Pub Date : 2022-12-14DOI: 10.3389/fctls.2022.1021691
Bianca Kerschbaumer, A. Bijelic, P. Macheroux
Fungi produce a plethora of natural products exhibiting a fascinating diversity of chemical structures with an enormous potential for medical applications. Despite the importance of understanding the scope of natural products and their biosynthetic pathways, a systematic analysis of the involved enzymes has not been undertaken. In our previous studies, we examined the flavoprotein encoding gene pool in archaea, eubacteria, the yeast Saccharomyces cerevisiae, Arabidopsis thaliana, and Homo sapiens. In the present survey, we have selected the model fungus Neurospora crassa as a starting point to investigate the flavoproteomes in the fungal kingdom. Our analysis showed that N. crassa harbors 201 flavoprotein-encoding genes amounting to 2% of the total protein-encoding genome. The majority of these flavoproteins (133) could be assigned to primary metabolism, termed the “core flavoproteome”, with the remainder of flavoproteins (68) serving in, as yet unidentified, reactions. The latter group of “accessory flavoproteins” is dominated by monooxygenases, berberine bridge enzyme-like enzymes, and glucose-methanol-choline-oxidoreductases. Although the exact biochemical role of most of these enzymes remains undetermined, we propose that they are involved in activities closely associated with fungi, such as the degradation of lignocellulose, the biosynthesis of natural products, and the detoxification of harmful compounds in the environment. Based on this assumption, we have analyzed the accessory flavoproteomes in the fungal kingdom using the MycoCosm database. This revealed large differences among fungal divisions, with Ascomycota, Basidiomycota, and Mucoromycota featuring the highest average number of genes encoding accessory flavoproteins. Moreover, a more detailed analysis showed a massive accumulation of accessory flavoproteins in Sordariomycetes, Agaricomycetes, and Glomeromycotina. In our view, this indicates that these fungal classes are proliferative producers of natural products and also interesting sources for flavoproteins with potentially useful catalytic properties in biocatalytic applications.
{"title":"Flavofun: Exploration of fungal flavoproteomes","authors":"Bianca Kerschbaumer, A. Bijelic, P. Macheroux","doi":"10.3389/fctls.2022.1021691","DOIUrl":"https://doi.org/10.3389/fctls.2022.1021691","url":null,"abstract":"Fungi produce a plethora of natural products exhibiting a fascinating diversity of chemical structures with an enormous potential for medical applications. Despite the importance of understanding the scope of natural products and their biosynthetic pathways, a systematic analysis of the involved enzymes has not been undertaken. In our previous studies, we examined the flavoprotein encoding gene pool in archaea, eubacteria, the yeast Saccharomyces cerevisiae, Arabidopsis thaliana, and Homo sapiens. In the present survey, we have selected the model fungus Neurospora crassa as a starting point to investigate the flavoproteomes in the fungal kingdom. Our analysis showed that N. crassa harbors 201 flavoprotein-encoding genes amounting to 2% of the total protein-encoding genome. The majority of these flavoproteins (133) could be assigned to primary metabolism, termed the “core flavoproteome”, with the remainder of flavoproteins (68) serving in, as yet unidentified, reactions. The latter group of “accessory flavoproteins” is dominated by monooxygenases, berberine bridge enzyme-like enzymes, and glucose-methanol-choline-oxidoreductases. Although the exact biochemical role of most of these enzymes remains undetermined, we propose that they are involved in activities closely associated with fungi, such as the degradation of lignocellulose, the biosynthesis of natural products, and the detoxification of harmful compounds in the environment. Based on this assumption, we have analyzed the accessory flavoproteomes in the fungal kingdom using the MycoCosm database. This revealed large differences among fungal divisions, with Ascomycota, Basidiomycota, and Mucoromycota featuring the highest average number of genes encoding accessory flavoproteins. Moreover, a more detailed analysis showed a massive accumulation of accessory flavoproteins in Sordariomycetes, Agaricomycetes, and Glomeromycotina. In our view, this indicates that these fungal classes are proliferative producers of natural products and also interesting sources for flavoproteins with potentially useful catalytic properties in biocatalytic applications.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46111178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-12DOI: 10.3389/fctls.2022.1072692
C. Ehm, D. Stephan
Fluorescent tubes, a continuous source of UVA radiation, are increasingly being replaced by ultraviolet light-emitting diodes (UV LEDs or UVEDs), which emit an almost discrete spectrum (5 nm bandwidth). This creates both problems and opportunities from a photocatalytic point of view. In this paper, we report the influence of UVED radiation on the performance of an industrially produced TiO2 photocatalytic coating by measuring the degradation of nitrogen oxide (NO) and toluene (C6H5CH3) from a test atmosphere in a laboratory test setup. The influence of four commercially available UVED types (365 nm, 385 nm, 395 nm, and 415 nm) on the performance of a commonly used photocatalyst was compared. In a subsequent investigation, we switched from continuous to pulse-modulated LED operation and investigated its influence on the photocatalytic activity of the assembly. We could show that UVEDs are suitable replacements for fluorescent lamps when carefully chosen to the absorption spectrum of the used photocatalyst. In addition, the pulse width and pulse frequency modulation of the LED current show non-linear correlations with the resulting photocatalytic activity. The activity remains unexpectedly high with short pulse widths and low frequencies. By adjusting the control of the UVEDs accordingly, much energy can thus be saved during operation without reducing the catalytic activity.
{"title":"The influence of pulse modulated UV LEDs of different wavelengths on the photocatalytic degradation of atmospheric toluene and NO","authors":"C. Ehm, D. Stephan","doi":"10.3389/fctls.2022.1072692","DOIUrl":"https://doi.org/10.3389/fctls.2022.1072692","url":null,"abstract":"Fluorescent tubes, a continuous source of UVA radiation, are increasingly being replaced by ultraviolet light-emitting diodes (UV LEDs or UVEDs), which emit an almost discrete spectrum (5 nm bandwidth). This creates both problems and opportunities from a photocatalytic point of view. In this paper, we report the influence of UVED radiation on the performance of an industrially produced TiO2 photocatalytic coating by measuring the degradation of nitrogen oxide (NO) and toluene (C6H5CH3) from a test atmosphere in a laboratory test setup. The influence of four commercially available UVED types (365 nm, 385 nm, 395 nm, and 415 nm) on the performance of a commonly used photocatalyst was compared. In a subsequent investigation, we switched from continuous to pulse-modulated LED operation and investigated its influence on the photocatalytic activity of the assembly. We could show that UVEDs are suitable replacements for fluorescent lamps when carefully chosen to the absorption spectrum of the used photocatalyst. In addition, the pulse width and pulse frequency modulation of the LED current show non-linear correlations with the resulting photocatalytic activity. The activity remains unexpectedly high with short pulse widths and low frequencies. By adjusting the control of the UVEDs accordingly, much energy can thus be saved during operation without reducing the catalytic activity.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48768336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-11-22DOI: 10.3389/fctls.2022.1049179
Qinglong Meng, Carlos Ramírez-Palacios, Hein J. Wijma, D. Janssen
Protein engineering is a powerful and widely applied tool for tailoring enzyme properties to meet application-specific requirements. An attractive group of biocatalysts are PLP-dependent amine transaminases which are capable of converting prochiral ketones to the corresponding chiral amines by asymmetric catalysis. The enzymes often display high enantioselectivity and accept various amine donors. Practical applications of these amine transaminases can be hampered by enzyme instability and by their limited substrate scope. Various strategies to improve robustness of amine transaminases and to redirect their substrate specificity have been explored, including directed evolution, rational design and computation-supported engineering. The approaches used and results obtained are reviewed in this paper, showing that different strategies can be used in a complementary manner and can expand the applicability of amine transaminases in biocatalysis.
{"title":"Protein engineering of amine transaminases","authors":"Qinglong Meng, Carlos Ramírez-Palacios, Hein J. Wijma, D. Janssen","doi":"10.3389/fctls.2022.1049179","DOIUrl":"https://doi.org/10.3389/fctls.2022.1049179","url":null,"abstract":"Protein engineering is a powerful and widely applied tool for tailoring enzyme properties to meet application-specific requirements. An attractive group of biocatalysts are PLP-dependent amine transaminases which are capable of converting prochiral ketones to the corresponding chiral amines by asymmetric catalysis. The enzymes often display high enantioselectivity and accept various amine donors. Practical applications of these amine transaminases can be hampered by enzyme instability and by their limited substrate scope. Various strategies to improve robustness of amine transaminases and to redirect their substrate specificity have been explored, including directed evolution, rational design and computation-supported engineering. The approaches used and results obtained are reviewed in this paper, showing that different strategies can be used in a complementary manner and can expand the applicability of amine transaminases in biocatalysis.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49260069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-11-01DOI: 10.3389/fctls.2022.1006564
Diego Flores-Oña, A. Fullana
In the present study, the photocatalytic activity of carbon nanoparticles (CNPs) in the degradation of methylene blue (MB) using sunlight was analyzed. The CNPs were synthesized by solvent-assisted hydrothermal carbonization (HTC) and were characterized by various spectroscopic techniques: TEM and SEM microscopy, UV-Vis, FTIR, Fluorescence, and XPS. By changing the conditions of the HTC process, the surface chemistry of CNPs was functionalized, thus a great quantity of oxygenated functional groups was generated, which eventually influenced the photocatalytic process. Next, tests were carried out with different types of nanoparticles, varying the concentration of the dye and the type of light used in the irradiation. As a result of this, more than 93% of MB degradation was achieved in 20 min of irradiation using sunlight. This result is promising since it has not been achieved by other nanomaterial. This research can be a potential starting point for the development of new solar photocatalysts.
{"title":"High efficient solar photocatalytic carbon nanoparticles","authors":"Diego Flores-Oña, A. Fullana","doi":"10.3389/fctls.2022.1006564","DOIUrl":"https://doi.org/10.3389/fctls.2022.1006564","url":null,"abstract":"In the present study, the photocatalytic activity of carbon nanoparticles (CNPs) in the degradation of methylene blue (MB) using sunlight was analyzed. The CNPs were synthesized by solvent-assisted hydrothermal carbonization (HTC) and were characterized by various spectroscopic techniques: TEM and SEM microscopy, UV-Vis, FTIR, Fluorescence, and XPS. By changing the conditions of the HTC process, the surface chemistry of CNPs was functionalized, thus a great quantity of oxygenated functional groups was generated, which eventually influenced the photocatalytic process. Next, tests were carried out with different types of nanoparticles, varying the concentration of the dye and the type of light used in the irradiation. As a result of this, more than 93% of MB degradation was achieved in 20 min of irradiation using sunlight. This result is promising since it has not been achieved by other nanomaterial. This research can be a potential starting point for the development of new solar photocatalysts.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41535265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-14DOI: 10.3389/fctls.2022.1032088
M. Ansorge‐Schumacher, Christoph Plikat
Considering the importance of biocatalysis in chemical synthesis, technologies allowing full exploitation of its potential are urgently wanted. Eleven years ago, our team proposed Pickering emulsions as a concept to overcome the severe restrictions set by the general requirement for the presence of water. In this brief perspective, we demonstrate that the insights into bioactive Pickering emulsions gathered meanwhile strongly designate it a key technology to non-aqueous and multi-step biocatalysis. Mainly, this relates to the extensive compatibility of this system with different solvents, materials, biocatalysts, reactions and demands on productive use. We here give a brief overview of the most relevant details, including recent results from our own research.
{"title":"Key technology to non-aqueous and multi-step biocatalysis: Pickering emulsions","authors":"M. Ansorge‐Schumacher, Christoph Plikat","doi":"10.3389/fctls.2022.1032088","DOIUrl":"https://doi.org/10.3389/fctls.2022.1032088","url":null,"abstract":"Considering the importance of biocatalysis in chemical synthesis, technologies allowing full exploitation of its potential are urgently wanted. Eleven years ago, our team proposed Pickering emulsions as a concept to overcome the severe restrictions set by the general requirement for the presence of water. In this brief perspective, we demonstrate that the insights into bioactive Pickering emulsions gathered meanwhile strongly designate it a key technology to non-aqueous and multi-step biocatalysis. Mainly, this relates to the extensive compatibility of this system with different solvents, materials, biocatalysts, reactions and demands on productive use. We here give a brief overview of the most relevant details, including recent results from our own research.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43458214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-23DOI: 10.3389/fctls.2022.867811
Jan-Moritz Sutter, Daniel E. Mitchell, M. Schmidt, M. Isupov, J. Littlechild, P. Schönheit
A branched chain aminotransferase from Thermoproteus tenax has been identified, cloned, over-expressed and biochemically characterised. A molecular modelling approach has been used to predict the 3D structure allowing its comparison with other related enzymes. This enzyme has high similarity to a previously characterised aminotransferase from Thermoproteus uzoniensis however its substrate specificity shows key differences towards the substrate α-ketoglutarate. Examination of the active sites of the two related enzymes reveals a single amino acid substitution of a glycine residue to a serine residue which could be responsible for this difference. When Gly104 in T. tenax was mutated to a serine residue and the resultant enzyme characterised, this single amino acid change resulted in a dramatic reduction in activity towards α-ketoglutarate with an 18-fold reduction in Vmax and a 20-fold Km increase, resulting in a 370-fold lower catalytic efficiency. Structural comparisons between the two related Thermoproteus enzymes and another branched chain aminotransferase from Geoglobus acetivorans has revealed that the serine residue affects the flexibility of a key loop involved in catalysis. This subtle difference has provided further insight into our understanding of the substrate specificity of these industrially important enzymes.
{"title":"Substrate specificity of branched chain amino acid aminotransferases: The substitution of glycine to serine in the active site determines the substrate specificity for α-ketoglutarate","authors":"Jan-Moritz Sutter, Daniel E. Mitchell, M. Schmidt, M. Isupov, J. Littlechild, P. Schönheit","doi":"10.3389/fctls.2022.867811","DOIUrl":"https://doi.org/10.3389/fctls.2022.867811","url":null,"abstract":"A branched chain aminotransferase from Thermoproteus tenax has been identified, cloned, over-expressed and biochemically characterised. A molecular modelling approach has been used to predict the 3D structure allowing its comparison with other related enzymes. This enzyme has high similarity to a previously characterised aminotransferase from Thermoproteus uzoniensis however its substrate specificity shows key differences towards the substrate α-ketoglutarate. Examination of the active sites of the two related enzymes reveals a single amino acid substitution of a glycine residue to a serine residue which could be responsible for this difference. When Gly104 in T. tenax was mutated to a serine residue and the resultant enzyme characterised, this single amino acid change resulted in a dramatic reduction in activity towards α-ketoglutarate with an 18-fold reduction in Vmax and a 20-fold Km increase, resulting in a 370-fold lower catalytic efficiency. Structural comparisons between the two related Thermoproteus enzymes and another branched chain aminotransferase from Geoglobus acetivorans has revealed that the serine residue affects the flexibility of a key loop involved in catalysis. This subtle difference has provided further insight into our understanding of the substrate specificity of these industrially important enzymes.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42296032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carbon dioxide reduction reaction (CO2RR) is a promising approach to accomplishing net zero CO2 emissions. Among CO2RR catalysts, nitrogen-doped graphene-supported single-atom catalysts show a remarkable conversion rate from CO2 to CO; however, the low production amount has been limited using the conversion H cell, hindering its industrial development. In this work, we synthesize a nitrogen-doped graphene-supported nickel-single-atom catalyst and conduct CO2RR in a flow cell, exhibiting a CO2-to-CO Faradaic efficiency of 96% and a partial current density of 144 mA cm−2. It can also achieve the highest partial current density of 204 mA cm−2 with a turnover frequency of 7,852 h−1. According to the techno-economic analysis, these preeminent activities meet the industrial criteria (Faradaic efficiency >60% and partial current density >100 mA cm−2). This activity enhancement using a flow system can significantly accelerate net-zero CO2 emission realization.
二氧化碳还原反应（CO2RR）是实现二氧化碳净零排放的一种很有前途的方法。在CO2RR催化剂中，氮掺杂石墨烯负载的单原子催化剂表现出显著的CO2向CO的转化率；然而，使用转化H电池的低产量受到限制，阻碍了其工业发展。在这项工作中，我们合成了一种氮掺杂石墨烯负载的镍单原子催化剂，并在流动池中进行CO2RR，表现出96%的CO2对CO法拉第效率和144 mA cm−2的部分电流密度。它还可以实现204 mA cm−2的最高局部电流密度，转换频率为7852 h−1。根据技术经济分析，这些卓越的活动符合工业标准（法拉第效率>60%，局部电流密度>100 mA cm−2）。使用流动系统的这种活动增强可以显著加速CO2净零排放的实现。
{"title":"A nitrogen-doped graphene-supported nickel-single-atom catalyst in the flow cell meets the industrial criteria of carbon dioxide reduction reaction to carbon monoxide","authors":"Y. Lu, Hsin-Jung Tsai, Wen Huang, Tsung-Ju Lee, Zih-Yi Lin, Shao-Hui Hsu, Sung-Fu Hung","doi":"10.3389/fctls.2022.915971","DOIUrl":"https://doi.org/10.3389/fctls.2022.915971","url":null,"abstract":"Carbon dioxide reduction reaction (CO2RR) is a promising approach to accomplishing net zero CO2 emissions. Among CO2RR catalysts, nitrogen-doped graphene-supported single-atom catalysts show a remarkable conversion rate from CO2 to CO; however, the low production amount has been limited using the conversion H cell, hindering its industrial development. In this work, we synthesize a nitrogen-doped graphene-supported nickel-single-atom catalyst and conduct CO2RR in a flow cell, exhibiting a CO2-to-CO Faradaic efficiency of 96% and a partial current density of 144 mA cm−2. It can also achieve the highest partial current density of 204 mA cm−2 with a turnover frequency of 7,852 h−1. According to the techno-economic analysis, these preeminent activities meet the industrial criteria (Faradaic efficiency >60% and partial current density >100 mA cm−2). This activity enhancement using a flow system can significantly accelerate net-zero CO2 emission realization.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41396963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-30DOI: 10.3389/fctls.2022.991270
Nicola Panza, M. Alberti, C. Damiano, A. Caselli
We have recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA] 2 [ZnBr 4 ] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h−1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2.
{"title":"Ammonium zincates as suitable catalyst for the room temperature cycloaddition of CO2 to epoxides","authors":"Nicola Panza, M. Alberti, C. Damiano, A. Caselli","doi":"10.3389/fctls.2022.991270","DOIUrl":"https://doi.org/10.3389/fctls.2022.991270","url":null,"abstract":"We have recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA] 2 [ZnBr 4 ] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h−1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48922505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-24DOI: 10.3389/fctls.2022.950384
Buzuayehu Abebe
Improvement in the synthesis techniques and their optimum properties to be up-to-date is the global need for industrially scalable applications. The sol–gel solution combustion synthesis (SG-SCS) approach is an easy, time-/energy-efficient, and creates regularly ordered porous materials that have significance in the ion-/mass-transport phenomenon. Furthermore, the approach also yields a decent heterojunction once optimized via the HSAB theory. Forming a heterojunction also tunes the crucial properties of the materials, thus, boosting the photocatalytic ability through charge transfer or/and synergistic roles. From the stability investigation results, the calcination temperature of 500°C is determined to be ideal. The X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) techniques confirmed the nanoscale size of the NPs and NCs. The porous nature of the materials is revealed from the scanning electron microscopy micrographs and BET analysis; consistent results are also noted from selected area electron diffraction and HRTEM. The detected stacking faults on the IFFT image of HRTEM also confirmed the porous properties of the NCs. The precise elemental composition and local heterojunction within Zn/Fe(III)/Mn(III) oxides were confirmed in the HRTEM, X-ray photoelectron spectroscopy, and energy-dispersive X-ray studies. The significant charge transfer capability of the NCs more than bare ZnO was evidenced from the electrochemical analysis. The NCs were also effective on acid orange 8 (AO8) and Congo red (CR) dye degradations.
{"title":"Synergetic and charge transfer properties of a metal oxide heterojunction: Photocatalytic activities","authors":"Buzuayehu Abebe","doi":"10.3389/fctls.2022.950384","DOIUrl":"https://doi.org/10.3389/fctls.2022.950384","url":null,"abstract":"Improvement in the synthesis techniques and their optimum properties to be up-to-date is the global need for industrially scalable applications. The sol–gel solution combustion synthesis (SG-SCS) approach is an easy, time-/energy-efficient, and creates regularly ordered porous materials that have significance in the ion-/mass-transport phenomenon. Furthermore, the approach also yields a decent heterojunction once optimized via the HSAB theory. Forming a heterojunction also tunes the crucial properties of the materials, thus, boosting the photocatalytic ability through charge transfer or/and synergistic roles. From the stability investigation results, the calcination temperature of 500°C is determined to be ideal. The X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) techniques confirmed the nanoscale size of the NPs and NCs. The porous nature of the materials is revealed from the scanning electron microscopy micrographs and BET analysis; consistent results are also noted from selected area electron diffraction and HRTEM. The detected stacking faults on the IFFT image of HRTEM also confirmed the porous properties of the NCs. The precise elemental composition and local heterojunction within Zn/Fe(III)/Mn(III) oxides were confirmed in the HRTEM, X-ray photoelectron spectroscopy, and energy-dispersive X-ray studies. The significant charge transfer capability of the NCs more than bare ZnO was evidenced from the electrochemical analysis. The NCs were also effective on acid orange 8 (AO8) and Congo red (CR) dye degradations.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46769250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-05DOI: 10.3389/fctls.2022.952944
E. Eppinger, J. Gröning, A. Stolz
The conversion of rac-phenylglycinonitrile by different variants of the nitrilase from Pseudomonas fluorescens EBC191 (EC 3.5.5.1) was studied and the amounts and chiral composition of the formed phenylglycine and phenylglycine amide compared. Muteins that converted rac-phenylglycinonitrile to extraordinarily high amounts of phenylglycine or phenylglycine amide were tested for the chemoenzymatic enantioselective one-pot synthesis of (R)- and (S)-phenylglycine and (R)- and (S)-phenylglycine amide. The chemoenzymatic synthesis combined the initial step in the traditional chemical Strecker synthesis which results in the formation of rac-phenylglycinonitrile from benzaldehyde, cyanide, and ammonia with the enzymatic conversion of the formed nitrile by the nitrilase variants. The aminonitrile synthesis was optimized in order to obtain conditions which allowed under mildly alkaline conditions (pH 9.5) maximal yields of phenylglycinonitrile and the in-situ racemization of the compound. The racemic phenylglycinonitrile was directly converted under the alkaline conditions without any interposed purification step by cells of Escherichia coli overexpressing recombinant nitrilase variants. The application of a mutant of E. coli defect in a (S)-phenylglycine amide hydrolysing peptidase (E. coli JM109ΔpepA) expressing a highly reaction- and (R)-specific nitrilase variant allowed the synthesis of (R)-phenylglycine with ee-values ≥ 95% in yields up to 81% in relation to the initially added benzaldehyde. These yields indicated a dynamic kinetic resolution which involved the racemization of (S)- to (R)-phenylglycinonitrile under the used alkaline conditions with the concurrent hydrolysis of (R)-phenylglycinonitrile to (R)-phenylglycine. The addition of resting cells of E. coli JM109ΔpepA synthesizing an amide forming nitrilase variant to the final product of the Strecker synthesis and/or using E. coli strains with an intact aminopeptidase gene resulted in the preferred formation of (S)-phenylglycine amide, (R)-phenylglycine amide or (S)-phenylglycine.
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