Journal articles on the topic 'Non-natural reactions'
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1
SAIGO, Kazuhiko, Atsushi SUDO, and Yukihiko HASHIMOTO. "Asymmetric Reactions Using Non-natural Chiral Auxiliaries." Journal of Synthetic Organic Chemistry, Japan 56, no. 5 (1998): 386–94. http://dx.doi.org/10.5059/yukigoseikyokaishi.56.386.
2
Harms, Vanessa, Andreas Kirschning, and Jeroen S. Dickschat. "Nature-driven approaches to non-natural terpene analogues." Natural Product Reports 37, no. 8 (2020): 1080–97. http://dx.doi.org/10.1039/c9np00055k.
3
Hyster, Todd K. "Radical Biocatalysis: Using Non-Natural Single Electron Transfer Mechanisms to Access New Enzymatic Functions." Synlett 31, no. 03 (May 7, 2019): 248–54. http://dx.doi.org/10.1055/s-0037-1611818.
Abstract:
Exploiting non-natural reaction mechanisms within native enzymes is an emerging strategy for expanding the synthetic capabilities of biocatalysts. When coupled with modern protein engineering techniques, this approach holds great promise for biocatalysis to address long-standing selectivity and reactivity challenges in chemical synthesis. Controlling the stereochemical outcome of reactions involving radical intermediates, for instance, could benefit from biocatalytic solutions because these reactions are often difficult to control by using existing small molecule catalysts. General strategies for catalyzing non-natural radical reactions within enzyme active sites are, however, undeveloped. In this account, we highlight three distinct strategies developed in our group that exploit non-natural single electron transfer mechanisms to unveil previously unknown radical biocatalytic functions. These strategies allow common oxidoreductases to be used to address the enduring synthetic challenge of asymmetric hydrogen atom transfer.1 Introduction2 Photoinduced Electron Transfer from NADPH3 Ground State Electron Transfer from Flavin Hydroquinone4 Enzymatic Redox Activation in NADPH-Dependent Oxidoreductases5 Conclusion
4
Hyster, Todd K., and Thomas R. Ward. "Genetic Optimization of Metalloenzymes: Enhancing Enzymes for Non-Natural Reactions." Angewandte Chemie International Edition 55, no. 26 (March 11, 2016): 7344–57. http://dx.doi.org/10.1002/anie.201508816.
5
Gober, Joshua G., and Eric M. Brustad. "Non-natural carbenoid and nitrenoid insertion reactions catalyzed by heme proteins." Current Opinion in Chemical Biology 35 (December 2016): 124–32. http://dx.doi.org/10.1016/j.cbpa.2016.09.004.
6
Wang, Zhipeng A., Yan-Yu Liang, and Ji-Shen Zheng. "Reductive Amination/Alkylation Reactions: The Recent Developments, Progresses, and Applications in Protein Chemical Biology Studies." Current Organic Synthesis 15, no. 6 (August 29, 2018): 755–61. http://dx.doi.org/10.2174/1570179415666180522093905.
Abstract:
The chemical modifications of proteins or protein complexes have been a challenging but fruitful task in the post-genomic era. Bioorthogonal reactions play an important role for the purpose of selective functionalization, localization, and labeling of proteins with natural or non-natural structures. Among these reactions, reductive amination stands out as one of the typical bioorthogonal reactions with high efficiency, good biocompatibility, and versatile applications. However, not many specific reviews exist to discuss the mechanism, kinetics, and their applications in a detailed manner. In this manuscript, we aim to summarize some current developments and mechanistic studies of reductive amination reaction and its applications. We hope reductive amination reaction can contribute to a wider scope of protein chemistry research en route in the chemical biology frontier as one of the well-known bioorthogonal reactions.
7
Taylor, James S., and Yung-Hian Leow. "Cutaneous Reactions to Rubber." Rubber Chemistry and Technology 73, no. 3 (July 1, 2000): 427–85. http://dx.doi.org/10.5254/1.3547600.
Abstract:
Abstract The three major adverse cutaneous reactions to rubber include natural rubber latex allergy, irritant contact dermatitis and allergic contact dermatitis. An overview of relevant aspects of the types of natural and synthetic rubber, rubber production, and specific chemicals used in compounding and vulcanization, as well as latex proteins is essential to an understanding of these reactions. Natural rubber latex allergy is a type I, IgE mediated, immediate hypersensitivity reaction to one or more proteins present in natural rubber latex with clinical manifestations ranging from contact urticaria to allergic rhinitis, asthma, and anaphylaxis. Over the past decade, natural rubber latex allergy has become a major medical, occupational health, and medicolegal problem. Individuals at highest risk are patients with spina bifida and health care workers. Diagnosis is based largely on clinical history and examination, and serologic and intracutaneous testing. Irritant contact dermatitis is non-immunologic and is the most common cutaneous reaction to rubber. Cumulative exposure to low-grade irritants impairs the barrier function of the skin and allows penetration of potential irritants and allergens. Diagnosis is based on history of exposure to known irritants, cutaneous examination, and exclusion of allergy. Allergic contact dermatitis is a type IV cell mediated, delayed hypersensitivity reaction which occurs primarily from exposure to rubber chemicals either directly or from residual amounts present in rubber products. Most cases present with an eczematous dermatitis, but purpura, lichenoid dermatitis, and depigmentation occasionally occur. Diagnosis is made on the basis of history, examination, and epicutaneous patch testing with rubber chemicals and rubber products. Treatment is with allergen and irritant avoidance and substitution, environmental control, personal protective equipment and topical and systemic pharmacologic therapy. A unified approach is needed in the diagnosis and treatment of adverse cutaneous reactions to rubber and it is important to remember that some patients may have both contact dermatitis and natural latex allergy. Determining the bioavailability and elicitation threshold of rubber allergens may be helpful in reducing allergic reactions from consumer and industrial rubber products.
8
Xu, Guangcai, Michele Crotti, Thangavelu Saravanan, Kim M. Kataja, and Gerrit J. Poelarends. "Enantiocomplementary Epoxidation Reactions Catalyzed by an Engineered Cofactor‐Independent Non‐natural Peroxygenase." Angewandte Chemie 132, no. 26 (April 14, 2020): 10460–64. http://dx.doi.org/10.1002/ange.202001373.
9
Xu, Guangcai, Michele Crotti, Thangavelu Saravanan, Kim M. Kataja, and Gerrit J. Poelarends. "Enantiocomplementary Epoxidation Reactions Catalyzed by an Engineered Cofactor‐Independent Non‐natural Peroxygenase." Angewandte Chemie International Edition 59, no. 26 (April 14, 2020): 10374–78. http://dx.doi.org/10.1002/anie.202001373.
10
Fu, Peng, and John B. MacMillan. "Carpatizine, a novel bridged oxazine derivative generated by non-enzymatic reactions." Organic & Biomolecular Chemistry 15, no. 25 (2017): 5275–78. http://dx.doi.org/10.1039/c7ob01178d.
11
Babbel, Justin, Courtney Ramos, Hannah Wangberg, Kate Luskin, and Ronald Simon. "Adverse reactions to food additives." Journal of Food Allergy 3, no. 1 (April 1, 2021): 8–23. http://dx.doi.org/10.2500/jfa.2021.3.210004.
Abstract:
Food additives are naturally occurring or synthetic substances that are added to food to modify the color, taste, texture, stability, or other characteristics of foods. These additives are ubiquitous in the food that we consume on a daily basis and, therefore, have been the subject of much scrutiny about possible reactions. Despite these concerns, the overall prevalence of food additive reactions is 1‐2%, with a minority of the wide variety of symptoms attributed to food-additive exposure being reproduced by double-blind placebo controlled challenges. Reactions can be broadly classified into either immunoglobulin E (IgE)- and non‐IgE-mediated reactions, with natural additives accounting for most IgE-mediated reactions, and both natural and synthetic additives being implicated in the non‐IgE-mediated reactions. Reactions that include asthma exacerbations, urticaria and/or angioedema, or anaphylaxis with ingestion of a food additive are most deserving of further allergy evaluation. In this article, we discussed the different types of adverse reactions that have been described to various food additives. We also reviewed the specifics of how to evaluate and diagnose a food additive allergy in a clinic setting.
12
Perry, Christopher, Emmanuel L. C. de los Santos, Lona M. Alkhalaf, and Gregory L. Challis. "Rieske non-heme iron-dependent oxygenases catalyse diverse reactions in natural product biosynthesis." Natural Product Reports 35, no. 7 (2018): 622–32. http://dx.doi.org/10.1039/c8np00004b.
13
Renata, Hans, Z. Jane Wang, and Frances H. Arnold. "Expanding the Enzyme Universe: Accessing Non-Natural Reactions by Mechanism-Guided Directed Evolution." Angewandte Chemie International Edition 54, no. 11 (February 3, 2015): 3351–67. http://dx.doi.org/10.1002/anie.201409470.
14
Kadokawa, Jun-ichi. "α-Glucan Phosphorylase-Catalyzed Enzymatic Reactions Using Analog Substrates to Synthesize Non-Natural Oligo- and Polysaccharides." Catalysts 8, no. 10 (October 19, 2018): 473. http://dx.doi.org/10.3390/catal8100473.
Abstract:
As natural oligo- and polysaccharides are important biomass resources and exhibit vital biological functions, non-natural oligo- and polysaccharides with a well-defined structure can be expected to act as new functional materials with specific natures and properties. α-Glucan phosphorylase (GP) is one of the enzymes that have been used as catalysts for practical synthesis of oligo- and polysaccharides. By means of weak specificity for the recognition of substrates by GP, non-natural oligo- and polysaccharides has precisely been synthesized. GP-catalyzed enzymatic glycosylations using several analog substrates as glycosyl donors have been carried out to produce oligosaccharides having different monosaccharide residues at the non-reducing end. Glycogen, a highly branched natural polysaccharide, has been used as the polymeric glycosyl acceptor and primer for the GP-catalyzed glycosylation and polymerization to obtain glycogen-based non-natural polysaccharide materials. Under the conditions of removal of inorganic phosphate, thermostable GP-catalyzed enzymatic polymerization of analog monomers occurred to give amylose analog polysaccharides.
15
Nakamura, Hitomi, Yudai Matsuda, and Ikuro Abe. "Unique chemistry of non-heme iron enzymes in fungal biosynthetic pathways." Natural Product Reports 35, no. 7 (2018): 633–45. http://dx.doi.org/10.1039/c7np00055c.
16
Wright, Dennis L. "Application of Olefin Metathesis to Organic Synthesis." Current Organic Chemistry 3, no. 3 (May 1999): 211–40. http://dx.doi.org/10.2174/1385272803666220202192919.
Abstract:
Abstract: The design and execution of complex molecule synthesis centers upon those reactions that are truly versatile and reliable, especially those that form carbon-carbon bonds. For many decades, alkene metathesis reactions have found great application in polymer synthesis, but it has only been recently that this reaction is finding a place in the arsenal of the synthetic chemist. This new role for the olefin metathesis reaction is directly related to the recent development of stable, well-defined catalysts for this reaction. Ruthenium and molybdenum catalysts, among others, are finding wide spread use in organic synthesis. These catalysts are able to promote the exchange of two independent alkenes and result in the formation of a new olefin. The most common use for this reaction involves an intermolecular variation whereby a tethered diene is metathesized to form a cycloalkene. This ring-closing metathesis (RCM) process has been shown to be remarkably versatile and is tolerant to a wide range of accompanying functionality. RCM reactions are now widely used for the preparation of carbocyclic, azacyclic, and oxacyclic systems. This review focuses on the versatility offered by these well-defined catalyst systems and focuses on their use in the synthesis of natural and non-natural products.
17
Flom, Julie D., and Scott H. Sicherer. "Epidemiology of Cow’s Milk Allergy." Nutrients 11, no. 5 (May 10, 2019): 1051. http://dx.doi.org/10.3390/nu11051051.
Abstract:
Immunoglobulin E (IgE)-mediated cow’s milk allergy (CMA) is one of the most common food allergies in infants and young children. CMA can result in anaphylactic reactions, and has long term implications on growth and nutrition. There are several studies in diverse populations assessing the epidemiology of CMA. However, assessment is complicated by the presence of other immune-mediated reactions to cow’s milk. These include non-IgE and mixed (IgE and non-IgE) reactions and common non-immune mediated reactions, such as lactose intolerance. Estimates of prevalence and population-level patterns are further complicated by the natural history of CMA (given its relatively high rate of resolution) and variation in phenotype (with a large proportion of patients able to tolerate baked cow’s milk). Prevalence, natural history, demographic patterns, and long-term outcomes of CMA have been explored in several disparate populations over the past 30 to 40 years, with differences seen based on the method of outcome assessment, study population, time period, and geographic region. The primary aim of this review is to describe the epidemiology of CMA. The review also briefly discusses topics related to prevalence studies and specific implications of CMA, including severity, natural course, nutritional impact, and risk factors.
18
Yu, Hui, and Feng Xu. "Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp3)–H to construct C–C bonds." Beilstein Journal of Organic Chemistry 19 (September 6, 2023): 1259–88. http://dx.doi.org/10.3762/bjoc.19.94.
Abstract:
Ether derivatives are widespread as essential building blocks in various drugs, natural products, agrochemicals, and materials. Modern economy requires developing green strategies with improved efficiency and reduction of waste. Due to its atom and step-economy, the cross-dehydrogenative coupling (CDC) reaction has become a major strategy for ether functionalization. This review covers C–H/C–H cross-coupling reactions of ether derivatives with various C–H bond substrates via non-noble metal catalysts (Fe, Cu, Co, Mn, Ni, Zn, Y, Sc, In, Ag). We discuss advances achieved in these CDC reactions and hope to attract interest in developing novel methodologies in this field of organic chemistry.
19
Cordero-Vargas, Alejandro, and Jeferson B. Mateus-Ruiz. "Visible-Light-Mediated Photoredox Reactions in the Total Synthesis of Natural Products." Synthesis 52, no. 21 (August 18, 2020): 3111–28. http://dx.doi.org/10.1055/s-0040-1707225.
Abstract:
In the last two decades, the field of photoredox catalysis (PRC) has grown impressively with reports of new synthetic methodologies and more efficient versions of known free-radical reactions. The impressive success of visible-light-mediated photoredox catalysis is, in great part, due to its low environmental impact, mild reaction conditions, clean reactions, and inexpensive methodologies. These features have allowed photoredox catalysis to emerge as a powerful tool in the synthesis of natural products; much excellent work was reported between 2011 and 2015. Since 2016, a number of more efficient and impressive total syntheses of natural products featuring photoredox catalysis have been reported. In this review, we summarize the recent synthetic applications of photoredox catalysis in the total synthesis of natural products between 2016 and 2020.1 Introduction2 Intermolecular Additions from Functionalized Substrates2.1 Intermolecular Additions from Alkyl Halides2.2 Intermolecular Additions from Alcohols and Carboxylic Acids3 Cyclizations from Functionalized Substrates3.1 Cyclizations of Carbon-Centered Radicals3.2 Cyclizations of Nitrogen-Centered Radicals4 Intramolecular Cyclization from Non-functionalized N–H Bonds4.1 Type I Radical Cascade4.2 Type II Radical Cascade4.3 Type III Radical Cascade5 Functionalization of Imines and Enamines6 Cycloadditions7 Miscellaneous7.1 Dehalogenation and Reductive Decarboxylation7.2 Thiyl Radical Promoted Cascade8 Conclusions and Perspectives
20
Legrand, Baptiste, Julie Aguesseau-Kondrotas, Matthieu Simon, and Ludovic Maillard. "Catalytic Foldamers: When the Structure Guides the Function." Catalysts 10, no. 6 (June 22, 2020): 700. http://dx.doi.org/10.3390/catal10060700.
Abstract:
Enzymes are predominantly proteins able to effectively and selectively catalyze highly complex biochemical reactions in mild reaction conditions. Nevertheless, they are limited to the arsenal of reactions that have emerged during natural evolution in compliance with their intrinsic nature, three-dimensional structures and dynamics. They optimally work in physiological conditions for a limited range of reactions, and thus exhibit a low tolerance for solvent and temperature conditions. The de novo design of synthetic highly stable enzymes able to catalyze a broad range of chemical reactions in variable conditions is a great challenge, which requires the development of programmable and finely tunable artificial tools. Interestingly, over the last two decades, chemists developed protein secondary structure mimics to achieve some desirable features of proteins, which are able to interfere with the biological processes. Such non-natural oligomers, so called foldamers, can adopt highly stable and predictable architectures and have extensively demonstrated their attractiveness for widespread applications in fields from biomedical to material science. Foldamer science was more recently considered to provide original solutions to the de novo design of artificial enzymes. This review covers recent developments related to peptidomimetic foldamers with catalytic properties and the principles that have guided their design.
21
Miao, Xiao-Yu, Yong-Ji Hu, Fu-Rao Liu, Yuan-Yuan Sun, Die Sun, An-Xin Wu, and Yan-Ping Zhu. "Synthesis of Diversified Pyrazolo[3,4-b]pyridine Frameworks from 5-Aminopyrazoles and Alkynyl Aldehydes via Switchable C≡C Bond Activation Approaches." Molecules 27, no. 19 (September 27, 2022): 6381. http://dx.doi.org/10.3390/molecules27196381.
Abstract:
A cascade 6-endo-dig cyclization reaction was developed for the switchable synthesis of halogen and non-halogen-functionalized pyrazolo[3,4-b]pyridines from 5-aminopyrazoles and alkynyl aldehydes via C≡C bond activation with silver, iodine, or NBS. In addition to its wide substrate scope, the reaction showed good functional group tolerance as well as excellent regional selectivity. This new protocol manipulated three natural products, and the arylation, alkynylation, alkenylation, and selenization of iodine-functionalized products. These reactions demonstrated the potential applications of this new method.
22
Boreham, Christopher J., Dianne S. Edwards, Krystian Czado, Nadege Rollet, Liuqi Wang, Simon van der Wielen, David Champion, Richard Blewett, Andrew Feitz, and Paul A. Henson. "Hydrogen in Australian natural gas: occurrences, sources and resources." APPEA Journal 61, no. 1 (2021): 163. http://dx.doi.org/10.1071/aj20044.
Abstract:
Natural or native molecular hydrogen (H2) can be a major component in natural gas, and yet its role in the global energy sector’s usage as a clean energy carrier is not normally considered. Here, we update the scarce reporting of hydrogen in Australian natural gas with new compositional and isotopic analyses of H2 undertaken at Geoscience Australia. The dataset involves ~1000 natural gas samples from 470 wells in both sedimentary and non-sedimentary basins with reservoir rocks ranging in age from the Neoarchean to Cenozoic. Pathways to H2 formation can involve either organic matter intermediates and its association with biogenic natural gas or chemical synthesis and its presence in abiogenic natural gas. The latter reaction pathway generally leads to H2-rich (>10mol% H2) gas in non-sedimentary rocks. Abiogenic H2 petroleum systems are described within concepts of source–migration–reservoir–seal but exploration approaches are different to biogenic natural gas. Rates of abiogenic H2 generation are governed by the availability of specific rock types and different mineral catalysts, and through chemical reactions and radiolysis of accessible water. Hydrogen can be differently trapped compared to hydrocarbon gases; for example, pore space can be created in fractured basement during abiogenic reactions, and clay minerals and evaporites can act as effective adsorbents, traps and seals. Underground storage of H2 within evaporites (specifically halite) and in depleted petroleum reservoirs will also have a role to play in the commercial exploitation of H2. Estimated H2 production rates mainly from water radiolysis in mafic–ultramafic and granitic rocks and serpentinisation of ultramafic–mafic rocks gives a H2 inferred resource potential between ~1.6 and ~58MMm3 year−1 for onshore Australia down to a depth of 1km. The prediction and subsequent identification of subsurface H2 that can be exploited remains enigmatic and awaits robust exploration guidelines and targeted drilling for proof of concept.
23
Mukherjee, Jhumpa, and Sriparna Ray. "Structurally Characterized Non-Heme Fe(IV)Oxo Complexes: A Brief Overview." Asian Journal of Chemistry 34, no. 11 (2022): 2771–85. http://dx.doi.org/10.14233/ajchem.2022.23863.
Abstract:
Iron(II) centers found in both heme and non-heme enzymes, are the most important metal centre responsible for effectively activating molecular oxygen. Activation of molecular oxygen is important for natural systems and many industrially important reactions. Iron(IV)oxo unit is one of the important intermediates found among the various high valent oxo iron intermediates formed during substrate oxidation in natural enzymes. In this review article, the different synthetic strategies were focused and followed to obtain the X-ray structurally characterized model iron(IV)oxo complexes with non-heme ligands. The ligands were categorized in three different classes and showed how designing a proper ligand, binding with Fe(II) center and reacting it with a suitable oxidizing agent can finally give rise to a system similar to natural systems. Stability of these complexes and some preliminary characterization have also been discussed. The crystallographic characterization of these synthetic models containing iron(IV)oxo intermediates was necessary to understand the mechanistic pathway they follow to mimic the difficult oxidation reactions performed by natural enzymes. In this review, not only the synthetic strategies for these non-heme iron(IV)oxo complexes were highlighted but a detailed structural analysis for these important intermediates were also discussed.
24
Hanson, Jeffrey, Dan Groff, Abi Carlos, Hans Usman, Kevin Fong, Abigail Yu, Stephanie Armstrong, et al. "An Integrated In Vivo/In Vitro Protein Production Platform for Site-Specific Antibody Drug Conjugates." Bioengineering 10, no. 3 (February 28, 2023): 304. http://dx.doi.org/10.3390/bioengineering10030304.
Abstract:
The XpressCF+® cell-free protein synthesis system is a robust platform for the production of non-natural amino acids containing antibodies, which enable the site-specific conjugation of homogeneous antibody drug conjugates (ADCs) via click chemistry. Here, we present a robust and scalable means of achieving a 50–100% increase in IgG titers by combining the high productivity of cell-based protein synthesis with the unique ability of XpressCF+® reactions to produce correctly folded and assembled IgGs containing multiple non-natural amino acids at defined positions. This hybrid technology involves the pre-expression of an IgG light-chain (LC) protein in a conventional recombinant E. coli expression system, engineered to have an oxidizing cytoplasm. The prefabricated LC subunit is then added as a reagent to the cell-free protein synthesis reaction. Prefabricated LC increases IgG titers primarily by reducing the protein synthesis burden per IgG since the cell free translation machinery is only responsible for synthesizing the HC protein. Titer increases were demonstrated in four IgG products in scales ranging from 100-µL microplate reactions to 0.25-L stirred tank bioreactors. Similar titer increases with prefabricated LC were also demonstrated for a bispecific antibody in the scFvFc-FabFc format, demonstrating the generality of this approach. Prefabricated LC also increases robustness in cell-free reactions since it eliminates the need to fine-tune the HC-to-LC plasmid ratio, a critical parameter influencing IgG assembly and quality when the two IgG subunits are co-expressed in a single reaction. ADCs produced using prefabricated LC were shown to be identical to IgGs produced in cell-free alone by comparing product quality, in vitro cell killing, and FcRn receptor binding assays. This approach represents a significant step towards improving IgG titers and the robustness of cell-free protein synthesis reactions by integrating in vivo and in vitro protein production platforms.
25
Keinan, Ehud, and Subhash C. Sinha. "Oxidative polycyclizations with rhenium(VII) oxides." Pure and Applied Chemistry 74, no. 1 (January 1, 2002): 93–105. http://dx.doi.org/10.1351/pac200274010093.
Abstract:
The consecutive oxidative polycyclization reaction with rhenium(VII) oxides represents a highly stereoselective synthetic tool by which polyenes that contain a bis-homoallylic alcohol can be transformed into poly-THF products in a single step. On the basis of a detailed study with model substrates, a set of rules is proposed to predict product configurations in the polycyclization reactions with trifluoroacetylperrhenate. This methodology is exceptionally useful for the synthesis of polyoxygenated carbon skeletons that contain many stereogenic centers, and for the Annonaceous acetogenins in particular. Many of these potent antitumor agents, including solamin, reticulatacin, asimicin, bullatacin, trilobin, trilobacin, squamotacin, rolliniastatin, uvaricin, rollidecins C and D, mucocin, goniocin, and cyclogoniodenin T, as well as chemical libraries of non-natural analogs, were synthesized using the oxidative polycyclization reaction in combination with the Sharpless AD and AE reactions.
26
Tolmacheva, Anna S., and Georgy A. Nevinsky. "Essential Protective Role of Catalytically Active Antibodies (Abzymes) with Redox Antioxidant Functions in Animals and Humans." International Journal of Molecular Sciences 23, no. 7 (March 31, 2022): 3898. http://dx.doi.org/10.3390/ijms23073898.
Abstract:
During the life of aerobic organisms, the oxygen resulting from numerous reactions is converted into reactive oxygen species (ROS). Many ROS are dangerous due to their high reactivity; they are strong oxidants, and react with various cell components, leading to their damage. To protect against ROS overproduction, enzymatic and non-enzymatic systems are evolved in aerobic cells. Several known non-enzymatic antioxidants have a relatively low specific antioxidant activity. Superoxide dismutases, catalase, glutathione peroxidase, glutathione S-transferase, thioredoxin, and the peroxiredoxin families are the most important enzyme antioxidants. Artificial antibodies catalyzing redox reactions using different approaches have been created. During the past several decades, it has been shown that the blood and various biological fluids of humans and animals contain natural antibodies that catalyze different redox reactions, such as classical enzymes. This review, for the first time, summarizes data on existing non-enzymatic antioxidants, canonical enzymes, and artificial or natural antibodies (abzymes) with redox functions. Comparing abzymes with superoxide dismutase, catalase, peroxide-dependent peroxidase, and H2O2-independent oxidoreductase activities with the same activities as classical enzymes was carried out. The features of abzymes with the redox activities are described, including their exceptional diversity in the optimal pH values, dependency and independence on various metal ions, and the reaction rate constants for healthy donors and patients with different autoimmune diseases. The entire body of evidence indicates that abzymes with redox antioxidant activities existing in the blood for a long time compared to enzymes are an essential part of the protection system of humans and animals from oxidative stress.
27
Kolb, Benedikt, Daniela Silva dos Santos, Sanja Krause, Anna Zens, and Sabine Laschat. "Sequential hydrozirconation/Pd-catalyzed cross coupling of acyl chlorides towards conjugated (2E,4E)-dienones." Beilstein Journal of Organic Chemistry 19 (February 17, 2023): 176–85. http://dx.doi.org/10.3762/bjoc.19.17.
Abstract:
Dienones are challenging building blocks in natural product synthesis due to their high reactivity and complex synthesis. Based on previous work and own initial results, a new stereospecific sequential hydrozirconation/Pd-catalyzed acylation of enynes with acyl chlorides towards conjugated (2E,4E)-dienones is reported. We investigated a number of substrates with different alkyl and aryl substituents in the one-pot reaction and showed that regardless of the substitution pattern, the reactions lead to the stereoselective formation (≥95% (2E,4E)) of the respective dienones under mild conditions. It was found that enynes with alkyl chains gave higher yields than the corresponding aryl-substituted analogues, whereas the variation of the acyl chlorides did not affect the reaction significantly. The synthetic application is demonstrated by formation of non-natural and natural dienone-containing terpenes such as β-ionone which was available in 4 steps and 6% overall yield.
28
Tietze, L. F., G. Kettschau, J. A. Gewert, and A. Schuffenhauer. "Hetero-Diels-Aider Reactions of 1-0xa-1,3-butadienes." Current Organic Chemistry 2, no. 1 (January 1998): 19–62. http://dx.doi.org/10.2174/1385272802666220126210654.
Abstract:
Many biologically active and widely distributed natural products contain a dihydro- or a tetrahydropyran moiety. One of the best methods for the synthesis of these compounds is the hetero Diels-Aider reaction of 1-0Xia-1,3-butadienes which leads to substituted and annulated 3,4-dihydro-2H-pyrans usually in excellent yields and high selectivity. Further transformations of these substances e.g. by hydrogenation yield the tetrahydropyrans with the basic skeleton of the carbohydrates. In this article at first theoretical aspects of the cycloaddition are discussed which include ab initio calculations of the energies and the coefficients of 1-oxa-1,3-butadienes and different dienophiles. In addition, calculations of the transition structure of the cycloaddition of acrolein and ethene are presented. In the second chapter general considerations on the regia- and stereoselectivity of the cycloadditions are presented. In the following parts different hetero Diels-Aider reactions with activated and non-activated 1-oxa-1,3-butadiens and their use in diastereoselective transformations and the synthesis of natural products as carbohydrates, alkaloids, terpenes, steroids, cannabinoids, mycotoxins, ionophores and antibiotics are described. A point of emphasis is the domino Knoevenagel hetero Diels-Aider reaction in which the oxabutadienes are formed in situ and which allows the highly efficient synthesis of complex dihydropyrans starting from simple substrates. In the final chapters enantioselective cycloadditions, reactions on solid support and cycloadditions under high pressure are discussed.
29
Chaudhary, Ankita, Divya Mathur, Ritu Gaba, Raaina Pasricha, and Khyati Sharma. "Greening up organic reactions with caffeine: applications, recent developments, and future directions." RSC Advances 14, no. 13 (2024): 8932–62. http://dx.doi.org/10.1039/d4ra00432a.
Abstract:
Among the diverse natural catalysts, caffeine has emerged as a green, expedient, non-toxic, and biodegradable catalyst. The main objective of this review is to present the existing knowledge pertaining to the exploitation of caffeine in various organic transformations.
30
Bornscheuer, Uwe T. "The fourth wave of biocatalysis is approaching." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2110 (November 27, 2017): 20170063. http://dx.doi.org/10.1098/rsta.2017.0063.
Abstract:
Biocatalysis has undergone a tremendous development in the past few years. A plethora of methods enable the rather rapid tailored-design of an enzyme for a targeted reaction such as asymmetric synthesis of a chiral building block by the combination of information from sequence and structure databases with modern molecular biology methods and high-throughput screening tools. Moreover, novel non-natural reactions could be implemented into protein scaffolds and new enzyme classes are emerging, both broadening the repertoire of reactions now available for organic synthesis. Furthermore, impressive examples of metabolic engineering—the combination of several newly introduced reaction steps in a microbial host—have been developed, paving the way for large-scale processes for both pharmaceuticals and bulk chemicals. This contribution highlights recent developments in this area and points out future challenges. This article is part of a discussion meeting issue ‘Providing sustainable catalytic solutions for a rapidly changing world’.
31
Freindorf, Marek, and Elfi Kraka. "URVA and Local Mode Analysis of an Iridium Pincer Complex Efficiently Catalyzing the Hydrogenation of Carbon Dioxide." Inorganics 10, no. 12 (December 1, 2022): 234. http://dx.doi.org/10.3390/inorganics10120234.
Abstract:
The catalytic effects of iridium pincer complexes for the hydrogenation of carbon dioxide were investigated with the Unified Reaction Valley Approach (URVA), exploring the reaction mechanism along the reaction path traced out by the reacting species on the potential energy surface. Further details were obtained with the Local Mode Analysis performed at all stationary points, complemented by the Natural Bond Orbital and Bader’s Quantum Atoms in Molecules analyses. Each of the five reaction paths forming the catalytic cycle were calculated at the DFT level complemented with DLPNO-CCSD(T) single point calculations at the stationary points. For comparison, the non-catalytic reaction was also investigated. URVA curvature profiles identified all important chemical events taking place in the non-catalyzed reaction and in the five reactions forming the catalytic cycle, and their contribution to the activation energy was disclosed. The non-catalytic reaction has a large unfavorable activation energy of 76.3 kcal/mol, predominately caused by HH bond cleave in the H2 reactant. As shown by our study, the main function of the iridium pincer catalyst is to split up the one–step non-catalytic reaction into an energy efficient multistep cycle, where HH bond cleavage is replaced by the cleavage of a weaker IrH bond with a small contribution to the activation energy. The dissociation of the final product from the catalyst requires the cleavage of an IrO bond, which is also weak, and contributes only to a minor extent to the activation energy. This, in summary, leads to the substantial lowering of the overall activation barrier by about 50 kcal/mol for the catalyzed reaction. We hope that this study inspires the community to add URVA to their repertoire for the investigation of catalysis reactions.
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Liu, Fenghua, Lingling He, Sheng Dong, Jinsong Xuan, Qiu Cui, and Yingang Feng. "Artificial Small Molecules as Cofactors and Biomacromolecular Building Blocks in Synthetic Biology: Design, Synthesis, Applications, and Challenges." Molecules 28, no. 15 (August 3, 2023): 5850. http://dx.doi.org/10.3390/molecules28155850.
Abstract:
Enzymes are essential catalysts for various chemical reactions in biological systems and often rely on metal ions or cofactors to stabilize their structure or perform functions. Improving enzyme performance has always been an important direction of protein engineering. In recent years, various artificial small molecules have been successfully used in enzyme engineering. The types of enzymatic reactions and metabolic pathways in cells can be expanded by the incorporation of these artificial small molecules either as cofactors or as building blocks of proteins and nucleic acids, which greatly promotes the development and application of biotechnology. In this review, we summarized research on artificial small molecules including biological metal cluster mimics, coenzyme analogs (mNADs), designer cofactors, non-natural nucleotides (XNAs), and non-natural amino acids (nnAAs), focusing on their design, synthesis, and applications as well as the current challenges in synthetic biology.
33
Ji, Yuemeng, Zhang Shi, Wenjian Li, Jiaxin Wang, Qiuju Shi, Yixin Li, Lei Gao, et al. "Aqueous-phase chemistry of glyoxal with multifunctional reduced nitrogen compounds: a potential missing route for secondary brown carbon." Atmospheric Chemistry and Physics 24, no. 5 (March 11, 2024): 3079–91. http://dx.doi.org/10.5194/acp-24-3079-2024.
Abstract:
Abstract. The aqueous-phase chemistry of glyoxal (GL) with reduced nitrogen compounds (RNCs) is a significant source for secondary brown carbon (SBrC), which is one of the largest uncertainties in climate predictions. However, a few studies have revealed that SBrC formation is affected by multifunctional RNCs, which have a non-negligible atmospheric abundance. Hence, we assessed theoretical and experimental approaches to investigate the reaction mechanisms and kinetics of the mixtures for ammonium sulfate (AS), multifunctional amine monoethanolamine (MEA), and GL. Our experiments indicate that light absorption and growth rate are enhanced more efficiently in the MEA–GL mixture relative to AS–GL and MEA–AS–GL mixtures and MEA reactions of the chromophores than in the analogous AS reactions. Quantum chemical calculations show that the formation and propagation of oligomers proceed via four-step nucleophilic addition reactions in three reaction systems. The presence of MEA provides the two extra branched chains that affect the natural charges and steric hindrance of intermediates, facilitating the formation of chromophores. Molecule dynamics simulations reveal that the interfacial and interior attraction on the aqueous aerosols with MEA is more pronounced for small α-dicarbonyls to facilitate further engagement in the aqueous-phase reactions. Our results show a possible missing source for SBrC formation on urban, regional, and global scales.
34
Moeller, Kevin D., Enqi Feng, Ruby Krueger, Zachary Medcalf, Polina Barzova, and Sarah Wagner. "Electrochemistry and Organic Synthesis: New Adventures with Olefin Coupling Reactions and Electrode Surfaces." ECS Meeting Abstracts MA2023-02, no. 52 (December 22, 2023): 2518. http://dx.doi.org/10.1149/ma2023-02522518mtgabs.
Abstract:
Electrochemistry has long offered opportunities to explore new modes of reactivity, new approaches for introducing selectivity into synthetic reactions, and new strategies for the synthesis of everything from complex molecules to complex, addressable molecular surfaces. In the talk to be given, two aspects of our efforts along these lines will be detailed. In the first, we will take a look at recent efforts to use anodically-generated reactive intermediates to convert readily available small molecules into functionalized synthetic building blocks and natural product derivatives. Key to these efforts are oxidation reactions that generate reactive radical cation and radical intermediates. In one application, newly available chiral lactols synthesized using methodology developed by the Lin (Cornell) and Miller (Yale) groups are being transformed into C-glycoside and aza-C-glycoside derivatives. The reactions take advantage of oxidation reactions of either enol ether or vinylsulfide groups. The cyclization reactions and the subsequent deprotection strategy needed for converting the cyclization products into a useful synthetic building block will be highlighted. In a second application of an anodic cyclization, the role of thioamides in reactions targeting the chrysosoporazine family of natural products will be discussed. The reactions seek to provide an efficient method for converting lignin derived building blocks into molecules that reduce the efflux of anticancer drugs from cells. Initial cyclization attempts utilizing amide based N-radicals and anodic olefin coupling reactions were not successful. Those reactions consistently led to over-oxidation of the products that contain a highly electron-rich aryl ring. The use of thio-amide derived radicals provides a method to circumvent this problem. In the second topic to be discussed, the question of how one might begin to induce asymmetry into such electrochemical cyclizations will be highlighted. The chemistry focuses on efforts to influence the course of both electrochemical oxidation and reduction reaction and non-redox based transition metal catalyzed reactions with the surface of an electrode.
35
Tommaso, Morena Di, Arianna Miglio, Paolo Emidio Crisi, Andrea Boari, Francesca Rocconi, Maria Teresa Antognoni, and Alessia Luciani. "Frequency of Blood Types A, B and AB in a Population of Non-Pedigree Domestic Cats from Central Italy." Animals 10, no. 10 (October 21, 2020): 1937. http://dx.doi.org/10.3390/ani10101937.
Abstract:
Blood transfusion reactions and neonatal isoerythrolysis are common events in the feline population due to the presence of natural alloantibodies in the AB blood group system. It is known that the frequency of feline blood types varies according to the geographic region and breed. Therefore, the aims of this study were to investigate the frequency of AB blood groups in non-pedigree domestic cats in Central Italy and estimate the risk of a life-threatening transfusion reaction and neonatal isoerythrolysis, caused by mismatched transfusion or incompatible random mating, respectively. The AB blood group was determined on non-pedigree domestic feline patients and potential blood donors submitted at the Veterinary Teaching Hospitals of the Universities of Teramo (Abruzzo Region, Teramo, Italy) and Perugia (Umbria Region, Teramo, Italy), and visited at veterinary practitioners in Rome (Lazio Region, Teramo, Italy) using commercial immunochromatographic cartridges and commercial agglutination cards. There were four hundred and eighty-three cats included in the study. The frequencies of the blood types were: 89.9% type A, 7.0% type B, and 3.1% type AB. The probability of an acute hemolytic transfusion reaction or a neonatal isoerythrolysis was 6.5%. Although the frequency of type B in non-pedigree domestic cats living in Central Italy was relatively low, to reduce the risk of fatal transfusion reactions, blood group typing is recommended before each transfusion.
36
Arnold, Frances H. "The nature of chemical innovation: new enzymes by evolution." Quarterly Reviews of Biophysics 48, no. 4 (July 16, 2015): 404–10. http://dx.doi.org/10.1017/s003358351500013x.
Abstract:
AbstractI describe how we direct the evolution of non-natural enzyme activities, using chemical intuition and information on structure and mechanism to guide us to the most promising reaction/enzyme systems. With synthetic reagents to generate new reactive intermediates and just a few amino acid substitutions to tune the active site, a cytochrome P450 can catalyze a variety of carbene and nitrene transfer reactions. The cyclopropanation, N–H insertion, C–H amination, sulfimidation, and aziridination reactions now demonstrated are all well known in chemical catalysis but have no counterparts in nature. The new enzymes are fully genetically encoded, assemble and function inside of cells, and can be optimized for different substrates, activities, and selectivities. We are learning how to use nature's innovation mechanisms to marry some of the synthetic chemists’ favorite transformations with the exquisite selectivity and tunability of enzymes.
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Ganley, Jack G., and Emily R. Derbyshire. "Linking Genes to Molecules in Eukaryotic Sources: An Endeavor to Expand Our Biosynthetic Repertoire." Molecules 25, no. 3 (January 31, 2020): 625. http://dx.doi.org/10.3390/molecules25030625.
Abstract:
The discovery of natural products continues to interest chemists and biologists for their utility in medicine as well as facilitating our understanding of signaling, pathogenesis, and evolution. Despite an attenuation in the discovery rate of new molecules, the current genomics and transcriptomics revolution has illuminated the untapped biosynthetic potential of many diverse organisms. Today, natural product discovery can be driven by biosynthetic gene cluster (BGC) analysis, which is capable of predicting enzymes that catalyze novel reactions and organisms that synthesize new chemical structures. This approach has been particularly effective in mining bacterial and fungal genomes where it has facilitated the discovery of new molecules, increased the understanding of metabolite assembly, and in some instances uncovered enzymes with intriguing synthetic utility. While relatively less is known about the biosynthetic potential of non-fungal eukaryotes, there is compelling evidence to suggest many encode biosynthetic enzymes that produce molecules with unique bioactivities. In this review, we highlight how the advances in genomics and transcriptomics have aided natural product discovery in sources from eukaryotic lineages. We summarize work that has successfully connected genes to previously identified molecules and how advancing these techniques can lead to genetics-guided discovery of novel chemical structures and reactions distributed throughout the tree of life. Ultimately, we discuss the advantage of increasing the known biosynthetic space to ease access to complex natural and non-natural small molecules.
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Chiba, Kazuhiro. "(Organic and Biological Electrochemistry Division Manuel M. Baizer Award, Digital Presentation) Electron-Transfer-Triggered Smart Reactions Boost a Better Anthropocene." ECS Meeting Abstracts MA2022-01, no. 42 (July 7, 2022): 1827. http://dx.doi.org/10.1149/ma2022-01421827mtgabs.
Abstract:
It is important that chemical reactions initiated by electron transfer associated with electrodes can be achieved by precise control of intramolecular and intermolecular electron transfer of organic compounds, which is difficult to achieve by general chemical methods. Expectations for a new production process that positively controls the electron transfer is also expanding dramatically. Here, the solvent that dissolves the substrate for reaction, the network structure of the ionic species in the solution, and the role of coexisting substances are exactly grasped, and the total energy consumption is controlled under milder conditions. If it is possible to develop a chemical process that reduces the consumption of substances such as reaction reagents to the utmost while significantly suppressing the above, it is expected that structural conversion of chemical substances based on the electron transfer process can be realized. This means that advanced control of the formation, stabilization, and subsequent reactions of active open-shell molecules opens the door to new chemical reactions that reduce excess reagent and energy consumption. There is a possibility that the atom economy will be dramatically enhanced by the electron transfer reaction process for the reagents that need to be charged. This achieves a chemical reaction that is regarded as "Electrons as Reagents", and it will be a core technology that will bring about innovation in the chemical substance manufacturing method that is currently produced with the production of a large amounts of unnecessary substances and energy consumption. Research achievements: In such a background, K. Chiba pioneered original organic electrolytic reactions based on the research activities on chemical synthesis of biologically active natural compounds, and achieved various carbon skeleton formation, chemical synthesis of useful substances and biologically active natural substances. One of the notable results is the electrolytic synthesis reaction method using a unique electrolyte solution composed of lithium perchlorate / nitromethane. It was shown that the cation species generated by electrode electron transfer using this electrolyte solution are stabilized and can be applied to the formation of a wide variety of intermolecular carbon-carbon bonds. That is, numerous electrode process-triggered reactions such as varied (hetero)Diels-Alder reactions, [3+2], and [2+2] cycloaddition reactions have been achieved. In addition, the olefin metathesis without transition metal catalysis was successful for the first time. The importance of the role of the electrolyte solution in the organic electrolysis reaction was widely shown. The elucidation of these reaction mechanisms and new findings on the action of the reaction field have contributed to the rapid development of the field in recent years by utilizing and enhancing the functions of various electrolyte solutions. In addition, the application of the new organic electrolysis method has widely developed chemical synthesis methods for natural and non-natural peptides, artificial nucleic acids, etc. It is noteworthy that it was successful in electrolytic synthesis of various aza-nucleosides by utilizing the cation species under the stabilizing action of the lithium perchlorate / nitromethane electrolyte solution. This basic skeleton paves the way for mass synthesis of nucleic acid derivatives, which are promising as therapeutic drug for covid-19. Furthermore, K. Chiba achieved organic electrolytic reactions that mimic the electron transfer process in the living body. Inspired by the bio-mimic chemical reaction system, he proposed a chemical process based on biphasic solutions. The key technology is the introduction of a solution system that combines a highly polar electrolyte solution and a hydrophobic organic solvent. By controlling the temperature, phase-fusion and phase-separation can be repeated, so that the product, for example, can be taken out from the reaction system while reusing the electrolyte solution. By forming reverse micelles in a hydrophobic solvent, a continuous reaction system can be constructed, which has led to the proposal of an important method for industrial application of electrolytic reactions and of multi-step medium-size molecule syntheses reducing environmental load. Outlook for the future: We must achieve a more efficient cycle of material, food and energy to support the world's population of 9 billion in the near future. For that purpose, it is extremely important to pay attention to and apply the functions of electrons involved in the production and decomposition of all chemical substances, including the elucidation and utilization of biological functions. The key technology of controlling electron transfer is indispensable for achieving a smart green society boosting a better Anthropocene.
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Hirbodvash, Zohreh, and Pierre Berini. "Surface Plasmon Electrochemistry: Tutorial and Review." Chemosensors 11, no. 3 (March 19, 2023): 196. http://dx.doi.org/10.3390/chemosensors11030196.
Abstract:
Surface plasmon polaritons (SPPs) are optical surface waves propagating along a metal surface. They exhibit attributes such as field enhancement and sub-wavelength localization, which make them attractive for surface sensing, as they are heavily exploited in surface plasmon biosensors. Electrochemistry also occurs on metal surfaces, and electrochemical techniques are also commonly applied in biosensors. As metal surfaces are integral in both, it is natural to combine these techniques into a single platform. Motivations include: (i) realising a multimodal biosensor (electrochemical and optical), (ii) using SPPs to probe the electrochemical double layer or to probe electrochemical activity, thus revealing complementary information on redox reactions, or (iii) using SPPs to pump electrochemical reactions by creating non-equilibrium energetic electrons and holes in a working electrode through the absorption of SPPs thereon. The latter is of interest as it may yield novel redox reaction pathways (i.e., plasmonic electrocatalysis).
40
Shokrollahi, Fatemeh, Kok Keong Lau, and Behzad Partoon. "Experimental Evaluation of Chemical Reactions Involved in Ultrasonic-Assisted Absorption of Bulk CO2." Processes 11, no. 12 (November 22, 2023): 3266. http://dx.doi.org/10.3390/pr11123266.
Abstract:
As the most mature natural gas sweetening process, absorption has always been improved to meet the separation requirement. Recently, ultrasonic irradiation has been proposed as a technique that can intensify CO2 absorption. However, further studies are still required, particularly focusing on the sonochemical effect. Since the influence of the sonochemical effect on the reaction pathway is still debatable, attention must be given to verifying the influence of ultrasonic irradiation on the chemical reactions of CO2 absorption. Hence, this work aims to evaluate the influence of OH˙ radicals generated by the sonochemical effect on the chemical reactions involved during CO2 absorption using promoter-free methyldiethanolamine (MDEA). For the evaluation, various samples under irradiated and non-irradiated conditions are analyzed using the HPLC characterization technique. The results show that the hypothesis of changing the reaction pathway due to the presence of the sonochemical effect is invalid. However, it can accelerate the generation of hydroxyl radicals (OH˙) via water sonolysis. Thus, the origin of sonochemistry in aqueous solutions is defined as water sonolysis. The analysis of the CO2 absorption rate also demonstrates the presence of accelerated chemical reactions (contributed by the OH˙ radicals), which could potentially make the slow kinetic MDEA more practical for industrial application.
41
Majhi, Sasadhar. "The Art of Total Synthesis of Bioactive Natural Products via Microwaves." Current Organic Chemistry 25, no. 9 (May 25, 2021): 1047–69. http://dx.doi.org/10.2174/1385272825666210303112302.
Abstract:
Natural products are the most effective source of potential drug leads. The total synthesis of bioactive natural products plays a crucial role in confirming the hypothetical complex structure of natural products in the laboratory. The total synthesis of rare bioactive natural products is one of the great challenges for the organic synthetic community due to their complex structures, biochemical specificity, and difficult stereochemistry. Subsequently, the total synthesis is a long process in several cases, and it requires a substantial amount of time. Microwave irradiation has emerged as a greener tool in organic methodologies to reduce reaction time from days and hours to minutes and seconds. Moreover, this non-classical methodology increases product yields and purities, improves reproducibility, modifications of selectivity, simplification of work-up methods, and reduces unwanted side reactions. Such beneficial qualities have stimulated this review to cover the application of microwave irradiation in the field of the total synthesis of bioactive natural products for the first time during the last decade. An overview of the use of microwave irradiation, natural sources, structures, and biological activities of secondary metabolites is presented elegantly, focusing on the involvement of at least one or more steps by microwave irradiation as a green technique.
42
Rochussen, Jeremy, Gordon McTaggart-Cowan, and Patrick Kirchen. "Parametric study of pilot-ignited direct-injection natural gas combustion in an optically accessible heavy-duty engine." International Journal of Engine Research 21, no. 3 (March 25, 2019): 497–513. http://dx.doi.org/10.1177/1468087419836877.
Abstract:
Natural gas is an attractive fuel for internal combustion engines in light of its potential for reduced greenhouse gas and particulate emissions, and significant reserves. To facilitate natural gas use in compression ignition engines, pilot-ignited direct-injection natural gas combustion uses a small pilot injection of diesel to ignite a more significant direct injection of natural gas. Compared to modern diesel combustion, this strategy is a promising technology for the reduction of CO2 emissions while retaining diesel-like efficiency without a significant CH4 emission penalty. To further develop this technology, investigation of in-cylinder combustion processes is needed to identify the primary fuel conversion processes. The objective of this work was to provide a framework of conceptual understanding by identifying key processes in a typical pilot-ignited direct-injection natural gas combustion event and characterizing their sensitivity to fuel injection parameters. A parametric sweep of injection pressure, natural gas injection duration, and relative timing of the diesel pilot and natural gas injections was performed in an optically accessible 2 L single-cylinder engine. Combined heat release rate and OH*-chemiluminescence reaction zone analysis was used to demarcate the transition from ignition reactions to primary natural gas heat release. Five distinct combustion processes were identified: (1) pilot auto-ignition; (2) natural gas ignition; (3) rapid, distributed partially premixed natural gas combustion; (4) non-premixed combustion; and (5) late-cycle oxidation. While natural gas ignition was found to be insensitive to injection pressure, it was strongly affected by the time between pilot and natural gas injections. Reducing the relative injection timing from +8° to −6° resulted in the primary natural gas heat release transitioning from non-premixed, to distributed partially premixed, to stratified premixed flame propagation as a result of increasing natural gas premixing. The presented measurements and analysis serve to refine an initial conceptual model of the combustion process and lay the groundwork for future, more focused studies of pilot-ignited, direct-injection natural gas combustion.
43
Shoker, Roaa M. H., Wasan Hamza Al-Shammery, and S. R. Al-Aidy. "A Review Article: Free Radical and Replacement Synthetic Antioxidant by Natural Antioxidant." Journal for Research in Applied Sciences and Biotechnology 2, no. 2 (May 11, 2023): 206–11. http://dx.doi.org/10.55544/jrasb.2.2.29.
Abstract:
Free radical may be responsible of several pathophysiology disease for threatening human life, and they are produced from endogenous and exogenous sources. Using the balanced amount of nutritious diet lead to a good health, may be neutralizing or scavenging free radicals by antioxidants compounds. daily diet have large number of vitamin A, E and C, carotenoids, polyphenols, etc. as natural antioxidants, the main bases of them are fruits, cereals, vegetables, and beverages. Enzymatic and non-enzymatic antioxidant substances are two different kinds that lessen the reactions of free radicals. In order to protect itself from reactive oxygen species, the human body uses an enzyme antioxidant. The two kinds of non-enzymatic antioxidants are natural antioxidants and synthetic antioxidants. The aim of this review is to knowledge a reasons which causes the free radical and balance them by natural antioxidant constituents, and replacement synthetic antioxidant by natural antioxidant, due to daily diet have large amounts from natural antioxidants, and natural antioxidants more effective than synthetic antioxidants, in additional they occurrence in nature and more inexpensive.
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Himiyama, Tomoki, and Yasunori Okamoto. "Artificial Metalloenzymes: From Selective Chemical Transformations to Biochemical Applications." Molecules 25, no. 13 (June 30, 2020): 2989. http://dx.doi.org/10.3390/molecules25132989.
Abstract:
Artificial metalloenzymes (ArMs) comprise a synthetic metal complex in a protein scaffold. ArMs display performances combining those of both homogeneous catalysts and biocatalysts. Specifically, ArMs selectively catalyze non-natural reactions and reactions inspired by nature in water under mild conditions. In the past few years, the construction of ArMs that possess a genetically incorporated unnatural amino acid and the directed evolution of ArMs have become of great interest in the field. Additionally, biochemical applications of ArMs have steadily increased, owing to the fact that compartmentalization within a protein scaffold allows the synthetic metal complex to remain functional in a sea of inactivating biomolecules. In this review, we present updates on: (1) the newly reported ArMs, according to their type of reaction, and (2) the unique biochemical applications of ArMs, including chemoenzymatic cascades and intracellular/in vivo catalysis. We believe that ArMs have great potential as catalysts for organic synthesis and as chemical biology tools for pharmaceutical applications.
45
Belchinskaya, Larisa, Lyudmila Novikova, Vladimir Khokhlov, and Jen Ly Tkhi. "Contribution of Ion-Exchange and Non-Ion-Exchange Reactions to Sorption of Ammonium Ions by Natural and Activated Aluminosilicate Sorbent." Journal of Applied Chemistry 2013 (December 25, 2013): 1–9. http://dx.doi.org/10.1155/2013/789410.
Abstract:
The effect of acid and alkaline activation of complex natural aluminosilicate sorbent on its chemical composition, surface properties, and adsorption capacity towards ammonium ions was studied. An increase in specific surface area of the sorbent by 1.3 times after acid treatment and by 1.5 times after alkaline activation was shown. The change of ion-exchange complex of sorbent as a result of activation was observed. Sorption isotherms of ammonium ions on natural and activated samples were obtained and were satisfactorily described by the Langmuir equation. The evaluation and comparison of desorbed cations of alkali and alkaline earth metals were carried out. It was confirmed that ion-exchange processes primarily contributed to sorption of ammonium ions by natural and acid-activated silica-alumina, in contrast to alkali-activated one, for which absorption of nonexchangeable ammonium ions increased adsorption capacity of ammonium ions by 1.5 times.
46
Pätsch, Sebastian, Jevy V. Correia, Benedict J. Elvers, Mareile Steuer, and Carola Schulzke. "Inspired by Nature—Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases." Molecules 27, no. 12 (June 8, 2022): 3695. http://dx.doi.org/10.3390/molecules27123695.
Abstract:
Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.
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Dondoni, Alessandro. "Selected Research Topics of the Dondoni Group over the Last Two Decades (2000–2020)." Synlett 31, no. 14 (May 7, 2020): 1361–71. http://dx.doi.org/10.1055/s-0040-1707107.
Abstract:
From a selection of research topics carried out in our laboratory during the last twenty years it becomes apparent that our main target was the discovery of new or improved synthetic methods together with new properties. Our efforts were made with the aim of being of some utility to other fields of research, with particular emphasis to glycobiology and heterocyle-based bioorganic chemistry. We performed new chemistry mainly in the field of carbohydrate manipulations taking as a primary rule the simplicity and efficiency manners. Toward this end, modern synthetic tools and approaches were employed such as heterocyle-based transformations, multicomponent reactions, organocatalysis, click azide–alkyne cycloadditions, reactions in ionic liquids, click photoinduced thiol-ene coupling, and click sulfur–fluoride exchange chemistry. With these potent methodologies in hand, the syntheses of carbohydrate containing amino acids up to proteins glycosylation were performed.1 Heterocyclic Glycoconjugates and Amino Acids2 Triazole-Linked Oligonucleotides: Application of Click CuAAC3 Non-Natural Glycosyl Amino Acids4 Non-Natural Oligosaccharides5 Calixarene-Based Glycoclusters6 Carbohydrate-Based Building Blocks7 Homoazasugars and Aza-C-disaccharides8 Synthesis of Glycodendrimers9 Peptide and Protein Glycoconjugates10 Conclusions
48
Giovannini, Mattia, Francesca Mori, Simona Barni, Giulia Liccioli, Lucrezia Sarti, and Elio Novembre. "Tailored Sublingual Immunotherapy in a Monosensitized Child with Natural Rubber Latex Allergy." Pharmacology 105, no. 11-12 (2020): 719–22. http://dx.doi.org/10.1159/000508140.
Abstract:
Adverse reactions to natural rubber latex (NRL) represent a group of clinical manifestations that include non-allergic reactions and immediate-type or delayed-type allergic reactions. NRL sublingual immunotherapy (SLIT) has been demonstrated to be an effective and safe practice for latex clinical manifestations with good patient tolerance. A pediatric case of NRL allergy managed with an effective tailored SLIT is described. This case is compelling because the girl, who did not have an atopic background, suffered from NRL allergy with high reactivity and unique monosensitization. To the best of our knowledge, this is the first case with this characteristic described to date. Moreover, the SLIT follow-up time reported was unusually long, extending from childhood to adulthood. The case described highlights several problems of real-life management, and it demonstrates how the pediatric allergist plays a key role in the management of all these issues in order to succeed in guiding the patient through the immunotherapy process with a personalized approach, in line with the precision medicine principles. However, further long-term clinical studies are needed to better define the natural history of NRL allergy and find new potential biomarkers of response to NRL immunotherapy.
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Derbaix, Christian M. "The Impact of Affective Reactions on Attitudes toward the Advertisement and the Brand: A Step toward Ecological Validity." Journal of Marketing Research 32, no. 4 (November 1995): 470–79. http://dx.doi.org/10.1177/002224379503200409.
Abstract:
The author investigates the impact of affective reactions elicited by television advertisements on two variables of major interest in advertising: attitude toward the advertisement (Aad) and postexposure brand attitude (Abp). Previous research has suffered from using non-natural settings, verbal measures of affect, and unknown brands. The author's study avoids forced exposure, uses a real program in which real commercials for unknown and known brands were embedded, and interviews subjects after they have viewed all the commercials. Thus, it offers a more natural setting in which to examine whether previously established relations between affective reactions and Aad and attitude toward the brand (Ab) still hold. The author measures affective reactions through facial expressions, as well as classical verbal measures, and finds that the contribution of affective responses to Aad and Abp is evident for verbal, but not facial, measures of affect. The impact of affective responses varies in a theoretically predictable way across familiar and unfamiliar brands, with the latter being more influenced by verbal affective reactions generated by the advertisement. The author presents several explanations for the results and offers issues for further research.
50
Lan, Ping, Dong Xue Li, A. Ming Chen, Li Hong Lan, Tao Xie, and An Ping Liao. "The Effect of Microwave on the Physical and Chemical Properties of Cassava Starch." Advanced Materials Research 396-398 (November 2011): 2083–87. http://dx.doi.org/10.4028/www.scientific.net/amr.396-398.2083.
Abstract:
Starch is a kind of natural polymers and belongs to the renewable resources. Starch grain in the interior has crystallization area and non-crystalline area where the chemical reactions occur. In this paper, the effect of microwave cassava starch on the physical and chemical properties and characterizated by infrared spectrum and scan electrical microscope (SEM) was investigated. The transparency increase, the viscosity reduce and the anti-sedimentation enhanced after microwave action on tapioca starch. The result of infrared spectrum and scan electrical microscope shows that the original basic structure of cassava starch by microwave has not been damaged but the crystalline structure has been destroyed, which results in the reducing of the crystallinity of starch, the increasing of the contact area of particles and reaction reagents and the improving of the reaction activities .