Cobalt complexes of pyrrolecarboxamide ligands as catalysts in nitro reduction reactions: influence of electronic substituents on catalysis and mechanistic insights

2017 ◽  
Vol 4 (2) ◽  
pp. 324-335 ◽  
Author(s):  
Sunil Yadav ◽  
Sushil Kumar ◽  
Rajeev Gupta
Keyword(s):  
Substrate Binding ◽  
Cobalt Complexes ◽  
Redox Potentials ◽  
Reduction Reactions ◽  
Square Planar ◽  
Aromatic Heterocyclic ◽  
Mediated Reduction ◽  
Nitro Reduction

Square-planar Co3+ complexes, displaying substrate binding abilities and facile Co3+/2+ redox potentials, function as efficient catalysts for hydrazine-mediated reduction of aromatic, heterocyclic, as well as aliphatic nitro substrates.

scholarly journals Crystal structure of steroid reductase SRD5A reveals conserved steroid reduction mechanism

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yufei Han ◽  
Qian Zhuang ◽  
Bo Sun ◽  
Wenping Lv ◽  
Sheng Wang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Biochemical Characterization ◽  
Substrate Binding ◽  
Binding Pocket ◽  
Substrate Binding Pocket ◽  
Transmembrane Segments ◽  
Therapeutic Molecules ◽  
Binding Cavity ◽  
Immune System Regulation ◽  
Mediated Reduction

AbstractSteroid hormones are essential in stress response, immune system regulation, and reproduction in mammals. Steroids with 3-oxo-Δ4 structure, such as testosterone or progesterone, are catalyzed by steroid 5α-reductases (SRD5As) to generate their corresponding 3-oxo-5α steroids, which are essential for multiple physiological and pathological processes. SRD5A2 is already a target of clinically relevant drugs. However, the detailed mechanism of SRD5A-mediated reduction remains elusive. Here we report the crystal structure of PbSRD5A from Proteobacteria bacterium, a homolog of both SRD5A1 and SRD5A2, in complex with the cofactor NADPH at 2.0 Å resolution. PbSRD5A exists as a monomer comprised of seven transmembrane segments (TMs). The TM1-4 enclose a hydrophobic substrate binding cavity, whereas TM5-7 coordinate cofactor NADPH through extensive hydrogen bonds network. Homology-based structural models of HsSRD5A1 and -2, together with biochemical characterization, define the substrate binding pocket of SRD5As, explain the properties of disease-related mutants and provide an important framework for further understanding of the mechanism of NADPH mediated steroids 3-oxo-Δ4 reduction. Based on these analyses, the design of therapeutic molecules targeting SRD5As with improved specificity and therapeutic efficacy would be possible.

Syntheses, theoretical studies, and crystal structures of [Ni(II)SSRRL](PF6)2 and [Ni(II)SRSRL](Cl)(PF6) that contains anagostic interactions

2020 ◽  
pp. 1-10
Author(s):  
Peyton C. Bainbridge ◽  
Rudy L. Luck ◽  
Nick K. Newberry
Keyword(s):  
Theoretical Calculations ◽  
Structural Data ◽  
Theoretical Studies ◽  
Redox Potentials ◽  
X Ray ◽  
H Nmr ◽  
Irreversible Oxidation ◽  
Square Planar ◽  
Reduced Products ◽  
Reversible Reduction

The syntheses of two square planar nickel complexes containing the condensation and subsequently reduced products obtained by reacting [Ni(en)3](BF4)2 and acetone are reported. The complexes 5,5,7,12,12,14-hexamethyl-1(S),4(S),8(R),11(R)-tetraazacyclotetradecane-nickel(II)[PF6]2 and 5,5,7,12,12,14-hexamethyl-1(S),4(R),8(S),11(R)-tetraazacyclotetradecane-nickel(II)[Cl][PF6] labelled as [Ni(II)SSRRL](PF6)2 and [Ni(II)SRSRL](Cl)(PF6), respectively, were found to have slightly different solubilities that allowed for their purification. The complexes were characterized by FTIR, 1H NMR, and UV–vis spectra. Redox potentials, determined by cyclic voltammetry, established that [Ni(II)SSRRL](PF6)2 exhibits a reversible oxidation (E1/2(ox) = 0.85 V) and reduction (E1/2(red) = −1.59 V), whereas [Ni(II)SRSRL](Cl)(PF6) displays an irreversible oxidation (Epa(ox) = 1.37 V) and reversible reduction (E1/2(red) = −1.62 V) relative to the ferrocene couple at 0.0 V. Single crystal X-ray determinations established that one of the compounds, [Ni(II)SSRRL](PF6)2, contained two [Formula: see text] anions, whereas the other compound, [Ni(II)SRSRL](Cl)(PF6), contained one Cl− and one [Formula: see text] anion. In the solid state, compound [Ni(II)SSRRL](PF6)2 was held together by H-bonds between H atoms on the Ni containing dication and F atoms in the [Formula: see text] anion. Compound [Ni(II)SRSRL](Cl)(PF6) crystallized in the form of dimers held together by interactions between H atoms attached to N atoms on adjacent cations binding to two Cl− anions in the middle with these dimers held together by further H-bonding to interstitial [Formula: see text] anions. Complex [Ni(II)SRSRL](Cl)(PF6) was found to contain anagostic interactions on the bases of NMR (downfield shift in C–H protons) and structural data (2.3 < d(H-Ni) < 2.9 Å), as well as theoretical calculations.

Oxidation of Cobalt(II) Bispidine Complexes with Dioxygen

2017 ◽  
Vol 70 (5) ◽  
pp. 576 ◽  
Author(s):  
Peter Comba ◽  
Bianca Pokrandt ◽  
Hubert Wadepohl
Keyword(s):  
Metal Ions ◽  
Coordination Sphere ◽  
Tertiary Amine ◽  
Cobalt Complexes ◽  
Decay Process ◽  
Oxidation States ◽  
Redox Potentials ◽  
Aerobic Conditions ◽  
High Degree ◽  
Derivatives Of

Bispidine (3,7-diazabicyclo[3.3.1]nonane) ligands, derivatives of diazaadamantane, possess a very rigid backbone and have a high degree of pre-organization for cis-octahedral coordination geometries. Despite their rigidity, they exert a flexible coordination sphere, resulting in stable complexes with a variety of metal ions in various oxidation states. Due to the known high III/II redox potentials of their cobalt complexes, the CoII bispidine complexes are generally resistant to oxidation by dioxygen. Discussed in the present study are various CoII bispidine complexes with tetra- and pentadentate bispidines, with one of these complexes shown to be unstable under aerobic conditions. The decay process has been identified as an oxidative elimination of the 2-methylene pyridine substituent at one of the tertiary amine donors, resulting in picolinate, which is found coordinated to a CoIII product, where the dealkylated N-donor remains unprotonated. The mechanism of this interesting reaction has been studied, and details of the resulting structure of the product complex are discussed.

Square-Planar Cobalt Complexes with Monodentate N-Heterocyclic Carbene Ligation: Synthesis, Structure, and Catalytic Application

2011 ◽  
Vol 30 (17) ◽  
pp. 4687-4694 ◽  
Author(s):  
Zhenbo Mo ◽  
Yuxue Li ◽  
Hung Kay Lee ◽  
Liang Deng
Keyword(s):  
Cobalt Complexes ◽  
Catalytic Application ◽  
Square Planar

scholarly journals Catalytic Efficiency of Basidiomycete Laccases: Redox Potential versus Substrate-Binding Pocket Structure

Catalysts ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 152 ◽  
Author(s):  
Olga Glazunova ◽  
Nikita Trushkin ◽  
Konstantin Moiseenko ◽  
Ivan Filimonov ◽  
Tatyana Fedorova
Keyword(s):  
Redox Potential ◽  
Substrate Binding ◽  
Catalytic Efficiency ◽  
Binding Pocket ◽  
Structural Features ◽  
Redox Potentials ◽  
Substrate Binding Pocket ◽  
Trametes Hirsuta ◽  
Special Cases ◽  
Almost All

Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly provides these differences. The purpose of this work was to study the features of the substrate specificity of four laccases from basidiomycete fungi Trametes hirsuta, Coriolopsis caperata, Antrodiella faginea, and Steccherinum murashkinskyi, which have different redox potentials of the T1 copper center and a different structure of substrate-binding pockets. Enzyme activity toward 20 monophenolic substances and 4 phenolic dyes was measured spectrophotometrically. The kinetic parameters of oxidation of four lignans and lignan-like substrates were determined by monitoring of the oxygen consumption. For the oxidation of the high redox potential (>700 mV) monophenolic substrates and almost all large substrates, such as phenolic dyes and lignans, the redox potential difference between the enzyme and the substrate (ΔE) played the defining role. For the low redox potential monophenolic substrates, ΔE did not directly influence the laccase activity. Also, in the special cases, the structure of the large substrates, such as dyes and lignans, as well as some structural features of the laccases (flexibility of the substrate-binding pocket loops and some amino acid residues in the key positions) affected the resulting catalytic efficiency.

Investigation of cobalt redox mediators and effects of TiO2 film topology in dye-sensitized solar cells

RSC Advances ◽  
2016 ◽  
Vol 6 (61) ◽  
pp. 56580-56588 ◽  
Author(s):  
Majid Safdari ◽  
Peter W. Lohse ◽  
Leif Häggman ◽  
Sara Frykstrand ◽  
Daniel Högberg ◽  
...  
Keyword(s):  
Solar Cells ◽  
Light Absorption ◽  
Dye Sensitized Solar Cells ◽  
Cobalt Complexes ◽  
Redox Potentials ◽  
Redox Mediators ◽  
Visible Light Absorption ◽  
Dye Sensitized ◽  
Sensitized Solar Cells ◽  
Interesting Alternative

Cobalt complexes represent interesting alternative redox mediators in dye-sensitized solar cells, with weak visible light absorption and a wide variety in redox potentials. Its diffusion in mesoporous TiO2 may, however, limit its performance.

Self-assembled gold nanofilms as a simple, recoverable and recyclable catalyst for nitro-reduction

2015 ◽  
Vol 3 (42) ◽  
pp. 21167-21177 ◽  
Author(s):  
Manikkavalli Mohan ◽  
Nagaboopathy Mohan ◽  
Dillip Kumar Chand
Keyword(s):  
Self Assembly ◽  
Recyclable Catalyst ◽  
Liquid Interfaces ◽  
Ambient Conditions ◽  
Reduction Reactions ◽  
Self Assembled ◽  
Nitro Reduction

A facile method to prepare gold nanofilms (AuNFs), from hexaazamacrocycle (L) stabilized AuNPs, by self-assembly at liquid/liquid interfaces is developed. A vial coated with AuNFs was used as a recoverable and reusable catalytic reservoir for nitro-reduction reactions in water under ambient conditions.

Humin as an electron donor for enhancement of multiple microbial reduction reactions with different redox potentials in a consortium

2015 ◽  
Vol 119 (2) ◽  
pp. 188-194 ◽  
Author(s):  
Dongdong Zhang ◽  
Chunfang Zhang ◽  
Zhixing Xiao ◽  
Daisuke Suzuki ◽  
Arata Katayama
Keyword(s):  
Electron Donor ◽  
Microbial Reduction ◽  
Redox Potentials ◽  
Reduction Reactions

Complexes of substituted benzothiazoles. 1. Cobalt(II), copper(II), and zinc(II) complexes of 2,2′-o-phenylenebisbenzothiazole; a potential N or S donor ligand

1979 ◽  
Vol 57 (1) ◽  
pp. 1-7 ◽  
Author(s):  
John Charles Thomas Rendell ◽  
Laurence Kenneth Thompson
Keyword(s):  
Copper Chloride ◽  
Cobalt Complexes ◽  
Chloride Complex ◽  
Donor Ligand ◽  
X Ray ◽  
Square Planar ◽  
Hydrogen Bonded

A series of cobalt(II), copper(II), and zinc(II) complexes of the title ligand are reported. 1:1 complexes of cobalt and zinc, M(OBT)X2 (M = Co, Zn; X = Cl, Br, I, NCS), have four-coordinate pseudo-tetrahedral stereochemistries while for copper (X = Cl, Br), distorted square geometries are suggested. Six-coordinate 1:1 derivatives are also obtained for cobalt and copper, M(OBT)(NO3)2 (M = Co, Cu), while the 1:2 derivative Cu(OBT)2(ClO4)2-2H2O may be square planar. OBT appears to coordinate as an N2 donor in all cases. Preliminary X-ray data confirm a distorted square CuN2Cl2 structure for the copper chloride complex. Hydrogen bonded chloroform solvate molecules appear to be present in three cobalt complexes (X = Cl, Br, NCS).

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