Characterization of the one-electron oxidized Cu(II)-salen complexes with a side chain aromatic ring: the effect of the indole ring on the Cu(II)-phenoxyl radical species

2017 ◽  
Vol 23 (1) ◽  
pp. 51-59 ◽  
Author(s):  
Hiromi Oshita ◽  
Takayoshi Yoshimura ◽  
Seiji Mori ◽  
Fumito Tani ◽  
Yuichi Shimazaki ◽  
...  
Keyword(s):  
Aromatic Ring ◽  
Phenoxyl Radical ◽  
Side Chain ◽  
Indole Ring ◽  
Radical Species ◽  
Salen Complexes ◽  
The One

Properties of the one-electron oxidized copper(II) salen-type complexes: relationship between electronic structures and reactivities

2014 ◽  
Vol 86 (2) ◽  
pp. 163-172 ◽  
Author(s):  
Yuichi Shimazaki
Keyword(s):  
Electronic Structure ◽  
Electronic Structures ◽  
Functional Model ◽  
Phenoxyl Radical ◽  
Catalytic Cycle ◽  
Model Systems ◽  
Galactose Oxidase ◽  
Primary Alcohols ◽  
Radical Species ◽  
The One

Abstract The Cu(II)-phenoxyl radical formed during the catalytic cycle of galactose oxidase (GO) attracted much attention, and the structures and properties of a number of metal-phenoxyl radical complexes have been studied. Some of the functional model systems of GO reported previously have shown that the Cu complexes oxidize primary alcohols to aldehydes and that the Cu(II)-phenoxyl radical species is formed in the catalytic cycle. Many Cu(II)-phenoxyl radical species have been produced by one-electron oxidation of the Cu(II)-phenolate complexes. On the other hand, one-electron oxidation of a Cu(II)-phenolate complex has the possibility to give different electronic structures, one of which is the Cu(III)-phenolate. From these points of view, this micro review is focused on the one-electron oxidized square-planar Cu(II) complexes of the salen-type ligands. Introduction of substituents into the phenolate moieties and conversion from a 5- to a 6-membered chelate backbone alter the electronic structure of the one-electron oxidized Cu(II) complexes and give rise to a different reactivity of benzyl alcohol oxidation. The relationship between the electronic structure and the reactivity is herein discussed.

scholarly journals Electrochemical and spectroscopic characterization of the conversion of the 7Fe into the 8Fe form of ferredoxin III from Desulfovibrio africanus. Identification of a [4Fe–4S] cluster with one non-cysteine ligand

1989 ◽  
Vol 264 (1) ◽  
pp. 275-284 ◽  
Author(s):  
S J George ◽  
F A Armstrong ◽  
E C Hatchikian ◽  
A J Thomson
Keyword(s):  
Amino Acid ◽  
Pyrolytic Graphite ◽  
Direct Electrochemistry ◽  
Spectroscopic Characterization ◽  
Cysteine Residue ◽  
Side Chain ◽  
Iron Protein ◽  
Plausible Model ◽  
The One

Desulfovibrio africanus ferredoxin III is a protein (Mr 6585) containing one [3Fe-4S]1+,0 and one [4Fe-4S]2+,1+ core cluster when aerobically isolated. The amino acid sequence contains only seven cysteine residues, the minimum required to ligand these two clusters. Cyclic voltammery by means of direct electrochemistry at a pyrolytic-graphite-‘edge’ electrode promoted by neomycin shows that, when reduced, the [3Fe-4S]0 centre reacts rapidly with Fe(II) ion to form a [4Fe-4S]2+ cluster. The latter, which can be reduced at a redox potential similar to that of the other [4Fe-4S] cluster, must include non-thiolate ligation. We propose that the carboxylate side chain of aspartic acid-14 is the most likely candidate, since this amino acid occupies the position of a cysteine residue in the sequence typical of an 8Fe ferredoxin. The magnetic properties at liquid-He temperature of this novel cluster, studied by low-temperature magnetic-c.d. and e.p.r. spectroscopy, are diamagnetic in the oxidized state and S = 3/2 in the one-electron-reduced state. This cluster provides a plausible model for the ligation states of the [4Fe-4S]1+ core in the S = 3/2 cluster of the iron protein of nitrogenase and in Bacillus subtilis glutamine:phosphoribosyl pyrophosphate amidotransferase.

The effect of π–π stacking interaction of the indole ring with the coordinated phenoxyl radical in a nickel(ii)-salen type complex. Comparison with the corresponding Cu(ii) complex

2019 ◽  
Vol 48 (32) ◽  
pp. 12060-12069 ◽  
Author(s):  
Hiromi Oshita ◽  
Takashi Suzuki ◽  
Kyohei Kawashima ◽  
Hitoshi Abe ◽  
Fumito Tani ◽  
...  
Keyword(s):  
Phenoxyl Radical ◽  
Side Chain ◽  
Indole Ring ◽  
Stacking Interaction ◽  
Type Complex ◽  
Π Stacking ◽  
Π Stacking Interaction

A side-chain indole ring showed stacking interaction with the Ni(ii)-phenoxyl radical, but had smaller effects in comparison with that of the Cu(ii)-phenoxyl radical.

Formation and Characterization of Co(III)−Semiquinonate Phenoxyl Radical Species

2007 ◽  
Vol 46 (15) ◽  
pp. 6083-6090 ◽  
Author(s):  
Yuichi Shimazaki ◽  
Ryota Kabe ◽  
Stefan Huth ◽  
Fumito Tani ◽  
Yoshinori Naruta ◽  
...  
Keyword(s):  
Phenoxyl Radical ◽  
Radical Species

Biochemical and Crystallographic Characterization of Homologous Non-peptidic Thrombin Inhibitors Having Alternate Binding Modes

1998 ◽  
Vol 54 (6) ◽  
pp. 1207-1215
Author(s):  
Corey L. Strickland ◽  
John. M. Fevig ◽  
Robert A. Galemmo ◽  
Brian L. Wells ◽  
Charles A. Kettner ◽  
...  
Keyword(s):  
Aromatic Ring ◽  
Thrombin Inhibitors ◽  
Side Chain ◽  
Crystallographic Structure ◽  
Binding Modes ◽  
Tetrahedral Geometry ◽  
Ligand Affinity ◽  
Covalently Bonded ◽  
Crystallographic Structures

The X-ray crystallographic structure of [N-(3-phenylpropionyl)-N-(phenethyl)]-Gly-boroLys-OH (HPBK, Ki  = 0.42 nM, crystallographic R factor to 1.8 Å resolution, 19.6%) complexed with human α-thrombin shows that the boron adopts a tetrahedral geometry and is covalently bonded to the active serine, Ser195. The HPBK phenethyl aromatic ring forms an edge-to-face interaction with the indole side chain of Trp215. Four HPBK analogs containing either electron-withdrawing or electron-donating substitutents at the 3′ position of the phenethyl ring were synthesized in an attempt to modulate ligand affinity by inductive stabilization of the edge-to-face interaction. Refined crystallographic structures of the trifluoromethyl (Ki = 0.37 nM, crystallographic R factor to 2.0 Å resolution = 18.7%), fluoro (Ki = 0.60; R factor to 2.3 Å resolution = 18.4%), methoxy (Ki = 0.91 nM, R factor to 2.2 Å resolution = 19.8%) and methyl (Ki = 0.20 nM, R factor to 2.5 Å resolution = 16.9%) HPBK analogs complexed with thrombin revealed two binding modes for the closely related com-pounds. A less than 1.5-fold variation in affinity was observed for analogs (trifluoromethyl-HPBK and fluoro-HPBK) binding with the edge-to-face interaction. The slight inductive modulation is consistent with the overall weak nature of the edge-to-face interaction. Owing to an unexpected rotation of the phenethyl aromatic ring, the 3′ substituent of two analogs, methoxy-HPBK and methyl-HPBK, made direct contact with the Trp215 indole side chain. Increased affinity of the 3′ methyl analog is attributed to favorable interactions between the methyl group and the Trp215 indole ring. Differences in inhibitor, thrombin and solvent structure are discussed in detail. These results demonstrate the subtle interplay of weak forces that determine the equilibrium binding orientation of inhibitor, solvent and protein.

scholarly journals Synthesis and Polymerization Kinetics of Rigid Tricyanate Ester

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1686
Author(s):  
Andrey Galukhin ◽  
Roman Nosov ◽  
Ilya Nikolaev ◽  
Elena Melnikova ◽  
Daut Islamov ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Single Step ◽  
Polymerization Kinetics ◽  
Scanning Calorimetry ◽  
Modulated Differential Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Polymerization Product ◽  
The One ◽  
Kinetics Of

A new rigid tricyanate ester consisting of seven conjugated aromatic units is synthesized, and its structure is confirmed by X-ray analysis. This ester undergoes thermally stimulated polymerization in a liquid state. Conventional and temperature-modulated differential scanning calorimetry techniques are employed to study the polymerization kinetics. A transition of polymerization from a kinetic- to a diffusion-controlled regime is detected. Kinetic analysis is performed by combining isoconversional and model-based computations. It demonstrates that polymerization in the kinetically controlled regime of the present monomer can be described as a quasi-single-step, auto-catalytic, process. The diffusion contribution is parameterized by the Fournier model. Kinetic analysis is complemented by characterization of thermal properties of the corresponding polymerization product by means of thermogravimetric and thermomechanical analyses. Overall, the obtained experimental results are consistent with our hypothesis about the relation between the rigidity and functionality of the cyanate ester monomer, on the one hand, and its reactivity and glass transition temperature of the corresponding polymer, on the other hand.

scholarly journals Congruence pairs of principal MS-algebras and perfect extensions

2020 ◽  
Vol 70 (6) ◽  
pp. 1275-1288
Author(s):  
Abd El-Mohsen Badawy ◽  
Miroslav Haviar ◽  
Miroslav Ploščica
Keyword(s):  
Boolean Algebra ◽  
Congruence Lattices ◽  
Descriptive Solution ◽  
The One ◽  
Special Case ◽  
Congruence Pair

AbstractThe notion of a congruence pair for principal MS-algebras, simpler than the one given by Beazer for K2-algebras [6], is introduced. It is proved that the congruences of the principal MS-algebras L correspond to the MS-congruence pairs on simpler substructures L°° and D(L) of L that were associated to L in [4].An analogy of a well-known Grätzer’s problem [11: Problem 57] formulated for distributive p-algebras, which asks for a characterization of the congruence lattices in terms of the congruence pairs, is presented here for the principal MS-algebras (Problem 1). Unlike a recent solution to such a problem for the principal p-algebras in [2], it is demonstrated here on the class of principal MS-algebras, that a possible solution to the problem, though not very descriptive, can be simple and elegant.As a step to a more descriptive solution of Problem 1, a special case is then considered when a principal MS-algebra L is a perfect extension of its greatest Stone subalgebra LS. It is shown that this is exactly when de Morgan subalgebra L°° of L is a perfect extension of the Boolean algebra B(L). Two examples illustrating when this special case happens and when it does not are presented.

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