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Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn2 RNRs superoxide (O2.−) was postulated to react with the MnII2 core to yield a MnIIMnIII‐peroxide moiety. The reactivity of complex 1 ([MnII2(O2CCH3)2(BPMP)](ClO4), where HBPMP=2,6‐bis{[(bis(2‐pyridylmethyl)amino]methyl}‐4‐methylphenol) towards O2.− was investigated at −90 °C, generating a metastable species, 2. The electronic absorption spectrum of 2 displayed features (λmax=440, 590 nm) characteristic of a MnIIMnIII‐peroxide species, representing just the second example of such. Electron paramagnetic resonance and X‐ray absorption spectroscopies, and mass spectrometry supported the formulation of 2 as a MnIIMnIII‐peroxide complex. Unlike all other previously reported Mn2‐peroxides, which were unreactive, 2 proved to be a capable oxidant in aldehyde deformylation. Our studies provide insight into the mechanism of O2‐activation in Class Ib Mn2 RNRs, and the highly reactive intermediates in their catalytic cycle. Nucleophilic reactivity: The reaction of a MnII2 complex with superoxide yielded a MnIIMnIII‐peroxide complex which mimics intermediates in class Ib Mn2 ribonucleotide reductases. The MnIIMnIII‐peroxide species displayed an unexpected nucleophilic character in aldehyde deformylation. [ABSTRACT FROM AUTHOR]

Abstract: The crystallization of a SrBi2Nb2O9 gel-glass obtained using the amorphous citrate method was studied by micro-Raman scattering, X-ray diffraction, and electron microscopy techniques. A citric acid–ethanolamine gel with the stoichiometric proportion of the metallic cations was prepared as polymeric precursor and calcined to obtain the amorphous complex. Nanocrystallites with a metastable fluorite-type structure nucleate from the amorphous complex below 500°C, as shown by X-ray scattering and confirmed by electron microscopy. The morphological study by scanning electron microscopy revealed the nucleation of nanocrystals in the glass-like amorphous powder after thermal treatment at 500°C. Raman features characteristic of the stable Aurivillius nanocrystals can be detected after thermal treatment at 550°C, while using X-ray diffraction the crystallization of the Bi-layered perovskite phase is observed only after treatment at 625°C or higher temperatures. Both X-ray and Raman scattering detected single phase nanocrystallites with Aurivillius structure above 650°C. The distinctive Raman features of the different SrBi2Nb2O9 nanocrystallites and its evolution with thermal treatment is presented. [Copyright &y& Elsevier]

Oxygenases have been postulated to utilize d 4 Fe IV and d 8 Cu III oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal-oxygen adducts, [Ni III (OAc)(L)] ( 1b ) and [Cu III (OAc)(L)] ( 2b ), L = N , N' -(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [Ni II (OAc)(L)] - ( 1a ) and [Cu II (OAc)(L)] - ( 2a ). The complexes 1a / b - 2a / b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, X-ray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para -substituted 2,6-di- tert -butylphenols ( p -X-2,6-DTBP; X = OCH 3 , C(CH 3 ) 3 , CH 3 , H, Br, CN, NO 2 ) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d 8 Cu III oxidant displayed a small increase in the rate constant compared to that of the d 7 Ni III oxidant. The d 8 Cu III oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDE C-H ) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b . It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.

Ribonucleotide reductases (RNRs) are essential enzymes required for DNA synthesis. In class Ib Mn 2 RNRs superoxide (O 2 .- ) was postulated to react with the Mn II 2 core to yield a Mn II Mn III -peroxide moiety. The reactivity of complex 1 ([Mn II 2 (O 2 CCH 3 ) 2 (BPMP)](ClO 4 ), where HBPMP=2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol) towards O 2 .- was investigated at -90 °C, generating a metastable species, 2. The electronic absorption spectrum of 2 displayed features (λ max =440, 590 nm) characteristic of a Mn II Mn III -peroxide species, representing just the second example of such. Electron paramagnetic resonance and X-ray absorption spectroscopies, and mass spectrometry supported the formulation of 2 as a Mn II Mn III -peroxide complex. Unlike all other previously reported Mn 2 -peroxides, which were unreactive, 2 proved to be a capable oxidant in aldehyde deformylation. Our studies provide insight into the mechanism of O 2 -activation in Class Ib Mn 2 RNRs, and the highly reactive intermediates in their catalytic cycle., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)