Size-selective catalytic activity of Pd nanoparticles encapsulated within end-group functionalized dendrimers

The synthesis and size-selective catalytic activity of Pd nanoparticles encapsulated within dendrimers functionalized with different-sized end groups is described. We designed and synthesized a series of fourth-generation poly(amidoamine) dendrimers having various extents of steric crowding on their periphery. This was accomplished by reacting the terminal amine groups of these dendrimers with epoxyalkanes substituted with different-sized alkyl groups. The modified dendrimers were characterized by 1H NMR, 13C NMR, and matrix-assisted laser desorption ionization mass spectrometry. Nearly monodisperse (1.7 +/- 0.2 nm) Pd nanoparticles were encapsulated within the interior of these dendrimers, and the resulting composite catalysts were used for the hydrogenation of three alpha-allylic alcohols having different sizes. The results showed a clear correlation between the extent of steric crowding on the dendrimer surface and the turnover frequencies (TOFs) for the substrates: more steric crowding on the dendrimer surface led to lower TOFs.     

高浓度盐系统中指肪酶的固定化及其催化活力

选择了四十多个可溶性的盐，实现了脂肪酶在高浓度盐系统中的固定化，并以 固定化脂肪酶的盐为催化剂，研究了正已烷中脂肪酶催化丁醇和乙酸乙烯酯间的转 酯化制备乙酸丁酯的反应和水溶液中橄榄油的水解反应，考察了高浓度盐系统中脂 肪酶的催化活力。     

Biomimetical catalytic activity of iron(III) porphyrins encapsulated in the zeolite X

The approach adopted for the obtention of zeolite-encapsulated FeP led to clean syntheses of biomimetical catalyst. The catalysts were obtained through the zeolite synthesis method, where NaX zeolite was synthesised around one of the cationic FePs: iron(III) 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (FeP1) or iron(III) 5-mono(2,6-dichloro-phenyl)10,15,20-tris(4-N-methylpyridyl)porphyrin (FeP2). The syntheses yielded pure FeP1NaX and FeP2NaX catalysts without any by-products blocking the zeolite nanopores. FeP1NaX and FeP2NaX efficiently catalysed the epoxidation of (Z)-cyclooctene by iodosylbenzene (PhIO) in DCE, giving rise to cis-epoxycyclooctane yields of 85% and 95%, respectively. Hydroxylation of adamantane shows a preferable alkane oxidation at the tertiary C---H bond, indicating a hydrogen abstraction through the Fe^IV(O)P^·+species in the initial step. The total adamantanol yields were 52% and 45% for FeP1NaX and FeP2NaX, respectively. Concerning selectivity, FeP1NaX and FeP2NaX gave an 1-adamantanol (Ad-1-ol)/2-adamantanol (Ad-2-ol) ratio of 20:1 and 11:1, respectively (after statistical correction). Therefore, these results indicate a free radical activation of the C---H bonds of adamantane as expected for P-450 models. In the cyclohexane oxidation catalysed by FeP1NaX in DCE, a cyclohexanol (C₆-ol) yield of 50% and an alcohol/ketone ratio of 10 was obtained. The hydroxylation occurs according to the so-called oxygen rebound mechanism, as expected for a P-450 model system. FeP2NaX is less selective (C₆-ol yield=25% and alcohol/ketone=1.2). One possible explanation is that a Russell-type mechanism involving O₂ imprisoned within the zeolite cages may be operating parallelly, generating both C₆-ol and cyclohexanone.     

Facile catalytic growth of cyanoacrylate nanofibers

High aspect ratio (>500), neat poly(ethyl 2-cyanoacrylate) nanofibers were synthesized catalytically by vapour phase polymerization under high relative humidity and ambient conditions.     

Improving the catalytic activity of Candida antarctica lipase B by circular permutation

Lipases (EC 3.1.1.3) play an important role in asymmetric biocatalysis. Tailoring these enzymes to novel, unnatural substrates is one of the primary challenges of protein engineering. We have used circular permutation, the intramolecular relocation of a protein's N- and C-termini, to explore the effects of altered active site accessibility and protein backbone flexibility on the catalytic performance of lipase B from Candida antarctica (CALB). Our combinatorial approach identified 63 unique functional protein permutants of CALB, and kinetic analysis of selected candidates indicated that a majority of enzyme variants either retained or surpassed wild-type CALB activity on a series of standard substrates. Beyond the potential benefits of these tailor-made lipases as new catalysts for unnatural substrates, our study validates circular permutation as a promising general method for lipase engineering.     

Enhanced catalytic activity of hemoglobin in organic solvents by layered titanate immobilization

A simple layered titanate immobilization can significantly enhance the Hb catalytic activity in organic media relative to native Hb, especially in hydrophilic dioxane systems, where the composites have an about 100 times enhancement. The interlayer water should be responsible for the increased nonaqueous catalytic activities of the immobilized Hb due to its strengthened resistance to the distorting of the Hb surface essential water layer by organic solvents.     

Enhanced catalytic activity of Ru through N modification toward alkaline hydrogen electrocatalysis

Exploring highly efficient electrocatalysts and understanding the reaction mechanisms for hydrogen electrocatalysis,including hydrogen oxidation reaction （HOR） and hydrogen evolution reaction （HER） in alkaline media are conducive to the conversion of hydrogen energy.Herein,we reported a new strategy to boost the HER/HOR performances of ruthenium （Ru） nanoparticles through nitrogen （N） modification.The obtained N-Ru/C exhibit remarkable catalytic performance,with normalized HOR exchange current d...     

Increase in catalytic activity of Pseudomonas fluorescens lipase upon its coprecipitation with hexadecane-1,2-diol suspension

A simple method for the noncovalent modification of Pseudomonas fluorescens lipase resulting in an increase in its catalytic activity in aqueous and nonaqueous media was suggested.     

Antioxidant activity of polyaniline nanofibers

Well-confined uniform polyaniline (PANI) nanofibers were synthesized by using photo-assisted chemical oxidative polymer- ization of aniline in the presence of different dopant acids,and the radical scavenging ability of the produced PANI nanofibers was determined by the DPPH assay.It was found that the antioxidant activity of PANI nanofibers was higher than conventional PANI, and increased with decreasing of averaged diameter of the nanofibers.The enhanced antioxidant activity was concerned with increased surface area of PANI nanofibers.     

Creation of a synthetically useful lipase with higher than wild-type enantioselectivity and maintained catalytic activity

[reaction: see text] We have found that two Geotrichum candidum lipase isozymes have remarkably different abilities to differentiate between enantiomers of ethyl 2-methyldecanoate. By rational recombination of selected portions of the two isozymes, we have created a novel lipase with an enantioselectivity superior to that of the best wild-type parent isozyme. Site-directed mutagenesis identified two key amino acid residues responsible for the improved enantioselectivity without compromised total activity of the reengineered enzyme.     

Silver(I)-imidazole cyclophane gem-diol complexes encapsulated by electrospun tecophilic nanofibers: formation of nanosilver particles and antimicrobial activity

Silver(I)-imidazole cyclophane gem-diol complex, 3 [Ag2C36 N10(O)4](2+)2(x)-, where x = OH- or CO3(2-), was synthesized and well characterized. The minimum inhibition concentration tests showed that the aqueous form of 3 is 2 times less effective as an antibiotic than 0.5% AgNO3, with about the same amount of silver. The antimicrobial activity of 3 was enhanced when encapsulated into Tecophilic polymer by electrospinning to obtain mats made of nano-fibers. The fiber mats released nanosilver particles, which in turn sustained the antimicrobial activity of the mats over a long period of time. The rate of bactericidal activity of 3 was greatly improved by encapsulation, and the amount of silver used was much reduced. The amount of silver contained in the fiber mat of 3, with 75% of 3 and 25% Tecophilic, was 8 times less than that in 0.5% AgNO3 and 5 times lower than that in silver sulfadiazine cream 1%. The fiber mat was found to kill S. aureus at the same rate as 0.5% AgNO3, with zero colonies on an agar plate, and about 6 times faster than silver sulfadiazine cream. The silver mats were found effective against E. coli, P. aeruginosa, S. aureus, C. albicans, A. niger, and S. cerevisiae. Transmission electron microscopy and scanning electron microscopy were used to characterize the fiber mats. The acute toxicity of the ligand (imidazolium cyclophane gem-diol dichloride) was assessed by intravenous administration to rats, with an LD 50 of 100 mg/kg of rat.     

Enhanced catalytic activity of ternary Pd-Ni-Ir nanoparticles supported on carbon toward formic acid electro-oxidation

Journal of Solid State Electrochemistry - Aiming to further promote the performance of PdNi for formic acid electro-oxidation (FAEO), ternary Pd-Ni-Ir/C nanocatalyst was synthesized via an ethylene...     

The effect of encapsulated Zn-POM on the catalytic activity of MIL-101 in the oxidation of alkenes with hydrogen peroxide

Zinc monosubstituted Keggin heteropolyanion [PZnMo₂W₉O₃₉]^5? was electrostatically bound to nanocages of MIL-101 polymer matrix. The Zn-POM@MIL-101 catalyst was characterized by XRD, N₂ adsorption, atomic absorption (AAS), and FT-IR spectroscopic methods. The catalytic activity of the new composite material, Zn-POM@MIL-101, was assessed in the oxidation of alkenes using aqueous hydrogen peroxide as oxidant. Zn-POM@MIL-101/H₂O₂ catalytic system demonstrated good catalytic activity in the oxidation reactions. Zn-POM@MIL-101 was reusable for three catalytic cycles. While the MIL-101 matrix is an active catalyst in these oxidation reactions, the presence of Zn-POM significantly changed the selectivity and reaction times.     

Control release of lactate dehydrogenase encapsulated in poly (vinyl alcohol) nanofibers via electrospinning

Sustained release of lactate dehydrogenase (LDH, EC 1.1.1.27) from electrospun poly (vinyl alcohol) (PVA) nanofibers was successfully achieved using the coaxial electrospinning technique. The presence of the encapsulated enzyme in the nanofibers was confirmed by infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was used to evaluate the morphology and diameter of the nanofibers. The conversion of lactate to pyruvate by LDH coupling with the reduction of the cofactor nicotinamide adenine dinucleotide (NAD⁺) to dihydronicotinamide adenine dinucleotide (NADH) produces an increment in the ultraviolet absorption (UV) at 340 nm. This change in the UV absorbance was used to follow the release kinetic of LDH from the PVA nanofibers and also as a measure to evaluate the residual enzymatic catalytic function. Most of the encapsulated LDH enzyme was released in a sustained manner from the PVA nanofibers within a period of 1 month.     

Enhanced adsorptive removal of toxic dyes using SiO2 nanofibers

Electrospinning method was used to synthesize porous SiO₂ nanofibers. The adsorption of Methyl Orange and Safranin O by porous SiO₂ nanofibers was carried out by varying the parameters such as pH, contact time, adsorbent dose, dye concentration, and temperature. Equilibrium adsorption data followed Langmuir isotherms. Kinetic adsorption followed second-order rate kinetics model. The maximum adsorption capacity for Methyl Orange and Safranin O was found to be 730.9 mg/g and 960.4 mg/g, respectively. Acidic pH was favorable for the adsorption of Methyl Orange while basic pH was favorable for the adsorptions of Safranin O. Modeling study suggested the major mode of adsorption, while thermodynamic study showed the endothermic reactions. This effort has pronounced impact on environmental applications of SiO₂ nanofibers as auspicious adsorbent nanofibers for organic material from aqueous solution.     

Sol-gel encapsulated horseradish peroxidase: a catalytic material for peroxidation

This study addresses the viability of sol-gel encapsulated HRP (HRP:sol-gel) as a recyclable solid-state catalytic material. Ferric, ferric-CN, ferrous, and ferrous-CO forms of HRP:sol-gel were investigated by resonance Raman and UV-visible methods. Electronic and vibrational spectroscopic changes associated with changes in spin state, oxidation state, and ligation of the heme in HRP:sol-gel were shown to correlate with those of HRP in solution, showing that the heme remains a viable ligand-binding complex. Furthermore, the high-valent HRP:sol-gel intermediates, compound I and compound II, were generated and identified by time-resolved UV-visible spectroscopy. Catalytic activity of the HRP:sol-gel material was demonstrated by enzymatic assays by using I(-), guaiacol, and ABTS as substrates. Encapsulated HRP was shown to be homogeneously distributed throughout the sol-gel host. Differences in turnover rates between guaiacol and I(-) implicate mass transport of substrate through the silicate matrix as a defining parameter in the peroxidase activity of HRP:sol-gel. HRP:sol-gel was reused as a peroxidation catalyst for multiple reaction cycles without loss of activity, indicating that such materials show promise as reusable catalytic materials.     

New mono- and tricyclopalladated dendritic systems with encapsulated catalytic sites

The preparation of a series of new macrocyclic carbodiazasilane molecules functionalized with the monoanionic [2,6-(CH2NMe2)2C6H3](-)[triple bond]N,C,N-pincer ligand has been accomplished. Palladation of these systems was possible through oxidative addition with [Pd(dba)2] affording exclusive formation of the meso diastereoisomer. The X-ray crystal structures of these novel ligands and of the palladium(II) complex 10 were determined and confirmed the stereochemistry of the organopalladium cage. Attachment of the para-OH functionalized carbodiazasilane macrocycle 16 to a central core led to the formation of the dendritic structure 18 which was palladated to afford the novel multimetallic dendritic system with encapsulated catalytic sites 1. This cyclopalladated carbosilane dendrimer (1) as well as the mononuclear organopalladium cage 10 can be conveniently converted into active Lewis acid catalysts for the aldol condensation reaction. The catalytic data showed higher reaction rates for the dendritic structure than for the corresponding mononuclear systems.     

NaY分子筛固载席夫碱钴配合物的制备、表征及其催化性能研究

利用“瓶中造船”（ship-in-a-bottle） 技术将双水杨醛缩乙二胺合钴（Cosalen）配合物封装于Y型沸石分子筛的超笼中,制备出固载型席夫碱钴金属配合物Cosalen/Y（SB）。同时采用浸渍方法将Cosalen负载于Y型分子筛的表面,制备了浸渍型的负载物Cosalen/Y（IM）。采用原子吸收、红外光谱、紫外光谱、X射线衍射、热重 差热和电镜扫描等方法对两者进行了表征。 结果表明 ,固载物Cosalen/Y（SB）中Cosalen已成功地进入了分子筛的孔道内。以分子氧为氧源,考察了Cosalen/Y（SB）对环己烷的催化氧化性能以及催化剂用量、溶剂、氧气压力对反应的影响。结果表明,Cosalen/Y（SB）具有较高的催化氧化活性和对环己醇、环己酮以及己二酸的选择性,有一步氧化环己烷生成己二酸的潜力。重复实验表明,催化剂稳定性较好,没有明显的活性组分流失。