This work introduces a new additive named 4,4'-trimethylenedipiperidine for the practical and ecofriendly preparation of ethyl 5-amino-7-(4-phenyl)-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine-6-carboxylate derivatives. This chemical is commercially available and easy to handle. It also possesses a low melting point and a broad liquid range temperature, high thermal stability, and good solubility in water. Based on green chemistry principles, the reaction was performed in a) a mixture of green solvents i.e. water and ethanol (1:1 v/v) at reflux temperature, and b) the additive was liquefied at 65 °C and the reaction was conducted in the liquid state of the additive. High yields of the desired triazolo-pyrimidines were obtained under both aforementioned conditions. Our results demonstrated that this additive, containing 2 Lewis base sites and able to act as an acceptor-donor hydrogen bonding group, is a novel and efficient alternative to piperidine, owing to its unique properties such as its reduced toxicity, nonflammable nature, nonvolatile state, broad liquid range temperature, high thermal stability, and ability to be safely handled. Furthermore, this additive could be completely recovered and exhibited high recyclability without any change in its chemical structure and no significant reduction in its activity. The current methodology has several advantages: (a) it avoids the use of hazardous materials, as well as toxic, volatile, and flammable solvents, (b) it does not entail tedious processes, harsh conditions, and the multistep preparation of catalysts, (c) it uses a metal-free and noncorrosive catalyst, and (d) reduces the generation of hazardous waste and simple work-up processes. The most important result of this study is that 4,4'-trimethylenedipiperidine can be a promising alternative for toxic, volatile, and flammable base reagents in organic synthesis owing to its unique properties.
The concept of de novo metabolic engineering through novel synthetic pathways offers new directions for multi-step enzymatic synthesis of complex molecules. This has been complemented by recent progress in performing enzymatic reactions using immobilized enzyme microreactors (IEMR). This work is concerned with the construction of de novo designed enzyme pathways in a microreactor synthesizing chiral molecules. An interesting compound, commonly used as the building block in several pharmaceutical syntheses, is a single diastereoisomer of 2-amino-1,3,4-butanetriol (ABT). This chiral amino alcohol can be synthesized from simple achiral substrates using two enzymes, transketolase (TK) and transaminase (TAm). Here we describe the development of an IEMR using His6-tagged TK and TAm immobilized onto Ni-NTA agarose beads and packed into tubes to enable multi-step enzyme reactions. The kinetic parameters of both enzymes were first determined using single IEMRs evaluated by a kinetic model developed for packed bed reactors. The Km(app) for both enzymes appeared to be flow rate dependent, while the turnover number kcat was reduced 3 fold compared to solution-phase TK and TAm reactions. For the multi-step enzyme reaction, single IEMRs were cascaded in series, whereby the first enzyme, TK, catalyzed a model reaction of lithium-hydroxypyruvate (HPA) and glycolaldehyde (GA) to L-erythrulose (ERY), and the second unit of the IEMR with immobilized TAm converted ERY into ABT using (S)-α-methylbenzylamine (MBA) as amine donor. With initial 60mM (HPA and GA each) and 6mM (MBA) substrate concentration mixture, the coupled reaction reached approximately 83% conversion in 20 min at the lowest flow rate. The ability to synthesize a chiral pharmaceutical intermediate, ABT in relatively short time proves this IEMR system as a powerful tool for construction and evaluation of de novo pathways as well as for determination of enzyme kinetics.
Sequentially precipitated Mg-promoted nickel-silica catalysts with ageing performed under various ultrasonic intensities were employed to study the catalyst performance in the partial hydrogenation of sunflower oil. Results from various characterisation studies showed that increasing ultrasonic intensity caused a higher degree of hydroxycarbonate erosion and suppressed the formation of Ni silicates and silica support, which improved Ni dispersion, BET surface area and catalyst reducibility. Growth of silica clusters on the catalyst aggregates were observed in the absence of ultrasonication, which explained the higher silica and nickel silicate content on the outer surface of the catalyst particle. Application of ultrasound also altered the electron density of the Ni species, which led to higher activity and enhanced product selectivity for sonicated catalysts. The catalyst synthesised with ultrasonic intensity of 20.78 Wcm-2 achieved 22.6% increase in hydrogenation activity, along with 28.5% decrease in trans-C18:1 yield at IV = 70, thus supporting the feasibility of such technique.
Wax esters are important ingredients in cosmetics, pharmaceuticals, lubricants and other chemical industries due to their excellent wetting property. Since the naturally occurring wax esters are expensive and scarce, these esters can be produced by enzymatic alcoholysis of vegetable oils. In an enzymatic reaction, study on modeling and optimization of the reaction system to increase the efficiency of the process is very important. The classical method of optimization involves varying one parameter at a time that ignores the combined interactions between physicochemical parameters. RSM is one of the most popular techniques used for optimization of chemical and biochemical processes and ANNs are powerful and flexible tools that are well suited to modeling biochemical processes.
In this work, advanced nanoscale surface characterization of CuO Nanoflowers synthesized by controlled hydrothermal approach for significant enhancement of catalytic properties has been investigated. The CuO nanoflower samples were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), selected-area electron diffraction (SAED), high-angular annular dark field scanning transmission electron microscopy (HAADF-STEM) with elemental mapping, energy dispersive spectroscopy (STEM-EDS) and UV-Vis spectroscopy techniques. The nanoscale analysis of the surface study of monodispersed individual CuO nanoflower confirmed the fine crystalline shaped morphology composed of ultrathin leaves, monoclinic structure and purified phase. The result of HR-TEM shows that the length of one ultrathin leaf of copper oxide nanoflower is about ~650-700 nm, base is about ~300.77 ± 30 nm and the average thickness of the tip of individual ultrathin leaf of copper oxide nanoflower is about ~10 ± 2 nm. Enhanced absorption of visible light ~850 nm and larger value of band gap energy (1.68 eV) have further supported that the as-grown material (CuO nanoflowers) is an active and well-designed surface morphology at the nanoscale level. Furthermore, significant enhancement of catalytic properties of copper oxide nanoflowers in the presence of H2O2 for the degradation of methylene blue (MB) with efficiency ~96.7% after 170 min was obtained. The results showed that the superb catalytic performance of well-fabricated CuO nanoflowers can open a new way for substantial applications of dye removal from wastewater and environment fields.
Corn-cobs are an agro-industrial waste and composed of cellulose mostly. In this study cellulose was isolated from the waste corn-cobs and modified to polymeric hydroxamic acid palladium complex 1 and characterized by using a variety of spectroscopic methods such as field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The complex 1 exhibited high catalytic activity towards Suzuki and Heck coupling reactions of activated and deactivated aryl halides to give the respective coupling products with high yield. Moreover, the complex 1 was recovered and recycled five times with no considerable loss of catalytic overall performance.
A detailed study on the surface properties of oleic acid-stabilized PtNi nanoparticles supported on silica is reported. The oleic acid-stabilized PtNi nanoparticles were synthesized using NaBH4 as the reducing agent at various temperatures and oleic acid concentrations, prior to incorporation onto the silica support. X-ray diffraction studies of the unsupported oleic acid-stabilized PtNi particles revealed that the PtNi existed as alloys. Upon incorporation onto silica support, surface properties of the catalysts were investigated using H2-temperature reduction (H2-TPR), H2-temperature desorption (H2-TPD) and H2-chemisorption techniques. It was found that for the bimetallic catalysts, no oxides or very little oxidation occurred. Furthermore, these catalysts exhibited both Pt and Ni active sites on its surface though the availability of Ni active sites was dominant. A comparison of the surface properties of these materials with those prepared without oleic acid in our previous work [N. H. H. Abu Bakar et al., J. Catal. 265, 63 (2009)] and how they affect the hydrogenation of benzene is also discussed.
The (R)-3-hydroxyacyl-ACP-CoA transferase catalyses the conversion of (R)-3-hydroxyacyl-ACP to (R)-3-hydroxyacyl-CoA derivatives, which serves as the ultimate precursor for polyhydroxyalkanoate (PHA) polymerisation from unrelated substrates in pseudomonads. PhaG was found to be responsible for channelling precursors for polyhydroxyalkanoate (PHA) synthase from a de novo fatty acid biosynthesis pathway when cultured on carbohydrates, such as glucose or gluconate. The phaG gene was cloned from Pseudomonas sp. USM 4-55 using a homologous probe. The gene was located in a 3660 bp Sal I fragment (GenBank accession number EU305558). The open reading frame (ORF) was 885 bp long and encoded a 295 amino acid protein. The predicted molecular weight was 33251 Da, and it showed a 62% identity to the PhaG of Pseudomonas aeruginosa. The function of the cloned phaG of Pseudomonas sp. USM 4-55 was confirmed by complementation studies. Plasmid pBCS39, which harboured the 3660 bp Sal I fragment, was found to complement the PhaG-mutant heterologous host cell, Pseudomonas putida PhaGN-21. P. putida PhaGN-21, which harboured pBCS39, accumulated PHA that accounted for up to 18% of its cellular dry weight (CDW). P. putida PhaGN-21, which harboured the vector alone (PBBR1MCS-2), accumulated only 0.6% CDW of PHA.
The aim of this study is to investigate the performance of combined solar photo-catalyst of titanium oxide/zinc oxide (TiO2/ZnO) with aeration processes to treat petroleum wastewater. Central composite design with response surface methodology was used to evaluate the relationships between operating variables for TiO2 dosage, ZnO dosage, air flow, pH, and reaction time to identify the optimum operating conditions. Quadratic models for chemical oxygen demand (COD) and total organic carbon (TOC) removals prove to be significant with low probabilities (<0.0001). The obtained optimum conditions included a reaction time of 170 min, TiO2 dosage (0.5 g/L), ZnO dosage (0.54 g/L), air flow (4.3 L/min), and pH 6.8 COD and TOC removal rates of 99% and 74%, respectively. The TOC and COD removal rates correspond well with the predicted models. The maximum removal rate for TOC and COD was 99.3% and 76%, respectively at optimum operational conditions of TiO2 dosage (0.5 g/L), ZnO dosage (0.54 g/L), air flow (4.3 L/min), reaction time (170 min) and pH (6.8). The new treatment process achieved higher degradation efficiencies for TOC and COD and reduced the treatment time comparing with other related processes.
This review provides a background, fundamental and advanced application of titania nanoparticles (TiO2) on the disinfection and killing of cancer cell through photocatalytic chemistry. It starts with the characteristic properties focused on the surface, light sensitivity, crystallinity and toxicology of TiO2 as a photocatalyst. Consequently, outline and design of photocatalytic reactor has been figured out based on the target organisms, including bacteria, viruses, fungi and cancer cells. Despite a large number of studies undertaken, limited selectivity and efficacy of TiO2 photocatalyst are still widely accepted problems. An ideal TiO2 photocatalyst should have the combined properties of highly stable reactive oxygen species yield and a greater degree of selectivity towards cancerous cell without damaging the healthy tissues. Hybridization of TiO2 with metal, metal oxide and carbon nano materials significantly improved both of stability and selectivity of TiO2, whilst maintaining its high Photodynamic reactivity.
Catalytic depolymerization of mannan composition of palm kernel cake (PKC) by mannanase was optimized to enhance the release of mannan-derived monomeric sugars for further application in acetone-butanol-ethanol (ABE) fermentation. Efficiency of enzymatic hydrolysis of PKC was studied by evaluating effects of PKC concentration, mannanase loading, hydrolysis pH value, reaction temperature and hydrolysis time on production of fermentable sugars using one-way analysis of variance (ANOVA). The ANOVA results revealed that all factors studied had highly significant effects on total sugar liberated (P<0.01). The optimum conditions for PKC hydrolysis were 20% (w/v) PKC concentration, 5% (w/w) mannanase loading, hydrolysis pH 4.5, 45°C temperature and 72h hydrolysis time. Enzymatic experiments in optimum conditions revealed total fermentable sugars of 71.54±2.54g/L were produced including 67.47±2.51g/L mannose and 2.94±0.03g/L glucose. ABE fermentation of sugar hydrolysate by Clostridium saccharoperbutylacetonicum N1-4 resulted in 3.27±1.003g/L biobutanol.
The solubility limitations of phenolic acids in many lipidic environments are now greatly improved by their enzymatic esterification in ionic liquids (ILs). Herein, four different ILs were tested for the esterification of dihydrocaffeic acid with hexanol and the best IL was selected for the synthesis of four other n-alkyl esters with different chain-lengths. The effect of alkyl chain length on the anti-oxidative properties of the resulted purified esters was investigated using β-carotene bleaching (BCB) and free radical scavenging method DPPH and compared with butylated hydroxytoluene (BHT) as reference compound. All four esters (methyl, hexyl, dodecyl and octadecyl dihydrocaffeates) exhibited relatively strong radical scavenging abilities. The scavenging activity of the test compounds was in the following order: methyl ester>hexyl ester⩾dodecyl ester>octadecyl ester>BHT while the order for the BCB anti-oxidative activity was; BHT>octadecyl ester>dodecyl ester>hexyl ester>methyl ester.
This paper reports on the optimization of palm oil mill effluent (POME) degradation in a UV-activated-ZnO system based on central composite design (CCD) in response surface methodology (RSM). Three potential factors, viz. O2 flowrate (A), ZnO loading (B) and initial concentration of POME (C) were evaluated for the significance analysis using a 2(3) full factorial design before the optimization process. It is found that all the three main factors were significant, with contributions of 58.27% (A), 15.96% (B) and 13.85% (C), respectively, to the POME degradation. In addition, the interactions between the factors AB, AC and BC also have contributed 4.02%, 3.12% and 1.01% to the POME degradation. Subsequently, all the three factors were subjected to statistical central composite design (CCD) analysis. Quadratic models were developed and rigorously checked. A 3D-response surface was subsequently generated. Two successive validation experiments were carried out and the degradation achieved were 55.25 and 55.33%, contrasted with 52.45% for predicted degradation value.
Separation and purification of oilfield produced water (OPW) is a major environmental challenge due to the co-production of the OPW during petroleum exploration and production operations. Effective capture of oil contaminant and its in-situ photodegradation is one of the promising methods to purify the OPW. Based on the photocatalytic capability of graphitic carbon nitride (GCN) which was recently rediscovered, photodegradation capability of GCN for OPW was investigated in this study. GCN was synthesized by calcination of urea and further exfoliated into nanosheets. The GCNs were incorporated into polyacrylonitrile nanofibers using electrospinning, which gave a liquid-permeable self-supporting photocatalytic nanofiber mat that can be handled by hand. The photocatalytic nanofiber demonstrated 85.4% degradation of OPW under visible light irradiation, and improved the degradation to 96.6% under UV light. Effective photodegradation of the photocatalytic nanofiber for OPW originates from synergetic effects of oil adsorption by PAN nanofibers and oil photodegradation by GCNs. This study provides an insight for industrial application on purification of OPW through photocatalytic degradation under solar irradiation.
Highly photocatalytically active copper chromite nanostructured material were prepared via a novel simple hydrothermal reaction between [Cu(en)2(H2O)2]Cl2 and [Cr(en)3]Cl3.3H2O at low temperature, without adding any pH regulator or external capping agent. The as-synthesized nanostructured copper chromite was analyzed by transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. Results of the morphological investigation of the as-synthesized products illustrate that the shape and size of the copper chromite depended on the surfactant sort, reaction duration and temperature. Moreover, the photocatalytic behavior of as-obtained copper chromite was evaluated by photodegradation of acid blue 92 (anionic dye) as water pollutant.
Double perovskite-type catalysts including La2CoMnO6 and La2CuMnO6 are first evaluated for the effectiveness in removing volatile organic compounds (VOCs), and single perovskites (LaCoO3, LaMnO3, and LaCuO3) are also tested for comparison. All perovskites are tested with the gas hourly space velocity (GHSV) of 30,000hr-1, and the temperature range of 100-600°C for C7H8 removal. Experimental results indicate that double perovskites have better activity if compared with single perovskites. Especially, toluene (C7H8) can be completely oxidized to CO2 at 300°C as La2CoMnO6 is applied. Characterization of catalysts indicates that double perovskites own unique surface properties and are of higher amounts of lattice oxygen, leading to higher activity. Additionally, apparent activation energy of 68kJ/mol is calculated using Mars-van Krevelen model for C7H8 oxidation with La2CoMnO6 as catalyst. For durability test, both La2CoMnO6 and La2CuMnO6 maintain high C7H8 removal efficiencies of 100% and 98%, respectively, at 300°C and 30,000hr-1, and they also show good resistance to CO2 (5%) and H2O(g) (5%) of the gas streams tested. For various VOCs including isopropyl alcohol (C3H8O), ethanal (C2H4O), and ethylene (C2H4) tested, as high as 100% efficiency could be achieved with double perovskite-type catalysts operated at 300-350°C, indicating that double perovskites are promising catalysts for VOCs removal.
Amyloid fibers are classified as a new generation of tunable bionanomaterials that exhibit new functions related to their distinctive characteristics, such as their universality, tunability, and stiffness. Here, we introduce the catalytic residues of serine protease into a peptide catalyst (PC) via an enzyme-mimic approach. The rational design of a repeating pattern of polar and nonpolar amino acids favors the conversion of the peptides into amyloid-like fibrils via self-assembly. Distinct fibrous morphologies have been observed at different pH values and temperatures, which indicates that different fibril packing schemes can be designed; hence, fibrillar peptides can be used to generate efficient artificial catalysts for amidolytic activities at mild pH values. The results of atomic force microscopy, Raman spectroscopy, and wide-angle X-ray scattering analyses are used to discuss and compare the fibril structure of a fibrillar PC with its amidolytic activity. The pH of the fibrillation reaction crucially affects the pKa of the side chains of the catalytic triads and is important for stable fibril formation. Temperature is another important parameter that controls the self-assembly of peptides into highly stacked and laminated morphologies. The morphology and stability of fibrils are crucial and represent important factors for demonstrating the capability of the peptides to exert amidolytic activity. The observed amidolytic activity of PC4, one of the PCs, was validated using an inhibition assay, which revealed that PC4 can perform enzyme-like amidolytic catalysis. These results provide insights into the potential use of designed peptides in the generation of efficient artificial enzymes.
The hybrid electrochemical system of photocatalytic fuel cell - peroxi-coagulation (PFC-PC) is a combined technology of advanced oxidation process (AOP) which involve the hydroxyl radical formation for simultaneous degradation of organic pollutant and electricity generation. The p-nitrosodimethylaniline (RNO) spin trapping technique was applied by analyzing the RNO bleaching performance to detect the OH at the PFC and PC reactors. The presence of UV light showed higher RNO bleaching rate at the PFC reactor (11.7%) with maximum power density (Pmax = 3.14 mW cm-2). Results revealed that the optimum of maximum power density was observed at iron plate size of 30 cm2. UV light became a limiting factor in the PFC system as a power source in the PFC-PC system. Meanwhile, iron plate plays an important role to supply the soluble Fe2+ ions by oxidation process and become a suitable catalyst for in-situ production of H2O2 and OH through the PC process to degrade the organic molecules.
The main prerequisite of an active visible-light-driven photocatalyst is to effectively utilize the visible light to induce electron-hole (e-/h+) pairs of expanded lifetime. To this end, for the first time, the ternary heterojunctions of CeO2/Fe3O4 /Graphene oxide and Ce3+/ Fe3O4 /Graphene oxide (CeO2/Fe3O4/GO and Fe2.8Ce0.2O4/GO) were prepared via facile ultrasonic-assisted procedures and employed for destruction of oxytetracycline (OTC) under visible light irradiation. The changes in the relative crystal structure, morphology, atomic and surface functional group composition, magnetic, and optic properties of magnetite were uncovered by various techniques. The substantial degradation and mineralization of OTC via visible light/Fe2.8Ce0.2O4/GO system were thoroughly discussed in terms of narrowed band gap energy, the principal function of Ce3+/Ce4+ and Fe2+/Fe3+ redox pairs and GO platelets, enhanced charge separation and transfer, and enlarged active surface area. Furthermore, the performance of visible light/Fe2.8Ce0.2O4/GO system was evaluated for treating real wastewater and its efficiency was investigated using a number of enhancers and scavengers. Finally, the generated byproducts in the course of photodegradation were determined and the oxidation pathway, photocatalytic kinetics, and plausible mechanism were proposed. The results confirmed that the introduced Ce ions and graphene oxide sheets boost the photo-catalytic efficiency of magnetite for photodegradation of OTC.
Due to the increase in price of petroleum and environmental concerns, the search for alternative fuels has gained importance. In this work, biodiesel production by transesterification of palm oil with methanol has been studied in a heterogeneous system using sodium hydroxide loaded on alumina (NaOH/Al2O3). NaOH/Al2O3 catalyst was prepared by impregnation of alumina with different amount of an aqueous solution of sodium hydroxide followed by calcination in air for 3 h. The prepared catalysts were then characterized by using x-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunner-Emmett-Teller surface area measurement (BET), scanning electron microscopy (SEM) and temperature-programmed desorption of CO2 (CO2-TPD). Moreover, the dependence of the conversion of palm oil on the reactions variables such as the molar ratio of methanol/oil, the amount of catalysts used, reaction temperatures and reaction times were performed. The conversion of 99% was achieved under the optimum reaction conditions. The biodiesel obtained was characterized by FT-IR and the pour point was measured.