scholarly journals Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

2016 ◽  
Vol 12 ◽  
pp. 732-744
Author(s):  
M Fernanda N N Carvalho ◽  
M João Ferreira ◽  
Ana S O Knittel ◽  
Maria da Conceição Oliveira ◽  
João Costa Pessoa ◽  
...  
Keyword(s):  
Amino Acids ◽  
Reaction Mechanism ◽  
Dft Calculations ◽  
Carbonyl Group ◽  
Transition States ◽  
Ninhydrin Reaction ◽  
Colored Product ◽  
Structural Analogy

A camphor-derived sulfonimine with a conjugated carbonyl group, oxoimine 1 (O2SNC10H13O), reacts with amino acids (glycine, L-alanine, L-phenylalanine, L-leucine) to form a compound O2SNC10H13NC10H14NSO2 (2) which was characterized by spectroscopic means (MS and NMR) and supported by DFT calculations. The product, a single diastereoisomer, contains two oxoimine units connected by a –N= bridge, and thus has a structural analogy to the colored product Ruhemann´s purple obtained by the ninhydrin reaction with amino acids. A plausible reaction mechanism that involves zwitterions, a Strecker degradation of an intermediate imine and water-catalyzed tautomerizations was developed by means of DFT calculations on potential transition states.

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

scholarly journals Catalytic mechanism of the colistin resistance protein MCR-1

2021 ◽  
Author(s):  
Reynier Suardíaz ◽  
Emily Lythell ◽  
Philip Hinchliffe ◽  
Marc van der Kamp ◽  
James Spencer ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Antimicrobial Resistance ◽  
Dft Calculations ◽  
Catalytic Reaction ◽  
Catalytic Mechanism ◽  
Cluster Models ◽  
Colistin Resistance ◽  
Resistance Protein ◽  
Catalytic Reaction Mechanism

Elucidation of the catalytic reaction mechanism of MCR-1 enzyme, responsible for the antimicrobial resistance to colistin, using DFT calculations on cluster models.

scholarly journals Comparison of liver glycosylasparaginases from six vertebrates

1992 ◽  
Vol 282 (3) ◽  
pp. 891-897 ◽  
Author(s):  
O K Tollersrud ◽  
N N Aronson
Keyword(s):  
Amino Acids ◽  
Reaction Mechanism ◽  
Basic Structure ◽  
Low Ph ◽  
Beta Subunit ◽  
Beta Subunits ◽  
Species Identity ◽  
Closely Related Species ◽  
Human Enzyme ◽  
Specific Antisera

Structural and physical properties of glycosylasparaginase (EC 3.5.1.26) from the livers of human, pig, cow, rat, mouse and chicken were compared. The enzyme in all species had a common basic structure of two N-glycosylated subunits of about 24 (alpha) and 20 (beta) kDa joined by non-covalent forces. Subunit-specific antisera against the rat glycosylasparaginase bound specifically and sensitively to the corresponding subunits from all species. Identity of 80% of the amino acids was found between the N-terminal sequences of corresponding pig and rat glycosylasparaginase alpha- and beta-subunits and the deduced sequence from a human glycosylasparaginase cDNA [Fisher, Tollersrud & Aronson (1990) FEBS Lett. 269, 440-444]. The beta-subunit from all three species has an N-terminal threonine reported to be involved in the reaction mechanism for the human enzyme [Kaartinen, Williams, Tomich, Yates, Hood & Mononen (1991) J. Biol. Chem. 266, 5860-5869]. The native enzyme appeared as a heterodimer among the mammals, whereas the chicken enzyme had a greater molecular mass and is probably either a tetramer or a heterodimer bound to an unrelated peptide(s). All glycosylasparaginases were thermostable, requiring temperatures between 65 degrees C and 80 degrees C to be irreversibly inactivated. In addition, they were unusually stable at high pH and remained active in the presence of SDS except at low pH. The pH maximum was between 5.5 and 6 except for the rat and mouse enzymes which had a broad maximum between pH 7 and 8. A number of other properties were observed which also distinguish the enzyme from individual and closely related species.

scholarly journals Adsorption of amino acids on MFI-type zeolite: DFT calculations and experimental results

2012 ◽  
Vol 4 (S1) ◽  
Author(s):  
Kai Stueckenschneider ◽  
Achim Zielesny ◽  
Gerhard Schembecker
Keyword(s):  
Amino Acids ◽  
Dft Calculations ◽  
Experimental Results ◽  
Type Zeolite

scholarly journals Site-directed mutagenesis at aspartate and glutamate residues of xylanase from Bacillus pumilus

1992 ◽  
Vol 288 (1) ◽  
pp. 117-121 ◽  
Author(s):  
E P Ko ◽  
H Akatsuka ◽  
H Moriyama ◽  
A Shinmyo ◽  
Y Hata ◽  
...  
Keyword(s):  
Amino Acids ◽  
Reaction Mechanism ◽  
Amino Acid ◽  
Bacillus Pumilus ◽  
Specific Activity ◽  
Sequence Similarity ◽  
Site Directed Mutagenesis ◽  
Dimensional Structure ◽  
Amino Acid Sequence Similarity ◽  
Directed Mutagenesis

To elucidate the reaction mechanism of xylanase, the identification of amino acids essential for its catalysis is of importance. Studies have indicated the possibility that the reaction mechanism of xylanase is similar to that of hen's egg lysozyme, which involves acidic amino acid residues. On the basis of this assumption, together with the three-dimensional structure of Bacillus pumilus xylanase and its amino acid sequence similarity to other xylanases of different origins, three acidic amino acids, namely Asp-21, Glu-93 and Glu-182, were selected for site-directed mutagenesis. The Asp residue was altered to either Ser or Glu, and the Glu residues to Ser or Asp. The purified mutant xylanases D21E, D21S, E93D, E93S, E182D and E182S showed single protein bands of about 26 kDa on SDS/PAGE. C.d. spectra of these mutant enzymes show no effect on the secondary structure of xylanase, except that of D21E, which shows a little variation. Furthermore, mutations of Glu-93 and Glu-182 resulted in a drastic decrease in the specific activity of xylanase as compared with mutation of Asp-21. On the basis of these results we propose that Glu-93 and Glu-182 are the best candidates for the essential catalytic residues of xylanase.

scholarly journals Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

2021 ◽  
Author(s):  
Fabian A. Watt ◽  
Lukas Burkhardt ◽  
Roland Schoch ◽  
Stefan Mitzinger ◽  
Matthias Bauer ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Coordination Mode ◽  
Quantum Mechanical ◽  
Structural Comparison ◽  
Anion Complex ◽  
Steric Factors ◽  
Group 15 ◽  
Detailed Reaction Mechanism ◽  
The Ideal

We present the unprecedented <i>η</i>3-coordination of the 2-phosphaethynthiolate anion in the complex (PN)<sub>2</sub>La(SCP) (<b>2</b>) [PN = N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate bridged (PN)<sub>2</sub>La(<i>μ</i>-1,3-SCN)<sub>2</sub>La(PN)<sub>2</sub> (<b>3</b>) and azide bridged (PN)<sub>2</sub>La(<i>μ</i>-1,3-N3)<sub>2</sub>La(PN)<sub>2</sub> (<b>4</b>) complexes indicates that the [SCP]<sup>–</sup> coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π-orbital of the [SCP]<sup>–</sup> ligand to the LUMO of complex <b>2</b>, rendering it the ideal precursor for the first functionalization of the [SCP]<sup>–</sup> anion. Complex <b>2</b> was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]<sup>–</sup> ligand to form the first CAAC stabilized group 15 – group 16 fulminate-type complexes (PN)<sub>2</sub>La{SPC(<sup>R</sup>CAAC)} (<b>5a,b</b>) (R = Ad, Me). A detailed reaction mechanism for the SCP to SPC isomerization is proposed based on DFT calculations.

The reactivity of stoichiometric tungsten oxide clusters towards carbon monoxide: the effects of cluster sizes and charge states

2015 ◽  
Vol 17 (17) ◽  
pp. 11499-11508 ◽  
Author(s):  
Shu-Juan Lin ◽  
Jing Cheng ◽  
Chang-Fu Zhang ◽  
Bin Wang ◽  
Yong-Fan Zhang ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Reaction Mechanism ◽  
Dft Calculations ◽  
Tungsten Oxide ◽  
Charge States

DFT calculations were carried out to study the reaction mechanism for tungsten oxide clusters with CO.

Fast and automated identification of reactions with low barriers: the decomposition of 3-hydroperoxypropanal

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Mads Koerstz ◽  
Maria H. Rasmussen ◽  
Jan H. Jensen
Keyword(s):  
Reaction Mechanism ◽  
Systematic Approach ◽  
Transition States ◽  
Semiempirical Methods ◽  
Reaction Products ◽  
Reaction Energy ◽  
Automated Identification ◽  
Reaction Discovery ◽  
Systematic Enumeration ◽  
Computational Resources

We show how fast semiempirical QM methods can be used to significantly decrease the computational expense for automated reaction mechanism discovery, using two different method for generating reaction products: graph-based systematic enumeration of all possible products and the meta-dynamics approach by Grimme (J. Chem. Theory. Comput. 2019, 15, 2847). We test the two approaches on the low-barrier reactions of 3-hydroperoxypropanal, which have been studied by a large variety of reaction discovery approaches and therefore provides a good benchmark. By using PM3 and GFN2-xTB for reaction energy and barrier screening the systematic approach identifies 64 reactions (out of 27,577 possible reactions) for DFT refinement, which in turn identifies the three reactions with lowest barriers plus a previously undiscovered reaction. With optimized hyperparameters meta-dynamics followed by PM3/GFN2-xTB-based screening identifies 15 reactions for DFT refinement, which in turn identifies the three reactions with lowest barrier. The number of DFT refinements can be further reduced to as little as six for both approaches by first verifying the transition states with GFN1-xTB. The main conclusion is that the semiempirical methods are accurate and fast enough to automatically identify promising candidates for DFT refinement for the low barrier reactions of 3-hydroperoxypropanal in about 15-30 minutes using relatively modest computational resources.

scholarly journals On the catalytic transfer hydrogenation of nitroarenes by a cubane-type Mo3S4 cluster hydride: disentangling the nature of the reaction mechanism

2019 ◽  
Vol 21 (31) ◽  
pp. 17221-17231 ◽  
Author(s):  
Vicent S. Safont ◽  
Iván Sorribes ◽  
Juan Andrés ◽  
Rosa Llusar ◽  
Mónica Oliva ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transfer Hydrogenation ◽  
Catalytic Transfer Hydrogenation ◽  
Efficient Catalyst ◽  
Highly Efficient ◽  
Catalytic Transfer

Transfer hydrogenation cluster catalysis operates through a panoply of cycles, according to DFT calculations, affording a highly efficient catalyst.

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