–0.26 MPa at room temperature is extremely effective for degradation of existing PCBs.

Direct hydroxylation of aromatics with a mixture of H2 and O2 gases over Fe- and Pd-incorporated zeolites

The hydroxylation of benzene and phenol with in-situ-generated oxidant was performed under mild reaction conditions over the bicatalytic system which has dual abilities of direct H2O2 generation and the hydroxylation activity by combining Pd-zeolite with redox zeolites such as TS-1, Ti-MCM-41, V-MCM-41 and Fe-zeolite. The amount of H2O2 formed directly from H2 and O2 increases with increasing Pd loading over zeolite up to 0.6% and subsequently decreases slightly as the Pd loading increases. The optimum amount of H2O2 produced is 6.4 mmol. Over Pd/HBEA + Fe/Y, when H2 : O2 = 40 : 40 ml/min is supplied, phenol conversion increases from 4.6% at 2 h to 13.6% at 8 h with high catechol selectivity in the range of 65–79%. The hydroxylation activities over redox catalyst with H2O2 are compared. Hydroxylation activity is improved by encapsulating FePc onto Y zeolite. In terms of TON, FePc/Y exhibits 3.5 times higher capacity than Fe/Y.

Selective oxidation of cyclohexane by an iron-palladium bicatalytic system under mild conditions; iron oxide/silica catalysts

In situ oxidation of cyclohexane to cyclohexanol and cyclohexanone was investigated with hydrogen peroxide produced from hydrogen and oxygen at a temperature of 30 °C and under atmospheric pressure. Three kinds of iron oxide/silica catalysts were prepared from ferric chloride, ferric nitrate and ferric hydroxide and the catalysts were characterized by X-ray fluorescence, X-ray diffraction and X-ray photoelectron spectroscopy and their activities were examined. The effective species of catalyst was found to be Fe 2O 3 on silica. Changing the iron starting materials affects the dispersity of iron oxide on silica, thereby resulting in a difference of catalytic activity. The catalyst originating from ferric hydroxide shows the highest dispersity and activity per unit atom of iron. The formation of a fine crystallite of iron oxide is important to increase the activity of the catalyst as is shown by the fact that catalytic activity is increased by decreasing the iron content of the catalyst.