The catalytic activity of high-valent iron-oxo active species of heme enzymes is known to be dependent on the nature of the axial ligand trans to the iron-oxo group. In a similar fashion, experimental studies on iron-oxo porphyrin biomimetic systems have shown a significant axial ligand effect on ethylbenzene hydroxylation, with an axial acetonitrile ligand leading to phenyl hydroxylation products and an axial chloride anion giving predominantly benzyl hydroxylation products. To elucidate the fundamental factors that distinguish this regioselectivity reversal in iron-oxo porphyrin catalysis, we have performed a series of density functional theory calculations on the hydroxylation of ethylbenzene by [Fe(IV)=O(Por(+.))L] (Por = porphyrin; L = NCCH(3) or Cl(-)), which affords 1-phenylethanol and p-ethylphenol products. The calculations confirm the experimentally determined product distributions. Furthermore, a detailed analysis of the electronic differences between the two oxidants shows that their reversed regioselectivity is a result of differences in orbital interactions between the axial ligand and iron-oxo porphyrin system. In particular, three high-lying orbitals (pi*(xz), pi*(yz) and a(2u)), which are singly occupied in the reactant complex, are stabilised with an anionic ligand such as Cl(-), which leads to enhanced HOMO-LUMO energy gaps. As a consequence, reactions leading to cationic intermediates through the two-electron reduction of the metal centre are disfavoured. The aliphatic hydroxylation mechanism, in contrast, is a radical process in which only one electron is transferred in the rate-determining transition state, which means that the effect of the axial ligand on this mechanism is much smaller.
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http://dx.doi.org/10.1002/chem.200802234 | DOI Listing |
Dalton Trans
January 2025
Chongqing Key Laboratory of Green Catalysis Materials and Technology, College of Chemistry, Chongqing Normal University, Chongqing 401331, China.
A deeper understanding of the mechanisms underlying transition metal-catalyzed transformation is crucial for developing innovative strategies to synthesize chiral organoselenium compounds. In this study, we developed and investigated a three-layer chirality relay model for the rhodium-catalyzed asymmetric hydroselenation of alkenes through density functional theory (DFT) calculations. In the back layer of this model, the four bulky substituents on the phosphorus atom of the bidentate chiral MeO-BIPHEP ligand were positioned on axial and equatorial bonds, thereby influencing the configuration of the middle layer.
View Article and Find Full Text PDFBiochemistry
January 2025
Laboratory of Clinical Biochemistry and Metabolism, Department of General Pediatrics, Adolescent Medicine and Neonatology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg im Breisgau 79106, Germany.
Human CblC catalyzes the indispensable processing of dietary vitamin B by the removal of its β-axial ligand and an either one- or two-electron reduction of its cobalt center to yield cob(II)alamin and cob(I)alamin, respectively. Human CblC possesses five cysteine residues of an unknown function. We hypothesized that Cys149, conserved in mammals, tunes the CblC reactivity.
View Article and Find Full Text PDFChem Asian J
January 2025
Nanjing University, School of Chemistry and Chemial Engineering, 163 Xianlin Avenue, 210023, Nanjing, CHINA.
Axial chiral biaryl skeletons are widely found in biologically active molecules, catalysts and chiral functional materials. However, highly catalytic stereoselective synthesis of tetra-ortho-substituted biaryls remains a challenging task. In this paper, we describe an efficient approach for construction of axially tetra-ortho-substituted biaryls via Suzuki-Miyaura coupling in the presence of a chiral monophosphate ligand developed by ourselves.
View Article and Find Full Text PDFJ Trace Elem Med Biol
January 2025
Center for Global Health Research (CGHR), Saveetha Medical College, Saveetha Institute of Medical and Technical Sciences (SIMATS), Saveetha University, Chennai, India. Electronic address:
[CuL(tmen)] is a sequence of four ternary mononuclear Schiff base copper(II) complexes that are derived from L-valine, suitable 5'-substituted-2'-hydroxyacetophenones (where the substituents are -Cl for L, -Me for L, -OMe for L, and -H for L), and tmen (where tmen-N,N,N',N' tetramethyl ethylenediamine). Without isolating the Schiff base ligand or producing any other intermediate products, all of the complexes were synthesised. These compounds were identified using elemental analysis, molar conductance, UV-Vis, FTIR, EPR, VSM-RT, and CD spectra.
View Article and Find Full Text PDFBiomed Pharmacother
January 2025
Czech Academy of Sciences, Institute of Biophysics, Kralovopolska 135, Brno CZ-61200, Czech Republic; Department of Biophysics, Faculty of Science, Palacky University, Slechtitelu 27, Olomouc 783 71, Czech Republic. Electronic address:
Platinum(IV) compounds possess distinct properties that set them apart from platinum(II) compounds. Often designed as prodrugs, they are reduced within cancer cells to their active platinum(II) form, enabling their cytotoxic effects. Their versatility also lies in their ability to be functionalized and conjugated with bioactive molecules to enhance cancer cell targeting.
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