Labeling study of avidin by modular method for affinity labeling (MoAL)

We studied the specific labeling of avidin with biotinylated modular ligand catalysts via MoAL, which we recently established. The labeling yield was found to depend on the linker length connecting the catalytic site to biotin in the modular ligand catalyst 1, and the maximum yield was obtained with 1d possessing octamethylene linker. The labeling reaction reached a maximum rate with only 4 equiv of the ligand catalyst. Presumably, all the subunits of avidin with homotetrameric structure formed a stable complex with 4 equiv of the catalyst because of the extremely high affinity. The ligand catalyst bound to avidin first catalyzed N-triazinylation of the ε-amino group of Lys111, and the resulting regenerated catalyst then catalyzed the reaction of Asp108 and CDMT.     

Peptide-cleaving catalyst selective for melanin-concentrating hormone: oxidative decarboxylation of N-terminal aspartate catalyzed by Co(III)cyclen

To provide a firm basis for the new paradigm of drug discovery based on catalysts for oxidative cleavage of N-terminal aspartate (Asp) residues of oligopeptides, oligopeptide-cleaving catalysts were searched by using melanin-concentrating hormone (MCH) as the substrate. MCH is a target for designing drugs to reduce obesity. Catalyst candidates containing the Co(III) complex of cyclen as the catalytic center were prepared by multicomponent condensation reactions. From three kinds of chemical libraries containing about 19,000 catalyst candidates, one compound was identified as the MCH-cleaving catalyst. On incubation with the catalyst, the N-terminal Asp residue of MCH was converted to the pyruvate residue by oxidative decarboxylation. Detailed kinetics analysis revealed the catalytic nature of the action of the catalyst. In addition, the kinetics data indicated that MCH can be cleaved with half-lives of 3 h or less with submicromolar catalyst concentrations if the structure of the catalyst is further improved.     

Photocatalysed decomposition of anthraquinone sulphonic acid (sodium salt) using ZnO

Anthraquinone-2-sulphonic acid-sodium salt (ASS) - an organic pollutant which is being used in the paper industry, has been photodegraded with ZnO as catalyst in the presence of visible and UV light. Combination of UV or visible light with the catalyst is more effective than with the catalyst or light alone for the photodegradation of ASS. The results on the effect of pH, effect of catalyst and pollutant concentration on the photodegradation of ASS were discussed. Kinetics of the photodegradation of ASS involving Langmuir-Hinshelwood mechanism has been discussed in detail.     

Natural catalyst for luminol chemiluminescence: application to validate peroxide levels in commercial hair dyes

Here, we report a hydrothermally treated green leaves (Moringa oleifera) extract exploited as an efficient and highly sensitive catalyst to catalyze the chemiluminescence (CL) reaction of luminol. In the absence of enhancer, this green and hydrothermally treated catalyst was found to significantly enhance the CL intensity ~3.5-fold compared with the traditionally used K₃Fe(CN)₆ catalyst. The structure and surface morphology of the catalyst was elucidated using X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The synergistic effect of the catalyst in the CL reaction was systematically investigated in the presence of hydrogen peroxide using ultraviolet–visible and CL spectroscopy. Studies showed that the sensitivity of the catalyst could be amplified by adjusting several parameters such as pH of the medium and concentrations of the base and luminol. The sensitivity of the novel-type catalyst was examined through the validation of hydrogen peroxide levels in commercial hair dye samples. Markedly, the catalyst displayed ultrasensitivity to hydrogen peroxide as the limit of detection of hydrogen peroxide using this catalyst was determined to be 0.02 μM under optimized conditions. In general, the proposed inexpensive, ecofriendly, and nontoxic catalyst could enable the determination of hydrogen peroxide for diverse analytical applications.     

Optimization of a Novel Two-step Process Comprising Re-esterification and Transesterification in a Single Reactor for Biodiesel Production Using Waste Cooking Oil

Waste cooking oil (WCO) has attracted attention as a non-edible feedstock for biodiesel. Although an alkali catalyst has several advantages over an acid catalyst in biodiesel production, biodiesel conversion from WCO is only 5.2% when using an alkali catalyst (NaOH), owing to its high free fatty acid (FFA) content of 4.2%. In this study, a novel two-step process in a single reactor, comprised of re-esterification of the FFAs with crude glycerol, using a Tin (II) chloride (SnCl₂) catalyst, and subsequent transesterification with methanol, using an alkali catalyst, was adopted, and each step was optimized. This study revealed that the FFA content after re-esterification should be approximately 1.5%, not only to save glycerol and the catalyst involved in the re-esterification, but also to achieve high biodiesel conversion during the transesterification. An alkaline catalyst was successfully used to produce biodiesel in the second step, and a 92.8% conversion to biodiesel was achieved under the optimized conditions (0.6% catalyst relative to WCO, 0.2mL-methanol/WCO, 70ºC, 3 h). Overall, this novel two-step process achieved highly enhanced biodiesel conversion (4.0% to 92.8%) with significantly reduced reaction time (12 h to 4 h) and methanol requirements (15 mL/g-WCO to 0.2 mL/g-WCO).     

Application of an insolubilized hepatic microsomal drug oxidase to the continous production of N-oxides

The optimum operating temperature and pH have been determined for a catalyst prepared by the insolubilization of a hepatic microsomal mixed-function oxidase on glass beads. Temperature is a more significant variable than pH in determining potential catalyst yield (total product/unit catalyst). An operating range of about 25–28°C is optimal with respect to catalyst life at pH 7.6. Like the purified soluble oxidase, the glass bead-mounted enzyme catalyzes the NADPH- and oxygen-dependent oxidation of a variety of amines, hydrazines, and thioureylenes. The catalyst has been used in a simple slurry reactor to prepare mg quantities of N-oxide metabolites of prochlorperazine, guanethidine, and ethylmorphine.     

The Effects of Catalyst Layer Deposition Methodology on Electrode Performance

The catalyst layer of the cathode is arguably the most critical component of low‐temperature fuel cells and carbon dioxide (CO₂) electrolysis cells because their performance is typically limited by slow oxygen (O₂) and CO₂ reduction kinetics. While significant efforts have focused on developing cathode catalysts with improved activity and stability, fewer efforts have focused on engineering the catalyst layer structure to maximize catalyst utilization and overall electrode and system performance. Here, we study the performance of cathodes for O₂ reduction and CO₂ reduction as a function of three common catalyst layer preparation methods: hand‐painting, air‐brushing, and screen‐printing. We employed ex‐situ X‐ray micro‐computed tomography (MicroCT) to visualize the catalyst layer structure and established data processing procedures to quantify catalyst uniformity. By coupling structural analysis with in‐situ electrochemical characterization, we directly correlate variation in catalyst layer morphology to electrode performance. MicroCT and SEM analyses indicate that, as expected, more uniform catalyst distribution and less particle agglomeration, lead to better performance. Most importantly, the analyses reported here allow for the observed differences over a large geometric volume as a function of preparation methods to be quantified and explained for the first time. Depositing catalyst layers via a fully‐automated air‐brushing method led to a 56% improvement in fuel cell performance and a significant reduction in electrode‐to‐electrode variability. Furthermore, air‐brushing catalyst layers for CO₂ reduction led to a 3‐fold increase in partial CO current density and enhanced product selectivity (94% CO) at similar cathode potential but a 10‐fold decrease in catalyst loading as compared to previous reports.     

The dehydration of fermentative 2,3-butanediol into methyl ethyl ketone

A solid acid catalyst consisted of sulfonic groups covalently bound to an inorganic matrice was developed to dehydrate 2,3-butanediol into methyl ethyl ketone. Rate constant and apparent activation energy of the dehydration reaction were determined. The decay course of the catalyst was a two-stage curve. The catalyst was deactivated more rapidly in the first stage than in the second stage. The strategy of maintaining constant degree of dehydration was employed to lengthen the lifetime of catalyst. Treatment of the 2,3-butanediol containing fermentation broth with activated carbon greatly facilitated the subsequent dehydration reaction.     

Enhancement of Treatment Efficiency of Recalcitrant Wastewater Containing Textile Dyes Using a Newly Developed Iron Zeolite Socony Mobil-5 Heterogeneous Catalyst

Fenton oxidation, an advanced oxidation process, is an efficient method for the treatment of recalcitrant wastewaters. Unfortunately, it utilizes H₂O₂ and iron-based homogeneous catalysts, which lead to the formation of high volumes of sludge and secondary pollutants. To overcome these problems, an alternate option is the usage of heterogeneous catalyst. In this study, a heterogeneous catalyst was developed to provide an alternative solution for homogeneous Fenton oxidation. Iron Zeolite Socony Mobile-5 (Fe-ZSM-5) was synthesized using a new two-step process. Next, the catalyst was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller analysis and tested against a model wastewater containing the azo dye Acid Blue 113. Results showed that the loading of iron particles reduced the surface area of the catalyst from 293.59 to 243.93 m²/g; meanwhile, the average particle size of the loaded material was 12.29 nm. Furthermore, efficiency of the developed catalyst was evaluated by performing heterogeneous Fenton oxidation. Taguchi method was coupled with principal component analysis in order to assess and optimize mineralization efficiency. Experimental results showed that under optimized conditions, over 99.7% degradation and 77% mineralization was obtained, with a 90% reduction in the consumption of the developed catalyst. Furthermore, the developed catalyst was stable and reusable, with less than 2% leaching observed under optimized conditions. Thus, the present study proved that newly developed catalyst has enhanced the oxidation process and reduced the chemicals consumption.     

Ion exchange resins as catalyst for the isomerization of alpha-pinene to camphene

Camphene is an industrial intermediate compound for commercial chemicals such as isoborneol, isobornyl acetate and camphor. Industrially, the conventional process for camphene production consists of the isomerization of alpha-pinene using acidic TiO2 as catalyst. The use of this catalyst presents problems such as considerable time for preparation, reproducibility and recovery of catalyst from products after the alpha-pinene isomerization. For the first time, a commercial exchange resin was used as catalyst for this reaction. Based on the concentration of product as a function of the reaction time, the path of the alpha-pinene transformation to camphene and byproducts is proposed. Temperature and alpha-pinene/catalyst ratio were studied in order to optimize the yield to camphene production. The obtained results were comparable with those reported for acidic TiO2.     

Palladium and phosphomolybdovanadate catalyzed olefin oxidation to carbonyls

A new homogeneous catalyst system has been developed for the oxidation of olefins to carbonyls — ethylene to acetaldehyde and higher olefins to ketones. The catalyst system was first developed for the oxidation of ethylene to acetaldehyde in Wacker-type acetaldehyde plants. The aqueous catalyst solution has three key components. A palladium(II) catalyst oxidizes the olefin to the carbonyl, which is analogous to the Wacker system but with only a fraction of its palladium. Keggin phosphomolybdovanadates of the general formula PMo_(12–x) V _x O ₄₀ ^(3+x)– provide a dioxygen-reversible vanadium(V)/vanadium(IV) redox agent for palladium(O) reoxidation, which is analogous to the copper(II)/copper(I) chlorides in the Wacker system. Chloride at centimolar concentrations, lacking in earlier reported palladium and polyoxometalate catalyst systems, is essential to maintain stable palladium(II) catalyst activity. Kinetic characterization and reaction engineering provided ethylene and oxygen reaction rates comparable to those obtained with the Wacker catalyst. A new, efficient method of preparing aqueous phosphomolybdovanadate solutions was developed for laboratory and large-scale production. This paper describes the catalyst system and its reactions with emphasis on the polyoxometalate chemistry.     

Solid-supported and pegylated H-Pro-Pro-Asp-NHR as catalysts for asymmetric aldol reactions

H-Pro-Pro-Asp-NH2 is a highly active and selective catalyst for asymmetric aldol reactions. Here, the versatility of H-Pro-Pro-Asp-NH2 has been further improved by immobilization on a solid support and functionalization with a short polyethylene glycol linker at the C-terminus. The development, synthesis, and the catalytic properties in aldol reactions of H-Pro-Pro-Asp-resin and H-Pro-Pro-Asp-Ahx-NH(CH2CH2O)3CH3 are described. For the solid-supported catalyst, TentaGel with a loading of 0.1-0.2 mmol g(-1) proved to be the optimal support. The solid-supported catalyst can be recycled at least three times without a significant drop in the catalytic activity or selectivity. Using the pegylated catalyst H-Pro-Pro-Asp-Ahx-NH(CH2CH2O)3CH3, only 0.5 mol % are necessary to obtain aldol products in up to 96% yield and 91% enantiomeric excess. In all cases, enantioselectivities are comparable to those obtained with the parent catalyst H-Pro-Pro-Asp-NH2. Thus, immobilization of H-Pro-Pro-Asp-NH2 on Tentagel as well as pegylation led to catalysts with selectivities comparable to the nonmodified catalyst, exhibiting additional distinct advantages such as facile reusability, ease of handling, higher solubility, and thereby greater versatility. handling, higher solubility, and thereby greater versatility.     

Biodiesel production from high acid value waste frying oil catalyzed by superacid heteropolyacid

Transesterification of waste cooking oil with high acid value and high water contents using heteropolyacid H3PW12O40 x 6H2O (PW12) as catalyst was investigated. The hexahydrate form of PW(12) was found to be the most promising catalyst which exhibited highest ester yield 87% for transesterification of waste cooking oil and ester yield 97% for esterification of long-chain palmitic acid, respectively. The PW12 acid catalyst shows higher activity under the optimized reaction conditions compared with conventional homogeneous catalyst sulfuric acid, and can easily be separated from the products by distillation of the excess methanol and can be reused more times. The most important feature of this catalyst is that the catalytic activity is not affected by the content of free fatty acids (FFAs) and the content of water in the waste cooking oil and the transesterification can occur at a lower temperature (65 degrees C), a lower methanol oil ratio (70:1) and be finished within a shorter time. The results illustrate that PW12 acid is an excellent water-tolerant and environmentally benign acid catalyst for production of biodiesel from waste cooking oil.     

Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic system

Chitosan-supported L-proline complex was synthesized and applied as a catalyst for the direct asymmetric aldol reaction in various organic solvents and water as well. It was found that the novel synthesized catalyst was able to efficiently catalyze the aldol reaction in various media. The catalytic capacity and stereoselectivity of the catalyst were obviously improved with the introduction of aqueous micelle, possibly because the micelle functioned as a hydrophobic pocket, like the hydrophobic portion in enzymes. Moreover, the present synthetic catalyst showed performance similar to that of enzymes and could be used as a model of enzyme catalysis to help better understand the mystic mechanism of enzymes.     

New stereoselective catalysts in doxycycline synthesis

Formation of the doxycycline diastereoisomer along with doxycycline during hydrogenation of the methacycline exocyclic double bond lowered the yield of the main product. The use of tris-(triphenylphosphine)-rhodium chloride (Wilkinson catalyst) as a catalyst provided higher stereoselectivity of the hydrogenation and resulted in predominant production of doxycycline. Inclusion of some ligands such as hydrazine or others into the composition of the compound rhodium catalyst increased its activity. The stereoselectivity during hydrogenation of the methacycline exocyclic double bond can be explained by different rates of hydrogen attachment to the two enantiomeric products of the compound rhodium catalyst addition to the exocyclic double bond.     

Transesterification of triglycerides in high and low quality oil feeds over an HT2 hydrotalcite catalyst

The use of a heterogeneous catalyst, in the transesterification reaction of refined and acidic cottonseed oil for the production of methyl-esters (biodiesel) has been studied. The basic Mg-Al-CO3 hydrotalcite catalyst used showed a high activity for methanolysis and esterification reactions in a refined and an acidic cottonseed oil as well as in a representative high water content animal fat feed. The experiments were performed in a temperature range between 180 and 210 degrees C, in a batch reactor. The methanol to vegetable oil molar ratio was 6 to 1, while the catalyst concentration was fixed at 1 wt.% of the oil mass. Non-calcined and calcined forms of the catalyst were tested. The activity of the calcined catalyst was lower than the initial activity of the non-calcined catalytic system but it appeared the same with the reused non-calcined system.     

Biorefining of platinum group metals from model waste solutions into catalytically active bimetallic nanoparticles

Bacteria can fabricate platinum group metal (PGM) catalysts cheaply, a key consideration of industrial processes and waste decontaminations. Biorecovery of PGMs from wastes is promising but PGM leachates made from metallic scraps are acidic. A two‐step biosynthesis ‘pre‐seeds’ metallic deposits onto bacterial cells benignly; chemical reduction of subsequent metal from acidic solution via the seeds makes bioscaffolded nanoparticles (NPs). Cells of Escherichia coli were seeded using Pd(II) or Pt(IV) and exposed to a mixed Pd(II)/Pt(IV) model solution under H₂ to make bimetallic catalyst. Its catalytic activity was assessed in the reduction of Cr(VI), with 2 wt% or 5 wt% preloading of Pd giving the best catalytic activity, while 1 wt% seeds gave a poorer catalyst. Use of Pt seeds gave less effective catalyst in the final bimetallic catalyst, attributed to fewer and larger initial seeds as shown by electron microscopy, which also showed a different pattern of Pd and Pt deposition. Bimetallic catalyst (using cells preloaded with 2 wt% Pd) was used in the hydrogenation of soybean oil which was enhanced by ~fourfold using the bimetallic catalyst made from a model waste solution as compared to 2 wt% Pd preloaded cells alone, with a similar selectivity to cis C18:1 product as found using a Pd‐Al₂O₃ commercial catalyst.     

The search for new hydrogenation catalyst motifs based on N-heterocyclic carbene ligands

A series of new iridium complexes containing N-heterocyclic carbene ligands (NHCs) has been prepared and tested for hydrogenation of primary (1-octene), secondary (cyclohexene), tertiary (1-methylcyclohexene) and quartenary (2,3-dimethyl-2-butene) alkenes. Taking inspiration from Crabtree’s catalyst, [Ir(COD)(PCy₃)(py)]PF₆, the labile pyridine ligand was exchanged with an NHC ligand, and was found to produce catalysts with similar activities and rates. Further refinement of the ligands produced the optimal version of the iridium phosphine/NHC combination: Using a smaller phosphine, tri-n-butylphosphine, a saturated NHC and the non-coordinating anion, tetrakis(3,5-bis(trifluoromethylphenyl))borate (BARF), a highly active catalyst that has substantially better longevity and stability, but similar activity, to the parent Crabtree’s catalyst was prepared in three steps. The effect of the BARF counteranion was explored, and was shown to improve even Crabtree’s catalyst, and is thus a general phenomenon for iridium catalysts in non-polar solvents. Mechanistic studies suggest that the catalyst resting state is a dimeric complex, presumably hydride-bridged, that dissociates into catalytically active species under catalytic conditions. Thus, the catalyst dead-end for Crabtree’s catalyst, hydride-bridged dimers and trimers, may in fact be a reversible resting state for the iridium complexes described here.     

Catalytic conversion of xylose to furfural over the solid acid SO₄ ²⁻-/ZrO₂-Al₂O₃/SBA-15 catalysts

Al-promoted SO? 2?-/ZrO?SBA-15 catalysts were prepared and characterized by XRD, BET, ICP and NH?-TPD techniques. The influence of introducing aluminum on the structure and surface properties of the catalyst and the catalytic activity for dehydration of xylose to furfural has been investigated. The introduction of the Al stabilizes the tetragonal phase of the ZrO? and thus increases the number and intensity of acid sites. Based on the characterization of the deactivated catalyst, the accumulation of byproducts is the main reason for the deactivation of the catalyst. Regeneration with H?O? can completely recover the catalytic activity of the deactivated catalyst.     

Synthesis of fatty acid methyl ester from palm oil (Elaeis guineensis) with Ky(MgCa)2xO3 as heterogeneous catalyst

Fatty acid methyl esters (FAME) were produced from palm oil using eggshell modified with magnesium and potassium nitrates to form a composite, low-cost heterogeneous catalyst for transesterification. The catalyst, prepared by the combination of impregnation/co-precipitation was calcined at 830 °C for 4 h. Transesterification was conducted at a constant temperature of 65 °C in a batch reactor. Design of experiment (DOE) was used to optimize the reaction parameters, and the conditions that gave highest yield of FAME (85.8%) was 5.35 wt.% catalyst loading at 4.5 h with 16:1 methanol/oil molar ratio. The results revealed that eggshell, a solid waste, can be utilized as low-cost catalyst after modification with magnesium and potassium nitrates for biodiesel production.