Enzymatic Synthesis of Ascorbyl Palmitate in a Rotating Bed Reactor

Ascorbyl palmitate, an ascorbic acid ester, is an important amphipathic antioxidant that has several applications in foods, pharmaceuticals, and cosmetics. The enzymatic synthesis of ascorbyl palmitate is very attractive, but few efforts have been made to address its process scale-up and implementation. This study aimed at evaluating the enzymatic synthesis of ascorbyl palmitate in a rotating basket reactor operated in sequential batches. Different commercial immobilized lipases were tested, and the most suitable reaction conditions were established. Among those lipases studied were Amano Lipase PS, Lipozyme ® TL IM, Lipozyme ® Novo 40086, Lipozyme ® RM IM and Lipozyme ® 435. Initially, the enzymes were screened based on previously defined synthesis conditions, showing clear differences in behavior. Lipozyme ® 435 proved to be the best catalyst, reaching the highest values of initial reaction rate and yield. Therefore, it was selected for the following studies. Among the solvents assayed, 2-methyl-2-butanol and acetone showed the highest yields, but the operational stability of the catalyst was better in 2-methyl-2-butanol. The tests in a basket reactor showed great potential for large-scale application. Yields remained over 80% after four sequential batches, and the basket allowed for easy catalyst recycling. The results obtained in basket reactor are certainly a contribution to the enzymatic synthesis of ascorbyl palmitate as a competitive alternative to chemical synthesis. This may inspire future cost-effectiveness studies of the process to assess its potential as a viable alternative to be implemented

ZnO Materials as Effective Anodes for the Photoelectrochemical Regeneration of Enzymatically Active NAD+

This work reports the study of ZnO-based anodes for the photoelectrochemical regeneration of the oxidized form of nicotinamide adenine dinucleotide (NAD+). The latter is the most important coenzyme for dehydrogenases. However, the high costs of NAD+ limit the use of such enzymes at the industrial level. The influence of the ZnO morphologies (flower-like, porous film, and nanowires), showing different surface area and crystallinity, was studied. The detection of diluted solutions (0.1 mM) of the reduced form of the coenzyme (NADH) was accomplished by the flower-like and the porous films, whereas concentrations greater than 20 mM were needed for the detection of NADH with nanowire-shaped ZnO-based electrodes. The photocatalytic activity of ZnO was reduced at increasing concentrations of NAD+ because part of the ultraviolet irradiation was absorbed by the coenzyme, reducing the photons available for the ZnO material. The higher electrochemical surface area of the flower-like film makes it suitable for the regeneration reaction. The illumination of the electrodes led to a significant increase on the NAD+ regeneration with respect to both the electrochemical oxidation in dark and the only photochemical reaction. The tests with formate dehydrogenase demonstrated that 94% of the regenerated NAD+ was enzymatically active

Spin-Coated vs. Electrodeposited Mn Oxide Films as Water Oxidation Catalysts

Manganese oxides (MnOx), being active, inexpensive and low-toxicity materials, are considered promising water oxidation catalysts (WOCs). This work reports the preparation and the physico-chemical and electrochemical characterization of spin-coated (SC) films of commercial Mn2O3, Mn3O4 and MnO2 powders. Spin coating consists of few preparation steps and employs green chemicals (i.e., ethanol, acetic acid, polyethylene oxide and water). To the best of our knowledge, this is the first time SC has been used for the preparation of stable powder-based WOCs electrodes. For comparison, MnOx films were also prepared by means of lectrodeposition (ED) and tested under the same conditions, at neutral pH. Particular interest was given to -Mn2O3-based films, since Mn (III) species play a crucial role in the electrocatalytic oxidation of water. To this end, MnO2-based SC and ED films were calcined at 500 C, in order to obtain the desired -Mn2O3 crystalline phase. Electrochemical impedance spectroscopy (EIS) measurements were performed to study both electrode charge transport properties and electrode-electrolyte charge transfer kinetics. Long-term stability tests and oxygen/hydrogen evolution measurements were also made on the highest-performing samples and their faradaic efficiencies were quantified, with results higher than 95% for the Mn2O3 SC film, finally showing that the SC technique proposed here is a simple and reliable method to study the electrocatalytic behavior of pre-synthesized WOCs powders

Spin-Coated vs. Electrodeposited Mn Oxide Films as Water Oxidation Catalysts

Manganese oxides (MnOx), being active, inexpensive and low-toxicity materials, are considered promising water oxidation catalysts (WOCs). This work reports the preparation and the physico-chemical and electrochemical characterization of spin-coated (SC) films of commercial Mn2O3, Mn3O4 and MnO2 powders. Spin coating consists of few preparation steps and employs green chemicals (i.e., ethanol, acetic acid, polyethylene oxide and water). To the best of our knowledge, this is the first time SC has been used for the preparation of stable powder-based WOCs electrodes. For comparison, MnOx films were also prepared by means of lectrodeposition (ED) and tested under the same conditions, at neutral pH. Particular interest was given to -Mn2O3-based films, since Mn (III) species play a crucial role in the electrocatalytic oxidation of water. To this end, MnO2-based SC and ED films were calcined at 500 C, in order to obtain the desired -Mn2O3 crystalline phase. Electrochemical impedance spectroscopy (EIS) measurements were performed to study both electrode charge transport properties and electrode–electrolyte charge transfer kinetics. Long-term stability tests and oxygen/hydrogen evolution measurements were also made on the highest-performing samples and their faradaic efficiencies were quantified, with results higher than 95% for the Mn2O3 SC film, finally showing that the SC technique proposed here is a simple and reliable method to study the electrocatalytic behavior of pre-synthesized WOCs powders

Modification and characterization of clinoptilolite for the co-immobilization of formate dehydrogenase and glycerol dehydrogenase enzymes

In the last decades there is a rising concern for the increasing concentration of carbon dioxide, considered the major responsible of Global Warming. A solution to this critical issue is the catalytic conversion of CO2 into high value-added products. Among the different strategies that could be applied, the enzymatic process of CO2 reduction to methanol, employing a sequence of three enzyme-catalyzed reactions, seems to be very promising. The simultaneous employment of formate dehydrogenase and glycerol dehydrogenase allows to reduce CO2 to formic acid, the first of the sequential reactions, and at the same time regenerate the nicotinamide cofactor, that is very expensive. To reuse enzymes, with a consequential reduction of cost, and increased their stability, they can be immobilized on a proper support. In this context, porous materials, such as zeolites, present appropriate features to be suitable for enzymes immobilization. In particular, they are well suited for the covalent immobilization technique due to the fact that they can be functionalized with different functional groups. Natural zeolites, like Clinoptilolite have the advantage to be low-cost materials largely diffused in different part of the world. Clinoptilolite was subjected to dealumination-desilication treatments to modify the zeolite’s morphology, increasing its specific surface area. According to the literature, the dealumination procedure was done with sequential acid attacks using HCl solutions. Instead, for the subsequent desilication process NaOH solution is required. The effects of desilication-dealumination treatments were investigated through complementary techniques such as N2 physisorption at -196 °C, XRD and SEM. The analysis revealed that the Clinoptilolite specific surface area increased by 400% following the dealumination-desilication procedure; at the same time the XRD analysis shows that the processed Clinoptilolite has the same main peaks of the unmodified one. Finally, the retained activity and the stability of the immobilized enzymes were evaluated, the results show that these aspects were enhanced by the modification through acid-alkaline attacks of the Clinoptilolite

Simultaneous CO2 reduction and NADH regeneration using formate and glycerol dehydrogenase enzymes co-immobilized on modified natural zeolite

In this work, the co-immobilization of formate dehydrogenase (FDH) and glycerol dehydrogenase (GlyDH) enzymes is proposed to reduce CO(2) into formic acid, an important chemical intermediate. The reduction of carbon dioxide is carried out by FDH to obtain formic acid, simultaneously, the GlyDH regenerated the nicotinamide cofactor in the reduced form (NADH) by the oxidation of glycerol into dihydroxyacetone. Natural zeolite was selected as immobilization support given its good properties and low cost. The natural zeolite was modified with subsequent acid-alkaline attacks to obtain a mesostructurization of the clinoptilolite. The two enzymes were co-immobilized on clinoptilolite, previously hetero-functionalized with amino and glyoxyl groups. The distribution of the enzymes was confirmed by fluorescence microscopy analysis. Furthermore, a great increase in the retained activity for the formate dehydrogenase enzyme was noted, passing from 18% to 89%, when the mesostructured clinoptilolite was used as support. The immobilization yield of formate dehydrogenase and glycerol dehydrogenase is around 100% with all the supports studied. The promising results suggest a possible development of this procedure in enzyme immobilization and biocatalysis. The biocatalysts were characterized to find the optimal pH and temperature. Furthermore, a thermal stability test at 50 °C was carried out on both enzymes, in free and immobilized forms. Finally, it was shown that the biocatalyst is effective in reducing CO(2), both by using the cofactor in the reduced form (NADH) or the oxidized form (NAD(+)), obtaining NADH through the regeneration with glycerol in this latter case

Recovery of humic acids from anaerobic sewage sludge: Extraction, characterization and encapsulation in alginate beads

Wastewater production is rising all over the world and one of the most difficult problems is the disposal of sewage sludge (SS). It is known that SS contains certain quantities of added-value compounds, such as humic acids (HA) which in turn have beneficial effects on soil quality and plant growth. On the other hand, SS can retain many pollutants, such as heavy metals. The present work aimed to implement an HA alkaline extraction protocol from anaerobic sewage sludge (ASS). Subsequently, the HA were quantified in ASS, in HA extract and in commercial HA, used as a benchmark, which gave results of 12.53%, 26.87% and 77.87% (on dry matter basis), respectively. FESEM and EDX analyses on lyophilized HA extract confirmed that no heavy metals had passed into the extract. Afterwards, in order to allow controlled release of the HA in soils, alginate beads containing the HA extract were created. Finally, a pot experiment in a greenhouse was performed using Chilean lettuce plants (Lactuca sativa L.) treated with alginate-HA extract beads. At the end of the greenhouse experiments, the hypogean dry biomass of the treated plants was significantly higher than for non-treated plants. The relevance of this study relies not only on the exploitation of green chemistry principles, by converting a waste stream into a high-value product, but also on the application of an approach following a circular economy model

Correction: Core-substituted naphthalenediimides anchored on BiVO4 for visible light-driven water splitting

Correction for 'Core-substituted naphthalenediimides anchored on BiVO4 for visible light-driven water splitting' by Simelys Hernández et al., Green Chem., 2017, 19, 2448–2462

Heterogeneous and Heterogenized Catalysts for Water Oxidation Reaction as Studied by Means of Sacrificial Oxidant

Hydrogen production from solar-driven water splitting (WS) reaction is considered a promising way to store solar energy. This process can be achieved directly by means of a photo-electrochemical cell (PEC), where light absorption, charge separation and WS occur in a single device; or indirectly, by coupling a photovoltaic device to an electrolyzer. WS is a thermodynamically uphill reaction, formed by two half reactions, i.e. the reduction of protons into H2 and the oxidation of water into O2. From a kinetic point of view, the latter is the most challenging one, being generally considered as the bottleneck for a widespread use of WS for hydrogen production. Thus, regardless of whether WS is carried out in direct or indirect configurations, the efficiency of the water oxidation catalyst (WOC) is a key determinant of the overall energy storage efficiency. The present thesis fits within this context, being focused on the study of different WOCs based on earth abundant elements (i.e. Mn and Co). Different heterogeneous Mn-based WOCs were studied, including: (i) different crystal structures of Mn oxides, both commercial and lab-made (i.e. MnO2, Mn3O4 and Mn2O3); (ii) a calcium manganese oxide (containing Ca2Mn3O8 and CaMn2O4) and (iii) lanthanum manganites (LaMnO3) prepared via sol-gel (SG) and flame spray pyrolysis (FP). On the other hand, the heterogenization of a homogeneous Co based WOC, i.e. the polyoxometalate Na10[Co4(H2O)2(PW9O34)2] (CoPOM), was investigated, as well. CoPOM is known to be a highly active WOC, comprising an active {Co4O4} core stabilized by oxidatively resistant polytungstate ligands. Transferring its solution reactivity to solid substrates is a fundamental step in the realization of a PEC