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

Waste valorization trough dehydrogenase enzymes immobilized on low-cost inorganic supports

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Enzymatic reduction of CO2 to formic acid using FDH immobilized on natural zeolite

The enzymatic strategy for methanol production starting from CO2 involves the use of three enzymes in series. The first enzyme of the series, which reduces CO2 to formic acid, is formate dehydrogenase (FDH). A problem with using free enzymes is their low stability. To overcome this limitation, the covalent immobilization on porous supports has been extensively studied in literature. This work presents a strategy of immobilization of the NADH dependent FDH from C. boidinii on natural zeolite to study the CO2 reduction reaction to formic acid. The support functionalization was carried out with glyoxyl (ZG) or amino (ZA) groups, to covalently bind the enzyme to the support. To carry out a covalent immobilization with ZA, glutaraldehyde was added after the ionic bond between the enzyme and the support. The samples were evaluated in terms of specific activity, immobilization yields and thermal stability. As a whole, the covalently immobilized enzyme exhibited higher thermal stability than the free enzyme, with a stability factor of ~15 with ZG and ~19 with ZA. Finally, FDH immobilized on ZG and ZA supports were tested for the production of formic acid in a CO2 saturated medium. The conversion, referred to NADH, was equal to 37 % with ZA and 34.6 % with ZG. Finally, the reusability of the biocatalysts was studied. The residual activity after 12 cycles was 80 % and 22 % with ZG and ZA, respectively

Augmented reality (AR) in minimally invasive surgery (MIS) training: where are we now in Italy? The Italian Society of Endoscopic Surgery (SICE) ARMIS survey

Minimally invasive surgery (MIS) is a widespread approach in general surgery. Computer guiding software, such as the augmented reality (AR), the virtual reality (VR) and mixed reality (MR), has been proposed to help surgeons during MIS. This study aims to report these technologies' current knowledge and diffusion during surgical training in Italy. A web-based survey was developed under the aegis of the Italian Society of Endoscopic Surgery (SICE). Two hundred and seventeen medical doctors' answers were analyzed. Participants were surgeons (138, 63.6%) and residents in surgery (79, 36.4%). The mean knowledge of the role of the VR, AR and MR in surgery was 4.9 ± 2.4 (range 1-10). Most of the participants (122, 56.2%) did not have experience with any proposed technologies. However, although the lack of experience in this field, the answers about the functioning of the technologies were correct in most cases. Most of the participants answered that VR, AR and MR should be used more frequently for the teaching and training and during the clinical activity (170, 80.3%) and that such technologies would make a significant contribution, especially in training (183, 84.3%) and didactic (156, 71.9%). Finally, the main limitations to the diffusion of these technologies were the insufficient knowledge (182, 83.9%) and costs (175, 80.6%). Based on the present study, in Italy, the knowledge and dissemination of these technologies are still limited. Further studies are required to establish the usefulness of AR, VR and MR in surgical training