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The Interactions in the Carboxyl Terminus of Human 4-Hydroxyphenylpyruvate Dioxygenase Are Critical to Mediate the Conformation of the Final Helix and the Tail to Shield the Active Site for Catalysis

Lin, Jang-Foung; Sheih, Yung-Lin; Chang, Tsu-Chung; Chang, Ni-Yuan; Chang, Chiung-Wen; Shen, Chia-Pei; Lee, Hwei-Jen
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 09/08/2013 Português
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4-Hydroxylphenylpyruvate dioxygenase (4-HPPD) is an important enzyme for tyrosine catabolism, which catalyzes the conversion of 4-hydroxylphenylpyruvate (4-HPP) to homogentisate. In the present study, human 4-HPPD was cloned and expressed in E. coli. The kinetic parameters for 4-HPP conversion were: kcat = 2.2±0.1 s−1; and Km = 0.08±0.02 mM. Sequence alignments show that human 4-HPPD possesses an extended C-terminus compared to other 4-HPPD enzymes. Successive truncation of the disordered tail which follows the final α-helix resulted in no changes in the Km value for 4-HPP substrate but the kcat values were significantly reduced. The results suggest that this disordered C-terminal tail plays an important role in catalysis. For inspection the effect of terminal truncation on protein structure, mutant models were built. These models suggest that the different conformation of E254, R378 and Q375 in the final helix might be the cause of the activity loss. In the structure E254 interacts with R378, the end residue in the final helix; mutation of either one of these residues causes a ca. 95% reductions in kcat values. Q375 provides bifurcate interactions to fix the tail and the final helix in position. The model of the Q375N mutant shows that a solvent accessible channel opens to the putative substrate binding site...

A Continuum of Progress: Applications of N-Hetereocyclic Carbene Catalysis in Total Synthesis

Izquierdo, Javier; Hutson, Gerri E.; Cohen, Daniel T.; Scheidt, Karl A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetter’s report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis.

Molecular Insight into Substrate Recognition and Catalysis of Baeyer–Villiger Monooxygenase MtmOIV, the Key Frame Modifying Enzyme in the Biosynthesis of Anticancer Agent Mithramycin

Bosserman, Mary A.; Downey, Theresa; Noinaj, Nicholas; Buchanan, Susan K.; Rohr, Jürgen
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Baeyer-Villiger monooxygenases (BVMOs) have been shown to play key roles for the biosynthesis of important natural products. MtmOIV, a homodimeric FAD- and NADPH-dependent BVMO, catalyzes the key frame-modifying steps of the mithramycin biosynthetic pathway, including an oxidative C-C bond cleavage, by converting its natural substrate premithramycin B into mithramycin DK, the immediate precursor of mithramycin. The drastically improved protein structure of MtmOIV along with the high-resolution structure of MtmOIV in complex with its natural substrate premithramycin B are reported here, revealing previously undetected key residues that are important for substrate recognition and catalysis. Kinetic analyses of selected mutants allowed us to probe the substrate binding pocket of MtmOIV, and also to discover the putative NADPH binding site. This is the first substrate-bound structure of MtmOIV providing new insights into substrate recognition and catalysis, which paves the way for the future design of a tailored enzyme for the chemo-enzymatic preparation of novel mithramycin analogues.

Photoredox Activation and Anion Binding Catalysis in the Dual Catalytic Enantioselective Synthesis of β-Amino Esters

Bergonzini, Giulia; Schindler, Corinna S.; Wallentin, Carl-Johan; Jacobsen, Eric N.; Stephenson, Corey R. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2014 Português
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The enantioselective oxidative C-H functionalization of tetrahydroisoquinoline derivatives is achieved through the merger of photoredox and asymmetric anion-binding catalysis. This combination of two distinct catalysis concepts introduces a potentially general approach to asymmetric transformations in oxidative photocatalysis.

Myeloperoxidase acts as a source of free iron during steady-state catalysis by a feedback inhibitory pathway

Maitra, Dhiman; Shaeib, Faten; Abdulhamid, Ibrahim; Abdulridha, Rasha M.; Saed, Ghassan M.; Diamond, Michael P.; Pennathur, Subramaniam; Abu-Soud, Husam M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Myeloperoxidase (MPO) is a heme-containing enzyme that generates hypochlorous acid (HOCl) from chloride (Cl−) and hydrogen peroxide (H2O2). It is implicated in the pathology of several chronic inflammatory conditions such as cardiovascular and pulmonary diseases and cancer. Recently we have shown that HOCl can destroy the heme prosthetic group of hemoproteins. Here, we investigated whether the HOCl formed during steady-state catalysis is able to destroy the MPO heme moiety and thereby function as a major source of free iron. UV–visible spectra and H2O2-specific electrode measurements recorded during steady-state HOCl synthesis by MPO showed that the degree of MPO heme destruction increased after multiple additions of H2O2 (10 μM), precluding the enzyme from functioning at maximum activity (80–90% inhibition). MPO heme destruction occurred only in the presence of Cl−. Stopped-flow measurements revealed that the HOCl-mediated MPO heme destruction was complex and occurred through transient ferric species whose formation and decay kinetics indicated it participates in heme destruction along with subsequent free iron release. MPO heme depletion was confirmed by the buildup of free iron utilizing the ferrozine assay. Hypochlorous acid...

C3N4-H5PMo10V2O40: a dual-catalysis system for reductant-free aerobic oxidation of benzene to phenol

Long, Zhouyang; Zhou, Yu; Chen, Guojian; Ge, Weilin; Wang, Jun
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 13/01/2014 Português
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Hydroxylation of benzene is a widely studied atom economical and environmental benign reaction for producing phenol, aiming to replace the existing three-step cumene process. Aerobic oxidation of benzene with O2 is an ideal and dream process, but benzene and O2 are so inert that current systems either require expensive noble metal catalysts or wasteful sacrificial reducing agents; otherwise, phenol yields are extremely low. Here we report a dual-catalysis non-noble metal system by simultaneously using graphitic carbon nitride (C3N4) and Keggin-type polyoxometalate H5PMo10V2O40 (PMoV2) as catalysts, showing an exceptional activity for reductant-free aerobic oxidation of benzene to phenol. The dual-catalysis mechanism results in an unusual route to create phenol, in which benzene is activated on the melem unit of C3N4 and O2 by the V-O-V structure of PMoV2. This system is simple, highly efficient and thus may lead the one-step production of phenol from benzene to a more practical pathway.

Further Characterization of Cys-Type and Ser-Type Anaerobic Sulfatase Maturating Enzymes Suggests a Commonality in Mechanism of Catalysis†

Grove, Tyler L.; Ahlum, Jessica H.; Qin, Rosie M.; Lanz, Nicholas D.; Radle, Matthew I.; Krebs, Carsten; Booker, Squire J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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The anaerobic sulfatase maturating enzyme from Clostridium perfringens (anSMEcpe) catalyzes the two-electron oxidation of a cysteinyl residue on a cognate protein to a formyglycyl residue (FGly) using a mechanism that involves organic radicals. The FGly residue plays a unique role as a cofactor in a class of enzymes termed arylsulfatases, which catalyze the hydrolysis of various organosulfate monoesters. anSMEcpe has been shown to be a member of the radical S-adenosylmethionine (SAM) family of enzymes, [4Fe–4S] cluster–requiring proteins that use a 5’-deoxyadenosyl 5’-radical (5’-dA•) generated from a reductive cleavage of SAM to initiate radical-based catalysis. Herein, we show that anSMEcpe contains in addition to the [4Fe–4S] cluster harbored by all radical SAM (RS) enzymes, two additional [4Fe–4S] clusters, similar to the radical SAM protein AtsB, which catalyzes the two-electron oxidation of a seryl residue to a FGly residue. We show by size-exclusion chromatography that both AtsB and anSMEcpe are monomeric proteins, and site-directed mutagenesis studies on AtsB reveal that individual Cys→Ala substitutions at seven conserved positions result in insoluble protein, consistent with those residues acting as ligands to the two additional [4Fe–4S] clusters. Ala substitutions at an additional conserved Cys residue (C291 in AtsB; C276 in anSMEcpe) afford proteins that display intermediate behavior. These proteins exhibit reduced solubility and drastically reduced activity...

Multi-Scale Computational Enzymology: Enhancing Our Understanding of Enzymatic Catalysis

Gherib, Rami; Dokainish, Hisham M.; Gauld, James W.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 31/12/2013 Português
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Elucidating the origin of enzymatic catalysis stands as one the great challenges of contemporary biochemistry and biophysics. The recent emergence of computational enzymology has enhanced our atomistic-level description of biocatalysis as well the kinetic and thermodynamic properties of their mechanisms. There exists a diversity of computational methods allowing the investigation of specific enzymatic properties. Small or large density functional theory models allow the comparison of a plethora of mechanistic reactive species and divergent catalytic pathways. Molecular docking can model different substrate conformations embedded within enzyme active sites and determine those with optimal binding affinities. Molecular dynamics simulations provide insights into the dynamics and roles of active site components as well as the interactions between substrate and enzymes. Hybrid quantum mechanical/molecular mechanical (QM/MM) can model reactions in active sites while considering steric and electrostatic contributions provided by the surrounding environment. Using previous studies done within our group, on OvoA, EgtB, ThrRS, LuxS and MsrA enzymatic systems, we will review how these methods can be used either independently or cooperatively to get insights into enzymatic catalysis.

Nickel-Catalyzed Regiodivergent Opening of Epoxides with Aryl Halides: Co-Catalysis Controls Regioselectivity

Zhao, Yang; Weix, Daniel J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Epoxides are versatile intermediates in organic synthesis, but have rarely been employed in cross-coupling reactions. We report that bipyridine-ligated nickel can mediate the addition of functionalized aryl halides, a vinyl halide, and a vinyl triflate to epoxides under reducing conditions. For terminal epoxides, the regioselectivity of the reaction depends upon the co-catalyst employed. Iodide co-catalysis results in opening at the less hindered position via an iodohydrin intermediate. Titanocene co-catalysis results in opening at the more hindered position, presumably via TiIII-mediated radical generation. 1,2-Disubstituted epoxides are opened under both conditions to form predominantly the trans product.

MauG, a diheme enzyme that catalyzes tryptophan tryptophylquinone biosynthesis by remote catalysis

Shin, Sooim; Davidson, Victor L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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MauG contains two c-type hemes with atypical physical and catalytic properties. While most c-type cytochromes function simply as electron transfer mediators, MauG catalyzes the completion of tryptophan tryptophylquinone (TTQ) biosynthesis within a precursor protein of methylamine dehydrogenase. This posttranslational modification is a six-electron oxidation that requires crosslinking of two Trp residues, oxygenation of a Trp residue and oxidation of the resulting quinol to TTQ. These reactions proceed via a bis-FeIV state in which one heme is present as FeIV=O and the other is FeIV with axial heme ligands provided by His and Tyr side chains. Catalysis does not involve direct contact between the protein substrate and either heme of MauG. Instead it is accomplished by remote catalysis using a hole hopping mechanism of electron transfer in which Trp residues of MauG are reversibly oxidized. In this process, long range electron transfer is coupled to the radical mediated chemical reactions that are required for TTQ biosynthesis.

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

Jones, Amanda C.; May, Jeremy A.; Sarpong, Richmond; Stoltz, Brian M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 03/03/2014 Português
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Catalysis and synthesis are intimately linked in modern organic chemistry. The synthesis of complex molecules is an ever evolving area of science. In many regards, the inherent beauty associated with a synthetic sequence can be linked to a certain combination of the creativity with which a sequence is designed and the overall efficiency with which the ultimate process is performed. In synthesis, as in other endeavors, beauty is very much in the eyes of the beholder.[**] It is with this in mind that we will attempt to review an area of synthesis that has fascinated us and that we find extraordinarily beautiful, namely the combination of catalysis and sigmatropic rearrangements in consecutive and cascade sequences.

Thyroid hormone responsive protein Spot14 enhances catalysis of fatty acid synthase in lactating mammary epithelium[S]

Rudolph, Michael C.; Wellberg, Elizabeth A.; Lewis, Andrew S.; Terrell, Kristina L.; Merz, Andrea L.; Maluf, N. Karl; Serkova, Natalie J.; Anderson, Steven M.
Fonte: The American Society for Biochemistry and Molecular Biology Publicador: The American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em /06/2014 Português
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Thyroid hormone responsive protein Spot 14 has been consistently associated with de novo fatty acid synthesis activity in multiple tissues, including the lactating mammary gland, which synthesizes large quantities of medium chain fatty acids (MCFAs) exclusively via FASN. However, the molecular function of Spot14 remains undefined during lactation. Spot14-null mice produce milk deficient in total triglyceride and de novo MCFA that does not sustain optimal neonatal growth. The lactation defect was rescued by provision of a high fat diet to the lactating dam. Transgenic mice overexpressing Spot14 in mammary epithelium produced total milk fat equivalent to controls, but with significantly greater MCFA. Spot14-null dams have no diminution of metabolic gene expression, enzyme protein levels, or intermediate metabolites that accounts for impaired de novo MCFA. When [13C] fatty acid products were quantified in vitro using crude cytosolic lysates, native FASN activity was 1.6-fold greater in control relative to Spot14-null lysates, and add back of Spot14 partially restored activity. Recombinant FASN catalysis increased 1.4-fold and C = 14:0 yield was enhanced 4-fold in vitro following addition of Spot14. These findings implicate Spot14 as a direct protein enhancer of FASN catalysis in the mammary gland during lactation when maximal MCFA production is needed.

Hydrogen Tunneling Links Protein Dynamics to Enzyme Catalysis

Klinman, Judith P.; Kohen, Amnon
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
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The relationship between protein dynamics and function is a subject of considerable contemporary interest. Although protein motions are frequently observed during ligand binding and release steps, the contribution of protein motions to the catalysis of bond making/breaking processes is more difficult to probe and verify. Here, we show how the quantum mechanical hydrogen tunneling associated with enzymatic C–H bond cleavage provides a unique window into the necessity of protein dynamics for achieving optimal catalysis. Experimental findings support a hierarchy of thermodynamically equilibrated motions that control the H-donor and -acceptor distance and active-site electrostatics, creating an ensemble of conformations suitable for H-tunneling. A possible extension of this view to methyl transfer and other catalyzed reactions is also presented. The impact of understanding these dynamics on the conceptual framework for enzyme activity, inhibitor/drug design, and biomimetic catalyst design is likely to be substantial.

Coordinating Subdomains of Ferritin Protein Cages with Catalysis and Biomineralization viewed from the C4 Cage Axes

Theil, Elizabeth C.; Turano, Paola; Ghini, Veronica; Allegrozzi, Marco; Bernacchioni, Caterina
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Integrated ferritin protein cage function is the reversible synthesis of protein-caged, solid Fe2O3•H2O minerals from Fe2+, for metabolic iron concentrates and oxidant protection; biomineral order varies in different ferritin proteins. The conserved 4, 3, 2 geometric symmetry of ferritin protein cages, parallels subunit dimer, trimer and tetramer interfaces, and coincides with function at several cage axes. Multiple subdomains distributed in the self- assembling ferritin nanocages have functional relationships to cage symmetry such as Fe2+ transport though ion channels (3-fold symmetry), biomineral nucleation/order (4-fold symmetry) and mineral dissolution (3-fold symmetry) studied in ferritin variants. Cage subunit dimers (2-fold symmetry) influence iron oxidation and mineral dissolution, based on effects of natural or synthetic subunit dimer crosslinks. 2Fe2+/O2 catalysis in ferritin occurs in single subunits, but with cooperativity (n=3) that is possibly related to the structure/function of the ion channels, which are constructed from segments of 3 subunits. Here, we study 2Fe2+ + O2 protein catalysis (diferric peroxo formation) and dissolution of ferritin Fe2O3•H2O biominerals in variants with altered subunit interfaces for trimers (ion channels)...

Construction of fat1 Gene Expression Vector and Its Catalysis Efficiency in Bovine Fetal Fibroblast Cells

Liu, Boyang; Yang, Runjun; Li, Junya; Zhang, Lupei; Liu, Jing; Lu, Chunyan; Lian, Chuanjiang; Li, Zezhong; Zhang, Yonghong; Zhang, Liying; Zhao, Zhihui
Fonte: Asian-Australasian Association of Animal Production Societies (AAAP) and Korean Society of Animal Science and Technology (KSAST) Publicador: Asian-Australasian Association of Animal Production Societies (AAAP) and Korean Society of Animal Science and Technology (KSAST)
Tipo: Artigo de Revista Científica
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The FAT-1 protein is an n-3 fatty acid desaturase, which can recognize a range of 18- and 20-carbon n-6 substrates and transform n-6 polyunsaturated fatty acids (PUFAs) into n-3 PUFAs while n-3 PUFAs have beneficial effect on human health. Fat1 gene is the coding sequence from Caenorhabditis elegans which might play an important role on lipometabolism. To reveal the function of fat1 gene in bovine fetal fibroblast cells and gain the best cell nuclear donor for transgenic bovines, the codon of fat1 sequence was optimized based on the codon usage frequency preference of bovine muscle protein, and directionally cloned into the eukaryotic expression vector pEF-GFP. After identifying by restrictive enzyme digests with AatII/XbaI and sequencing, the fusion plasmid pEF-GFP-fat1 was identified successfully. The pEF-GFP-fat1 vector was transfected into bovine fetal fibroblast cells mediated by Lipofectamine2000TM. The positive bovine fetal fibroblast cells were selected by G418 and detected by RT-PCR. The results showed that a 1,234 bp transcription was amplified by reverse transcription PCR and the positive transgenic fat1 cell line was successfully established. Then the expression level of fat1 gene in positive cells was detected using quantitative PCR...

Impact of residues remote from the catalytic centre on enzyme catalysis of copper nitrite reductase

Leferink, Nicole G. H.; Antonyuk, Svetlana V.; Houwman, Joseline A.; Scrutton, Nigel S.; Eady, Robert R.; Hasnain, S. Samar
Fonte: Nature Pub. Group Publicador: Nature Pub. Group
Tipo: Artigo de Revista Científica
Publicado em 15/07/2014 Português
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Enzyme mechanisms are often probed by structure-informed point mutations and measurement of their effects on enzymatic properties to test mechanistic hypotheses. In many cases, the challenge is to report on complex, often inter-linked elements of catalysis. Evidence for long-range effects on enzyme mechanism resulting from mutations remains sparse, limiting the design/redesign of synthetic catalysts in a predictable way. Here we show that improving the accessibility of the active site pocket of copper nitrite reductase by mutation of a surface-exposed phenylalanine residue (Phe306), located 12 Å away from the catalytic site type-2 Cu (T2Cu), profoundly affects intra-molecular electron transfer, substrate-binding and catalytic activity. Structures and kinetic studies provide an explanation for the lower affinity for the substrate and the alteration of the rate-limiting step in the reaction. Our results demonstrate that distant residues remote from the active site can have marked effects on enzyme catalysis, by driving mechanistic change through relatively minor structural perturbations.

Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina

Kurta, Sergiy A; Mykytyn, Igor M; Tatarchuk, Tetiana R
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 15/07/2014 Português
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On the basis of X-ray diffraction and mass spectrometric analysis of carrier γ-Al2O3 and catalysts CuCl2/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands “Harshow” and “MEDС-B” was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl2 cation stoichiometry and structure of the proposed model crystal quasichemical industrial catalyst permeated type MEDС-B for oxidative chlorination of ethylene. On the basis of quantum-mechanical calculations, we propose a new mechanism of catalysis crystal quasichemical oxidative chlorination of ethylene reaction for the catalysts of this type (MEDС-B) and confirmed the possibility of such a mechanism after the analysis of mass spectrometric studies of the active phase (H2 [CuCl4]) catalyst oxidative chlorination of ethylene. The possibility of the formation of atomic and molecular chlorine on the oxidative chlorination of ethylene catalyst surface during Deacon reaction was displaying, which may react with ethylene to produce 1,2-dichloroethane. For the active phase (H [CuCl2]), catalyst offered another model of the metal complex catalyst oxidative chlorination of ethylene deposited type (firm ‘Harshow...

DNA–Based Asymmetric Catalysis: Role of Ionic Solvents and Glymes

Zhao, Hua; Shen, Kai
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Recently, DNA has been evaluated as a chiral scaffold for metal complexes to construct so called ‘DNA-based hybrid catalysts’, a robust and inexpensive alternative to enzymes. The unique chiral structure of DNA allows the hybrid catalysts to catalyze various asymmetric synthesis reactions. However, most current studies used aqueous buffers as solvents for these asymmetric reactions, where substrates/products are typically suspended in the solutions. The mass transfer limitation usually requires a long reaction time. To overcome this hurdle and to advance DNA-based asymmetric catalysis, we evaluated a series of ionic liquids (ILs), inorganic salts, deep eutectic solvents (DES), glymes, glycols, acetonitrile and methanol as co-solvents/additives for the DNA-based asymmetric Michael addition. In general, these additives induce indistinguishable changes to the DNA B-form duplex conformation as suggested by circular dichroism (CD) spectroscopy, but impose a significant influence on the catalytic efficiency of the DNA-based hybrid catalyst. Conventional organic solvents (e.g. acetonitrile and methanol) led to poor product yields and/or low enantioselectivities. Most ILs and inorganic salts cause the deactivation of the hybrid catalyst except 0.2 M [BMIM][CF3COO] (95.4% ee and 93% yield) and 0.2 M [BMIM]Cl (93.7% ee and 89% yield). Several other additives have also been found to improve the catalytic efficiency of the DNA-based hybrid catalyst (control reaction without additive gives >99% ee and 87% yield): 0.4 M glycerol (>99% ee and 96% yield at 5 °C or 96.2% ee and 83% yield at room temperature)...

The Development of Visible-Light Photoredox Catalysis in Flow

Garlets, Zachary J.; Nguyen, John D.; Stephenson, Corey R. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Visible-light photoredox catalysis has recently emerged as a viable alternative for radical reactions otherwise carried out with tin and boron reagents. It has been recognized that by merging photoredox catalysis with flow chemistry, slow reaction times, lower yields, and safety concerns may be obviated. While flow reactors have been successfully applied to reactions carried out with UV light, only recent developments have demonstrated the same potential of flow reactors for the improvement of visible-light-mediated reactions. This review examines the initial and continuing development of visible-light-mediated photoredox flow chemistry by exemplifying the benefits of flow chemistry compared with conventional batch techniques.

Electrostatic transition state stabilization rather than reactant destabilization provides the chemical basis for efficient chorismate mutase catalysis

Burschowsky, Daniel; van Eerde, André; Ökvist, Mats; Kienhöfer, Alexander; Kast, Peter; Hilvert, Donald; Krengel, Ute
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Chorismate mutase (CM) is a textbook model for enzyme catalysis. Although it promotes a simple unimolecular reaction, the origins of its 2-million–fold rate acceleration have been debated for decades. The relative importance of electrostatic transition state stabilization versus ground state destabilization has been a particularly contentious issue. High-resolution crystallographic snapshots of an engineered CM variant and its complexes with substrate, transition state analog, and product now provide strong experimental evidence that properly positioned active-site charges are essential in this system and that preorganization of the substrate in a reactive conformation contributes relatively little to catalysis. A proper understanding of the role of electrostatics in this and other enzymes is important for ongoing efforts to design new enzymes de novo.