A New Thiolate-Bound Dimanganese Cluster as a Structural and Functional Model for Class Ib Ribonucleotide Reductases.

In class Ib ribonucleotide reductases (RNRs) a dimanganese(II) cluster activates superoxide (O2 ⋅- ) rather than dioxygen (O2 ), to access a high valent MnIII -O2 -MnIV species, responsible for the oxidation of tyrosine to tyrosyl radical. In a biomimetic approach, we report the synthesis of a thiolate-bound dimanganese complex [MnII 2 (BPMT)(OAc)2 ](ClO)4 (BPMT=(2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-methylthiophenolate) (1) and its reaction with O2 ⋅- to form a [(BPMT)MnO2 Mn]2+ complex 2. Resonance Raman investigation revealed the presence of an O-O bond in 2, while EPR analysis displayed a 16-line St =1/2 signal at g=2 typically associated with a MnIII MnIV core, as detected in class Ib RNRs. Unlike all other previously reported Mn-O2 -Mn complexes, generated by O2 ⋅- activation at Mn2 centers, 2 proved to be a capable electrophilic oxidant in aldehyde deformylation and phenol oxidation reactions, rendering it one of the best structural and functional models for class Ib RNRs.

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 N2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Temporal trends in treatment strategies and clinical outcomes among patients with advanced chronic kidney disease and ST-elevation myocardial infarctions: results from the Bremen STEMI registry.

BACKGROUND: Although the detrimental effects of advanced chronic kidney disease (CKD) on prognosis in coronary artery disease is known, there are few data on the efficacy and safety of modern interventional therapies and medications in patients with advanced CKD, because this special patient cohort is often excluded or underrepresented in randomized trials. METHODS: In the present study all patients admitted with ST-elevation myocardial infarctions (STEMI) from the region of Bremen/Germany treated between 2006 and 2019 were analyzed. Advanced CKD was defined as glomerular filtration rate < 45 ml/min. RESULTS: Of 9605 STEMI-patients, 1018 (10.6%) had advanced CKD with a serum creatinine of 2.22 ± 4.2 mg/dl at admission and with lower rates of primary percutaneous coronary intervention (pPCI) (84.1 vs. 94.1%, p < 0.01) and higher all-cause-mortality (44.4 vs. 3.6%, p < 0.01). Over time, advanced CKD-patients were more likely to be treated with pPCI (2015-2019: 90.3% vs. 2006-2010:75.8%, p < 0.01) and with ticagrelor/prasugrel (59.6% vs. 1.7%, p < 0.01) and drug eluting stents (90.7% vs. 1.3%, p < 0.01). During the study period a decline in adverse ischemic events (OR 0.3, 95% CI 0.1-0.7) and an increase in bleedings (OR 2.2, 95% CI 1.3-3.8) within 1 year after the index event could be observed in patients with advanced CKD while 1-year-mortality (OR 1.0, 95% CI 0.7-1.4) and rates of acute kidney injury (OR 1.2, 95% CI 0.8-1.7) did not change in a multivariate model. Both, ticagrelor/prasugrel (OR 0.48, 95% CI 0.2-0.98) and DES (OR 0.38, 95% CI 0.2-0.8) were associated with a decrease in ischemic events at 1 year. CONCLUSIONS: During the observed time period STEMI-patients with advanced CKD were more likely to be treated with primary PCI, ticagrelor or prasugrel and DE-stents. These changes probably have contributed to the decline in ischemic events and the increase in bleedings within 1 year after STEMI while overall mortality at 1-year remained unchanged for this high-risk patient group.

A Pseudotetrahedral Terminal Oxoiron(IV) Complex: Mechanistic Promiscuity in C-H Bond Oxidation Reactions.

S=2 oxoiron(IV) species act as reactive intermediates in the catalytic cycle of nonheme iron oxygenases. The few available synthetic S=2 FeIV =O complexes known to date are often limited to trigonal bipyramidal and very rarely to octahedral geometries. Herein we describe the generation and characterization of an S=2 pseudotetrahedral FeIV =O complex 2 supported by the sterically demanding 1,4,7-tri-tert-butyl-1,4,7-triazacyclononane ligand. Complex 2 is a very potent oxidant in hydrogen atom abstraction (HAA) reactions with large non-classical deuterium kinetic isotope effects, suggesting hydrogen tunneling contributions. For sterically encumbered substrates, direct HAA is impeded and an alternative oxidative asynchronous proton-coupled electron transfer mechanism prevails, which is unique within the nonheme oxoiron community. The high reactivity and the similar spectroscopic parameters make 2 one of the best electronic and functional models for a biological oxoiron(IV) intermediate of taurine dioxygenase (TauD-J).

Spectroscopic Characterization of a Reactive [Cu2 (µ-OH)2 ]2+ Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction.

CuI /TEMPO (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl) catalyst systems are versatile catalysts for aerobic alcohol oxidation reactions to selectively yield aldehydes. However, several aspects of the mechanism are yet unresolved, mainly because of the lack of identification of any reactive intermediates. Herein, we report the synthesis and characterization of a dinuclear [L12 Cu2 ]2+ complex 1, which in presence of TEMPO can couple the catalytic 4 H+ /4 e- reduction of O2 to water to the oxidation of benzylic and aliphatic alcohols. The mechanisms of the O2 -reduction and alcohol oxidation reactions have been clarified by the spectroscopic detection of the reactive intermediates in the gas and condensed phases, as well as by kinetic studies on each step in the catalytic cycles. Bis(µ-oxo)dicopper(III) (2) and bis(µ-hydroxo)dicopper(II) species 3 are shown as viable reactants in oxidation catalysis. The present study provides deep mechanistic insight into the aerobic oxidation of alcohols that should serve as a valuable foundation for ongoing efforts dedicated towards the understanding of transition-metal catalysts involving redox-active organic cocatalysts.

Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center.

In soluble methane monooxygenase enzymes (sMMO), dioxygen (O2) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono- or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, 1-trans, that activates O2 to form the corresponding iron(IV)-oxo complex, 2-trans, via a mechanism reminiscent of the O2 activation process in sMMO. The conversion of 1-trans to 2-trans proceeds via the intermediate formation of an iron(III)-superoxide species 3, which could be trapped and spectroscopically characterized at -50 °C. Surprisingly, 3 is a stronger oxygen atom transfer (OAT) agent than 2-trans; 3 performs OAT to 1-trans or PPh3 to yield 2-trans quantitatively. Furthermore, 2-trans oxidizes the aromatic C-H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3, represents new domains of oxoiron(IV) and superoxoiron(III) reactivities.

After ten years of follow-up, no difference between supportive care plus immunosuppression and supportive care alone in IgA nephropathy.

The randomized, controlled STOP-IgAN trial in patients with IgA nephropathy (IgAN) and substantial proteinuria showed no benefit of immunosuppression added on top of supportive care on renal function over three years. As a follow-up we evaluated renal outcomes in patients over a follow-up of up to ten years in terms of serum creatinine, proteinuria, end-stage kidney disease (ESKD), and death. The adapted primary endpoint was the time to first occurrence of a composite of death, ESKD, or a decline of over 40% in the estimated glomerular filtration rate (eGFR) compared to baseline at randomization into STOP-IgAN. Data were analyzed by Cox-regression models. Follow-up data were available for 149 participants, representing 92% of the patients originally randomized. Median follow-up was 7.4 years (inter quartile range 5.7 to 8.3 years). The primary endpoint was reached in 36 of 72 patients randomized to supportive care and 35 of 77 patients randomized to additional immunosuppression (hazard ratio 1.20; 95% confidence interval 0.75 to 1.92). ESKD occurred in 17 of the patients with supportive care and in 20 of the patients with additional immunosuppression. Additionally, the rates of eGFR loss over 40% and annual eGFR loss did not differ between groups. Two patients died with supportive care and three with additional immunosuppression. Thus, within the limitations of a retrospective study, over a follow-up of up to ten years, and using an adapted primary endpoint, we failed to detect differences in key clinical outcomes in IgAN patients randomized to receive added immunosuppression on top of supportive care versus supportive care alone.

Zero Diffusive Sodium Balance in Hemodialysis Provided by an Algorithm-Based Electrolyte Balancing Controller: A Proof of Principle Clinical Study.

Restoring and controlling fluid volume homeostasis is still a challenge in contemporary end-stage kidney disease patients treated by intermittent hemodialysis (HD) or hemodiafiltration (HDF). This primary target is achieved by ultrafiltration (dry weight probing) and control of intradialytic sodium transfer (dialysate-plasma Na gradient). The latter task is mostly ignored in clinical practice by applying a dialysate sodium prescription uniform for all patients of the dialysis center but unaligned to individual plasma sodium levels. Depending on the patient's natremia, a positive gradient gives rise to intradialytic diffusive sodium load and postdialytic thirst. On the contrary, a negative gradient may cause unwanted diffusive sodium removal and intradialytic symptoms. To overcome these challenges, a new conductivity-based electrolyte balancing algorithm embedded in a hemodialysis machine with the aim to achieve "zero diffusive sodium balance" in HD and online HDF treatments was tested in the form of a prospective clinical trial. The study comprised two phases: a first phase with a conventional fixed-sodium dialysate (standard care phase), followed by a phase with the electrolyte balancing control (EBC) module activated (controlled care phase). The results show a reduction in the variability of the intradialytic plasma sodium concentration shift, but it is overlain by a small but statistically significant increase in the mean plasma sodium levels. However, no clinical manifestations were observed. This sodium load can be explained by the design of the algorithm based on dialysate conductivity instead of sodium concentration. Furthermore, the increase in plasma sodium can be corrected by taking into account the potassium shift during the treatment. This study showed that the EBC module incorporated in the HD machine is able to automatically individualize the dialysate sodium to the patient's plasma sodium without measuring or calculating predialytic plasma levels from previous laboratory tests. This tool has the potential to facilitate fluid management, to control diffusive sodium flux, and to improve intradialytic tolerance in daily clinical practice.

Effects of Two Immunosuppressive Treatment Protocols for IgA Nephropathy.

The role of immunosuppression in IgA nephropathy (IgAN) is controversial. In the Supportive Versus Immunosuppressive Therapy for the Treatment of Progressive IgA Nephropathy (STOP-IgAN) Trial, 162 patients with IgAN and proteinuria >0.75 g/d after 6 months of optimized supportive care were randomized into two groups: continued supportive care or additional immunosuppression (GFR≥60 ml/min per 1.73 m2: 6-month corticosteroid monotherapy; GFR=30-59 ml/min per 1.73 m2: cyclophosphamide for 3 months followed by azathioprine plus oral prednisolone). Coprimary end points were full clinical remission and GFR loss ≥15 ml/min per 1.73 m2 during the 3-year trial phase. In this secondary intention to treat analysis, we separately analyzed data from each immunosuppression subgroup and the corresponding patients on supportive care. Full clinical remission occurred in 11 (20%) patients receiving corticosteroid monotherapy and three (6%) patients on supportive care (odds ratio, 5.31; 95% confidence interval, 1.07 to 26.36; P=0.02), but the rate did not differ between patients receiving immunosuppressive combination and controls on supportive care (11% versus 4%, respectively; P=0.30). The end point of GFR loss ≥15 ml/min per 1.73 m2 did not differ between groups. Only corticosteroid monotherapy transiently reduced proteinuria at 12 months. Severe infections, impaired glucose tolerance, and/or weight gain in the first year were more frequent with either immunosuppressive regimen than with supportive care. In conclusion, only corticosteroid monotherapy induced disease remission in a minority of patients who had IgAN with relatively well preserved GFR and persistent proteinuria. Neither immunosuppressive regimen prevented GFR loss, and both associated with substantial adverse events.

Intensive Supportive Care plus Immunosuppression in IgA Nephropathy.

BACKGROUND: The outcomes of immunosuppressive therapy, when added to supportive care, in patients with IgA nephropathy are uncertain. METHODS: We conducted a multicenter, open-label, randomized, controlled trial with a two-group, parallel, group-sequential design. During a 6-month run-in phase, supportive care (in particular, blockade of the renin-angiotensin system) was adjusted on the basis of proteinuria. Patients who had persistent proteinuria with urinary protein excretion of at least 0.75 g per day were randomly assigned to receive supportive care alone (supportive-care group) or supportive care plus immunosuppressive therapy (immunosuppression group) for 3 years. The primary end points in hierarchical order were full clinical remission at the end of the trial (protein-to-creatinine ratio <0.2 [with both protein and creatinine measured in grams] and a decrease in the estimated glomerular filtration rate [eGFR] of <5 ml per minute per 1.73 m(2) of body-surface area from baseline) and a decrease in the eGFR of at least 15 ml per minute per 1.73 m(2) at the end of the trial. The primary end points were analyzed with the use of logistic-regression models. RESULTS: The run-in phase was completed by 309 of 337 patients. The proteinuria level decreased to less than 0.75 g of urinary protein excretion per day in 94 patients. Of the remaining 162 patients who consented to undergo randomization, 80 were assigned to the supportive-care group, and 82 to the immunosuppression group. After 3 years, 4 patients (5%) in the supportive-care group, as compared with 14 (17%) in the immunosuppression group, had a full clinical remission (P=0.01). A total of 22 patients (28%) in the supportive-care group and 21 (26%) in the immunosuppression group had a decrease in the eGFR of at least 15 ml per minute per 1.73 m(2) (P=0.75). There was no significant difference in the annual decline in eGFR between the two groups. More patients in the immunosuppression group than in the supportive-care group had severe infections, impaired glucose tolerance, and weight gain of more than 5 kg in the first year of treatment. One patient in the immunosuppression group died of sepsis. CONCLUSIONS: The addition of immunosuppressive therapy to intensive supportive care in patients with high-risk IgA nephropathy did not significantly improve the outcome, and during the 3-year study phase, more adverse effects were observed among the patients who received immunosuppressive therapy, with no change in the rate of decrease in the eGFR. (Funded by the German Federal Ministry of Education and Research; STOP-IgAN ClinicalTrials.gov number, NCT00554502.).

The Photoconversion of Phytochrome Includes an Unproductive Shunt Reaction Pathway.

Phytochromes are modular bimodal photoswitches that control gene expression for morphogenetic processes in plants. These functions are triggered by photoinduced conversions between the inactive and active states of the photosensory module, denoted as Pr and Pfr, respectively. In the present time-resolved resonance Raman spectroscopic study of bacterial representatives of this photoreceptor family, we demonstrate that these phototransformations do not represent linear processes but include a branching reaction back to the initial state, prior to (de)activation of the output module. Thus, only a fraction of the photoreceptors undergoing the phototransformations can initiate the downstream signaling process, consistent with phytochrome's function as a sensor for more durable changes of light conditions.

Temperature Dependence of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Hexanuclear Cobalt Complex.

The synthesis and characterization of a hexanuclear cobalt complex 1 involving a nonheme ligand system, L1, supported on a Sn6O6 stannoxane core are reported. Complex 1 acts as a unique catalyst for dioxygen reduction, whose selectivity can be changed from a preferential 4e-/4H+ dioxygen-reduction (to water) to a 2e-/2H+ process (to hydrogen peroxide) only by increasing the temperature from -50 to 25 °C. A variety of spectroscopic methods (119Sn-NMR, magnetic circular dichroism (MCD), electron paramagnetic resonance (EPR), SQUID, UV-vis absorption, and X-ray absorption spectroscopy (XAS)) coupled with advanced theoretical calculations has been applied for the unambiguous assignment of the geometric and electronic structure of 1. The mechanism of the O2-reduction reaction has been clarified on the basis of kinetic studies on the overall catalytic reaction as well as each step in the catalytic cycle and by low-temperature detection of intermediates. The reason why the same catalyst can act in either the two- or four-electron reduction of O2 can be explained by the constraint provided by the stannoxane core that makes the O2-binding to 1 an entropically unfavorable process. This makes the end-on µ-1,2-peroxodicobalt(III) intermediate 2 unstable against a preferential proton-transfer step at 25 °C leading to the generation of H2O2. In contrast, at -50 °C, the higher thermodynamic stability of 2 leads to the cleavage of the O-O bond in 2 in the presence of electron and proton donors by a proton-coupled electron-transfer (PCET) mechanism to complete the O2-to-2H2O catalytic conversion in an overall 4e-/4H+ step. The present study provides deep mechanistic insights into the dioxygen reduction process that should serve as useful and broadly applicable principles for future design of more efficient catalysts in fuel cells.

A New Domain of Reactivity for High-Valent Dinuclear [M(µ-O)2 M'] Complexes in Oxidation Reactions.

The strikingly different reactivity of a series of homo- and heterodinuclear [(MIII )(µ-O)2 (MIII )']2+ (M=Ni; M'=Fe, Co, Ni and M=M'=Co) complexes with ß-diketiminate ligands in electrophilic and nucleophilic oxidation reactions is reported, and can be correlated to the spectroscopic features of the [(MIII )(µ-O)2 (MIII )']2+ core. In particular, the unprecedented nucleophilic reactivity of the symmetric [NiIII (µ-O)2 NiIII ]2+ complex and the decay of the asymmetric [NiIII (µ-O)2 CoIII ]2+ core through aromatic hydroxylation reactions represent a new domain for high-valent bis(µ-oxido)dimetal reactivity.

Light-Dark Adaptation of Channelrhodopsin Involves Photoconversion between the all-trans and 13-cis Retinal Isomers.

Channelrhodopsins (ChR) are light-gated ion channels of green algae that are widely used to probe the function of neuronal cells with light. Most ChRs show a substantial reduction in photocurrents during illumination, a process named "light adaptation". The main objective of this spectroscopic study was to elucidate the molecular processes associated with light-dark adaptation. Here we show by liquid and solid-state nuclear magnetic resonance spectroscopy that the retinal chromophore of fully dark-adapted ChR is exclusively in an all-trans configuration. Resonance Raman (RR) spectroscopy, however, revealed that already low light intensities establish a photostationary equilibrium between all-trans,15-anti and 13-cis,15-syn configurations at a ratio of 3:1. The underlying photoreactions involve simultaneous isomerization of the C(13)═C(14) and C(15)═N bonds. Both isomers of this DAapp state may run through photoinduced reaction cycles initiated by photoisomerization of only the C(13)═C(14) bond. RR spectroscopic experiments further demonstrated that photoinduced conversion of the apparent dark-adapted (DAapp) state to the photocycle intermediates P500 and P390 is distinctly more efficient for the all-trans isomer than for the 13-cis isomer, possibly because of different chromophore-water interactions. Our data demonstrating two complementary photocycles of the DAapp isomers are fully consistent with the existence of two conducting states that vary in quantitative relation during light-dark adaptation, as suggested previously by electrical measurements.

NirN protein from Pseudomonas aeruginosa is a novel electron-bifurcating dehydrogenase catalyzing the last step of heme d1 biosynthesis.

Heme d1 plays an important role in denitrification as the essential cofactor of the cytochrome cd1 nitrite reductase NirS. At present, the biosynthesis of heme d1 is only partially understood. The last step of heme d1 biosynthesis requires a so far unknown enzyme that catalyzes the introduction of a double bond into one of the propionate side chains of the tetrapyrrole yielding the corresponding acrylate side chain. In this study, we show that a Pseudomonas aeruginosa PAO1 strain lacking the NirN protein does not produce heme d1. Instead, the NirS purified from this strain contains the heme d1 precursor dihydro-heme d1 lacking the acrylic double bond, as indicated by UV-visible absorption spectroscopy and resonance Raman spectroscopy. Furthermore, the dihydro-heme d1 was extracted from purified NirS and characterized by UV-visible absorption spectroscopy and finally identified by high-resolution electrospray ionization mass spectrometry. Moreover, we show that purified NirN from P. aeruginosa binds the dihydro-heme d1 and catalyzes the introduction of the acrylic double bond in vitro. Strikingly, NirN uses an electron bifurcation mechanism for the two-electron oxidation reaction, during which one electron ends up on its heme c cofactor and the second electron reduces the substrate/product from the ferric to the ferrous state. On the basis of our results, we propose novel roles for the proteins NirN and NirF during the biosynthesis of heme d1.

Magnetic titanium dioxide nanocomposites for surface-enhanced resonance Raman spectroscopic determination and degradation of toxic anilines and phenols.

Mesoporous M-TiO2 NCs, functionalized by PATP, can capture toxic anilines and phenols by azo coupling. Loading these nanodevices with Ag NPs offers the possibility for a sensitive quantitative determination of target compounds by SERRS spectroscopy, which allows multiplex detection because of the specific vibrational fingerprints. Sensitivity and selectivity can be further enhanced by concentrating the hybrid particles by an external magnet and compound-specific binding (anilines versus phenols). The bound toxic compounds can be degraded by TiO2-assisted photocatalysis after removal of the loaded hybrid particles from the sample solution with an external magnet. The degradation process can be enhanced in the presence of plasmonic Ag nanostructures.

A self-improved water-oxidation catalyst: is one site really enough?

The homogeneous catalysis of water oxidation by transition-metal complexes has experienced spectacular development over the last five years. Practical energy-conversion schemes, however, require robust catalysts with large turnover frequencies. Herein we introduce a new oxidatively rugged and powerful dinuclear water-oxidation catalyst that is generated by self-assembly from a mononuclear catalyst during the catalytic process. Our kinetic and DFT computational analysis shows that two interconnected catalytic cycles coexist while the mononuclear system is slowly and irreversibly converted into the more stable dinuclear system: an extremely robust water-oxidation catalyst that does not decompose over extended periods of time.

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.

Trapping of a phenoxyl radical at a non-haem high-spin iron(II) centre.

The activation of dioxygen at haem and non-haem metal centres, and subsequent functionalization of unactivated C‒H bonds, has been a focal point of much research. In iron-mediated oxidation reactions, O2 binding at an iron(II) centre is often accompanied by an oxidation of the iron centre. Here we demonstrate dioxygen activation by sodium tetraphenylborate and protons in the presence of an iron(II) complex to form a reactive radical species, whereby the iron oxidation state remains unaltered in the presence of a highly oxidizing phenoxyl radical and O2. This complex, containing an unusual iron(II)-phenoxyl radical motif, represents an elusive example of a spectroscopically characterized oxygen-derived iron(II)-reactive intermediate during chemical and biological dioxygen activation at haem and non-haem iron active centres. The present report opens up strategies for the stabilization of a phenoxyl radical cofactor, with its full oxidizing capabilities, to act as an independent redox centre next to an iron(II) site during substrate oxidation reactions.

Potential-dependent surface-enhanced resonance Raman spectroscopy at nanostructured TiO2 : a case study on cytochrome b5.

Nanostructured titanium dioxide (TiO2 ) electrodes, prepared by anodization of titanium, are employed to probe the electron-transfer process of cytochrome b5 (cyt b5 ) by surface-enhanced resonance Raman (SERR) spectroscopy. Concomitant with the increased nanoscopic surface roughness of TiO2 , achieved by raising the anodization voltage from 10 to 20 V, the enhancement factor increases from 2.4 to 8.6, which is rationalized by calculations of the electric field enhancement. Cyt b5 is immobilized on TiO2 under preservation of its native structure but it displays a non-ideal redox behavior due to the limited conductivity of the electrode material. The electron-transfer efficiency which depends on the crystalline phase of TiO2 has to be improved by appropriate doping for applications in bioelectrochemistry.