A high-spin alkylperoxo-iron(iii) complex with cis-anionic ligands: implications for the superoxide reductase mechanism

The N3O macrocycle of the 12-TMCO ligand stabilizes a high spin (S = 5/2) [FeIII(12-TMCO)(OOtBu)Cl]+ (3-Cl) species in the reaction of [FeII(12-TMCO)(OTf)2] (1-(OTf)2) with tert-butylhydroperoxide (tBuOOH) in the presence of tetraethylammonium chloride (NEt4Cl) in acetonitrile at -20 °C. In the absence of NEt4Cl the oxo-iron(iv) complex 2 [FeIV(12-TMCO)(O)(CH3CN)]2+ is formed, which can be further converted to 3-Cl by adding NEt4Cl and tBuOOH. The role of the cis-chloride ligand in the stabilization of the FeIII-OOtBu moiety can be extended to other anions including the thiolate ligand relevant to the enzyme superoxide reductase (SOR). The present study underlines the importance of subtle electronic changes and secondary interactions in the stability of the biologically relevant metal-dioxygen intermediates. It also provides some rationale for the dramatically different outcomes of the chemistry of iron(iii)peroxy intermediates formed in the catalytic cycles of SOR (Fe-O cleavage) and cytochrome P450 (O-O bond lysis) in similar N4S coordination environments.

Bioenhanced Rapid Redox Initiation for RAFT Polymerization in the Air

A well-controlled bioenhanced reversible addition-fragmentation chain transfer (RAFT) in the presence of air is carried out by using glucose oxidase (GOx), glucose, ascorbic acid (Asc acid), and ppm level of hemin. The catalytic concentration of hemin is employed to enhance hydrogen peroxide (H₂ O₂ )/Asc acid redox initiation, achieving rapid RAFT polymerization. Narrow molecular weight distributions and high monomer conversion (Ð as low as 1.09 at >95% conversion) are achieved within tens of minutes. Several kinds of monomers are used to verify the universal implication of the presented method. The influences of the pH and feed ratio of each component on the polymerization rate are assessed. Besides, a polymerization rate regulation is realized by managing Asc acid addition. This work significantly increases the rate of redox-initiated GOx-deoxygen RAFT polymerization by using simple and green reactants, facilitating the application of RAFT polymerization in areas such as biomedical applications.

Antisymmetric Spin Exchange in a μ-1,2-Peroxodicopper(II) Complex with an Orthogonal Cu-O-O-Cu Arrangement and S = 1 Spin Ground State Characterized by THz-EPR

A unique type of Cu₂/O₂ adduct with orthogonal (close to 90°) Cu-O-O-Cu arrangement has been proposed for initial stages of O₂ binding at biological type III dicopper sites, and targeted ligand design has now allowed us to emulate such an adduct in a pyrazolate-based μ-η¹ :η¹-peroxodicopper(II) complex (2) with Cu-O-O-Cu torsion φ of 87°, coined ^⊥ P intermediate. Full characterization of 2, including X-ray diffraction (d _O-O = 1.452 Å) and Raman spectroscopy (ν̃_O-O = 807 cm^-1), completes a series of closely related Cu₂/O₂ intermediates featuring μ-η¹ :η¹-peroxodicopper(II) cores with φ ranging from 55° (A, cis-peroxo ^C P; Brinkmeier A.et al., J. Am. Chem. Soc.2021, 143, 10361) via 87° (2, ^⊥ P type) up to 104° (B, approaching trans-peroxo ^T P; Kindermann N.et al., Angew. Chem., Int. Ed.2015, 54, 1738). SQUID magnetometry revealed ferromagnetic interaction of the Cu^II ions and a triplet (S _t = 1) ground state in 2. Frequency-domain THz-EPR has been employed to quantitatively investigate the spin systems of 2 and B. Magnetic transitions within the triplet ground states confirmed their substantial zero-field splittings (ZFS) suggested by magnetometry. Formally forbidden triplet-to-singlet transitions at 56 (2) and 157 cm^-1 (B), which are in agreement with the exchange coupling strengths J _iso inferred from SQUID data, are reported for the first time for coupled dicopper(II) complexes. Rigorous analysis by spin-Hamiltonian-based simulations attributed the corresponding nonzero transition probabilities and the ZFS to substantial antisymmetric (Dzyaloshinskii-Moriya) exchange d and provided robust values and orientations for the d , J , and g tensors. These interactions can be correlated with the Cu-O-O-Cu geometries, revealing a linear increase of J _iso with the Cu-O-O-Cu torsion and a strong linear decrease with the Cu-O-O angle. Relevance of the ^⊥ P intermediate for O₂ activation at type III dicopper sites and a potential role of antisymmetric exchange in the concomitant intersystem crossing are proposed.

Development and Characterization of Films for Food Application Incorporating Porphyran Extracted from Porphyra dioica

Non-biodegradable plastic is one of the biggest environmental problems of our lifetime and, considering the present societal needs, it will get worse. Consequently, there is an urgent need to develop sustainable and renewable alternatives to plastic, such as plastic-like materials obtained from biodegradable polymers, namely sulfated polysaccharides, considered one of the most viable alternatives. There is also a need to obtain these materials in an environmentally and economically sustainable way. The hereby developed process of obtaining film-forming solutions from semi-refined porphyran (PorphSR) uses a green solvent (hot water) with a high extraction yield of semi-refined porphyran (26.66 ± 0.27%) in a reproducible way and with low levels of contaminants. The obtained semi-refined porphyran showed good antioxidant potential in all tests performed: HPSA (Δ0.066 ± 0.002), DPPH (2.23 ± 0.78%), FRAP (0.420 ± 0.014 eq. ascorbic acid µg mg−1 of extract) and ABTS (20.46 ± 0.90%). After being cast into films, the most notable antioxidant properties were those of the semi-refined porphyran in the DPPH, FRAP and ABTS assays and of the pectin, (PorphSR_PcT and PorphSR_PcT_Gly) in the HPSA assay. Morphologically, the films showed relatively homogeneous and low roughness surfaces. It is concluded that the described method to obtain semi-refined porphyran is feasible and reproducible, and that the developed films, mainly PorfP2_PcT_Gly, proved to be a potential candidate for non-biodegradable plastic substitutes.

Enhancing Chemo- and Stereoselectivity in C-H Bond Oxygenation with H2O2 by Nonheme High-Spin Iron Catalysts: The Role of Lewis Acid and Multimetal Centers

Spin states of iron often direct the selectivity in oxidation catalysis by iron complexes using hydrogen peroxide (H₂O₂) on an oxidant. While low-spin iron(III) hydroperoxides display stereoselective C-H bond hydroxylation, the reactions are nonstereoselective with high-spin iron(II) catalysts. The catalytic studies with a series of high-spin iron(II) complexes of N4 ligands with H₂O₂ and Sc³⁺ reported here reveal that the Lewis acid promotes catalytic C-H bond hydroxylation with high chemo- and stereoselectivity. This reactivity pattern is observed with iron(II) complexes containing two cis-labile sites. The enhanced selectivity for C-H bond hydroxylation catalyzed by the high-spin iron(II) complexes in the presence of Sc³⁺ parallels that of the low-spin iron catalysts. Furthermore, the introduction of multimetal centers enhances the activity and selectivity of the iron catalyst. The study provides insights into the development of peroxide-dependent bioinspired catalysts for the selective oxygenation of C-H bonds without the restriction of using iron complexes of strong-field ligands.

Highly Selective and Catalytic Oxygenations of C-H and C=C Bonds by a Mononuclear Nonheme High-Spin Iron(III)-Alkylperoxo Species

The reactivity of a mononuclear high-spin iron(III)-alkylperoxo intermediate [Fe^III (t-BuL^Urea )(OOCm)(OH₂ )]²⁺ (2), generated from [Fe^II (t-BuL^Urea )(H₂ O)(OTf)](OTf) (1) [t-BuL^Urea =1,1'-(((pyridin-2-ylmethyl)azanediyl)bis(ethane-2,1-diyl))bis(3-(tert-butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C-H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C-H bonds of aliphatic substrates with high chemo- and stereoselectivity in the presence of 2,6-lutidine. While 2 itself is a sluggish oxidant, 2,6-lutidine assists the heterolytic O-O bond cleavage of the metal-bound alkylperoxo, giving rise to a reactive metal-based oxidant. The roles of the urea groups on the supporting ligand, and of the base, in directing the selective and catalytic oxygenation of hydrocarbon substrates by 2 are discussed.